Thread: Fitting a 250mm chuck on a face plate, 12x36 lathe

Hi,
Here another job I have done, and thought that some of you may have had the idea of putting a bigger chuck on you lathe.

There have been a few jobs on my lathe were I have needed a larger chuck than the 200mm one that came with it. It has mainly been odd shapes or needing the centre hole to be larger. I would like a bigger lathe like RC's but funds are way off for something like that for a while.

So to compromise when I bought my 250mm rotary table I bought a 250mm 4 jaw chuck for it, and thought it could get some use on the lathe as well.
I looked around for a back plate but the largest I could find was 200mm in the D1-4 cam lock mount. All the 250mm ones are D1-6 mount.

I have 2 face plates because I picked up a spare a while back off ebay. I measured the 2 and found one to be spot on in diameter. The holes for the chuck bolts would just make it with having enough meat to tap to get the threads in.

A chuck needs a register to keep it centered and a face plate doesn't have enough thickness to machine one. So I come up with the idea to press fit a bush with a collar machined on it into the bore then machine the outside to suit.
In my scrap box I had a piece of round bar 108mm dia with a 51mm hole drilled through it left over from a job. It was just the right size as I needed 100mm outer and a minimum of 52 inner, to leave a 3mm + wall thickness on the bush that goes into the 58.5mm centre hole of the face plate.

I started out with boring the hole in the centre of the face plate to make sure it ran true, the face was ok because I had cleaned it up when I got it.

I then mounted the chunk of bar in the 3 jaw and machined back far enough for the bush to be able to go inside the bore of the face plate and machined the outside a little over the needed 100mm. I just took enough out of the centre to clean it up because I wanted as much wall thickness as possible so it wouldn't collapse.
The bush was machined to 0.05mm over size for a press fit into the face plate. I then cut it off in the band saw, then remounted it in the lathe back wards and cleaned up the other side.

After this was done the face plate went into the oven and the bush/register went into a plastic bag in the freezer for about 30 minutes. Once the face plate was a little bit hotter than could be handled I cleaned the bush with a rag in case of moisture, smeared on a little oil on to stop any rust in the future then pressed them together, they went together easy without needing much pressure.

I then mounted the face plate back on the lathe turned the register down to 100mm for a light press fit into the chuck and faced the front to clean it up and ruining true.

I used the DRO on the mill to drill the holes after setting it up square to make sure the holes came through in the right spots and taped them M12 to suit. The holes are deep enough that I got 8 threads into the face plate which is plenty. They just broke through on the back for the last 2 threads because of the back plate webbing design, as can be seen in the photo. This is what I was talking about earlier with the face plate having enough meat to tap into for the bolt holes.

After mounting the chuck I checked for clearance between the chuck jaws and the lathe ways, with the jaws at there recommended maximum (which is nearly half way out) it has 14mm clearance.

With a chuck this size you need to keep the speed down to a 1000rpm or under as it's big for this size lathe. I read somewhere on the packaging that the top speed for this chuck is 1200rpm but can't find it again.
I ran this one to check for balance at 1000rpm and it was a bit scary. I will only be using it low speed for those awkward and larger jobs.

Dave