 undersize holes for press fit bushings, Trust me this is Porsche 914 related |
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| Harpo |
 Jun 20 2015, 03:54 PM
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#1
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Senior Member  Group: Members Posts: 1,304 Joined: 21-August 11 From: Motor City aka Detroit Member No.: 13,469 Region Association: None  |
When I went to remove my hood hinges the bolts had seized to the hinges. To prevent this from happening again I'm going to install bushings (bronze or similar) in my hood hinges. Because I want to make sure the bushing doesn't move I want to drill an undersize hole but I don't know how much smaller.
The bushing OD is 15.03mm is a 15.00 drill enough of an interference? Otherwise the next size down is 14.5mm Thanks David |
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| toolguy |
Jun 20 2015, 04:26 PM
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#2
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Senior Member Group: Members Posts: 1,276 Joined: 2-April 11 From: San Diego / El Cajon Member No.: 12,889 Region Association: Southern California 
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.03mm is .0012 inch. . it might fit if you freeze the bushing first. . .
If it were me, press fit interference for something around 15mm [9/16] would be .0005 thousands inch. FWIW, If you don't freeze it to shrink it, since it is brass / bronze it will probably press in and just shave off the excess and not stay tight after usage. Drilling a percision hole without an accurate mill will be a shot in the dark. . you're playing with thousandths of an inch. . A hand drill or a cheap drill press wont cut it. . I generally drill the hole close to the diameter and ream it to the correct diameter with percision reamers. . Another way to do it is once the bushing is in place, center punch the steel hood bracket all around the bushing to expand the steel. |
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| bdstone914 |
Jun 20 2015, 04:56 PM
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#3
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bdstone914 Group: Members Posts: 5,060 Joined: 8-November 03 From: Riverside CA Member No.: 1,319 |
QUOTE(toolguy @ Jun 20 2015, 03:26 PM)  .03mm is .0012 inch. . it might fit if you freeze the bushing first. . . If it were me, press fit interference for something around 15mm [9/16] would be .0005 thousands inch. FWIW, If you don't freeze it to shrink it, since it is brass / bronze it will probably press in and just shave off the excess and not stay tight after usage. Drilling a percision hole without an accurate mill will be a shot in the dark. . you're playing with thousandths of an inch. . A hand drill or a cheap drill press wont cut it. . I generally drill the hole close to the diameter and ream it to the correct diameter with percision reamers. . Another way to do it is once the bushing is in place, center punch the steel hood bracket all around the bushing to expand the steel. (IMG:style_emoticons/default/agree.gif) A twist drill can drill a hole larger than the diameter as the drill want to untwist under load. You may want to try it on a test piece first. I am sure I have extra hood hinges if you need them. Bruce |
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| Harpo |
Jun 20 2015, 06:39 PM
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#4
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Senior Member Group: Members Posts: 1,304 Joined: 21-August 11 From: Motor City aka Detroit Member No.: 13,469 Region Association: None |
Thanks for the suggestions. I do have a spare hinge bracket so I will try with that first. I will freeze the bushing and heat up the hinge.
David |
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| r_towle |
Jun 20 2015, 09:21 PM
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#5
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Custom Member Group: Members Posts: 24,705 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States
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Are you planning to take the hood off a lot in the future?
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| Harpo |
Jun 21 2015, 04:46 AM
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#6
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Senior Member Group: Members Posts: 1,304 Joined: 21-August 11 From: Motor City aka Detroit Member No.: 13,469 Region Association: None |
Once the car is painted and the hood has been refitted I hope to never have to remove the hood again.
David |
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