I've done what you said, with a couple of different bits of stock a few times and yes the high point is always in line with jaw 2.
I think the jaws that are in there are soft jaws since there are machining marks on them and when I filed off the burrs it felt like mild steel.
I put the other (definitely soft) jaws in and found that one jaw was in the wrong place. It turns out that I have to mount them in the order 2-3-1 for them to meet at the centre. They seem fine then.
Found a C spanner on eBay to get the chuck off:
I think that's the right one. Cheaper to CNC mill my own though.
Regarding the oils, one official cross reference I found was Texaco Rando HD (only reason I remember that, is that's what we used to use at work before switching suppliers).
What Rando HD is, is a pretty standard hydraulic oil with some basic additives, for use in most normal hydraulic systems.
The slideway lube you linked to will most likely have tack additives, so it sticks better, and I personally wouldn't be putting it in a gearbox.
Try some of your local agricultural merchants/dealers, as they normally stock hydraulic oil, although 68 is not a very common oil (32, 46 and 100 are all far more common)
I dismantled the 3 jaw chuck - there wasn't that much swarf inside. It made no difference to the runout though I didn't really expect it to. I did it so I can try and machine the jaws. The problem is if I machine the jaws it is surely only going to be accurate at the diameter I machine it?
I've been looking at getting a new 200mm chuck - wow what a lot of money! I'll need one of these backplates:
I've googled and apparently this chuck is reasonable quality - it's also the cheapest I found:
I don't know how long that is on offer for?
Either that or a new Pratt chuck is £229.
Last edited by Jonathan; 20-04-2011 at 04:51 PM.
Dremel mounted on cross slide, will help rescue the existing jaws. Just make sure you clean all the grinding dust back of once you're finished.
Remember a three jaw chuck isn't good for accurate work. For accuracy you really need to be using a 4 jaw, or collets.
I've reground the chuck jaws using the die grinder. I found a grinding stone that looked fine however the shaft was 1/4" not the 6mm I needed. I put it in the mini lathe with the 4 jaw chuck and carefully turned it down to fit. I used the autofeed on the lathe and took off 1 thou at a time.
I measured the runout the same as before and got 0.09mm (10mm from chuck) to 0.15mm (@50mm). It was the same with smaller stock too. I've not tried anything bigger than the diameter I ground it at (50mm ish) which might be the problematic one since then the corners of the jaws will be in contact.
I'm happy with that for now. It's clearly not as good as a new chuck, but good enough for most things. It just means I'll have to use the 4 jaw a little more often.
Last edited by Jonathan; 20-04-2011 at 10:11 PM.
It seems the chuck is not too bad so why not buy new jaws for it.
Soft jaws are not really high precision they are really made to hold custom parts and being soft will be wearing quickly.
Using a 4 jaw chuck you will be getting jaw marks on your work so should be avoided at all cost you just cannot get the correct even grip without marks. Then add the time for centreing.
Edit: Found some jaws, not checked if they're the right ones:
Considering that whole new chuck is £125 they seem a lot...get what you pay for I suppose.
Last edited by Jonathan; 21-04-2011 at 12:00 PM.
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