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Post by engineeringtech on Mar 13, 2009 18:42:56 GMT
Hi!
I just bought a new aluminum handwheel for my Bridgeport vertical mill. (manual feed handwheel) The center hole on the new knob was .375" diameter, and I needed .499" to match the old broken knob. It's supposed to me a sliding slip fit on the shaft, but not so loose that it spins or feels loose.
I carefull balanced the wheel by wrapping lead solder opposite the side with the handle, then chucked the wheel in my lathe. I spun it up very slow, and it seemed to run very true. I drilled out the hub to .484 diameter. I didn't have a .499 reamer, and thought I could get away with the .500 reamer. I wound up with a hole that is closer to .5035 than .4990. And the handle slides too loose to make me happy. I should have anticipated the oversized hole. The reamer shank was very short, and my lathe tailstock is slightly low. (This tailstock has no adjustments, and can't be easily fixed.)
I know I could re-chuck the wheel, bore it out, pressfit a brass or aluminum sleeve, then ream all over. Is there anything else I could do?
Thanks for listening!
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Post by Tel on Mar 13, 2009 20:07:34 GMT
Short of shimming it, which I don't think would be very successful in this case, your plan to plug and re-bore is probably the best approach.
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Post by Deleted on Mar 13, 2009 20:07:36 GMT
Hi. A lot of us have landed up with oversize holes: you are not alone! I'm assuming the wheel is not meant to slide up and down the shaft, and that you would wish to remove it at some time. If the wheel has a keyway you could either shim up the key to take up the 4 thou slack, or make a new key to do the same job. Of course, if the fitting is permanent there's always Araldite......
JB
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SteveW
Elder Statesman
Posts: 1,399
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Post by SteveW on Mar 13, 2009 22:44:55 GMT
Chances are you're going to need to bore the hole out even more so that when plugged there is enough metal there to be cut back and still be robust enough to last.
If you are careful a shrink fitted plug could be to best way to start.
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Post by maninshed on Mar 14, 2009 17:54:52 GMT
Yep over bore it and either press in or loctite a plug in and strart again. Go to 3/4 or even and 1" so you have plenty of metal to go at.
Regards Martyn
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Post by engineeringtech on Mar 17, 2009 16:41:46 GMT
Thanks all. I figured on having to rebore and fill. But I had to ask.
Particularly like the idea of the shrink fit plug. I'd rather not heat the wheel. Was wondering if I could chill down the plug with freeze spray and then inserting it into the oversized hole. Has anyone here tried that?
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SteveW
Elder Statesman
Posts: 1,399
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Post by SteveW on Mar 17, 2009 21:19:19 GMT
Particularly like the idea of the shrink fit plug. I'd rather not heat the wheel. Was wondering if I could chill down the plug with freeze spray and then inserting it into the oversized hole. Has anyone here tried that? You can keep it simple by using boiling water and your freezer spray to get approaching 200C differential between them but you'll have to be quick and best do the math to get the correct sizes at the temperatures used. If you overlap the sizes to much you could burst the wheel in an instant. Else use locktite and remember to include room for it. A neat trick here is to include a wasted area for the 'glue'. |
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Post by petercolman on Mar 20, 2009 20:09:46 GMT
Dont try the high interference shrink fit as you will burst the casting, simply machine the hole out oversize, make the new centre and get it right for fit on the shaft and having machined an undercut in the outside diameter, stick the whole lot together with araldite standard, not rapid. The clearance betwen the bush and wheel can be quite large say .008"and it will come up on center. BTW it helps to warm the glue first to aid flow.
Peter
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hew
Member
Posts: 7 
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Post by hew on Mar 21, 2009 9:40:02 GMT
Crude but effective is to run a bolt through the hole. :oYou'll need a bit of taper on the end to get it to start but when it's going it will displace some of the metal inwards. It may end up undersize so ream to size or simply hit on, if you want you could fill with epoxy if you wanted complete bearing.
Hew
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Post by johnstevo on Mar 22, 2009 12:30:37 GMT
If it's an alloy hand wheel you could try bumping the top of the hole with a slug of steel whilst supporting the bottom on a substantial base.
The idea is to squash the length so the surplus goes into the hole, you only usually get a few thou to move this way not 1/16 of an inch but that all you need.
nothing to loose if it doesn't work as you will still have to rebore and sleeve.
John S.
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Post by engineeringtech on Mar 27, 2009 15:53:41 GMT
Good ideas here. Thanks. I think I'll try bumping the hole first. That's all for now!
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Post by blair on Apr 14, 2009 15:35:53 GMT
Hi, I am new here but couldnt help, helping here, the fellow, who sugessted bumping the length with a slug is a good idea. Useing a ball bearing at least 1/4 bigger than the hole will work good as well you put the bearing on the bore it wont fall rite because it is much bigger, give the bearing a good whak with a soft hammer on both ends of your bore and that will close the diameter in by a few thou easially, we use the practice alot in the shop where I worked for 12 years our pieces were all big stainless parts for customer like praxair and power plants, so the id was critical and the parts way to big and value added to start again. this works good give it a try next time if you have already fixed it.
Thanks
blair
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