Cutting an external thread on the nose of a milling chuck

I want to cut an external thread on the nose of an R8 milling chuck (the sort that takes an end mill shaft with a flat on it , and clamps it in with a screw against that flat). My purpose is to create a 12 TPI male thread with which to hold a boring head that has a female 12 TPI socket.I imagine the chuck steel is extremely hard. The nose is 1 5/8" diameter and I want to end up with a threaded nose with 1 3/8" external diameter. What cutting tool/material/insert should I use and what speed should I turn it at on a Myford Super 7.

Any advice gratefully received!

Edited By Adam Harris on 10/02/2016 10:05:32

Edited By Adam Harris on 10/02/2016 10:24:32

Hi Adam,

I think I'd be inclined to use an R8 blank-end arbor instead - you probably need to loctite a larger diameter lump on this one to get the size you need...

**LINK**

or try rethreading a dedicated boring head shank (6th one down) although this might be hard too.

Edited By Jon Gibbs on 10/02/2016 10:13:38

Hi Jon, thanks for your very fast reply. Actually I gave the wrong target external diameter - it should be 1 3/8" not 1 1/4". Anyway I agree I could put a bigger lump on the end of the Chronos 1 1/8" diameter nose (they do not do an arbor wuth a bigger nose), but to prevent pulling movement it would involve threading the arbor nose and the internal face of the lump and then threading the external face, which would mean cutting 3 threads! I could also thread a sleeve to fit in my existing boring head but that again would involve cutting 3 threads. It may be that that is the only way if it is totally impossible to thread hardened chuck steel effectively....

.

Adam,

I agree with Jon, and as a 'true believer' I would happily use Loctite 638 on a simple sliding fit.

MichaelG.

Hi Adam,

Well if you only want to cut one thread you could just turn a parallel spigot (with flat) on the arbor and have a snug fitting bore on the "lump" with a set-screw as well as loctite. Provided the tightened set-screw is below the core of the thread on the "lump" it won't get in the way.

Alternatively you could mill some slots on the arbor and the threaded "lump" and screw on some small blocks to prevent rotation like this on my fly-cutter which is mounted on an arbor cannibalized from a face-mill.

HTH

Jon

If it's single pointing you try to avoid then Jon's suggestion of a blank arbour with a lump bonded on it sounds best... and if you do stuff the threading you can easily have more goes.

I must admit to quite enjoying the few threads I've cut though with my chester lathe's thread dial indicator and gear options I usually have to run a test piece first to be sure I've marked the right spot on the thread dial for repeat cuts to be correct.. (It'd be so much easier if the thread dial's gear options were indexed in some way)

As has become usual on this forum, the answers to the OP's question (with the best of intentions) have become a bit like the the question "What's the best way to get to Limerick?" Answer: "I wouldn't start from here sir!"

My experience with the sort of tooling described is that they are not that hard and can be cut with replaceable tip TC tools. I haven't tried threading such materials but I would have thought that if the turning to size is successful then threading with a TC tip tool would be worth a go - HSS would probably be a struggle and you would break the tip off. TC tips have better geometry than home made HSS tools. For turning I'd use the slowest direct speed on the Myford and a reasonable feed - don't try and take fine cuts. For threading I'd put it into back gear but I'd want a good runout for the threading tool. I think one of the secrets to success is being fairly bold. Experiment and tell us your results!

But, as others have said, I wouldn't start from here - but perhaps I'm too timid

HTH,

Rod

It's a fair cop - I'm afraid you're right Rod.

Jon

Possibly re-thread the arbor for one of these :- **LINK** (scroll down the page for the R8 arbor).

Nick.

This is the best suggestion of the lot. The arbors are inexpensive and not particularly hard. You should be able to work with HSS tools.

Thanks Rod for the advice on how to cut the threads. Nick/John, the Arceurotrade Arbor has an 18tpi and is only 1.5" in external thread diameter so not I think possible to re-thread to 12 tpi with external thread diameter of 1 3/8" unless the 18 tpi thread depth is only 1/16"....would it typically be only 1/16" deep?

18 tpi whitworth form 0.036" deep

Neil

Edited By Neil Wyatt on 10/02/2016 19:26:14

Thanks Neil - I will buy the Arceurotrade R8 arbor then and re-thread it. Many thanks to everyone for their advice.

Neil, just to finish up on this subject, as regards cutting the 12 tpi thread I am confronted with the only suitable RDG carbide inserts for 55deg thread cutting stating they are limited to 1.5mm pitch (do not know why!), and 12 tpi is about 2.1mm pitch - I saw in a related post you recommending the Tracy Tools thread chaser sets for finishing off a thread with the correct profiled peaks and troughs, and wonder if the combination of cutting the thread first with the above mentioned carbide insert and finishing it off by hand with the Tracy 12 TPI whitworth chaser would be a satisfactory procedure for me? Thanks, Adam

Incidentally I do have an Eclipse H5 55 degree thread cutting tool but I think a carbide insert would be more effective on the hard R8 arbor than H5 cutting material, or would the H5 (5% Cobalt) tool be good enough?

In my experience the blank arbors supplied by Arc (and others) turn really nicely using HSS,

Finishing with a chaser will give a nice end result, but you can just round off the corners of the thread using a sponge-backed abrasive block.

The issue with Whitworth form is that if the top of the thread is insufficiently rounded, you will probably end up cutting it too deep to make it fit. Better to truncate the top of the thread a little, than cut it too deep.

Neil

Many thanks as always Neil. I will drop the idea of the carbide insert and proceed with the Eclipse H5 then. I have actually just already gone ahead with the Tracy purchase as I thought nice idea to have in one's arsenal anyway! Adam

As you know inserts should match the helix angle. For most 'average' purposes it's not so critical so some sources only offer one 'average' threading insert. Shop-Apt for example list them by TPI such as here: **LINK**

pgk thanks for that