A Lathe Project

This is a project I start to gain skills on design and metalworking. Usually I only do simple pieces.

1. The idea: A precision mini-drill aimed to drill pcb boards (only the drill, not stand). It will hold typical carbide drills with a mini collet and rotate to about 10.000 rpm. Future work will include doing a stand for manual drilling and, why not, using in an always wished cnc machine.

2. The draft: I start about two weeks ago doing some drawing in acad. Below is the current state.

Some tolerances are fairly tight (in the order of several um); for example, the fittings of the bearings must be done with a tolerance of 10 um or less.

I’m sure this is not the best design, with lot questionable things. But I’m also sure it would be a lot better than the cheap drill I actually use for pcb drilling (and even the dremel).

3. The first piece: And this is the first finished (almost) piece I do some days ago. It’s done on 2024 aluminium and looks pretty cool.

I’m satisfied with quality and precision. For example:

• Diameter vary from to from 23.990 (front) to 23.983 (back). Maybe there’s a very slight misalignment of the spindle, fixable doing a simple adjust.
• In the rear I measure 15.995 and the bearing fits without pressure, so interference fit was not achieved, but it’s ok.
• Int the front, the bearing doesn’t fits easily; the measure I get from the hole is 15.975, so it’s a bit more tight than the target interference but I think that heating the piece will do the job. Thermal Expansion Coefficient Al 2024-T3 = 22.68 um/m C -> the hole will expand 18. 144 um raising temperature by 50 ºC.

I didn’t measure all sizes; only the critics ones.

4. The next: The next piece I want to do is the one in the center; but currently I don’t have the required tools (boring tools for deep hole), and after struggle myself if make or not the tools, I decided go the easy way and do an ebuy. May be meanwhile I try the main axis.

Overall

The more I detail the draft, the more find myself saying “how the hell will I do this piece?”. But that’s the idea.
Up to this time I have read several books on metalworking, but now I realize how different is theory and practice.