Saturday, January 12, 2013

Four Jaw Chuck Soft Covers

All this four jaw work in the shop has me making all kinds of accessories for the darn thing. One thing that four jaw chucks do really well is hold onto things. Every machinist wants the things they clamp to not move with the least amount of clamping force. One of the reasons the four jaw chuck holds so well is most of them have serious serrated jaws. I can tell you that the chuck I have most certainly has teeth like a white shark. When dialing in the runout its fairly easy to push the part perpendicular to the serrations and actually drag the part surface along these nasty grippers leaving some really unwanted marks. I have formed up jaw covers before and have a decent selection in my box. Of course none of the covers I have fits the crocodile four jaw that I've been using lately. Time to make some covers. Its an easy job but with one or two subtle features.
 In this picture you can see the small serration within the larger that are causing me headaches. For my jaw covers I like to use thin copper sheet. I had some .030 thick sheet around so I cut out some blanks. The size of the blanks can be developed with a piece of paper if you want. I generally just run a tape measure around the jaw to determine the length of the blank. Cut a couple of extra for setup pieces while your at it. Invetiably you may loose one during forming or if you don't you will surely loose one under the machine at some point so an extra is great.
 Here is one jaw cover blank. I have marked a centerline on it to help align it for the initial bends. One good reason for using thin soft copper is you can easily hand form it. I like to use the actual jaw as a male forming die whenever I need to make a set of these.
Here we have the copper jaw cover blank clamped in my universal Kurt vise sheetmetal brake. The centerline was aligned with the center of the chuck jaw and clamped in the vise. The blank is automatically perpendicular to the chuck jaw because its sitting on the bottom of the Kurt vise.
This is the first bend. The thin copper is easy to bend by hand. The blank is now unclamped and rotated to make the second angled bend.
The first bend is indexed on the opposite side of the jaw. The reason for this is just for access to the blank for the bending.
Ok, two bends now and the blank is well indexed with the jaw. Coming up is one of the subtle tricks of making nice jaw covers.
If you examine chuck jaws closely you will notice they are concave so they grab round things well. What I like to do is preform this concave radius into the jaw cover before I make the next bends. You will see why in the next picture.
You see how the blank has poofed out a little from the angled surface from the radius forming. If you didn't add this preforming to the blank the first time you used the covers on something round it would distort the covers and try to make up that material from all the subsequent bends. Since these covers wrap around the jaws it makes for ill fitting covers that are sprung open and are loose.
Here we have the next two bends in nice and snug to the chuck jaw. I have slid the blank to the top of the jaw so I can mark the retention tabs. Notice I have positioned the blank just below the chamfer on the jaw. This will end up as their final position after the retention tab is bent.
I transferred the notch marks directly off the jaw. One cut with a pair of snips and they are ready to form.
Back in the vise for forming. Using the jaw insures the fit will be snug with all the bends indexed properly.
For the small tabs I just used a plastic caulking tool to bent the retention tabs around. These are the second subtle feature of jaw covers. If you don't add these then you will be fishing your jaw covers out of a filthy chip pan forever more. They always seem to fall out at just the right moment to annoy you.
I suppose you could cut off the excess if you wanted. I like the extra material to help guide the cover on the jaw. You can see the serrations made marks in the inner surface of the copper just from some light clamping. Already doing their job.
I cut two extra blanks but bozoed a bend, and snipped the wrong line for a retention tab on another. My tough luck that I don't have any spares now. "Life's tough, Its even tougher if your stupid." (John Wayne)

Thanks for looking.

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