[flojor10]

I am a newbie at cnc, I just finished building my 20x20x5 diy cnc. I am not happy with precision I have with it (+/-.01 in) and want to start to build one that can mill aluminum with .005-.001 precision. I would like to reuse most of the components of my old machine. I am unsure whether to go with a moving gantry or table, and what material to use. Should I upgrade to a 4 axis design or stay 3 axis? I need better precision and I have a budget of around 200$. Any ideas, tips or machine plans would be greatly appreciated.

Here are some of the components I would like to reuse:

SBR 12 Rails- 4x 20in rails and 2x 8in rails

3 300oz/in Nema 23 Steppers+ Driver Board 1/16 stepping capable

Acme 3/8-12 Lead Screws

3 Anti-backlash nuts and Motor Couplings from Dumpster Cnc

George F.

[CaptainVee]

I think the biggest improvement would come from switching to ball screw spindles.

[ger21]

I don't think the screws have anything to do with your lack of precision.
If the best you can get is .01", then it's probably due to the quality of your fabrication, or flex in the machine. It's not that difficult to build a wood machine with acme accurate to within .005", if you have the fabrication skills, and use a good design.

To machine aluminum to .001, you'll need a machine that's about 100 times more rigid than what I see in the picture. Personally, if I was mainly cutting aluminum, I'd use profile rails like THK's or Hiwin's, and ballscrews, and build the machine out of steel and/or aluminum. Multiply your budget by 15.

The best thing you can probably do for $200, is rebuild the wooden structure. The rails you're gantry is running on should be longer, and the bearings should be at least 8" apart, with the gantry sides being triangulated. This will give you far more rigidity. From the looks of it, I'd guess you can push on the top of your gantry and move it 1/4".

[cyclestart]

I am not happy with precision I have with it (+/-.01 in)

Without knowing how the measurement was done the number has no context. (+/-10 over 20" is a different figure than than +/-10 over 1" etc etc). If the measurement came from a test cut there are many factors to consider. Looking at your machine, flex would be one of those factors.

The dimensions of your machine suit moving table. The problem is to maintain 20" x travel with the existing rails, a typical moving table design needs longer rails to get the same travel as a moving gantry. Here's a link with a bit of design info:
The Hobby CNC Router: Builders Guide Step 1

Triangles are your friend when fighting flex.

[Walky]

Switch to SBR16 if you can, I've found them to have a much nicer fit than the SBR12. Also, I agree that you'll need a much, much rigid structure than the one on the pictures.

[RossMosh]

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I'd start looking there if you want something for working with metal. Even if you're talking about soft metals. Mills are just heavier in every way. You can mill some aluminum on good wood routers, but it's definitely not what they are designed for.