[Weekender]

Hi Guys,

My first time on the forum. Hope you can help !
I nearly lost a tool during machining and fortunately stopped the program before any damage ensued.
I think there are some broken washers in the drawbar assembly, so I would like to replace the lot.
I have taken the air cylinder off the top in preparation for replacing the washers and found an allen screw
at the other end deep inside past the gripping fingers. I assume that this screw needs to be loosened
prior to removal of the drawbar assembly, but it just won't move !
Can anyone advise the correct method of removing the drawbar assembly in order to replace the Belleville
Washers ? Your help would be most appreciated.

[emexcee380]

Sounds like you're on the right track.

Not tremendously knowledgeable about Bridgeport/Hardinge VMC's
but most VMC drawbar designs are similar.

At the top of the drawbar is (usually) a preload nut followed by a
certain number of belleville washers stacked in a specific arrangement.
A common number is 128 bellevilles, stacked 4 concave then 4 convex.

At the bottom is a collet of some sort. Sounds like yours is the segmented
or "finger" type. A simpler type uses 6 steel balls to grasp the retention
knob.

If you see what looks like an allen socket looking up thru your spindle taper,
this is the fixing screw. If it won't loosen with the top of the drawbar being
held by a helper, it might be loctited. If so, you'll have to heat it to approx.
500-degrees F. to break the loctite bond. (Let's hope not ! )

Once you loosen and remove the center fixing bolt remove the segmented
collet (often simply held together with a circular spring or oring). Then remove
the drawbar out the spindle taper.

Use a telescoping magnet to begin pulling out the bellevilles from the top
paying attention to the orientation. Even if you find no broken ones, bellevilles
(like) any spring tend to "sack" after x-number of cycles, thus decreasing
the available retention spring force of the drawbar. Go ahead and replace them.

Don't buy OEM - the delivery will suck and the price will suck even more. Just
Google "belleville washers" and buy what you need from a belleville mfg. (just
like the machine tool builder did.)

Hope this helps.

emexcee380

[Weekender]

Thanks heaps emexcee380.
I will persevere with trying to loosen the screw.
Thought crossed my mind. Should I be compressing the washers somehow before
trying to loosen the screw ? Maybe I am fighting the spring pressure of the bellevilles.
What do you think ?

[emexcee380]

Thanks heaps emexcee380.
I will persevere with trying to loosen the screw.
Thought crossed my mind. Should I be compressing the washers somehow before
trying to loosen the screw ? Maybe I am fighting the spring pressure of the bellevilles.
What do you think ?

Weekender,

No, it's not necessary to compress the drawbar to remove the collet fixing screw.
(It's also not necessary to loctite it - but sometimes people / builders do it.)

What is the size of the allen socket fixing the collet to the drawbar? Probably M6
or M8. You might get good results from using an air impact gun with an extension
and correct allen socket. Use at least 100 psi to loosen it. If that doesn't do it - it's
probably (unnecessarily) loctited. Honestly though, in 25+ years of working on
machine tools I've never encountered a collet fixing screw that was loctited or
couldn't be loosened.

Here's another idea. If you can't break the fixing bolt loose, why not remove the
preload nut at the top (note how far it's screwed down / how many threads are
exposed above it for reassembly) and then try to remove the drawbar with the
collet still attached. In actual operation, when the drawbar is compressed to
release the toolholder from the spindle, the collet is pushed downward into a
recess in the spindle that allows it to open. When it's retracted to the CLAMPED
position the collet is pulled upward into a diameter that closes it around the retention
knob. So you might be able, with a helper at the bottom keeping the collet fingers
fairly closed, to pull the the entire drawbar and collet out the bottom.

Do you have a parts manual that shows the drawbar / collet assembly?

Good luck !

emexcee380

[Weekender]

Thanks emexcee380,
I will try the impact driver option first and hopefully that will work !
The Allen key is 6 mm. I will fit a new extended key to get the best fit and give it a go.
I have a parts manual but it shows minimal detail and it is the ball option, not the gripper
option on my machine. Failing loosening the screw, I will see if dropping the assembly
downwards is a viable option.

Thanks again, much appreciated.

[emexcee380]

Thanks emexcee380,
I will try the impact driver option first and hopefully that will work !
The Allen key is 6 mm. I will fit a new extended key to get the best fit and give it a go.
I have a parts manual but it shows minimal detail and it is the ball option, not the gripper
option on my machine. Failing loosening the screw, I will see if dropping the assembly
downwards is a viable option.

Thanks again, much appreciated.

Senor Weekender,

If your collet is a ball-type you can remove the drawbar and collet as one assembly
out the bottom of your spindle.

Position the Z-axis over a wooden block and remove the top preload nut. Tap on the
top of the drawbar with a hammer and a plastic or wooden block to avoid damaging the
threads and drive the drawbar through the stack of bellevilles until it falls out.You might
have to find a long soft (brass) drift to tap the drawbar through the belleville stack. No
need to remove the ball collet. Try to contain and catch the collet balls - probably
5 - 6 six mm steel balls.

Good luck !

emexcee380

[Weekender]

Thanks emexcee380,
Hope to try the Air Impact Driver this week !
Sorry about the confusion, but my machine uses grippers not balls.
The Manual I have shows balls.
I will let you know how I get on.
Cheers.

[emexcee380]

Thanks emexcee380,
Hope to try the Air Impact Driver this week !
Sorry about the confusion, but my machine uses grippers not balls.
The Manual I have shows balls.
I will let you know how I get on.
Cheers.

Weekender,

Even if your drawbar uses a segmented collet instead of balls to grip the
retention knobs you can still probably remove the drawbar and collet out
the bottom of your spindle as an assembly. Though you'll need a helper
to keep the collet as closed as possible as you drive it out with a long,
soft (brass) drift through the belleville washer stack.

It certainly will be easier if you can remove the fixing bolt and collet
segments first however. That's the normal disassembly procedure.

Good luck.

emexcee380

[Guiz912]

Sounds like you're on the right track.

Not tremendously knowledgeable about Bridgeport/Hardinge VMC's
but most VMC drawbar designs are similar.

At the top of the drawbar is (usually) a preload nut followed by a
certain number of belleville washers stacked in a specific arrangement.
A common number is 128 bellevilles, stacked 4 concave then 4 convex.

At the bottom is a collet of some sort. Sounds like yours is the segmented
or "finger" type. A simpler type uses 6 steel balls to grasp the retention
knob.

If you see what looks like an allen socket looking up thru your spindle taper,
this is the fixing screw. If it won't loosen with the top of the drawbar being
held by a helper, it might be loctited. If so, you'll have to heat it to approx.
500-degrees F. to break the loctite bond. (Let's hope not ! )

Once you loosen and remove the center fixing bolt remove the segmented
collet (often simply held together with a circular spring or oring). Then remove
the drawbar out the spindle taper.

Use a telescoping magnet to begin pulling out the bellevilles from the top
paying attention to the orientation. Even if you find no broken ones, bellevilles
(like) any spring tend to "sack" after x-number of cycles, thus decreasing
the available retention spring force of the drawbar. Go ahead and replace them.

Don't buy OEM - the delivery will suck and the price will suck even more. Just
Google "belleville washers" and buy what you need from a belleville mfg. (just
like the machine tool builder did.)

Hope this helps.

emexcee380

Thanks emexcee380,
Hope to try the Air Impact Driver this week !
Sorry about the confusion, but my machine uses grippers not balls.
The Manual I have shows balls.
I will let you know how I get on.
Cheers.

Hello,
I’ve got the same question and same problem right now.
I tried to remove the collet gripper (segmented - not balls) with Allen key 8mm and air impact gun as well but NOTHING is moving.
Machine is a Bridgeport HARDINGE XR1000 .

I’d like to access to drawbar and remove it to replace the disk spring washer (Belleville) as well.


Thanks so much for your help !

[bptcontrols]

Spindle is a precision mechanism with high speed bearings. Do not use hammer on drawbar, you can damage the bearings.

Replacing the belville washer stack is not something to guess about or 'try'. If not done right can damage spindle: eg. tool comes loose it will score spindle tool nose taper. A wrecked spindle will cost over $3k to repair. Number and orientation of washers is critical. Drawbar tension critical. Not enough may not hold tool; or too much and release mechanism may not be able to release tool; incorrect orientation will not allow enough travel for retention knob to fall clear of ball or claw.