Casting a Lathe Chuck Backing Plate

[vtsteam]

I need a 4 jaw chuck for my new lathe to work on the Rider engine I'm building. I got the chuck from Shars, but it needed a backing plate. I did consider just bolting it to my faceplate, as I do with my 3-jaw. But unfortunately the faceplate has a six slot pattern, and the new chuck has a 4 bolt pattern.

The faceplate is not easily milled for another set of slots without a carbide mill, and I really don't like this faceplate much anyway. I'll probably make a new one some day.So I decided instead to make more conventional backing plate for the 4-jaw -- I'm thinking it may be my main go-to chuck anyway, in future.

So I band-sawed out a simple 6-3/4" disk out of 3/4" plywood for a pattern, rammed it up in greensand, and did a little larger melt than I had before in my A6 crucible. The iron is from a brake disk -- about 11 pounds was melted, and I added .35% ferrosilicon. The furnace had been fairly extensively patched, and completely re-coated in ITC 100HTceramic coating.

For some reason the furnace took much longer to melt that iron, about 50 minutes compared to 20 in the prior 3 runs. I was using off road diesel instead of regular diesel. It seems to have different characteristics, and I'm wondering if the furnace damage as well as slow melting is a result of the recent change. I will probably switch back to regular diesel -- particularly here in winter temperatures, when viscosity is heavier for these light oils.

Everything did eventually melt -- I did have to add iron as the melt progressed to fit it all into the A6. But when I went to pour, the crucible again stuck to the firebrick plinth. I had put cardboard under it, but I think the longer melt and fuller crucible resulted in slag dripping down the outside to weld the crucible to the plinth.

This discovery right at the pour meant I couldn't easily get the ring shank onto the crucible -- the firebrick was too large to set it in the ring. But because the shank I'm using now is expandable I was able to stretch it down over the top of the crucible, and pour that way.

\Unfortunately in the excitement of trying to get the crucible situated in a shank in time to keep it hot, I wasn't able to do as good a job slagging just before pouring it. I had slagged once while it was in the furnace, however.

Anyway the pour was accomplished, and the crucible returned to the furnace to cool down slowly.

I had put a big riser in the center. The sprue showed pieces of slag, the riser looked clean, and shrinkage was very apparent as it cooled.

[vtsteam]

And, here is the break out. I was pretty well pleased with the casting, considering the pattern making was about a 10 minute afterthought on a day I hadn't actually planned to cast on....., and the problems I had with the crucible sticking when I did.

[vtsteam]

And here it is being machined on the new lathe's faceplate, which it will eventually replace. To clamp it, I simply drill two holes in the plate, tapped them, and bolted it in place.

[RussellT]

The casting looks good from the machining.  Well done.

Russell

PS Yes, I remember the engines well,  I still have mine here.

[vintageandclassicrepairs]

 

John

[tom osselton]

 

[vtsteam]

Thanks Russel, John, Tom!     

I bored the through hole and turned the back registers and drilled for the spindle mounting bolts. That was made easier because when I'd built the lathe, I made a gauge for the spindle mount. It definitely came in handy this time around. The one face fits the spindle, the other fits the fixture to be attached, and bolt hole patterns for 3 and 4 bolt fastenings are located.

I tapped the backing plate then bolted it to the spindle. I put a final light truing cut on the face, then I turned the front register to fit the new 6" 4-jaw chuck. I will mount this with hex head cap screws, rather than Allen screws -- much easier to remove than those on the import mini-lathes, as there's room on my lathe to swing an open-end wrench behind the spindle bolts, and the backing plate bolts.

I need to  drill the backing plate for the chuck mount. I think I'll also drill holes for my 5" 3-jaw chuck, as they can share the same backing plate. The 3-jaw won't have a register, because I just bolt it up lightly, and then tap it into center using an indicator on a bit of shaft held in the chuck. Then tighten the mounting bolts. No runout due to mounting. Worked great when it was mounted on the faceplate, and I'm sticking with that method.

The 4-jaw does have a register, just for convenience in mounting. Obviously you can true up any gripped workpiece in an independent 4-jaw chuck using the chuck jaws.

Plug gauge back and front, and the backing plate ready to drill for the chuck(s):

[vtsteam]

Okay, end of the day, how to locate hole centers in backplate to fit the chuck? I don't have any transfer screws, and didn't want to make some -- and especially not for M10, since they'd probably never see use again, and besides, my lathe isn't functioning at this stage to make them.

You could measure out the locations, using a square (there are 4 bolts), if you had a center point to work from, but the center of the backing plate was bored out. I could possibly stuff a piece of wood in there, saw off flush and find a center there to work from.

Or you could put it on a mill and drill there -- probably the smart way to do it. I don't have rotary table, so I'd have to do it by coordinates, no DRO either so I'd have to read dials remembering backlash, etc. But also my mill is in a really cold space right now, and the setup would be like minor torture.

So, I decided on another way. I found a piece of stiff cardstock and laid it on top of the chuck. Then poked a pencil through it to locate a threaded hole. I put one of the M10 bolts through that hole and screwed it in a short way. Did the same for all the other mounting bolts.

Then I took a small hammer and tapped all around the chuck back face outline. This is the same way you make custom fiber gaskets. The light tapping cuts the paper to the shape of the surface it is lying on.

[vtsteam]

The finished paper template lying on the chuck:

[vtsteam]

Here is the template on the backing plate. It fits over the register. I taped it down and the used a transfer punch of the same size as the holes to line up and punch the hole locations. Though a transfer punch doesn't bear against paper like it does in a hole, it is useful as a visual guide to center the punch.

This isn't exemplary precision machine layout, but it is as likely to be as accurate as doing it with a square and measurements from a wooden center -- in my hands at least!  And the register is what really counts in mounting the chuck, as long as the bolts pass though the plate in line with the tapped holes.

[vtsteam]

And at the very end of the day, here is the 4 jaw chuck mounted on the lathe. 

All that's left to do is turn the rim of the backing plate smooth to match the chuck circumference.

[awemawson]

Many years ago I invested in two sets of Transfer Punches, Imperial and Metric. They sit quietly in the corner of a cupboard for months at a time, but when I invite them to come out and play they make jobs like this quite simple.

[vtsteam]

This needed transfer screws to make it simple. The chuck is threaded and the holes are blind.

[awemawson]

If the threaded hole is countersunk slightly you can place a suitable sized ball bearing in it, locate your work piece over it and give it a sharp tap with a mallet

[vtsteam]

Sounds like a good idea for some other project. But in this case, not countersunk, no ball bearings, (though both could be remedied) but beyond that, and this applies to sharp transfer screws to a somewhat lesser extent, I just don't want to hit a brand new 25 pound chuck on the face with enough force to indent ball bearings onto a cast iron backing plate in four places. 

[awemawson]

You hit the backing plate as it has less mass !

[vtsteam]

Please do. Take your newly turned 10 pound backing plate with registers on both faces and a 40mm bore and pound on it somewhere with enough force to dent it simultaneously and accurately while resting on top of 4 ball bearings in 10mm tapped holes spaced 6 inches apart. 

Different folks, different strokes. 

[awemawson]

I know I'm not going to convince you Steve, but it really isn't that brutal, just a tap with a dead blow hammer over each ball. And if you paint the backplate with layout blue first and are careful bringing the two together it needs hardly anything to produce a witness mark that you can pick up with an optical centre.

[vtsteam]

Ah, change of plan. Now we're using four taps of the hammer and layout blue and an optical center. I think since this new strategy requires tapping with a mallet over the four bearings, you need to both locate and immobilize the backing plate and chuck in relation to each other.

Since the chuck and backing plate in question are different sizes and the rim of the backing plate is still rough, you may want to turn yourself an arbor the same size as the bore to clamp in the 4-jaw  -- then indicate that to the center of the chuck by adjusting the independent jaws, then place the backing plate over the new arbor, and clamp them together so that the plate won't also rotate around center after each mallet tap. Then if you tap with your mallet over each location, you will have something to use your optical center on. 

But, naturally you won't convince me, because my chuck is already mounted via a piece of paper. 

[krv3000]

A good job 

[vtsteam]

Thanks Bob! 

[RotarySMP]

Nice casting. Looks like the iron came out nice and clean. Good one!

[vtsteam]

Thanks.