Supermax Vari-speed noise

My old Supermax (Bridgeport clone) mill has been trouble free for years. It has a head nearly identical to the Bridgeport 2J2 with a variable speed belt drive. Suddenly it developed a once per revolution clank in the spindle drive. It seemed less at the lowest speed setting, but was still there.

I prepared to remove the motor by setting to the lowest speed and compressing the spring. The mill was noise free when running with the spring compressed. On a whim I removed the spring compression screws and ran the mill. It was noise free through out the speed range. Everything seemed normal for a few weeks but the noise returned. The same fix worked again. I can't see any issues with a visual inspection. The upper quill bearing runs smoothly as does the rest of the quill. Does anyone have an idea as to what is happening?

Lohring Miller

could be sheeve bearings (horrible plastic things) or key (another horrible plastic thing ,in my Taiwanese mill).

Interesting you say it's quiet in low speed because that's whats wrong with mine. I suspect the hurth coupling twixt pully and spindle, exacerbated by the mill's single phase motor (the rattling noise stops immediately when the power is cut).

also worth checking the thrust bearing and how it is seated in its carrier.

Bill

Thanks for the ideas. I'm pretty sure the noise is coming from the motor end and I've suspected the motor bearings but will look harder. By the way, my motor is a 3phase running off a rotary phase converter.

Lohring Miller

OK I took the motor and its variable sheave apart. The keys are steel and the movable sheave has two bronze bushings in it. The spring end bushing looks more worn and has .009" clearance on the motor shaft. The other bushing has .005" clearance. Both are round within less than .001". There's actually very little play though when the sheave slides on the shaft. See the pictures below.

I'm pretty sure the noise is from the motor end since the frequency doesn't change with the belt position. The motor shaft runs very smoothly with no load. Despite the sheave bushing wear there doesn't seem to be any big issues. Could a lack of lubrication cause the noise? Any other thoughts?

Lohring Miller

That would certainly make the noise. worth checking the thrust bearing and sheave bearings on the sindle side while you have it apart.

I had one last year. that I sold. it had a noise, that was the pin for the brake shoes letting the make a constant noise. you can tell if that is it when running by moving the brake handle around. it will make the noise stop. if that is it, I drilled the pin out and put a bolt in place, you have to watch for clearance under the plate the pin go in. jonathan

well, today I found the problem with my mill.

The gear lever was slightly out of adjustment, preventing the hurth coupling from fully engaging. . A quick tweak and the thing is quiet

Bill

Did you measure runout wear across the length of the motor shaft? As the shaft and pulley bushings wear, especially in the "sweet spot" of maximum wear where the pulley mostly resides during operation - the pulley can develop a one-per knock. The motor pulley is under constant tension from one direction due to the design of the belt drive system. If there is excess wear on the motor shaft and/or bushing, the pulley can rock back and forth sliding up and down on the shaft's key on every revolution. I'm currently rebuilding the drive system on my Bridgeport and have looked at the drive mechanism pretty closely (although mine has plastic bushings and keys). If you're confident it's a one per rev from the motor shaft I'd be suspicious that might be it.

If the motor shaft's worn you can have it welded up and cut back down to size and re-hardened. Or it could be as simple as replacing your bushings. The noise almost going away at the lowest speed, where the belt is in the deepest position on the split pulley would push the sliding pulley sheave to its outermost position on the motor shaft. I suspect you'll find the shaft wear to be at its lowest in that location.

Thanks. When I get back to the shop I'll check the motor shaft. However, I did measure it several places to check for out of round. The wear on the upper bushing is also suspect.

I'm trying to avoid tearing the quill end of the drive apart, but I may need to look there as well.

Lohring Miller

The motor shaft measures the same diameter within .0005 everywhere. I greased the sheaves and reassembled the motor. The same clank reoccurred shortly after running the mill a few minutes. It stops about 2/3 the way toward the lowest speed. There is a very definite spot where it stops and starts. While clanking, the lower sheave has noticeable axial runout. This stops when the clank stops.

All this sounds like shaft wear, but the shaft checks out. The upper bushing wear could explain it, but the sheave position shouldn't matter. In any case, I plan to replace the sheave bbushings. Any other thoughts?

Lohring Miller

remember, the belt position also changes , so the clanking could easily be the sheeve rocking. as it rotates in that one position.

might be worth checking the 'flatness' (conical shape) of the sheeves , they may be worn more in one area (especially if the machine has been used at only one speed).

With the motor and its pulley system off, I would remove the spring and carefully inspect the wear to confirm it is maximal at the higher speed location and less at the lower speed location. Based on what you're saying, it sounds like the shaft is ok, but the bushings are worn. Also, again, take a look at the key and the keyway both on the shaft and the pulley to make sure it hasn't unevenly worn itself. I'd definitely replace the key while you are replacing the bushings too. I'd also replace the motor bearings while you're at it. Cheap and easy to do while you have the motor off anyway. See the H&W video below to see the basic process, which I assume will be similar for your Supermax clone. All of the H&W videos are good, might want to take a look at them for general info.

Well, it was the bushings. I machined two new bronze bushings with .002 to .003 clearance compared to the .005 to .009 clearance of the old bushings. Everything now runs as smoothly as the machine did 20 years ago.

Thanks for all the help and suggestions.

Lohring Miller

I have the same problem, did you pen in place the bushings with screws like from the factory?