Second ballnut for improve accuracy

[dazp1976]

There's no point buying expensive ballscrews unless the whole machine is built to the same very high standard.

To be honest it makes me laugh when I see figures quoted in the 0.001 range or higher from DIY builders because they are just fooling them selfs. Just leaning on the bench while measuring will affect most DIY machines as it deforms to match the bench movement at this level or precision. Measurments taken in the morning will be different than in the after noon and as the machine heats up, most don't even own measuring devices that are calibrated to that level.!

Precision of 0.01mm is about as good as you should expect from a DIY machine with C7 screws and bearings. Even then only expect this over a short distance because the thread pitch will vary over the length. Anything above this is a bonus and will most certainly vary over a length not much more than 300mm.!

Keep it real folks, then you won't be dissapointed.

Yeah. I'm happy enough with the 0.025mm I got it to. It's took me a long time of taking it apart, tweaking and rebuilding. The amount of thin alu foil shimming everywhere is ridiculous!!! lol.
The machine is over travelling a bit on proper calibration.
I've been cutting a few 300x150mm squares and they've actually been coming out at 299.98x148.98mm. I'll leave it at that
I won't need to go over 400x180mm in size so I add extra onto the edges of drawings. I'll leave it there as being within +/- 0.05mm for anything is good enough for me.

I do still need to work on the head. I need to make a spacer for it that's 0.14mm difference from end to end to bring it more square. I've got the column tilted atm. It's level with the table but not as it lifts and lowers. There is also still an issue with X where the screw mounts aren't perfectly straight with it. This is causing a tilt in the table as it travels full length so I'm limited to 300 of the 500mm available.

Yes I've had accidents with crashing dial indicators and there's stil loads of tweaking to do.