Thread: Bronze bush. What type of bronze?

Hi all,

I am looking at bushing the shafts on my norton style feed gearbox on my 12x36 chinese lathe. It is noisy in operation and there is excessive wear on either the shafts or in the cast iron where the shaft moves on. I wish to machine these out and replace with a bronze bush. I have done a search here on bronze bushes but I am none the wiser other than I now know there are numerous types of bush material, being lead, phosphor and/or sintered. Doing a google search revealed that you can also get an oil impregnated bronze bush material too. Given that I am only going to need a small amount, I don't think cost would be a factor.

Given it's a rather basic, slow reving piece of equipment, will any type do? I mean anything would have to be better than steel on CI for a bearing?

Once again, thanks for your help in advance.

Simon

Hi Simon,

Why not ball bearings, one of the casting cracked on mine and I had to make a new selector.. it uses ball bearings..




Regards
Ray

Originally Posted by RayG

Hi Simon,

Why not ball bearings, one of the casting cracked on mine and I had to make a new selector.. it uses ball bearings..




Regards
Ray

HEY now your talking! That was my first thought. If I had it my way I would replace all with sealed bearings and remove the need to oil them. However I thought that there would not be enough meat in the casing or room between shafts to allow for machining to the outer race size.

Obviously I would need a ball bearing that has a small as possible outer race for the size of the shaft. That would require very small balls

Exactly which bearings did you replace? Looks like you made a new selector as well? Looks great!

Thanks for your reply Ray,

Simon

Is the damaged or worn area on the shaft going into the gearbox or is the wear in the selector lever?
In regards to the type of bronze you want to use for this application,it really wouldnt matter.
If you were able to find some old water valve shut off spindles of a suitable diameter they would be fine,other wise the amount you are looking for the cost would be minimal.

Simon, if it were me I would use whatever my local bearing shop had in the nearest size. Which would probably be a plain phosphor bronze. If you have a choice, and you think lubrication may be sporadic, oil impregnated would be nice I guess. I believe cast iron actually makes a pretty decent bearing as it contains graphite.

Originally Posted by Bryan

I believe cast iron actually makes a pretty decent bearing as it contains graphite.

Well there you go. I learn something every time I go on this site. Cheers,

Simon

Originally Posted by pipeclay

Is the damaged or worn area on the shaft going into the gearbox or is the wear in the selector lever?
In regards to the type of bronze you want to use for this application,it really wouldnt matter.
If you were able to find some old water valve shut off spindles of a suitable diameter they would be fine,other wise the amount you are looking for the cost would be minimal.

Hi Pipeclay,

The selector levers seem OK. The shaft that the selector levers are on use ball bearings at each end. I have since replaced those with japanese bearings. It is mainly the input shaft that has the bottom change gear on it that picks up the feed from the headstock gear and a second shaft that has various sized gears (with a keyway) on it that seem to be worn.

I will probably make more sense when I have a chance to remove it from the lath again. I'm at home with man flue at the moment so I'm not very active.

Cheers,

Simon

G'Day Simon,
Once you get the gearbox apart you may find the bushes are standard off the shelf sizes that a local bearing supplier carries ( or can order in ) this saves a hell of a lot of work.
In my case it worked out a lot cheaper to buy the longest bearings I could find and part them off to the required size.
Regards,
Martin

Originally Posted by toolman49

G'Day Simon,
Once you get the gearbox apart you may find the bushes are standard off the shelf sizes that a local bearing supplier carries ( or can order in ) this saves a hell of a lot of work.
In my case it worked out a lot cheaper to buy the longest bearings I could find and part them off to the required size.
Regards,
Martin

Hi Martin,

I had thought of that but I have just assumed (at this stage) that the shaft must have wear as well as the cast iron. In which case the shaft may need a small amount of machining, especially if it is no longer round. Doing so would mean a slightly oversized (from standard) bush would need to be made.

Perhaps I am incorrect. Under "normal" conditions, does the outer bush or bearing tend to wear much more than the shaft itself?

Once again, until I get it apart and take some readings, it's all speculation at this stage. I would like to have 90% of it planned out before I take it apart but I think it may not work that way!

Cheers,

Simon

Hi Simon,

I didn't fit the ball bearings, that was factory original, I think it would be a bit tight for room anyway. I'd stick with bushing. I did make the new selector though.

One of the properties of Spheroidal Graphite cast iron, is that the excess carbon forms little balls of graphite, which is one of the reasons why cast iron wears so well in machine tool applications. It is also very stable, even more stable if aged for a few years.

Regards
Ray

I have heard of a few people putting a bush or bearings in the tailstock end support as well, some of them have had a lot of wear.
I have been thinking about it, but mine are fine at the moment because I keep them oiled well.

Dave

Originally Posted by RayG

Hi Simon,

I didn't fit the ball bearings, that was factory original, I think it would be a bit tight for room anyway. I'd stick with bushing. I did make the new selector though.

One of the properties of Spheroidal Graphite cast iron, is that the excess carbon forms little balls of graphite, which is one of the reasons why cast iron wears so well in machine tool applications. It is also very stable, even more stable if aged for a few years.

Regards
Ray

Hi Ray,

I thought the same thing so I think I will be looking to re bush where I can. I'm assuming the assembly would be too large and have too much mass to do it on the lathe so the project will have to wait until I have a mill. I think if I look after the lubrication side of things then bronze bushes will be more than sufficient.

As for the properties of cast iron, I just assumed that the cheap castings on this machine would not be SG iron. But as per usual I learn something new every day on this forum. The members on here are amazing and so willing to give up their knowledge and experience. It's a steep learning curve when self teaching about machining but it's an even steeper learning curve when it comes to machine tool improvement/repair.....

Hi Dave,

I have also looked at fitting bearings to the rear mounting of the leadscrew and saddle drive shaft. There is plenty of material there to fit some bearings. There is some play there on mine but it is of little consequence at the moment. I wonder if the people who fitted bearings machined down the shaft to fit a smaller bearing or just fitted a bearing that fits directly over the leadscrew shaft?

Cheers,

Simon

Hi All
Just to add a little to this Thread. I have had lots of success using needle roller bearings to replace bronze. They are available in a great range of sizes and types, even fitted with seals. Hardened steel runners are also available for the bearing to revolve on, these can be fitted with Locktite to the shaft making the whole thing repairable.
Cheers
Ray

G'Day Fellas,
Just to elaborate a little, when I rebuilt the gearbox on my previous lathe I replaced the mild steel shafts with new ones made from ground silver steel, so the fit of the off the shelf bushes was pretty close to perfect. I cut oil thrower grooves inside the bushes (.002" cut @ 8 TPI with an internal threading tool then reamed), each of the gears had a spacing collar at one end with a miniscule oil hole, these were drilled out to 2 mm to give the oil some chance of circulating. With any luck the gearbox should outlast the rest of the lathe.
I should add that at the time I had my new lathe up and running so I wasn't under any pressure and could (and did) take my time on this project.
Regards,
Martin

Thanks Ray, That sounds like an inviting proposition. I will investigate that idea further.

Hey toolman, you really have outdone yourself with that one!
I have been wondering how the gears get lubricated. The oil holes direct lubricant into the shaft bearings and then it gets dispersed by a worm thread arrangement that is machined into the shaft. So the oil flows along the shaft but there does not seem to be any way that the oil finds its way into the gears. I'm thinking of drilling some more oil points above the gears....

I'm keen to improve the lubrication system BEFORE I re bush ANYTHING otherwise it will be for nix!

Cheers,

Simon