I'm having a senior's moment while trying to figure out where to set my compound for thread cutting (UNC). The zero mark on my lathe is perpendicular to the lathe centre line. Does that mean I turn it to show 30 degrees or 60 degrees?
Guess I could just try both, but anybody who knows the "right" answer is welcome to set me straight.
Thanks, Chris
Set it to 29 or 29.5 degrees. HTH
turn it to 60 degrees, that is 90-30 . right now your compound is set perpendicular, therefore at 90
cheers T.Alan
When you get confused about setting your compound for threading, the easiest way to determine which lines you want to read is to place the compound parallel with the cross slide, with both handles at the same end. At that point, turn the compound 29 or 29-1/2 degrees. Depending on how your lathe is marked, it will either read 29 degrees, or it will read 61 degrees. Remember that you want to feed your compound at slightly less than the half angle of the thread you intend to cut. Remember also that you want the compound to advance in the direction that keeps the tool load such that it pushes against the lead screw. Otherwise the pressure of the cut can allow the carriage to wander away from the screw. That means that if you intend to chase an external right hand thread, the handle of the compound would be towards the tailstock. If you intend to chase a RH internal thread, it would then be towards the headstock.
Hope this helps~
Harold
Hey Harold,
After I get mine set-up for threading and in place the "first" time, I put a dot of paint (nail-polish) on the compound at the 29.5 line. I still have to line it up, but I don't have to think about it. Just have to remember what the heck that paint mark is for!! Does THAT seem familiar to the OP??
I am however going to have to think about this "thread chasing" business and position for the compound. I'm not at all sure what purpose it is that would see you do that. Mind you, I don't think I've ever "chased threads" either, so maybe I just need to look at that.
Take care.
Brian Laws>
On a similar thought, I screwed up some threads by not using the thread dial correctly. This prompted me to read the manual.
My rockwell lathe manual says it is ok to close the half nuts on any of the 4 numbered positions for odd threads. My atlas manual says to only use the opposite positions for odd threads, ie only use
1 or 3. I believe they both have the same pitch leadscrew so I am wonder if the rockwell manual could be wrong.chuck
Different number of teeth in the gear at the bottom of the thread dial, and a different numbering on the dial.
Assuming an 8 pitch lead screw, the Atlas has a 16 tooth gear on the dial and numbered marks representing 1/2" of travel.
The Rockwell probably has a 32 tooth gear and numbers only at one inch of travel, and lines at the 1/2".
Although, the Atlas thread dial I have stuck on my Logan, only has numbers 1 & 2.
Paul K. Dickman
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