I just bought a 6" 4 Jaw independent chuck for my Myford ML7, but I can't get a backplate around here. What steel would you suggest I use to make one? I was thinking along the lines of 4140, but if 1045 is alright, it's easier to get here... Any ideas?
Cast iron, if you can get it. You may be able to find a partially machined backplate that you can finish to fit, for example:
I've made a couple Ajust-Tru to Hardinge spindle backplates from hot rolled low carbon plate that I'm pleased with. Pick a material that's easy to machine and that won't move too much when you turn half the blank into chips. Don't bring any feature to its final dimension until you've roughed the whole part. There's no good reason to go to the expense and trouble of using 4140.
You really should use a cast iron round. Cast iron is a dead material, dimentionally stable and easy to machine. Steel is absolutely the wrong material because it will sing when subjected to vibration and amplify tool chatter.. This is the reason that all machine tools use cast iron. Don't reinvent the wheel. Steve
Thanks for the tips... I've just called up a couple of raw stock shops, and the only thing they can get that would sort of work as a 6" disc is 1045... They shrugged at the mention of cast iron, I'd probably need to get it cast somwhere... (Yep, you guessed, I'm not in the US). So basically, I'll cut it out of 1045, and scrounge around for a cast iron "something" that might do the job later... (No, no scrapyards either... Isn't it annoying?)
Don't give up on the cast iron. I'll bet that there's a foundry within
50 miles of you. All you have to do is make a wooden disc pattern,with or without central hole, and have them cast it for you. About a 2 percent draft on the edges. Might be fun, too. Maybe have them do a couple of them. Heck, they may even have some stuff around that you could use.
Ricardo D. Med> Thanks for the tips... I've just called up a couple of raw stock
Contrary to the cast iron recommendations you will get I have, over the years, made a number of "back plates" for various size chucks, usually to allow a chuck to be used on a lathe with a different size spindle. I have always used plain old steel - whatever was available in the scrap barrel. In fact I frequently used thick walled steel pipe or tubing, threaded it to fit the spindle, welded a flat plate to it and then re-mounted it on the spindle and machined it all over to fit the chuck. Never had a problem with them and some of them were still being used the last time I visited home forty years after I made them.
Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)
Just finished one for a 5" 4-jaw to fit on a asian 7x10;
6061T-something-or-other plate. It was thick enough and big enough and it was in the pile of stuff-to-make-stuff-with.
Here's what I did, with a small trick I did to make mark the centres of the holes for the chuck on the plate.
First off I mounted the plate straight to the spindle - three threaded holes in the plate matching the spindle ones. That part was simple because a while ago I made a good template for the spindle holes (after several not quite so good templates). I screwed studs into the threaded holes and bolted the plate on good and tight; then turned the front to match the spindle nose. Turned the plate around and put the studs in from the other side, bolted it down and indicated to make sure it was flat on the back side, then turned the edge and the front to match the chuck.
Here's the little trick. I mounted the 4-jaw with the jaws gripping the step on the front of the backplate. Adjusted the jaws until the outside of the chuck and the back-side of the chuck ran true, then mounted a transfer punch in the cross-slide and twiddled the hand wheels until the punch went in one of the chuck mounting holes nicely. Took the chuck off, ran the punch point up to the face of the backplate and scribed a circle. Measured the circle dia, divided by 2^1/2, set the dividers to that and scribed the centres.