View Full Version : Deep Hole Taps

09-19-2004, 11:07 PM
Does anyone know if long taps are available (without special order). I need to tap a 1/4" x 20 through-hole that will be about 2 1/2" deep. None of my taps will go that deep.

I guess I could make one in a pinch but wanted to know if long taps are a stock item.

Thanks, Ken

09-19-2004, 11:23 PM
MSC #04700209, OAL=6", $15.59 each.
I would probably just braze a piece of drill rod to the end of an old tap, cut short and grind the OD.

Since its a through hole, you could always thread it from both sides. http://bbs.homeshopmachinist.net//wink.gif

[This message has been edited by Joel (edited 09-19-2004).]

John Stevenson
09-20-2004, 02:32 AM
They are called pulley taps.

09-20-2004, 07:11 AM
You can't tape from both sides. The threads wouldn't be in sync.

09-20-2004, 07:24 AM
Actually you want a nut tap,they are plenty long and the shank is reduced below the thread root.A common pulley tap is just a long shanked tap with the standard thread length and shank diameter.

Besides Joel,if you run the tap down from the top and then up from the bottom,the bottom set of threads will be lefthand right? http://bbs.homeshopmachinist.net//wink.gif

09-20-2004, 07:25 AM
Pulley taps have a long shank to tap a hole at some distance. The shank is not reduced and will not tap a through hole.

Extension taps have a reduced shank, and will tap a through hole. They are available from most tool houses.

kap pullen
09-20-2004, 07:28 AM
Put your pulley tap in the electric drill, and simply reduce the shank on the pedistal grinder as required.
No muss, no fuss, no big deal.


John Stevenson
09-20-2004, 08:02 AM
Pulley taps here have reduced shanks.
Nut taps don't have a driving square here, they have a 1/4 radius that the nut can drop off so the machine never has to stop.
It's griped by two pairs of 'pincers'
they swop over to allow the nuts already tapped to pass between the pincers then drop off the end of the tap.


Pulley taps at the top with reduced shank.
Nut taps at the bottom.

John S.

09-20-2004, 09:53 AM
Extension tap is the correct name in the USA.

A thread forming tap would be good in this case, although they may be an expensive special. If not a special, they'll still be expensive.

If the threaded hole will have full length thread engagement with the male part the tap hole can be substantially larger than the usual size specified on thread charts, like a tap hole equivalent to something less than a 60% thread. A #3 (.213") drill might be a good size for a cutting tap.

Needless to say, tap alignment with the drilled hole is much more critical with deep tapping. Even a fraction of a degree misalignment will be off a fair amount at the other side of your workpiece and the tap may not tolerate it.

Generally speaking, unless the length of thread is needed for adjustment purposes it's not good practice to tap this deep.

kap pullen
09-20-2004, 10:46 AM
Hope you didn't pay much for those taps.

John Stevenson
09-20-2004, 11:01 AM
No idea Kap, had 'em years, like a lot of stuff it was probably a job lot.
Got the real long one when I was feeling bad and the doctor told me to keep away from work http://bbs.homeshopmachinist.net//biggrin.gif

John S.

Paul Alciatore
09-20-2004, 12:16 PM
You definitely want one with a reduced shank, whatever it is called. Check before buying.

I'm with DR on the shorter threads idea. Unless you really, realy need the threads extending the full length, I would consider drilling out a clearance diameter for all but 3/4" to 1" of the hole. That's more than enough threads for most any purpose. This is the normal way things are done.

Paul A.

Mike W
09-20-2004, 01:23 PM
I agree with Paul about drilling a clearance diameter. If I needed a longer one, I would just mig weld a piece of steel on the shank to make it longer.

09-20-2004, 02:11 PM
The MSC part # above is an extension tap with an undercut shank. For whatever reason, here in the states 1/4” pulley taps have a 1/4” shank diameter as JC noted (at least where I shop). Just another minor difference in terminology, and I am confident that Ken realizes what he needs.

Rob, are you sure, or is Weird correct? http://bbs.homeshopmachinist.net//wink.gif (note winking smiley)

09-20-2004, 02:58 PM
I use "pulley" style taps quite often...I have some that are 5" long, 1/4 shank, and i have some about 8" long, 1/4 shank..

I also have 6" long reduced shank...

My advice is if you can get the 1/4 shank taps then do it..the reduced shank ones are kind of weak..


09-20-2004, 08:21 PM
Tapping a hole 10 diameters deap sounds funny. but I take it have to have it a trough thread?.

I forget. how many diameters deep makes for max strength on a bolt 1.5, 2 ???

[This message has been edited by tattoomike68 (edited 09-20-2004).]

09-21-2004, 11:04 PM
Tatoo - You hit it on the head. About an hour after I posted, I realized I could just tap one end and over-bore the other side. It's to micro-adjust an axle setup. The adjuster has to be threaded all the way for a lock nut but the "hole" didn't need to be.

Thanks everyone for the replies.