Frozen Morse Taper Arbor

I have a BF 25 milling machine (sold by various retailers, mine is from HBM machines) which has a collet chuck with an MT3 arbor and a drill chuck also with MT3 arbor. Both arbors are threaded for the drawbar.

I have used both in the past and for the last 8 months the collet chuck has been in there; I went to change it for the drill chuck and the arbor would not budge. First I went through the usual method by just releasing the upper collar at the top of the drawbar and then unscrewing the drawbar - this merely resulted in the drawbar refusing to turn undone as soon as it reached the top of the collar (that should exert a downwards pressure on the arbor to release it).

After trying this several times I tried using a copper-head hammer to hit the top of the drawbar, hoping to release it by this more violent manner. I then chose to use a wedge in the slot in the axis just above the arbor - this had absolutely no effect either.

I have then used a jet of hot air to heat up the outer Morse taper shank, hoping that would expand the holder and release the arbor inside it, but that was also without any result. Nothing moves that arbor whatsoever.

I have read of people using a flame to heat up the holder but I am wary of what that might do to the bearings above the arbor holder...

Has anyone similar experiences, or does someone have a better idea of how to release this arbor? I'm thinking that it might have become cold-welded to the holder?

side mill a bit of scrap with the drawbar loose and nothing under the nose

Unless it's welded in, it should drop out

edit: and make sure the "drop" distance under the nose is only about 1mm

Edited By Ady1 on 30/05/2023 10:24:31

Thanks, I will try that later this morning - thought the last work I did was 'side milling' some 3 weeks ago, but of course with the drawbar in as it should be!

Hello Trevor,

Sorry to hear of your difficulty. I don't know the mill but I assume it is a vertical, not horizontal. If you have a lathe as well you might try to make a jack to force the collet chuck to release, I don't think it will have cold welded into place.

Unscrew the closing nut for the collet chuck and put a close fitting 8 mm plate behind it having two threaded holes for jacking screws to bear on a solid part of the machine somewhere behind the chuck. Refit the chuck closing nut to grip the plate and use the two screws to apply load to the plate.

Add heat with a hot air gun as you have done previously above the chuck and belt the drawbar end to apply shock from time to time. Leave it a while, add turns equally to the jacking screws and leave a thick rag below it to protect the table while you go off to have a cup of tea. It will come out I promise!

Moral. Don't leave assembled with the drawbar pulled up tight after use, take time to strip down and put things away in future.

Regards Brian

+1 on Brian's suggestions. Rather amazing that leaving a taper under tension like that for some hours, or even overnight, can often work wonders. I guess it is the reverse process of leaving it under drawbar tension for extended periods that created the bond in the first place. A bit impact added to the mix as suggested can often be the final straw that breaks it loose too.

Hi Trevor, please be wary of using a hammer to assist with taper removal it may damage the bearings ! Remember these are small machines and not to industrial spec, it is common practice to use this method in industry but these machines are fitted with different tapers that break much easier and of course the bearings are far more robust.

There was an extensive post on groups.io relating to this problem and after much perseverance the problem was solved -- a load read but lots of ideas https://groups.io/g/emcoV10lathe/topic/94147274#22906

John

From the most recent thread, on this topic, that I posted on:

I use couple of wedges, one from each side, to loosen the MT, if a light tap (with a white- or yellow-metal mallet) does not free it off. Wedges are strung together to prevent droppage and it only needs the drawbar to be loosened, so the cutter and holder cannot drop out completely until under-control removal.

Has worked, for me, on every occasion. I have a couple of pairs, in two thicknesses, which have covered all my requirements. There used to be MT3 tapers with threaded collars - these collars were tightened against the end of the socket to perform easy removal. Arceurotrade used to stock them but not sure if they do now.

When fitting tapers, make sure they do not get ‘shrink-fitted’ together. Ensuring the male taper is warmer than the socket, or at the same temperature, will avoid this (common?) problem. That is along with not over-tightening the drawbar. Morse tapers generally do not slip under axial load (no drawbar needed for drilling operations).

Patience and persistence.

5 tactics available:

• Tapping the drawbar sharply with a hammer applies a peak shock pressure to the joint that's likely to unlock it. When the taper is normally tight, tapping the drawbar with a hammer is unlikely to damage the bearings. Folk worry it might, but I've never seen a report of actual damage, and the method has been in use for about 160 years. I think most of the shock energy in the blow is absorbed by releasing the taper, and has little impact on the bearings. Pounding on a jambed taper is ill-advised!
• Soaking in penetrating oil. This helps if the cause is corrosion or gummed up oil sticking the taper together.
• Heat is effective against corrosion, gummed up oil, and a tightly wedged taper. It works by expanding the metal on the outside of the joint faster than the inside. Simply blasting the whole lot with a torch and keeping it hot is more stressful than quickly heating the outer to sizzling hot (a little above 100°C) and then letting the whole thing cool down for an hour, less if cooling is available, repeat several times. Each hot/cold cycle moves the joint slightly and it will eventually give. You might speed the process by giving the slightly loosened drawbar a couple of sharp taps with a hammer immediately after the torch is switched off. Heat and shock together,
• Wedging applies a steady pressure which is kind to the bearings but has little shock effect. I use two slotted wedges sliding over each other from opposite sides to release drill chucks. One wedge is supported with a lump hammer whilst the other is banged home with a small one.
• Ady's sideways cutting method has worked well for me. Set the mill up to take a heavyish interrupted cut into some awkward scrap. Undo the drawbar. Side-cutting with more than normal vibration and chatter is good at undoing taper joints.

In the absence of corrosion or gummed/caramelised oil, the most likely cause of a serious jamb is putting a cold taper into a hot socket and then over-tightening the drawbar. When the hot socket cools, the resulting shrink fit is super-tight, even after the drawbar is undone. Even worse when in place long enough for a little corrosion to take place as well. Or for the oil to gum up. (3 in 1 isn't a good choice on tapers..)

Dave

Edited By SillyOldDuffer on 30/05/2023 12:37:36

Edited By SillyOldDuffer on 30/05/2023 12:38:42

When I had an Open End Morse Taper Sleeve stick min my RF 25, I made up the fittings shown on page 2 of my Albums.   28 /11/2018 .

The thread and shop made nut (Overlength to increase thread engagement ) was 1/4 BSF, but any fine thread

(5//16 BSF,, 1/4 or 5/16 UNF , or M6 ) should do.

(ME 40 threads may be a lttlke too shallow to withstand the forces involved, and are not available as studdinbg A F IK  )

Howard

Edited By Howard Lewis on 30/05/2023 12:44:25

Thanks for all of the (very rapid) responses to my question!

Just to be clear, I have not used a 'normal' hammer on the drawbar to attempt release, I used a copper-head hammer ("lump hammer" - to avoid any sharp-blow damage to the top of the drawbar.

I have also tried using some penetrating oil above the arbor (in the slot) to no avail.

The arbor in question is not old, nor was it corroded and there was no swarf or any particulate matter when I last fitted it - as a habit I always ensure both parts of a taper is clean whether it be on my Myford lathe or the milling machine. When I am fitting these arbors it is never immediately after heavy work and there's no question of major temperature differences.

I'm lucky in that my workshop is in a double-insulated-walled building behind my house and is connected to the central heating system since I built a conservatory coupling it to the house.

I'll take on the advice given and try in half an hour or so - and report the findings!!!

Okay... Well I have in the meantime performed further actions on this "immovable" arbor... just for reference the machine is viewable (in English) at <**LINK**> though bought it from the Dutch agent and I also have the table power feed attached on the left hand side of the table.

(a) I took a substantial piece of scrap steel, mounted in the table vice, put a 12mm side mill bit in the collet chuck and proceeded (without the drawbar inserted!) to mill the side of this scrap. I used manual feed, not the powered table feed that I also have on the machine. I moved the workpiece at different rates - purposely causing a great deal of vibration, far more than one would ever allow during 'normal' use. The result? A great deal of swarf (!) but a very good cut apart from the roughness from vibrations caused by all the "bad" operator's feed technique! The arbor did not become loose at all, but the milling cutter did get a couple of its teeth damaged in the operation (that doesn't worry me, it's the machine I am concerned with, not the loss of a cutter).

(b) I took a steel rod, identical in diameter to that of the drawbar, and inserted it such that it met the top of the arbor (I did not want to risk damaging the thread of the drawbar), and gave it several hammer blows. Nothing shifted at all.

(c) I allowed things to settle (i.e. I went for a cup of tea and a quick puff of my pipe) and returned to the workshop and took a can of "Freeze-It" which I often use during fault-finding on electronic circuit boards (that's my profession, electronics design, and also the 'other' hobby I have) and used that to cool off the arbor to the extent that it was around zero degrees C. I then again used the steel rod inserted above the arbor and gave several hammer blows, and once again nothing shifted at all.

I have now rotated the milling head (it is a vertical mill but can be rotated) so that it is in a horizontal position to perhaps gain a further insight into what the problem might be. I have now decided to take a rest (and returned to this desktop computer to write the above!) - I feel that I must be missing something fundamental.

It sounds like you have the best-possible fit of male and female tapers

… Noting, of course, that Morse taper is designated ‘self holding’

I can only suggest that a much bigger temperature differential is required

Warm the outside as much as you dare, then apply liquid nitrogen to the male [collet chuck] and act swiftly with that hammer.

MichaelG.

Edited By Michael Gilligan on 30/05/2023 16:07:23

Hi Trevor, it might sound a bit counter intuitive, but if you could heat just the arbore instead of cooling it, and then allowing it to cool down, even if you do it a couple or more times, it might give you a chance. The idea of heating it, is it will have to expand, but of course the spindle wont allow it to expand its diameter, so its length will increase. However when it cools, both its length and diameter will contract, and repeating the cycle may just make it contract enough to come out. The expansion and contraction will only be very small, so it shouldn't distort the arbore by any significant amount.

Regards Nick.

Rather than heat anything where the bearing temperature is the limitation, a running bearing shouldn't go much above 60 deg C, try applying a cooling liquid up into the bore of the holder, something like a pipe freezer liquid. The severe alternative would be to lower the head so the spindle itself is resting on metal, put as large a diameter bar into the spindle from the top and hit it with a solid hammer, don't pussy foot with a lead hammer you need a good sudden impact blow to break the taper.

Yours sound pretty bad, all my jammed stuff dropped out

Brian mentioned a constant pressure system, like with a ball joint breaker you crank up the pressure and walk away letting nature take its course

Unscrew the closing nut for the collet chuck and put a close fitting 8 mm plate behind it having two threaded holes for jacking screws to bear on a solid part of the machine somewhere behind the chuck. Refit the chuck closing nut to grip the plate and use the two screws to apply load to the plate.

That would be my next route, use decent gear like high tensile hex bolts so you can really crank up the pressure

Can be used in tandem with the temperature route and a few hammer blows

You're going to be the forum master morse taper unjammer when you get this sorted, ugh

Isn't hitting the draw bar top etc going to ruin the bearings, unless the spindle bottom is carefully supported?

Tony

As I say, again and again, if you have a choice between MT3 and R8, always choose the R8. Morse taper was designed for drills and works very well with them, not mills. Ignor the Morse taper fans, they are wrong, these stuck MT threads are a perennial feature of the forum. Just check out the number of stuck R8 threads.

Edited By old mart on 30/05/2023 16:50:13

My old Emco miller gets collet and drill chucks stuck quite often, I use a thin rod that fits inside the internal drawbar thread on my machine, then tapping it with a hammer cannot damage the thread as possibly would hitting the drawbar directly

For future reference, NEVER put na cild taper into a warm sicket.

Stating bthe obvious, the socket will cool and shrink onto mthe male mtaper.

Again obvious, but Morse tapers, being self gripping,  do not need the draw bar to be particularlybtight.

Willthe tapers not break when the tapered drift is hammered through the slot in the quill, when it has been heated?

What I did not say about my extractor for open end sleeves, is that the intermediate nut is there to allow the split "top Hat" piece can be hammered (lightly) through the small end of the taper, to be expanded to grip the sleeve when the small taper on the stud is pulled into the centre drilling in nthe split "top hat".

If the taper won't brteak loose when the long nut is really tight, a sharp tap with a mallet will often do the job..

Howard

Edited By Howard Lewis on 30/05/2023 16:56:36

As Michael said, you may have the perfect fit, even if you dont want it !

You are not alone, I had a somewhat similar experience some years ago with a tapping unit which fitted into my milling machine spindle, using a morse taper sleeve.

Problem was, it fitted too well to the sleeve ! Got the unit free of the spindle OK, but no way could I remove the sleeve, which I needed for another job. Tried everything I could think of, and in the end the only way that worked was to make up a holder to support it and use a flypress to press it out. Lucky enough the sleeve was open end.

No use to you I know, but these things can really bond to each other