Tool Holder Falls from the Spindle!

[cngbrick]

Thank you, I will complete the steps. Have to get a correct size nut first, however.

One question, what do you mean by thrust bushing?

The thrust bushing is what you refer to as the "circular object" in your first picture.

 

[AndrewZ]

The thrust bushing is what you refer to as the "circular object" in your first picture.

Right, the thrust bushing won't indeed even come out of the draw bar. Although I haven't tried applying considerable force.

It will take until tomorrow to get the measurement.

 

[cngbrick]

You don't need to remove it, push it up against the drawbar head and measure from there to place your mark on the shaft. Normally the collets will screw in past the mark, if not, the drawbar is too long or the thread pitch has stretched at that point (or the thread is otherwise bad).

 

[CarbideBob]

Is this your basic air impact up top on a R8?

 

[AndrewZ]

Is this your basic air impact up top on a R8?

Probably... Here is a picture. The compressed air comes through three cables on top of the drawbar.

One more observation. The spindle also made a high pitched ringing sound when the RPM was high. Not sure if this is in any way important.

 

[cngbrick]

Is the ringing a new symptom? Have you run it before at high speed without ringing? Did the ringing only occur when the collets became loose?

More items to check: is the pneumatic drawbar motor axis centered over the spindle axis? Is the pneumatic motor releasing the drawbar properly before the spindle is turned on? If the drawbar motor hasn't properly released due to binding and the spindle starts before coming down in Z then that could loosen the drawbar. Check the drawbar socket for any burrs that might catch on the drawbar as well.

 

[AndrewZ]

Is the ringing a new symptom? Have you run it before at high speed without ringing? Did the ringing only occur when the collets became loose?

More items to check: is the pneumatic drawbar motor axis centered over the spindle axis? Is the pneumatic motor releasing the drawbar properly before the spindle is turned on? If the drawbar motor hasn't properly released due to binding and the spindle starts before coming down in Z then that could loosen the drawbar. Check the drawbar socket for any burrs that might catch on the drawbar as well.

I haven't heard anyone complain about ringing, but the machine has been used rarely over the past few years. The ringing occurred when the collet was at least seemingly still tight in the spindle and no milling operation was performed, it dissipated by lowering RPM.

I can say that the Z axis was lowered before the spindle was turned on when the tool holder came out.

Very large drill was used for facing. The drill started to drop slowly after a pass of facing was completed from one side. After tightening it, the facing operation continued. This time the collet dropped instantly after one surface pass was done, when the tool hit the surface for a second pass.

 

[cngbrick]

What condition is the varidrive system? Are the bearings good? When running in low gear the varidrive is rotating counter to the spindle. Binding between the drawbar head and varidrive could loosen the drawbar in theory but I expect the bearings would have to be in bad shape or the drawbar would have to be bent.

You basically need to inspect and measure. First priority would be figuring out if the length of the drawbar is ok, then look for anything that would cause misalignment or binding.

With regards to the collets: do you have full contact in the spindle? Blue up the spindle taper and tighten a collet in there to check for contact.

 

[winger]

Another thing that can happen is the spacer is worn allowing the shaft to try threading in too far. Had that problem. Need to put some antisieze there occasionally.

Dave

 

[CarbideBob]

Remove the air ratchet and tighten by hand while holding the brake. Nice solid seat or gradual tightening over a few turns? This is a feel thing.
The bar only needs to get into the holder by 1.5-2.5 times the dia. Blue it. More is a waste and problem. Add washers or cut the bar.
Pin in the spindle still? I remove these as they get burred and stop things. Then it comes loose when cutting. You will see this as scaring on the keyway.
Air pressure or leaks to the impact wrench up there?
Sometimes the impact just goes bad inside and makes no power.
A rare duck is that the impact does not retract enough to be clear for running. The whine makes me curious here.

Curious problem and for sure me 2 cents or less from the peanut gallery.
Let us know what you find as this a puzzle to be solved.
Bob

 

[cngbrick]

Is the thread damaged at the point it stops screwing in?

 

[AndrewZ]

Is the thread damaged at the point it stops screwing in?

The measurement was rechecked and actually the collet seems to reach above the line. Simple numeric error, old post deleted. Approximately 3/4 inch in. Screwing the draw bar halts in a single stop, no gradual tightening although it may go a bit further with a lot more force.

The collets are approximately 44.4 mm / 1.75 inches deep. They also have a slight 5.5mm / 0.22 inch dent before the thread which was not accounted for before. Interestingly though the bar only goes approximately 39 mm / 1.5 inch in, at least easily.

I do not see a damaged thread, but can provide more pictures.

 

[AndrewZ]

Another thing that can happen is the spacer is worn allowing the shaft to try threading in too far. Had that problem. Need to put some antisieze there occasionally.

Dave

The spacer... the ring shape on the draw bar again?

It does not look too bad, but is this possible to verify?

 

[AndrewZ]

What condition is the varidrive system? Are the bearings good? When running in low gear the varidrive is rotating counter to the spindle. Binding between the drawbar head and varidrive could loosen the drawbar in theory but I expect the bearings would have to be in bad shape or the drawbar would have to be bent.

You basically need to inspect and measure. First priority would be figuring out if the length of the drawbar is ok, then look for anything that would cause misalignment or binding.

With regards to the collets: do you have full contact in the spindle? Blue up the spindle taper and tighten a collet in there to check for contact.

Apologies for a newbie question, what does the term "blue up" mean? I will inspect the collet-spindle contact tomorrow and also see if I can inspect the motor bearings and further take a look at the impact wrench.

What in the system holds the draw bar down (or collet up)? I wasn't able to find much documentation behind the mechanism.

 

[cngbrick]

Blue up means to put some Prussian blue marking paste, as thin a layer as you can spread on one component face, and bring that face into contact with its corresponding mating face. The blue on one face will transfer to the other face and act as an indicator of how well the surfaces match. Any burrs or dings present will push the surfaces away from each other and only the high spots will get some blue transfered from the other face.

The drawbar is simply held in place by gravity and rests on top of the spindle if everything is in good condition. When you bring the quill up (the quill is the spindle carrier), the head of the drawbar protrudes from the top of the milling machine head and becomes accessible to the impact wrench socket. When you press the pneumatic drawbar button air pressure causes the impact wrench to move down, engage the drawbar head with the socket and rotate the drawbar to loosen or tighten the collet at the other end of the drawbar.

The drawbar is simply a screw that pulls the collet into the spindle. You are looking for any damage that would prevent the screw from tightening properly. This could be elongation of the drawbar, wear, misalignment of the impact wrench, leaking hoses or seals, worn out impact wrench motor, burrs, binding, low air pressure, lack of lubrication (drawbar threads periodically need graphite based lube), etc.

I have had two issues with mine: shearing dowel pins (I have a 2 piece press-fit drawbar) and over extended high speed/high rpm +Z move that pushed the drawbar into the impact wrench socket before the limit switch stopped the motion and resulted in a thrust bushing friction welding itself to the end of my spindle. That required removal of the spindle and regrind of the spindle end to correct, thankfully the taper was not affected by the rapidly loosening tool holder.

 

[AndrewZ]

Blue up means to put some Prussian blue marking paste, as thin a layer as you can spread on one component face, and bring that face into contact with its corresponding mating face. The blue on one face will transfer to the other face and act as an indicator of how well the surfaces match. Any burrs or dings present will push the surfaces away from each other and only the high spots will get some blue transfered from the other face.

The drawbar is simply held in place by gravity and rests on top of the spindle if everything is in good condition. When you bring the quill up (the quill is the spindle carrier), the head of the drawbar protrudes from the top of the milling machine head and becomes accessible to the impact wrench socket. When you press the pneumatic drawbar button air pressure causes the impact wrench to move down, engage the drawbar head with the socket and rotate the drawbar to loosen or tighten the collet at the other end of the drawbar.

The drawbar is simply a screw that pulls the collet into the spindle. You are looking for any damage that would prevent the screw from tightening properly. This could be elongation of the drawbar, wear, misalignment of the impact wrench, leaking hoses or seals, worn out impact wrench motor, burrs, binding, low air pressure, lack of lubrication (drawbar threads periodically need graphite based lube), etc.

I have had two issues with mine: shearing dowel pins (I have a 2 piece press-fit drawbar) and over extended high speed/high rpm +Z move that pushed the drawbar into the impact wrench socket before the limit switch stopped the motion and resulted in a thrust bushing friction welding itself to the end of my spindle. That required removal of the spindle and regrind of the spindle end to correct, thankfully the taper was not affected by the rapidly loosening tool holder.

Thank you, understood.

There was an issue before with the tool not tightening properly which was caused by leaking air. The collet was shaky then, and later refused to tighten at all. But this time seemingly the collet was tight and decided to pull out on its own. I state again that quite large diameter drill was used.

Regarding the lubricant, regular off the shelf oil was used on the drawbar.

Sounds like the issue could also be that the taper is not clean enough? It has not been cleaned ever I recon...

 

[cngbrick]

The taper and collet have to be perfectly clean before blueing. Preferably you would use a new or nearly new high quality collet for this (Hardinge or another quality brand) or better yet, a solid tool holder. Make sure you have a tool in the collet as well.

You mention drill but I assume you mean end mill since you say this was a facing operation? Can you post a picture of the tool?

 

[AndrewZ]

The taper and collet have to be perfectly clean before blueing. Preferably you would use a new or nearly new high quality collet for this (Hardinge or another quality brand) or better yet, a solid tool holder. Make sure you have a tool in the collet as well.

You mention drill but I assume you mean end mill since you say this was a facing operation? Can you post a picture of the tool?

Good news.

Before blueing I noticed that the collet was able to turn few degrees when all the way in the spindle. So, after all the collet alignment screw was not screwed in as much as it should. After screwing it in properly the feel is much tighter. In fact so tight that the collets stick to the spindle.

I did not yet test whether the collet still falls down... fingers crossed it does not. I would guess this was the issue, even though it is unclear how a loose screw causes the fall.

Yes an end mill. I can post the exact tool if the issue persist, but the look was something in the ball park to the image below.

 

[cngbrick]

Good news.

Before blueing I noticed that the collet was able to turn few degrees when all the way in the spindle. So, after all the collet alignment screw was not screwed in as much as it should. After screwing it in properly the feel is much tighter. In fact so tight that the collets stick to the spindle.

I did not yet test whether the collet still falls down... fingers crossed it does not. I would guess this was the issue, even though it is unclear how a loose screw causes the fall.

Yes an end mill. I can post the exact tool if the issue persist, but the look was something in the ball park to the image below.

The alignment screw may have prevented the collet from fully seating in taper when tightening the drawbar. It then came loose under power.

The alignment pin should not cause binding of the collet, the collet should slip in and out easily. The pin is just there to prevent the collet from rotating when tightening the drawbar, it should bear no load when the drawbar is properly tightened.

 

[AndrewZ]

The alignment screw may have prevented the collet from fully seating in taper when tightening the drawbar. It then came loose under power.

The alignment pin should not cause binding of the collet, the collet should slip in and out easily. The pin is just there to prevent the collet from rotating when tightening the drawbar, it should bear no load when the drawbar is properly tightened.

Bad news... the problem is like hydra, as one issue is solved three new ones appear!

I am now getting the following noise from the machine: http://sndup.net/tsf6

Both grinding and ringing. The grinding originates from the upper portion, and the ringing I am not quite sure where it comes from and it may vanish for a period, sounds like some sort of friction perhaps.

Furthermore, all collets won't tighten up properly, it is as if the bar is not properly grabbing them. However, that is a smaller problem.