Adaptor płatę?

I have an SC3, which I bought about 9 years ago and fitted a 125mm four jaw chuck to it.  Bought an adaptor plate to fit the spindle and machined it in situ to fit the chuck.  Obviously an independent four jaw requires less accuracy than a non independent chuck.

A 100mm chuck should be capable of holding more than 1.75″ diameter, don’t you have the external jaws? If there is something fouling the jaw steps, then, as already mentioned some soft jaws would work. A 125mm chuck would probably require an adaptor plate, and by looking through ebay there are lots of barstock offcuts, some cast iron, but most mild steel that could be machined on your lathe to make the chuck adaptor for a larger chuck. You would need to first make a drawing of the spindle flange, and then attach the blank disc to the spindle, or a faceplate if you have one. Don’t worry about drilling/and or tapping holes in the plate to hold it on, there will be plenty of room to drill mounts in other parts of the plate later. We have chuck backplates with up to a dozen holes in them, plain and tapped and they work just fine. Also mentioned is a four jaw independent which is so much more versatile than a scroll chuck, just takes more time to set up to use.

This is why lathes used to be supplied with a faceplate (often rather than a chuck to keep apparent cost down) and the end caps should have been cast with a chucking spigot.

On 28 August 2025 at 23:23 Steve Huckins Said:

External jaws still didn’t work as the outer steps cannot close down to less than 2.5 inches as then they touch in the centre.

So put a packer between the jaw and the workpiece, effectively increasing its diameter to something the jaws will hold without bottoming out.

Visualise the copper jaw protectors used on standard jaws and bulk them up a bit. Or superglue (gel, gap-filling) some pieces of key stock to the part.

Soft jaws every time, when you have almost machined them down, weld some pieces onto whats left, and away you go again.

Chris Gunn

Hi Steve, you can always make one of these, which I did to face a few blanks, I used a slice of BMS that would fit in the outside jaws. Just turn the ring up with the recess in it, before cutting the slots.

Regards Nick.

As someone else mentioned, the %” to 4″ adapters are good & save you a fair bit of work making your own.

Still a novice myself, within reason & size constraints, you can make any chuck fit any lathe , only on my third back plate did i feel i’d finally “nailed it”

I view making a chuck plate one of those “rites of passage”

However,someone on this forum posted a picture of a re machined 5″  4 jaw independant chuck to fit direct to a 4″ spindle flange.

I thought this was very clever,& would like to emulate one day, maybe the poster can repost the picture?

Incidently, i sometimes run a 5″ chuck on my mini lathe!!, i think on an sc4 you’ll find any expended effort or cash well worthwhile.

A few words of caution.

The size of chuck supplied with a lathe is the one which the manufacturers have based their lathes design around. When the standard chuck is gripping within its designed range. Then the jaws usually miss things like the Carriage casting and the Cross-slide.

Fitting a larger chuck will alter the original configuration. At the new maximum gripping diameter the jaws will undoubtedly hit something, unless great care is exercised at all times. Not to mention the additional weight on the bearings, both static and dynamic. Plus the overhang that the new configuration of a larger chuck brings. The body of the larger chuck usually means it is deeper front to back, so there will some loss of maximum work length that can be done with tailstock support. With any work held in the new chuck being further away from the spindle bearings, than was originally intended.

There is also the fact that although the chuck can hold and pass larger diameters through the body of the chuck. The restriction of what can be passed through the spindle itself. Makes this extra capacity only suitable for short pieces of work.

At the end of the day the choice is down to the individual, but having a different point of view might make the difference in making the right choice.

Regards

Gray,

The four jaw i fitted was a thin type too keep the centrifugal mass down.  When mounting the part in the chuck as said make sure that the jaws clear the bed.  Also you may have to imaginative about how the tool is held in the tool post and the type of tool used.  With some tool positions you may not be able to machine the whole face in one go.