FuryRebuild
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| posted on 9/11/19 at 12:41 PM |
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center / gun drilling bolts
I've been trying to find any formula that states what the ratio of metal to remove is safe when centre-drilling bolts?
Can anyone point me in the right direction?
Thanks
M
When all you have is a hammer, everything around you is a nail.
www.furyrebuild.co.uk
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steve m
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| posted on 9/11/19 at 07:06 PM |
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Why do you want to drill holes in bolts ?
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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coyoteboy
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| posted on 9/11/19 at 11:04 PM |
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If youre going to drill out the centre, the only way of knowing if it's safe is to accurately assess the load on the bolt. There's no
magic formula, no material removal will be "safe" unless the bolt is a unloaded cosmetic item; whatever you do you will be eating into
design margin.
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harmchar
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| posted on 10/11/19 at 04:52 PM |
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This is going to be an interesting topic. Not sure if there is an actual formula for working out the lost strength in a drilled out bolt, but a simple
experiment in the garage would be to torque up a bolt through a plate and see what torque the head shears. Now do the same for a drllied out bolt and
I'll bet you 5 beer tokens that the torque is less. Bolt will be more likely to fail at head.
The bike forums are full of subject matter of saving weight by drilling material to the point that it is just stronger than it has to be. Problem with
doing it on car parts is it's more difficult to judge the forces that each bolt will see.
Can we ask for what purpose you would require to centre drill a bolt for? If it's for saving weight, there is better places to do that. If
it's for a college or uni project look up Drillium.
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jacko
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| posted on 10/11/19 at 08:23 PM |
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Can a bet it's something to do with suspension bolts and grease nipples gentlemens bet that is
Jacko
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Bluemoon
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| posted on 11/11/19 at 10:00 AM |
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quote:
Originally posted by jacko
Can a bet it's something to do with suspension bolts and grease nipples gentlemens bet that is
Jacko
Yep probably, may do that on mine.
Strength reduction will be less than you might first think, as the center of a bolt takes less stress most of it will be around the edge, i.e. think
about tube and solid rod... BUT as Cyitebiy states, it will have some effect!
You can get drilled bolts for vacuum system use (experimental physics ect), not cheap but a common use for drilled bolts..
[Edited on 11/11/19 by Bluemoon]
[Edited on 11/11/19 by Bluemoon]
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coyoteboy
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| posted on 11/11/19 at 10:25 AM |
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Assuming thin drilling (relatively - 1mm in a 10mm bolt eg)
If your bolt is loaded in shear you're reducing it by the area reduction (approximation).
If your bolt is loaded in tension you're also reducing strength by the area reduction.
If your bolt is loaded in bending, eeeew design it properly.
If your drilling is larger, you start interacting with the stress field nearer the threads, at which point you can get odd deformations (think thread
angle compressing the bolt and allowing it to slip through like a ratchet).
[Edited on 11/11/19 by coyoteboy]
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nick205
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| posted on 12/11/19 at 05:11 PM |
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To the OP, can we ask what you need want to do with them?
When building my Indy I centre drilled 2x M8 socket bolts to feed the front indicator wires through for fitting to the GRP nose cone. No real load on
the bolts and they were changed shortlyafter SVA as well.
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907
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| posted on 13/11/19 at 07:53 AM |
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I've had hollow bolts and shafts on several of the bikes that I've owned, including wheel spindles and swing arm pivots. Proper stress
points.
However; I'm sure that the o.d. will have been up-sized to allow for the missing centre.
i.e. A 25mm tube could be lighter and stronger that a 20mm solid bar. Not just a question of drilling the 20mm bar.
Paul G
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