Single point threading

Dave Paine said:
I know how I made my first mistake when trying to use the compound set to the 29.5 deg angle. I read the scale on the compound and overlooked the axis which was the reference for the angle. I expect I am not the only person falling for this mistake.
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No you are not. I figure you haven't lived until you done this. My first threads gave me a feeling I'll never forget. :)
 
Dave Paine said:
I know how I made my first mistake when trying to use the compound set to the 29.5 deg angle. I read the scale on the compound and overlooked the axis which was the reference for the angle. I expect I am not the only person falling for this mistake. My Grizzly lathe made it easier to fall into this trap.

In this picture I have moved the compound to have the scribe mark at the 30 deg mark. On my G9249 lathe, the only number shown is 0 (zero). The marks go up to 55 deg either side of 0.

View attachment 228260

After making some bad threads I also changed to using the carriage. I later realised my mistake was setting the angle to the wrong 30 deg, as in 30 deg from parallel to the lathe bed. It needed to be 30 deg from perpendicular to the lathe bed, or the face of the chuck. Easy mistake for a woodworker just starting out on a metal lathe.

I have a decent mitre gauge for the table saw so I cut a block of wood to 29.5 deg.
View attachment 228261

I glued a small magnet into the wood so it holds to the side of the compound.

View attachment 228262

I do not understand why Grizzly did not have the scale going to 60 deg. My lathe needs an angle block in order to set angles less than 35 deg (or 55 deg) depending on how the angle is defined.

View attachment 228263

Interesting post earlier discussing the potential origin of 29.5 deg angle. It is easier to use the carriage.
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Another frustrating thing for me on this type of compound (similar to my G0709 14 x 40 lathe) is it's not graduated around the complete 360 (or at least 180). I mounted an indicator on the head stock and indicated off the side of the compound to check 0 deg. Basically verified the 0 deg. pointer on the compound. Then blued and scribed with a square on the compound additional lines at 45 deg. increments all around the compound.

Bruce
 
Some great info here...thanks to all on this site..

One of the things about threading and feeding in with the compound that seems non-intuitive is that while we require that each pass be in perfect registration with the last, by feeding in with the compound set at an angle we are moving the tool in 2 directions (in relation to the work)... i.e. at 29 degrees feeding in 10 thousands results in the tool moving inward approx 8.746 thou and to the left 1.296 thou.
Which means our new starting point is not the same...


rich
 
willthedancer said:
That said, the use of coated carbide makes for slick surface for the chip to flow across, and much higher surface speeds, allowing for a high finish that is more scratch and tear resistant when in contact with the curled chip. It's a cheat that buys some grace when plunge threading, and often good enough.
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Those of us tackling threads with a greater lead might not have your lightning reflexes, NC, or a hydraulic tracer........
 
rpmMan said:
One of the things about threading and feeding in with the compound that seems non-intuitive is that while we require that each pass be in perfect registration with the last, by feeding in with the compound set at an angle we are moving the tool in 2 directions (in relation to the work)... i.e. at 29 degrees feeding in 10 thousands results in the tool moving inward approx 8.746 thou and to the left 1.296 thou.
Which means our new starting point is not the same...
Click to expand...

Alternatively...could we set the compound at 90 deg (parallel to the spindle) and then use the infeed and the compound feed to do this?... ie. for each thou in-feed move the tool to the left with the compound 1.296/8.746 or approx 0.148 thou?

rich
 
Go for it, Rich! Report back with how it works for you. I personally have trouble dialing in 'approximately' 0.00148" on my compound...
 
I like the 29.5 degree compound method. I have enough trouble remembering to return the cross slide to zero for the next pass, let alone trying to remember a different number to return it to for each pass with the plunge method.

Tom
 
When I worked as a machinist and tool maker most of the lathes we had at work had built in thread stops which spoiled me. Now, at home with my 1930's vintage 15" South Bend lathe when doing just a quickie I'll either mark or zero the dial for threading, but for those jobs that really count I use a thread stop I made that attaches to the cross feed V ways to thread with. I like having the cross feed hand crank wheel knob right at 9:00 so I can get the tool out quickly if something isn't going right. Just push the hand wheel down quickly! Always having the hand wheel in the same position helps make it "automatic" as to how to react if something goes wrong. Works for me anyways; YMMV.

Ted
 
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