Thread: Is there such a thing as an undersize tap?

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

Undersize taps are available. Mostly used for tough to tap materials. Rough tap with the undersize tap them finish with the full size tap.

Originally Posted by snowshooze

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

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.

Originally Posted by snowshooze

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

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

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!

Originally Posted by kustomizer

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.

Daaaaa. PERFECT!!!
Thanks,
Mark

Originally Posted by Hardplates

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

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

Originally Posted by Nerdlinger

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!

It get's so tangled up...
It wasn't but a couple years ago I figured out the H sizes...
Thanks!
Mark

Originally Posted by Nerdlinger

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!

GL.... ah... the lingo...
Thanks!
Mark

Hey Guys...
Thank you so much.
I got it. We all done here...
I knew you would come through.
Mark

Originally Posted by snowshooze

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

Putting the assembly in boiling water with rockset is like heat for loctite.

It's used on the threaded connection on guns for suppressor quick detach mounts which I have seen glow orange. I don't know what it's rated temp is but it's more than 500

Sounds like you solved the issue... for future readers, I have done this pretty easily using a single point thread mill. Both by sneaking up on the major diameter to get the fit, and by putting a slight taper on the program.


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use a regular tap and anodize without masking the thread.

I don't believe it is standard off-the-shelf, but I do have a few H0 taps of different sizes and different origins ( Vermont, Emuge, Fette, OSG).
I know I've got them from Toolbuyer's Network, who got just about everything under the sun from everywhere, but they are no longer around.
I also have a shitton of 1/2-20 H7 which saved my butt in Inco. They are Kennametal brand on the shank, but came in a Boeing box.
And then there are the nameless 3/8-16 H12 .....

Nonetheless, if you need something just-a-bit-unusual, you may be able to find it readily available.
If not, then there is always NorthAmericanTool.