All he has to do in anneal it, and it will cut like butter.
I turned down a generous offer from a fellow member here of having a couple of ball screws worked on for free, because I had found a coworker that was going to do it for one heck of a price (and I would have felt guilty having him do it for free). Unfortunately, when he found out the hardness, he said there wasn't any way he could do it.
So now here I am needing some done. I have the drawings in .pdf format, but am hesitant to post them because they are from a set of plans I purchased. But I think it would be ok to email them to those interested in quoting the work.
I'm almost afraid to see any quotes, but think I'm out of options.
Last edited by CNCadmin; 02-28-2005 at 01:41 PM.
He thought about, and mentioned it. But that is something he has never done.
I'm only slightly familiar with annealing (heating something to a certain point, and if I remember correctly, letting it cool at room temp?). Is it something that can be done with a torch? Does it stay pretty localized? I'd hate to have it travel up the ballscrew a few inches.
I do have an extra piece that he can practice on, if he is interested in trying. Any tips/tricks to doing it right?
Most rolled ballscrews are only hardened for a small amount of thickness. I usually design the ends to take this into account and grind the ends, using a tool post grinder, through the hardened surface. Then it threads like normal steel. Starting with a minor diameter of .5, I would grind to .375 and then thread. If you don't have a tool post grinder, I have seen some use a 4" grinder and do it by hand to the softer steel. Sooner or later though you have to be able to put it through the spindle hole of a lathe.
It is not as big a problem as it all sounds. You will need a "real" lathe! Other than that, it all is a piece of cake. Harbor Frieght sells several torches. I use one I bought for about 40 bucks, it has one hell of a flame (close to 40"), one tank of propane and something for everyone to see.
Cut the screw to length. Heat the end(s) that you want to machine till the metal glows a Bright Orange color. Start at the end and work it up and try to keep the heat in the general area that you want to machine. You will see and actual "line" where it glows and where it stops. Maybe add about 1/2" or so past. Your screws will not likely be used at either end so removing the hardness is really not a problem (and you can wrap to stop heat going up too far on the screw,,,,,but again, not a biggie). Keep the heat source moving.
Once done, let it cool to room temp.
Give it a try! You can do it. If your lathe is "beefie", you can do this. If not, send it out.
You will either be able to cut thru "like butter" or not. You will know right away if you removed the hardness. Take several small cuts to begin with. Let the tool do what it does and don't push it. Once thru the hard surface, the rest is no different from any stock you have on hand.
How does he prevent it from warping?
Heat the ends quickly, let it cool slow (maybe a rag heat sink, but don't over-do the need to quickly cool). I have done this with all kinds of acme and ball leads, and "for the most part" they lay flat as the stock stuff. I have a small flat plate, I can roll a piece around and get it "flat enough" for the stuff I work with.
Screws by nature want to spring and twist. Do it a few times and you will see what works for you, and build on it. The lathe is the most important thing. The average bench top will struggle (add grinder) and the larger ones (add coolant/oil) will have less of a problem.
I read somewhere that you don't need to anneal the ends at all. Because the screw is only case hardened, you can take another approach: On a "real" lathe, set the depth of cut for your first pass to be large enough to cut through the entire thickness of the hardened outer edge in one pass. Once that is done, machine it like any other soft steel.
This might seem counter-intuitive, but it does make sense. I have not personally done this. Has anyone here? Does it work?
Have you tried to use ceramic inserts. I have cut 60 rockwell steel with ceramic inserts pretty successfully. I have held + or - .0005 on dimensions consistently. If you haven't found anyone to do the work PM me and I'll check out the prints.
I wish I had a lathe myself, to try some of this.
I'm going to print this out when I know I'll be seeing him again, and show him all of your guys' ideas. Any others?
A good carbide tool WILL get through the case without that much of a problem. Carbide is pretty amazing stuff. I've used carbide end mills to hog out a Sossner High Speed Steel tap broken off in aluminum. The end mill chopped up that HSS like it was leaded steel, it was amazing.
Annealing will certainly work, but as the others have stated, once through the case, it'll machine, no problem. I'd first try turning off the case, then if that doesn't work, go for the annealing.