How to do fine threads

Hi Luc,

The standard way to cut any thread on a tube, is to use a mandrel ! 5/8" 27 should be easy.
Turn up a piece of bar long enough to hold in the three jaw plus the length of your work.
Turn to suit your tube. Make it a good fit for your tube without it binding.
Drill and thread the free end, any convenient size.
Countersink the threaded end.
Mark the mandrel so that you can put it back into the three jaw in exactly the same place it came from.
I use a pop mark to indicate jaw 1 and a scribed line to indicate the face of that jaw.
Now slit the mandrel at the threaded end, down its length about 2/3 of the length of the workpiece.
Make a cone that will fit on your screw and fit the countersink that you made in the mandrel.
Using a screw with the cone on it, screw it into your mandrel.
Now when you put your tube onto the mandrel, tightening the screw will cause the mandrel to expand gripping your workpiece.
If your tube is very long, make the mandrel longer and use a hex head bolt with a center drilled in the head. Then support it with a live center in the tailstock.
 
I found this chart on line for the PM1127, if it is the same as yours, I figure the closest I could come to 27tpi is this:

H 60 (Z1 - Z2)
30 50 (Z4 - Z3)
80 H ( L )
position A = 26.6667 tpi, which I think is as close as it will come with the gears the manual indicates are provided. This is with a top gear fixed at 40T and assumes you have the inch lathe.pm1127 threads.JPG

If your chart is different, perhaps you can post a copy.
 
Quote... And how would that work? Zero max does not do definite ratios and the motion is choppy,

I think you got it backwards... A Zero-max is made to do constant precision movements
if run at designed speeds. Just put a digital RPM meter on one and watch...
The output shaft is regulated precisely .Accurate speed holding.
I have one on my mill lathe for making twisted octagons... You would waste some rods
until you got it set for the threads you want, but then you could go to town....
 
Back
Top