Thread: Thrust on plain bearing lathes

PDW, to make it very clear, the bearing surfaces are cylindrical, not conical. Thrust is causeing the rear bearing to close up around the spindle.

There were never any shims in the splits in the bushes, but now it seems like there should be.

Hi Phil,
What part of my very poor explanation do you not get?

Hi Ewan,
Bare with me as I am disgusting at explaining things. Your explanation is pretty clear. It seems to me that the bore of the bush is parallel, and the outside of the bush is conical to match the headstock. This is a split bush so there are two halves with the split running parallel to the spindle. Where the two halves of the bush meet there SHOULD be shims so that there is clearance for the spindle and when the conical bush, ie the two halves with the shims are forced into the conical hole, it can't go any further. The same as putting a larger taper into the hole, it won't go in as far but the bearing wont close up on the spindle and bind because the shims are holding the halves apart.

Phil

Gotcha Phil.
I've just machined an LG2 washer and put it behind the spindle nose and also removed the thrust race. It seems to have made a huge difference. I will try shimming the bush though and putting the thrust bearing back in. Pics tonight.

Good evening just been reading through your woes with your Mars.There is a Mars here and close at hand is on the resto 'to do list'.
As i see now you have grasped the mod to the thrust brg.Iwill check this one and see if it has been modded.
There is a New Visby here with the same type of adjustment bronze cones many years ago we refurbished the head stock on that and it is shimmed with a t brg on the change gear end of the h/s spindle. will let you know what I find with the Mars. Its actually a Great Scot forgot to mention earlier. John.

Hi John,
Thanks for replying. I'd be very interested to see what your machine has. I know mine has been messed with in all sorts of area's so it wouldn't surprise me if the bearings were modified too.
The washer was a bit of a try it and see scenario, it certainly was better then the machine as it was, but i don't think its a long term solution.
However, the biggest cause of the problems came to light this arvo whilst messing about before i had started to shim the bearings. I had a bar in the chuck and an indicator on the top of the chuck to check play. With a reasonable force i could clearly feel the play in the bearings and adjust it out so i could use feelers to get an idea of the shims required. However, for a reason that unknown, i gave the bar a bit more oomf and before i knew it i had movement more than the Zentimess could handle. The whole bearing was moving in the tapered housing. Of course if it were shimmed and tightened it would not move at all.
I will shim them up and re-assemble, then see how she goes.

Looking good Ewan, I think you might have this one sorted.
Thanks for the pics.
By the way, the best way to set bronze bushes is with leads, pronounced like a lead pencil.
They are a waxy type of plastic now but they used to be bits of lead wire of a set diameter and when the bush was tightened down
they would flatten out to a certain width which would then equate to the amount of clearance between the bush and journal.

Phil

Originally Posted by Steamwhisperer

Looking good Ewan, I think you might have this one sorted.
Thanks for the pics.
By the way, the best way to set bronze bushes is with leads, pronounced like a lead pencil.
They are a waxy type of plastic now but they used to be bits of lead wire of a set diameter and when the bush was tightened down
they would flatten out to a certain width which would then equate to the amount of clearance between the bush and journal.

Phil

Plastigauge is the name I'm familiar with for that. Very, very old memories of using it to set bearing clearance on my hotted up Honda 500/4 motorbike.....

PDW

That's the name I was trying to think of, it bugged me all last night! Be easier than feelers and then trial and error.