4130 steel for lathe chuck backplate?

I want to make a backplate for a 5" Bison 4 independent jaw chuck (the one recently on sale at Enco). I've read that cast iron is preferred for this, but since my spindle is not threaded (Wabeco D3000E lathe) I don't have to worry about galling threads. Online Metals will sell me a

4" x 1" disk of 4130 alloy steel for $17. That is cheaper than any of the rough-cast backplates I can buy and I won't have to make a pile of iron dust. It appears that 4030 is the only material they sell in a 4" diameter. So will 4130 work acceptably for machining a backplate or is this a bad idea?

The chuck really only needs a 4" back "plug" since the recess on the back of the chuck is only 3" in diameter and the mounting holes are within that circle. The lathe spindle plate is under 4"

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4130 can be used for axles, etc.. for high strength...

I got a couple of back plates for 6" chucks, they are made of steel. Don't know what kind.

Have not heard of cast iron for back plates...


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If you don't mind machining the material (not bad, but tougher than mild steel), there's not much wrong with the choice. Cast iron is used for its dampening qualities, so you minimize chatter. You might encourage a little more with chrome moly, but I can't imagine it will make a significant difference for your application. I imagine you mean 4130, not 4030?


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Harold and Susan Vordos

I think mild steel would work just fine. Why not just go to the closest welding shop and get a 4 inch square of 1" plate and turn it round?

Pete Stanaitis


lens wrote:

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No answer for "lens", but another question about chuck backing plates: Why are they so expensive? They're just a hunk of cast iron. Enco (Bison brand): 6" plain (no threads) $46; 6" threaded $54. I'll bet the Chinese could make one to sell for $5. Bob

Reply to
Bob Engelhardt

The chief advantages of cast iron are low cost, and easy machinability.

How about a cast iron barbell weight from Wal-Mart? I know a recent thread was critical of this material, but I would give it a try.

Reply to
Richard J Kinch

Couple of reasons for using cast iron. The gray stuff is usually a lot easier to machine than steel, it's somewhat softer so it doesn't wear the spindle threads and has a somewhat more damping effect on vibrations than steel does. If you ding it, it doesn't raise burrs, either. Castings are usually cheaper to make out of iron than steel, too. I've gotten disks of gray continuous cast from MSC to make backplates for my 7x chucks, those are stud mounted. I've made threaded backplates for a South Bend from hot-rolled flame-cut slugs from a crane outfit, too. Cleaning off the flame-cut surface wasn't fun.


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Cast iron is much stiffer than steel, so it won't allow the chuck to twist out of axis when taking heavier cuts. In this case, the steel plate will be such a small diameter and rather thick that it might work.


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Cast iron is considerably *less* stiff than steel. Its modulus of elasticity, depending on the exact alloy, varies from around 12 million psi(common gray cast iron) to 25 million psi(malleable cast iron). Steel is 30 million psi, aluminum about 10.

Ned Simmons

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Ned Simmons

Cast iron is also very stable if aged properly. That's why you see it used in angle plates and such.

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Dave Lyon

That will work fine. I made some years ago out of steel for a 12" lathe. Worked great.

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Richard W.

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