Tap shank sizes

For taps with a full diameter shank, the shank dia is approximately equal to the major diameter of the tap's thread. Note that the major diameter of a tap is larger than nominal in order to insure clearance with a mating thread. For example, the shank of a 1/4-20 tap is .255. MH has tables that list the major dia of taps.

I have no idea where the odd diameters of reduced shank taps come from.

Can I hold a .225 tap shank with a .250 collet?

Or is that a big no-no?

Also, how much "play" do these collets have, can I hold a .240 shank in a .250 collet, for example?

i

ER16 collets have a 0.039" closure

Tap collet sizes:

Metric "round shank" collet sizes: Inch "round shank" collet sizes: Generally, ER collets can close up to 0.039" from their maximum size. You can also generally insert a tool that is up to 0.001" larger than their max, but it's not suggested in most cases.

This is not true of ER8 or ER11 in some cases and at times, the collet nut hits the ends of its threads before the collet is fully closed to its minimum. ER32, ER40 and ER50 are said to have a larger closure range but it can damage the collet if abused.

Tap collets are better than round shank collets in most cases because they hold the "square" at the bottom of the tap shank too. A round shank collet is perfectly fine for tapping when you are not worried about slippage in the collet or when the material is easy to tap.

I have LOTS of round shank collets here so if you ever need something special and can't find it via Techniks, MSCdirect.com or McMaster, etc. Let me know. I'm not the cheapest, but I'm the nicest. I generally get between $28 and $40 per collet.

Regards, Joe Agro, Jr. (800) 871-5022

01.908.542.0244 Automatic / Pneumatic Drills: Spindle Drills: Tapping: Site: V8013-R

Joe, thanks. Does it mean that a .250 collet can be used to hold .211 to 0.25" shanks?

Joe, thanks again and one more question. What about TG100 collets, what "play" do I have with them?

i

In theory, yes. You should be able to hold 0.211" to 0.251"... But I try not to go over 0.020" below the stated maximum whenever possible. I would use 5.5mm collets for a 0.211" shank.

If the tap shank sizes are too small for standard collet sizes, shim with thin brass tubing, wet-dry paper or other material that's fairly consistent in thickness.

When round items don't fit together properly, think like a lathe owner would.

I don't know the first thing about TG collets except to go to the experts and ask questions when other experts ask me questions.

That having been said, here is what Techniks says on their web site for TG75, TG100 and TG150 collets:

1/64" closure range (0.015625" for the unpleasable also reading this thread.)

Here are the web links:

In a pinch, I am a distributor for Techniks and can order these for folks. Just let me know what you need, where to send it and pay me vy PayPal, CCard, mailed check, etc. :)

Regards, Joe Agro, Jr. (800) 871-5022

01.908.542.0244 Automatic / Pneumatic Drills: Spindle Drills: Tapping: Site: V8013-R

========= machine tap drivers have two functions (1) these precisely locate/center the tap; and (2) these drive the tap, generally through the square shank.

for pictures and info see {watch the wrap}

shank and square sizes

-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

Yep, Joe is one of the nicest folks here. And I'm unpleaseble too.

I have TG75, TG100, and TG150 sets. If you got a set by 1/64s it will do any diameter that comes along. Don't know if its still true, but they gave these sets away on eBay when eBay first started. I also bought full 5C, DA180, and 2J sets at that time. I like collets.

Karl

OK, thanks. For tapping purposes, I really need them in size greater than 1/4", and up to 1/2" at most. 1/2" can hole at least a 5/8" spiral tap IIRC.

I have a small set of ER16 collets for smaller sizes, I hope that they cover the entire range up to 1/4".

I will try to measure a few taps and see what sizes I really need before buying giant sets. Plus, I have some TG100 collets already:

3/32 1/4 5/16 3/8 15/32 1/2 5/8 11/16 3/4 7/8 1

i

Ignoramus11979 wrote in rec.crafts.metalworking on Tue, 15 Mar 2011 10:35:05 -0500:

ER collets have about 1mm range. The metric ones are engraved as 7-6 or 6-5 etc. indicating the range they can hold. The larger size is the relaxed size, and the smaller size is the smallest you should hold.

The inch sized ones are similar, but the relaxed size is close to a fractional size. I find they still have about 1mm (.039") range.

They have more than enough grip to hold the shank of a tap. The tap will break from torque before it will slip.

BTW, make sure the ER collet is in the nut before inserting the tool(tap). It will snap into a ridge in the nut, witch is necessary to remove the collet.

dan wrote in rec.crafts.metalworking on Tue, 15 Mar 2011 23:09:21 GMT:

This pertains to ER 16 collets. Other sizes are different.

I forgot to add that you can get them with a square recess in the end that is made to drive tap shanks.

The ER-16 should handle any size you need.

But the collets used in tap chucks are small versions of Jacobs Rubberflex collets -- six radial steel plates joined by six pads of rubber between them.

Yep -- as long as you make something behind it to grip the square end of the shank. That's what the tap chucks from Jacobs have. The end of the shank sticks out behind the collet to between two steel plates which are clamped down with a special setscrew which is LH thread on one end and RH thread on the other, so the plates move equally out or in from both sides.

Enjoy, DoN.

Which collets? ER collets are designed so the bottom end of the size range on one is the top end on the next down, so you should be able to find one which fits.

R8 or 5C collets have a very narrow range and should not be used like this.

Look up the range for the collets which you are using, since you did not specify which ones.

The RubberFlex collets used in the Jacobs tap chucks typically cover the needed range in two collets.

Probably they match some full-sized shank size somewhere in the set.

Note that there are also MT-1 collets specially made for holding taps -- concentric grip plus a square holder at the bottom.

Enjoy, DoN.

Oops, ER-16s go only to 1/4". :-(

stuff to think about...

MT holders cannot be used in CNC tapping...

Give Techniks a call at (800) 597-3921. They sometimes stock oversized collets like a 3/4" for ER25, etc.