[digits]

Hi, I have a CNC'ed X1 (CNCFusion kit ) with the standard ACME screws. I was making some tooling at the weekend and all of my circular pockets are distinctly deformed at the point the X-axis changes direction. Right to left seems worse than left to right - could this be down to an interaction with the direction of tool rotation?

Anyway, is there anything I can do about it? I am running Mach 3 - it has software backlash correction, but that seems like a last-resort from the manual. I'd also need to know what the backlash actually is - any ideas how I measure it?

I believe the X1's ACME nuts are adjustable, is it possible to adjust it without removing the table by cranking the table all the way over to the right and then using a long screwdriver to adjust the set-screws?

Cheers.

[Pres]

Backlash compensation won't do much to help you machine round circles.
The only way to do it right is to remove backlash - as much as possible.

Yes, you can adjust the leadscrew nuts some amount by changing the pressure on the nut split screws.
(make sure they are well lubed & also the ways)

Long term, the best solution is get ball screws -as accurate as you can afford to buy.

Checking backlash is covered in many other posts - just search for them.

To me, the "acid test" of any mills accuracy is how round it can machine a circle.

Good luck,
Pres

[sld4121]

Backlash is basically the amount of "non-movement" you have in your machine axis when you reverse direction. Simply measured by using an indicator.

Even IF you upgrade to ball lead screws, you could still have backlash and quadrant marks, just to a lesser degree. You may also have an issue with your settings. How much error are we talking about?? How much error can you live with?? How much are you willing to spend to get "perfect circles"??

In any case, measure your backlash and add the compensation amount. It should help and you will also find your point to point operations will be more accurate as well.

[digits]

Backlash compensation won't do much to help you machine round circles.
The only way to do it right is to remove backlash - as much as possible.

Yes, you can adjust the leadscrew nuts some amount by changing the pressure on the nut split screws.
(make sure they are well lubed & also the ways)

Long term, the best solution is get ball screws -as accurate as you can afford to buy.

Checking backlash is covered in many other posts - just search for them.

To me, the "acid test" of any mills accuracy is how round it can machine a circle.

Good luck,
Pres

Thanks - I am looking to upgrade from my X-1 to something larger and faster, but I do need it to make some parts right now. I will have a play with the split nuts.

[digits]

Backlash is basically the amount of "non-movement" you have in your machine axis when you reverse direction. Simply measured by using an indicator.

Even IF you upgrade to ball lead screws, you could still have backlash and quadrant marks, just to a lesser degree. You may also have an issue with your settings. How much error are we talking about?? How much error can you live with?? How much are you willing to spend to get "perfect circles"??

In any case, measure your backlash and add the compensation amount. It should help and you will also find your point to point operations will be more accurate as well.

Thanks - I don't expect perfection, but I would expect circles to 'look' round even if measurements indicate otherwise. I would estimate that I have about 0.5mm of error - which looks awful. I will have a go at actually measuring it tonight though.

[sld4121]

I would certainly expect much better than .5 mm even with acme screws.
Yes, adjust the split nut first as that is where the bulk of your backlash is probably coming from. Then, measure and tweak the backlash comp to see if you can get more improvement. FYI - In my experiences, you will probably always see the quadrant marks though.

Good luck!!

[phantomcow2]

You should not have to remove the table to adjust teh antibacklash nuts on your X1. Just crank it over as far as possible as you've described.
There is not enough room to fit the standard, low cost, 5/8"-.2 ballscrew in the X1. But You can get a 3/8" ballscrew in there just fine, get two nuts and preload them. I suspect it will be around 100 dollars, but it will be well worth it. Call Roton for prices that are not a guess!

[pastera]

This is not my page but shows how it can be done.
http://www.aonx97.dsl.pipex.com/WS-page/X1CNC/X1CNC.htm

You can fit the 5/8" ball screws with the extended axis kits but you need to do a fair amount of cutting.


Aaron

[digits]

I would certainly expect much better than .5 mm even with acme screws.
Yes, adjust the split nut first as that is where the bulk of your backlash is probably coming from. Then, measure and tweak the backlash comp to see if you can get more improvement. FYI - In my experiences, you will probably always see the quadrant marks though.

Good luck!!

I didn't adjust anything, but cut some more pockets last night at a much lower feedrate - 50mm/min 4mm slot mill, 0.5mm/pass - it was much rounder, so I guess either the machine or the endmill were flexing when I was cutting at 250mm/min.

I will have a play with the split nuts and see if that improves things.

[digits]

You should not have to remove the table to adjust teh antibacklash nuts on your X1. Just crank it over as far as possible as you've described.
There is not enough room to fit the standard, low cost, 5/8"-.2 ballscrew in the X1. But You can get a 3/8" ballscrew in there just fine, get two nuts and preload them. I suspect it will be around 100 dollars, but it will be well worth it. Call Roton for prices that are not a guess!

I think I'd be looking at well over £100 in the UK - $100 might buy me 3/4 of a ball nut! I can't even fall back on eBay as eBay in the UK is useless!

[digits]

This is not my page but shows how it can be done.
http://www.aonx97.dsl.pipex.com/WS-page/X1CNC/X1CNC.htm

You can fit the 5/8" ball screws with the extended axis kits but you need to do a fair amount of cutting.


Aaron

Thanks - that is a good site. I am beginning to think that I should have bought a pair of mills so that I'd have one to use to modify the first

[pastera]

If you get the extended axis kits you can use the old parts to machine the new ones.

Aaron

[digits]

If you get the extended axis kits you can use the old parts to machine the new ones.

Aaron

Mine is a Super X1-L so it has both the extensions and the stupid tilting column out of the box! I suppose I could order spare parts and mill those, but I'd rather use my X-1 to build a whole new, bigger machine! It's just a shame that that's the hard way round

Right now, I'm trying to make some tooling to allow me to make a motor plate to mount the X3 motor on my X2-head. I have some nice contours on that plate, so I'm hoping I can dial some of the backlash out with a tweak to those split nuts.

I had also hoped to use the X-1 to cnc out a motor pulley, but right now I just don't think it would be round enough

[pastera]

How about making some Delrin nuts? You would only need a length of leadscrew to make a homebrew tap (or a lathe).

Aaron

[phantomcow2]

How about making some Delrin nuts? You would only need a length of leadscrew to make a homebrew tap (or a lathe).

Aaron

Dumpster CNC mentioned that delrin nuts will flex too much for use on milling machines. He specifically mentioned the Sieg X2.
"Friction is one variable that can cause backlash with these lead nuts, I've tried these on a Sieg X2 mini-mill and with the gibs tightened, the backlash was .003-.005 due to the natural flexing of the Delrin... the tighter the gibs, the more the Delrin flexed. The high friction of the mini-mill gibs makes these a poor choice for that type of machine."

[BrendaEM]

I saw some anti-backlash projects here:

http://www.billsbest.com/thatlasacme.html
http://www.cnczone.com/forums/showthread.php?t=20527

And a delrin/acetel gib project here.
http://www.fignoggle.com/machines/x2...gibsAcetal.htm

This X1 looks like it has ballscrews (see page bottom):
http://www.embeddedtronics.com/micromill.html

I also wonder if you can make some kind of anti-backlash situation using a heavy preload spring, such as a car valve spring. I would guess you would want just enough preload to negate the linear force, but not so much to add additional resistance to already inefficient acme screws.

It would seem that even the lubricant used on acme threads would have some effect on the backlash: Do you expect the grease to take the slack out, or should you worry that it would give a false preload inidication.

I assume that sometimes the choice of tool path can have a bearing on the amount of backlash; in other words, taking up the backlash before making a cut, though that may not help you make a circle.

[It seems to make a case for optical encoded servo motors.]

[digits]

I was cutting a motor mount last night, after having adjusted the X-axis split nut, and the results were much better, though perhaps that's just because the circle I was milling was far larger than before.

It's just a shame that I now have nice round chunks gouged out of the clamps I spent a week making because my toolpath was slightly larger than I'd realised - D'oh!

I still think some of the problems are down to machine and endmill rigidity - slower cuts are much cleaner, and I don't think speed wouldn't affect backlash, unless the cutting force is actually compensating for or making it worse.

I went to the London Model Engineering Exhibition on Saturday - and saw some stunning 3D milling from a ball-screwed X3. I am now convinced that ball-screws are a must for my next machine!

[Pres]

..... . I am now convinced that ball-screws are a must for my next machine!

Yes, and your EXISTING machine also!

X1's love having balls too

[digits]

Yes, and your EXISTING machine also!

X1's love having balls too

Yes, but unfortunately ballscrews cost real money in the UK - I'm looking at over £200/$400 per screw/nut/bearings in my next machine, and I've got more than 3 screws to save up for!

[LongRat]

Just buy them from the US then. Even with import charges, you are looking at a huge saving compared with anything available here. That's what I did for the ballscrews for my X2.