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Milling Collet Jammed in Taper

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Martin Dilly 205/03/2019 12:03:37
18 forum posts
3 photos

I have a Hobbymat milling machine with a bit of a problem. After doing some work on a rotary table I now find the milling collet is jammed in the taper. I normally unscrew the drawbar a few turns and give it a slight tap and out it pops. This time nothing happened and when I unscrewed the hex nut on top of the drawbar a bit more the nut came off. I suspect the thread on the nut has stripped to some extent, as when screwing it back on it now just keeps turning.

I thus have only the end of the drawbar to tap. I'm reluctant to use anything harder than my lead hammer, and have left a good squirt of WD-40 in there overnight in the hope that it might seep down and free things up. So far no change.

Any suggestions that don't involve buying a new machine would be most welcome.

John Hinkley05/03/2019 12:10:55
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738 forum posts
245 photos

Have you got a short piece of tubing that will go over the collet and at the same time butt up against the spindle face? If so, lower the spindle/tube combo down until it is supported by the table (maybe introduce a bit of softer plate - brass, or even wood? - to protect the table) and then give the drawbar a smart whack. The tube will hopefully prevent the spindle bearings taking much, if any, of the blow and with luck and a following wind, the collet should pop out!

That's what I would try, first.

John

 

Edited By John Hinkley on 05/03/2019 12:11:45

not done it yet05/03/2019 12:21:12
3163 forum posts
11 photos

Firstly, you will lose a large amount of your impulse if striking on a loose thread.

One suggestion might be to do some side milling without the drawbar being tight. It is there to retain the tool in position, after all. Beware that running with the tool loose in the taper could cause damage, so care is needed if trying this.

One cause of over-tight morse tapers is a mismatch of temperature when fitting. A cold taper tightened into a warm taper can result in an extremely tight 'shrink-fitted' tool.

A heavier mallet is another alternative - probably OK as long as you don't use a steel hammer! Never a steel hammer, ever, for this job.

larry phelan 105/03/2019 12:28:11
458 forum posts
11 photos

Yes,that,s what I would try,and before someone shoots me down,let me say that I tend to use a smart tap with my lump hammer,since I dont have a lead hammer.I find it,s better than fooling around with a too light hammer.

Something I came across last week in Lidl might be of interest to other members with millings machines.

I have a LUX mill,on a stand,which brings the top of the spindle quite difficult to reach for changing drawbars.

Tried standing on a beer crate,not very steady,not high enough,not safe. Came across a small fold up set of steps,well made light to handle rock steady,and all for 16 Euro !

Down side is that if SWMBO see,s them they,re gone !!

Might be worth looking at.

SillyOldDuffer05/03/2019 12:41:04
4536 forum posts
971 photos

Posted by Martin Dilly 2 on 05/03/2019 12:03:37:

...

I'm reluctant to use anything harder than my lead hammer...

Fortune favours the brave! As it's jammed, you're going to have to hit it harder. Position a bit of aluminium plate (2 or 3mm thick) on top of the drawbar to cushion the blow and then hit the drawbar with an ordinary steel hammer. Do it somewhat more energetically than has been tried before.

John's tubing suggestion sounds like a good idea but I suspect the worry about drawbars and bearings is greatly overstated. If you search the literature you find loads of gents fretting about the possibility that they might damage a bearing by hitting the drawbar and none who've actually broken one!

The key is in the 'sharp whack' - breaking the taper's grip is about momentum, not pounding. Ineffectively banging on the drawbar without breaking the taper is likely to hurt the bearings - eventually. My theory is that, normally, most of the energy that might damage a bearing transfers into the ejected tool, but only if the tool comes out. In other words, don't pussy-foot.

Dave

peak405/03/2019 12:44:50
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790 forum posts
67 photos

Is the drawbar a smaller size than the hole up the spout of the collet?

If so, insert a length of threaded rod upwards from the nose end. add a nut and spacers if required to load the threaded rod to pull the collet out as one might extract an old bush from a hole.

You might not extract the collet immediately without stripping the nut, but with a decent amount of pre-load downwards, use your nomal method of tapping the upper end of the collet.

If you can't get a rod upwards to thread into the reverse end of the collet, use thinner threaded rod with a nut on top.

N.B. if possible disengage the downfeed from the quill to save damaging the rack or pinion gear, and ideally support the lower end of the quill on a block of wood to the table to save dining the internal bearings.

Good Luck

Bill

Edited By peak4 on 05/03/2019 12:47:07

Martin Dilly 205/03/2019 14:09:44
18 forum posts
3 photos

Thanks for the input, Bill. I should have mentioned that the cutter is still in the milling collet. As far as I recall each end of the collet is a blind hole anyway. I'll try to get the cutter out anyway; reducing the mass of the whole stuck unit may not be a bad plan anyway, and it'll avoid having to have something soft to catch the thing when/if it eventually comes out.

not done it yet05/03/2019 14:16:39
3163 forum posts
11 photos

Regardless of all the advice of hitting it with a steel hammer, do avoid doing that. using a softer metal between the two contacting surfaces is allowable, but not direct hitting steel on steel as the bearing contact surfaces will indent if the contact is good.

Think here why brass drifts are used to remove items from holes, not steel drifts. steel on steel will indent; brass on steel will deform the brass first. I have a workshop manual from the 1940s, for an engine with roller bearing mains, and it warns against striking the end of the crankshaft (with a steel hammer) to avoid bearing damage. If they were knew back then, it is the correct advise, even now.

Andrew Johnston05/03/2019 14:17:09
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4719 forum posts
532 photos

I normally tap the collet/tool sideways to release it rather than banging on the drawbar. Remember the theory that you shouldn't mill without using a collet drawbar as the sideways vibration loosens the driving taper? It makes sense to reproduce those forces. smile

Andrew

Martin Dilly 205/03/2019 14:18:47
18 forum posts
3 photos

Many thanks, gents, for the replies, and so soon! I'll go and have another try later. Meanwhile a bit of belated Googling suggests that a Y-shaped wedge applied between the business end of the collet chuck and the quill might help to force things apart without applying hammers, lump, lead or otherwise.

Brian Oldford05/03/2019 14:25:08
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533 forum posts
4 photos
Posted by Martin Dilly 2 on 05/03/2019 14:18:47:

Many thanks, gents, for the replies, and so soon! I'll go and have another try later. Meanwhile a bit of belated Googling suggests that a Y-shaped wedge applied between the business end of the collet chuck and the quill might help to force things apart without applying hammers, lump, lead or otherwise.

If you are going to use a "wedge" technique it would be better to use two to form a pair of folding wedges thus eliminating any tendency to bend anything sideways IYKWIM.

Peter Tucker05/03/2019 16:37:47
179 forum posts

Hi Martin,

Make a couple of split wedges to fit between your collet chuck and the end of the spindle, a small tap on the end of the wedge will free your taper.

Peter.

peak405/03/2019 16:47:58
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790 forum posts
67 photos
Posted by Martin Dilly 2 on 05/03/2019 14:09:44:

Thanks for the input, Bill. I should have mentioned that the cutter is still in the milling collet. As far as I recall each end of the collet is a blind hole anyway. I'll try to get the cutter out anyway; reducing the mass of the whole stuck unit may not be a bad plan anyway, and it'll avoid having to have something soft to catch the thing when/if it eventually comes out.

Yes it will be a blind hole. Sorry I read your original post as a collet stuck in the taper as opposed to a collet chuck jammed.

As mentioned elsewhere, try milling something with the drawbar loose ( leaving it in situ, to avoid damage if it does release.)

There are pairs of wedges available for separating chucks from quills or arbors, which aught to do the job.
I'm sure a bit of work on the mill will make a pair for you. On the bright side, you might even release the chuck whilst you're making them. wink

Tim Stevens05/03/2019 18:08:38
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1049 forum posts

There is a hole right through the spindle and I suggest that it is likely that it is the same diameter from the top of the taper upwards. With any luck it is a larger diameter than the small (upper) end of the taper. So, it should be possible to turn a slug of mild steel to that diameter. If the slug is long enough, it could be used to contact the taper and knock it out. A shorter slug could be drilled and tapped for a push-rod (which could be made from the remains of the draw bar).

Before you do this, make a measured sketch of the drawbar dimensions, so you can make up a new one. I have used a plain mild bar of the thread size (often 8mm) with a sleeve towards the top end, held in place with a couple of steel roll-pins - and a square filed carefully on the extreme end. You can't mill the flats if your mill is out of commission - but perhaps you could use the now-stuck cutter for this job, with no drawbar, and see if that helps to loosen things. Worth a try?

Regards, Tim

Neil Wyatt05/03/2019 19:31:11
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Moderator
16277 forum posts
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74 articles

Get some pipe freezing spray or something like 'Shock Unlock' and use a tube to direct a good dose into the drawbar hole of the collet. Leave for a minute or two, repeat, then give a sharp tap with brass drift.

Neil

roy entwistle05/03/2019 19:37:13
1005 forum posts

I would use Plus Gas rather than WD40

Roy

Martin Dilly 205/03/2019 20:33:23
18 forum posts
3 photos

Many thanks again to those who've come up with more possibilities. One difficulty is that the drawbar minus its hex head is jammed in the threaded hole in the top of the collet taper, so the top of that is all I can tap, smite or batter. I suspect its slight flexing when hit may reduce the shock load on the actual collet.

Pete Rimmer05/03/2019 20:41:28
367 forum posts
12 photos

I saw this happen once before to a guy I know. He complained about the same problem and that the nut had come off but the drawbar wouldn't release. Bashed it for a day and a half before he realised there was a second nut on the drawbar which acted as a lock-nut for the longer first one.

He loosened that second nut and the collet popped out.

Howard Lewis06/03/2019 10:47:27
2153 forum posts
2 photos

When I had an open ended MT sleeve jam in the Mill/Drill, there quill was too narrow to admit a drift the contact the back of the sleeve.

I made up a sort of top hat bush, with a thick rim (3mm) the outer edge was tapered, and the bore was tapered (using a centre drill ) and split, four or six times with a hacksaw. The OD of the rim, before splitting was greater than the bore of the sleeve. A tapped plug, with an outer taper to match the top hat taper, was Loctited to a piece of studding, The top hat was fed onto the studding, closely followed by a nut.

A Cup, with recess larger that the outer end of the MT sleeve was made up an fitted over the studding. The studding and split top hat was tapped (pushed ) through the MT sleeve so that the split end popped out of the inner end. The cup was placed over the studding, followed by a plain washer and a nut. Tightening the nut pulled the tapered p[lug into the split top hat and expanded it so that it overlapped the end of the sleeve. Further tightening pulled the sleeve free from the quill. If plain tension does not shift the collet, a slight tap on the end will often jolt things free.

Crude, but it works (repeatedly! )

If the above is not clear, PM me and I'll take a picture of the gadget, and E mail it to you

Howard The one with FAT fingers

Edited By Howard Lewis on 06/03/2019 10:47:55

Edited By Howard Lewis on 06/03/2019 10:48:36

Martin Dilly 206/03/2019 11:06:31
18 forum posts
3 photos

Thanks, Howard. I've just realised that, even if I can dislodge the collet from the taper it will still have the headless drawbar screwed firmly into its top end! Luckily the Hobbymat mill has a head that can be rotated to about 45 degrees, so it ought to be possible to get the whole thing out.

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