Converting a 40 Taper Pull Stud From M16 to 5/8-11

I have quite a few BT40 holders with M16 pull stud threads that were given to me. I know they are no use in my Fadal 4020 because of tool changer compatibility, but I have a Series II Bridgeport with a 40 taper and 5/8-11 drawbar. I share tooling between them by removing the pull stud for use on the Bridgeport. SO.... My question is has anyone converted the pull stud threads on a tool holder from metric to inch? Or is it even an idea worth entertaining? And if so what would be your M.O. to achieve it? My first and only thought was to use a Helicoil/Recoil, ironically the dia. of the bore just before the threads and also the M16 thread major dia is the exact same size of the drill used for 5/6-11 recoil at 21/32 (16.5 mm). I don't see an issue with the slight reduction in wall thickness of the holder at the pull stud as a result of doing this. Please keep in mind I'm just a broke homegamer so free holders + some work is very beneficial to me. Am I missing something that could cause operability/safety concerns by doing this?

Thank you in advance to anyone willing to chime in, give advise, experiences or even just calling me a for even trying this,

JustSteve

Up here in Canada, there seems to be a surplus of CAT40 holders, not too many NMTB 40, and even fewer metric equivalents of the former with M16 drawbar threads.

A colleage of mine recently acquired a mill with an "ISO 40" taper, 5/8-11 drawbar. He also had from a previous life a box of OZ32 collets which, as near as we can tell, can only be held by DIN 2280 tool holders (NTMB/ISO 40 holders with M16 drawbar threads.)

So here we are, scrounging for NMTB 40, whilst CAT40s are found holding down stacks of papers, propping open doors, and rusting away in piles in surplus bins.

For my friend, he need only make up two new drawbars - one with an M16 thread, the other with an elongated thread to also capture CAT40 holders. But I suggested casually, if he didn't mind messing with a brand new and very expensive holder, to bore it out, then braze in a bushing pre-drilled/tapped for 5/8-11. If one drills a cross-hole and drops in the braze material from that hole, it should fill and surround the entire bushing making it as strong as the original.

In my case, I don't care for metric toolholders and drawbars, but I would like to avail of all the CAT40's. In my case, with my power-drawbar, switching out drawbars is a non-starter, but if I could, say, make a new drawbar with an extra inch of thread, and if my NMTB40's have enough clearance past their existing threads to accept the full length of the longer drawbar, then with one NMTB+CAT-lengthened drawbar, I could potentially handle both NMTB40 and CAT40 toolholders.

So there's my suggestion - bore your metric toolholders to accept a 5/8-11 tapped bushing and braze them into your toolholders.


Torin...

What you want is an adapter with a metric male thread on one end and a female 5/8 thread on the other , that replaces the pull stud . These adapters are available one exsample can be found here BT40 to ISO40 Adapter | DZ Sales – dzsalesllc

I had thought about that but didn't think there'd be enough meat between the male and female threads, and I think the drawbar will bottom out before pulling the taper fully up into the spinmdle, but I'll revisit the dimensions of those little adapters. It would be a much better alternative to modifying my drawbar. Thanks for the suggestion.

Many moons ago when I was fairly green about tapers. I needed a
Cat40 that would hold a 1.5" shank. J&L wanted about $350 for one,
but they also had a BT40 for a buck and a quarter.

I figured they were the same thing. When I got the holder, the
pull studs I had wouldn't fit, so I just ran a tap down it. Put
the Cat40 pull stud in and got to work.

Of course the machine was a little pissy, groove height and all, so
I just hand loaded it. It was an ODDBALL tool, only needed for one
job, but it ran it about 6 or 7 times.

Drawbar, NO tool changer machine. Run a tap down it. Its not perfect,
its not ideal, but if you aren't running big HP #s(Its a Bridgeport),
you should be fine.

Its a little a little(I don't stutter when I talk, only when I type) sloppy,
but it worked for me. It'll locate on the taper anyways. Try one and see.