EDM / Tap disintegrator

I understand EDM machining, at least the basics but I don't understand how the technique can be selective, say removing a HSS tap from an aluminium crankcase?

Steve

message

understand how

aluminium

You point it at the tap and not the crankcase - simple really

The electrode on those simple ones is a thin walled copper or brass tube, and the idea is to sink it down so that the webs of the tap are cut off allowing you to blow or pick the bits out, never touching the base material.

AWEM

It's not. Get the aligment wrong, and you'll quite quickly be removing aluminium rather than HSS!

In this case, alum is said to work. Selective! Cordless!

Nick

In article , Steve W writes

Actually, for removing a tap from aluminium, some dilute sulphuric acid (battery acid) would work as well (and be a lot cheaper). Keeping it warm and stirring occasionally will speed things up, and you may have to build a little plasticine reservoir, and replace the acid once or twice.

Don't mess with concentrated sulphuric acid unless you have the necessary knowledge, and even the dilute stuff will damage eyes (and clothing).

Don't try it on steel; dilute H2SO4 will attack iron/mild steel/carbon steel; it won't attack copper, bronze or aluminium. Stainless steels will vary, try it first. Not sure about brass, may de-zincify, do some research.

I don't recommend you use hydrochloric acid in your workshop, it will work slower and will give off hydrogen chloride fumes which will rust things quickly.

David

I have a lot of experience with sulphuric acid - that's the one where you didn't realise the splashes got you until the jeans come out of the wash full of holes :-)

Especially after you mixed it with potassium chlorate and it popped and crackled a bit (the scars hardly show any more :-)

Mark Rand RTFM

In message , Steve W writes

Try very dilute and partially neutralised Chromic Acid! At a certain pH level and suitably diluted it will dissolve cotton but not wool! Which is how I once took a long ride on a London bus with no underpants and trousers that appeared to be intact but were no longer sewn together at the seams!

In article , Steve W writes

True, but even acetic acid will do this if left on for long enough. Use your old decorating clothes, and stick them straight in the wash if you are in any doubt about splashes.

David

BTDTGTTS!

In my mis-spent youth, when the anal-retentives had not quite got control of the asylum, I used to do this in my home lab if I ran out of matches. Bit of sulphur at the side to catch fire... (Whatever you do, don't try this at home if you haven't got the expertise).

David