Help - bearing removal on 28-40 lathe

[bogmonster]

Hi,

Finally decided to bite the bullet and replace the bearings on my lathe. Not very experienced at this kind of work so wanted some advice before I screw it up The shaft is out and the bearings are off the shaft. Had to dress the shaft where the spindle lock goes but as there was a bur but that was easy. Disassembly was all very easy with bits of tube, vice, wooden block, mallet. Now for the bits I am unsure about....

The front and rear bearings are tapered roller bearings. The outer shells are in the casting of the headstock. There is only the smallest of rims on the inside and no obvious knock out points for a punch. I probably can get a punch on it but is there a special tool for this job?

EDIT: The outer shells are now out. Used a punch and the came out easily. Just stuck the the middle bearing now. Good news is it is small so I can take it to a man who can if I get stuck.

Also, there is a third bearing that is a standard sealed ball race. This is part of the speed control. I have got the outer section removed and the bearing came away with the outer and thus I have a similar issue.

I guess I could make a tool but sounds like heavy lifting for what I am sure is a common problem.

On reassembly I guess pack bearing with grease. How do I know how tight for the bolt that pulls it all together? Obviously if the shaft gets stiff to turn then that is bad. If the shaft has play that is bad. Is that it?

Cheers, BM

 

[bogmonster]

Ok, no ideas yet - how about this? I have found a short length of steel tube that fits through the inner race. I could weld that tube to the inner race and I could then press the end of the tube. I do have a 6 ton flypress and an arc welder to hand.

Any good?

EDIT: Ok, vice and punch worked in the end I have the bearings but will need to order up a new belt as well and then put it back together again.

BM

 

[jurriaan]

As for packing with grease: shielded bearings would be ideal, they're greased for life and dust won't get in. If you get open bearings and you need to insert grease, don't use too much - 1/3 housing volume is enough, more causes overheating, which makes the grease thin and it will run out.

http://connect.timken.com/packing-tapered-roller-bearing-with-grease

 

[bogmonster]

Thanks for the link - looks like there will be a lot of help there. I already have the bearings so will go with what I have I think. The middle bearing is sealed but the front and rear taper bearings are Timkin two part taper bearings. The bearings were getting noisy and quite a lot of heat build up at faster speeds. Then remaining very noisy until the grease had cooled back down. I don't do much spindle work so the lathe tends to run at low speeds but I recently tried a few pens and the lathe really didn't like these. I think a lot ogf grease had tricked away as well.

Fortunately the bearings weres still operational so no shaft damage but this was a well overdue operation.

I am getting a new belt from AntiFriction - www.afc-uk.com. They were recommended to me and I was pleasantly surprised with the price and the fact they had the item in stock given it is a bit of an odd-ball belt on the lathe.

Should have the belt tomorrow so I can put it all back together and see how many bit I have left over.

BM

 

[CHJ]

Never had the shaft out of mine but basic practise with shaft bearings is:-
Tighten shaft/bearings clamp nut up firmly with spanner whilst rotating shaft by hand until it feels tight to turn by hand but runs smoothly. Undo nut half a turn, shaft should move freely.
Do nut up firmly by hand and lock.

This is an old thread of the assembly by a past member

 

[bogmonster]

Thanks for the help so far. Shaft and new bearing back in. Still sounds like a bag of nails. Damn, still not fixed.... The next problem is missing key on the motor side of the variable speed drive. One of the cones just spins and wobbles on the shaft. The key is supposed to slide with the cone so it should have pins which are also missing. On the other side is a grubs crew with a brass tip to take out slack. Brass tip fell off - my fault

Anyway. I don't think there is too much wear so off to see if my local machine shop can make a new key.

Makes you wonder what kind of numpty lost the key in the first place but decided not to bother replacing.

By the way, on the thin chance anybody else does a belt change, the original spec belt is no longer available from what I can find. A Gates 28x9x750 will fit ok though. The original belt, a 28x8x765 is strangely shorter :?

Anyway, the bearings are much better. Ran the lathe at full speed for the first time and no horrible bearing noise and no detectable heat build up.

BM

 

[bogmonster]

Almost there, new key machined. Custom job to take out as much slack as possible. While the motor is off I decided to take a look at the arcing in the motors centrifugal switch. The contacts are not in great shape so off to a motor repair shop. It looks like new contacts will not be available so they may fit an electronic switch. I beleive it uses voltage and current sensing to determine when the motor is up to speed and then electronically disengages the starter winding. This sounds like a far better system to me but still waiting for a quote. Don't want to spend too much more on this but at least the lathe will be in great working order.

Not sure it was one of my best buys but I will get there in the end....

BM

 

[CHJ]

While the motor is off I decided to take a look at the arcing in the motors centrifugal switch. The contacts are not in great shape so off to a motor repair shop. It looks like new contacts will not be available so they may fit an electronic switch. I beleive it uses voltage and current sensing to determine when the motor is up to speed and then electronically disengages the starter winding. This sounds like a far better system to me but still waiting for a quote. Don't want to spend too much more on this but at least the lathe will be in great working order.

BM

Be very cautious on the electronic starting configuration, make sure the module being fitted can have the start-up time scale adjusted.

Replacement motors with this type of starting often fail to work on older machines because they have a set starting time of X seconds before cutting out.

If as you say the unit trigger is power related as opposed to time you may well be OK.

If the motor mechanical load is such that it can't reach synchronous speed before the start winding is switched out it will just grind to a halt.
The slow speed 6 pole motor fitted to the 28-40 is a robust high torque beast but you need to get assurance that anything you pay for to be fitted will start it under load when say you have it set to a higher spindle speed.

.

 

[bogmonster]

Hi Chas,

I share similar concerns but I think these guys know their stuff. However I also didn't like the price they quoted me :shock:

I took the motor apart last night. I have cleaned up the contacts with abrasive paper and contact cleaner and to be honest I don't think they are too bad. The bearings are rough but these are easy to replace. The motor repair place wanted 100 pounds just to replace the bearings for what I think is probably 15 quid in parts and maybe 20 mins in labour - a bit steep I thought. Anyway, all back together (with original bearings for now) and all is running well. I have got a note of the bearing numbers now so I will order some up and replace one evening.

As for the switch, I think as long as I clean it occasionally, and especially if it starts to arc again, then it will go on for years. If it does die then I will consider an electronic switch at a later date.

I am going to be turning today so I will see how it performs.

This is the first time I have taken an induction motor apart and was surprised at how simple it was. If others have arcing contacts in old motors I would recommend cleaning them up sooner rather than later.

I don't want to spend much more keeping the lathe running as I am looking to replace it at some time anyway. However I intend to fund the new lathe through bowl sales and my bowl sale fund just got emptied on a bandsaw

BM

 

[renderer01]

Hello Bogmonster,
Just wanted to say well done on the rebuild, its a problem for me to carry out engineering work as I dont have a clue and I doubt I would ever be brave enough to attempt it.
One thing I understand implicitly is emptying the woodturning coffers for new equipment my new lathe arrives tommorow can hardly wait. Just pray nothing goes wrong for couple of months.

Rend.

 

[bogmonster]

Well, motor centrifugal switch is still playing up

I have been looking into fitting the electronic relay myself. There are a number of types. I think a potential relay is the best option. It uses back emf in the starter winding to disengage the start winding at the right point. Trouble is I don't know what the trigger voltage should be. Looks like it will be somewhere in the 350v ballpark. I have found a variable relay model made Supco. They have instructions on how to set correctly for a given motor.

My only concern is the safety timeout that kills power at 1 to 1.5 seconds. That does not sound long to get over the large inertia of a large lump of tree. I think it would work in all but the worst case scenarios.

Anybody tried potential relays ? I may just try, they are not very expensive. I wish there was a version with variable timeout as well.

If I knew the Back emf I could get a fixed relay with no timeout.

BM

 

[CHJ]

Worst case scenario you could always manually start with a momentary contact push button in the capacitor/starter wiring line instead of the centrifugal switch.
Hold down whilst you switch on and let motor get to speed.

Make sure the push button feed is motor side of the on switch, a bit of a fudge but if a centrifugal switch or a working electronic equivalent is not available then there's nothing to loose apart from needing a bit of extra dexterity if you can position the switches conveniently.

All precautions with wiring and switch housing to be observed of course.

Can you set the lathe to high speed and check the starting timing, or is it too unreliable?
On the subject of the electronic delay being adequate, given you would have it in slowest speed if you had a large lump on the lathe the motor may not have much more loading than when in high speed.

 

[bogmonster]

Hi Chas,

It has worked for 2 days with only one bad arc so I can easily play. On full speed with a light load (would not want to start at full speed with a heavy load anyway) I think 1 second will be enough to get up to 75% of full speed which is the target area. I hardly ever run the lathe at full speed anyway - occasional pen and even then 1800 RPM is plenty fast enough. I have turned some big bowls - OK, I have turned some stupidly big bowls given the size of the lathe And these can have a slow start up speed. To be honest I think I have probably had my fun with really big bowls so not sure if this is such an issue anyway. Not just that, nobody has room in their houses for monster bowls

My thinking is to spend 20 quid on the variable relay. If this works then great. At a minimum I should be able to work out the EMF using this. If it does not work under high load I can swap it out for fixed potential relay with no timeout function.

Buying 2 relays will still be far cheaper than getting somebody else to do the job and I may learn something. Also, I think the place I took the motor was going to go for a simple to wire up job with a combined relay and cap that simply takes the place of the starter cap. I don't think this is ideal because you end up with a less precise capacitor value and less precise relay trigger voltage. Result = additional strain on the motor and reduced life.

What the folks at the motor place did do was give the motor a good once over and the windings are in good order so if I can overcome this little bump then it should go on for years to come.

I will do my best not to electrocute myself and if I have any doubt will get my neighbour who is rather good at this sort of thing to give me some help.

I nearly bought a Union Graduate yesterday on evil bay. Was in the frame until the last 20 seconds. I knew my bid was far too low really but sometimes you get lucky...

BM

 

[CHJ]

Hope you don't have to hump that motor on and off very often, that's some brute. The 3ph 1hp unit on my machine is about half the size and weight, mind you the whole set of castings and accessories in the later machines are only about 3/4 of the weight of the older models.