Ballscrew or leave alone?

[manofgresley]

Hi all.

As anybody a strong opinion on whether or not to change the standard drive shafts on my cnc converted milling machine to Ballsrews or leave the originals in.

Can anyone recommend which Stepper Motor Drive couplings are best for CNC application.

Regards

Ray

[birchy]

I'm dithering about with a Warco WM16 mill which I plan to convert to CNC but was planning on leaving the standard lead screws in and seeing how it performs. If it turns out to be crap, then I'll look at anti-backlash nuts, followed by ball screws. Ball screws cost about 5x the standard acme lead screws, but are they *really* 5x better?

[C_Bubba]

All I can say is when I converted my RF-31 back about 2000, I left the original lead screws in and within about 2 months (even with a one shot oiler), I had worn the bronze nut out enough to "walk" it down the screw with no rotational movement of either the screw or nut.
Worth 5x, Yep!

My thoughts anyway.

[i2i]

ballscrews all the way...worth 20 times the cost of the leadscrews.

[Jonathan]

Leadscrews are OK to get started, as it's generally very easy to just add motors and use the original screws. You can probably then change to ballscrews without wasting much if any money on parts. However, you'll soon find that backlash, low efficiency and wear (to name but a few) make the overall machine much less useful than it could be.

[Ross77]

ballscrews all the way...worth 20 times the cost of the leadscrews.

What he said..

You can easily get rid of backlash in lead screws by tensioning (or compressing) two nuts together but the resultant friction is often more of a problem than the backlash. My little mill has has this type of anti-backlash and I can get pretty much zero backlash but the friction is so high it is difficult to turn the hand wheel and impossible to get smooth motion. as already pointed out this will also result in the screw wearing out quickly.

The halfway house is to use brass nuts and a hydraulic tensioning system to self adjust for the wear and then replace the nuts as when they totally wear out. but by the time you set that up it is probably easier and cheaper to get a ball screw.

Don't be tempted to use delrin, been there done that and it has no place in milling machine. I've learnt from my mistakes and I'm getting ball screws for the next one.

[russell]

As anybody a strong opinion on whether or not to change the standard drive shafts on my cnc converted milling machine to Ballsrews or leave the originals in.

Clearly, yes some people have strong opinions.

Personally I think it depends on what you intend to use the machins for. I am using Delrin anti backlash nuts on my converted Chinese mill but then it is only a toy for learning and occasional use in model engineering. I have 1 thou backlash on both X and Y axes and it gives very little friction at that setting.

If you are going to use the mill every day for production purposes there is no question that ballscrews are necessary.

... just my 2 centimes worth.

Russell.

[Ross77]

Clearly, yes some people have strong opinions.

I am using Delrin anti backlash nuts on my converted Chinese mill but then it is only a toy for learning and occasional use in model engineering. I have 1 thou backlash on both X and Y axes and it gives very little friction at that setting.

Delrin will have reduced friction But I found that it just acted as a damper and masked the backlash. measuring low backlash only under a no-load condition. Once the load is applied it compresses until the the other edge of the screw is in contact( ie play in the screw/nut). The amount of compression is dependant on the load so you end up with varying amounts of error on the work piece.

[russell]

Delrin will have reduced friction But I found that it just acted as a damper and masked the backlash. measuring low backlash only under a no-load condition. Once the load is applied it compresses until the the other edge of the screw is in contact( ie play in the screw/nut). The amount of compression is dependant on the load so you end up with varying amounts of error on the work piece.

Agreed, this can be a problem but like everything it depends on the design. Some use springs to compress the split nut and of course these flex under load. I am just using screws to adjust it with no flexibility. My first attempt did have a flexibility problem which I traced to the flange on the nut flexing. It was cured by backing it with a substantial steel washer.

Again, horses for courses.

Russell.

[i2i]

at the end of the day, you're going to cnc a manual mill for what reason. You want an accurate computer controlled milling machine that will cut metals from ally to probably steel.

The first need is accuracy, which means ballscrews.

You don't need to go any further.