Backplate Material Selection

[pntrbl]

I realize backplates are usually made out of cast iron, but to make a long story short, I can buy 1018, 4140, or even O1 for just about the same price as a piece of cast iron. Ductile or grey. Somewhere around $30 for a 6"x2" round for any of the above.

It may not matter because as usual I just don't know any better, but I'll be looking to mount a 55lb 10" 4jaw on a 550lb 11" lathe. That chuck's gonna look like a 454 in a Chevy Nova! I'm thinking I better be damn sure I've got a good piece of tough metal attaching it to the machine.

So what would you guys do? .... or .... Would you do it all?

FWIW, top end on the lathe is 1525 rpm. That could be scary .....

SP

[Renegade]

Cast iron machines and threads easier than the other materials mentioned,plus it has better vibration dampening qualities.
Nothing wrong with using 1018 it just won't finish as nice as the 4140 or the cast.

[Evan]

There is nothing magic about a back plate and it isn't going to ring with a chuck hanging on it. Strength isn't an issue. To give some perspective think about the driveshaft in a rear drive front engine vehicle. It may turn at thousands of rpm, transmit hundreds of foot lbs of torque and yet is of such thin material that welding it is difficult. A serviceable back plate can be made from whatever metal is handy and machinable. Once a thickness of about 1/2" is reached in the size you are speaking of the point of diminishing returns is reached and thicker material will not provide a significant benefit.

[Willy]

I may be missing something here, but I am just wondering how far you can open the jaws on a 10" chuck on 11" lathe without the jaws striking the ways.

[pntrbl]

You ain't missing much Willy because the question has come up before. The chuck was/is "available" for use, and being as I don't have a 4 jaw.

Currently my only chuck is an 8" Skinner 3 jaw and I have had occasion to run it with the jaws reversed and extended past the body. My left index and right thumb had some complaints during the 1st session, but I've had the same setup in the chuck several times since then with no foul language being needed.

With jaws reversed the 10" will still accept an 8" dia part on center before the jaws clear the body. My fingers are very happy about this.

A 6" 4 jaw would be ideal for what I'm doing on a daily basis and I've been looking. A decent looking used one went off on E-Bay this morning for $127 plus shipping .... so I'm still looking.

SP

[Willy]

Hey if ya got it lying around you might as well mount it on the lathe.
As you said with the jaws reversed it will still give a substantial amount of capacity that you otherwise wouldn't have.
Besides it's not doing anybody any good gathering dust on a self.

[J.Ramsey]

I guess you could make it out of the end of a beer can.
Drive shafts are made of steel or aluminum DOM tube that is easily welded and subjected to different kinds of torque and harmonics,put rims with cleats on a vehicle with a hollow automotive driveshaft and dump the clutch and see what happens, more than likely it will resemble a licorice stick I would guess your not so much interested with the dampening qualities as some people might be by putting a chuck that large on a lathe of that size.

[quadrod]

ok i have to ask the stupid question, can the chuck back plate be made out of aluminum-aluminymum-alllummminnum, oh you get what i mean.

[Renegade]

If they can be made out the end of a beer can........ why not?

[Evan]

Aluminum will work fine. 6061, 2024 or 7075 will all do. 2024 and 7075 in a T4 or T6 temper are as strong or stronger than mild steel.

[J Tiers]

A 6" 4 jaw would be ideal for what I'm doing on a daily basis and I've been looking. A decent looking used one went off on E-Bay this morning for $127 plus shipping .... so I'm still looking.

Well, whatcha want to pay for one?

A 6" 4 jaw plain back chuck will set you back $86 (plus shipping) at Victor Machinery, price from website tonight.

an 8" would be $95.

As I look again, I see that they may not be the Bison I bought for something like that price a while back. (they say to ask for a quote on Bison). But a 4 jaw only needs a few things right about it, compared to a 3 jaw, so it may be OK.

Bound to be better than a pig in a poke ebay monstrosity, though...

And you might as well ask what they want for a Bison brand. I'd guess it to bw worth the difference.

Ain't ANY way I'd pay $127 for a 6" 4 jaw used chuck on ebay. I'd start thinking at $50, maybe. Any more and I'd need to see the thing before I pried open my wallet.

I'm every bit as bad as what John S claims about Alistair....... although I WILL pay for quality if I need to, and I expect quality in proportion to the $$.

[pcarpenter]

Yeah...the bigger problem than only having 1" of jaw to way clearance is that if you need to work close to the chuck you are talking about top-of-carriage to jaw clearance which may be even smaller or non-existant.

Paul

[Evan]

Yabut, it should at least hold the same as a smaller chuck. Regardless of the size of the chuck if the jaws are approaching the ways it will hold about the same size work no matter what size body it has.

The main drawback is the weight and reduction in center to center distance. On my SB9 there is no difference between way and carriage clearance.

[pcarpenter]

I dunno...I have a 6" three jaw and a 7-8ish three jaw and the chuck jaws are both wider and longer on the larger chuck. With smaller parts, this makes no difference. However, there is a diminishing return on chuck size as they do have a larger swing (outside) as you open them up to accomodate the same internal diameter.

I just looked this morning at some lathe damage caused by someone opening a chuck beyond the amount of clearance they had over the cross slide while the chuck was parked with the back side of the jaws straddling the cross slide. They then appear to have tried to start the lathe. as there was a big "whack mark" on the top of the cross slide. It's a good thing that even geared head lathes are actually belt driven (at the motor).

Paul

[pntrbl]

Well thanx for checking in on the subject guys. I think my Logan's similar to Evan's SB9 in that the section of the carriage that first approaches the headstock is tapered for clearance. Other than my knuckles the first thing I typically have to watch for is the compound/cross slide/etc. getting into the jaws.

I'm gonna be conventional for once in my life and use ductile iron for the plate. I've drilled and tapped cast before but never turned it. Magnet in a bag huh?

JTiers, I watched a used 6" Bison 3 jaw go by at over 2 bills on E-Bay last week. I'll bet it was a nice chuck but new couldn't have been much more. I swear E-Bay's getting harder all the time.

OTOH there's an E-Bay store called Discount Machine with what must be an import that will show up at my front door for just over $70. Dimensionally similar but in fact slightly larger in thickness etc. as the one Victor has at $86 plus shipping. The Discount Machine ad says it's hardened. Got a balance dimple.

If someone could please tell this computer dummy how to post a link to it I'd sure like to put it up for the board's opinion.

SP