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beanbag
09-20-2012, 06:53 AM
Hello,

Just wondering how much lateral float or free play a tap holder is required to have, or none at all?
I'm thinking of doing a bunch of holes on a manual mill. I'm guessing a few thou off for drilling without spotting first, and another few thou due to not being super careful returning to the exact same position.

Here's one I built for doing "hand tapping" with a CNC machine. It is spring loaded for vertical play. There is a little bit of play due to clearance between the inner rod and outer tube. This was for blind holes, and that white delrin ring was a depth stop. The holes were spotted first, and the tapping code moved the machine to the positions of the holes in the same order, so there shouldn't have been much error in the positioning.

http://i139.photobucket.com/albums/q286/beanbag137/tapholder_zps25c68da1.jpg

BTW, I don't really know what I am doing, so that is why I asked. I'm not even sure this holder has any real float because under torque, that (pair of opposing) socket head screw leans against the slots.

Hopefuldave
09-20-2012, 02:29 PM
Hi BB,
I don't have a floating tap-holder, but the floating reamer holder I have has about 1/4" total play (i.e. it can move the reamer axis anywhere inside a 1/4" circle) - I don't use it a lot, but when I need it there's no substitute! It does, however, hold the reamer "straight" without allowing any angular or rotational movement.

I imagine you could put together something like an Oldham coupling inside the holder, with the shafts bearing against the front and back internal faces, maybe with a thrust bearing to take up axial play? It'd take a bit of thought though - I may have to run it through Crap-O-CAD as it sounds an useful tool! I'll post up a .jpg if I get it together :)

Dave H. (the other one)

tdmidget
09-20-2012, 02:51 PM
Hello,

Just wondering how much lateral float or free play a tap holder is required to have, or none at all?
I'm thinking of doing a bunch of holes on a manual mill. I'm guessing a few thou off for drilling without spotting first, and another few thou due to not being super careful returning to the exact same position.

Here's one I built for doing "hand tapping" with a CNC machine. It is spring loaded for vertical play. There is a little bit of play due to clearance between the inner rod and outer tube. This was for blind holes, and that white delrin ring was a depth stop. The holes were spotted first, and the tapping code moved the machine to the positions of the holes in the same order, so there shouldn't have been much error in the positioning.

http://i139.photobucket.com/albums/q286/beanbag137/tapholder_zps25c68da1.jpg

BTW, I don't really know what I am doing, so that is why I asked. I'm not even sure this holder has any real float because under torque, that (pair of opposing) socket head screw leans against the slots.
I won't argue with that . A stop on a tap is just begging for broken taps. You say you are allowing for not relocating over the hole. Why? When you drill the hole, tap it then while you are still over it. No error that way. Allowing the so called float is only a way to start crooked, Again, a new way to break taps.

Evan
09-20-2012, 03:07 PM
I can't see any way of providing lateral float for a tap in a milling machine that wouldn't increase the risk of breaking the tap. However, allowing the part to float laterally should work fine.

Hopefuldave
09-20-2012, 03:38 PM
OK, a quick Crap-O-CAD, important points are that the internal bore of the rear body needs to be diameter of the Oldham disc plus the float, hole in the front cap larger than chuck stub plus float, a ball thrust bearing could go between the cap and the disc on the chuck stub? I'd make the Oldham disc either out of bronze or a low-friction plastic if the tapping loads are low enough!

I haven't put any fixings in, and the rear body might be easiest to make as a tube and plug-with-slot?

http://i979.photobucket.com/albums/ae279/hopefuldave/Daft%20Ideas/Floatingtapholder_zps3130bc0d.jpg

Using an Oldham coupling should get around TD's concern as the tap will be held parallel to the drilling - if the hole is chamfered / countersunk the tap should self-centre, and it's much less likely to break that way than an off-centre tap rigidly held (don't ask me etc....)

Dave H. (the other one)

beanbag
09-23-2012, 02:12 AM
A stop on a tap is just begging for broken taps.

This was hand tapping, so the stop worked great to get the hole to the right depth.



You say you are allowing for not relocating over the hole. Why?


because that allows for only 1 tool change instead of 2N-1 tool changes. (Where N is a large number)

beanbag
09-23-2012, 02:13 AM
I can't see any way of providing lateral float for a tap in a milling machine that wouldn't increase the risk of breaking the tap. However, allowing the part to float laterally should work fine.

How would you let the part float laterally without rotating or pulling upwards?

oldtiffie
09-23-2012, 03:09 AM
Originally Posted by beanbag

Hello,

Just wondering how much lateral float or free play a tap holder is required to have, or none at all?
I'm thinking of doing a bunch of holes on a manual mill. I'm guessing a few thou off for drilling without spotting first, and another few thou due to not being super careful returning to the exact same position.

Here's one I built for doing "hand tapping" with a CNC machine. It is spring loaded for vertical play. There is a little bit of play due to clearance between the inner rod and outer tube. This was for blind holes, and that white delrin ring was a depth stop. The holes were spotted first, and the tapping code moved the machine to the positions of the holes in the same order, so there shouldn't have been much error in the positioning.

http://i139.photobucket.com/albums/q286/beanbag137/tapholder_zps25c68da1.jpg

BTW, I don't really know what I am doing, so that is why I asked. I'm not even sure this holder has any real float because under torque, that (pair of opposing) socket head screw leans against the slots.



I won't argue with that . A stop on a tap is just begging for broken taps. You say you are allowing for not relocating over the hole. Why? When you drill the hole, tap it then while you are still over it. No error that way. Allowing the so called float is only a way to start crooked, Again, a new way to break taps.

+1 with tdm.

The hole to be tapped and the mill/drill quill axis must be aligned/concentric.

Here is a diagram of a "floating" tap-holder:

http://www.machineryhouse.com.au/Print?Code=T004B&All

The self-aligning collet on the shank of the tap plus the ("X" and "Y"?) free-to move axially clamps on the square shank of the tap all causes the tap to be aligned with the tapping head and the machine quill axis.

The square clamps each align to the tap (in the collet) - that is where the so-called "float" is.

If the tapped hole axis can be accurately aligned to the machine quill later the driill can be done as first process and the tapping as a later/follow-on process.

beanbag
09-23-2012, 03:26 AM
If the tapped hole axis can be accurately aligned to the machine quill later the driill can be done as first process and the tapping as a later/follow-on process.

What counts as "accurately aligned"?

oldtiffie
09-23-2012, 03:54 AM
On mine, as regards concentricy with the machine quill axis - as good as a collet in the quill.

As regards "positioning" on the machine table "X" and "Y" co-ordinates - as good a you can repeat on a DRO/rotary-table/using machine "X" and "Y" dials/lead-screws.

If the "X" and "Y" grippers on the tap square shank are as seen as ordinary tap-wrench bodies but on round/cylindrical forms it will be easier to see or visualise.

JCHannum
09-23-2012, 11:07 AM
Tiffie's tap holder doesn't float. It is a clone of the Jacobs style tap holder used by several different tapping head manufacturers. When set up properly, the clamps for the flats on the tap are free to move in only one axis, no float there. The rubberflex collet is drawn up tight to firmly center the tap in the chuck, no float there either.

The oldham coupling will provide axial float for the tapping head and is in fact used by several different tapping head manufacturers to provide axial float, which is an important feature in a tapping head as tapping is often performed in a second operation machine and precise location is not expected as a matter of course.

Hopefuldave
09-23-2012, 01:14 PM
Agreed, re (http://www.machineryhouse.com.au/Print?Code=T004B&All) that's not a *floating* tap-holder!

The whole point of the floating holder (tap *or* in my case, reamer) is that the tool will self-centre in a slightly off-axis hole *and then track it accurately* - I've found the reamer holder can cope easily with a hole up to an eighth of an inch off-centre, and reams on-centre and parallel with respect to the initial drilled / bored hole. This is a real time saver! I've heard (only heard, as I'm in a country that Doesn't Like Guns) that a lot of gunsmiths use floating reamer holders with piloted reamers when chambering barrels to ensure that the chamber and barrel are concentric, allowing the reamer to float means it has to follow the barrel bore and isn't canted at an angle such that it cuts a "conical" chamber. Most chamber reamers appear to be solid carbide, so even more fragile than HSS taps... Pricy, too!

For a floating tap holder, I suspect that a stiff spring could go between the stub to mount the tap-holder chuck on and the front cap; in combination with an adjustable-depth cap this would let you set the depth of thread by arranging the stub to pop out of the slot at the required depth - an Oldham coupler looks a lot like a dog-clutch to me, after all! I think the Oldham disc would need to be held in position axially though, maybe a circlip in an internal groove in the holder body engaging an external groove in the disc would work? All conjecture and daft ideas, admittedly!

Dave H. (the other one)

beanbag
09-24-2012, 12:56 AM
The oldham coupling will provide axial float for the tapping head and is in fact used by several different tapping head manufacturers to provide axial float, which is an important feature in a tapping head as tapping is often performed in a second operation machine and precise location is not expected as a matter of course.

Do you mean radial /lateral float?

I still have not figured out whether a tap holder is supposed to have float or not.

Can an oldham coupling actually float when under torque?

I was thinking a very simple thing is loose fit tube-inside-a-tube holder, with the attachment / pivot point up very high. That sort of simulates lateral float with a minimal amount of tilt.

oldtiffie
09-24-2012, 02:34 AM
Originally Posted by JCHannum

The oldham coupling will provide axial float for the tapping head and is in fact used by several different tapping head manufacturers to provide axial float, which is an important feature in a tapping head as tapping is often performed in a second operation machine and precise location is not expected as a matter of course.


Do you mean radial /lateral float?

I still have not figured out whether a tap holder is supposed to have float or not.

Can an oldham coupling actually float when under torque?

I was thinking a very simple thing is loose fit tube-inside-a-tube holder, with the attachment / pivot point up very high. That sort of simulates lateral float with a minimal amount of tilt.

Jim Hannum is quite correct.

Here are a selection of Oldham's Couplings:

http://www.google.com.au/search?q=oldham's+coupling&hl=en&rlz=1W1IRFC_enAU360&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=3_1fUJmUBNCaiAfJ4oH4BQ&sqi=2&ved=0CB4QsAQ&biw=1920&bih=851

http://www.google.com.au/#hl=en&sugexp=les%3B&gs_nf=1&cp=16&gs_id=20&xhr=t&q=oldham's+coupling&pf=p&rlz=1W1IRFC_enAU360&sclient=psy-ab&oq=oldhams+coupling&gs_l=&pbx=1&fp=1&biw=1920&bih=851&bav=on.2,or.r_gc.r_pw.r_qf.&cad=b

http://en.wikipedia.org/wiki/Coupling

outback
09-24-2012, 07:20 AM
Beanbag;
That is a pretty cool tool. I may make one of those myself.

How are you holding the tap in the tool?
Jim

beanbag
09-24-2012, 08:45 AM
Beanbag;
That is a pretty cool tool. I may make one of those myself.

How are you holding the tap in the tool?
Jim

That little socket head screw (actually a pair) presses against the square end of the tap.

Evan
09-24-2012, 11:51 AM
How would you let the part float laterally without rotating or pulling upwards?

That depends entirely on the part. A flat plate is simple if it is allowed to have at least three extra holes present that are not on the same line or preexisting holes are available. Simply bolt it to the table or a jig plate using bolts/studs that are somewhat smaller than the holes. Rather than tighten them leave just enough clearance that the part can move laterally only. It will then centre on the tap when the hole is started. A jig with the same effect can be made without much work for just about any part that needs to be machine tapped.

This assumes that the initial location of the tap for each operation is constrained by coordinates that place it in the centre of the correct location for the hole as referred to the location of the restraining studs. This is trivial for CNC operations but would require a pre calculated set of positions for manual tapping.