Adjusting SB 9 Thread Dial

[Slow Dave]

I posted 6 plus months ago about problems I was having on my SB 9 B threading with an original SB thread dial I purchased separate from my lathe. I got lots of good suggestions but my attention had to be focused on the construction of a new shop building and I never did figure it out. Now the building is done I have more shop time to try to figure this out.

The problem is that each new pass is slightly to the left of the previous pass so I end up with a multi thread and eventually a total mess. I tried everything suggested and the problem continues. I tore the apron apart and cleaned it all up but there was no apparent problem there.

Today I came across a brief discussion on adjusting the thread dial. I looked into it futher and found some SB instructions from 1946 on installing and adjusting thread dials. I am wondering if this could be the problem. What are the symptoms of an out of adjustment thread dial.

Thanks

Dave

 

[hsracer201]

Have you made single pass threads and measured them to verify that it is in fact the thread dial?

Are you sure you are engaging the half nuts and not turning with the power feed?

ETA: if a model B has a power feed. Just covering the basics.

 

[Christian James]

When you brought this problem up the last time, you were asked several times to post pictures which you still haven't done. Don't be surprised if people don't respond if you won't post pics. I would suggest a picture of your gear train for a start and also suggest you remove the apron and show us your "nuts" first.

Cheers

 

[Dobermann]

My experience has been that if the threading dial is off index, it's off consistently with each pass. That is, the proper engagement point for the half-nuts may be slightly before or slightly after the index mark comes around but it's always the same and proper threads are being cut. If you're experiencing "creep" and the thread is moving on the work piece, then I'd be very suspicious that you have a gear tooth count problem someplace in the gear train.

 

[m-lud]

When you back up for your next cut you need to go past the starting point then forward to the starting point to allow any slack in the drive train to be taken up before starting another cut. You may already know this.

 

[Slow Dave]

Thank you for the replies. I am sorry about not posting photos as my computer skills are minimal. When I thread by reversing and not releasing the half nuts the threads come out fine. Previously I had thought that either it was a thread dial issue or there was a half nut issue. I pulled the apron apart and inspected and cleaned everything. All appeared fine and there was little wear.

If it was a gearing issue would the threads come out correctly when not rleasing the half nuts and reversing?

I have been engaging the half nuts well before the tool comes in contact with the material so any play would likely be taken up before the tool hit the metal.

As Doberman pointed out and I suspected, an out of adjustment dial would likely result in rough engaging of the half nuts but not the creep situation I have. That is why I asked about the symptoms of an out of adjustment thread dial. I have counted the teeth on the stud gear and screw gear several times and all seems to be correct. I have also tried different TPIs with the same results.

I greatly appreciate all the responses. I am sure the answer is some simple thing and I will feel totally bone headed when it is finally figured out.

Thanks again.

Dave

 

[Slow Dave]

Mystery solved and Mllud22 gets the prize. I have no idea why this worked but it does. My usual practice is to engage the half nuts with the tool tip about an inch before where the threads are going to start in order to take up any slack in the machine. This morning I bumped that up to 2" and it started threading perfectly. I tried this with the material extending different lengths from the chuck and it worked on each.

Thank you for putting up with my dumb questions. Your responses were all very helpful in getting me to think about the problem from multiple directions.

Dave