Bearing fit

Munroast · 19 Mar 2021

I am replacing a small bearing on an 8mm shaft (it is a guide on a band saw). The knackered bearing was an interference fit. It's replacement is just a tad loose (I measure them both at 8mm), there is no play, I can't see light through the gap...

I have manage to get it on tight-ish with a single layer of ptfe tape.

Could there be a better way ?

Would 'thread lock' work ? not really keen to spend a fiver on some thread lock to secure a £1.70 bearing, but would it work better than ptfe

Bodgedbuild · 19 Mar 2021

If the shaft isn't too hard, tap it with a centre punch which will create a dimple with a raised edge. Use Locktite stud and bearing fit for good measure but a centre punch mark should ensure the bearing is tight

jj4091 · 19 Mar 2021

Get an imperial bearing. 5/16 inch

Belle427 · 19 Mar 2021

Loctite retaining compound is made for this job but as you say not cheap.

sxturbo · 19 Mar 2021

If bearings are slightly loose on a shaft you should use bearing retaining compound. Loctite 620 or something like that.

(Loctite do a lot of different bearing retaining compounds)

Munroast · 19 Mar 2021

Bodgedbuild said:
If the shaft isn't too hard, tap it with a centre punch which will create a dimple with a raised edge. Use Locktite stud and bearing fit for good measure but a centre punch mark should ensure the bearing is tight

As in the end of the shaft in hope to splay the shaft a little (I would worry I may bend the shaft a little), or do you man on the contact side, (which seems a good idea, and a cost effective one.).

Belle427 said:
Loctite retaining compound is made for this job but as you say not cheap.

That is the term I was looking for, thanks, I suspected there would be a special something for the job.

Think I will just go with the PTFE tape that I tried last night, seems to be holding it well, if it fails I will try something else, the bearings are only £1.70 so no big loss.

It does not seem to be the best of designs to me, surprised it has ever worked well (which in fairness it has). As you can see it is the back support for the blade, this is well and truly bolluxed.

frutbunn · 19 Mar 2021

Just out of curiosity what make of bearing are you using, there is some absolute s***e out there made to any old tolerance. Shouldn't that bearing have shields in as well.

cdbe · 19 Mar 2021

I've successfully sleeved the hole for a bearing with a bit of beer can - it was my Bosch drill and the bearing had seized and the whole thing had spun and worn the hole slightly oversized. Lasted the life of the drill. I think it was Carlsberg!

Munroast · 19 Mar 2021

frutbunn said:
Just out of curiosity what make of bearing are you using, there is some absolute s***e out there made to any old tolerance. Shouldn't that bearing have shields in as well.

an Ebay special for £1.70 inc postage - LOL

Yes it is a double Z shielded bearing, I guess the original shield long since disintegrated. they have even started to chew through the ball bearings. Presumably if I hadn't said "thats not working properly" the enire bearing would have been consumed.

Anyway, the new bearing is in and it is working just perfectly,

Burnerman · 19 Mar 2021

Just wondering if you are running the blade a little slack, or maybe its blunt to put so much pressure on the bearing face?
John

Munroast · 19 Mar 2021

Burnerman said:
Just wondering if you are running the blade a little slack, or maybe its blunt to put so much pressure on the bearing face?
John

It could have been both of them, blade was in the correct way though - It is not a machine I have used much and when I went to use it last week the noise it was making prompted me to take a peep inside. The side guides were also chewed to buggery and screws missing. Just total lack of care and probably zero understanding of how to set it up

frutbunn · 19 Mar 2021

Munroist said:
an Ebay special for £1.70 inc postage - LOL

That probably explains it. I rebuild quite a few scooter engines, bike hubs as well as 4x4 gear/transfer g/boxes, only ever use European or Japanese ones from known manufacturers. Next time either measure the bearing, look for the bearing number or take it along with you and buy your bearing from a proper bearing stockists. When I rebuild anything, any dubious bearings are thrown away regardless of condition. One of my own engines had previously been rebuilt with Russian bearings and had done virtually no miles since its rebuild, hadn't even been run in, they still went straight in the scrap pile.

Burnerman · 19 Mar 2021

Munroist said:
It could have been both of them, blade was in the correct way though - It is not a machine I have used much and when I went to use it last week the noise it was making prompted me to take a peep inside. The side guides were also chewed to buggery and screws missing. Just total lack of care and probably zero understanding of how to set it up

Don’t want to show grandma how to suck eggs, but I set the blade guides with around 1/2mm clearance and make sure the blade always rides on the top of the crowned top wheel. Tension wise its a bit of a lottery but the blade shouldn’t whine or contact the bearing in normal use.
John

Bodgedbuild · 19 Mar 2021

Munroist said:
As in the end of the shaft in hope to splay the shaft a little (I would worry I may bend the shaft a little), or do you man on the contact side, (which seems a good idea, and a cost effective one.).

On the side, a similar thing is done with valve guides on a car cylinder head if they are not tight and there is not enough "meat" in the head to ream out and fit guide inserts. An engineering shop will Knurl the guides to create a trough with a raised ridge. it works well because it also acts as an effective route for lubrication.

Harry Bloomfield · 19 Mar 2021

Munroist said:
Would 'thread lock' work ? not really keen to spend a fiver on some thread lock to secure a £1.70 bearing, but would it work better than ptfe

You can buy 'bearing fit' from the thread locker source. That should do it.

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Bearing fit

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