"Pete C." wrote in message ...

PrecisionmachinisT wrote:

"Pete C." wrote in message ...

PrecisionmachinisT wrote:

"Pete C." wrote in message
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- The actuator mounting will lift from it's non-contact idle position
when actuated so it is in contact with a flange at the top of the
spindle while pushing down on the drawbar. This is so no toolchange
force is applied to the spindle bearings which could damage them.


Not in my experience, although a quill-type spindle cartridge does need to
have a means of positively locking it in the full up position.

The machines I used to work on were this way, perhaps designs changed in
recent years. The force was always applied between the spindle and the
drawbar such that no force was applied to the spindle bearings.



- The actuator travel is such that the drawbar will apply a push to the
toolholder at the end of the stroke to pop free a sticking toolholder.


Hammering on the top of a conventional drawbar is the usual method, which
doesn't seem to damage spindle bearings so far as I've been able to
ascertain.

A rap with a hammer vs. pressing hundreds of pounds with a hydraulic
actuator. Perhaps they've beefed up spindle bearings in recent years as

The actuator bottoms out internally after the tool releases, thus the max pressure that is placed onto the bearing is the same in either case.

The max compression of the belville spring washer stack is constant,
yes. The pressure will vary if a washer or two has failed, and again on

Pressure ( on the spindle bearings ) (or on the flange, if one were present) is limited to the amount needed to release the tool, or to the total system pressure, whichever comes first.

Fadal for instance, makes use of this fact in order to set bearing preload; an indicator is placed on the spindle flange with a tool in place and the drawbar clamped, then the tool is released, the resultant change in indicator reading is noted and then the preload nut is adjusted accordingly...

Do you want a link to the procedure ?

no machine I have worked on was any of this force applied to the $800
spindle bearings. The actuators all floated and pushed down on the

My experience differs, and in fact I've never seen a system as you describe, the exception possibly being where a drawdar was actually being turned like for example the old devlieg jig bores.

drawbar while effectively pulling against the flange on the spindle as
opposed to being rigid mounted to the head casting and pushing down
against the drawbar. This was dozens of different brands and models of
machine.


Not saying such a system does not exist, but since it's your claim, you'd be more convincing if you could link me to the mechanical drawing of one ( which shouldn't be too hard since you've seen dozens ).

--out of curiousity, I'd like to see at least one.


spindle speeds have increased so they can more readily handle the
toolchange load. Or perhaps you haven't looked at the actuator closely
enough since without looking at the prints it's not immediately obvious
that the force is not applied to the bearings.

No, it's immediately obvious from my having actually worked on them for going on 35 years now.

Well, I worked on them as in serviced them for about 6 years, including
changing out belville washers on the drawbars and replacing a few sets
of spindle bearings, so there is no question that the machines I worked
on then ('90-'96 or so) did not apply toolchange forces to the spindle

The piston plate is about 4x6 and recieves air at ~90 psi, which means the total possible thrust pressure that's capable of being placed onto the drawbar on this 40 taper mill here sitting to the left of me works out to be about 2520 lbs which is well under the max static engineering load limit of the 7210 bearings which comes in at around 7081 lbs

bearings. Take a close look at the prints for one of your machines to
see where the force is really being applied.

It's oftentimes called an "orientation bridge"

Ball bearing elements are like any other metallic object in that to cause any permanent deformation to occur, forces in excess of yield.must be applied.