Is there such a thing as an undersize tap?

snowshooze said:

Hi guys...
I am wondering if there are undersize taps.
Like a h-2
I want to tap a hole, and have to force a set screw in there.
Can't use lock-tite as temperatures will soak at 400F +
In Aluminum. 5/16 coarse.
Maybe I should just take my roll tap and top it on the grinder for interference...
Set screw goes into assembly, to remain there forever...
I am also wondering if I salted the steel set screw, if it would real quick seize up in position.
Thanks,
Mark

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snowshooze said:

Hi guys...
I am wondering if there are undersize taps.
Like a h-2
I want to tap a hole, and have to force a set screw in there.
Can't use lock-tite as temperatures will soak at 400F +
In Aluminum. 5/16 coarse.
Maybe I should just take my roll tap and top it on the grinder for interference...
Set screw goes into assembly, to remain there forever...
I am also wondering if I salted the steel set screw, if it would real quick seize up in position.
Thanks,
Mark

Click to expand...

kustomizer said:

We have a few parts where we use a plug type roll form tap but stop short of where the screw has to go so it makes the last turn or so itself and they lock in good if you dont take them out put them back in.

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Hardplates said:

Could use rockset or just regular glycerin from the drug store works well also

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Nerdlinger said:

Emugee “self-lock” taps are supposed to have some fancy shape to them that results in some sort of interference fit with the screw. I tried it once with absolutely no luck. I don’t know what but I must have been doing something wrong, so it may be worth a try.

I believe in machinery’s handbook or somewhere I read “GH_” on taps is “Ground High” and every “_” is .0005” over nominal. So a GH3 is .0015” larger that nominal on the OD. Likewise a less-common “GL_” tap would be “Ground Low” by .0005” for every “_”. It still sounds made up but I think it’s about right. So maybe you can look for some “GL” taps. Otherwise you could probably have some made for you at a reasonable price from Regal.

Good Luck!

Click to expand...

Nerdlinger said:

Emugee “self-lock” taps are supposed to have some fancy shape to them that results in some sort of interference fit with the screw. I tried it once with absolutely no luck. I don’t know what but I must have been doing something wrong, so it may be worth a try.

I believe in machinery’s handbook or somewhere I read “GH_” on taps is “Ground High” and every “_” is .0005” over nominal. So a GH3 is .0015” larger that nominal on the OD. Likewise a less-common “GL_” tap would be “Ground Low” by .0005” for every “_”. It still sounds made up but I think it’s about right. So maybe you can look for some “GL” taps. Otherwise you could probably have some made for you at a reasonable price from Regal.

Good Luck!

Click to expand...

snowshooze said:

Will that make it be forever stuck?
Interesting...
Thanks!
Mark

Click to expand...