getting MT3 tools to release from the taper on mill spindle

[andrew lynerParticipant @andrewlyner71257]

I have searched all over about this and there seems to be not a lot of recent discussion so I thought it could be usefully resurrected.

Sealey mini lathe problem.

Cart before horse, I think the answer is to do up the draw bar only finger-tight. .

But if ever it's stuck it still needs persuading. I felt very guilty, whacking the top of the draw bar with my club hammer so I just made a hammer / drift with 25mm steel rod with a diameter 'head', turned down to a bit under 16mm, so that it just slides down the spindle and taps the top of the taper with a lovely sharp 'crack', compared with the evil thump that the lump hammer applied to the top of the draw bar. I had even distorted the thread but I hope that the bar is of ropier steel than the tools.

I was surprised not to find this method suggested elsewhere and also surprised at the variety of spindle layouts that people described over the years.

[andrew lynerParticipant @andrewlyner71257]

[Nigel Graham 2Participant @nigelgraham2]

Some use wedges between the chuck and spindle-nose, but you have to be very aware of what the wedges are bearing against; and opposing-wedges are better than a single one by not introducing a rather unfair side-load.

I think I have tried using two wedges drawn together by a clamp.

I managed to lose the plain-type drawbar for my Myford VMC mill during a house move, but when measuring and studying the manual so I could make a replacement, discovered I could make an ejecting one. The secret is a collar that engages a diameter step inside the spindle – but this machine also has an R8 taper, much easier to release than Morse, and the draw-bar also prevents the just-released tool from accidental free-fall.

[not done it yetParticipant @notdoneityet]

Mini lathe or mill problem? Title and post are different?

For MT3 get one of these and use MT2 tooling in the sleeve?

https://www.arceurotrade.co.uk/Catalogue/Adaptors-Sleeves/Morse-Taper-Open-Sleeve-with-Release-Nut

The one thing I would not do is use a steel hammer to directly thump a drawbar to release any tool from a taper. Use a soft drift, not steel!

I use wedges to remove MT2 tapers. Lathe uses MT4, so more difficult (always uses a sleeve) but still use a soft mallet, not a steel hammer. Not needed often as generally a centre is needed and that is always cut in the chuck, or an ER collet chuck gets used.

One thing to keep in mind is to avoid fitting a cold taper into a warm socket.

[HopperParticipant @hopper]

I'm still not convinced that whacking a spindle or taper with a copper hammer or brass drift is much easier on the bearings than using a steel hammer and drift. Still jars the heck out of the bearings and puts impact force on the points of the balls or rollers. Self-eject draw bar is the best way if it can be arranged. Not sure one your model mill though?

[not done it yetParticipant @notdoneityet]

Hopper,

I have an engine workshop manual for a 1940s engine with a two bearing crank supported by timken roller bearings. The manual states perfectly clearly not to strike the end of the crankshaft with anything steel, to avoid bearing damage. I think the engineers knew what they were on about, so I follow their recommendations. The manual is for a Wisconsin V4 engine.

For steel-on-steel the impulse force will be much greater but for a shorter time period. Clearly they considered the same force.time product was better if the time was longer for the same energy transfer. I am not prepared to argue with proper engineers.

[AdrianRParticipant @adrianr18614]

If you do need to hit it I think using the smallest hammer possible is best. To shift the taper you are not trying to force the tapper out, you are trying to use a localised shock wave to free the taper.

I keep my tapers and sockets clean and dry. I don't tighten the draw bar, just nip it up. If I have to, I use a 2oz hammer to give a small fast tap.

One day I will make a captive draw bar.

[andrew lynerParticipant @andrewlyner71257]

It's so complicated to predict what happens during a collision. Masses and materials involved plus speeds are all relevant. Years ago I was tapping gently on a shaft and just managed to spread the end with the hammer. (Embarrassing! I had to take it down the road to a man with a fly press) A press / puller is favourite when there's something to supply the 'reaction' force. Not always available at the roadside, though.

At least taking out my draw bar and replacing with the wider rod takes the stress of the threads. I was impressed how small a tap would release the taper. The bar/hammer is about 300g. I could always put a brass end on it if I need to use it often.

I wonder how the pressure from the workpiece compares with the force from a drawbar. It's marginal in the tailstock of the lathe as the taper can slip round if it hasn't settled in convincingly. Some cutting operations don't exert a lot of force into the taper. I will try using minimal effort in tightening the drawbar in future.

[Mike PooleParticipant @mikepoole82104]

I thought the point of copper mallets and soft drifts was to avoid damage to the end of a shaft. Applying a shock with a steel or copper mallet still puts a shock force through a very small point of contact in the case of a ball race. It would be interesting to see what the difference is between a blow from the same weight mallet of different materials.

Mike

[HOWARDTParticipant @howardt]

On my four year old mill 3mt, I have always struck the drawbar with a hammer. Bearings are still original ball races and the spindle still runs the same as new. I am happy to continue doing this as I prefer a tight tool spindle fit. Within reason you cannot hold a tool too tightly, while it can be too loose.

[JasonBModerator @jasonb]

Yes Mike cant see it makes any difference to the bearings if you hit the drawbar or a bit of bar down the end.

Even using a self ejecting drawbar will need to put the same load into the tooling to get it apart maybe even more as you don't get that shock

13yrs of using a copper hammer on my drawbar and it still seems OK.

[Clive FosterParticipant @clivefoster55965]

Its the sharpness of the blow more than the actual force that does the work.

On my Bridgeport I now use a club hammer held right up against the head. A sharp swivel flick of the wrist gives sufficient impact to shift any tooling, including one notoriously tight drill chuck. Using a lighter hammer of dead-blow needs much more belabouring. OK R8 tooling moves easier than MT as its not a self holding taper but the principle still applies.

I wonder if impact stimulated ringing of the drawbar also contributes. Many years ago I had a rotary lawnmower (Acto?) whose official flywheel puller was, from memory, about 6 or inches of inch (ish) diameter steel bar screwed onto the end of the crank after removing the flywheel retainer nut. A bit of upward force on the flywheel with one hand and a moderate rap on the bar with an engineers hammer easily separated flywheel from taper to the accompaniment of a distinct ringing sound. I'd tried a number of ways to remove the flywheel before forking out for the official tool, including a couple of serious pullers, with no success. Sideload vibration is well known for loosening morse tapers so I do wonder if the drawbar could be arranged to produce such effects.

Clive

[Howard LewisParticipant @howardlewis46836]

Presumably, there is no slot in the spindle through which a drift could be inserted.

A captive drawbar removes the need for hammering.

On my old RF25, my solution was to remove the nut retaining the pulley to the spindle, and to turn mack the under side of the nut for approx 3 mm. A piece of plate was then bored to be a good fit over the newly turned aprt of the nut. Two holes drilled and tapped, equidistant about the centre hole. the plate and nut were then refitted to the Mill/Drill . A second plate waqs drilled with two clearance holes, on centre distance to match the two tapped holes, with a central tapped hole.

When it is necessary to remove the tooling, the drawbar is slackened and the second plate clamped to the one under the nut, by two long bolts. A third bolt is screwed into the central tapped hole, and used as forcing screw.

If the taper does not break when the forcing screw is tightened, a very light tap on the forcing screw does the job.

My threads were 1/4 BSF, so a similar fine thread would be the modern equivalent.

HTH

Howard

[not done it yetParticipant @notdoneityet]

For the disbelievers, or those that think they know better than the engineers who made the service manual I referred to earlier, here is the pic of the exact part I made reference to.

 

I will add a pic to my album, showing the crankshaft bearing arrangement for those that still do not think it refers to tapered roller bearings.

Enough evidence or still convinced that a  steel hammer is perfectly OK to be hammering your bearings.  Likely why lots on the forum have had failed bearings in their mills?

Edited By not done it yet on 22/04/2020 14:06:03

[Peter G. ShawParticipant @peterg-shaw75338]

The point is, surely, that any tapping or banging, or whatever onto the end of a collet such as a MT3 collet must produce a shock load onto the bearings regardless of the type of bearing. When all said and done, the collet is wedged into the mandrel, and if you hit the end of the collet in an attempt to remove it, that shock loading that you impart travels through the bar, drawbar or whatever, onto the collet, and thence onto the mandrel which in turn tries to move in the same direction as the original hit. And what stops the mandrel from moving? The bearings which are at the other "side" restrained by the mandrel housing.

This why George McClatchie's idea, and mine, keep the forces within the mandrel. In both instances the drawbar is anchored to, and inside, the mandrel at one end, whilst the other end pushes against the end of the collet which is wedged into the mandrel. Therefore the releasing force is totally held within the mandrel, and not via the bearings.

Peter G. Shaw

[not done it yetParticipant @notdoneityet]

Peter, I agree entirely. But it is clear that roller bearings, with a line contact for each roller is far better than ball bearings which have only point contact only between the races.

Back then, the engineers were clearly fully aware of the damage to the roller bearings that can be caused by thumping with a hard hammer. Presumably a soft hammer is adequately safe with roller bearings (up to a point of course – they do say “tapping” and not downright thumping). I expect any ball bearing will not withstand being hit with any heavy hammer, or even soft mallet, anywhere near as well as the roller type.

[SillyOldDufferModerator @sillyoldduffer]

Since Mr Morse invented his taper in 1864 it's been used on millions of machines. I've come across plenty of concern in the historical press and on the internet that releasing the taper with a blow will damage the bearings, but zero actual examples of bearing damage in normal circumstances.

Machines do get damaged by hammering tapers, but the reports I've seen have always involved jammed tapers, typically after Mr Gorilla has inserted a stone cold tool into a hot machine and then over-tightened the drawbar. (I expect we've all met the chap who can't resist nipping up nuts and bolts by hitting the spanner with a hammer, or even whacking a home-made extender.)

In my experience the drawbar doesn't need to be more than hand-tight plus about one third of a spanner turn. I've not had a taper spin at that tension and they release easily when tapped sharply with an ordinary hammer. I use a soft aluminium cushion as well. A single sharp blow is enough, not heavy. The cushion deforms rather than the drawbar and the aluminium slows down the shock force slightly, which travels down the drawbar and breaks the taper. Breaking the taper absorbs energy that would otherwise enter the bearing, which is why it's important to avoid pounding. On my mill the shock action of a rubber mallet is too slow to break the taper.

Sharp hitting is a useful engineering technique, but only done the right way and in the right circumstances. Like cracking eggs open on the edge of a saucepan it needs a certain amount of practice!

Dave

[not done it yetParticipant @notdoneityet]

SOD,

Your aluminium cushion is clearly not the same as hitting directly with a steel hammer. It is much equivalent to the babbit mallet (not a lightweight springy rubber bouncing/deforming thingy), but not regarded as a hard metal like steel.

The babbit mallet shown in the pic is not exactly small, either! The difference those engineers are making, between hard and soft is that a steel hammer is hard and babbit is soft.

I often use a copper mallet, sometimes an aluminium mallet, but mostly an old woodworking mallet. Never do I use a steel hammer. Never ever. I try to look after my machines as best I can.

Any thing that will deform when hit with a steel punch (not a hardened centre pop!) should suffice and will invariably be better than that steel hammer direct – that many appear to use without any particular regard to the well-being of their expensive machinery.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by not done it yet on 22/04/2020 13:50:03:

.

.

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I wonder what the cost of a babbitt hammer that size would be these days

… and also whether I would have the strength to hold it like that.

MichaelG.

[old martParticipant @oldmart]

What you have to remember is that Morse tapers were used on millions of drilling machines without a drawbar and the spindle had an extraction slot in it to utilise a wedge for extraction. Most of the forces in drilling are axial and if the tapers are clean and fitted properly, they will never give trouble. A drawbar had to be added when the side forces caused by milling caused the tooling to fall out.

I can only repeat what I have said many times before, If you have a choice of MT or R8 when buying a machine, always go for the R8.

[Peter G. ShawParticipant @peterg-shaw75338]

and the spindle had an extraction slot in it to utilise a wedge for extraction.

I've no experience whatsoever of this system other than seeing MT3 collets with a slot in them, presumably to release whatever was held in the collet. But thinking about this, if the spindle, or I presume mandrel, has this slot in it, then doesn't that mean that all the forces are contained within the spindle/mandrel and thus kept away from the bearings?

Peter G. Shaw

Edit.

Actually, I don't think it was a MT3 collet as such I saw, but a MT2 to MT3 sleeve.

Edited By Peter G. Shaw on 22/04/2020 21:33:02

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Peter G. Shaw on 22/04/2020 21:31:35:

[…]

then doesn't that mean that all the forces are contained within the spindle/mandrel and thus kept away from the bearings?

.

Not at all, Peter …. It just means that the bearings are loaded radially instead of axially, when you thump it.

Of course, in the ‘design case’ all that clever stuff with wedges and vectors is going on : But we’re talking about a stuck taper.

MichaelG.

[Mike PooleParticipant @mikepoole82104]

Every bearing manufacturer stress not transmitting force through the balls of a bearing when fitting, this applies to pressing as well as striking. Taper rollers will probably tolerate more abuse than a ball race but is must be a practice to be avoided if possible. Ideally a self ejecting drawbar will not put any force through the bearings. Supporting the spindle so the force of the blow does the work of driving out the taper tool rather than impacting the bearings. If a taper is stuck hard then a support block to the table could be very helpful at directing the force to the taper rather than bouncing the spindle in its bearings. I found many years ago that a solid block to the ground under a steering arm greatly assists in breaking the taper of the ball joint.

Mike

[andrew lynerParticipant @andrewlyner71257]

So, basically we're saying that tools with an MT3 taper should be provided with a U shaped 'puller / pusher' which pushes the back end of the taper and pulls back the front of the spindle, thus avoiding any forces against the bearings. Sort of thing a chap could probably knock up with some beefy angle iron and a bit of imagination.

Sticking Taper could happen through bad luck and a small amount of corrosion (nervous sweat?) so you'd better get to it fellas.

[Martin KyteParticipant @martinkyte99762]

Is the impact on the bearing to an extent at least, self limiting?.

My thinking is this

Sufficient force has to be generated to overcome the 'stic-tion' of the taper which is resisted by a reaction force on the one of spindle bearing. As soon as the taper 'lets go this force dissapears and any residual impact, presumably stored in the elesticity of the draw bar merely serves to accelerate the taper tool plus drawbar. Further more the bearing affected is the opposing bearing to that which takes drilling forces and probably much of the milling thrust too.

Self ejecting draw bars must also exert a force on the bearing which OK would rise to a max at the point of the taper coming free so should be therefor the minimum required. I'm not convinced that the forces generated by a sharp tap on a drawbar which is nipped up only with sufficient force to seat the taper is much greater.

Someone must have done a proper analysis on this at some point in the past. I'm not sufficiently versed in stress analysis to comment further. I'd be interested in comments from more qualified members, I am afetr all merely thinking aloud.

regards Martin

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