# Working with taps on a mill



## picclock (Apr 15, 2011)

I seem to spend a lot of time tapping holes by hand after they have been drilled on the mill. Also the 'wonky' problem where the thread is never exactly perpendicular to the metal is very annoying.

I've tried threading with a tap in the mill chuck but my mill doesn't have enough torque for anything above M4 - and tapping M12 by hand drives me barmy (probably already was), 

Anyhow in my mindless tedium of using a hollow bar extension on a large tap I came up with the fairly obvious idea of making a tap holder with reduction gearing that would either fit in a chuck or into the mill taper. If the holder was internally geared at 10:1 or more it would enable my rather feeble mill torque to tap the hole.

Has anyone already made something like this ? or seen plans for something similar ? or has any better ideas ?

Thanks for reading.

picclock


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## kvom (Apr 15, 2011)

I use the tap in the spindle to start the tap vertically a couple of turns, then finish with a hand wrench. For small taps I prefer to have some feel, esp. in blind holes. I have tapped through holes in back gear using a spiral flute 10-32 tap.


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## Dave G (Apr 15, 2011)

You might consider a tapping guide. To handtap small holes square to the work surface I use a piece of steel with a hole in it drilled perpendicular thats a light clearance fit around the shank of the tap. Just lay the guide on top of your work and hold with one hand while tapping with the other. They're easy to make and most small taps have the same shank diameter so one guide hole will work with many size taps.Dave


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## MachineTom (Apr 15, 2011)

What you need is a Tapping Head, Designed for use in a DP it will work on a mill if there is enough vertical travel available. They come in sizes based on max tap size. 

They have reduction gears, clutch and reverse, all controlled with the force of the quill. Push the quill down the tap turns, release handle tap stops, retract quill tap turns reverse.

Ebay is the source as new units are $$$$.

If you don't have back gears this is the way to tap on a mill.


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## dickda1 (Apr 15, 2011)

Has anyone tried the Chinese tapping heads from places like CDCO? I like the cheap price - better than one can pay for a good used one. A far amount of precision is necessary for an item like this and as MachineTom noted, you usually pay for that. I am hesitant.


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## xo18thfa (Apr 15, 2011)

dickda1  said:
			
		

> Has anyone tried the Chinese tapping heads from places like CDCO? I like the cheap price - better than one can pay for a good used one. A far amount of precision is necessary for an item like this and as MachineTom noted, you usually pay for that. I am hesitant.



I bought the larger one. It's not very good. The tap does not line up at all with the holder. Has a huge (1/8") eccentric when you rotate it.


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## xo18thfa (Apr 15, 2011)

Here's what I use. It's a standard 0-3/8" drill chuck with a 3/8" x 24 threaded mount. A short length of 3/8" dia steel rod for a shaft. Old long shank drill bit for a handle. The shaft rides in a standard 3/8" ID, 1/2" OD oilite bearing. Just chuck this thing into the mill, drill press or lathe tailstock. This size does 1/4 x 20 into steel. 3/8 x 40 into cast iron.

28 years, never broke a tap. Never. Any tap, any metal. 0-80 into stainless steel, piece-o-cake.


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## Maryak (Apr 15, 2011)

Bob,

What a great idea...........Thanks :bow: :bow:

Best Regards

The other Bob


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## picclock (Apr 16, 2011)

@ Bob (xo18thfa) 

This is pretty much what I'm doing now (at least when I need it really straight). Although the large tap sizes are bigger than 3/8 (largest is 1/2" bsp) around 20mm into steel, more commonly 1/8thbsp (13mm) and various metric sizes to 12mm.

Its really more a case of saving time and effort by trying to use the power of the machine. Mostly I'm tapping into mild steel up to 13mm thick. 

I also have issues with the taps slipping in the chuck as the force goes up. So then its the large tapholder and muscle. 

@MachineTom , dickda1
Tapping heads - I never new such things existed but something similar was what I had in mind.
If they were more competitively priced I'd probably get one if available for the size of taps I use.

Although crude the device outlined below should allow direct tapping of most of the holes I do, and by fitting a reversing switch on the mill motor will also allow speedy tap removal. Driven shaft and output shaft would be supported by two bearings, and the gears are what I could get hold of from HTC or similar. 

Only thing that's difficult for me to figure is to make a tap holder which will support the tap squarely but prevent rotation by locking onto the flats at the end of the tap.


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## Tin Falcon (Apr 16, 2011)

PL what tap are you using ?
use only gun taps under power

Spiral flute for blind holes 
spiral point for through holes
forming taps for strong holes in mailable metal (use special drill sizes)
Hand taps should only be hand powered and often reversed. 
Tin


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## picclock (Apr 16, 2011)

@ Tin normally spiral point although I'm not sure it matters for thin materials

picclock


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## xo18thfa (Apr 16, 2011)

The biggest drawback with the drill chuck method is the tap slipping in the chuck. I've found by tightening the chuck a bit at the time using each of the three holes on the chuck, the grip is much better. Trying to tighten the chuck all at once from one hole is not as good.

Mine is a smaller 0-3/8" Want to do a bigger 0-1/2"


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## MachineTom (Apr 22, 2011)

To hold the tap buy a set of Tap sockets, they have an o-ring to hold the tap in, and a 1/4 or 3/8 square drive end, then add a hex to square adapter, no slip no more. 

This is what I'm taslking about.


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## Tin Falcon (Apr 22, 2011)

Another trick for quick tapping in aluminum is the handy dandy cordless portable electric drill with clutch. just chuck up the tap and go at it a tap guide, the ones that have Multiple holes in them could be used as well. have not done this a lot but the bit I did worked great . nice for 1/4 - 20 sized holes . Please use a gun tap. 

The other real nice machine I have used is a Flex Arm to buy new they are pricey IIRC about over $ 1000.00 for the low end models but I am sure many here could engineer there own to satisfaction. Need a HF reversible straight line drill some steel tube a bit of plate some drill rod make a few hat bushings and maybe some assorted fasteners. 

Drawing of one model here
http://flexarminc.thomasnet.com/Asset/S-36-arm-only.pdf

I used one of these in the model / training device shop I worked in for a while . they are fast and the tap is always perpendicular to the table (when set up properly) the down side is you do need a bit of table space that stays uncluttered.
Another option to consider if doing lots of holes.
Tin


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## gjn (Apr 25, 2011)

FWIW, here's how I approached the problem. I have a blank 3MT arbor which fits both the tailstock on my lathe and the spindle on my mill/drill so the jig can be used on both machines. The jig I made is bored 1" to fit snugly over the blank, parallel, end of the 3MT arbor. The other end of the jig is bored 3/4" diameter for 1.25" and then drilled 1/2" for a further 1/2". A series of collars are made to fit into the 1.25" recess and these are drilled to take the various size tap shafts I have.

The appropriate collar is inserted into the jig, the tap put into the collar and the 2 cap-screws then screw down onto the flats at the end of the tap (which is extending down into the 1/2" x 1/2" recess - this stops the tap from turning. A tommy bar is used to turn the whole jig.

So far I've used it to tap from 3/16" up to 3/4" threads with no problems.


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## picclock (Apr 26, 2011)

I think I may have found a solution to the tapholding problem.

http://mikesworkshop.weebly.com/improved-chuck-for-taps.html

This looks like a really neat idea which will allow taps to be held by the square end without slipping, and yet is simply adjusted by a single screw.

@gjn
Its a good solution, but to give you some idea of the grief I am having tapping 1/2" BSP holes, the tap holder arms are so long that they hit the mill column, and I can only get good rotation in the vice with the table moved to the limits of X and Y. I tried it with a smaller tap holder and it broke :'(

If I have to do too much of this I will end up with muscles 

Definitely moving up the tuit list.

Best Regards

picclock


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## gjn (Apr 27, 2011)

Picclock

The thing is that my tommy bars are removable so if you run into clearance issues (which I do when I use a long bar on the lathe) - I just turn the jig through 180 degrees then shift the tommy bar to the next hole, you could have the holes every 90 degrees in the body of the jig to make it easier if required.

Rgds - Gavin


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## Allthumbz (Apr 29, 2011)

xo18thfa  said:
			
		

> Here's what I use. It's a standard 0-3/8" drill chuck with a 3/8" x 24 threaded mount. A short length of 3/8" dia steel rod for a shaft. Old long shank drill bit for a handle. The shaft rides in a standard 3/8" ID, 1/2" OD oilite bearing. Just chuck this thing into the mill, drill press or lathe tailstock. This size does 1/4 x 20 into steel. 3/8 x 40 into cast iron.
> 
> 28 years, never broke a tap. Never. Any tap, any metal. 0-80 into stainless steel, piece-o-cake.



Looks like it to short enough to avoid clearance issues- good idea!

Nelson


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## picclock (Apr 29, 2011)

Just for reference, 1/2" BSP requires a tap drill of 3/4" and if memory serves its pitched at 19 tpi. 3/8 or even M12 is fairly easy to do normally, but when you get to using taps that have a minimum thread dia of 3/4" it requires a lot more torque, huge tap holder and reasonable grunt.

So to be able to power tap this is no mean thing. I take the thing about tommy bars at 90 degree increments, but it would be a lot faster under power.

Best regards

picclock


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## gjn (Apr 29, 2011)

I agree about the power thing, I'm just not that brave......


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