ace
Statesman
Posts: 528
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Post by ace on Jun 15, 2008 23:04:54 GMT
Hi all
I am about to purchase a new 3 jaw chuck to replace my original that has seen better days. However there are many available but due to funding the one I am looking at requires bolting on to a back plate and my question is how do I ensure that it is bolted on dead center. my old chuck is on a back plate but is only 100mm dia and the new one is 125mm so it won't fit.
Any ideas from the pro's............. ;D ;D ;D
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Post by baggo on Jun 15, 2008 23:28:31 GMT
Hi Steve,
The usual thing is to buy a part machined backplate i.e. one that has the thread and the spindle register machined, and then machine the face to match the register in the chuck. That way the new chuck should run true to the spindle, Various ME suppliers sell the part machined backplates.
John
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Post by circlip on Jun 16, 2008 9:09:04 GMT
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Post by circlip on Jun 16, 2008 11:29:09 GMT
A second post as opposed to a mod. Ace, The accurate part is the location between the bore of the BACK of the CHUCK and the diameter of the REGISTER turned on the backing plate, about 0.001" interference, warm the chuck and chill the backplate to fit.
The bolt holes don't have to be super accurate, so make sure these are lined up before final location/fitting.
Regards Ian.
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Post by Nigel Bennett on Jun 16, 2008 11:55:42 GMT
The other way is to turn the backplate register to a rattle fit in the chuck. Fit the chuck, leave the bolts lightly nipped up. Piece of ground bar in the chuck - make sure it's round and not "lobed" - and check eccentricity with a clock gauge. Tap chuck true with a soft mallet, keep on clocking/tapping until it runs true, tighten up screws.
Works if your chuck scroll is worn to enable you to repeatedly hold work of the same diameter accurately.
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Post by circlip on Jun 16, 2008 17:27:29 GMT
Sorry Ace, my old laptop is reading wrong again, was sure you said NEW chuck, if your going to use an old one, why are you replacing it?? Also if you rely on tapping and flatulating with a slide fit on your backplate it's going to affect the balance of the lathe. Hey, you could fit a much larger backplate and add bob weights.
Regards, your eccentrically ( and excentrically) Ian.
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ace
Statesman
Posts: 528
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Post by ace on Jun 16, 2008 20:59:41 GMT
Again many thanks chaps. I think I will have a go at machining a part machined back plate from Chronos as per John's suggestion as they sell them threaded for a Myford. Ian I am buying a new chuck not fitting an old one, the original chuck is over 40 years old and has seen some action by the look of it. there is a lot of wear in the jaws and when I grip something in it does not run true. I have stripped it down and the is wear in both the jaws and the chuck body, and there are signs that the previous owner has caught the chuck on the cross slide or something as there is damage on two of the jaws. So I think its time the old girl had a new one and with a bit of luck the motor switch will be sorted tomorrow. My sparky thinks the problem is due to the coil sitting to one side and is preventing the thingy from connecting properly with the other thingy, or something like that he said. ;D ;D ;D. I will post a pic of my new chuck and plate if it goes well, if not then I won't. ;D  ;D Steve |
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Post by circlip on Jun 17, 2008 7:15:42 GMT
A very astute Sparks you've got there Steve, we ALL forgot the thingies  ;D ;D |
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ace
Statesman
Posts: 528
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Post by ace on Jun 18, 2008 21:19:08 GMT
Circlip
My knowledge of electrics is as extensive as it is with computers, and when he started to explain the problem all I could hear was ..... blar blar blar. ;D ;D ;D
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;D
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