[TheForge] Re: re-pouring bearings - a novel

Fri Nov 21 00:15:01 2003

Thanks for all the replies.  I will probably be re pouring the bearings next
week depending on what work comes in  the shop over the next few days.  In the
last few weeks I have been running stock through a planer and then truing it up
with a jointer plane.  Finding the time to pour these bearings and get the
machine set up will pay for itself quickly.
I had been leaning towards using the tin based babbit (more expensive must be
better) thank you  for setting me straight on the type I should be using Tom.

John

John

"[email protected]" wrote:

> > From: John Newman <[email protected]>
> > I bought a 12" woodworking jointer the other day and I think I am going
> > to have to re-pour the bearings in it.  I had a few questions for those
> > of you that have done it.  What is the best way to get the old babbit
> > out? melting with a torch, or chipping?  I am going to get a mandrel
> > turned to pour around, should I have collars machined in to act as a
> > dam?  And lastly what type of babbit would be good for this the local
> > supplier has about 20 grades of babbit.
> >
> > John
>
> Dear John. The torch is the fast way to get the lead out (so to speak) if
> you can do it safely, watch for popping and splattering when hot babbit
> meets trapped oil, you may have to chip some too. If some is stuck in the
> bottom, don't worry too much. If there are anchor holes, drill them out, so
> the new babbit will get in there.
>
> The rule of thumb for babbit is: for heavy load, slow rpm use harder (less
> lead) babbit, for lighter loads, high rpm use softer babbit (more lead).
> Jointers and planers would fall into the medium to high rpm category. Hard
> babbit is for steam engines, big slow pumps, hit and miss engines, etc., and
> the like.
>
> Even if you machine collars, you will still need damming material for a
> proper seal. Nothing more irritating than to have everything all set up and
> then watch all your fresh babbit dribble into the dirt. Use whatever you can
> rig up to hold the damming material in place, the clay stuff will melt and
> fall right off if you don't back it up, trust me on this. Don't try to fill
> a gap more than 1/8" with the clay, use leather or rope or wood or
> something, and use the clay as a final seal.
>
> In some applications with a lot of vibration, or if there is no good  way to
> anchor the pour, I will clean and degrease the box thoroughly, and TIN the
> interior or the casting with paste soldering flux, solder, and a torch. Once
> the interior is tinned, you KNOW the babbit will stick when you pour it in.
>
> Also, do not overheat the babbit. When a pine stick inserted into the ladle
> starts to char, it is hot enough. heat as quickly as you can because the
> molten babbit oxidizes quickly in air, and a skin forms. If you get a crust
> floating on top you are probably too hot and waiting too long. Skim quickly,
> and pour fast. The molten babbit should look clean and shiny, just like
> mercury. Always melt more than you think you need, so you don't come up
> short, or you have to start over. Much easier to file off a little extra
> than to start at page 1. Wear long sleeves.
>
> It helps a lot if you warm up the mandrel and bearing box a little, while
> the babbit is melting, otherwise they will chill the babbit so fast it won't
> make it into everywhere it needs to go. Heat at least until the dew is gone.
> If you overheat the mandrel, the babbit will take forever to set up, and you
> may melt out the damming stuff. I suppose that this might be obvious, but I
> must remind you that the machine needs to be sitting dead level when you
> pour the babbit, um, for obvious reasons.
>
> If the bearing is two pieces, pour the bottom first, then file it level with
> the box. Round the edges of the fresh bearing a little at the "seam". If you
> cut oil grooves, stop short of the ends of the babbit. I personally think
> babbit bearings run longer without the grooves, but that is another story.
>
> Add a 1/16 or more shim on both sides before pouring the top half, so you
> have room to scrape if necessary, and so you will be able to take up for
> wear later just by thinning the shims and scraping a little, rather than
> re-pouring.
>
> Check the fit with bluing, and scrape if necessary before pouring the top
> half. It is nightmarish to try to scrape the top and bottom simultaneously.
> If the shaft has two or more bearings, pour and scrape all the bottoms first
> until the shaft is perfectly fitted, then pour and fit the tops.
>
> If you soot up the mandrel with acetylene before installing, it helps keep
> the babbit from sticking. A micro-thing coat (just a smear) of high-temp
> neverseez can work too. Never use grease of any kind. On large dia.
> bearings, I have used a thin sheet of paper, rolled around the shaft and
> pasted. The paper chars away, and leaves a little clearance to get the shaft
> back out. You won't need this.
>
> If the bearing is one piece, or vertical, all the above still applies, you
> just dam, preheat and pour.  Wait until the mandrel and babbit are COOL and
> spray some penetrating solvent into the ends, and gently twist the mandrel
> to get it out. The mandrel will often stay hot longer than the pour, and be
> goodnstuck if you try to wrench it loose before it cools. Completely. Cold.
>
> Hope this is helpful. There are lots of ways that will work, these are just
> suggestions.
>
> Tom Troszak
>
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