file Frage Ball Screw replacement for wearing thread nuts

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15 Apr 2016 20:12 #33203 von finch
Hi guys,

It's looking like we are going to have to change all of our machines screw bushing nuts as they have once again become worn, and now there is almost a mm of slack on all axis as a result of the screw being loose inside the bushing.

We are looking at upgrading our machine - using an 8 or 10 mm miniature bearing ball screw, and replacing the screw rod with a precision threaded rod

Has anyone already tried this? , or can anyone think of why this was not offered as a standard, given how often, and how labour intensive a job replacing the bushings and re-aligning the machine is.

Nick

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03 Okt 2016 14:07 #37956 von Doug
I would be interested in details of how you achieved this modification if you progressed it.

It's something worth looking in to but I presume would require bespoke housings to be made to hold the ballscrew.

DOug

Stepcraft 2/840, StoneyCNC industrial HF spindle, 4th axis, TurboCAD 2016 Professional 64 bit, MeshCAM, GWizard feeds & speeds calculator, UCCNC
Hobby use: guitar building (luthiery), www.facebook.com/DougShortGuitarBlog/

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03 Okt 2016 18:50 #37969 von Calleja
It will be a great idea and also for Stepcraft to upgrade to ball screw system.

Stepcraft 2 430
Kress 800 FME
UCCNC + UC100
Cut2D Desktop

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05 Okt 2016 23:35 #38031 von peterg1000
What would be ideal would be to replace the nuts on the leadscrew with ball nuts - trouble is that these are really expensive items!! They would not be justified unless the leadscrew bearings were made to guarantee minimum end play ( < 0.001" say ) as well.

Peter

SC 420/2, Industrial VFD spindle from StoneyCNC
UC100 + UCCNC
Cut2D, Autosketch10, Draftsight, Eagle 9.5.1


There is no problem, however simple, that cannot be made more complicated by thinking about it.

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06 Okt 2016 03:18 - 06 Okt 2016 03:19 #38033 von Doug
I mentioned this to Rory in a recent e-mail and he commented that ballscrews are a "different ball game" in terms of integration. Sadly, I don't think that this is a simple matter of making or sourcing a small ballscrew unit that can just slot into the existing mount. Look at the small clearance between the brass nut and the track rollers. This would likely be showstopper on its own sadly.

Doug

Stepcraft 2/840, StoneyCNC industrial HF spindle, 4th axis, TurboCAD 2016 Professional 64 bit, MeshCAM, GWizard feeds & speeds calculator, UCCNC
Hobby use: guitar building (luthiery), www.facebook.com/DougShortGuitarBlog/
Letzte Änderung: 06 Okt 2016 03:19 von Doug.

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06 Okt 2016 05:02 #38036 von finch
Well, we have had continual y axis jams as a result of the bushing system. And attempted, I think 8-9 large 3d prints with around 6 rolls of pla.... none of them have finished. We have sourced a balls crew relatively cheaply compared to the machine price, they should be on there standard for a machine of this cost !

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06 Okt 2016 09:27 - 06 Okt 2016 09:28 #38039 von peterg1000

finch schrieb: Well, we have had continual y axis jams as a result of the bushing system. And attempted, I think 8-9 large 3d prints with around 6 rolls of pla.... none of them have finished. We have sourced a balls crew relatively cheaply compared to the machine price, they should be on there standard for a machine of this cost !


Y axis problems are difficult to resolve unless "tuning" is meticulous. I spent days getting mine right. I even went to the lengths of measuring the torque required to move it over the whole range of positions - very tedious but worthwhile, I've never had a a suspicion of jam fortunately.

There are many potential sources of friction, and you'll have to identify and rectify each in turn. In particular the adjustable rollers on the Y axis must be very carefully adjusted to just, and only just remove free play after the X-axis is finally adjusted.

Kinematically speaking this is a poor design with 16 potential contact points when only 5 are needed, but all machines of this type have this problem to a greater or lesser extent.

On top of that it is vital to ensure that when the gantry is at the opposite end to the drive, the end bearings line up exactly with the leadscrew. I had to relieve the bearing seats to achieve this on mine - only by a fraction of a mm, but it made a huge difference to the driving torque required.

Overall it is not a five minute quick tweak to get it all correct - patience is well rewarded.

It is not the ball screws where the major cost lies, but in the recirculating ball nuts. A set of four would probably add 25% or more to the kit price, quite apart from changes necessary to mount them and adjust the machine correctly. A whole new ball park if you will forgive the pun!

Peter

SC 420/2, Industrial VFD spindle from StoneyCNC
UC100 + UCCNC
Cut2D, Autosketch10, Draftsight, Eagle 9.5.1


There is no problem, however simple, that cannot be made more complicated by thinking about it.
Letzte Änderung: 06 Okt 2016 09:28 von peterg1000. Begründung: typo correction

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06 Okt 2016 12:50 #38043 von finch
Agreed, the biggest cause of error by far we found, was the brass bushings wearing loose with use, by the end we could move the gantry by .5 to 1mm with y axis screws stationary.


I just had a quote for 4 ball screws ( 1.5, 1.5, 1,and .35 meters with 4 ballscrews, bearing blocks and couplers, 6x20 mm linear rails, with 12 linear blocks with grease nipples for $550 posted. We paid over 3000 for our machine. I think we've paid 200 pounds for the custom balk screws to replace the y, x, and z screws.

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09 Okt 2016 04:07 #38098 von Proto
Saw this, could be a solution.

Stepcraft ballscrew nut holder

Now if I could just find a supplier in the US :)

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09 Okt 2016 10:41 #38102 von peterg1000
Hi

Wow!! A solution at last perhaps. I wonder if the original Stepcraft ballscrews can be retained or if they would need to be replaced - hopefully not.

I found this catalogue for the manufacturing company - lots of mouth watering goodies there.

The adaptor looks to be pretty simple - if enough interest could be raised on this forum then I'm sure they could be manufactured commercially at a sensible cost. Is it possible to put together a list of interested parties on this forum??

I for one would be interested in doing this modification.

Peter

SC 420/2, Industrial VFD spindle from StoneyCNC
UC100 + UCCNC
Cut2D, Autosketch10, Draftsight, Eagle 9.5.1


There is no problem, however simple, that cannot be made more complicated by thinking about it.

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09 Okt 2016 10:57 #38103 von Proto
I'd be interested, but I'm also interested to know how much the ball screw nuts cost since they want you to call for the price. That may be a deal breaker for me. I have a brand new machine I haven't even been able to use yet because I'm waiting for missing parts, one of which happens to be a ball screw nut :) Would rather do this from the start than disassemble everthing, but I don't think I can wait any longer.

Moore International FGR 10x3 Carry Ball Screws NUT

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09 Okt 2016 11:45 #38104 von peterg1000
Hi,

I'd just found Moore myself - looks promising.

I'll fire off an email to Moore expressing potential interest and see what they can offer in the way of price breaks. It wouldn't surprise me if thay are talking £50 + for small quantities. The adapter should be more reasonable - I would guess < £5 once setup costs have been absorbed. Incidentally, unless I am mistaken and read the catalogue incorrectly, the tap required for the adapter thread is M18x1 not M20x1

The thing that grates with me is that the originator suggested cutting a flat on the ball nut to make it fit - ughh!! Milling a shallow recess in the mounting plate would seem a more rational engineering solution - more difficult though I agree. You'd need your Stepcraft to be working if another mill isn't available.

Quoted backlash appears to be 0.06mm ( 0.0024") but apparently this can be bettered if matched screws and nuts are supplied. Expect to need a mortgage for these!!

Peter

Peter

SC 420/2, Industrial VFD spindle from StoneyCNC
UC100 + UCCNC
Cut2D, Autosketch10, Draftsight, Eagle 9.5.1


There is no problem, however simple, that cannot be made more complicated by thinking about it.

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09 Okt 2016 16:37 - 09 Okt 2016 16:37 #38106 von finch
We purchased our Miniature ballscrew from the Uk, we had a mount like that one shown, 3dprinted out of nylon which arrived, and looks great, and fits.

The stepcraft screw, is not designed to have balls in it, so you gonna have to fork out ~200 pounds for a set of 3 custom ballscrews, and then do some DIY to get them mounted

I can post pics of our one, once we have all the bits
Letzte Änderung: 09 Okt 2016 16:37 von finch.

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09 Okt 2016 17:26 #38108 von peterg1000
Hi Finch

So Stepcraft use a non-standard lead screw - that's a bummer!! It looks just like the Eichenberger ones too.

I guess any new screws would need the appropriate end treatment to get them to match the existing - at least there is minimal machining required - turn to size and grind a flat at one end after annealing?

Do you have a note of any of the critical dimensions such as lead screw length etc, and center height above the mounting plate? The ball nut adapter looks fairly straight forward to DIY in aluminium or brass and would require the purchase of an appropriate M18x1 tap. I've a mini-lathe and mini-mill that would make that very straightforward.

Do please post some pics - I've wanted to ball nut the machine for ages, using backlash correction doesn't always seem to do the business when I'm milling pcb's.

Peter

SC 420/2, Industrial VFD spindle from StoneyCNC
UC100 + UCCNC
Cut2D, Autosketch10, Draftsight, Eagle 9.5.1


There is no problem, however simple, that cannot be made more complicated by thinking about it.

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09 Okt 2016 19:27 #38109 von finch
Pete, it's pretty easy.

I'm not too sure about the compatability, but I believe, you need a ballscrew to install a ballnut. Goodluck trying to figure out what sized ballnuts will work with a leadscrew. I understand that leadscrews use bushings only and are never intended to have bearings running up the thread.

Remove one of your existing Y screws, measure up the threaded length, and measure the end diameter, the ballscrew shops machine most ends to whatever you like.

Our initial plan, is just replace old leadscrew, with new ballscrew machined so the ends match, so we can use the rest of the machine as is.

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09 Okt 2016 20:40 #38114 von Proto

peterg1000 schrieb: The thing that grates with me is that the originator suggested cutting a flat on the ball nut to make it fit - ughh!! Milling a shallow recess in the mounting plate would seem a more rational engineering solution - more difficult though I agree....


I agree, not sure what his logic was.

Could anyone be kind enough to explain how the ends are different, and just the basic differences between a lead screw/ball screw? I'm a bit new to all this and haven't really researched that aspect so far.

I'm kind of disappointed to read about these problems when I haven't even started using my machine yet!

Peter, like you, I want to do some basic prototype PCB's and also some stuff with aluminum (or aluminium :) ).

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09 Okt 2016 21:50 #38116 von Doug
I'm interested in this modification in the longer term. I haven't even started using my machine yet though!

I could swallow a couple of hundred pounds for a significant upgrade to improve backlash and longevity.

Doug

Stepcraft 2/840, StoneyCNC industrial HF spindle, 4th axis, TurboCAD 2016 Professional 64 bit, MeshCAM, GWizard feeds & speeds calculator, UCCNC
Hobby use: guitar building (luthiery), www.facebook.com/DougShortGuitarBlog/

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09 Okt 2016 23:07 - 09 Okt 2016 23:10 #38119 von peterg1000
Hi,

Sorry - I've been a bit lax in my terminology, I written lead screw on occasions when I should have said ball screw. I think lead screw is properly applied when an Acme or similar thread is used - but I will bow the those more knowledgeable than I.

Unfortunately we cant get aluminum in the UK, all the stockists have here is alumunium so I'm stuck with that!!

On reflection, I'm 99% certain that the ball screw used is going to be a standard off the shelf item, otherwise the tooling costs would have been prohibitive for a startup enterprise. Stepcraft were after all building down to a price so as to gain a foothold in the market.

The picture in a previous link shows the FGR ball nut on a standard Stepcraft ball screw, so I think that makes it almost certain that it's a standard item. Perhaps there is someone in the know who can confirm that.

I don't at the moment see any need to go over the top with the end bearings - this is a light weight machine, so fitting double row angular contact bearings wouldn't make sense. In any case the smallest I have been able to find are 10mm id, so wouldn't be of use for a 10mm ball screw. In the event I think all the existing ball screws have 3mm ends of various lengths machined to fit ball bearings or coupling sleeves.

Peter.

SC 420/2, Industrial VFD spindle from StoneyCNC
UC100 + UCCNC
Cut2D, Autosketch10, Draftsight, Eagle 9.5.1


There is no problem, however simple, that cannot be made more complicated by thinking about it.
Letzte Änderung: 09 Okt 2016 23:10 von peterg1000. Begründung: Typo!!

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10 Okt 2016 03:12 #38120 von Proto

peterg1000 schrieb: Unfortunately we cant get aluminum in the UK, all the stockists have here is alumunium so I'm stuck with that!!


Not to get off topic, but it was my understanding that aluminum and aluminium were the same thing, we just call it differently here and there. Am I wrong?

If we can get the parts and make the pieces etc., I'm willing to give it a try just doing a single axis, like X or Z just to see how it works. I just can't afford to spend a lot at the moment since I just got my machine and I have accessories and enclosure etc. to get.

Post back when you get the details about the cost.

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10 Okt 2016 06:00 #38122 von Worldhusky

Proto schrieb:

peterg1000 schrieb: Unfortunately we cant get aluminum in the UK, all the stockists have here is alumunium so I'm stuck with that!!

Not to get off topic, but it was my understanding that aluminum and aluminium were the same thing, we just call it differently here and there. Am I wrong?


No - not at all! That's the same stuff with different names. But I never heard about "alumunium". :huh:
Aluminium versus aluminum

It's not only about tools it's also about skills! ;)

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