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kenny_10
11th May 2014, 11:00 PM
Hi all.

How is the best way to tackle this problem of a worn bearing.. see pic.
Its the counter shaft bracket of a lathe I'm rebuilding.. I'm assuming it's made of cast iron ?
This is the side that takes the drive pulley.. other side is not too bad.

Kenny.

KBs PensNmore
11th May 2014, 11:22 PM
Is it possible to take a photo of the whole bracket? It makes it easier to recommend a fix, if people can see the whole thing. If the bracket can be removed, I would get it bored and then make a bush to fit with a new bearing.
Kryn

Bryan
12th May 2014, 05:40 AM
Yes, it would be cast iron. Looks like a job for a vertical mill and a small boring head. You might get away with a drill press and a 'super drill' http://www.woodworkforums.com/showthread.php?t=182477&p=1752707#post1752707. You would need to provide some way of piloting it. And you would have to figure out how to align it with the other hole.

Michael G
12th May 2014, 07:56 AM
An indication of size would be good.
It may have worn that way because of inadequate lubrication, so while it is in pieces check how lubricant gets in. It may be that you have a blocked grease nipple or something. If there is no grease nipple, it may be worth considering putting one in.
As for the repair, bushing and sleeving is what I'd do too. Probably phosphor bronze.

Michael

Hornetb
12th May 2014, 02:36 PM
I have the same problem in the same location on the countershaft of my Hercus 9a. I suspect that it is a combination of the belt to motor being perhaps a little too tight, but then it might have nothing to do with tightness as either way it is the bearing on the motor/pulley side that is going to take the angular strain, and lack of lubrication. My bearing has two oil holes in the top that you need to keep on top of with regard to lubrication and of course, once the bearing wears the oil is lost even faster.

Luckily for me I have another parts lathe with some flogged out countershaft bearings, what I planned to do when I got around to it was to bore the bearing out on the mill or even the lathe (hadn't decided which yet) and press fit in a 3/4" ID bronze bushing to suit the new countershaft I have here. I have two bushing so I get to have two goes at it if I stuff one up.

The part that I was mulling over was how to indicate the bearing block in true given the internal hole is flogged out and it isn't a precision round part on the OD. The ends of the bearing block "might" be perpendicular to the hole but to be honest I haven't looked that close yet.

My situation is perhaps a little easier as they are only small blocks, while yours looks like a larger odd shaped part.

nadroj
12th May 2014, 02:57 PM
The part that I was mulling over was how to indicate the bearing block in true given the internal hole is flogged out and it isn't a precision round part on the OD. The ends of the bearing block "might" be perpendicular to the hole but to be honest I haven't looked that close yet.


The Hercus has semi-floating (pivots in one plane) and adjustable countershaft plain bearings. That makes it easy to fix - just make it approximately right and install it with the provided adjustments.
It's a very well thought out design.

Jordan

kenny_10
14th May 2014, 08:08 PM
An indication of size would be good.
It may have worn that way because of inadequate lubrication,
Michael
Michael.
The shaft is approx 19.1 mm dia.. It appears the machine has been starved of oil for some time.. all oil holes on the lathe were caked with dirt and metal.
The easiest solution is your bush..just have to work out how to hold it so I can bore it in line with the other side.
The other alternative is to enlarge the worn section and braze in an appropriate sized plug of cast iron. This will overlap the original hole and will be mostly removed by boring.
Ken

nadroj
14th May 2014, 10:37 PM
I'd try to mount it to a lathe cross slide, and use a boring bar between centres.
The challenge would be to ensure the holes end up parallel to the other pair of holes in the bracket.
Maybe a bar could be put through those holes, and this could be tested with a bed-mounted dial indicator.

Jordan

Michael G
14th May 2014, 10:53 PM
The easiest solution is a bush..just have to work out how to hold it so I can bore it in line with the other side.


A between centres boring bar would do it, but you probably haven't got a spare lathe around to do it on.

My method (not necessarily the best one but one that I think would work for me) would be to bore out the hole so it is round again and then bush it. Make the bush with a hole smaller than finished size and then using an adjustable reamer with pilot (that last bit is very important), take the hole out to its finished size. The adjustable reamer size that has 3/4" in its range starts at 23/32", so I'd have the hole in the bush around that size to start with.
Securing the bush is probably best done with some bearing locking adhesive (remembering to let it set for at least a day before trying to ream it). For added security you could do a scotch key as well.
Provided that your initial boring out to size is reasonably well aligned with the existing hole, the bore in the bush will be close to aligned and using the pilot on the reamer will get it pretty much spot on.

Michael