Bridgeport j head brake rubbing?

Hi,

I recently rebuilt my j head top half with H&W bearings and it is much quieter. However there was a ticking noise from the front pulley... which I eventually traced to rubbing on the brake shoe. If the brake handle is in exactly the right spot the brake doesn't rub, but otherwise it does in one spot and makes the front pulley ring.

The springs holding the brake segments together seem pretty strong still, though maybe that might be one thing to replace?

The brake shoe segments don't appear worn or have any bumps which seem to make contact.

I also get some sense of vibration / lack of smoothness in the quill Downfeed when the machine is running (which is not there when the spindle is not turning).

Any suggestions would be appreciated.

Thanks!
Phil

Phil,

Vari-Speed or Step mill?

It is possible to assemble with the springs on the wrong side of the brake shoe. Brake handle symptom.
Jam nut for the brake assembly is lose or the cap screw is to long - tick from rubbing
To puzzle it out reassemble it "right" and "wrong". The correct assembly will be more obvious
and the fit and clearance will be more apparent.
John.

Hi,

This is a step pulley j head model... thanks.

Diagrams and a couple of things to check.
If the large pulley #25 for the lo-speed timing belt was removed it might not be completely seated. The aluminum bore is 'sticky' on the steel shaft. Then the retaining ring #24 being not perfectly flat will clip the underside of the step pulley. Look for a clean mark to verify.
As the brake springs are located on the centerline of the shoe this is not an install problem as it would be on the Vari-Speed mill.
Still have to look at #'s 17, 12, 13, and 14 as they may not be seated or tightened all the way for the engagement problem.


Vibration is related to the pulley. Be sure it is seated.
See if the the v-grooves of the two step pulleys line up. The belt should be horizontal and the v's
should be at the same height.
John

Hi,

I dismantled the head (again) and found the brake rubbing in one spot
on the pulley rotation consistently... it seems to be making contact with the
brake shoe outer circumference directly adjacent to the Brake Lock Stud (part 17
in diagram).

A picture is attached showing the brake block assembly with the Lock Stud and a brake ring screw installed, placed inside the pulley as it would sit in the actual assembly.

The clearance between the brake block and the pulley seems *very* tight, arrows drawn to point to the tightest points... it seems a bit surprising that the assembly should be this tight. I double checked and the hardware and brake block are clean, nothing causing them to be expanded.

I'm tempted to just file / sand down the brake block to make clearance?

I also checked the runout of the pulley with respect to the spindle bearing pulley sleeve, and got somewhere around .0035" TIR.

Thanks,
Phil

Phil,

I had one of these problems a very longtime ago. Brake was fine before the tear down but hung up after assembly. Took that head off two or three times.
Check the bore diameter and compare to the brake assembly, pins #17 and 14 in place. Seems that I may have flipped the brake over as the bore in the step pulley had a taper and the worn shoes need to match that. Otherwise the pins themselves would not quite seat and that, you can measure with calipers as the O.D. of the shoes will be oversize if #14 rides on a burr in the hole.

Another quill vibration source is when the step washer for the drawbar is missing. This keeps the top of the drawbar on centerline if so equipped.

John

Thanks. I'm beginning to suspect the .0035" runout I see on the spindle bearing pulley sleeve to be the source of why the brake gets hung up now in one spot. Whether that's expected with the H&W bearing replacements I used? Not sure.

I do have the step washer on the drawbar... thanks for the suggestions!

-Phil

This might be a head-slap moment but the O.D. of the cartridge does not rotate, remember the pins are held by the slots in the upper housing.
The bearing cartridge still has to fit in the bore and that will locate the position of the step-pulley brake bore.
I used some never-seize for aluminum.
Put this sub-assembly together and fidget with it ( I'm using tech terms here) until it spins free. Tighten it up and assemble.
Like a cylinder head, just draw up the brake shoe mounts evenly until it has a good fit. If it sticks, take a dead-blow hammer and smack the upper housing 180 from the sticky point to get the assembly to move to a clearance point. Big hammer, soft face dead blow.
And a couple more images.

Good Luck!
John

Hi,

Yes I realize the bearing pulley sleeve doesn't rotate (other than when the pins are rotated by the cam ring. )

But if the pulley has .003" runnout relative to the bearing cartridge then the pulley might be imbalanced and touching the brake as it rotates?

-Phil

The pulley is keyed and mounted to #20, Spindle Pulley Hub. The bearing cartridge is mounted on the S.P. Hub so these two elements are concentric and true to each other. The outside diameter of the bearing cartridge is out of round and this could cause a position error in the X-Y direction but the error in location is mitigated by the bore in the housing. Error may be reduced by half,...split the difference of the error.

The out of round bearing cartridges generally are egged where the pins have been located. This creates an interference fit between the bore and the cartridge resulting in scoring of the aluminum bore.

The problem could be:
Axial displacement between the brake shoes and the pulley-bearing cartridge sub-assembly.
Some detail is preventing the brake shoes from collapsing.

"If" it worked before disassembly it should go back together as before.
I have on occasion, removed material from the ends of the brake where the flat paddle surface is engaged.
Cleaned up the opposite hole, fulcrum.
Or just tapped and tightened till it worked.
John

Hi,

I ended up disassembling the bearings in the pulley sleeve to check them... everything fine there. I was able to reposition the brake shoe a bit to reduce the rubbing... but ultimately I took the brake shoe (phenolic) to my spindle sander for wood and took about 1/32" off both the pivot screw side and the flat paddle side.

This fixed the issue with no appreciable reduction in braking effectiveness.

It also significantly reduced the vibration felt in the quill handle.

Thanks John for all your suggestions!

-Phil

How old is the V-belt?
Some will take a "set" shape if under tension and not used for a long period of time.
Older belts can get hard. New belts seem to be more elastic.
Any vibration is related to some rotational motion, but you already knew that.
John

The belt is brand new, came with the H&W kit. The remaining vibration (felt in the quill handle) is most significant when the quill is at the top of its range... it seems to reduce when the quill is 1-2" down.

-Phil