Spark erosion commission

Hello All,

Can anyone help me find an affordable way of getting keyways spark eroded into two gear cutters I have acquired?

One is completely without a keyway, the other comes with a 1/8 inch wide version. I am looking for 1/4 inch drive in each.

Regards

Brian

These cutters probably don't need a keyway for the sort of strain they are designed for. Only very heavy production work is likely to need keyways; most work does not fall into this category. Colin

Better off without keys so when it gets jammed it just slips and does not rip up the work, damage you division device and bend the arbour etc.

Dull

There have been a couple of very simple designs in ME or MEW in the last few years I think and some oare on the web. Since it is only a couple off you don't need teh most sophisticated design. The simple ones just use a resistor to charge a capacitor from a 12-24v supply, then as the electrode touches the work and sparks the current is passed through a solenoid coil to lift the electrode up off the work thus breaking the circuit. Gravity makes it fall and repeat. It could be lashed up in an hour or two depending on how fancy you make it,.

You could make a special dual size key for the one that has a slot, using Al or brass to provide some relief in a jam.

Hi Brian

You don't mention the diameter or size of the cutters, If your arbour is in good order and the collars are in good condition you may not need a key If you keep the feed and depth of cut light. If you are hand feeding if the cutter stops you stop.

The biggest risk I find with milling with large cutters on an arbour is when they jam under power feed, the perfect combination to turn your arbour into a boomerang while creating special effects sounds and even fast moving objects that hopefully miss you..... Hmmm

One possible (Left field) solution would be to epoxy a keyed collar as large in diameter as practicable on each side of the cutter. Then use a key on each side of the cutter. If you make them from mild steel you should be able to broach them in the lathe or file them. Epoxy in sheer is very strong and the cutter with collars would still be clamped on the arbour leaving little possibility of the joint failing

Regards
John

Thank you all for the suggestions,

Colin and Dull. You may be right, but I would be happier with a driving key

Bazyle. I had thought of that and might adopt it in the end, the plain cutter will have to rely on clamping force

John. These are the standard 60-65 mm diameter gear cutters with 1 inch bore, the cutter width is 1/4 inch at the bore. Again, I would rather have a drive and cut gear teeth under power, it leaves a better finish. The mill, a small Senior, actually slips the internal; segmented drive belt if the going gets tough, so there is overload protection

Regards Brian

Brian,

have you considered "World’s simplest EDM machine" which can be found on the Model Engineering web sites DVD - **LINK**

**LINK**

**LINK**

Hello Vaughan and Bazyle,

Useful references for me to follow up, thank you both for tracking them down.

Kind regards

Brian

Brian, If by chance you are going to be near Waterloo Ontario Canada in the near future you are welcome to drop by and I will EDM your keyways for you on my homebuilt EDM system. It is based on the Ben Fleming design from USA.

PM me if you will be traveling near me and want to do some EDM.

If you build an EDM of your own, beware of any that oscillate the electrode. By nature, due to necessary mechanical clearance for a moving electrode,they are much less accurate than machines with their electrode on a precision slide (like the Fleming EDM). You do NOT need to oscillate or vibrate the electrode for EDM, and NO high precision commercial EDM systems do.  The most critical factor , by far, that I have found for good EDM performance is using a commercial EDM dielectric oil and having adequate, even flow of flushing oil through the gap where the sparking is occurring. Water, kerosene, etc have been tried on my machine but the best performance has been with Rustlick or Valvoline EDM oils. Check your local oil supplier or mouldmaking materials suppliers to find a true EDM oil - it makes a huge difference.

I recall the EDM described in ME was by a gent called Walker and in addition to being an electrode jiggler it had some open conductor strap and tack head "switches" for connecting capacitor banks that operated at 220V line voltage, which could be extremely dangerous. Also, very special paper wound capacitors were specified, which may be hard to find and expensive, and are NOT necessary for a working EDM.

Cheers JD

Edited By Jeff Dayman on 13/09/2014 17:23:23

Edited By Jeff Dayman on 13/09/2014 17:28:23

Hello Jeff,

That is a very generous offer, thank you very much.

Being UK based I can't take it up, more's the pity. It would have been nice to see it in action too. Thank you also for the warnings on a home built EDM machine; I am learning quite a lot about the process one way or another.

Kind regards

Brian