Sourcing cast iron disc for back plate

[Tomzo]

Greetings,

The package I got with my 8x16 lathe came with a 4 jaw chuck but it is the self centering type which, apart from square stock, does not have the utility of an independent 4 jaw chuck. I have watched a ton of videos, got my DRO going on the mill for bolt circles, and am ready to tackle the project. However, I am having a hard time sourcing a chunk of cast iron (I presume that is the preferred material) to make the back plate out of. Anybody got any tips as to where to find suitable stock for this? The chuck will be 125mm.

Thanks

Tom

 

[Watchwatch]

McMaster Carr
3/4x8 #8926K44

The smaller diameters only come in 1ft chucks which are expensive. Thicker discs are available.


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[woodchucker]

McMaster Carr.. DuraBar or Cast Iron.
Also backplates should be avail online.. many sources.

 

[Illinoyance]

WTTool.com has unfinished cast iron backplates.

 

[Tomzo]

Thanks - I found those on McMaster Carr. Too bad the .750 ones only come in 8" diameter. Turning that down might get a bit hairy on my lathe. From what I understand the appropriate method for a project like this would be to bore out the center bore and drill/tap the hole circle to adapt to the existing plate (3 hole circle), mount that up to the lathe, then turn it to the correct diameter, face it to the desired size (and to make it parallel to the existing plate), create a shoulder for the register on the 4 jaw, and then pop it back on the mill, center it up, and drill/tap the holes for the 4 Jaw. Sounds easy! I will have to get creative with tool holding on my lathe with something 8" diameter turning on there!

 

[Watchwatch]

Drill a bolt hole pattern slightly over your desired diameter on the disc and leave about .005 web. Use a hacksaw if you can’t snap the webbing.


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[Tomzo]

Drill a bolt hole pattern slightly over your desired diameter on the disc and leave about .005 web. Use a hacksaw if you can’t snap the webbing.


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Ah- good idea! Of course, it could also be an excuse to get a rotary table....

 

[Illinoyance]

Where To Buy

Dura-Bar has dozens of distributors across the United States, Canada, Mexico, and China. Find one near you today!

www.dura-bar.com

 

[WobblyHand]

Speedy Metals sells cast iron by the inch. I bought 2" of 5" diameter cast iron from them recently. I am finishing up a set tru back plate today. The iron is oversized a little so just order what you actually need.

Machines easy, but is really messy! Cover everything up for at least a 3 foot radius, chips and dust go everywhere. I wore a respirator, since there's a lot of dust generated.

 

[Tomzo]

Digging around on Little Machine Shop I found this (not sure why I did not look there first):

Backplate Lathe Chuck Adapter, 5" to 4" 4771

Lathe Chuck Backplate Adapters 4771 Fits a 5" chuck on a 4" flange; This is a semi-machined adapter plate. The side that attaches to the lathe flange ...

littlemachineshop.com

Since they are here in SoCal the shipping is not crazy. I figured that even if the bolt circle included was not quite right I could just drill another set, mount it up, face the front, turn the shoulders for the registration, and then drill/tap the bolt circle for the 4 Jaw.