Harrison L5 chuck datum

My L5 chuch screws on to a small threaded nose, but when run is seen to be out by a country mile. I checked the vertical face on the nose - zero run out, i checked the turned part of the nose between the face and the thread and got one thou run out. Im concluding the chuck or backplate is at fault. Chuck is 8" emco in good nick, 4 jaw scroll. Any advice or suggestions before I lay out for a new chuck - does anyone offer off the shelf threaded back plates?

Fizzy, I think that Tony (Lathes) stocks them or you could do as I did for my small (150mm) 4 jaw and buy s/hand catch plates. Remove the pin, face it and then machine to suit. Works for me and has done for 6 years now. Nathan.

More info required.

Is the lathe new to you?

Is the lathe not new to you and it has just started showing runout?

Are all mating faces scrupulously clean?

Are the jaws in the correct slots or even correctly loaded (ie not one pitch of the scroll out of position). There should be plenty of information available regarding putting jaws into chucks if you google it.

Martin C

Hi

Had it a few years, always been the same. All is clean, jaws in correct slots and matched set. What I havnt done is remove the backplate and check it.....tonights job

When you say it has 'always been the same', do you mean it has always had the run out?

Before you take the backplate off, don't forget to dot mark which hole in the backplate lines up with which hole in the chuck.

Is there run-out on the chuck body, and/or on a workpiece held in the chuck?

If the body is running true, but the workpiece of out, it would suggest either the scroll is damaged/running off centre, or one or more jaws is dodgy.

If the body is obviously a mile out as well as the workpiece, then it suggests that it's the interface between chuck and backplate isn't running true (or the backplate/chuck combination on the spindle). This could be either a bit of swarf, a ding somewhere, or when the backplate was originally machined to fit the chuck, then there was something up with the lathe spindle/backplate interface, which is now absent.

Clean and blue up the backplate/spindle joint and make sure there is good contact where there should be.

Only after checking the spindle/chuck interface, check the chuck side of the backplate for trueness; if it's off, re-machine in situ and refit the chuck, using the same blueing procedure.

I has this when I recently bought my second hand Warco gearhead. both chucks were virtually new, and wobbled excessively. Straight D1-4 camlock on these with no backplates.

There was at least 10 thou out on both the 3 & 4 jaw Scroll chucks. Several hours with a bearing scraper (on the chucks, not the spindle) and a tube of blue, and the final runout is less than a thou.
N.B. I only scraped the actual internal taper, not the flat bit.

Bill

Edited By peak4 on 15/01/2019 18:03:46

thanks for all the input - i will try to get time toinvestigate and let you know wnat I find.

Turns out the backplate was miles out in every possible way - I have trued it up and ive got about one thou runout so a massive improvment....need to do the same with the four other chucks now (I inhetited them). Thanks all.