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Threading Oversize, How?


Dec 21, 2005
Waukesha, WI
Wanting to cut a #6-40 thread 0.007 oversize. Can the chasers in a die head typically be moved in and out to cut under or oversize or do they lock in place to always cut on standard pitch?

How far can a split die generally be adjusted? I already cracked one. Maybe if I took a torch to the die opposite the adjusting screw I could anneal it enough to make it more adjustable.

The thread is 3/4” long so to much flex for the diameter to single point it. A follower rest could have possibilities but hoping for another option.
I have often used a 5/16D Geometric die head with 1/4-40 chasers to cut .275-40 male threads. The die heads have quite a large range of adjustment.

Hi adh2000:
I'd still single point it or threadmill it.
The trick to single pointing a long skinny thread is to do it in stages, regardless whether you turn it or mill it.

Another way is to rig up a simple follow rest.
Often times you can just drill a hole in a bit of Delrin round bar, chop half of it away so your tool can get access and stuff it in the tailstock, then push it over the workpiece.
It won't last very long before it's chewed up but it does work.
If you need better, you can make it out of 660 bronze.

I do have Geometric die heads and they work well but I find them to be a PITA to set up for oversize threads if you're just going to make one or two.


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Would it be easier to make the male part smaller? Maybe plate it?
My understanding is that galvanised bolts are cut to standard thread size and form. The plating makes the male part larger. The nuts are cut oversize to allow for oversized bolts and yet more plating inside the nut.
Bill D
To me it would seem the female part is harder to replace? The part which is easiest to replace in the field should be normal off the shelf threads. Any custom should be in the more permanent portion.
Bill D