getting MT3 tools to release from the taper on mill spindle

[Neil WyattModerator @neilwyatt]

Posted by Martin Kyte on 23/04/2020 12:21:25:

Posted by mgnbuk on 23/04/2020 07:47:55:

Self ejecting draw bars must also exert a force on the bearing

No. The whole idea of an ejecting drawbar is that it puts not load on the spindle bearings.

Nigel B.

Think about it.

Whilst the taper is still tight the spindle the toolholder/drawbar assembly are essentially one piece locked together by the taper.The spindle is constrained from moving by the lower spindle bearing. Force is applied to the top of the drawbar putting a downwards force on the spindle and taper tooling assembly.As the spindle is constrained the bit that gives is the taper. If no opposing force is applied to the outer part of the spindle, in our case through the lower spindle bearing the taper CANNOT part company with the spindle. Try ejecting a taper with the quill unlocked and all that happens is the spindle is moved downwards. Therefor self ejecting drawbars must also exert a force on the lower spindle bearing albeit in a controlled way.

regards Martin

The QR system I made for my mill has a screw on cap on top of the spindle to take the force and puts no load on the bearings at all. I think most work like this.

Neil

[Martin KyteParticipant @martinkyte99762]

OK, point taken.

regards Martin

[Mike PooleParticipant @mikepoole82104]

Ega’s solution is very elegant and is likely to be suitable for most spindles which are unlikely to be too hard to tap. When I bought a mill I was sure that it would not have a morse taper spindle and went R8, the reason was that I had a Rodney with a 2 morse spindle, by the time I owned this the Myford collets were hard to find and expensive, the finger type morse collets seemed like a solution. I erred on the side of a bit tight with the drawbar and soon found just how reluctant they can be to release if given a bit to much on the drawbar. Although the finger collets also fit my Myford I moved on to an ER chuck which also has the benefit of retaining the through spindle facility although this Is minimal on the small bore Myford. As I still have the Rodney I may try ega’s type of conversion just for fun as now I have a mill it is retired.

Mike

[andrew lynerParticipant @andrewlyner71257]

I don't seem to be able to add a 'Like' to posts on this forum. Am I missing something or is the facility really not there?

[VicParticipant @vic]

There was a thread on at least one forum where a German gentleman has made a self extracting drawbar for his MT3 626 Mill. I happened to use M12 for my drawbar and had a spark plug tap of a different thread I could use to tap the top of the spindle on my Warco VMC so I bought a corresponding die to make a drawbar and it works very well. Quite why companies like Warco don’t ask for this to be included in the specification of the machines they buy is beyond me. Self extracting drawbars have been around it seems for more than a few decades.

I no longer have a link for the relevant thread but if it helps the German 626 mill in question was yellow in colour. Sorry I can’t be more help.

[andrew lynerParticipant @andrewlyner71257]

I thought I'd finish off the story with a successful solution to the sticky MT3 tapers. I made up a pair of opposing wedges to fit round the shaft, between spindle and tool. The combined angle is about 7 degrees . I made up a further U spacer to suit the particular gap with my RM25 collet holder. A gentle tap between two light hammers releases the taper every time with no trauma to any bearings – brilliant. Leaving the drawbar in place avoids the tool falling out

[andrew lynerParticipant @andrewlyner71257]

Incidentally, I heard an opinion that thin paper on a morse taper could improve grip with less tension and make extraction easier.

Anyone else ever heard of that idea/

[Martin KyteParticipant @martinkyte99762]

That sounds absolutely bizarre!

regards Martin

[egaParticipant @ega]

Posted by andrew lyner on 24/11/2021 14:28:22:

Incidentally, I heard an opinion that thin paper on a morse taper could improve grip with less tension and make extraction easier.

Anyone else ever heard of that idea/

It's in one of the recommended books and mainly intended to protect the female taper from less than perfect male tapers.

[Martin KyteParticipant @martinkyte99762]

Well I can understand (maybe) why it may improve badly fitting tapers. But thats not exactly what the original comment suggested. With tapers in good nick I cannot see how it could possibly improve the grip and at the same time make it worse so removal is easier.

regards Martin

[Howard LewisParticipant @howardlewis46836]

Having concerns about what I might be doing to the bearinmg on my RF25 Mill, I made up a simple extractor.

The left hand threaded nut retaining the pulley was removed and a register turned for half its depth.

A piece of 1/4" plate was bored to be snug fit on the register on the nut.

Two holes drilled and tapped, 1/4 BSF symmetrically about the centreline

The nut was replaced on the spindle, trapping the plate beneath it, and tightened..

A matching plate (But with the central hole tapped 1/4 BSF and the outer holes 1/4 clearance ) was made.

Two 1/4 BSF studs with knurled heads were fed through the upper plate, and a long 1/4 BSF setscrew screwed through the centre hole.

To remove a taper from the spindle, the drawbar is slackened by aboutb half turn, and the "lloose" plate secured to the capive one with bthe two knurled mhead studs. The central setscrew is then tightenen onto the drawbar.

Usually this breaks the taper when sufficiently tightened, If not, a light tap with a small mallet does the trick.

Howard

[egaParticipant @ega]

In operation, the taper's main job is to resist rotation; contrariwise, when it comes to removal, axial pressure is normally involved.

[Tony Pratt 1Participant @tonypratt1]

Posted by andrew lyner on 24/11/2021 14:28:22:

Incidentally, I heard an opinion that thin paper on a morse taper could improve grip with less tension and make extraction easier.

Anyone else ever heard of that idea/

Yes one of the many things passed on to me by the old sweats from years ago.

Tony

[SillyOldDufferModerator @sillyoldduffer]

Posted by andrew lyner on 24/11/2021 14:28:22:

Incidentally, I heard an opinion that thin paper on a morse taper could improve grip with less tension and make extraction easier.

Anyone else ever heard of that idea/

Putting paper under a machine vice is recommended sometimes too. Opinion varies. At first I thought 'good idea', now I'm not sure, thinking 'leaves on the line'.

Papering a taper seems an unlikely wheeze to me. As tapers have to fit coaxially together accurately, the paper would have to be carefully cone-shaped and inserted without wrinkling. Possibly a bodge to get some more work out of a damaged taper that ought to be replaced.

Dave

[old martParticipant @oldmart]

If you carefully check the internal dimensions of the spindle relative to the fitted length of the tooling, you may be lucky to find that there is an internal shoulder and space to make a self extracting drawbar. In my drawing, the black part is threaded onto the drawbar and loctited in place. I used it on an R8 spindle, but there is no reason why it would not work on a Morse taper as well. There would need to be at least 2 diameters of thread engaged in the tooling to accept the strain, but even more strain is used when bashing the top of the drawbar anyway. The top end on the drawbar will also need threading and nuts locked in place but no loctite as they will need to be removed easily if required. The drawbar will have to be fitted from the bottom of the spindle. I would like to also modify the drill mill also some day.

[andrew lynerParticipant @andrewlyner71257]

So many ways of killing a cat.

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