Trueing up chuck jaws

[irving2008]

I want to mount my pencil air-powered diegrinder on my lathe's cross-slide so I can true up the jaws of my chuck, along the lines of this article (at the bottom of the page).

The tricky bit will be getting the grinding wheel shaft parallel to the bed so that the jaws end up ground parallel... The cross-slide on my lathe is mounted on an ungraduated swivel and I have yet to find an accurate way to lock it so the slide travel is perpendicular to the bed...

The best solution I have come up with to get the slide perpendicular to the bed is to put the DTI on the cross-slide and the plunger on one edge of the chuck face, then spin the chuck to find the min and max values and rotate to set it midway, then keeping the chuck stationary, traverse across the face of the chuck and adjust the slide swivel to get the same reading and keep traversing back and forth and adjusting until it is constant across the face. That gets the slide right, but then how do I get the die grinder shaft parallel to the bed. Its not long enough to DTI sensibly along the shaft over the travel of the saddle.

Suggestions?

[irving2008]

No, of course I'll use the longtitudinal feed to feed the grinder into the jaws but i need to use the cross-slide to mount it on else it will be too low on the saddle alone and i'll still need the cross-slide to position it offset relative to chuck centre line. The issue is how to position the grinding wheel parallel to the bed. Or are you suggesting it doesnt need to be as long as sufficient of the wheel contacts the jaws while traversing along the bed? I realise you move it in and out of the jaws till no more metal is being removed so maybe the alignment of the grinding wheel is not critical as long as some of the wheel contacts the jaws.

[irving2008]

Bingo, you got it Irving (I was thinking you were wanting to feed using the cross-slide) Gritted teeth and a gentle hand to the ready!! The aim of getting the grinding wheel as large as possible is to retain use of the contact area of the jaws.

The centre height etc is marginal...main thing is to get the wheel down the middle.

How far out is it at present?

As I understand it you open the jaws, lock with the retainer then feed the grinder into the middle. Spin the chuck up at a low RPM (easy with my VFD) then move the grinder sideways on the cross-feed until it contacts the spinning jaws. move in/out longtitudinally until no more sparks on any jaw. move sideways a few thou and repeat until all jaws look smooth and unpitted. Not sure the size of the wheel matters that much as the spinning chuck gives it an effectively circular cut on the radius of the chuck although it needs ideally to be large relative to the width of the jaw otherwise grasping small items might be tricky. The wheel must be smaller than the chuck internal opening, the one I have is about 18mm dia and the opening of the chuck is 23mm, so I'll be able to pass beyond the jaws. I think the rigidity of the mounting of the grinder body is critical if a good parallel cut is to be achieved, so I am thinking of using some 50 x 50 steel angle bolted down with T-bolts and a strap over...

Making the retainer is a problem right now tho. The solution I think is to holesaw a 22mm hole in some 1/4" Ali sheet and then cut into 3 segments as shown in the article, drill and slot, then bolt together and use a file to even the edges up (I can't use the mill yet, but maybe I'll wait a couple of weeks till I can - its nearly done).