Tolerance rings or thin sleeve to repair fixed varispeed disk bore

For pretty much all the 16 years I've owned it my 2J2 Varispeed Bridgeport head, 1 1/2 hp motor, has had occasional rattle fits. Which I put down to just one of those things given its a 1979 vintage machine. Recently it has got regular enough and loud enough to make investigation essential.

On strip down I discovered that the fixed varispeed disk on the motor has no key fitted. Clearly the disk had been mostly supported by the pressure of the belt holding it against the lower motor bearing. Over the years the sleeve has run independently enough to grind off maybe 1/8" off its hub and to start wearing flats on the ball cage of the motor lower bearing! I'm amazed that it didn't come to grinding halt years ago.

Was little surprised to see that the disk bore and the part of the motor shaft it sits on appear to be metric dimensions.

The bore in the disk itself has worn sort of hour glass shape. The taper end is about 25.4 mm Ø and the hub end about 25.7 mm Ø. The wear tapers seem to be about the same. The motor shaft measures 25 mm Ø where the sleeve goes. About 5 mm between the taper wear seems still to be close enough to correct diameter of 25 mm to feel a sliding fit on the shaft but not close enough to stop it wobbling.

My proposed cure is to bore out maybe 10 or 12 mm from each end and fit either a tolerance rings or thin steel sleeves bored in situ to fit the shaft so it is properly supported at both ends. Looks like a tolerance ring needs about 2 mm overbore whilst I figure I can get a glued in place sleeve in 1 mm overbore. Only 3 mm depth of keyway in the sleeve so a full length sleeve or tolerance ring will probably thin the keyway down too far. Tolerance ring has the advantage of gripping the shaft which should take some of the load off the key. But the grip may make installation difficult.

What does the team think is the best way to proceed?

Either way boring out concentrically at each end is going to be interesting. Presumably a tolerance ring will be slightly more tolerant of error than a sleeve.

I had to re-make all the moving varispeed disk bushes before putting it into service. Very pleased to see that my efforts are still holding up just fine after 16 years. I can only assume the fixed motor sleeve was still apparently securely fixed on its shaft when I did this so I saw no reason for a deeper inspection that would have revealed the missing key. According to the folk I got it from, the rump of InterCity Machine Tools, they had re-built that machine some years before for a previous owner when they were still actively in the machine reconditioning business.

If the sleeve is beyond sensible fixing plan B is to convert it to VFD and timing belt drive. I have a "professional" VFD conversion kit removed from another machine but don't approve of the control aspects. A lot of electrical re-jigging will be needed to make a satisfactory conversion integrated with the other control aspects. As supplied I suppose the kit might do for a Myford!

Thanks

Clive

Check archives for Moglice. and reeves drives repair. They sell premade sleeves to glue in to repair the bore. Bore has to be reamed to fit the new sleeve with glue.
A true hack would pack it with jb weld and bore on the lathe. The milling machine could do it but it is not running .
Bill D

Clive,

This is one man's opinion. I have always thought the vari-speed system to be slow and clunky to adjust versus a dainty little knob and potentiometer for adjusting spindle speed. Think of all the nice things a frequency drive allows, and with the variety of drives available and their reasonable prices, it seems a much better way to address your situation. That really wasn't the focus of your question but..it is this mans opinion.

Stuart

On equipping with a VFD: most of these are designed as constant output torque. This is not really what the application calls for, because when you slow down your VS, you are improving the torque delivery to the tool. Not so with a VFD, unless you go the route of a vector feedback drive and an encoder on the motor.

The standard VFD allows for you to run the motor with plenty of overspeed capability that you didn't have before, so choose your timing pulleys in such a way as to give more mechanical advantage to the motor at low rpms (when you need more torque, but the motor is not putting out more torque, only the same torque). You want to keep the motor rpm up as much as you can if running a facemill or a tap so the motor doesn't fault out the drive on overload. But gearing down via the pulley set is an option.

Timing belts can also produce a whine of their own which can be annoying at certain speeds. The belt is right up there near your head, too, so you can hear it real well I swapped out one drive I had built and changed it to an Eagle PD belt and pulley system. Herringbone pattern belt and pulleys, nice and quiet at any speed. I also put encoder feedback on that mill motor, and bought a drive that used vector feedback, so it would turn that spindle no matter what.

On the other mill retrofit, I put a multi-rib belt and pulley system on there. That is also a nice quiet running system. Machined my own set of sheaves for that one, with a high and low range. 't was a pain to switch manually, though.

If I were you, I'd probably just rebuild the VS system if you plan to just use the machine normally. VFD is a practical necessity for cnc operation.

Thanks for the advice gentlemen.

Bill
As I'm in the UK getting the repair sleeves isn't so easy. Frankly by the time all is set up to machine the bore back true making a sleeve is trivial.
As I have a bit in the middle that is still the correct size and my S&B 1024 has a 5C native taper in the spindle my plan A is to put an alignment spigot in a collet, fit a four jaw chuck and carefully tighten down to hold the disk. I've done similar a few times before and it works very well. Especially on the sort of impossibly lumpy stuff with nowt to indicate on that ought to do better on a mill.

automarc, HuFlungDung
I'd assumed that the noise was due to the moving disk bushes being worn out. As mine had the formed in place turquoise bushes which are officially unfixable (really, hold my beer!) replacing them was absolutely a never to be repeated once in a lifetime experience. I picked up the VFD because it was local, the price was right and it came off a Bridgeport so would be an easy bolt on. However the control box set up is completely unsuitable for a UK built Bridgeport. Just a stand alone box. Admittedly a neat box but all it does is run the motor.

The late, and sadly missed, Adama demonstrated that a simple VFD with single speed belt drive works well enough. At some time mine will get a VFD but its going to be done right retaining the UK forward-off-reverse switch up on the head and the knee level main control panel. Pretty much all new innards in the big electrics box needed. Objectively a two speed belt drive would be best to maintain power at lower speeds but finagling in a simple change set-up isn't easy. I've contemplated Fadal style twin belts, electromagnetic clutches on an intermediate shaft and a shop made spline and face cam shifter with two free running pulleys on the main spindle. All more engineering than I'd like and all needing keyhole surgeon skills to fit.

Off to the workshop for another coat of looking at, currently marginally more inclined towards tolerance rings. £5 a pop in a suitable size.

Clive

you can get moglice from diamant in germany.

We Wrote the Book

I believe Turcite is a British version of the same basic epoxy material.

Bill D.

turcite vs garlock vs moglice vs ??

Where to buy Moglice in small quantities?

Supplier of Turcite B in UK Found