Backing Plate

[Chipper5783]

As Joshua and others have pointed out, cast iron is a great choice. I recently got a C5 collet chuck, for which I needed a D1-4 mounting plate. I got a semi-finished one from Shars (pretty reasonable, under $60). It cut nicely. The fit on the spindle was good - I did need to work a little bit out of the taper to make the plate sit right down on the flat part of my spindle (per the fitting procedure described on various machining sites). The only annoyance was the 5" blank was 4.945" diameter and the chuck I was mounting was 4.954" - I ended up skimming the OD of the chuck by 0.005" to clean up some shop wear (just a very small step, that only I know about). It all looks good and the runout on a piece of ground dowel is 0.0005" (per the catalog).

I elected to trim the back plate to a snug fit in the register of the chuck (perhaps 0.0005" interferenace - just takes a bump from the hand to break it free). I recognize that there is some debate about whether the fit ought to be snug, or slightly loose, then adjust the chuck position before finally tightening the bolts as a method to work out the last bit of runout (a poor man's SetTrue). I'd be glad to hear folks comments on whether the register out to be snug or adjustable (perhaps it depends on whether it is a good sized 4 jaw used for rough work, or a delicate little work holding device).

Anyway, with my one back plate from Shars, I am happy with the result.

 

[4GSR]

I've made a couple of back plates out of 4145HT several years ago. But I had a 16" Axelson lathe at my disposal, too. I sure miss that lathe! This was back before Shars and Little Machine Shop started carrying back plates, and the people there were carrying them wanted over $100 a piece for the back plates. Since then, I've bought a couple from LMS for my 9" SBL. They are nice and fit perfect! They are also made from cast iron. I highly recommend using one's made of cast iron. They are less likely to lock up and gaul the threads on your spindle like a steel back plat would! When I mount the steel back plate on my lathe, I apply some Never Seize to the threads. Sure makes it easier to break loose, too! Ken

 

[george wilson]

Cast iron has ALWAYS been the choice for backing plates. A steel one is an anomaly. If somebody made it,they might have done it out of ignorance,or just had the steel available.

Some chucks that can stand very high RPM'S are made of SEMI STEEL,though. That could be what you're seeing. But,even my 3000 RPM Hardinge HLVH uses cast iron back plates.

 

[aametalmaster]

I have made lots from just plain mild steel. I have bought used chucks with steel backing plates and I just use them. Yes I agree cast iron is preferred and I have turned them also. But if it what I have its what I use..Bob

 

[aametalmaster]

 

[atlas ten]

I also made one from steel
Jack

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[chevydyl]

The two I made are cast iron, one from LMS, for my Bison 5c, problem is they have spigots which place the chuck jaws farther away from the bearings, so for my Bison 3 jaw I opted to buy an 7.5 inch slug from speedy, and machined it all including threads on my lathe, I had to adapt a d1-6 chuck to a 1-1/2-8 threaded spindle nose, the backing plate is flush keeping the jaws as close to the spindle bearings as possible, just something to consider. I had to make an internal indexable threading tool to do the job, quite fun