Fehlmann Picomax 50 CNC conversion/refurb

[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:

[Agathon]

Hi Hanermo2 and thanks for your very comprehensive and convincing post on your experience of servos. I'm coming to the same conclusion. Steppers are fine for hobby machines, but for anything a bit more industrial a servo is the way to go. Fehlmann certainly dropped steppers within a couple of years and went to servos.

The Fehlmann is a slightly odd machine in that it's a drilling machine with milling capability - so despite it's industrial specification in terms of mass, the design is a compromise, with milling, and then CNC, as an afterthought. With that said they sold well in their home market. The latest generation of Fehlmann machining centres are built round a conventional square slide-way for the Z axis, but they still produce a manual and semi-cnc/manual version of the Picomax: http://www.fehlmann.com/en/products/...picomaxr-21-m/

I was interested in what you mentioned about direct drive. When Fehlmann switched to servos (see pic) they mounted the motors remotely - not sure if it's a belt or gear drive, but suspect belt. The latest semi-cnc/manual of the drill mill that I have also has remote servos - I'm not sure about their machining centres.



Having reassembled the ball-screw, replacing it proved interesting since the nuts, or rather the keys in the nuts, didn't want to go into the key-way. The key-way or the keys were obviously minutely out of line with each other. A rub over a stone got them to slide in, but the results from the screw were disappointing - still not sure why. It could be an alignment issue - which seems strange given the precision nature of the table and the screw, but it's the sort of thing I've regularly encountered with precision machine tools - a lot of fettling takes place when these things are built. Anyway, I decide to but the nuts on the in the original orientation which seems better, but I can't get the backlash better than 0.01 without sacrificing the smoothness of the screw. I will tinker some more today.

I've had 20 years experience rebuilding machine tools and generally I've found that even if a bearing's tracks look good through a loupe they may well be slightly rough when under load. This is sometimes due to poor fitting (hammering the inner) and tiny imperfections are left on the bearing tracks which will only show up under a microscope. I suspect that the ball-screw and nut assembly have similar issues. I'm not about to replace them so will live with the 10 microns of backlash.

Thanks for your offer of the Kluber Isoflex. This is a product I'm familiar which since it's specified by some of the manufacturers I deal with. I actually use an SKF LGMT2 which has a similar specification and was more readily available at the time I needed it. In fact the Fehlmann's central lubrication system covers everything from the spindle bearings through to the ball-screws and everything in-between. The Vaseline used was just to get the balls to stick to the nut during assembly - it will soon wash out.

If you're ever in my "neck of the woods" you'd be more than welcome to visit.

[Agathon]

I forgot to say that it would be nice to see a photo or even a video of you CNC machine(s).

David

[Agathon]

I will, and may put in 0.1 micron glass scales (thats the plan, anyway).

I forgot to ask about the above which intrigued me. What control system are you using? Are you planning on linking the scales back to the controller in a closed loop? Can this be done?

[Agathon]

Spent the evening trying different permutations of the ball-nut assembly and the best I can achieve on both axes is 10 microns. If this were a conventional manual machine I'd be overjoyed with 4 tenths of a thou! In fact the very expensive Swiss machines that I sell have a backlash from new of around 0.01-0.02 mm.

Anyway, the machine is running very nicely and the back-lash compensation on Mach3 is working well.

As I frequently say to my customers "it's a metal cutting machine not a grinding machine" so I don't expect nor want to machine to tolerances better than +/- 0.005. I certainly don't think it will be a problem in respect of climb milling.

More soon...

[hanermo2]

Yes, the scales can feed back to the controller, at least thats what the makers say.
CSMIO-IP-S on lathe, from cslabs.

Somewhat expensive, very good, very good value for money.
Even if I only got dros from the scales, it would be good enough for my use via sw macros.

I am aiming for extreme resolution, repeatability, and fairly well willing to spend money.

I forgot to ask about the above which intrigued me. What control system are you using? Are you planning on linking the scales back to the controller in a closed loop? Can this be done?

[hanermo2]

Swiss backlash 0.01 mm new ??

I would have expected your picomax to have zero to 0-1-2 microns backlash.
I suspect the bs fixed end bearings are not properly adjusted/preloaded, or ..
.. your ballnut is loose/failed somehow and has no preload.

Easy enough to test.
Dti screw end, while loading back/forth with a prybar of some type, separately on screw end and on nut end/assy.
One should have a major deviation vs the other.

Spent the evening trying different permutations of the ball-nut assembly and the best I can achieve on both axes is 10 microns. If this were a conventional manual machine I'd be overjoyed with 4 tenths of a thou! In fact the very expensive Swiss machines that I sell have a backlash from new of around 0.01-0.02 mm.

Anyway, the machine is running very nicely and the back-lash compensation on Mach3 is working well.

As I frequently say to my customers "it's a metal cutting machine not a grinding machine" so I don't expect nor want to machine to tolerances better than +/- 0.005. I certainly don't think it will be a problem in respect of climb milling.

More soon...

[Agathon]

I've checked everything and it's all correctly adjusted - first thing I thought of was movement in the pillow-block bearings but there's no movement here. If I take the ball-nut preload one increment higher on the vernier the screws become notchy. It's probably just down to wear and tear. We'll see what the performance is like in practice.

[Robin Hewitt]

You are being very vague, is this sprung or a simple crush?

[Agathon]

You are being very vague, is this sprung or a simple crush?

Crush.