Today my boss asked me to quote how long it would take to M/C a 3 mm pitch acme thread 16mm dia. 500mm long in s/s on a manual m/c I said I did not even want to think about it What would be your best guess!

Too long :o Sorry, never made one over 5" let alone over 19". That should be a real PITA to make on a Manual Lathe. I feel very sorry for you right now. That's kind of like getting hit in the head with a brick when you first walk through the door in the Morning. (nuts) (wedge) :eek: :frown:

I've done a similar job but not in ss, a new cross feed screw for a mill - make sure you use free cutting :D . its a spindly workpiece with a wide cut, same challenges I'd guess would hold true for manual or cnc? takes a while, the trick to it is to become proficient adjusting the travelling steady. to have it all come out within a thou, iirc I had to ever so slightly increase pressure as steady moves further away from the tailstock. if its just the thread, maybe a couple of hours, but that's just a guess, longer if multiple ops, grinding the acme tool, turning the OD etc etc

It sounds like you can see the writing on the wall! :eek:


Only if this were an urgent need, and a high paying expiditing fee would get me to attempt such a project. Cut acme threads are not as strong as rolled and with such a small diameter, flex will be a major PITA on such hard material. If your shop is setup to do this type of work on an ongoing basis, then it is probably a snap. The learning curve is ahead of the game. Turning a 30:1 ratio of spindly length vs dia. is not going to be a walk in the park.

I'd look for some metric stainless rolled thread acme rod, cut the ends per print and call it a day.

A challenge is one thing. Penny foolish and pound wise is not a game of chance I'd consider unless someone is willing to make it worth my time in a one off scenario. At a minimum, my qoute would be a flat hourly rate plus materials.

DC

McMaster Carr lists a 16mm x 3 precision ACME but not in SS.

I am 100% with Many from One; unless this is a very "special" application and money is no object. Tell the boss to buy a piece of T-Rod and machine your end forms.

The only way out is suicide

I made a carriage feed for my Atlas and it took quite a while. Call me cheap but as a hobby it was fun to make. For work I would go some other ways as reccomended. The only tips I could give you is make sure everything is straight on the lathe. Use a follow rest with lots of oil. I also used a carbide cutter ground for the angles and only took a few thou. off on every pass.
Would I do it again. NO but it was a good learning experiance for an amature.
John

The biggest I have chased was a 18" acme 4 start 21" long but in white iron with a B/H of about 670 (rockwell of 60) and on a CNC VTL. This takes use about 3hrs just to chase not counting boring minor and counterbore. We chase alot of 4.5" 2start 4" long in same material and can do this complete in about 45mins. But we also use CBN tipped form tools..