[Dan S]

I have been tossing around the idea of getting a mini lathe to help in the construction of my router. After looking at what it would cost to have ball-screws turned down, and collets made, I think it justifies buying the tools and doing the job myself.

Does a 7 X 12 from homier or Cummins have the ability to turn down rolled ball screws?? I know people turn down drill rod, but I don’t know how that compares to the hardness of ball screws.

Anyone have any experience with this?

[Moondog]

Hello Dan...

I am in the same situation as you. I went and bought a Lathe/Mill Comination machine about 1 month ago. Whatever you spend on the machine allow the same again for tooling.

I bought my lead screws (too hard to make) and am in the process of completing all of the Bearing Support Blocks for the Y & Z axis. For the block design I just copied the specs from an NSK specs catalogue. I also made my own lead nut from Delrin.

Next I will use the lathe to bore the pulleys to size etc..

Metal Machining was all new to me and I have thoroughly enjoyed learning new skills and having the satisfaction of making it myself.

At the end of the day you won't save money overall, but the machine will pay for itself with the savings in parts.

cheers

Frans

[cncadmin]

I believe that http://www.industrialhobbies.com/ is providing a ball screw turning service so he maybe able to do the machining for you.

[JFettig]

Im sure its capable of turning the screws, I am also sure that it wouldnt be fun and you would need some decent carbide. If you ran it at about 400rpm and a little coolant from time to time and turned right next to the chuck, you might be able to get through them, I have personally never turned rolled ballscrews or drill rod on my lathe, but I have done some stainless and regular cold roll steel, If you do it right next to the chuck(seems dangerously close) and low rpm and light cuts you can probably do it.

One thing that I wish I could do is knurl stuff, so far I havent been able to, Its probably a user error but the lathe doesnt seem to be ridgid enough for what I have.


Jon

[Chagrin]

It gets clumsy spinning long rods (ballscrew) and I believe the largest diameter rod you can put through the headstock is 1/2". With proper homebuilt steady rests it can be done, but it's a heckuva lot easier letting someone else do it

[Moondog]

Dan.. don't even consider the Ball Screws.. cheap enough to buy.. its the Ball nuts and Bearing blocks where you can save money. Plus lots of other things.

[Dan S]

It sounds like my post might have confused some people. I’m not going to try any make balls-crews, right now I’m planning on buying precision ball screws and nuts from industrial hobbies as well as angular contact bearings.

1. http://www.industrialhobbies.com/Mer...t_Code=5-8_PBS
2. http://www.industrialhobbies.com/Mer...t_Code=5-8_PBN
3. http://www.industrialhobbies.com/Mer...egory_Code=odd

I drew this up in AC real quick. The ball-screw is white, angular contact bearing red, “thrust nut” green, and locking nut blue. The pulley would mount on the end. At most I would be looking at turning down the last 2 inches of each end like this.





All the mini lathes I have looked at have spindle bores of between .75” and .8” so I won’t have a problem getting the ball screw through. I think with regard to the free end whipping, I could take care of that with an oversized bearing or two, and some kind of simple wood jig.

So it sounds to me like I can do it I just need to go slow and take small cuts?

[Moondog]

Dan...

If you use an Angular Contact bearing you will need a housing for the bearing. If you use a Double Angular Contact Bearing (mostly used) you do not need a Thrust Bearing. Also you need to use a spacer between the bearing and the nut. Have a look at the NSK site at the bearing block arrangements.

Isel have an excellent Rolled Lead Screw 16mm that is ideal for a Z Axis and they sell for less than $100 with the ends already machined.


cheers

[Moondog]

here is the detail for an Isel Lead Screw 16mm that sells for $68.29 machined both ends.

They also have Ball Nuts at very good prices. This is what I bought and it is very good quality.

https://sdp-si.com/eStore/ part number Hl5136M20458

[Dan S]

Moondog I’m planning to use two angular contact bearings one on each end apposing each other, and then putting the ball screw under tension to zero out mechanical backlash.
It’s not really a thrust bearing, but a special nut that will grip the ball screw so that it can be placed under tension.

[Moondog]

Dan.. you don't need angular bearings both ends. If you do you'll need to use a nut on both ends as well.

Normally you only need to support 1 end. Often the other end is not supported, ie. left floating.

Using a double angular on the support end will eliminate movement. Backlash comes from the Ball Nut and not from the support bearings.

[Dan S]

My x axis will be 36" long and my y 24”. The servos will be able to drive them at 150 ipm, so I will need to support both ends or it will whip like crazy.

[Moondog]

Dan.. I understand what you are doing.... you are doing extra that will give you no extra benefit. Here is what is used on Big machines.

Drive End: Double Angular Contact bearing in housing with lock nut.
Support End: Normal Bearing in housing and No Nut. not needed.

The Drive end with lock nut eliminates any movement.
Backlash is only in the Ball Nut and you can eleiminate that with with Pre-loaded Ball Nuts.

Also if you need to set it up with a Dial Indicator to ensure that it is perfectly paralel or you will create friction. That is why they usually recommend to have the support end with some play (i.e. oversized bore) to allow for any mis-alignment.

[Dan S]

Moondog I see where your coming from now, that brings be back to my original question. Is one of these mini lathes up to the job of turning down the ends of the ball screw?

[InventIt]

Dan,
The way I understand it, ball screws are hardened on the outside ie: "Case Hardened" If need be you could carefuly grind through the case hardened metal (.020-.040) then easly turn to your specs on the lathe. As far as wether a mini lathe can handle the job, I don't know, I would think it would be able to though. As long as the screws can fit through the headstock. Use carbide tooling and don't use coolant unless you can get a steady flow. Intermitent spurts of coolant on carbide tools will crack the carbide and render it useless.

FWIW, a lathe is a tool you can do ALOT of little projects on. For the cost of the mini lathes and some tooling it's a small price to pay for such a usefull tool. Once you own a lathe you'll think of all kinds of projects for it.

[cncadmin]

I have a 7x10 and could not cut the ball screw, it was imposable, to much cutting force for that little machine to handle.

[JFettig]

I wish I had some ballscrew to try.

but for all this means, at about 300-400rpm I can take .03" off the radious(.06 off diameter) in mild steel AND stainless steel very close to the chuck. This is with 3/8" carbide indexable tools.

Jon

[RotarySMP]

The cheap rolled ball screws from McMaster-Carr are through hardened according to a thread on the 7x12 Yahoo group recently.

Another option is to drill into the shaft and braze in a shaft extension of carbon steel and machine the bearing mount into that.

I have a 75x75mm block of high quality tool steel which I tried facing on the 7X12. Couldn't do it very well, but could turn it into swarf. I bet you can turn down the end of a 3/4" diameter rolled ball screw on the 7x mini lathe. Wouldn't be nice to the machine, and you'd probably chip a couple of small radius carbide positive rake inserts, or have twenty trips to the grinder to resharpen the M42, but I bet you could do it

A 36" long shaft is going to be a PITA to machine, you will have to make up some sort of support to stop it whipping around out behind the headstock.

[ESjaavik]

My ballscrews (of different brands) were case hardened. No problem turning when getting under the hardening.

My problem was that I don't have an independent 4-jaw chuck for my small lathe. And the 3-jaw cannot center well enough. So you'd better budget for a 4-jaw. It can be centered as good as your patience allows.

I solved the problem by using a larger lathe for which I have Jacobs collets and power enough to go through the hardening in one go. Since the lathe you look at does not have the power nor the stiffness for this, use a grinder to get below the very shallow hardening. Be sure to cover your lathe from the headstock and back when doing it. Grinding swarf does no good in the ways or mechanics.

If it's through hardened you can't do it yourself, as everything including the threads must be ground. But I can't imagine any leadscrew is through hardened, it would be too brittle.

[JFettig]

I turned one end of my ballscrew for my lathe, It was a little trouble getting it to sit right in the jaws but after that it wasnt too bad.
What I learned is that my indexable tooling did not like the stuff, it just chattered and deflected like crazy, I grabbed a brazed carbide and it ate through it like butter, no problem. My bandsaw didnt like it though I gotta cut it with a chopsaw at work tomorow,

About the jaws, you gotta make sure the jaws sit on the high spots on the screw, takes some careful adjustment, i thought I wrecked something when mine were flopping all over like it was extremely bent.

Jon