Gallery, Projects and General > How to's
Threading by hand
wongster:
Only acquired a 1/4" hand reamer. Limited reamers around the area I searched. I'll give that a shot. Like to sand on the lathe as the finishing is really nice :)
DMIOM:
--- Quote from: wongster on June 19, 2010, 09:30:43 PM ---....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. ......
--- End quote ---
Hi Wong,
you really should try to accomodate all three setscrews when you're actually using the dieholder.
The two dimpled ones are the main securing mechanism, but the central one which bears on the slit has a different function - the conical point acts as a wedge and gives a measure of control of the size being cut by the die.
If you screw in as hard as you can on that central setscrew, it opens out the split in the die, so the circumference is greater, and the finished thread can be a little oversize; relax the wedging pressure in the split then when the other two main securing setscrews are tightened, the split is closed and the resultant thread is slightly undersize. Also, because its in the split, the central setscrew does give some rotational anchor, but doesn't have great holding power axially.
The normal method is to apply as much pressure as you need to the central setscrew, and then tighten the other two to (a) hold the die in the holder, and (b) push in against the wedge effect of the first screw that has pre-set the amount of open split.
Dave
wongster:
Roger that, Dave. Thanks for the tip. I thought about it. Since I'm using 4-jaw chuck, I can easier mark out the dimple holes position using Dean's method (90 degree to each other). Once the 2 points are center punched, I can use a divider to measure the distance and halves it. This will give the point for the center screw. To avoid error, I just need to drill a slightly bigger hole for the center screw.
To make it more accurate, I can use the divider to mark an arc from each known point and drop a perpendicular line to the base line. I remember doing that doing my secondary school days. Hope my memory didn't fail me...
andyf:
Hi Wong,
Pics below. This was a scrapbox project, and the three different outside diameters on the holder reflect the outline of the lump of steel I found. The piece I used for the mandrel was a bit short, and the stub screwed into the end was added so it would self-eject from the tailstock. The finish on the parallel part would have been a lot better if I had left enough metal for a finishing cut when turning it down to fit the bore in the holder :doh:
The six M4 screws were made from silver steel, then hardened and tempered. Four have rounded ends and two are pointed to go in the splits in the dies. It would have been fiddly to hold stock screws to modify their ends, and I reckoned that the pointed ones would need hardening so they weren’t damaged when they pushed into the split. It was easier to make the screws and part them off one by one on the end of a silver steel rod.
The tommy bar screws into the side of the holder and is locked in place by a nut with a washer beneath, concave on one side to suit the curved surface.
As to the DTI holder, I used a tiny dovetail cutter on my mill, but it would be easy enough to file the dovetails to a good enough fit. They don’t have to resist any substantial forces from the DTI finger.
Andy
wongster:
Hi Andy,
Thanks for the pics.
I assume the tommy bar can swing freely and not hit the bed. So the holder would just "hang" on the mandel so that you can advance the die by just pushing it forward? I may still be able to do this with the piece still in the chuck.
Appreciate your taking the time to take the pics.
Regards,
Wong
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