3 jaw chuck lubrication issue

I recently acquired an M250 with a rusted and stuck 3 jaw scroll chuck. Now dismantled and cleaned it is an iron 3 jaw scroll chuck, 6.5" diameter, mounting D1-3, with ID plate missing. The mounting plate was taken off the chuck body by the previous owner, and it lacks the M10 bolts. The plate is 20.6mm thick and the holes 34.8mm deep, what length should the cap head bolts be?...I guess they need to be grade 12.9 and 50mm long.

More interestingly, and the main question is that this chuck has an oiler hole, but despite a thorough clean I could not find the outlet. No oil appeared inside the chuck, so I took the oiler out to find a blind hole!! Photos attached. Has anyone information about this? Many (most) chucks don’t have an oiler, so one answer will be ‘do nothing and don’t oil this way!’. However the base of the hole is close to the recess at the inner diameter of the body, where it houses the jaw side of the scroll. Pratt supply a heavy chuck grease, and others on this forum have suggested a light oil that leaves a thin wax film for lubrication. With this in mind, any ideas about what size the passageway should be would be welcome.

Thanks

Richard

I would make the bolts about 3mm shorter than the bottoming out length. I would forget oiling, or greasing except after dismantling to clean. If you have a mill, you can make sets of soft jaws in mild steel and aluminium

If you are going to lube the scroll plate then use graphite grease or maybe copperease.

There are two areas to lube on a three jaw chuck. The internal side of the scroll plate with the gear teeth on it engaging with the chuck key barrels and sealed up away from swarf invasion likes grease. I once used black moly grease on my old Drummond chuck. Bad move. It sprays little black dots out the chuck key barrel holes all over the workshop on a hot day when the grease gets thin! Since then I use clear wheel bearing grease etc.

The other side of the scroll plate, with the actual scroll on it that engages with the teeth on the chuck jaws, is best lubed with a thin oil such as you use for general lathe lubrication (EG hydraulic oil or in my case leftover engine oil) to try to minimize the swarf that sticks to it.

LOL @ the blind hole. Classic Chinese QC! Any sized small hole should do the job. The hole in the end of your oil can spout will be the limit to flow anyways.

Edited By Hopper on 18/02/2022 11:45:31