Fehlmann Picomax 50 CNC conversion/refurb

[Neale]

3 microns is an interesting number BUT what about the backlash?

when I was testing the touchplate setup on my router, I was getting repeatability to within +-0.003mm. Quick back-of-envelope sums showed that this was equivalent to one microstep. Might this be why this magic number is there? Mind you, my backlash is a bit more than that..

[Agathon]

As it happens Neal I've just run some more tests. Prepare to fall asleep! Contrary what the fool in the vid says, the Y does seven cycles!

Despite all the grunting (not mine) the steppers don't appear to be losing steps at 2500mm/min.



Actually, I don't know what the backlash is yet. I would think it was small but I need to set-up a proper test.

[Agathon]

Just measured the back-lash at 0.03mm on each axis. I'm a little surprised by this since I can't push/pull either axis by more than 0.01mm. The motors are coupled to the screws with flexible star-type couplings (see pic) - which are original and in good condition, but I have to say I've always been suspicious of. Now they are robbing me of precious microns!

Seriously though I can live with 0.03mm.

[Robin Hewitt]

Seriously though I can live with 0.03mm.

I used to tell myself that I could live with a slight backlash but deep in my heart of hearts I knew it wasn't true.

I move 5um per step. Could I watch it step 6 times without moving the table then sleep at night?

Difficult question...

[Agathon]

I used to tell myself that I could live with a slight backlash but deep in my heart of hearts I knew it wasn't true.

I move 5um per step. Could I watch it step 6 times without moving the table then sleep at night?

Difficult question...

I'm not sure I can either! After I posted I took another look and the back-lash is at the feedscrew. I think I slackened the pre-load on the X too much and need to tighten up the Y. Watch this space....

[Agathon]

Decided to strip the ball-screws and repack with new balls:

[Clive S]

Decided to strip the ball-screws and repack with new balls:

Very nice vid. Would you mind giving a link to where you purchased the balls from. Tnx

[Robin Hewitt]

I have my nuts sprung together one quarter ton. I hold the X screw in tension, Y and Z I crush angular contact bearings together. Everything is one quarter ton and feels glorious.

I sprung my Roland mini-mill to 200 lbf, I don't have a magic formula, I just use whatever seems right.

Do you have a way to inject oil in to the nuts or do you depend on that grease? I started fitting narrow bore nylon tube to carry oil but one of the push fit connectors didn't fit and I wanted to play cutting stuff so I left it out. I think I have to strip back and finish the job. Gravity feed is traditional but would that need wider bore piping? Such fun.

For a moment I was worried that I might have put you off with talk of backlash. Glad to see you back.

[hanermo2]

I have a comment.
I have seen credible comments from guys with experience, that the grease used in milling spindles, had great effect.

Re: heating at higher rpms, power used, etc.
Like 30-50% of the power went to heat, vs 5%, with better grease.
And noise decreased 50% or so, by tfar method.
(That Feels About Right).

Kluber Isoflex 15 is the gold std, for high end machine tool industrial spindles.
It is very expensive.
You need very little, about 1.5 cm3 for a big spindle bearing.

I bought a 50 gm tube, for 1 micron spindles I am making, 4 of, experimental/commercial test samples, with real abec 9/iso 2, bearings in 25 and 40 mm D.
I will make 4 test spindles, 2 of 25 mm and 2 of 40 mm, with both bearings, and see how they work.
Yes, the spindle at 40 mm is now hardened, ground, polished, has 2 microns tir (in spec, just) but I will use a soft lap and diamond paste to reduce the error a bit.

Anyway, better grease has reportedly made a major difference on spindles.
If You want some, I am happy to mail some Kluber "unicorn snot value" grease to You, free.
I doubt the grease has any major effect on accuracy .. but ..

I think it quite probable, perhaps, the grease can/will point out the next error in the chain.
Contact me any way You want, if You want to try some.
One email is greystoneprecision at the google mail dot com.

I do know for a fact, that modern cnc lathes (tools) use P4 bearings or better, since the packaging on mine says so.
And my factory training.
And these bearings do very much benefit from rgw better grease, mostly at higher speeds 2-5k and up.

Personally, I doubt it matters at low speeds, but think I might well be wrong.
CNC machining is often about corner cases, and stuff works different to what one might expect.

The tiny balls in bs supports and nuts actually run really fast at their surface speed.
Anyway, You want a bit, You can have some.
No conditions at all.

Decided to strip the ball-screws and repack with new balls: