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Chuck Backing Plate Material

T

torx10

Member
I've got a 5" (125mm) 5C collet chuck on the way from Amazon via the "Slow Boat from China" and will need to make a backing plate to mount it on my CX-706 lathe. They all seem to be made from cast iron. Is there any reason mild steel or even aluminum couldn't be used for a chuck adapter/backing plate?

I watched a video by British You Tuber, Steve Jordan this morning, and he started with a 2.7 Kg. (5 lb.) cast iron barbell weight. Has anyone tried this as a source material? These weights being round to begin with are appealing, as I recently made an adapter for a 4" ER40 collet chuck, starting with a 4.25" square of 3/4" steel plate (hot rolled) and, even with cutting off the corners on the bandsaw to start with an octagon, that was a lot of interrupted cuts to get it round.

So why is cast iron the Holy Grail for backing plates?
 
You can get thin slices of cast iron round from McMaster-Carr.

I don’t think cast iron is necessary, I’ve made a number of backplates from whatever steel I could get in the appropriate size.
 
torx10 said:
Is there any reason mild steel or even aluminum couldn't be used for a chuck adapter/backing plate?
Click to expand...
No reason at all. Aluminum may change too much with extreme temperatures. Pratt/Burnerd sells backing plates in both cast and steel. I think cast is used due to tradition, and it is cheap, and is strong -enough- for the purpose.
torx10 said:
cast iron barbell weight
Click to expand...
Really this is a mine field. Cast iron weights can have all kinds of hard inclusions, from casting carbides to junk steel added to the mix. I've machined a weightlifting weight or 2 when i was young and poor, and never again! The cost of broken cutters was higher than buying 1045 steel by a looong shot.
 
Isn't cast also very good at dampening vibrations, I thought that was part of the reason it is normally used

Can you not buy a blank backing plate for your machine and turn in place?
 
For really nice material, a recommendation I followed was South Bend backing plates from Grizzly. It always worth checking their parts lists. But be aware Grizzly uses UPS.
 
I have a CX706 as well. AIUI, the spindle nose on the lathe has a 7.125 degree taper and the backing plate needs to have a matching taper of the exact right length so that the chuck mounts solidly and concentric to the lathe spindle. I think it would be very challenging to get the right taper and the right length so the back plate pulls up securely to the spindle nose.

Mr. Crispin on Youtube did some grinding on the tapered nose of his lathe in a recent video if you want to see an approach.

I haven't verified this but I believe the interface on the CX706 is a "DIN 55027" (aka "ISO 702/111") standard. As I read it, this is exactly the same as the more common D1-3 mount except that it is secured with a 'bayonet' rather than the cam lock studs. I *think* one should be able to 'convert' a D1-3 backplate by replacing the cam lock studs with simple threaded studs. MAYBE. But I could be entirely wrong.

See the attached pdf for details on various sizes of the different mounting systems.

HTH, please report back what you end up doing. If I ever want to have a collet chuck, I will need to solve this issue too!

Craig
 

Attachments

Just a little reality check.

Aside from grinding, turning the taper carefully on the lathe works well enough. We sometimes get caught up in modern methods and forget that the old methods employed skillfully yield the same results for the tolerances that we can dream to achieve without the fancy tools.

From my stand point. I would turn a plate to attached to the existing mount drill for both mounting and provide holes to mount the 5C chuck and fasten it. Re-turn it to true it and then cut it to fit your 5c chuck backside using clamps and adhesive to center it.

Once you have it fastened temporarily you remove the entire assemble and mount with proper fasteners.

Think outside the box.
 
My last lathe (Churchill Cub) had an A style mount. Same taper as D but bolt on instead of camlock. Not easy to find back plates for. Over the time I had it I made I think 3 backplates for it.

I set the taper by indicating directly on the spindle nose and adjusting the compound. Then I cut the taper and removed the chuck while leaving the new back plate in place on the chuck to flip it it and check fit. Rinse and repeat until you get it just right.
 
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