Colchester Student Gamet bearings preloading technique

[prepman]

There seems to be scant information on the correct way to set the preload on these bearings, specifically on the Colchester Student.
I found vague references to it. Most refer to the heating effect of the preload, but none give the means of getting there.
As the replacement is the cost of a kidney, a less ambigous approach is required.
Has anyone in the forum done it and have a procedure?

 

[Lewis_RX8]

Interested to see what you find here , I also looked around and found it hard to find any real figures for play or measurements especially hard to find anything from Colchester themselves

On another fourm someone said Colchester liked to get service calls out to fix these issues so that may be it

 

[mcostello]

As an aside, I have a Colchester Triumph. I have trouble with it turning a taper. It is not setting parallel to the ways and needs fixing. When trying to diagnose the problem,(post here somewhere) I took the spindle apart and checked the bearings. Nothing wrong and noticed that there was 24 holes for preload springs and only 20 springs. Ordered a set of springs ($250+USD), The spindle did not overheat and it took out most of the taper, from .012 inn 2", to .002 in 2". Was not supposed to be needed but it helped. Now to get that last few thousands out.............

 

[prepman]

As an aside, I have a Colchester Triumph. I have trouble with it turning a taper. It is not setting parallel to the ways and needs fixing. When trying to diagnose the problem,(post here somewhere) I took the spindle apart and checked the bearings. Nothing wrong and noticed that there was 24 holes for preload springs and only 20 springs. Ordered a set of springs ($250+USD), The spindle did not overheat and it took out most of the taper, from .012 inn 2", to .002 in 2". Was not supposed to be needed but it helped. Now to get that last few thousands out.............

According to the little info I've gleaned, it's the rear bearing that has the springs? The front is double taper roller. The bearing nut at the head stock seems load bearing up going by temperature. Can you elucidate?

 

[addjunkie]

Dont know about your lathe, but on big rotating machines an allowance for thermal expansion is often built in, and allowed for in alignment.

 

[prepman]

Dont know about your lathe, but on big rotating machines an allowance for thermal expansion is often built in, and allowed for in alignment.

It's specifically this Gamet bearing.






I'm familiar with large machines 10,000HP and upwards and they were all pressure fed plain bearings are you are refering to lathes only?

 

[prepman]

Interesting discussions....I'm also a member of this site.

404 | Model Engineer & Workshop Magazine

It looks like we've lost a piece!404: Page not found This page could not be found. Maybe try a search? If it's a forum topic you are looking for, ...

www.model-engineer.co.uk

Chipmaster...... https://www.model-engineer.co.uk/forums/postings.asp?th=137982

 

[Stupoty]

This may be superfluous info but it's good to take the chuck off when doing the preload as all that mass can make it seem like there spinning smooth but actually they are a bit tight.

For my taper bearing lathe I took it to a very slight drag then backed it off a bit ran the spindle for a bit to get it warm and checked how tight they were after that, if still lose then I snugged it up a bit more.

There should (generally) be a small amount of drag as far as I understand, it shouldn't just keep turning forever like a spun bike wheel.

You can put a long bar in the chuck and try to pull the spindle in different directions to see if you can feel it moving after setting the preload, if you can feel clicking or a movement then it's too lose.

If they are too tight then they will heat up quicker and maybe lock up (but they should heat up way before locking up, little adjustment steps and all that)

Stu



(mileage may vary caveats apply)

 

[prepman]

This may be superfluous info but it's good to take the chuck off when doing the preload as all that mass can make it seem like there spinning smooth but actually they are a bit tight.

For my taper bearing lathe I took it to a very slight drag then backed it off a bit ran the spindle for a bit to get it warm and checked how tight they were after that, if still lose then I snugged it up a bit more.

There should (generally) be a small amount of drag as far as I understand, it shouldn't just keep turning forever like a spun bike wheel.

You can put a long bar in the chuck and try to pull the spindle in different directions to see if you can feel it moving after setting the preload, if you can feel clicking or a movement then it's too lose.

If they are too tight then they will heat up quicker and maybe lock up (but they should heat up way before locking up, little adjustment steps and all that)

Stu



(mileage may vary caveats apply)

Thanks. Yes it sort of confirms the findings on the web. If these bearings weren't so ridiculously costly it wouldn't be a great issue. I'll take the chuck off and try. I need to see where chuck runout is coming from anyway. It's had a few heavy collisiond recently as the feed lever was jamming when heavy load and couldn't release it. Hopefully slackening the shaft clutch wayyyy back will stop a re-occurence.

 

[daedalusminos]

Have you contacted the 600 group, found them to be very helpful in the past

 

[Lewis_RX8]

Have you contacted the 600 group, found them to be very helpful in the past

Good idea , Worth a email or phone anyway

 

[Carl Wilson]

I don't know if this'll help. Maybe not. On my Harrison lathe, which has Gamet bearings too, the procedure given in the manual is to wrap string around the spindle at the camlock hub, then pull with a spring balance to check the bearing static friction. In other words, the point where the spindle starts to turn.

There are figures given in kgF for the amount of static friction then you adjust the bearings to achieve that.

I have never adjusted mine, but I think if I had to I would tighten them both up as much as they would go. Then you know you are starting with both at the same point. Then gradually back both off the same amount, say 1/4 or 1/2 a turn, until the figure on the spring balance is correct.

 

[Laurie Tedcastle]

Good idea , Worth a email or phone anyway

Gamet bearings is now a division of HB Bearings of Holmfirth. They are very helpful.
The following may be of interrest:-

There's some tech info in the Gamet brochure.

Laurie

 

[mcostello]

My front bearing is single taper, no double, no front adjustment nut. Rear bearing does have the springs. Did not take off the chuck, did not know of it. It's been on there about 5 years with moderate use so must be no problems.

 

[prepman]

My front bearing is single taper, no double, no front adjustment nut. Rear bearing does have the springs. Did not take off the chuck, did not know of it. It's been on there about 5 years with moderate use so must be no problems.

Yes some were like that. They went to double taper front to take the headstock casting (expansion) out of the equation apparently. It's a bit of an enigma as the rear sprung bearing will still tension the front section of the front taper (as yours) and the nut tightens up the rear taper of the front bearing. So if I've got it correct, it is forward endfloat that is controlled by this and the bearing is pre-loaded to greater load than it will experience.
I like to understand the logic behind it then everything falls into place (hopefully)

 

[prepman]

The reason why my tailstock alignment check was wrong. Not the usual centre I use. Put it in the headstock MT.

 

[prepman]

As an aside, I have a Colchester Triumph. I have trouble with it turning a taper. It is not setting parallel to the ways and needs fixing. When trying to diagnose the problem,(post here somewhere) I took the spindle apart and checked the bearings. Nothing wrong and noticed that there was 24 holes for preload springs and only 20 springs. Ordered a set of springs ($250+USD), The spindle did not overheat and it took out most of the taper, from .012 inn 2", to .002 in 2". Was not supposed to be needed but it helped. Now to get that last few thousands out.............

I am on the horns of dilemma. I don't really want to take the spindle apart to investigate, but like all old lathes it's history is shaded in mystery. There were lots of things amiss, which I've fixed one at a time. But the amount of taper seems to be inconsistent. For all I know there maybe no springs at all. It's certainly been messed around with over the years.
The problem with ball and roller bearings is that it's the cage that does all the work. The balls or rollers take the weight. The more they're tightened the more load on the cage. These bearings must be designed to allow for this wear and therefore adjustable?
I'm assuming that springs pull/push the shaft backwards against the front rollers?
I just don't like mysteries.

 

[Martin-Sy]

Which Student model is it that you have.
AFIK the round head versions do not use spring pre-load whereas the Student 1800, Master 2500, Triumph 2000 do.

From the Round head student manual:

HTH.
Martin

 

[awemawson]

Most precision spindles allow for growth due to thermal changes away from a fixed point. So the Colchester spindles, as I understand it, have the front taper bearing set to a pre-load, and the rear bearing has the springs so that the spindle can expand as it warms up against the springs.

 

[prepman]

Which Student model is it that you have.
AFIK the round head versions do not use spring pre-load whereas the Student 1800, Master 2500, Triumph 2000 do.

From the Round head student manual:

View attachment 327011


HTH.
Martin

Yes I have that diagram. But there are anomalies in other areas with manual. Don't be offended but have you actually had the spindle apart? Parts of mine are in the Clausing manual and not in this. The tailstock and the apron is similar (pre-safety).
It's looking like curiosity will win out, I think, and force me to dismantle it.