The question about drawbar for milling machine.

[Colin LLoydParticipant @colinlloyd53450]

Posted by DMB on 27/12/2017 15:57:05:

Colin Lloyd,

Hi,

Go to –

mikesworkshop.weebly.com

Mill mods and Tooling

23 Captive Drawbar

I think this is the simplest, neatest design yet for what you want

John

Edited By DMB on 27/12/2017 15:57:44

Edited By DMB on 27/12/2017 15:58:17

Thanks John – and yes it seems to be a neat solution – if I could only work out how it actually works. Despite the text explanation, I can't understand what the drawbar is pushing against – and without knowing this I cannot make a bespoke version to fit my particular milling machine drawbar – whereas I unsderstand fully my swing bridge design. Perhaps a cross section of mikesworkshop version would help to explain the principle. In the meantime, I will try and draw a cross-section of mike's and see if that helps me.

Colinj

[JasonBModerator @jasonb]

The one on Mikes site has a flange on the drawbar the pushes against the underside of that "cap" as the bottom of the cap is fixed to the spindle the drawdar pushes downwards when undone so releasing the taper. The advantage of this over your sis that as hhe drawbar is undone and starts to bear against your flat par it will push the quill down so you will only get it to release when the quill is locked, not really an issue but just one more thing to do each time.

If you imagine the underside of mikes "cap" is the underside of your swinging bar then they work in the same way.

[Neil WyattModerator @neilwyatt]

My approach was a 'collar' on that drawbar that tightens against the top of the spindle to lock and when wound up presses underneath a semi-permanent cap on the top of the spindle to unlock. The cap has a hole for the end of the drawbar and the arrangement makes the drawbar captive.

Neil

[Colin LLoydParticipant @colinlloyd53450]

Posted by JasonB on 27/12/2017 16:32:30:

The one on Mikes site has a flange on the drawbar the pushes against the underside of that "cap" as the bottom of the cap is fixed to the spindle the drawdar pushes downwards when undone so releasing the taper. The advantage of this over your sis that as hhe drawbar is undone and starts to bear against your flat par it will push the quill down so you will only get it to release when the quill is locked, not really an issue but just one more thing to do each time.

If you imagine the underside of mikes "cap" is the underside of your swinging bar then they work in the same way.

Thanks Jason for the explanation – it helped. But I don't think this will work on my particular Amadeal XJ16-300 mill which doesn't have the necessary spindle protuberance above the spindle locking nut to allow mike's cap to work. As you can see from the diagram below – the spindle locking nut is virtually a flush fit on the spindlewith no opportunity to drill the cross spindle holes. So I think my only choice is to go with some form of over-the-top bridge setup.

Colin

[JasonBModerator @jasonb]

Colin, is the top of your drawbar hexagonal for a spanner or does it have a hex recess for a key? If hex for a spanner how long is the hex section?

Edited By JasonB on 27/12/2017 17:31:11

[Neil WyattModerator @neilwyatt]

Posted by Colin LLoyd on 27/12/2017 17:10:47:

Posted by JasonB on 27/12/2017 16:32:30:

The one on Mikes site has a flange on the drawbar the pushes against the underside of that "cap" as the bottom of the cap is fixed to the spindle the drawdar pushes downwards when undone so releasing the taper. The advantage of this over your sis that as hhe drawbar is undone and starts to bear against your flat par it will push the quill down so you will only get it to release when the quill is locked, not really an issue but just one more thing to do each time.

If you imagine the underside of mikes "cap" is the underside of your swinging bar then they work in the same way.

Thanks Jason for the explanation – it helped. But I don't think this will work on my particular Amadeal XJ16-300 mill which doesn't have the necessary spindle protuberance above the spindle locking nut to allow mike's cap to work. As you can see from the diagram below – the spindle locking nut is virtually a flush fit on the spindlewith no opportunity to drill the cross spindle holes. So I think my only choice is to go with some form of over-the-top bridge setup.

Colin

Colin, you can do what I did and thin the locknut down by a few threads.

Neil

[I.M. OUTAHEREParticipant @i-m-outahere]

I think Jens Eirik has the same issue i have with my HM 46 ( RF46 ) in that the splined shaft dissapears down inside the spindle as the quill is lowered meaning it can't have a permanently fitted captive nut system .

I was thinking of cutting a thread on the outside of the spline then making a cam/ lever operated device that would screw onto the threaded spline after the drawbar had been loosened and by pulling on the lever it would use a cam action to push on the end of the drawbar .

Probably end up being a pia if a lot of tool changes were needed.

I did have another design in the back of my head that would lock into a groove cut into the spline and grip like a pair of pliers and use either a cam action or a captive socket wrench design that uses the drawbar thead to push the MT free but i still haven't thought it out enough to ensure it would work .

Ian.

[Colin LLoydParticipant @colinlloyd53450]

Posted by JasonB on 27/12/2017 17:29:46:

Colin, is the top of your drawbar hexagonal for a spanner or does it have a hex recess for a key? If hex for a spanner how long is the hex section?

Edited By JasonB on 27/12/2017 17:31:11

Hi Jason, my drawbar top has a square section for spanner (10mm each side) and 12mm deep.

[Clive FosterParticipant @clivefoster55965]

Simplest answer is to put a socket adapter in your battery impact driver or hammer drill and use that to undo the drawbar. About three rattles and its off.

Given that the cumulative number of times Bridgeport (let alone other makes) drawbars have been bashed by uncaring, club hammer welding, piecework motivated, gorrillaiods over the years with no discernible statistical effect on spindle bearing life must be way beyond convenient, or even inconvenient, counting the whole thing is something of a non issue.

Clive.

Edited By Clive Foster on 27/12/2017 18:42:45

[VicParticipant @vic]

I made a a self extracting drawbar for my VMC mill. It works on the differential thread principle? The draw bar is threaded M12 x 1.75 for tooling and I tapped the top of the quill M14 x 1 I think. I’ll try and find a link for the guy who came up with the idea. I used a spark plug tap to tap the quill.

Edited By Vic on 27/12/2017 18:59:08

[VicParticipant @vic]

Here it is.

**LINK**

It’s Ralph’s post at the bottom of the page with pictures.

Correction on my earlier post, I think the M14 spark plug tap is x 1.25. In any case it works ok and I found a matching die easy to find.

This idea should work on any 626 style mill and may work on some similar mills.

[John McNamaraParticipant @johnmcnamara74883]

One hardware free solution to tightly stuck tapers is to reprogram your biocomputer, the one that sits above your shoulders to instruct your arm servo to use less force on the spanner!

If the taper will not release with a light tap of the lead hammer you over tightened.

Regards
John

[MuzzerParticipant @muzzer]

Posted by Clive Foster on 27/12/2017 18:35:55:

Given that the cumulative number of times Bridgeport (let alone other makes) drawbars have been bashed by uncaring, club hammer welding, piecework motivated, gorrillaiods over the years with no discernible statistical effect on spindle bearing life must be way beyond convenient, or even inconvenient, counting the whole thing is something of a non issue.

Bridgeports are almost exclusively either R8 or 30/40 taper, so don't require any great effort to be knocked out. Simply loosening the drawbar does most of the work.

As John Mc suggests, consistently getting a Morse taper stuck means you are over tightening. If the taper and socket are clean, knick-free and lubricated, you shouldn't need much more than a smart tap with a brass hammer to release it.

Murray

[DMBParticipant @dmb]

Colin,

I agree with John Mc, Muzzer, that a Morse taper should only need light push to engage as MTs are self-gripping, unlike R8 etc and should only need light tap on top of drawbar to release. What no one has said is that the collar prevents the drawbar from axial movement, in this case, rising up as it unscrews from the back end of the MT. As it can only rotate and not travel axially, it still unscrews and forces the MT down and therefore breaks the grip of the taper, so the chuck drops out of the bottom of the spindle.

I made a drawbar with same thread each end and put an ordinary hexagon nut on the top end, screwed down to a certain depth and fixed with a cross pin to stop it moving. This formed the " collar". I then made a top hat shaped cap with a hole in the top to fit over the drawbar. The inside was bored out to fit over the top of the spindle and locked to the spindle with radial grubscrews. Not very effective so I will soon be copying the mikesworkshop idea as he cross drilled the spindle, giving positive locking of the top cap. The 2 pins also better for hand release rather than keep using spanners on hexs.

Hope this helps

John

[mahgniaParticipant @mahgnia]

This is how I did this on my X2:

**LINK**

It uses differential thread principle (LH v RH)

Andrew

Edited By mahgnia on 28/12/2017 00:44:06

[thaiguzziParticipant @thaiguzzi]

Yep.

Beaver in my UK workshop with a 30 INT taper running in a professional enviroment, Tom Senior now with a 2MT taper running in a hobby enviroment, always used a brass hammer, never had a problem with removal or bearings going kaput.

I really don't know what the fuss is all about.

Posted by Muzzer on 27/12/2017 22:13:48:

Posted by Clive Foster on 27/12/2017 18:35:55:

Given that the cumulative number of times Bridgeport (let alone other makes) drawbars have been bashed by uncaring, club hammer welding, piecework motivated, gorrillaiods over the years with no discernible statistical effect on spindle bearing life must be way beyond convenient, or even inconvenient, counting the whole thing is something of a non issue.

Bridgeports are almost exclusively either R8 or 30/40 taper, so don't require any great effort to be knocked out. Simply loosening the drawbar does most of the work.

As John Mc suggests, consistently getting a Morse taper stuck means you are over tightening. If the taper and socket are clean, knick-free and lubricated, you shouldn't need much more than a smart tap with a brass hammer to release it.

Murray

[Colin LLoydParticipant @colinlloyd53450]

To all the forum members who imply that you shouldn't over-tighten the drawbar – I agree (and I don't over-tighten) – but that was not my point. I just don't like giving anything a mild tap with a (in my case copper) hammer when a less neanderthal method can be applied. I am dealing with small lightweight lathe and milling machines with appropriate small and lightweight bearings but with the same frictional forces applying to the tapers as for hulking great brute machines. It seems to make sense, if it can be achieved, to apply some model engineering finesse to the procedure.

Colin

[JasonBModerator @jasonb]

I did mention it in a thread a few months back, you still need to apply the same force to the end of the tool to break the taper, just depends on whether you want to apply it slowly or in one quick burst. machine size does not really come into it, as small taper spindle will have less friction and less bearing surface than a large machine with a bigger MT and bigger bearings.

This is why the designs that bear against the moving quill are better than one on the outer casing of the machihe as there is no force against the bearings, your swing out bar will still be pushing down on the spindle bearings.

J

[John HaineParticipant @johnhaine32865]

I would really like to know how the percussive force of tapping the top of the drawbar with a hammer compares with the forces exerted by applying a heavyish cut.

[Colin LLoydParticipant @colinlloyd53450]

Posted by JasonB on 28/12/2017 13:20:49:

I did mention it in a thread a few months back, you still need to apply the same force to the end of the tool to break the taper, just depends on whether you want to apply it slowly or in one quick burst. machine size does not really come into it, as small taper spindle will have less friction and less bearing surface than a large machine with a bigger MT and bigger bearings.

This is why the designs that bear against the moving quill are better than one on the outer casing of the machihe as there is no force against the bearings, your swing out bar will still be pushing down on the spindle bearings.

J

I'm no automotive engineer, but I know that items on my car fail quicker from percussive potholes than from prolonged steady oscillation on motorways. But the point about the moving quill is well taken – just that, in my case, it looks more trouble than it is worth to create such a solution.

[Tim StevensParticipant @timstevens64731]

A comparison of 'percussive force' from tapping a drawbar and 'forces' from a heavyish cut is not easy. In fact the two are different things, measured in different ways. The force bit is easier – we are all familiar with forces of gravity, Pounds force, Kilograms force, and Newtons (as well as various easily forgotten stuff from the sixties and seventies). Force is a vector quantity, and so it involves the direction of the load as well as the load in Newtons etc, so in full, the force exerted on a tool requires a knowledge of the load on it, and the direction of the load (and both will vary as a cut is taken, of course).

Percussive force is not the same sort of thing, it involves time as well as force. Hit with a copper hammer and it distorts as it hits the surface, spreading the impact out over time. Hit with a hard steel hammer, of the same mass and at the same speed, and there is much less distortion, and the load is applied more quickly, so it has more effect in separating the parts. Unfortunately it also has more effect in damaging the bearings etc. So, my point is that a comparison of the amount of steady force, with the amount of force in an instant, is not possible. Rather like not being able to compare speed with acceleration, I suppose.

Of course, some machining operations, especially interrupted cuts, do involve the sudden application of force, and this too could be described as 'percussive force', (and they are what causes tooling to chip), but this only occurs at the commencement of cutting for a very short time, not continuously.

Now I have read this through, it could be explained better, – I just hope it helps someone. Perhaps it might help them to explain it better, too?

Cheers, Tim

[Howard LewisParticipant @howardlewis46836]

Many years ago, my physics master taught me that a suddenly applied force produced twice the force of a gradually applied one. he illustrated this by drawing graphs of force vs time.

The gradually applied force resulted in a triangular diagram, whereas the suddenly applied force showed a rectangle, of double the area.

Reverting to my earlier post about my method of breaking the taper, as with any puller of this type, if tightening gradually does not break the taper, a shock to the already tightened puller, almost always produces the desired result.

The exception seemed to be removing the rear brake drums on 1940s/50s Vauxhall cars (probably true for any semi floating axle). A blowlamp applied to the drum then did the trick!

I am not advocating doing the same to your milling machine, even with a heat gun!

Howard

Edited By Howard Lewis on 29/12/2017 12:05:40

[BC ProfParticipant @bcprof]

Please don't confuse the Impulse of a force F x t ( the are under the Foce against time graph ) with the applied force.. If the same mass masses of copper and steel hit an object with the same velocity the force exerted on the object will be less because of the distortion of the copper and hence the increased time in contact ( the rate of change of momentum will be less in the case of the copper )

The problem with the ' it it wiv in ammer ' approach is the difficulty of applying just enough force to release the taper and no more .

Brian

[VicParticipant @vic]

Cackhandedness and machine tool ownership don’t go well together. When I was a young lad they never let any students on their summer break anywhere near machinery. Only trained youngsters were allowed.

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