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Threading by hand

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andyf:
Hi Wong,

I made a dieholder with an 18mm through hole, and an 18mm diameter mandrel with a 2MT taper on the end to fit in my tailstock. The dieholder is free to slide along the mandrel as the thread is formed on the workpiece.

The dieholder has a tommy bar screwed into it from the side, but unlike No1_sonuk, I turn the workpiece rather than the dieholder. The tommy bar is just long enough to drop down between the bedways of my lathe and prevent the dieholder from turning as I rotate the lathe spindle and workpiece using the spindle handcrank shown half-way down this page: http://andysmachines.weebly.com/miscellaneous.html . 

I decided that it would be easier to turn the handcrank in free space than to contrive some way of locking the spindle and turning the dieholder in an area which is confined by the chuck to the left, the tailstock to the right and the lathe bed underneath. The carriage needs to be up against the headstock so the tommy bar doesn't hit it as threading proceeds and pulls the dieholder slowly leftwards along the mandrel. 

Andy

Dean W:
Wong, the problem you had with the tool suddenly cutting too much sounds like you had a chip welding problem.  When
this happens, a small chip gets stuck to the tip of your tool, and the tool doesn't want to cut.  After you get into the cut
a little more, the chip comes off and suddenly starts cutting what you had dialed on all at once.

For getting the holes in the right place on your die stock, you can use simple chuck indexing.  The jaws of your three jaw
chuck are spaced just right.  Check out the pics.




Find or cut a piece of stock that lets one of the chuck jaws rest on it while the piece of metal rests on the lathe bed.





Then use the cutting tool in the tool post to engrave a small line.  Just crank the cross slide in until the tool bit touches
your die stock and use the carriage to run it in and make the line.





Here's another view. 
After you make one line, remove the piece of metal from under the first chuck jaw, rotate the chuck a bit, and do the
same for the next two lines, until you have three lines total.  Now you have three perfectly spaced lines.





To finish the line, use a divider or your dial caliper, set it to where you want the hole distance from the end of the
die stock, and make a scratch over each of the three marks.





You'll have cross marks like this, and you can use a punch to mark for drilling.  Set up your drilling operation carefully
and you'll have the holes done in a minute, and you can tap them.





The die stock I have for my Taig lathe has the setup that sonuk mentioned.





A pin goes through the center and turns freely.  The pin can be held in a drill chuck.
I think you would do best not to try to tap a hole in the die stock for the pin.  You have a good chance of getting
it slightly off, and you'll have the same problem you started with in getting a good straight thread using a die.  If
you let the die stock float on the pin it will be in line with whatever you are using to hold it, like a drill chuck.

Good luck!

Dean

wongster:
Hello Andy,

Can I trouble you to take a pic of your holder when you have some bit of extra time?

I like your DTI holder but the dovetail is so small for me to mill it out.  I'll figure that out later after I completed the torch and the dieholder.

Regards,
Wong

wongster:
Hi Dean,

This is a clever way of indexing without a rotary table!  The die I have has a slit for a long pointed bolt and 2 dimples at 45 degree.  I'll get the first hole right and hopefully don't need the other 2 dimples to hold the die in place while turning the holder.

The pin through the die holder has to be slip fitted? I'm still experimenting how to cut accurately enough to slip fit, press fit etc.  But this seems a easier option.

Thanks for your help with the pics!

Regards,
Wong

Dean W:
Yes, the hole is a close running fit on the pin.  Do you have any reamers?  If you have one in a size the same as a piece of stock
sized material you're set.  Say a 9mm piece of round stock, and drill and ream the die holder for 9mm.  If the piece of round stock
is a little tight, you can make it a nice running fit with a bit of emery or wet 'n dry paper.  Spin the piece in the lathe and sand it
lightly until you get a nice fit.  If you do that, make sure to clean the lathe well to get rid of any abrasives.

Dean

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