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Taper identification

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Me.29/10/2020 09:49:18
136 forum posts
30 photos

I suspect this must have been covered on here numerous times but I can't find it.

How do I identify the taper in my Milling machine. The machine has only come with one taper arbor that fits into the spindle - there's nothing to identify the tool with a part number so all i have are the measurements to go by.

Its a Herbert machine from the 50's so it used to use a Herbert taper but I can see it has been modified to take more standard tooling but what that is is yet to be confirmed.

If someone can explain how to post a picture on here I will show the machine and the tool i have. As they say a pictures says a 1000 words.

JasonB29/10/2020 10:11:39
21979 forum posts
2534 photos
1 articles

posting photos

Howard Lewis29/10/2020 14:21:47
5744 forum posts
13 photos

If it is an elderly an ex industry machine, it may well have an International Taper. (30, 40 or 50 depending on size )

They may, now, be designated as BT.

ISO Tapers look similar, but will be to Metric dimensions, rather than Imperial

Take a look at what Arc Euro offer, they do both BT and ISO adaptors, which may give you a clue.

The INT and ISO tapers locate on the taper, but drive on two dogs on the machine quill that engage in slots in a flange on whatever tool / arbor is being fitted.

Other tapers, such as Morse will be less steep, since they are intended to drive on the taper.

Morse tapers are only slightly less than 3 degrees, but vary slightly according to the size (So a 1MT will not be the same angle as a 2MT nor a 3MT, and so on )

There are other tapers, but probably unlikely to be the one in your machine.



Me.29/10/2020 15:09:45
136 forum posts
30 photos

taper ?.jpeg

Alistair Robertson 129/10/2020 15:23:43
143 forum posts
6 photos

That looks like BT30 taper. The thread in the top should be M12 i.e. 12mm x 1.75mm pitch.

All 30 (or 40, 50 etc) are the same but the thread may vary, either metric or imperial.

Me.29/10/2020 15:30:13
136 forum posts
30 photos

Thanks _ i'm hoping it is, but when i look at the spec of the BT 30 it shows 31mm not 34mm as shown in my Pic.

Long shot I know but what are the thoughts of using this taper as a sleeve, as I know it fits in my spindle - should I machine the insides out to a new taper that I know i can get tooling for ?? and if so which one..... ?

Opinion is greatly accepted.

not done it yet29/10/2020 15:59:20
6514 forum posts
20 photos

Very easy to measure the taper.

Stick it in your lathe Chuck and zero a dial gauge (mounted on the carriage) against the taper, then move the carriage a known amount. Use the results to calculate the angle. Refer to engineering tables for the type.

John Haine29/10/2020 16:15:37
4407 forum posts
261 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

Emgee29/10/2020 16:48:50
2311 forum posts
277 photos

Is this the same machine mentioned recently in a thread that Lord John had modified ?


colin vercoe29/10/2020 16:53:55
59 forum posts

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

Alistair Robertson 129/10/2020 17:54:20
143 forum posts
6 photos

I would suggest that the BT30 taper is far superior to similar sized tapers especially R8 as the gauge line is at a much larger diameter and is a lot stiffer. It is possible to use INT30 which has a parallel section on top but if I get a good deal on any of them I usually cut off the straight bit and re-tap the thread a bit further (They are not hard). to be used with a common drawbolt.

When I bought my Novamill I started with a couple of ER chucks for a while but I now have almost 60 various tools from ER 8 to ER 40 plus drill chucks and touch sensors and even an alignment camera.

old mart29/10/2020 17:59:03
3495 forum posts
216 photos

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.

Pete White30/10/2020 07:50:14
151 forum posts
16 photos
Posted by Me. on 29/10/2020 09:49:18:.

Its a Herbert machine from the 50's so it used to use a Herbert taper but I can see it has been modified to take more standard tooling but what that is is yet to be confirmed.

That tool shown in the pic fits the spindle and looks to be imperial, it will measure 1 3/8 a shade further on the taper? Which makes it the standard NS taper, If the machine has been modified what was it before, because now it takes very difficult to find tooliing?

It would be good to see a picture of the modification to the machine, has the spindle been sleeved and remachined to rectify damage?

Am I missing something here?


Edited By Pete White on 30/10/2020 08:02:23

Me.30/10/2020 08:06:37
136 forum posts
30 photos

Hi All

Thanks for the input - I think Pete is correct in his diagnosis as he has the same machine but has already made a adapter sleeve.

It is Herbert machine so can only assume it is still the original Herbert taper - which would imply that the taper is of the same taper angle as the BT30 ISO30 ?? just slightly fatter in diameter.

Would I not be best to get a BT40 taper and turn it down to fit the Herbert spindle taper. or would an adapter sleeve be the best option. I know Pete has done this and it works well.


John Haine30/10/2020 08:59:02
4407 forum posts
261 photos

If you're going to be turning why not just make one from a bit of reasonably FC steel?

Depending where you're located I could lend you a BT30 holder to see if it fits?

Edited By John Haine on 30/10/2020 09:00:21

Alistair Robertson 130/10/2020 10:00:03
143 forum posts
6 photos

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!


Pete White30/10/2020 10:52:24
151 forum posts
16 photos

I have just looked up the gauge dim of a BT 30 taper at 31.75 clearly to small to fit the machine, which is 1 3/8 ?

Am I right in saying the size of a bt ? is the same with a shade as a int ? the difference being at the thin end, designed on bt for auto tool changing ?

Emgee30/10/2020 11:19:30
2311 forum posts
277 photos
Posted by Pete White on 30/10/2020 10:52:24:

I have just looked up the gauge dim of a BT 30 taper at 31.75 clearly to small to fit the machine, which is 1 3/8 ?

Am I right in saying the size of a bt ? is the same with a shade as a int ? the difference being at the thin end, designed on bt for auto tool changing ?

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.


quorn on bantam.jpg

emco bt30.jpg

erikson tenthset boring head.jpg

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

Me.30/10/2020 11:31:31
136 forum posts
30 photos

That was really helpful - so all the 20 30 40 50 etc tooling has the same taper angle so from what Pete tells me and the reply from Emgee I am guessing the best option is the taper sleeve adapter.

Pete has already given me pointers towards this option but I will need help on the best way to set up to turn an internal and external taper to make a sleeve.

Alternatively - what would be the thoughts of having the spindle re-machined to take a 40 taper, there seems to be loads of meat on it to do this.

Alistair Robertson 130/10/2020 12:13:31
143 forum posts
6 photos

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.

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