Source for Reasonably Priced Ballscrew?

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SteveHGraham
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Source for Reasonably Priced Ballscrew?

Post by SteveHGraham »

I decided to see about making my CNC mini lathe function. Hooking a KFlop up to Windows 10 is a real adventure. Assuming I manage that, I would like advice on a source for a reasonably priced ballscrew. The plans I used specified a plastic nut and a multiple-lead screw, and the accuracy is not great (z direction). The x accuracy is better, so I don't plan to mess with it right now.

I tried to get this question answered at CNCZone, but it seems like you have to know the Pope to get a response over there. I have seen people recommend a Chinese Ebay vendor called linearmotionbearings2008.

It looks like I need 20" of thread plus 2" turned down to 1/4" in diameter to be on the safe side. The travel is more like 12", but the screw has to be long to extend into the right-hand mount.
Every hard-fried egg began life sunny-side up.
WJH
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Re: Source for Reasonably Priced Ballscrew?

Post by WJH »

Cheapest source is Ebay, but you'll need two ball nuts to remove backlash. McMaster Carr would be the easiest place to get what you need. Look at the different diameters of ballscrew stock, one size is much cheaper than the others.
choprboy
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Re: Source for Reasonably Priced Ballscrew?

Post by choprboy »

If you are looking for quality ballscrews and slides, try Automation Overstock. The stock is always variable and sometimes oddball sizes or custom turned ends, but the prices seem great. Most is listed in metric only... One of these I was going to get around to building a CNC and order from them.
http://www.automation-overstock.com/cat ... sp?cat=147

http://www.automation-overstock.com/pro ... F-24P-C3Z4
10mm dia, 4mm pitch, 430mm overall length (16.9"), 300mm travel (12"). including nut $163
http://www.automation-overstock.com/pro ... 4W-1CVH-L8
18mm dia, 8mm pitch, 485mm overall length (19"), 400mm travel (15.7"), including nut $151
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Grantham
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Re: Source for Reasonably Priced Ballscrew?

Post by Grantham »

To wind up with about 20" of travel, you will need a 600mm machined end ballscrew. The machined ends and ballnut
take up about 4", leaving you with about 19.5" of travel. Both ends are machined to 10mm. One end of the ballscrew is threaded. BK12 and BF12 end supports support the ballscrew and a ballscrew nut housing is used to attach the ballnut to your plate. You might want to consider linear bearing with shaft (also 600mm). What ever length you decide, allow about 4" (100mm) for the ends and ballnut.

To answer your question, Bangood.com seems to have the best prices, but it doesn't hurt to check with aliexpress.com Ebay and Amazon are also good. I have had good luck with all 4 sources.

If you decide to go this route, I have a drawing of the 24 screw hole positions to attach the linear bearings and ballscrew assembly. It will need to be at least 6" wide. I have a 300mm ballscrew on the Z axis that gives me a little over 7" of travel.

Have fun!

Rod
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SteveHGraham
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Re: Source for Reasonably Priced Ballscrew?

Post by SteveHGraham »

I appreciate the responses.

I need to know one thing: do I really need hardware on the far end from the stepper? Is the purpose of the hardware on the far end to prevent the screw from shifting back and forth? That would certainly make sense, and it would be better than what I have now.

The arrangement I have has a bearing between the stepper and screw, to prevent the screw from moving back and forth. It then goes through the screw, and the end by the headstock is unsupported. The nut holds it up. There is significant motion from longitudinal bearing slop.

Just to be clear, there is no way the tool will travel 20"; the only reason I want that much thread is that the screw will have to extend past the carriage and so on. The current screw is about 22", with the last 2" turned down to 1/4". I would be pretty surprised if I ever find a situation where the tool will move 14".
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choprboy
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Re: Source for Reasonably Priced Ballscrew?

Post by choprboy »

Depends on what your requirements for precision, repeatability, and load carrying are. Without a far end support the screw is more likely to flex and wobble leading to inaccuracies (also, will your single end support be able to handle both axial load and torsional loading perpendicular to the race). For a vertically suspended/supported load, like a free-hanging carriage that doesn;t see much dynamic force it may not matter. For a horizontal load with high forces and speeds it could matter alot. Its the same reason some high-precision lathes and mills have intermediate retractable leadscrew supports to prevent the screw from sagging.
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SteveHGraham
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Re: Source for Reasonably Priced Ballscrew?

Post by SteveHGraham »

Okay, thanks.

Today I found a surprising new source of backlash. It turns out there will be all sorts of error in the lead screw if you fail to tighten the screws that hold the bracket the stepper is attached to. Apparently, leaving them finger-tight and forgetting all about them was not best practice.
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WJH
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Re: Source for Reasonably Priced Ballscrew?

Post by WJH »

SteveHGraham wrote:Okay, thanks.

Today I found a surprising new source of backlash. It turns out there will be all sorts of error in the lead screw if you fail to tighten the screws that hold the bracket the stepper is attached to. Apparently, leaving them finger-tight and forgetting all about them was not best practice.
Previously you stated your conversion of a manual lathe resulted in something that was no good for any sort of precision, or something along those lines. Perhaps fixing the problem areas you identified will result in a machine that will surprise you in a good way? But again it is a mini-lathe?
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SteveHGraham
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Re: Source for Reasonably Priced Ballscrew?

Post by SteveHGraham »

I feel certain that having the screw immobilized will have a positive effect on accuracy. I am brave enough to make that prediction.

I'm not totally sure the screws were always loose. I haven't worked on the lathe in a long time, and it may be that I loosened them for some reason and forgot about it. I hope they were always loose, because as you imply, it would be easier to fix loose screws than a hopeless lead screw.

I made a test part today, and while it's a far cry from real machining (I used a piece of wooden mop handle), it showed that the lathe will be able to produce stuff machined to within +/- 0.005" of spec in the z-direction. That's plenty good enough for turning wood, and it will also be good enough for metal objects like machine handles.

The x-axis is pretty good; the backlash is miniscule.

I used wood today because I figured it would be less likely to destroy the lathe in a crash. I should really get some plastic. But the wood will be useful, because it can be turned into tool handles and bench dogs.
Every hard-fried egg began life sunny-side up.
WJH
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Re: Source for Reasonably Priced Ballscrew?

Post by WJH »

SteveHGraham wrote:I feel certain that having the screw immobilized will have a positive effect on accuracy. I am brave enough to make that prediction.

I'm not totally sure the screws were always loose. I haven't worked on the lathe in a long time, and it may be that I loosened them for some reason and forgot about it. I hope they were always loose, because as you imply, it would be easier to fix loose screws than a hopeless lead screw.

I made a test part today, and while it's a far cry from real machining (I used a piece of wooden mop handle), it showed that the lathe will be able to produce stuff machined to within +/- 0.005" of spec in the z-direction. That's plenty good enough for turning wood, and it will also be good enough for metal objects like machine handles.

The x-axis is pretty good; the backlash is miniscule.

I used wood today because I figured it would be less likely to destroy the lathe in a crash. I should really get some plastic. But the wood will be useful, because it can be turned into tool handles and bench dogs.
If I convert my lathe, I will need it to be accurate enough to produce "fits" on shafts. Something tells me theres better ways to do that, i.e. grinding.
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SteveHGraham
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Re: Source for Reasonably Priced Ballscrew?

Post by SteveHGraham »

Search me. CNC is fun, though, even if you suck at it.
Every hard-fried egg began life sunny-side up.
Magicniner
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Re: Source for Reasonably Priced Ballscrew?

Post by Magicniner »

WJH wrote:
SteveHGraham wrote:Something tells me theres better ways to do that, i.e. grinding.
CNC your grinder then ;-)
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