posting photos

See **LINK** for BT series dimensiuons. However the table there doesn't give 34.4 mm for that dimension for any size!

Actually BT tapers do drive on the tapers, I think the slots in the flange are to allow an auto tool changer to lock the collet from rotating during the change. My Novamill uses BT30 and the taper is pulled in by a drawbar, or a pullstud on the auto change version. Neither the machine nor the Easy-change chucks that came with it use the slots.

It's possible that the taper is a bit over-long but actually a BT30 – check other dimensions against the table above. All BT / ISO tapers have the same angle but different lengths/diameters.  That could account for the slightly larger measurement.

If it is a BT taper I suggest you stay with it. You can get ER collet chucks on BT shanks; and you can certainly get BT30 collets to go direct in the spindle from AliBaba.

Depending on what it's made of you could potentially bore it out R8 if there is enough meat at the narrow end (R8 needs 24.1 mm bore). Or just drill/bore/ream and Loktite in an ER parallel-shank chuck. It's quite easy to turn these tapers too to make your own – so you could make one in the lathe to take a parallel shank chuck if the one you have is hard or you don't want to risk it – and of course if it's some odd size you could make one to fit.

This might help too.

Edited By John Haine on 29/10/2020 16:17:44

Edited By John Haine on 29/10/2020 16:23:33

Hi the measurement given in your chart might refer to the Gauge Line measurement, this is a little further back the taper and not at the end where you are measuring from, the picture you have posted shows a line further back on your taper where it fits your taper this is the Gauge LIne measure here and see what you get.

Cheers Colin

The difference between the drawing size of 31mm and your measured 34mm is probably of no concern. Try measuring the diameter where the witness mark is, the extra rust would show where the tool does not enter the spindle. The 30 INT size is a step up from R8 and tooling in that size is not too hard to find. Modifying the spindle to R8 would be difficult, and the taper angle is not the same as 30 INT.

As John says, the best thing to do is to borrow a BT30 fitting of some type and try it in. If it fits you know what to look out for/buy in the future. The only advantage of machining out to BT40 is that second hand tooling is easier to get hold of but new BT30 is cheaper than BT40 so you "pays your money and takes your choice" as they say!

Alistair.

You are correct Peter, ISO, INT, BT, SK all share the same taper angle, only the diameters change within 20, 30, 35, 40 and 50 types.
The parallel portion on ISO and INT can be removed and replaced with a pull stud after tapping a bit deeper.

Picture show an ISO30 having the portion removed and the modified part with pull stud.

Emgee

Edited By Emgee on 30/10/2020 11:20:18

The only real advantage of a 40 taper is that you can sometimes get a bargain lot at a factory clearance/liquidation.

About 25 years ago a friend bought what he thought was a box with 10 bits of 40 sized tooling but when he went to pick it up after paying the cashier there were 10 boxes with 10 holders in each!!

I really don't know why you want to change it from the 30 taper as it is lighter to hold in place when inserting the drawbolt and easier to catch when it is released. also remember BT30 is an M12 thread and BT40 is M16 so the hole through the spindle has to be drilled out if not big enough.

If it's in between 30 & 40 then it sounds like it's a 1 3/8NS (non-stick). I did wonder about that but the suggestion that it had been re-machined fooled me, unless someone had just taken off a small amount to clean it up.

Brian