Fehlmann Picomax 50 CNC conversion/refurb

[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]

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.

[Robin Hewitt]

It was a bit of a bodge springing mine, I added a spacer and 2 Belleville washers. Well 6 spacers and 12 washers to do all the bearings and nuts. But the reward was out of all proportion to the effort.

[Agathon]

It was a bit of a bodge springing mine, I added a spacer and 2 Belleville washers. Well 6 spacers and 12 washers to do all the bearings and nuts. But the reward was out of all proportion to the effort.

So, if I'm interpreting that correctly, you have a double ball-nut set-up like my machine?

I could do something like this although it would mean making a new retaining flange. I have to say that apart from grinding spindles, I'm not a fan of spring-loaded solutions. I'm also not convinced that backlash of 0.01 is much of an issue. My conventional mill has about 0.25 backlash and it's only a problem with heavy climb-milling or slot milling and then it can be overcome by reducing the feed rate and the depth of cut. Mind you the table and slide alone must way 200kg - mass helps, as do well adjusted gibs.

I meant to have asked what the rest of you mill consists of Robin - got any pics?