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

[info@reciprodyne.com]

> From: John Newman <johnnewman@sympatico.ca>
> 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