Seized bolts in aluminium

bromleybysea

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I had to disassemble the burners on my stove because the thermocouple on one has gone and it's the only way to get the top plate off. (Force 10 stove, Sabaf burners) The burners are two-piece aluminum castings held together with thin stainless screws, I reckon about 3/4mm. Inevitably, the screws have seized into the castings and have snapped off. I need to drill them out and replace with slightly oversize bolts and nuts but it's proving difficult to drill the bolts out as the drill flexes and wanders off the bolt into the much softer aluminum, even using a drill press. Any tips on how best to drill these bolts out of the alloy?
 

Poignard

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I had to disassemble the burners on my stove because the thermocouple on one has gone and it's the only way to get the top plate off. (Force 10 stove, Sabaf burners) The burners are two-piece aluminum castings held together with thin stainless screws, I reckon about 3/4mm. Inevitably, the screws have seized into the castings and have snapped off. I need to drill them out and replace with slightly oversize bolts and nuts but it's proving difficult to drill the bolts out as the drill flexes and wanders off the bolt into the much softer aluminum, even using a drill press. Any tips on how best to drill these bolts out of the alloy?

As you have already found, unless you can stop the drill bit from wandering, you are on a hiding to nothing. What I would do is to get a sharp centre punch and centre pop the screw. Then I would use a sharp centre drill to drill out the broken screw. If the centre drill is too short to drill right through you will, at least, have a hole to guide a normal twist drill. If I possibly could, I would clamp the burner plate onto the table of a drill press. Then drill at slow speed.

A centre drill is the best thing to get the hole started because it is very rigid. Spot drills are also much more rigid than twist drills but not as readily available as centre drills but you can get them from MSC/J&S Industrial Ltd.
 
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VicS

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Surely you dont mean ¾ mm thats minute!

However if you have an problems in finding a centre bit I have a box full with drilling tips ranging from 1/32" to 3/16"

You are not far away if you need to borrow one.
Assuming thats Bromley nr. Sevenoaks
 

Poignard

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Chemical question for VicS

My knowledge of chemistry doesn't extend much beyond mixing a G & T but I notice that when a s/s fastening becomes seized into aluminium. a whitish substance appears (some kind of oxide?) and it seems that this is what is actually holding the fastening. Whatever this stuff is, I was wondering if there is any chemical that could be used to dissolve it or break it down, without damaging the aluminium or s/s. Something very penetrative that seized parts could be soaked in. Plusgas sometimes helps when the corrosion is not too severe but, as far as I know, it is just oil in a solvent and doesn't attack the corrosion.
 

VicS

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Its aluminium oxide but its volume is greater than the metal it replaces so it locks the screw in tightly. I think the joint would be impenetrable to anything that might dissolve it.

Heat is usually the way forward to expand the aluminium but I dont think it will work on small screws.
 

Poignard

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Its aluminium oxide but its volume is greater than the metal it replaces so it locks the screw in tightly. I think the joint would be impenetrable to anything that might dissolve it.

Heat is usually the way forward to expand the aluminium but I dont think it will work on small screws.

Thanks for that. I'll carry on dreaming!

Mind you, there would be a fortune to be made for the inventor of such a product. ;)

Well, I'd buy a tin of it, anyway
 

Shibumi

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Is there any length of the SS screw left on either side of the aluminium and, if there is, can you get to it with mole grip type tools to exert a turning force?

Also, how thick is the aluminium compared to the diameter of the SS screw?

If the thickness of the aluminium is not much more than the diameter of the screws, and you can get to both surfaces, then clean off all the powder both sides, scrub some vinegar or similar mild acid into the mix using a brass wire brush or similar, then tap the dead end of the screw from both sides and, basically, keep 'working' it - they usually go in the end.

If the ally is thick compared to the diameter of the screws you will probably have to bore around them and use washers or whatever.

Steve
 

Neil

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There are kits (eg QuikCenter) available to hold drills centred in order to drill out a broken bolts or studs. I have no practical experience, but after a disastrous attempt to drill out a snapped ss bolt from an outboard casting, I wish I'd heard of it beforehand........

Something like this :
http://www.youtube.com/watch?v=RbDF9P1uDyk
 

macd

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Not much help to the OP (unless he has a good mate at a local aerospace facility), but the best way to do it is spark erosion. Magical at removing v hard things from softer things (like that tap I broke in the expensive bottom yoke of a racing bike...)
 

Hoolie

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I'm not sure of the way the burners are held together, but can you ignore the broken bolts and drill new holes alongside for replacements?
 

bromleybysea

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Thanks for all the advice. The alloy is very thick and the screws are thin- using a mole wrench just snapped one off, so I think the centre drill approach and then drilling out oversize and replacing with bolts and nuts is the way to go. It really pi**es me off that something made for marine use is almost bound to fail in this way. The Force 10 stove was nearly £800 when I bought it and is now nearly twice that. Burners you can get apart shouldn't be too much to ask at that price.
 

Amulet

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I had to disassemble the burners on my stove because the thermocouple on one has gone and it's the only way to get the top plate off. (Force 10 stove, Sabaf burners) The burners are two-piece aluminum castings held together with thin stainless screws, I reckon about 3/4mm. Inevitably, the screws have seized into the castings and have snapped off. I need to drill them out and replace with slightly oversize bolts and nuts but it's proving difficult to drill the bolts out as the drill flexes and wanders off the bolt into the much softer aluminum, even using a drill press. Any tips on how best to drill these bolts out of the alloy?
If the geometry allows it, drill a hole in a bit of mild steel and clamp it on top as a guide to the drill.
 

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