Acceptable wear limits on a milling machine

Hiya,

got a thread running over in the manual machine tools section detailing the rebuild of my Beaver mill.

As I am stripping it down I am noting some wear on the ways for the knee, saddle and table.

Its a big old beast and I didn't have the chance to see it working before I got it so can't tell how much movement there was on the different axis.

So, in general, what sort of wear can you get away with on the relevant surfaces? Whats the best way to measure the wear and what would you do to fix it?

Any advice gratefully received

Thanks,

Paul.

I refurbished an old Bridgeport, the worst wear was to the saddle slides, about 20 thous dip in the middle of the knee. I attacked it with files and scrapers, a straight edge and a surface plate, took about ten days to get it to an acceptable condition. Very satisfying but I wouldn't do it again. There was some wear in the table slides but I learned to live with it. Regrinding is possible but you have to decide how much you are prepared to put into it. The trouble is, there is often wear everywhere, screws, bearings etc. Once I had the worst sorted, I treated it as an ongoing project and dealt with things as they became necessary (essential).

Dave

Thanks Dave,

been reading up on scraping, may end up having to do some but was trying to figure out which bits would need it most as I don't really want to spend days scraping every surface

Any advice on how to measure wear on the different surfaces?

Cheers,

Paul.

Thanks guys, off to read up on tramming

Also need to understand better how much wear you can take out with adjusting the gibs. The way on the edge of the knee where the saddle gibs clamp onto has a slight groove worn in it about 5 thou deep, need to figure out how much this will affect things.

cheers,

Paul.

Paul, I your photo show a groove in the surface, is it possible to make a wider gib so that it runs on the unworn part?

I used a 12" X 2" X 1" straight edge and 18" surface plate for the top of the Bridgeport knee. If you have an adjacent flat (reference) surface it's possible to do a quick check with a sensitive DTI and stand. It is most important to establish a reference surface (you measure from this to the part you are working on) before removing any material, if there is no adjacent or opposite surface you will need to work from a surface plate. without the reference surface, your part may finish up flat but could be tilted in any direction. I found it best to mark out the high areas with a felt tip pen and remove the material with a file, grinder or whatever means is quickest, do a little at a time and check often to ensure you don't take too much off. Once you have the area reasonably flat, you can start with scrapers and blue to get a bearing surface. Carbide scrapers are best, you can make them, you can also make them from old files but will spend as much time sharpening them as using them. If the part is worn hollow in the middle but not at the ends, keep a small area at each end intact and use these as your reference, remove the ends when you have got the middle part flat and then scrape to finish. Don't waste too much time on surfaces with scratches or gouges, if the rest of the surface is OK, just dress the scratches flat with a smooth file.

Dave