Thread: Cam Lock to screw n chuck

I had a similar dilemma trying to fit an 8" 4-jaw chuck to my old Macson. In my case the backing plates to suit the headstock flange are not an off the shelf thing and to make one from scratch would require a really big slab of material so I modified the threaded backplate that came fitted to the NOS chuck.

This is slightly different to what you need to do - your existing backplate is threaded for the mounting bolts that came through the chuck but in my case the backing plate was drilled through with nuts on the rear of the chuck backing plate. That required me to drill and tap holes in the original Macson backplate for mounting the chuck itself plus a another group of 4 smaller screws to hold what I will call the intermediate backplate in place.

Clear as mud right? In the first photo I have shown the original Macson backplate from a much larger chuck (that I wanted to keep usable for that big chuck), the cut-down threaded backplate that came with the 8" chuck (you can see the remaining thread in the middle that I have been too lazy to bore out).
It is looking like Swiss Cheese now but in your situation you only need to have mounting holes for your existing backplate (suitably cut to match the D1-3 backplate) to attach to the D1-3 backplate.
IMG_1117.jpg

This is with the intermediate backplate screwed to the Macson backplate with 4 x countersunk screws. These screws allowed me to have the intermediate backplate secured in position and give the chuck register a tiny skim to ensure the chuck was correctly positioned with respect to the headstock. Given I machined the back of the chuck backplate to match the register of the Macson backplate I was pretty close but a bees whatsit out. This will probably be your biggest challenge given you don't have a functional 4-jaw. It will also be reasonably big - is your 3-jaw really accurate and do you have outside jaws?

IMG_1118.jpg

Now the chuck is attached to what is effectively a slightly thicker backplate. You can see in this case the chuck and the intermediate backplate are smaller in diameter than the original Macson backplate - that has been left so it can still be used with the 14" 3-jaw if I have the need.
This has worked very well for me so was worth the dicking around to get the original chuck threaded backplate machined.

IMG_1119.jpg

Thanks for the elaborate post!
I don't think my 3 jaw is accurate and I don't have outside jaws.
At this early stage of my maching experience, I don't have the skills/knowledge/tools to drill and tap holes accurately enough.

Hi Vic,

Originally Posted by Vicval01

Thanks for the elaborate post!
I don't think my 3 jaw is accurate and I don't have outside jaws.
At this early stage of my machining experience, I don't have the skills/knowledge/tools to drill and tap holes accurately enough.

In that case make some soft jaws for the chuck ! You can easily achieve 10ths of a thou or better with them.

Small_Gear-01.jpg Soft_Jaws-01.jpg

Here is a simple idea to make some to suit any chuck. These were made from parted off pieces of a toothed pulley. The hole, in my case was 16 mm diameter drilled off set, were large enough to fit over the chuck jaw.
NOTE: You do have to use a disc inside the jaws to apply tension to them for maximum accuracy.

In the first picture I'm boring out a gear that was needed for my mill !

Most informative! Thanks.

Here's the next step of the process:
I bought the chuck backplate as previously described.
It needs some modification.
The mounting holes in the 4 jaw need to be marked and drilled and tapped for the backing plate. That I can do.
I'd like some advice on the following:
The inset of the new backing plate is about 4 mm smaller in diameter than the original recess, so I need to centre the plate to the chuck in order to line up the holes concentrically.
The original screw in backing plate hole shoulder is slightly larger than the hole in the new one.
Do I machine the old shoulder to fit the new plate hole and mark the holes from there, or is there another way?
I have photos ready to upload but I get no response when trying to upload or attach anything. I have resized the pics.
I can't seem to find a way to delate previous attachments. There is no delete facility in 'Manage attachments'

Thanks

I actually machined the back plate of my 3 jaw a fraction smaller to I have a tap true chuck, not set true as Bisson call it with grub screws to hold it, works fine for me.
I posted about it many years ago.

The recess does nothing to hold my chuck in this situation, the backplate is only around 0.5mm smaller from memory , just the Allen head bolts hold it.

It's done some really heavy work over the years without moving, and accurate work if if I want to set it exactly.

[Thanks for that info. I managed to get the pictures up.
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