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Bolt Broken Flush [message #299815] Tue, 16 October 2018 13:44 Go to next message
Kakugo is currently online  Kakugo   Italy
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(18) Geoff Duke
This is a question that has long dodged me, and the Internet seems to struggle to provide an answer.

I've broken my fair share of bolts and I've found those which broke flush to the surface are probably the hardest to remove because it's just so hard to properly center a drill bit.
On large bolts you can weld another bolt and pray everything goes according to plan (which often does), but small bolts broken flush in light alloy are another thing completely.
Very very rarely you can just cut/punch a slot in them with a small Dremel cutting wheel, but most of the time it means a trip to the machine shop, provided you can still find one, where you are often told that given the labor involved "it's just not worth it, mate", possibly a garbled way to tell you not to waste their time on such trivial matters. think

I've seen several novel ways to center a drill bit if the bold is in deep and they are very intriguing and may try one or more in the future, but so far I haven't found any "easy" way for bolt broken flush. Machine shops use very accurate (and very expensive) bench drills for the purpose, but these are out of question for the average tinkerer. And budget bench drills are the best way to turn your thread into a metallic pulp. Laugh
Does anyone know of a tool or method that may be worth experimenting with? Even a 50% success chance is worth a shot.

Thanks.
Re: Bolt Broken Flush [message #299816 is a reply to message #299815] Tue, 16 October 2018 16:36 Go to previous messageGo to next message
Quazi is currently offline  Quazi   United Kingdom
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(22) Giacomo Agostini
A bit of heat is a must in most cases, obviously more delicate operation with ally, a left handed drill bit can be your friend too, as it will sometimes free it off as your drilling the hole into it, if it snags it'll sometimes come out.

I get this all the time, welding to it is the prefered option but not always an option. A heat gun is next, centre punch, l/h drill bit, plenty of four letter words, an da box of miracles.


Usually works for me. Laugh

[Updated on: Tue, 16 October 2018 16:36]

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Re: Bolt Broken Flush [message #299818 is a reply to message #299816] Tue, 16 October 2018 21:04 Go to previous messageGo to next message
Gearbox is currently offline  Gearbox   United Kingdom
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(15) Kenny Roberts
Is the bolt flush or just below the surface. If below, you can use a steel dowel of the same diameter as the hole with a guide hole down its centre to use as a pilot for your drill. You will need to measure the hole and get someone with a lathe to turn up the dowel and centre drill it. Hope that makes sense.
Similar if the bolt is above the surface, just adapt with a stepped hole down the dowel. Step to locate and smaller centre hole to guide the drill.
If flush, then more difficult to use that idea. Possible to build the top of the bolt up with weld and then put a nut on it. Heat from the welding often helps loosen the bolt.
Re: Bolt Broken Flush [message #299819 is a reply to message #299818] Wed, 17 October 2018 11:49 Go to previous messageGo to next message
Kakugo is currently online  Kakugo   Italy
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(18) Geoff Duke
Gearbox wrote on Tue, 16 October 2018 22:04
Is the bolt flush or just below the surface. If below, you can use a steel dowel of the same diameter as the hole with a guide hole down its centre to use as a pilot for your drill. You will need to measure the hole and get someone with a lathe to turn up the dowel and centre drill it. Hope that makes sense.
Similar if the bolt is above the surface, just adapt with a stepped hole down the dowel. Step to locate and smaller centre hole to guide the drill.
If flush, then more difficult to use that idea. Possible to build the top of the bolt up with weld and then put a nut on it. Heat from the welding often helps loosen the bolt.
Actually I saw a very neat way to "guide" a drill bit in the first case by using a bolt drilled in the middle using a lathe. I still have my father's old late. I've never used it and it's a piece of junk but since this is just a case of drilling a hole in a cheap Allen head bolt I may try my hand at it. All I need are some cobalt-alloy drill bits which our Chinese friends sell for cheap. Wink

However, as you say, if flush you are in trouble. think
And if you have a 5mm stainless steel bolt broken flush in a Zamak piece you are in serious trouble. Laugh
Re: Bolt Broken Flush [message #299821 is a reply to message #299819] Wed, 17 October 2018 21:58 Go to previous messageGo to next message
Gearbox is currently offline  Gearbox   United Kingdom
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(15) Kenny Roberts
Now you are just complicating things.. Laugh
Re: Bolt Broken Flush [message #299829 is a reply to message #299821] Fri, 19 October 2018 10:38 Go to previous messageGo to next message
Kakugo is currently online  Kakugo   Italy
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(18) Geoff Duke
Gearbox wrote on Wed, 17 October 2018 22:58
Now you are just complicating things.. Laugh
https://photos.smugmug.com/Mixed-Gallery/i-fxLsctQ/0/182434b9/M/IMG_0643-M.jpg

Is that complicated enough for you? Laugh
Re: Bolt Broken Flush [message #300142 is a reply to message #299815] Fri, 04 January 2019 14:11 Go to previous message
Kakugo is currently online  Kakugo   Italy
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(18) Geoff Duke
Not pretty but it worked:

https://photos.smugmug.com/Mixed-Gallery/i-jD3R6NM/0/4baf7515/L/IMG_0672-L.jpg

Now I have a spare right BMW footpeg. Laugh

The trick was not so much cutting a slot in it but using the right amount of heat: different materials expand at different rates but, much more critically, post-mortem revealed the bolt was coated with that blue paste Germans love (I think it's Loctite 203) and I absolutely loath.
BMW and Daimler shop manuals say heat to 100°C to weaken, but I've found it's either a heat gun at 200-250°C or the blowtorch. Lesson learned.
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