[HELP] Threading Troubles

[EdK]

(10-22-2013, 04:27 PM)stevec Wrote: ...

Willie's thought about the thread indicator gear having loosened is worth checking out.

Steve,

I did that as my first attempt at diagnosis. I think I'm going to take it off of the lathe and dismantle it and see if I can see anything the doesn't look right. I did watch it go around to see that it turned smoothly and checked all of the gear teeth to make sure none where chipped.

Ed

[Mayhem]

I'll be watching this with interest Ed as I have encountered the same problem on my lathe the last time I cut a thread. Leaving the half nuts engaged is risky for me, given the time it takes for my lathe to stop.

Steve - you made a comment about the thread dial type and I wonder if you could explain that a little more? Sorry but I am on my phone and it isn't easy to go back and check your exact words.

[stevec]

Darren, was it my sarcasm about the Chinglish on Ed's thread counting dial?
the title of the threading chart is written "INDICAOR" instead of INDICATOR.
Check the 2nd pic in his post.

[f350ca]

Is this possibly the first time you've cut 20 tpi on this lathe? The reason I ask, there was one tpi don't remember which that my Taiwanese 14x40 wouldn't cut if I opened the half nuts, same problem your getting. Would cut all the others I tried with no problem.

[TomG]

Ed,

Double check the pitch of the leadscrew over a good distance. Just because it's supposed to be imperial, doesn't mean that it is. This sure smells like a metric leadscrew to me.

Tom

[awemawson]

I must admit I tend to drop the half nut clasp always on one point on the indicator 'just to make sure' despite theoretically being able to use multiple positions.

[EdK]

(10-22-2013, 07:25 PM)f350ca Wrote: Is this possibly the first time you've cut 20 tpi on this lathe? The reason I ask, there was one tpi don't remember which that my Taiwanese 14x40 wouldn't cut if I opened the half nuts, same problem your getting. Would cut all the others I tried with no problem.

Greg,

I have cut 1/4-20 and 7/16-20 threads before and that's what's so perplexing. I've never left the half nuts engaged when cutting imperial threads and have had no problems in the past.

Ed

[EdK]

(10-22-2013, 09:03 PM)TomG Wrote: Ed,

Double check the pitch of the leadscrew over a good distance. Just because it's supposed to be imperial, doesn't mean that it is. This sure smells like a metric leadscrew to me.

Tom

Tom,

See my response to Greg. I have cut these threads, and more, in the past without keeping the half nuts engaged. I will take a measurement of the lead screw threads as you suggested though if for no other reason than to remove one culprit from the equation and for my peace of mind.

Ed

[EdK]

(10-23-2013, 02:37 AM)awemawson Wrote: I must admit I tend to drop the half nut clasp always on one point on the indicator 'just to make sure' despite theoretically being able to use multiple positions.

I always choose a number from the chart and use that same number for each pass even if it's not required.

Ed

[Mayhem]

(10-22-2013, 06:31 PM)stevec Wrote: Darren, was it my sarcasm about the Chinglish on Ed's thread counting dial?
the title of the threading chart is written "INDICAOR" instead of INDICATOR.
Check the 2nd pic in his post.

That explains it Steve! I was reading this on my phone when I posted my initial reply and missed that.

When this happened to me, I was trying to cut a 6tpi thread, using the same mark on the threading dial. When taking a scratch pass I measured a 6tpi trace. Took another and had an identical trace running parallel to the first. This is on a lathe with a 2tpi Acme leadscrew. As such, I am really hoping that Ed can get to the bottom of this...

Also, 20tpi will measure the same as a 1.25 metric thread (and vice versa). You have to measure the threads over an inch to check that a crest will line up exactly on the 0 and the 1" mark (for a 20tpi). However, this obviously isn't Ed's problem but I thought I would point it out