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Mill MT4 taper mod question-Release

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Chris Mate05/12/2021 19:51:17
83 forum posts
8 photos

Hi, I like latest opinions on modifying an MT4 arbor for ER32 collets etc, by undercutting a section around the centre of it so it release easier. The drawbar is 16mm.

Is this a bad idea-?

oldvelo05/12/2021 20:17:39
280 forum posts
54 photos

Not recommended to reduce the contact area.

Insert the morse taper into the socket 1/3 of it's length and slap it home firmly if the taper and socket are in good condition this is firm enough to drive the tool holder with the drawbar snugged up omly to hold it there.

You can make it a lot easier to release by not winching it up with a big long spanner.

Put your right thumb on the jaws of the spanner and apply pressure with three fingers with pinky as no 1 and

snug up firmly.

A forcing screw device to push the taper free is prefered over bashing it free withe a hammer.

Chris Mate05/12/2021 20:58:13
83 forum posts
8 photos

Thanks, I try this method.

Paul Lousick06/12/2021 05:21:18
1901 forum posts
673 photos

The spindle on the mill I have now and my previous one both had a slot on the side for inserting a tapered wedge for removing Morse taper tools. (same as those on a drill press) The quill has to be in the full down position to access the slot. Have you checked if there is one on your mill.

taper removal.jpg

Edited By Paul Lousick on 06/12/2021 05:24:50

Chris Mate06/12/2021 05:51:18
83 forum posts
8 photos

Paul, this mill has that, and I am looking at that too. I once modified a G-Clamp to press out a drillpress(MT2) the small taper holding the chuck(From both sides), but that is only used if a new chuck is fitted to MT2 arbor(Rarely). Not sure if I can come up with something non intrusive to bearings with least moving parts after looking at all opinions.

Edited By Chris Mate on 06/12/2021 05:51:58

JasonB06/12/2021 06:58:36
22029 forum posts
2540 photos
1 articles

You can buy an exanding wedge which opens up as you pull down on the handle rather than hit it.

The only downside is they are really meant for tanged tools so 1. may not have anything to bear on if the taper ends below the slot, 2 you can damage the edge corner of the taper if it is not relieved, 3 need to lift the drawbar out the way.


Edited By JasonB on 06/12/2021 07:31:52

ega06/12/2021 10:53:03
2402 forum posts
196 photos

I think that in some circumstances relieving the centre of a less-than-perfect taper shank (as is sometimes seen on commercial items) may actually improve its grip.

I only ever nip up my drawbar by hand and, when this is not in use, use and recommend the Facom versions of Jason's expanding wedge which avoids the need for a third hand!

not done it yet06/12/2021 13:33:41
6520 forum posts
20 photos

Is it something like THIS ?

If so, there are options to extract from the end of the spindle.

1. A pair of suitably sized wedges - I use these whenever possible if the MT is tight.

2. Thread the end of the ER, extend the spanner flats and use a suitable nut to jack out the arbor (much like some Clarkson collet holders?). A bit like THIS

Chris Mate06/12/2021 13:34:37
83 forum posts
8 photos

-Adaptors Sleeves/Morse Taper=Open Sleeve with Release Nut.
I am also looking at this, however what this exactly is and how it fits or replace the MT4 for ER32 I am not sure about yet. They said I may be able to get this but its not something they stock.

If somebody can explain what excactly this part is, meaning if I buy it will it be fitted with an ER32 chuck on an MT4 arbor, but with the nut(16mm) added, and just work-?

Edited By Chris Mate on 06/12/2021 13:35:10

Edited By Chris Mate on 06/12/2021 13:36:30

old mart06/12/2021 14:47:10
3524 forum posts
217 photos

I have seen the centre 1/3 of several sizes of Morse taper shanks with factory produced relief as they are chemically blacked rather than relieved at a later date. As ega mentions, this may improve the grip in worn tapers. I don't personally like them as they are slightly tricky to slam home into the spindle. That applies to tanged tapers, of course. Some spindles might be convertable to captive drawbars which could help break the taper.

I always say that if buying a new mill which has the options of Morse Taper or R8, always choose R8, it was designed as a mill spindle and has advantages in use. Morse tapers were designed for drills and most of those have the extraction slot. The drawbar was not part of the original plan.

John Hinkley06/12/2021 14:58:08
1219 forum posts
397 photos


If you mean THIS EXAMPLE then, no, it won't do what you want. You would need to get a sleeve to reduce your MT4 to MT3 or 2 then fit an ER32 collet chuck with matching MT into that. You would still be stuck with how to remove the sleeve. You would be far better off, in my opinion, to obtain an ER32 collet chuck on an MT4 taper shank. Like this:

er32 to mt4.jpg

Then you're back to square one with the extraction problem! Though it shouldn't be a problem if you do it correctly.

Easy for me to say, he said smugly, as an R8 user!


Howard Lewis06/12/2021 15:34:42
5751 forum posts
13 photos

I made up an extractor for the 3MT tapewr on my machine.

Removed the pulley retaining nut (L H thread in my case ) Turned a register for about half the thickness of the nut .

Bored a plate to match the register, with btwo symmetrically plkaced tappings outboard. Made up a second plate with throughn holes on the same centres as the tapping (Imn used 1/4 BSF but M6 would quite a good alternative ) tapped a central hole, again 1/4 BSF.

Fit plate under nut, ready for needed to extract tooling.

To remove Taper.Tooling

Slacken Drawbar about half to one turn, fit tpo plate and screw the outer bolts into the lower plate.

Screw down the central bolt to bear on the Drawbar head,


Hopefully the taper with then break

If not fightem central bolt as much as possible, and if still obstinate, a light tap will break the taper



SillyOldDuffer06/12/2021 15:46:42
7923 forum posts
1725 photos
Posted by Chris Mate on 06/12/2021 13:34:37:

-Adaptors Sleeves/Morse Taper=Open Sleeve with Release Nut.
I am also looking at this, however what this exactly is and how it fits or replace the MT4 for ER32 I am not sure about yet. They said I may be able to get this but its not something they stock.

If somebody can explain what excactly this part is, meaning if I buy it will it be fitted with an ER32 chuck on an MT4 arbor, but with the nut(16mm) added, and just work-?


Do you mean one of these, as sold by ArcEuro?


If so, it's no good to you. It's a reducer - a big MT taper on the outside, with a smaller MT taper inside. For example, a reducer with an MT4 outer an MT2 inner allows MT2 tooling to be plugged into an MT4 spindle. The MT2 tooling is secured and released in the usual way with a drawbar. The Release Nut pulls the reducer out.

What exactly is the problem you're trying to solve? MT works quite well. Three reasons why it might be difficult to eject an MT taper:

  • The drawbar was overtightened by the operator. (Some chaps can't resist heaving on spanners and then whacking them extra tight with a hammer. Don't! ) I find hand-tight plus a 1/3 turn about right. Experiment to find out what works on your machine. It's a balance - enough tension to stop the taper slipping during a cut, but not enough to wedge the taper so tight a short sharp tap on the drawbar undone 5 or 6 turns won't release it. Note 'short sharp' - never pound on a drawbar!
  • An accidental super-tight shrink fit was created by inserting a below room temperature male into a hot female spindle and allowing the pair to cool. Avoid by warming the male before insertion or letting the mill cool down. To release a shrink fit it may be necessary to quickly warm the spindle with a gentle flame before applying a sharp tap, or wedges.
  • The tapers corroded together or are glued together by ancient oil turned into varnish. Dribble penetrating oil down the drawbar and leave overnight, if that doesn't work warm the spindle and/or wedge as above. Several heat cycles may be necessary. Avoid by sensible maintenance - don't leave taper tools stuck together for a long time.

In my experience appropriately tightened clean tapers release without bother. The sharp tap needed doesn't worry me: in theory it might damage the bearings, in practice it doesn't. (Pounding on jambed tapers is a different story.)

As per NDIY I use an MT / ER32 collet chuck most of the time on my mill, occasionally swapping it for a fly-cutter, boring head, drill chuck or circular saw. None of them slip or refuse to release and not much violence is needed.

Copper headed hammers are recommended for applying the sharp tap but I use an ordinary hammer with a home-made aluminium disc on a handle interposed to protect the drawbar head.

MT is the original quick release system. It's still popular after well over a century. There are better quick release systems, but I suggest MT is fine for amateur purposes. I don't feel any need to modify it on an 1100W mill.


Chris Mate06/12/2021 16:46:26
83 forum posts
8 photos

Ok, thanks for all the info, I don't want to loose a MT size down, so the above idea not what I want.

So I stick to my original plan of MT4 & ER32 Collets, I will then convert the drill & others to straight shanks with the intention not to have to take out the MT4, only change the ER 32 collets. I will go with the light tention of drawbar and tapping if necessary, I can use and have 2 wedges with the mill. If I have problems with nthe straight shank conversions, its easy go back to MT4.

This mill with the swivel bed, I could only get in MT4 and with a 30L coolant tank, (Thats why I am trying to make the most out of the coolant affair as an experiment), no options here. I see on these smaller mills the manual say R8 or MT4, however even those other mills without swivel bed also has MT4 where I live, I am sure I saw them 3 years back with R8.

Edited By Chris Mate on 06/12/2021 16:47:14

old mart06/12/2021 18:06:40
3524 forum posts
217 photos

Having a MT4 spindle has the advantage of being equivalent to R8 in stiffness, but there is not as much tooling about. The er32 collet set would be very useful and would not need changing often except for drill chucks and shell mills. As I said earlier, there could be a possibility of adding a captive drawbar, some are held at the top of the spindle and others like mine are utilising an internal step in the lower part of the spindle bore just above the upper part of the tooling.

JasonB06/12/2021 18:29:07
22029 forum posts
2540 photos
1 articles

Although the sleeve from ARC will be no good to you NDIY was suggesting threading the body of your existing ER32 holder so an ejector ring can be added, not to use the actual item shown.

I dare say if you don't want to thread the holder a pair of concentric threaded rings could be placed around the body of the ER32 holder and when screwed apart one would bear on the back of the nut, the other on the mill's spindle nose and pop the taper apart without loading the bearings.

old mart06/12/2021 18:40:35
3524 forum posts
217 photos

_igp2476.jpgWith the right lathe and carbide single point threading, the OD of the er32 could be threaded ok, but the extractor would interfere with the spanner flats. Perhaps a sleeve could be fitted to the er holder which had spanner flats at the lower part and threads at the top. It would have to be short enough to leave a gap between it and the spindle nose and be smaller diameter than the nose for a nut to work. Some measuring would be required before any metal was cut.

 This is the way I made a captive drawbar as there was room inside the spindle to do so.




Edited By old mart on 06/12/2021 18:45:00

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