Halfnut, Revisited...

Good evening all, I was in the shop listening to some tunes and turning a piece of aluminum earlier today. As I finished my part, I set the ol' Heavy 10 for threading 14 TPI on a 1" outside diameter. As I went about the usual set up, I got ready and began threading. Since I don't yet have threading dial, I stop the spindle and reverse to get decent repeatability. Today I noticed a bit of double threading on this coarser thread and went into a panic. So much for a relaxing hobby
My first reaction was indicating the halfnut. I found roughly .02~.03 play. The leadscrew had a .01~.015 shift. I knew I had some wear and it never bothered me much. I hardly ever thread at home so this hasn't been an issue before.
I was wondering if you guys think my halfnut play was the cause for double threading? I could probably shim the leadscrew and get most of the shifting taken out but I'm worried about the half nut. Is there a recommended place to get replacements?

You may have closed the halfnuts early or late, and they didn't mesh properly with the leadscrew -- instead of meshing, the peaks of the nuts and screw may have come together. If your halfnuts have burrs, these burrs can be caught and driven by the leadscrew.

Regards.

Mike

Most likely you engage the haft nut on a chip that worked it's way out.

BEFORE you start threading .. Oil the lead screw with it revolving ... insert 2" wide clean chip brush in the middle of the brush bristles and with a slight twist clean the lead screw.
A good habit to keep accurate your threading.
Robbie

PS
If it happens again..look elsewhere

Thanks gents, a thorough cleaning is on order.

.010 play in the half-nut wouldn't be much of an issue if you were using the threading dial and always going in the same direction with the cut. You probably wouldn't even notice it. But the continual reversing and going back and forth is probably causing you to cut both sides of the thread and fuch up your threads.

I guarantee you there are a hell of a lot of machines out there with a lot more slop than that still cutting nice looking threads.

There are a couple of guys that list on E-pay that offer "rebuilding" services for South Bend half-nutz.

Frank

if the half nuts locked down all the way and were not released, then i would think it was just a matter of the play not being completely taken up before the tool started cutting.

i like to put a little resistance via the handwheel to insure all slack is taken up before the tool starts cutting, something as simple as the handwheel coming around and falling is enough to cause your trouble.

I went back and practiced on a some remnants. I'm getting favorable results putting a bit of drag on the hand wheel. After inspecting my set up, I discovered the tool post was not completely tight allowing the tool to move enough to cause deviation. I'll chalk this up to operator error. I'll have to remember the 6 P's next time.
Proper
Planning
prevents
Piss
Poor
Performance

Unspoken here is, this is yet another reason why the 29 degree compound setting
is a good idea. That setup loads the halfnut in one direction only, and will automatically
take the lash out of the system in about one turn of the cut.

Mr. Rozen, thanks for that reminder. I have become complacent in my ways. In school I was taught to set the compound to 29 degrees and I always have. I have in the last six months began working in a new shop. We make shafts for animal rendering machines. These shafts vary between 19~24 feet in length by 6 to 8 inches in diameter. It gets tense on the last operation which is threading the very end with 1 1/2-12 threads. At work the senior machinist prefers his lathe set up with the compound at 0 degrees, I suspect for clearance. He also cuts a small space for the threading tool to stop in after cutting a pass. This gives him an area to safely disengage the lever. This technique works well and I have adopted it. A few weeks ago I had to do some threading at home and decided to try setting my lathe in the same fashion. I'm guessing my older lathe has more wear than the lathes at work so I'll be going back to the 29 degree method. Thanks for observing this post.