Step belt J-head rattling sound with backlash on step belt

aribert · Jul 16, 2019

Greeting all:

I typically lurk here on PM and post on the HSM forum. But I figured the knowledge base on this forum might be greater. In the 15+ years I've owned my existing J-head B'port, I only lubed the head - no other service has been needed.

I am building up a replacement B'port (my existing J-head step belt is a 1 hp w/ a 32 inch (not a typo) table - I've outgrown the small table). The new machine has a 42 inch table. I bought the head for the new machine at an estate sale 18 months ago - configured with a 1.5 hp motor that spins the head at twice the speed of a standard step belt B'port. Finally acquired a B'port missing its head so now I have married the two and am beginning to debug the head.

Since the head had been out of service for several years or more, I (over)lubed the head before running it under power. Under power, the new to me J-head makes a irregular rattling sound. In comparison, my existing B'port (with the belt in the same position on the pulleys) is very quiet. With the v-belt loosened there is noticeable backlash in the spindle step belt pulley. My existing (quiet head) does not exhibit any backlash on the same pulley.

I expect to dismantle the upper portion of the head in a day or so to investigate but I figured I would ask here for any guidance. Looking at the B'port exploded view, it appears that the step belt pulley is keyed to the "spindle pulley hub". Is this correct? If so, I'm hoping that all I need to do is to recut the keyway in the aluminum step pulley. I found on line a B'port J-head rebuild procedure published by Industrial Tool and Machineworks. Any other references I should look at / be aware of?

naru · Jul 17, 2019

https://www.amazon.com/Guide-Renovating-Bridgeport-Milling-Machine/dp/1482368005

A very useful guide to be sure, also available in other head styles but this one should be the one for you.

aribert · Jul 17, 2019

Thank you for the response and link.

Since I was not intending or expecting to dig into this head I did not consider buying the repair/rebuild book in advance and I am intending to dig into to this head either later today or tomorrow, so I'm looking for any pertinent advice. If I get stuck or have issues, I order the book.

jhruska · Jul 17, 2019

Belt noise; a v-belt will a take a 'set shape' and could be a source. Look at the belt while running, replace or adjust tension.
When is the sound present? Hi and/or Low speed?
Low speed, when the assembly does not clear the hub completely. Check the two pins, bearing cartridge to lift ring, see that they are tight.
High speed, wear in the hub 'crown' of both upper and lower will produce a clatter usually under load during an intermittent cut. Drilling a hole the sound usually goes away. Wear in parts #20 an #57.
Takes a lot of miles before the keys and keyway wear enough to knock.
Test the brake while running. Does it affect the noise?
Check the pulley set screws. Expect to find two(2) one to seat and the second to dog the first in place.
Load the spindle; collet with a pin or a drill chuck. Hold the body of the chuck while the spindle runs, Hi and Low range.
Objective is to isolate the the source of the sound to either a component or a speed range.

John

donie · Jul 17, 2019

I believe your problem is part 57, and its mating part #20 "I think", those parts are the clutch for direct belt drive. Those parts can get pounded from too hard fly cutting.

aribert · Jul 17, 2019

John:
Thank you for the response - my answers are below each of your questions. Aribert

jhruska said:
Belt noise; a v-belt will a take a 'set shape' and could be a source. Look at the belt while running, replace or adjust tension.

I've played w/ belt tension, no change in rattle. Belt when loosed, in free state, is more circular than oval shaped (like a belt that has a pronounced set).

When is the sound present? Hi and/or Low speed?

High speed - the faster the more pronounced.

Low speed, when the assembly does not clear the hub completely. Check the two pins, bearing cartridge to lift ring, see that they are tight.

I made new pins as the first maintenance item to even be able to shift between Hi and Low

High speed, wear in the hub 'crown' of both upper and lower will produce a clatter usually under load during an intermittent cut. Drilling a hole the sound usually goes away.

With the belt in the highest spindle speed (5540 rpm) I used a nominal 7/16 carbide drill into a block of mystery metal (file test like medium carbon steel) noise still there. In high at the lowest spindle speed, 1320 rpm, the noise by and large was gone when drilling and was more noticeable on spindle coast down after turning off the power (drill retracted from the block) than when running.

Wear in parts #20 an #57.
Takes a lot of miles before the keys and keyway wear enough to knock.

Test the brake while running. Does it affect the noise?

No - BUT I just discovered (not running) that if I hold the brake the step pulley does not have any backlash (but the drawbar/spindle has the same amount of backlash detected on the step pulley w/o applying the brake. Clamping a tool to the drawbar hex and freehand holding a cheap plastic protractor I see a solid 5 deg of backlash on the drawbar with the brake engaged. Looking at my existing step belt head that runs quiet the backlash is barely perceptible and appears to be less than 1 deg

Check the pulley set screws. Expect to find two(2) one to seat and the second to dog the first in place.

Thanks for the dual set screw reminder. I see the set screw on the motor step pulley but see no provision for a set screw on the spindle step pulley.

Load the spindle; collet with a pin or a drill chuck. Hold the body of the chuck while the spindle runs, Hi and Low range.

Noise is still there in Hi - did not notice any change in the rattle.

Objective is to isolate the the source of the sound to either a component or a speed range.
View attachment 261188 View attachment 261189 View attachment 261190 View attachment 261191
John

I suppose I could try to take some video (audio)tomorrow and upload to youtube, if that helps, before I begin to dismantle the upper part of the head.

gustafson · Jul 17, 2019

Two things from experience

I bought my very first bridgeport[9x32 which I loved] that the place I worked gave up because the head was 'flogged' rattled like you could not believe.

but it had an extra long drawbar, which I thought would be useful in the CNC mill we were using, so I swapped it before I took it.

turns out the extra length drawbar was causing the noise, head was quiet as a mouse

Second, friend has an Interact at my shop. varispeed, but also rattles. i don't think the UK [mebee Singapore?] heads are as good.

Rattles.

not bushings

Lean on the lo/hi lever and it shuts up.

Not my machine so I have not tried to adjust or whatever to shut it up

that's my input

Mark Rand · Jul 17, 2019

Is it possible that the internal spline on part 57 is worn and that the play is between part 57 and the spindle splines?

I don't know if Bridgeports suffer from this at all, but my Beaver milling machine has/had poor or no heat treat on the equivalent of part 57, leading to the internal splines being severely worn. I'm currently in the process of making a replacement, since spares are no longer available.

jhruska · Jul 18, 2019

gustafson said:
Varispeed, but also rattles, not bushings.
Lean on the lo/hi lever and it shuts up.

The radial splines on parts #20 and #57 when new are square, like a crown gear with square teeth. As they wear the shape is very much like a trapezoid.
The rattle is pronounced during intermittent cuts as the cutting tool enters and exits the cut the gear teeth make contact and then clearance.
Drilling a hole, ex; 1/2" drill, creates constant pressure so the gear teeth stay in contact therefore no rattle.

Here is where the Hi-Lo gets involved. With the mill running and taking a cut, a Servo Feed unit to drive an axis, pushing up on the lever will force the parts #20 and #57 together so those worn trapezoid shaped teeth make steady contact.

The detent plate is key as it sets the engagement location of #20 and #57.
Originally Bridgeport provided as original equipment a detent plate with a sliding block. Then the engagement detent for Hi range could be adjusted for wear. See attached.
That adjustable plate is discontinued but they are not hard to make.

So, if your friends' mill had an adjustable detent plate most of the rattle could be eliminated.

This is for the Vari-Speed head only.

John

jhruska · Jul 18, 2019

aribert;

This may sound screwy but try it anyway

With the mill running in Hi rotate the cam ring, not so far to disengage the splines but enough to vary the pressure of engagement between #20 and #57- the direct drive. Why? Because I found that too much downward pressure on #57 creates a noise.
Another thing to check;
The spindle step pulley19, is keyed 21, to the spindle pulley hub 20. If the bore of the spindle step pulley is oversize then it may wobble/oscillate and be a source of noise. A brinnel-fretting type of wear.

The low speed hub is rotating even tho the mill is in Hi range. The belt retainer plates should be screwed in tight and the hub should run tru on the shaft. Likely not pertinent to the problem but on the need to know list.

John

aribert · Jul 18, 2019

All:
Thank you for your responses. Parts 57 & 20 seem the common culprits.

John:
I did as you suggested, ended up rotating the cam lever from high to low a bit more than 1/3 of the travel in the slot (until I could just begin hearing a rubbing sound and backed off a tad) and the rattle was greatly reduced at 1320 rpm - to the point where I would have ignored the remaining rattle/noise. At 5440 rpm I think there was more rattle, hard to tell since there was also much more overall mechanical noises.

All:
Follow up question - can this rattle be ignored w/o damaging adjoining parts? I could turn a new set a cam pins with a smaller OD that would lift a bit less while still keeping the splines engaged (still ignoring the worn splines). I would presume that I would need to monitor the backlash when the spindle is locked and repair the head when the backlash angle grows - no idea what the wear limit might be but I can't image the splines lasting much longer if the backlash grows to say 8, 9 or 10 degrees. I am making an assumption that the splines are fairly small.

If I need to dismantle the upper part of the head to replace parts in the near future, I might as well do it now before I sell off the short table B'port so that I am not without a mill while repairing the new one.
Aribert

Nmbmxer · Jul 18, 2019

Have you run it with the drawbar removed?

On mills I've used that had pn 57/20 adjustment issues "a rattle" doesn't even begin to describe the noise, it was like a roaring death hammer.

I've had one with the splines on the spindle that rattled, I put heavy grease on it and it sounded better for a while. Its easy to pull the spindle and if you apply grease it won't hurt anything and if it helps you've identified the culprit.

Edited to add that out toolmaker suggested levering a 2x4 between the side of the running spindle nose and the column as a way to load up the spindle splines without have to actually cut anything.

jhruska · Jul 18, 2019

aribert said:
All:
Follow up question - can this rattle be ignored w/o damaging adjoining parts? I could turn a new set a cam pins with a smaller OD that would lift a bit less while still keeping the splines engaged (still ignoring the worn splines). I would presume that I would need to monitor the backlash when the spindle is locked and repair the head when the backlash angle grows - no idea what the wear limit might be but I can't image the splines lasting much longer if the backlash grows to say 8, 9 or 10 degrees. I am making an assumption that the splines are fairly small.

Run it. no other collateral damage will occur.
Parts are still available, pins, cam ring, and #'s 20, 57 tho pricey.
The threads for the pins, 1/4-24 unless my memory is fogged. These threads are in the bearing cartridge and tend to wear egg shaped thus affecting depth of engagement. Threads are usually trashed when the two tiny setscrews are not backed off.
Sometimes the cam ring has excessive wear.
The fix is to R&R the top end and drill-tap new threads for the pins in the bearing cartridge with a slight counter bore so the pins seat on a flat surface. The cartridge bore is probably overdue for a clean-up and a new coat of light grease.

Some thoughts:
Heads can be swapped from one mill to the other.
The "new mill" has wear from long term use. Inspect the rest of the machine for wear, quill feed and feed stop both up and down. Gib wear or binding, screw wear adjustment or way wear-center of travel. Gibs could be bottomed out or the knee gib could be stuck.
Tables can be swapped but there will be a clash of dissimilar way wear surfaces.
The mill with the small table may be in better overall condition.
Regards, John

aribert · Jul 18, 2019

Nmmbxer
No change in rattle w/o drawbar. The noise probably not anywhere near a a "roaring death hammer"

John:
Based on very limited use, the new to me large table B'port (table, saddle and knee ways appear to be worn similar to my existing small table B'port (discounting a few divots someone drilled and milled into the longer table). I have yet to adjust any gibs. I plan to use both machines interchangeably the next several months then buy/mount a modern DRO on the large table machine and put my existing B'port up for sale. Long term my goal is that selling my existing small table B'port will: upgrade from a 32 to 42 inch table, upgrade from 1 hp to 1.5 hp, upgrade to a new DRO (existing machine has an antique Mitutoyo cube DRO), pay for a VFD to replace the static phase converter and ideally w/ enough coin left over that I might be able to pay for the 57 & 20 when needed.

All:
Based on comments from Nmbmxer and John, I will leave the head parts 57 & 20 alone - I can live with the rattle. I was concerned that this rattle could have a rapid domino failure effect. Once again, thank you all for your responses.

donie · Jul 18, 2019

I bought the Bridgeport new in 1980, then proceeded to absolutely beat the crap out of it until 2006, if you can manage to apply a small amount of sticky grease like the black disk brake stuff to the faces of part 57 and 20, it will run quiet for a little while. I am sorry you bought my beat to crap Bridgeport!

aribert · Jul 19, 2019

donie said:
I bought the Bridgeport new in 1980, then proceeded to absolutely beat the crap out of it ...I am sorry you bought my beat to crap Bridgeport!

Not me, I paid $20 for the head at a "garage sale". I spent more for an offshore drum switch to be able to run it.

Sent from my 5049W using Tapatalk

majohnson · Jul 20, 2019

Mine was rattling and I came across a post about bull gear making noise. Elongating the slots got rid of the noise. I would of sworn it was a bearing failing.

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