spark eroder plans

As part of my new fishing/boating hobby I find myself working on outboard motors. One thing I have discovered is that when dismantling
an old outboard you can guarantee that no matter how careful you are a number of bolts are going to be seized and will shear off. So far I've been lucky enough to be able to drill them out, but at some point there will be one I can't do that with. Does anyone have plans, or links to plans, for a very basic spark eroder that would remove the snapped bolts? I'm sure I have seen small, basic, spark eroders for just this purpose.
On a related note, any tips for removing seized bolts would be helpful in case there are any I haven't tried yet. Mostly steel or stainless steel bolts in aluminium, and the corrosion is obviously due to years of being in salt water.
Thanks Kevin
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Kevin wrote:

There was one published in model engineers workshop possibly a few years ago now
There is an online index which should help you find the issues.
A quick look suggests issue 57 onwards.
Bob
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Hi Kevin, You could join SMEE, then you could follow the construction plans they are running in their journal, for a simple Spark eroder. As to how to do it without, first try not to let it happen by wrapping ALL bolts and screws in PTFE tape when screwing into Ally. Next, make a sleeve to to act as a guide for drilling out the broken screws, it is ridiculous to try drilling centrally without one. Facom do a pretty good kit, also from Snap-on I believe, that provides a drill guide, a drill and a splined insert to grip the broken bit. Always use heat to expand the Ally and break the corrosion, it is not worth even trying without, but don't use Oxy-Acetylene. It is better to get the whole casting warm than just the area around the screw. If you can put the parts in an oven they will heat nice and evenly, and you will not try too soon to undo the broken bits. Failing that a large soft flame from a Propane/Butane/Mapp torch. If you get the "feel" for when a screw is going to break, use heat before it is too late. Then try to undo the screw, if it moves a little , don't go Yippee and continue, work the screw back and forth till it is free enough to get it out. On outboards you can expect the screws to be a problem, and Stainless is not a good idea because of electrolytic corrosion problems. That's all for now otherwise you will end up with a book. T.W.
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Kevin heeft ons zojuist aangekondigd :

Take a look at this: http://homebuiltedm.tripod.com / Not quite finished it yet myself. There is also a Yahho-group for support. Dirk
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In article

Kevin,
I work on assorted old Japanese motorbikes.
If you don't possess a set of left-hand drill bits, go and buy some *now*.
They are absolutely brilliant for this problem. I've not met a snapped bolt yet that didn't grab, and just spin out when hit with a LH drill bit.
--
Nigel

When the only tools you have are an X3 mill, a
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l

T.W.
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In article

<G>
S'true.
--
Nigel

When the only tools you have are an X3 mill, a
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On Sun, 14 Mar 2010 00:21:22 +0000, Nigel Eaton

You must live in a parallel universe of perfect rusty bolt removal as my experience is the exact opposite!
I've found left handed drills to be almost the worse method of removal, very closely behind the tapered helically threaded tap like remover bits that are so hard they nearly always snap regardless of previous heat/cold/penetrating fluid.
If a left handed drill cuts properly then it won't grab and the force exerted on the fastener and its thread is minimal. All you end up with is possibly a nice neat hole ready for a properly engineered extractor.
The very best by far are the 6 or 8 parallel splined ones with a sliding hex collet (snap on do them but they are also available from someone else, maybe Facom) , next best the fast spiral very stubby ones (again snap on), followed closely by the tapered 4 spline square ones, mine are either Britool or Eclipse, anyway I've had them many years and they still do the job.
As for preventing seizing, nickel/lead anti seize on exhaust studs (probably now banned as it was so good) and Loctite medium strength screwlock / studlock everywhere else, stop the moisture getting in the crevice in the first place and most of the problem goes away.
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It's nice here... :^)

Oh I agree entirely on the "remover" bits.

I tend to start off with a small size, carefully centred, then work up.
I've *never* got too near the thread before the remains span out.
Maybe I'm just blessed... :^)

Never tried them.
--
Nigel

When the only tools you have are an X3 mill, a
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I'll keep on with my winchester of nitric acid. Works perfectly for getting steel bits out of aluminium (needs proper setting up though) :-)
Mark Rand RTFM
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