Milling Babbitt

[cdlenterprises]

Anybody ever have to mill babbitt? Any recommendations on tool geometries?

[HuFlungDung]

Ya, I just use the same tooling as I do when milling lead

[Kipper]

Originally Posted by HuFlungDung Ya, I just use the same tooling as I do when milling lead

:rofl:

[NC Cams]

Seriously, babbit is an alloy of lead, tin, bismuth and sometimes copper and antimony.

Although there was ROFL when the comment of lead machining was made, in all seriousness, machining babbit is pretty much like machining/milling lead - it all depends, however on WHICH alloy of babbit that the member is trying to machine.

If it is bearing babbit (probabably), you'll end up seeing lead or tin based babbit. They should maching pretty much alike unless there is a lot more alloy material as opposed to a predominance of lead. Perhaps with some more information or material confirmation, more specific info (speeds, feeds, tool geometry and such) can be provided.

If bearings are the trying to be machined, not just any geometry will work. The wrong geometry and/or speeds/feeds will tear the material instead of cutting it which can ruin the finished bearing properties.

[Geof]

Originally Posted by cdlenterprises Anybody ever have to mill babbitt? Any recommendations on tool geometries?

I have turned and bored babbit on a lathe and found that a tool with extreme rake worked best; it was more or less slicing the material off. I also used kerosene as a cutting fluid.

Based on this if I was milling I would use the high helix micrograin carbide cutters designed for aluminum because they effectively have a large rake. But I am not sure about filling the cooolant tank up with kerosene; your insurance company may object when you burn the building down so I would stick with a regular coolant.

[cdlenterprises]

Wow, judging by the first two responses, I must be the only one in the world that has actually machined lead and is attempting babbitt . Actually it is bearing babbitt and the application is for hydrostatic bearings for hi-speed impellers. the design calls for three off-center arcs to cut on the ID. This process has been in use for many, many, many years. I just kind of inherited it. They are basically "milling" with a 4 flute carbide reamer that has provided satisfactory results until recently (we're getting what looks like fine chatter on the bearing surface - big ) My first thought was to take a diamond file and break the cutting edge of the tool since the material is so soft it would take 532 years for the edge to wear in itself. It's working OK so far but I'm thinking of redesigning the cutter. Just looking for some suggestions. I like the idea of adding rake. I think I'll also try specifying a .001-.002 cylindrical land to add a burnishing effect.

Now it's time for another beer to dream up some more entertaining (ridiculous?) questions.....

[NC Cams]

You are not the only person who's ever machined bearing babbit - I worked for a VERY well known bearing company that did it on a production basis, and as I indicated in post #4, there are some considerations needed to PROPERLY machine it - as in cut it without tearing it, which is easy to do unless you use the proper speeds, feeds and tool geometry. Not only have I been involved with babbit machining but also the machining of lead based bearing bronze which also is VERY technique sensitive.

It would be nice to know which bearing alloy is being used - as in lead or tin based babbit. They each have their idiosyncracies with regard to machining. When you use the proper techniques, you'll readily generate mirror like finishes and bearing surfaces that will wear well and conform to the shaft as needed. Do it wrong and you'll have a sloppy fit and a poorly performing bearing that could be siezure prone.

I'll check my reference materials as I do have the info for precision boring of leat based babbit - it should work for tin based babbit with care. SHould you have an alloy that is contaminated with copper or other alloys that result in a "harder" alloy, you may have some issues to deal with that you'll have to work out on your own.

CAUTION: since lead is probably going to be contained in ANY babbit you're working with, you'll need to take appropriate breathing protection - other protection for hazardous material machining is also advised.

[Adobe Machine]

wow, I was taught how to scrape babbit ( as in 6 cylinder chevy's, Dodge and others of that era..) My boss, mentor could pour and scrape 2-3 engines a day, not ever having to use more than .001-.002 shims for correct fit.

I was pretty young at the time, and my job was to pull the oil pans/heads and reassemble with adjusting the valves, but I remember how nice and smooth the bearings looked when he was finished, his tool was a re-worked file with a taped handle..really a lost art.

I did have a babbit bearing lathe that in fact I poured and fitted the headstock bearings..But I kinda cheated and honed the bearing to exact size, after a couple of trail fits, the lathe was smooth and would give a good finish...

Did not mean to hi-jack a thread, just never thought babbit bearings would be machined.

Adobe (old as dirt)

[Kipper]

Originally Posted by NC Cams Seriously, babbit is an alloy of lead, tin, bismuth and sometimes copper and antimony. Although there was ROFL when the comment of lead machining was made, in all seriousness, machining babbit is pretty much like machining/milling lead - it all depends, however on WHICH alloy of babbit that the member is trying to machine. If it is bearing babbit (probabably), you'll end up seeing lead or tin based babbit. They should maching pretty much alike unless there is a lot more alloy material as opposed to a predominance of lead. Perhaps with some more information or material confirmation, more specific info (speeds, feeds, tool geometry and such) can be provided. If bearings are the trying to be machined, not just any geometry will work. The wrong geometry and/or speeds/feeds will tear the material instead of cutting it which can ruin the finished bearing properties.

I was grinning with him not at him...Made me grin anyway Not a lost art completely as it still has to be done with some old motors.

[NC Cams]

Traditionally, babbit is machined or scraped. Anymore, however, the machining is done via precision boring (as Clevite used to do) or broaching (as done by DAB and some of F-M's bearings). Both methods have their benefits and liabilities.

Precision boring offers some flexibilities that broaching does not, especially when you run intentional eccentrictity (out of roundness) in the bearing bore. When you bore, you typically bore round unless you intentionally bore into a out of round housing fitted shell or force the cutter axis to approach the bore at a slight angle to generate an intentional elliptical path. When you broach the bearing, you have to shape the broach for each bearing which makes for expensive tooling. I personally favor precision boring but a lot of very good bearings are/were broached over the years.

Elliptical bores are beneficial to a con rod, especially if the cap and/or big end of the rod is flimsy. The bore WILL pull out of round at high speed due to inertial loading. By making the bore out of round/elliptical by as much as 0.002" (larger from 12 to 6 o'clock as compared to the diameter from 3 to 9 o'clock), you can actually improve the siezure resistance of the bearing - especially at high speeds or under trailing throttle/engine braking situations.

Clevite at one time sold a "Deltawall" bearing which offered a unique application of non-symeterical bearing walls in concert with eccentricty which did a lot to help race engine bearing life. GM's Moraine Div used to use a "con ecc" (concentric/eccentric) bearing which came at the same problem in a slightly different way.

I don't know if either feature is still offered but, if you are boring/scraping bearings, it may not be in your better interest to make a perfectly round bearing surface. In an economy of words, GOOD bearings are NOT necessarily round. And highly stressed bearings are most certainly NOT round either.

[Adobe Machine]

NC Cams..You are right..I'm using some TRW "Race Bearings" that you in fact helped develop years ago..These bearings are a "harder" material than stock bearings, thus requires a forged crankshaft and I do like .001 more clearence than stock with a Blower motor.

I understand that the drag racers are using these bearings with even bigger clearences than I do, plus very low oil pressue to lower parisitic drag..it would scare me, but have seen some fuel (nitro) and alcohol motors do this and the bearing will last a lot of races..

Adobe (old as dirt)

[NC Cams]

Essentially there are 3 commonly used babbit materials. They are SAE-12 (tin based), SAE-13 (Lead based, harder) and SAE-15 (lead based, softer).

The "harder" #13 lead alloy has a different alloy content which gives it a bit more strength and corrosion resistance than its "softer" brother.

The tin based babbit offers better "surface properties" than lead. This is a dimensionless yet relative ability of the material to carry load while not deforming and/or siezing or scuffing while rubbing against the crank under marginal lubrication situations or under severe detonation-like load conditions.

Back to the original question, that of machining. When machining babbit, you want to use the following conditions:

Surface footage = 1000 SFM or faster
Depth of cut = 0.005 to 0.010"
Feed per rev = 0.003" to 0.005"
Nose radius = 0.030" to 0.080"
Back rake = 0 to 5 deg
Front clearance = 2 to 4 deg
Side clearance = 3 to 5 deg
Place the tool ABOVE the part C/L by 1/32" to 1/16"

Cutting or burnishing fluids:
Lead based babbit: can usually be cut or burnished dry due to self lube characteristics of lead.

Lead based babbit, alternate: use kerosene or a mixture of 96% mineral seal oil & 4% Anglomol 40 (chlorinated paraffin wax).

Tin based babbit: mixture of 60% Castor oil soap, 12% glycerine and balance water, diluted to suit the job.

Tin based babbit, alternate: 6% lard oil, 4% chlorinated lard with balance light filtered spindle oil (as in Mobile Velocite, use a low/lowest viscosity grade).

If you can NOT meet the preferred surface footage, a reduced cutting depth will be necessary.

The surface finish will not be "mirror like" with the above specs. You will see a "grain" or grooved pattern which should be in the 30AA range. Surface "grooving" is desireable as it holds and channels oil which aids in the development and maintenance and retention of an oil film in the load zone.

Clearance = a "thumb" rule is that you run 0.001" of clearanc per inch of journal diameter. This does NOT mean however that you run 0.010" clearance with a 10" diameter shaft. Clearances at or above 0.003" (regardless of shaft size) tend to really place a high demand for oil from the pump, which if can not be met by the pump, results in low oil pressure.

For drip fed oil systems (oil is fed to the clearance space by runoff feed and clearance controls oil feed rate), clearances of 0.0005" to 0.00012" will suffice. These usually use/need low viscosity "spindle oil". For higher clearances and/or pressure fed systems, higher viscosity spindle oils or Dexron III provide good lube films and stable/low vibration spindle operation.

High clearances do wonders for keeping the journal cool via flooding with oil. HOWEVER, high clearances cause a net reduction in the potential oil film thickness. When this happens, the loads from the crank are ultimately concentrated over a smaller net area. Higher clearances can result in unstable spindle shafts - our cam grinding spindle will actually start to vibrate (which causes surface chatter), when clearance is high and/or oil viscosity drops as temp rises. This is a real PITA to deal with when you are trying to generate mirror finishes on cam lobes or journals.

High clearance creats sort of a "point" contact like that which would take place between a 1" journal in a 2" housing as opposed to a 1.998" journal in the same 2" housing. Same load only concentrated on a smaller area which results in higher unit stress on the bearing in the load zone with the 1" journal as compared to the 1.998" journal.

A lot has transpired since I worked for Clevite and, before them, TRW. Sadly, both companies are now either defunct or "divisions" or merely "brands" now owned by the companies that gobbled them up via acquisition and/or mergers. I'd be inclined to believe that a lot of the "technical continuum" and/or technical heritage that got passed from generation to generation of engineers in my day fell by the wayside in the process of these consolidations.

No doubt the materials are better and the technologies and analysis capabilities probably more efficient and capable but you have to wonder how much of the "continuum" got lost, forgotten or disposed of over the years.