My original intent was to shape the part and then cut the threads with a die - I bought one of these to replace my Horrible Freight die which wouldn't cut anything back last October while working on my first engine. The problem is that stud is too short to get more than about one turn cut - and it's a tapered die so it wouldn't cut that turn properly.
It seemed the thing to do would be to cut threads on my big lathe. This turned into (so far) a three day long wheel-spinning marathon (so far!) that has not resulted in one successful thread being cut. My lathe is a Sieg SC4 from Little Machine Shop, where it's called the LMS3540. Going by the specs on the lathe, it can cut 6-32 threads with the proper selection of gears. (There are two main ways of changing gears: some lathes have gearboxes and the gears are selected with levers or knobs or some way of picking the ones you want; in others, gears are changed by replacing one gear with another - this lathe is one of the latter). There are four gears that are changed, and LMS includes a wide selection of gears that will allow you to cut up to 80 turns per inch. This pic is from the lathe's user manual.
For those really interested in this, I did a diagnostic video showing the problems before I figured out how to get around it. I won't embed it inline here because I don't think there's that much interest in it, but it can be seen here.
Web searches and searches of all the online machinist forums I subscribe to followed. I found nothing about it not being to cut pitches above 28 - but I found that Sieg themselves says the SC4 can only cut 8-24 TPI threads. That's quite a bit less than the 7-80 TPI range LMS has in the manual and doesn't include the 28 TPI threads I've already cut with it.
I enlisted Mrs. Graybeard, who has a good knack for fixing things, got her up to speed on what was going on, what I'd done, demonstrated the interference problem and then said, "tell me where I'm being stupid". No luck.
Last night, just as I was shutting down the lights in the shop, I had a thought. What if I put the parts "outside the box". I figured I'd try it first thing this morning. That was it. It fits, and I think all the gear combinations will fit. I cut one test piece to #8-32 to verify it was right and everything went as expected.
I need some sort of field expedient cover for that.
couldn't you leave off the stud, drill and tap a hole of the appropriate threading, and then use a small section of threaded rod? Or would that not be strong enough? (Red Threadlocker! or JB Weld.)
ReplyDeleteOr can you actually weld something that small?
ReplyDeleteFunny you mention that. The reason I put that part into 3D CAD was to check if I had room to counterbore a screw head into the part - no, I don't. So then I figured the emergency fall back plan was to do exactly what you say. Cut off the stud, drill and tap it, saw the head off a screw and LocTite it into place.
DeleteI like using set screws for threaded studs, you can get them long enough and the thread is clean on both ends.
Delete-Joat
Just get some 1/16 plastic sheet from the hobby store (maybe Home Depot or Lowe's?) and make a cover. It doesn't have to be "Osha Approved", it just has to keep things away from the gears.
ReplyDeleteThose plastic campaign signs made from the corrugated plastic stuff (that looks like cardboard, are a cheap, stiff material to make quickie enclosures from. Stuff cuts easy with a box cutter or utility knife. And you can use the handy-man's secret weapon to hold it together - duck tape.
ReplyDeleteOr, cardboard. It doesn't have to be strong-strong, just strong enough to keep your fingers and other skinly parts away from the gears.
Good luck. Can't wait to see the final product.
I made the panels in my mill enclosure out of that stuff. White corrugated plastic. I've used up all the scrap in other little things, but there's always more.
DeleteIf you've got a cat, just put it between you and the gear. That way if something goes wrong, you're not sacrificing anything important...
ReplyDelete}:-]
The male cat read this and I've gotta say I've never seen a cat do that with his claws before.
DeleteSee what I mean?
Delete}:-]
By the way, just a thought, but if you could get ONE thread cut with the tapered side of the die, why couldn't you just flip the die over and cut the REST of the threads with the untapered side? You would need to be careful, of course, especially with an item that small, but the started thread should be enough to let you engage to die.
I guess you're doing this just for fun, but these kinds of parts are usually just something you buy, like screws. I just took a quick gander at McMaster-Carr, and the smallest externally-threaded clevis rod end is 10-32, but somebody somewhere has to make these.
ReplyDeleteNot just doing it for fun, but doing it for education. Someday, I'm going to have some obscure part that needs to be threaded on the lathe and it would better to know how to do it than to go find a custom part.
DeleteOtherwise, I would have already cut off the stud and threaded in a 6-32 screw that I had cut the head off.
You need to get yourself a watchmakers lathe! Nothing like the satisfaction of successfully threading an 0-80 stud 0.100" long!
ReplyDeleteI basically have one - my Sherline. It's a little bigger than a typical watchmaker's lathe, but there are a few guys who use them as such.
DeleteOne of the model makers decided that the standard sized screws he could use just were wrong for his models, so he developed ways of making things like a .025-300 TPI screws. Made his own dies and then tapped the wire with it.
There's a threading set for the Sherline, but I'm concerned that I'll need to do it on this lathe at some point.
.025-300????
DeleteThe mind boggles.........