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Homing switches for the mill

My cnc mill itsn’t ready yet, but I hope it will be soon so I’ve been starting to learn a bit of gcode. Meanwhile here are my homing switches.

My approach here it’s very similar to the homing switches I did for the lathe some time ago. For X and Y axis I’d use the same type of micro optical switches; maybe RPI-131 from Rohm , maybe ee_sx1103 from Omron, not sure. For the Z axis I’d use a more typical H21A2 from Fairchild. Of course optical switches are only advisable when you can protect them from chips and debris.

home_swt_01 home_swt_02 home_swt_04home_swt_04After intalling and testing you should configure homing switch location and travel range for every axis (a trial-error process). Now I know the cutting envelope of my machine is 206 x 162 x 172 mm (8.1 x 6.37 x 6.77 inches).

Regarding to the nice spindle distribution box: I learn that doing deep pocket milling by hand in polyamide it’s a very unpleasant task (at least this 48x66x21 mm pocket).

home_swt_05Pleas note this is the only one polyamide part on the mill; other plastic parts are delrin made.

Broken

ultimas 024I use to do climb milling almost all the time, without any issue. Up to this day. Seems it’s widely known that climb milling can be dangerous if you have backlash in your machine. Well, this was not the case. After I broke the 5mm endmill in the picture I’d found the knobs (both) where pulled out of position by about 0.5mm. Maybe my fault; previously I had disassembled the whole crosslide to clean and install delrin nuts.

ultimas 030A bit later I continue, using 1/4″ three-flute carbide end mill. I don’t remember very well, but I was about to take about 0.3mm on the side, climb milling again. I begin ok, but suddenly, when the endmill was about to exit, the thing grasp into the corner and get stuck into the part. The tip of the endmill was out of position by about 2mm; a rotation in the headstock, purely by flex of all the parts of the headstock and column, was evident (maybe 1º). After unstuck the endmill from the part, the headstock return to his position. I was a bit shoked and forgot to take a picture. Luckily the endmill didn’t break, and there was no damage in the machine (picture doesn’t show original part damage, just a fraction).

Probably as most of my cuts are rather light cuts, there’s no problem with climb milling (max 1mm DOC and 0.5 for side milling). Some things that, perhaps, played against this time, were:

  • Thinner endmill. Usually I use a 3/8 endmill for side milling.
  • Two spacer blocks and a long ER16  chuck, giving a less rigid setup.
  • Slow cutting speed.
  • Cutting both on the front and on the side (6x11mm).
  • Less tight gibs. Previously it was not so easy to move the free carriage with the hand.

The good thing is that when things like this happens, you can go to Youtube and check videos like this, and feel a bit better.

One last thing…. now I’m convinced that an accelerometer-based automatic stop is a MUST on any cnc.

Killing cnc noise and Delrin nuts

I’ve been struggling in this days.

First, here my nice Z axis delrin nut. This was supposed to be split type, but I get (luckily) a perfect fitting so it wasn’t required. I grind my own threading bit, not bad for free hand.

delrin_nut-01 delrin_nut-02 delrin_nut-03

Turning the Z axis knob feels very soft, better than my manual mill. I’m not interested in measuring backlash by now, so  please don’t ask.  I also did a delrin nut for the X axis… but I’m still pissed because a stupid error, so I will not show it (seems to work well, though). Just remember…. when threading, always check a table with drill sizes for both, steel and soft metals, like this.

Later, when I test X and Z axis, an annoying idle-motor noise made me pissed again (not near like this, luckily).  All the world says that microstepping it’s noisy and you should live with it, but what annoys me was the fact that when I connect only one motor, there was no noise at all. After some fighting with a hammer against my crappy controller, I was able to eliminate the noise (better said, doing it almost inaudible) doing two simple things:

First, I connect the ground from the 5V supply to the ground of the 24V supply (brown cable). Seems I misunderstood STK672-050 datashet, which says you can use separated grounds for logic and power supply.

Second, I add a ferrite bead to the supply wires of every board. Seems to work better with at least a turn. I will bought a bunch on eBay (not snap type, just plain toroidal).

fixing_noiseNevertheless I should note that I’m driving the motors at 2.5A, not 3A as it should be, so maybe I find some noise later, but it’s ok for now. Please remember, I’m talking about idle motor noise; running motors will always do some noise.

I was easily able to get 70 IPM’s, seemingly without losing steps. I hope to do more testing once the whole thing get finished.

Just a last thing… using a laboratory regulated supply I found that when I set a current at 2.3A, the current draw from the supply, for the Z axis going up, was 1.25A. Not a surprise, but an interesting empiric data.

No THAT Monster

Here I will share some thoughts regarding Sherline milling machines.

First, Sherline mills are great machines.

  • Almost unbeatable price/quality.
  • Compact and lightweight.
  • Lots of accessories and even a cnc kit.

Second, these are nice machines, but not perfect. It seems most users are happy with their Sherline’s, but pointing most obvious weaknesses it’s healthy.

  • Weak column. A 10mm thicker column would be great.
  • Short throat. You need two spacer blocks on the headstock to be able to use the full Y travel.
  • No provision for delrin nuts.
  • Annoying motor location (inherited from the lathe, obviously).
  • No leadscrew/ways protection out of the box.
  • Gib system (it seems I’m the only one that hate the gib system, so ignore this).

Third. I think the “monster mill” philosophy it’s wrong. Basically, and this is my personal opinion, extending every axis and changing to ballscrews it’s not worth nor advisable. May be extending X axis and putting to ballscrew on Z axis, but a full monster mill it’s really ugly to me. I should also say that I prefer model  5000 over 2000, but I don’t think 2000 model be a bad deal.

So this:

column-headstock_2And still a lot of work ahead.

UPDATE: We are in 2015 and Sherline has a lot of new products and enhacements. Now they have a nice ways cover and a big spacer to give more throat.

Leadscrew/Ways Cover

A cover for the Sherline mill it’s a must if you wish your mill last. This is the typical “accordion” cover, a very practical solution actually:

Now here’s the leather/delrin cover I actually use. Tough not pretty, a good thing about it is that it allows easy access to X axis lock screw (something that I use a lot).

leather_cover-01leather_cover-02And here’s the new cover for my modified Sherline cnc mill:

sherline leadscrew covercnc_cover-02A bit radical but effective and easy to clean (I hope). I will comment the whole design once completed.

Now, the next things I need to tackle will be anti-backlash nuts and column mount.

Big fly cutter

Here is a very simple but highly useful accessory I made from a 13x13x40 mm block and a broken end mill.

flycutter-01 flycutter-02And here’s a 76x140mm flated surface.

flycutter-03There was some vibration due to the unbalanced rotating mass, something that I fix later adding a simple counterweight. And of course I took advantage of a not-perfectly trammed head to get a nice finish (about 15um less in the middle, not bad).

Finally a picture showing how useful is the side plate.

flycutter-04

UPDATE (01/09/13)

In the last working round I just note some upset behavior related to, I guess, thermal expansion. The DOC can increase, easily, 0.02mm after a couple of millimiters of feed. You can learn to deal with this, but now I think that a bigger mass cutting bit it’s a better idea (of course this doesn’t matter if you use coolant). Anyway, no matter what flycutter you use, I think a double finishing pass it’s always a good idea (0.03 and then 0.02 mm for example).

Cutting Thick Stock

Soon I will need to cut some 1″x3″ aluminum bars. I know the right tools to cut thick aluminum bars and plates are things like this:

horizontal_band_saw vertical_band_sawBut of course I can’t have these monsters into my small apartment.

Some guys say you can turn a wood band saw into a metal band saw adding some speed reducer and changing the blade. In fact, up to this point I’ve used  a cheap wood band saw as is to cut thick aluminum stock without problems (up to 1″). But I wanted something more appropriate and smaller, so I took a look at the Proxxon band saw.

Proxxon band saw

At first it seemed perfect, but after reading some amazon comments, I discarded this option (easy to understand if you read the specs: 85 watts; my wood saw it’s 250 watts). So I bought a Starret St1010 portable band saw, and start to convert it into a vertical band saw. Here’s the work.

band_saw-01 band_saw-02 band_saw-03 band_saw-04  band_saw-05band_saw-06band_saw-07

All was going well, but then I realized the damn thing was too noisy, at least to be used into an apartment. Here are the noise measurements at 1 mt of the running saws:

  • Cheap wood saw: 71 db
  • Starret metal saw: 84-89 db (it has variable speed)
  • My vacuum cleaner at full speed: 84 db

Noise reason was simple… metal gears inside. Tough at low speed noise level it’s similar to my vacuum cleaner, it’s much more annoying.  So, I will better off ordering a metal saw blade for my wood saw, and left my converted Starret saw into a corner, at least for now :cry:.

Shopping

After a almost three week home confinement because health issues (first my kid and then me) it’s great to take a travel through some hardware stores spread through the city. Yesterday was raining and today was sunny, so was a perfect day to walk. Here’s what I bought.

shopping

  • 6 mm two flute end mill. The size I most use. I ruin mine when it fell from my table; a small nick in some edge and say good bay to the good finish (I tried to resharpen it by hand… impossible).
  • 2 mm two flute end mill.
  • 3 mm two flute end mill.
  • 8 mm four flute end mill. As I understand two flute end mills works better for aluminum, but I use this size only for face/side milling and finishing, not for roughing.
  • 4mm tap set.  I have a set with one 4mm tap. But you always end up requiring the three set. Great Indian quality for the price.

Though usually I bought on eBay from sellers like NorthbayCuttingTools (great seller btw), there’s nothing as to look, touch and bought.