chuck back plate

[chip's]

I am going to have to make a back plate for my 6" 4 jaw chuck. I found a piece of cast about right. It is only .910 thick. I believe this is a bit thin. Will this be ok to use or will it be too thin for good thread connection by the time I get the land cut? I thaught about making a steel shoulder and bolting it to the cast to make it thicker before I machined it. What do you all think?

[yf]

How long is the thread and register on the spindle nose?

If its shorter than the thickness of the backplate then it might be OK.

I made a backplate out of hot rolled with no boss at all. Works fine, and has less overhang.

[gizmo2]

Chips, are you a broke bloak, such as meeself? What are the virtues of this chunk of cast iron? In your possession and paid for??? Good enough. I think I'd inlet that shoulder about 3/8" into that plate and braze it in place. Then you get some mechanical strength besides just the bolts, like a tenon in a chair leg. Then check out past threads on the subject on proper back plate fitting, and you'll be good to go!

[JCHannum]

I have done this with a 4 jaw myself. I don't think I would do it with a three jaw.
I made sure the threads were all in the main body, and as much of the register as possible. The addition becomes a distance piece at this point.
I have had no problems.

[docsteve66]

I think JCH and I did it aboutthe same way. I was meditating one day, about this great big (comparetivey speaking) 8 inch 4 jaw, and my little bitty 1 1/2 X 8 tpi nose.

why hang the chuck way out when i could take a piece of pipe (if need be) and slip it into the chucks hole? Get the threads nice, get it to register and turn it to size to fitthe chuck and then all you have to worry about is over comming the torque when cutting and thetendncy of the chuck to try to come off the "pipe". Thosetwo problems boil down to is: "make sure the chuck cannot move inrelation to the "pipe" ". No precision involed, key, drill tap, braze, cross pin (which I like but the hole would be so deep and small), super glue? .

Or maybe I leave a flange on the rear end and bolt the flange to the chuck. Thin flage is ok since it carries only torque and "screwing load" (to me-Screwing load is the axial loads imposed by the cutting tool, which may be trying to move the work toward the headstock ortail stoack. That was what I would do.

Mediation drifted to sleep and when I waked, i did it! Short easy sweet job, due to the careful planning, aid by having a chunck i cast iron in the scrap box.
the housing of the 4 jaw has no runout, there is zero vibration at higher speed, I like it!!!!!! I see no reason not to use a "pipe" inserted INSIDE any chuck (so long as the pipe is short nuff that the working parts can work. Then drill and tap or key the pipe to hold a flange to tranfer spindle rotation to chuck.


Still meditating about why its a bad idea on the three jaw. Mind explaing JC? I would go look at my 3 jaw but temp here is about 35 F. Gonna try to inspect a 3 jaw before ground hog day, but i thrust JCH more than me anyway.
Steve

[JCHannum]

Stteve, with a four jaw chuck, as long as it is tight and not out of balance things are OK.
With a three jaw chuck, if it doesn't line up the same when you remove and remount it, there can be problems. I don't think the set up will give any mechanical problems, but may not be as repeatable as one might want. Then again, I don't get real hung up about runout on a three jaw anyway.

[chip's]

Thanks fellows. I don't have alot of extra money to put into the tools. When I got the chance to get a nice cushman 6" for $80.00 I thought it a good buy. The only problem is that is has a short taper mounting plate. I figured I could make a nice plate out of a steel weldment as I have before. I just like the cast better. I happened on this piece, it is the right O.D. for the chuck and right I.D. to run a 1 1/2- 8 thread in. The only real thing wrong with it is the thickness. The spindle of my lathe would stick into the chuck about .375 if I don't screw or braze (thanks giz2) a piece on the back. The chuck has a big enough hole for it to fit ok. For $ 5.00 I thought, I could work things out with your help.
Thanks for all your help everyone, Rick.

[walnut_charlie]

I've made several backing plates from cast iron barbell weights. They are cheap to buy new at sporting goods stores or they can be found at garage sales and thrift stores for almost nothing. They come in a variey of sizes.
Walnut Charlie

[chip's]

Walnut_Charlie,
Thanks so much for the information. That is exactly where I got the cast. It was a weight from big 5, for $5.00.

[Thrud]

Rick
If you have to I would make it out of steel, but not out of welded up sections. I do not know where the mounting holes are on your Cushman chuck, but most 4 jaw chucks have a smaller hub (the back is hollowed out to reduce weight) than 3 jaw chucks. My 6-1/4" Bison has a 3-1/2" BP with 4 10mm (all my chucks have metric fasteners) mounting bolts from the front of the chuck. So if this is true with yours as well, make a smaller diameter steel backplate so that the chuck has minimum overhang. Cast is better, the Bison 4" cast BP is cheap in the US.

[Dick Payne]

I have also used barbell weights with good success for my Smithy 1220 3in1 machine.
On an earlier posting someone on this BB suggested Victor Machinery. They have a rough cast iron 6" back plate for $12.50.
It is 1/2" thick with a thicker section in the center for threaded spindles. The next cheapest is about $43 from Enco for a 1" thick rough cast iron back plate.

------------------
Dick

[chip's]

Thanks so much everyone for all the replies. I will try and get it done in the next couple of weeks.

[yf]

Some auto brake discs can be made into backplates. They are usually of very good quality cast iron and are pretty uniform and machine nicely.

[chip's]

Thanks all, this disc seems to be good iron. I just wish I could get the time to do it.