The question about drawbar for milling machine.

To minimise loading the bearings, make an extractor for the Drawbar.

My method was to remove the pulley retaining nut, (On the RF25 Mill/Drill, it is a Left Hand Thread) and turn back the hexagon for a length of 3mm. I then made up a 3mm plate with a central hole that was a running fit on the new plain diameter of the nut, and with two symetrically placed tappings, towards the outer edge. Then made up a similar plate, but with with two clearance holes to match the tappings in the first plate, but with a central tapping. (Threads were 1/4 BSF in my case, but M6 nowadays, I would expect).

Dimensions are not critical, as long as the captive plate provides a large enough area bearing on the underside of the nut, but do not take too much off outside the thread. Midway between the hexagon and the thread O D should be O K.

Place the plate with the large hole over the shaft, and refit the nut with the plain diameter locating in the hole in the plate, and tighten the nut to retain the pulley.

When you want to release the Morse (or other) taper, Slacken the Drawbar by about half a turn. Secure the other plate with two setscrews (With nuts below the upper plate to make the setscrews captive) through the clearance holes into the tappings on the captive plate, (equally), and run a setscrew through the central tapping, and tighten it to apply load to the Drawbar. This should break the taper, without loading the bearings. It it doesn't, an additional light tap with a mallet should produce the desired result.

If 0.5D thread engagement for M6 worries you, either weld nuts below the plate, or if a glutton for punishment, use loose full nuts below the plate instead of tappings.

Once the taper is released remove the two outer setscrews and the upper plate, and put aside, ready for use, next time.

Howard

Having looked at the various suggestions for releasing the taper/drawbar without resorting to use of a soft hammer - and failing to work out how some of them work - my fault with my limited appreciation of terms used in metalworking - I wondered whether a simple swing bridge above the drawbar that is bolted to the spindle housing would suffice. The diagram illustrates, in principle if not in practice, what I mean. I haven't made it yet - as forum members may have suggestions for either saying it won't work or improving it. The gap between the drawbar (in red) and the bridge is sufficiently small so that unscrewing the drawbar forces it against the bridge and, by reaction, releases the taper spindle. The slotted bridge allows the bridge to be swung completely out of the way for either withdrawing the drawbar or maintenance/changing of the belt drive.

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

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.

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

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, 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

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

Neil

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.

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

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

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

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.

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

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,

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

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

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.