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Using the Sherline Angle Plate

June 13, 2011 igarrido

One of the things that I would love to have it’s a horizontal milling machine. Sometimes, when working on a part, I find myself thinking “this would be easier if I had a horizontal mill”. I mean something like this:

A guy sells this beauty on ebay, but he doesn’t ship to my country. Here’s another. Sure, you can buy the conversion kit from Sherline, but changing from one setup to another it’s way too much trouble. Meanwhile an alternative solution it’s the Sherline angle plate (here’s the short version):

This can be bolted directly into the milling table, but a better solution it’s to make four tapped holes in the tooling plate. To clamp the parts to the angle plate I build a clamping kit composed of a stop strip and a “cross” clamp.

As you can see, angle plate squareness it’s not perfect:

The gap it’s not as bad as it seems in the picture: at the top there’s about 0.050 mm. Some strips of aluminum foil will help to compensate this (finding how much it’s a trial-error process).

My first attempt to align the stop bar was to use an indicator over the headstock, but a square was more reliable in the end (you can guess why).

Here is the part ready for the face mill:

And here’s the final result:

That is.

Micro table saw

May 16, 2011March 22, 2018 igarrido

This long desired project is finally finished. Now I can clean-cut metal, plastics or wood stock easily and with minimal loss. I think everyone working on small parts must have one.

The idea

Some time ago I was working on my cnc lathe and get tired of my options to cut stock, so I decided I needed a mini table saw before continue. Proxxon micro table saw seemed to be exactly what I needed, but I choose to make my own.

My start point was a 1/4″ 51x17cm aluminum plate, a 1/15 hp ac/dc 5000 rpm Dayton motor, three proxxon saws, and, of course, the Proxxon micro saw as a reference design. I got three of these motors for $16.00 plus shipping on ebay (well, I order two, but, the seller forgot to ship them at time and kindly add a third). Please don’t ask for motor a source; the original seller isn’t available anymore.

Building

I began designing key elements: the table itself, the motor mount and the saw rotating support. Once I build these parts and put them together I got a functional saw, that help me to build the rest of the parts.

One of the tricky steps was to cut the aluminum rectangle to size and square it. As the length was larger than sherline table travel, a two step mill and hand filing was required.

Fence was made of delrin and aluminum, and has two locking screws. Assembly allow some degree of adjusting so delrin guides slides without play over aluminum.

Angle guide was made of delrin and a 1.5×12 mm brass bar. Tough at first I thought that was really unnecessary, it’s a must to cut bars.

Timing pulleys and belt are 3mm pitch / 9mm wide HTD, and were ordered at sdp-si.com, an awesome site. Here’s the order:

Part Number     Quantity    Unit Price    Extension
————————————————————————
A 6R23M040090     1        $6.13/Each    $6.13
A 6Z23-017DF0908     2        $5.19/Each    $10.38

A dust receptacle it’s a must, as without it you get a mess of chips lying around. I build this using 3mm policarbonate (Lexan) sheet and 1.6m screws.

Table support was made using hard some wood I salvaged from an old stepladder.

Tough you can make thumb screws on the lathe, I choose to buy them on ebay. I got a bunch of 30 (three types) for $5,74 plus shipping from a Uk seller. They are nice.

Testing

I got three proxon saws: for wood, hss for metal and carbide tipped. The first only works for soft wood; for hard woods carbide tipped must be used. The hss one works great for thin metal sheets, but clogs on thick plates. With the carbide tip saw I can cut 9.5mm (3/8″) of aluminum, tough not really fast (the saw clogs a bit). In this test I cut 6.5mm (1/4″) without problems:

Tough a little more of power would be welcomed, the motor seems to do the work. Something not clear to me is that Proxxon states this cutting capacities for their saw:

Wood 5/16″ (8mm)

Plastic & Circuit Boards 1/8″ (3mm)

Non-Ferrous Metals 1/16″ (1.5mm)

tough it uses a 1/10 hp motor while mine is only 1/15 hp, and I can cut 6.5mm aluminum (more than four times proxxon capacity). Maybe it has to do with lack in rigidity or something else.

Overall

There was a lot of work in designing and building this tool, but was worth, and now is one of the main tools in my shop. And it seems to have better cutting capacities (an precision, I guess) than the Proxxon one.

Draft drawings are available if someone is interested.

Update

Here are the drawings for the main parts. Please note that these are not detailed building instructions.; no tolerances, no part lists, etc.

Some things to note:

I use R4 bearings: 1/4×5/8x.196 (metric 6.35×15.875×4.98). Bearings, bearing housings and spindle must fit without or very little play. Thread-locking fluid may be used in bearing housings if any play.
Spindle axis length should be some less than nominal (40*) to reduce axial play (this was a trial-error to me).
Pulley set screws must use thread-locking fluid. Without this, screws may get loose (this happened to me, not a nice experience).
The motor mounting block was designed to fit a specific motor.
I think the angle guide system can be enhaced by cutting a guide with a T profile (4th pic, below). A dovetailed guide would be even better.
A thicker table (let’s say, 3/8) would be another enhacement.

CAD drawings HERE.

Micrometric Obsesion

December 10, 2010 igarrido

Some time ago I note parallelism of milled parts sometimes was not as good as it could be, and though I didn’t bother, this time I wanted to try to enhance this. So this is about more measurements and tweaks.

Vise Horizontal Parallelism

The first suspicious was the vise, so I begin with it. After some measurements of the vise bed width, lapping was accomplished to enhance the numbers. Here are the before and after.

1. Vise bed width

Lapping did remove most of bottom anodizing, but was worth.

2. After bottom lapping.

Corners get a little over-lapped, maybe this can be reduced by fixing paper to surface (I don’t care anyway).

Vise Vertical Squareness

I took measurements at two points near the middle of the jaw. Before bottom lapping there was a minimal tilt to the left:

3. Column-jaw squareness.

After lapping the tilt was also minimal but change to the right. So I did remove the jaw and softly lap the top. After this almost no tilt was detected (see below), at least in the middle of the jaw.

4. Column-jaw squareness, corrected.

Finally I took measurements at six points. Here’s what I get.

5. Jaw to column measurements.

Vertically was ok, but horizontally there was some concavity. This was not a surprise, as I noticed this before but don’t think this would be an issue.

Test

As a test I mill a small aluminum block and took measurements at the ends. They were 9.341 and 9.343 ; a difference of 0.002 (nice). Previously this difference, for similar parts, was around 0.010, as I remember. But the main enhancement, supposedly, should be in the Y axis, but it wasn’t. The widths vary 0.030 from side to side, in a distance of 9 mm. Too much for me.

6. Test.

So what happened? After a lot of work I found four main reasons:

When measuring, I don’t take into account error in squareness of the column to the table.
When a part is clamped in the vise, there’s some deflection of the back side.
When the movable jaw is pressed, it also lift up a little bit.
Some time ago I lap the column’s gib and tough it feeled tight, it happens to be a little wider on the middle.

Some Measurements

Several measurements were taken.

1. Table to column squareness. Measurements every 1cm, over a section of the travel.

7. Table to column measurements.

2. Squareness of the fixed jaw to the column, without load.

8. Squareness without load.

3. Squareness of the fixed jaw to the column, with load at top.

9. Squareness with load.

Here’s some interesting. According to previous measurements (look Figure 5), this difference should be only 6um (and not 24um). Figure 11, part 5, explains this (gray box).

4. Deflection, or how much the jaw goes back with load.

10. Deflection.

With all this I was able to figure out the complete picture. After some struggling with the numbers, I got the diagram below.

11. Summary diagram.

I conscientiously don’t take in account for table unevenings. In previous measurements I get a difference of around 6um from side to side, in the middle of the table (see previous post). This difference act pointing the square some micrometers towards the column.

Deflection compensation and jaw lapping

To compensate deflection, I Mill jaw support surface. As the headstock had a very light angle towards the back (look next section), this provided a compensation angle. Otherwise some padding would have been required.

12. Jaw suport retouch.

Moreover, I found that only the external face of the fixed jaw was ground, and after some examination and measurements I opt for lap it on both sides (this seems to explains concavity). It was an almost impossible job (I don’t recommend to anyone), but after many hours of hard work I get satisfied with the measurements: at least regarding to width, maximum measured variation was of 0.003 (I took measurements at 15 points and check with a good rule).

13. Jaw lapping.

After all this I check again, and the jaw seemed to be compensated (look Figure 11, part 4).

14. Squareness measurement after milling.

15. Squareness measurements, indicator in vertical position.

Then I repeat the test with the aluminum block, milling both sides. I found that the initial difference was reduced only to 0.020, not enough. Something more was happening.

Gib

I did the classical head alignment test and get a damn 0.060mm difference in the Y axis (I did this measurement some years ago, and it was not as bad). It looks as if the headstock was inclined, as this difference can’t be explained by the column deflection alone.

16. Headstock axis totable squareness

After some thinking, a found the problem. Some weeks ago I noted a play in the headstock when lock it in place. After disassembling some wear was detected (look below), seemingly caused by some play in one end of the gib (poor lubrication was not the cause). So I lap the gib using 320 grit sandpaper, until the fit feeled similar in both sides. After that the play in the headstock was reduced and fit seemed to be improved.

17. Column saddle wear.

But now, trying to explain the numbers, I checked the gib straightness using a rule and a back light, and was clear that the gib was ticker in the middle, on the not lifting side. After straightening using sandpaper, install and recheck, the alignment difference was reduced to 16 um, a lot better. After repeating the milling test, I get a width difference of 12um.

18. Gib adjustment.

Vise Jaw Lift

There were still 12um, and then I noted something: in the milling test I use two parallels, and when the part is held, the one in near the movable jaw gets looser than the other. So I did one more test: press down strongly the part while tighten the vise. After repeating the test one more time, finally I get a difference of 0.001.

Professional guys know well this issue (look here). After you visualize how the part is grip, it’s clear what it’s happening.

19. The final issue.

The lift problem will affect mainly small parts, so I think having a smaller vise should be a must to work with very small parts.

Conclusions

I’m not pretending to have micrometic presicion, but get the most from my machine doing all can be done to improve it. There’s nothing bad with it, it has a very good accuracy for the money, but you can always improve things.

It’s well know that accurate of a machine depends on a build-up of a lot of inaccuracies. But identifying and measuring them is another thing. Though this was a very tedious journey, now I have better idea on where innacuracies are, how they sum-up and how can be reduced.

After a lot of work I was able to enhance the vise a little bit, but now I think that a better deal is to left the sherline one as is and buy a chinese screwless vise for high precision work. Some time ago I bought one, but it’s still waiting for me to make the clamps (look here). It’s worth to note that the sherline one is ok for most of works, and it’s aluminum body allows to be less careful, as opposed to an all-ground steel and heavier vise.

Regarding the gib issue, I believe all the gibs in a new machine can be lapped to improve the fit, but clearly a “good fit” can be misleading if the gib it’s not checked properly.

straightness

Milling table tweaks

September 25, 2010 igarrido

Having a tooling plate is almost a must for anyone that owns a Sherline milling machine. It helps to protect the table and can be adapted to specifics needs. When I bought mine (A2ZCNC brand), I don’t worry about how well aligned the top surface was; I supposed it was good enough. But someday I took some measurements, and this is the history. Please note this this is not a review about the mill or the tooling table precision, but rather some reference information.

Base Table Measurement

I use my 2um test indicator to get measurements at six points:

So there’s a small tilt on the X axis (around 0.0243º); I don’t know usual this is, but I was not happy with that. Please note this is a three year machine, used lightly, so this wasn’t caused by worn or misuse.

Tooling plate width

I’m really not able to measure how flat the plate is, so I only took a few thick measurements using a digital micrometer.

Looks ok.

Installed Tooling Plate

Here’s what I get with the installed tooling plate, after filing bottom protroudings (see below).

After that I search for a way to enhance this numbers.

First Try

Flattening tooling plate sole. Bottom side of tooling plate holes seemed to have protruding sourrondings. I’ve noticed this before but didn’t take care as if protruding were equals this wouldn’t, at least in theory, have any effect . But one day I noticed some round marks left on the mill table, so I just pick up a file and take out protrudings (I used a small flexible flat file).

Padding. To enhance top surface alignment, I cut some nylon and aluminum foil and play a while.

Here is the best I got after this tweaks.

Milling the plate

Padding was a rather ugly solution, so after some weeks I choose to face mill the plate surface. This was a two-step process, as tooling plate area is larger than max milling area. Please note this was done to fix a milling table issue, not related to the tooling table itself.

After milling lapping was required, so I just pick some 350 and 500 grit sand paper and begin the process. A recently acquired cheap granite surface plate was used as lapping surface.

After around an hour, I got a nice finish, so I tested, and surprise: borders where lower than center area.

This was in part, I think, due to the fact I did most of the lapping work in perpendicular direction; bad idea. Anyway this lapping process will always take a little more material from the borders; to compensate for this an abrasive area smaller than the plate should be used (not showed here).

Bad

Not too bad

Fixing this required several hours of hard work and and continuous test. Here is the final result.

Not bad.

A final tip: here is how I clean dust in threads.

Aligning pins

Aligning of the milling vise is a tedious process, so to avoid this, or at least to help, I bored some holes and turn some pins. Two pins at plate sole to fix the table, two to align the vise at center and two to align the vise at the left.

Boring precise holes it’s not and easy task. Hole position must be carefully calculated, and fitting must be tight enough to avoid pins fall apart, and lose enough to allow to remove and put them back by hand. Having this on mind, some micrometers more or less can make the difference. I fail the first time in bottom holes, and the top left holes ended with a little play. As show below, align is ok for most of works (this is a 2um indicator).

Center position

Left position

Conclusions

It’s clear that in the manufacturing process of the tooling plate lapping was done first and threading later, leaving the undesired protroudings. To correct this, filing and/or lapping can be used. I’ve said there were protroudings at the sole, but the top surface also had small protroundings (10 um, not noticeable by eye). I recently bough a Sherline tooling plate (for another machine), and in this is clear that lapping (or some kind of surface grind) was the final step; in fact, the plate comes with some fine dust.

In regard to the milling table tilt, may be this is within expected tolerances for this machine, but must be corrected to help to machine precision parts; 28 um it’s a lot.

After a lot of work I got acceptable tolerances and a nice finish. Its clear that now this tooling plate should be used only in this machine and in the same position always, but this is not a problem.

It would be interesting to hear about similar measurements from others, may be I was unlucky, or may be I’m expecting to much precision from this things. This of course doesn’t change my concept about Sherline products as high quality, super nice machines; in fact I’m getting parts for the cnc version of this mill.

Replacing Sherline Spindle Bearings

January 26, 2010 igarrido

Some time ago I buy a used (indeed abused) Sherline manual lathe planning convert it to cnc (a in-course project). The headstock spindle of this lathe had a worn feeling so new bearings were needed. Replacing bearings was easier than expected (no strong hits were required), and here is what work for me.

Things required

Electric stove (something like this)
Leather gloves
1 1/4″ soft metal rod
Hammer
A small part to protect spindle from damage when hammer is used.
Oviously a pair of new 6004ZZ bearings. Mine were Japan made.

Disassembling

Remove front cover and back nut.
Set stove to medium level an heat headstock for a few minutes. Don’t now exact temperature, but you should not be able to touch without gloves. Too hot it’s not good of course.
Wearing the gloves hit the spindle back while holding headstock by hand. Be careful as spindle and front bearing may jump away.
Use the rod to hit rear bearing from inside.
Place back front bearing in spindle housing, but in reverse position, an hit spindle back again.
Wait headstock to cold (20 min or more).

Preparing

At this point some cleaning and checking is required.

Clean bearing housings and spindle, using sand paper and oil if required (I use 600 grit aluminum oxide paper). I found some nasty brown coating in the rear bearing, may be some kind of glue.
Search for nicks in bearing housing borders, and file if required (those may difficult bearing fit).
Check front bearing fit on spindle; you should be able to move it by hand (a little force may be required).
Coat spindle, bearings and housings with oil.

Reassembling

This is pretty much the inverse process.

Heat headstock as before.
Mount front bearing on the headstock and insert spindle. Hit spindle nose while holding by hand, until complete fit. No too much force should be required. Remove assembly from headstock.
Mount rear bearing; careful alignment is required. (I should hit a bit as the border had a nick and filing was not perfect).
Put back spindle, hitting should not be required.
Ensure bearing fit are ok and wait to cold.

Adjusting Preload

Once the headstock is cold you can mount in the lathe and put back the nut to adjust preload (Sherline instructions here). To me this was a bit hard as the nut was a bit tight, so adjustment was difficult. I adjust preload so there was very low friction added. Measurements were:

Nose runout: 0.008 mm
Nose play: 0.003 mm (may be a bit tight but I can’t get any greater)
Face runout: 0.006 mm

Final Thoughts

After checking old bearings, I realized that front bearing was severely worn, while rear bearing doesn’t feel bad.

I would like to try 7004 angular contact bearings, but haven’t found a provider (there’s only a ceramic version on ebay, costing around $100).

Update

Now I’m pretty sure the nasty brown coating was bearing retaining compound. I suppose this is required when there’s some play between the assembled parts. Maybe I should have use this for spindle-bearing assembly.

Update 2

I forgot to say it seems original and new bearings where normal class (or ABEC1). I guess that normal bearings will do the work, but with ABEC3 bearings costing US10 on ebay (as Andy points out), there’s no reason to spare.

Some Robots

January 25, 2010 igarrido

I love robots. Here are some.

GBot (2004). This was part of my final thesis. I made it with scratch parts and aluminum profiles, using mainly a saw, a file and a drill (at this time I don’t had a lathe or milling machine). I programed (C) this robot to search and collect cans. It’s based on a AVR microcontroller.

Line follower (2004). I build two of this toys for my university robotics lab. Making competitions between student teams was fun. It’s based on a PIC microcontroller (16F628).

Scorbot. I buy this toy on 2008. It was disassembled, cleaned, fixed, and reassembled. It’s in working condition, but calibration is needed before delving into programming. Some day I plan to make a plataform and continue playing with it.

An industrial robot from a university exhibition. Very nice.

If there’s someone interested in robot circuits, here are:

Runout

January 24, 2010 igarrido

Usually I try to work the way I dont need to take too much care of my lathe runout, but its a good idea to have some reference values. Here are some simple measurents I take. I use a swiss 0.002 mm test indicator and some grounded steel rods.

Spindle internal tapper: 0.006 mm. Sherline specs states 0.0005″ (0,0127 mm) , so its ok.

Spindle play 0.005 mm. Again within sherline specs: 0.0002″ (0,0054 mm).

Spindle face: 0.014 mm. This suprise me as spindle face its the reference surface for chucks. There’s no spec for this, buts seems to much to me.

2.5″ 3 jaw chuck: 0.094 mm. Sherline states a max of 0.003″ (0,076 mm) runout, so its a bit out of specs.

Another 2.5″ 3 jaw chuck: 0.124 mm. I buy it used and seems it has a lot of use, but don’t think this explain this value.

2.5″4 jaw chuck: 0.080 mm. Almost within specs (buy used but in good condition).

3.1″ 3 jaw chuck: 0.024 mm. Better. This is was also buy used. This was a surprise as visually jaws doesn’t look to met “perfectly” when closed.

WW adaptor: 0.006 mm. Seems this doesn’t add noticable runout.

WW 3/16 collet: 0.024 mm. This is a lot for this type, but to be fair may be I ruin this (never used) collet as I tight without the steel rod (of course this should never be done). Ups. Maybe should I order a new one.

WW 0.25″ collet: 0.014 mm. This time no mistake was made. I read somewhere that no more than 0.0005″ (0,0127 mm) is ok for this collets.

Chinese ER16 chuck: 0.040 mm, at 40 mm from spindle nose. That’s a lot; don’t now if its due to poor quality or larger distance from nose. I must say this cheap chuck looks well made, but I did correct back thread as this was so oviously deviated.

Threaded ER16 chuck: 0.006 mm. I buy this from a guy on ebay, not chinese, and must re-bore internal cone and front thread to make it usable, so this explain this good reading.

ER32 chuck: 0.016 mm. Accounting the spindle face “runout”, cost (around$50), the fact this is mounted in a faceplate and still don’t get the bolts, this doesn’t seem to be a bad value (will take another reading when buy the bolts).

ER32 threaded chuck (“Beal Tool”): 0.006 mm. Sell as pencil chuck for the taig lathe; I did must face the back (final adjustment was carefully made using sand paper). Its seems a good value, but as I remember there’s a small amount of axial deviation (don’t save those readings).

6 mm milling collet: 0.016, 0.030 and 0.070 mm at 3, 13 and 23 mm from spindle nose.

3/16 mm milling collet: 0.006, 0.004 and 0.010 mm at 3, 13 and 23 mm from spindle nose.

So???

I buy ER chucks and collets looking for precision and avoiding marks on work. Now its doesn’t seem a great deal (collets add more runout). Nevertheless ER16 chucks are handy for the mill. And ER32 chucks can work great as vertical fixtures.
Jaw chucks seems to have too much runout. Measuring first chuck face runout on border gives me 0.032 mm, so may be I need to re-face spindle (I would lost ER16 threaded chuck precision tough).
I would like to buy precision pin gages to be able to measure ER and WW collets (and to take better measurements).

Anyway, how much runout is acceptable depends on your particular needs, and for killing precision a independent jaw chuck or a special-purpose-on-spindle-turned fixture should be the way.

Update: I re-face spinle nose and now face runout is less than 0.004 mm, and first chuck runout drop from 0,076 mm to 0.054 mm and second drop from 0.124 mm to 0.104 mm. Due to some chatter issues I take around 0.1 mm, but sure can be less if well done. I forgot to check spindle align, but it’s better do it before re-face (may be turning a test rod and measuring both sides).

Making Gears

March 21, 2008 igarrido

The Idea

Gears are by far the most used transmission elements in mechanical systems. Though you can design and build a lot of robotic toys without dealing with gears, more sophisticated (cool!) designs will claim the use of specific gears. At this point you have three options:

Use a collection of scratch gears: not really an option, as you will end up with a lot of different and incompatible gears of random sizes.
Buy: commercial gears are costly, so you will need a lot of money.
Make your owns: that requires special tools, but gives you more design freedom.

Having the capacity of design and build gears opens the hobbist a lot of possibilities to build and play. I always wanted to have the capacity to make gears, and tough I have a Sherline mill, It’s not enough. So I decided to pick a simple method and build my own tools, and here’s the report.

The basic idea was to adapt a lathe spindle to work as indexer driven by a stepper motor. The motor must have enough torque (static) to allow cutting small gears without undesired vibrations; for large gears or other works a lock will be required.

Of course, this tool will allow to make only involute gears, the most common gear type, but they will suffice for most cases.

Design

I started ordering a Taig lathe spindle, arbor and mounting for about $80, and from my stock I got two plastic sprockets, a belt and a stepper motor. And of course, some aluminum (6061) was needed.

The design was done around this parts. Main concerns were:

As sprockets were plastics, mounting bushings were required.
To allow rotating in the Z axis, the mounting base required some type of round clamp system.
A manual block system was added to fix the spindle when needed.
I made the motor mount adjustable in the vertical to adjust belt tension.

The belt system provide a a 3.6:1 reduction, so driving the motor in half step mode gives a minimum of 0.25 degrees per step or 1440 steps per revolution, enough for me. Here is the acad drawing.

And here are the finished parts.

Black anodizing gives a cool look. The belt I had at hand was a bit more than the required length, and making a padding block was more cheap than buying a new belt.

The circuit

The motor was nema23 size, 4 volt ! 1 amp. I designed a board around a PIC16F628, using a simple cmos motor driver scheme. Minidin connectors were used for power, motor and serial port (I hate db9 ones).

To drive the motor in half step mode, a minimum of 2 amps were required, and a power supply I got from an old ethernet switch some years ago was handy. Tough the 5 volt line has a nominal 5 amp capacity, the voltage drops to 4 volts when the motor is energized (two coils), so chopping was not required. 12 volts line was used to feed a 5v regulator for the logic.

I write the pic program in assembly, a bit tedious work, but the final code was pretty. The system work this way:

Button 1: step forward
Button 2: step backward
Button 3: step size decrease
Button 4: step size increase
Buttons 3,4 (at the same time): reset.
Backlight on 3 seconds after a button is pressed.

Here is the set.

I plan to build a plastic box at some time, as a small chips from the lathe can roast the board.

Preparing

Before using the indexer, some stuff was needed:

A support arbor: I modify a taig arbor to support small gears.
A cutting tool: I don’t like the sherline gear cutting tool, so made one that uses small hand made inserts.
A reference center to calibrate headstock Z axis.
A plastic gear used as pattern to make the cutting inserts: I choose one from my bag of scrap gears.
The virgin gear part.

The cutting tool I’ve made support two inserts, so this way shape imprecisions in the inserts are canceled a bit (at least in theory). To make the inserts, a 3/16″ tool blank is grinded until, in front of some light, the cutter match the plastic gear. Then the tip of the tool bit is cutted with a dremel cutting wheel. A small grinding wheel can help to give final finish.

As noted in the image, I’ve done and extra insert, to do a prior cutting before using the shape-matched ones, saving my hard-to-made gear cutters from wearing.

The choosed pattern gear has the following parameters:

m = 0.6 (metric “module”)
Z = 40 (tooth number)
Pitch diameter = Dp = m*pi*z =
Pitch diameter = m*z/2 = 24
Outside diameter Do = D + 2m = 25.2
Tooh depth = ht = 2.2 * m = 1.33 (there are slight variations of this formula)

Module was deducted using the formula m = Do / (Z + 2). In this case, measured outside diameter was 5.21, giving m = 0.6. Note that if the module has more than one decimal may be it be a inch gear. I found that there are no business standard in scratch gears; sometimes two gears that seems to be compatible at first doesn’t match at all when you take measurings. Please note that the pitch diameter is important as states the distance beetwen two mate gears: for pitch diameters D1 and D2, there must be an inter-axis distance of D1/2 + D2/2.

A First Gear

The first step was to fix the Z axis using the center.

Later, the blank gear is centered in the arbor using a dial indicator. This is tedious, as when you tighten the screw, the blank easily get out of center.

Here is the first cutting pass. Cutting was a lot more soft than what I expected.

After the this prior cut, final inserts are installed and the Y axis is calibrated. Cutter-blank distance is reseted, and several rounds are done until reach the 1.33mm calculated advance. Note that both inserts must reach the same distance from the spindle axis, so this requires to fix one and adjust the other using some reference surface.

An here is the result. Not bad. Deburring of front cutting side was done using a knife, something a bit difficult (second image).

A simple verification: the size of two engaged gears must be 25.2+25.2-1.2= 49.2. Actual value is around 49.25, so it appears there was a slight oversize; then I took another measuring, using two small steel rods: the plastic gives 25.05, and the metal 25.01. So it appears that is the plastic the oversized one, at least in part.

Of course this isn’t a high precission high endurance gear, but it’s great for the hobbist.

Overall

Making gears this way requires a lot of setup time, but the whole process is pretty simple: calibrate, set cutting depth, go forward and backward, rotate a step, go forward, etc. I do several rounds, but now I think that for this gear size only two rounds are required: a heavy and a finish cut, using the same inserts. Also I think that only one good shaped insert will do the work.

As mentioned, a critical point here is the shape of the cutting tool, so this method will work only if you have enough skills to give your cutting tool the gear tooth shape. As an alternative, you can buy gear cutting modules, but these are costly and one unit covers only a range of tooth (z) at one pitch size (m).

Note the with this method you can’t make a reduction gear from a single piece; for this, you have to make two assembly pieces. Anyway, reduction can be provided by the motor, so that’s not a issue.

One of my to-do things in my list is automate my mill, something that will decrease tooth cutting time to a breeze.

That wasn’t an easy work. The short way would had to buy the Sherline rotary table or indexing tool. Anyway, the tool works fine, at least for small gears. A now doing a gears seems to be a really easy task to me.

Update: source code here (you need MCP from microchip).

Homemade Anodizing

January 18, 2008 igarrido

I ‘m been busy doing some aluminum parts, and after you work hard in a part you want it look beautiful and last long. So here is when anodizing comes. Most of the experience here is based on Ron Newman’s Anodizing Aluminum, the best anodizing guide on the net.

A Brief Overview of Anodizing

I don’t now much about chemical reactions, so this overview will be very basic and not fully precise.

Anodizing is a process to colorize and protect aluminum. Through an electrolytic process a fine coating layer of aluminum oxide is grown. This layer has open pores on it, ones that can be filled with color dye and sealed. Aluminum oxide is a very hard material, so though only a few microns depth, this layer protect the part from small scratches and gives it a beautiful and professional finish.

There are at least two anodizing types, depending on the coating thick: Type II (1.8 μm to 25 μm thick), and Type III (thicker than 25 μm) or “hard anodizing”. Hard anodizing obviously is more durable, but also more difficult to do at home, so the anodizing done here will be Type II.

The main steps involving in anodizing aluminum are:

Clean: remove any grease or dust.
Desmut: remove smut generated from previous step.
Coating: create oxide layer
Dye colorize: fill oxide pores with special dye.
Sealing: seal pores so the dye stay in the surface.

Every step requires a specific chemical, and time and/or temperature control.

What do you Need

The things do you need to anodize are:

Some plastic pots.
A metal pot.
Distilled water (at least 5 lt).
A battery charger or power supply of several amps. Note that some chargers have a “auto-shutdown” and can’t be used.
Current meter (10 Amp at least).
Caustic soda (lye) solution, the one used to clean pipes.
Nitric acid solution (10%). I think that this is not really required for 606X aluminum types.
Sulfuric acid solution (15%).
Aluminum wire. Mine is 1.5 mm diameter.
Graduated glass beaker.
Anodizing sealer. I got “ALSE22 ” from Caswell.
Anodizing color dyes. I got red, block and brown from Caswell.
A small balance or method to weight sealer powder.
Anode. Aluminum foil will suffice.
Some support to hang the parts over the pot. I build a nice stand for this.
Electric cable.
Rubber globes, security glasses, old waring, etc.

Below is some of this stuff (the funnel was never used).

Here is my stand and anode setup. The holes and screws allow easy mount of the aluminum wire. As can be noted, this pot fits only small pieces (the only ones I can machine).

Mounting a mini-anodizing line

Please note that the chemicals used here are potentially dangerous and that some nasty gases are produced.

First time anodizing will be hard, but once you have a mounted anodizing line and doing some runs, anodizing will be rutine and take only a couple hours. Here is how I build mine:

Water (small pot). This will be used to clean when passing the pieces between pots.
Nitric acid solution (small pot): 500 ml watter + 100 ml nitric acid (68%).
Sulfuric solution (large pot): 1000 ml water + 150 ml sulfuric acid (98%) (NEVER add water to acid, ALWAYS add acid to water).
Dye solution (large pot): 1000 ml water + 15.6 ml dye.
Sealer solution (metal pot): 600 ml water + 5 grams sealer.

I store the pots for later reuse, but discard sealer (I’m not sure if can be reused; anyway 1 lb package from Caswell will last).

Area and Time Calculation

In the electrolysis process the oxide coating layer grows up to a maximum thickness; after that, the coating remains the same thickness but the part begins to shrink. Hence electrolysis time is a important parameter. It depends on current and total cathode area. Less time will result in a thinner oxide layer; too much time will result in a smaller part. I use the “720 amp-min per square foot” rule to deduce this simple formula:

Full Thickness Time = (A / 929) *720/ I

Where A is the full cathode area in cm3 and I is the nominal current and the result units are minutes.

There are some area calculator for simple shapes on the net; they can help you to do a rough estimate.

For my first try, the total area was roughly 100 cm2, and with a nominal current of 2.4 Amp this gives 31 minutes.

First Attempt

Of course I will not try to anodize my beloved parts in this attempt. Instead, I machined some scraps of 6061 and 2024. The last is know to not be easily anodizable.

So the procedure is:

Calculate total area for the cathode.
Clean the parts to remove dust. Rinse and/or use acetone.
Cut aluminum wire and make hangs for every part. A good electrical contact is a must for a good anodizing. Also please note that the contact points will not be anodize, hence these should be in a less visible area.
Put 2 min in lye solution. After this step parts should not be touched and should not stay out the water.
Put 10 min in nitric acid.
Put in the electrolysis bath and measure how much current is being draw. Estimate time based on this current.
After half the required time has been elapsed, measure current again and recalculate time with this current. The current will go up in the process, so this will be a rough average or nominal current. Temperature should be in the 20-23 ºC range. The solution will heat up after a while, but I that shouldn’t be a problem when you don’t do continued runs.
Heat dye solution to 60º and put parts for 15 to 20 min.
Boil the sealer solution and put the pieces for 15 to 20 min.

Prior cleaning

I clean the parts with acetone before the lye solution. This is the last time you can touch the parts.

After lye solution

After the lye 6061 parts looks the same. However, 2024 get covered with a blackish smut. As far as I know this is due to the copper content in this alloy type.

The lye solution pot

This is the pot size I use for lye, nitric acid and water.

After the nitric acid

Again, 6061 parts look the same, but in the 2024 ones the smut has vanished. I’m not sure if this step is required for 6061 parts; anyway nitric acid doesn’t eat aluminum, so this will not hurt.

In the electrolysis bath

At the start, the meter measures 2.2 Amp, increasing up to 2.6 after 30 min. So I use a nominal current of 2.4 Amp for the time calculation.

After the electrolisys process

After this process, 2024 get darked as the parts in Ron Newman’s info; but 6061 remains almost the same. This lead me to make a mistake. I once read that 2024 anodizes faster than 6061, so I thought most action was by 2024 and 6061 parts get almost nothing coating. Also, I measure the diameters of the 6061 round parts an were the same before the process. So I repeat the process for 6061 parts alone (recalculating time of course). After the elapsed time, the parts looks the same, so something was wrong I think… I measure again, and they were 0.05 mm less in diameter! Then I realize that the 6061 were already coated, and the the second run only eats the surface.

In the dye solution

For sure the most easy way to heat the dye solution will be use a cup heater, but I don’t have a small enough one to fit my pot. So put my pot in a large metal pot and surround with boiled water. After a while the dye reach 55º, and I put the parts inside. This is bit less that the specified, but enough I think.

After the dye

When the parts left the dye solution, It was clear that something was wrong with the 2024, and that the 6061 don’t get a uniform color. Anyway I decided continue and finish the process.

In the sealing pot

And the final step: boil the seal solution and put the parts 15 to 20 minutes.

The final result

Well , that’s my first anodizing, far from perfect.

Second Attempt

This is the second try. Here is my improvements and corrections:

Surface spots were caused, I think, because of time out of the water (or solution). This time I will take the part straight from a pot to another.
The first time I don’t use pure caustic soda, but a special cleaner… bad idea. May be this cause the small pits.
I clean the parts in normal water, this time I will always use distilled water.
2024 parts were anodized only at the bottom; a bad contact was probably the fail.
This time I will heat the die to the specified temperature: 60º.

Here an extra step is required: remove the previous anodizing in a lye solution. Please note that the lye solution will get dirty, so don’t use the same you use to clean parts.

After putting the parts in the electrolytic solution, I notice that the current was a bit less that the first time, so adjust time accordingly.

So here is the result. Much better.

After sealing a slight white smut was covering the parts; I successfully remove it from 6061 parts, but remains in the 2024 ones. I think that this was partly due to the fact that after removing previous anodizing 2024 surfaces got a bit porous.

Further

After some anodizing rounds I’ve found that:

Bad contact is the most common cause of failure. To minimize this, contact points must have some spring capacity. Play with some wire patterns to get something that work. A god wire contact must be able to support the part as this moves.
A large part loosen at the half of anodizing will be a headache as this will change the required anodizing time.
No anodizing parts get a dark smut, so after a while they’re easy to identify.
If dimensional fit is critical for a part, be sure to don’t have to repeat your anodizing.
Some numbers: 167 cm^2 -> 2.7 Amp; 180 cm^2 -> 3.5 Amp. So I think a 6 Amp supply will suffice for the capacity of the pots I use. These are 15x15x8 cm, and I guess the will support no more than 300 cm^2 of parts.
I try to use a standard PC supply, but the one I used was cheap, so 12 volts were 10 at 2 amps or so. I think I will buy a standard 13.8 volt – 6 Amp supply.
To much parts can be trouble to handle, so splitting in groups will be a more secure way.
The metal pot should have the at least the same deep as the plastic pots; mine is lower an that is a problem. Parts should not touch the bottom of the pot and shouldn’t be near the surface (as the water level lowers).
Without care, this anodizing will not stay too long without small pits. Though more hard than aluminum, due to its small width, anodizing layer will peel after some rub or shock.

That’s all. If you want to learn how to anodize I encourage you to visit Ron Newman’s Anodizing Aluminum among other resources.

Playing with my AVR Development Board

November 22, 2007 igarrido

Some time ago I design and build a development board to play with. It uses an AVR ATMega 8535 microcontroller, that has plenty of cool features.

(schematic here)

This board has a buzzer, 4×4 keypad, lcd, two leds, a pressure sensor and a expansion connector. It runs a program that:

Take samples from the eight ADC channels (625 samples/sec for every channel).
Send sample data through the serial port.
Reads key inputs (and do a “beep”).
Display the analog level from an ADC channel in the LCD. Keys 1 to 8 select the channel.
Display air pressure and estimated altitude, when press button 16.

It also has a bootloader that allow easy updates (a program that allows send the code trough the serial port without special hardware).

Also time ago, I begin to develop a java program to show the input data in the PC. I left unfinished, and now that I want to test some sensors, I decided to make it usable. Tough not completely finished, now it will be useful.

To test the ADC, the board has a pot that allows swing between 0 and 5 volts, but I wanted to look something more interesting, so build a simple sine function generator around the XR2206 chip.

This chip powers from 10 to 26 to volts (is use 12V), and the output is centered around half that. You can control the signal amplitude and try to lower the signal center (changing resistors values), but that saturates the signal at the lower level. So I took the basic application’s circuit, added some jumpers and a shift stage. Then build and after adjusting the amplitude and shift I get a nice signal between 0.2 and 4.8 volts, ready to feed my AVR board (please note that you shouldn’t use TL072, but a rail to rail opamp rather). That’s how it look:

Due to the fact the serial of most computers is limited to 115200 bps, and that every sample takes two bytes, the max samples I can send per second is 5000, hence 625 per channel. Even low, it’s nevertheless useful for a lot of things.
Future enhancements will include showing two or more channels in the same window and the option of selecting the channels to acquire and so increasing the sampling speed per channel.