Need Help!- Ballscrew, Turning Down and Threading

[ringram2077]

Hi
I have been working on cncing my X2 mill and have a question about machining the hardened ballscrew (from Roton). I didn't think I could to start with but my 7x10 mini lathe will turn down the ballscrew to fit through the bearings. This stuff is really hard at least compared to what I have worked with before. I will need to thread a section to accept 3/8-24 nuts. Question is will a standard 3/8-24 die with a hand holder work for this operation ? Also what is the best way to hold the ballscrew while the die is turned ? I know the ballscrew is really hard but I don't want to screw it up holding it in a vise.

Thanks
Richard

[tauntdesigns]

I'm getting ready to start work on a set of ballscrews for my lathe. I was going to leave it in the lathe chuck. After turning it down, i was going to just go ahead and use a die at that time. I may have to have a friend put the lathe chuck key in the chuck and hold it still while I turn the die.

I waiting on some carbide lathe tools that I just ordered to come in,
Jack

[maxboostbusa]

I myself would cut the threads with a threading tool while it was chucked up. The outside of my screws were fairly hard and the inside was better but still tough. A die would probibly be fine on this, but if its chucked up already you may as well cut them with the lathe and be sure they start correctly. I rarely use anything other than a threading bit to make OD threads on stock in a lathe. Just my 2 pennys though.

[ringram2077]

I would like to make the threads with the lathe but I do not have experience doing threads with the machine. Is there a "how to" for the HF mini lathe for making threads ?

Noobie forever

Richard

[maxboostbusa]

Look on www.mini-lathe.com and www.littlemachineshop.com they have articles on threading with the mini lathes. Its not that hard, and you need to learn to do it sometime anyway, because there will be a day when you dont want to buy that high dollar tap and die to make a special thread on something. Read it clamp some scrap round up and make the cuts. Check them with a thread pitch guage until you get what looks correct. Turn the threads off and do it again. Keep on until it seem pretty easy. Then you can do a piece to screw a nut on and it will show how the differences in a few thousanths can make a difference. When its not quite enough it wont start very good at all and will be super hard to turn, couple thou. more and you will probibly have a general sized thread that will thread a nut fairly well, take a couple more off and then you will have a loose fit. Taps come with different H limits which is how tight the threads will be to a given bolt size and pitch. Some dies are adjustable and can do the same thing to a degree. Threading it on the lathe gives you that advantage. If its going to be assembled and disassembled alot then a tighter thread tolorance can be used so it will allow more cycles before the threads start to loosen up. On the other end if you want to have a piece of alum. or something coated (anodize, chrome etc.) then you may want a looser thread to allow for the thickness of the coating. If you didnt it may be to tight to thread together and you just wasted the machine time and coating costs. If you need any help on figuring it out let me know I will send some other links or articles about threading on a lathe. Its not all that hard.

[cadmonkey]

Practice on some cold rolled stock. I bought a chunk of 5/8 at the LHS and have made one test "screw" - one or two more and I'll hit the real deal. I'm also doing it on the 7x10, but Nook screws. I'm sure minilathe or littlemachineshop give a good tutorial on how to set the gears - it took me a few minutes to figure out how to get the gears to all mesh up correct but get a good carbide tipped thread cutting bit or 6 and take it REAL slow. Get in deep enough that the die can thread on if it's tapered entry die, if it is then once you've run it on an off, flip it around and run it on so the threads are clean all the way to the bearing journal. Took my a total of about 3 hours to do the first test - 1.5hr last night (most of it tuning the grinder attachment I made to bust through the case hardened screw section) and another hour tonight polishing the journals and threading the preload section. Gotta hit my tool supply store at lunch tomorrow and grab some more brazed bits...long weekend and I want to have at least one ballscrew done by the end of it.

[philbur]

The axis of a lathe cut external thread can be made parallel to the ball screw axis to a high degree of precision. Equally, a lathe cut internal thread in the nut can and should be at right angles to the nut end face, also to a high degree of precision. These facts are important where you are going to use the nut to apply preload to a bearing. When you use a tap and die invariably the threads end up slightly misaligned, no matter how careful you are. The hand cut threads will probable work after a fashion but the lathe cut threads will give you a much better chance of a good fit up and consistent preload.

Phil

Originally Posted by tauntdesigns I'm getting ready to start work on a set of ballscrews for my lathe. I was going to leave it in the lathe chuck. After turning it down, i was going to just go ahead and use a die at that time. I may have to have a friend put the lathe chuck key in the chuck and hold it still while I turn the die. I waiting on some carbide lathe tools that I just ordered to come in, Jack

[cadmonkey]

Ditto Phil - There was no question in my mind to at least get the threads started with the lathe and merely use the die to chase them and make them pretty and whatnot.

I checked with feeler gauges under my nut (store bought not self turned) and it was less than my thinnest feeler at the one spot where i could even get it started with the nut just starting to touch the bearing face.

Thread turning I would have to say is an art, but one well worth learning, I plan to do a whole lot more of it. This hobby is sucking my wallet dry. But at least I remember where the $$ went unlike in my previous hobby (sitting at a bar...)

[ringram2077]

Thanks for the info and links. I think I will get a piece of 5/8" rod a practice. The thing about threading on the lathe that is not clear is the little thred dial. I don't knoe exactly how that is suppose to be used. It seems to me that it you start the tread feed and turn off the machine at the end of the run, back off the tool, reverse the motor to move the tool back to the beginning, turn off the machine, reverse the motor, set the tool depth, start to second pass ...... in other words you never disengage the feed once you start then everything should stay aligned on each pass. Is this a correct assumption ??

[hoss2006]

There is an old school description of how to cut threads on a lathe
about half way down this page.
Hoss

[mrcodewiz]

You can certainly do it this way. The threading dial is for people like me who can't reverse the lathe. On my lathe, I have to take my cut, disengage the threading halfnuts, move the cutter back, and move the carriage back to the right of the piece. The threading dial stays engaged so you can pick the thread back up. I believe your method would work as long as you don't need to cut double-start threads.

I think the threading dial would be easiest regardless because you wouldn't be stopping and starting the motor all the time - just cut, release halfnuts, move carriage, repeat.

Originally Posted by ringram2077 Thanks for the info and links. I think I will get a piece of 5/8" rod a practice. The thing about threading on the lathe that is not clear is the little thred dial. I don't knoe exactly how that is suppose to be used. It seems to me that it you start the tread feed and turn off the machine at the end of the run, back off the tool, reverse the motor to move the tool back to the beginning, turn off the machine, reverse the motor, set the tool depth, start to second pass ...... in other words you never disengage the feed once you start then everything should stay aligned on each pass. Is this a correct assumption ??

[cadmonkey]

That's how I did it. If you're turning a 3/8-24 you can start on any number 1~8 according to the chart on the change gear cover. Just make sure you always engage on the same number each time - i.e. - first pass engage on 1 and then every pass you do after that start on 1 also. If you break a tool (take LIGHT cuts to avoid) you'll need to engage into a cut with no tool in and then insert a new tool in the cut to align the bit to the threads you've already cut. That little section that ends up being flat at the end of the cutting pass won't affect the threading of the nut - I'm using the same thread and it's easy-peasy. I've started working on the real screws after 2 trial screws. The real thing is a tad harder I can tell from facing the one I've worked on, but with the threads removed there's not much meat left to get to the 10mm bearing journal, which I'll polish to size with emery cloth and cutting lube.