The Birth of a Grub Screw

[awemawson]

Only a mini project this one!

For some time I've needed a 5/8" x2" BSF socket grub screw in HT steel to complete my Edwards Box & Pan Folder rebuild project:

http://madmodder.net/index.php/topic,8981.0.html

For some reason they seem now to be extinct - shorter ones no problem but this needed the full length to make the necessary adjustments so I needed to make one - very simple except for the hex socket. Now I can EDM funny shaped holes were it not for the fact that my Eurospark diesinking EDM machine had a leaky set of bellows so was out of commission - so first repair the EDM machine:

http://madmodder.net/index.php/topic,9319.0.html

OK EDM now up and running so all systems GO 

So what do we want - well one of these but without the cracked hex hole 

[awemawson]

So now we need to make a male electrode. Simple milling job using a 5C collet holder with a hexagonal body. Needs a central hole, as diesinking is best done with copious flushing, and this lets me flush through the electrode. It's also useful for alignment when setting up.

[awemawson]

Now what to make it from - needs to be a tough high tensile steel. All I had to hand was a rather rough bit of 5/8 re-bar until I hit on a 2" x 5/8 BSF HT bolt on eBay - so that's what I used.

[BillTodd]

I have machined the head of a CS cap screw to make a grub in the past. Will be watching with interest:)

Bill

[awemawson]

So the bolt needs decapitating, and a central hole counterdrilling, as if you don't do this the electrode flushing hole will leave a pillar in the socket like a security fitting.

Note that I use thick brass shim round the threads to save them from the chuck jaws

[awemawson]

Then it needs setting up in the newly repaired EDM machine and a hole popping

[awemawson]

Now I decided to sink in 10mm - the original was 25 mm deep - far more than necessary. Take about 15 minutes so while it was at it I went off to put the window back in the Goose shed that was blown out in last nights winds. The machine has a micrometer 'stop cutting' adjustment so I left it to it.

This was the result

[awemawson]

All together a very satisfying mini-project that went smoothly. And the need for the grubscrew prompted me to fix the EDM machine 


Andrew

[mattinker]

Very nice!

Regards, Matthew

[Pete.]

Very cool. The only way I could have done that is with a rotary broach I think.

[John Stevenson]

Why couldn't you have just used a bit longer set bolt and left the head on ?

Just asking ?

[Pete W.]

Hi there, Andrew,

That's very interesting - an enviable facility.  I didn't realise EDM was so quick, 10 mm in 15 minutes is much faster than I thought.

What happens, corrosion-wise, to your Keats Vee angle plate when the fluorescent green tide goes out?  Does the fluorescent green soup have corrosion inhibiting properties?  If so, maybe that explains why it's so expensive.

[awemawson]

Why couldn't you have just used a bit longer set bolt and left the head on ?

Just asking ?

'cos I'm pig headed and wanted it 'original' 

(Actually I think the clamp arms would foul it.)

Nice hole though isn't it 

Andrew

[awemawson]

Hi there, Andrew,

That's very interesting - an enviable facility.  I didn't realise EDM was so quick, 10 mm in 15 minutes is much faster than I thought.

What happens, corrosion-wise, to your Keats Vee angle plate when the fluorescent green tide goes out?  Does the fluorescent green soup have corrosion inhibiting properties?  If so, maybe that explains why it's so expensive.

I was blasting rather faster than you would if ultra precision was called for - look at the bottom of the hole and you will see that the surface finish is quite granular, although the walls are smooth. At a lower current and hence lower speed the finish would be far better.

Well not sure about the corrosion properties, but although I dug that Keates out of my ammo box of EDM bits yesterday it had last been used at my previous workshop six years ago and I doubt that I scrupulously cleaned it then. It was 'workshop ready' if not 'salesroom ready'. However when the bellows first started leaking I slide a bit of galvanised sheet in the tank to stop the splashes coming though the vents, and that sheet was very marked up to high tide mark after only a couple of months immersion. It's probably the zinc that causes the issue. Normally I use copper or graphite electrodes, but on the rare occasions that I've used brass for convenience the electrode wear has been much faster - again zinc involved.

When it was first made the machine was designed to use paraffin as an electrolyte, and it would still happily use it, and it would be mammothly cheaper. But I hate the smell and don't fancy having large quantities of flammable liquids  in the workshop.

Andrew

[NeoTech]

You got a diesink.. I just went "you gonna make an electroce for what?" and then went -"wtf, he got a die sink..  ".. Screw is nice.. but that die sink ;)

[awemawson]

You got a diesink.. I just went "you gonna make an electroce for what?" and then went -"wtf, he got a die sink..  ".. Screw is nice.. but that die sink ;)

They are a much undervalued machine in my opinion. Loads in tool dealers sitting unloved    If only for removing the odd broken tap or ht screw that's sheared off they are useful. And as the 'tooling' is only male forms of what you want, in easily worked materials (copper or graphite) very complex shapes can be made with little trouble in the hardest of materials without distortion.

The 'clever' bit is allowing for the slight 'side wall arcing' that makes the hole a certain proportion bigger than the tool. I have reams of tables of allowances graphing cutting current against size against oversize, but I confess I just guess rather than calculate. In this case I allowed 10 thou (254 microns) and it worked so the key comes out with a pneumatic 'pop' sound from the socket 

Andrew

[John Stevenson]

Is your wire eroder working ?
Can it do 10mm HSS ? or rather can you ?

[awemawson]

Yes John it is and yes (sort of) can I. I'm not too hot on programming it though as I don't use it very often. email me what you had in mind

Andrew

[NeoTech]

Aquiring one of those around here cost like a left arm, your nuts and the first born child of 3 generations.. they are horribly expensive..

[awemawson]

Give me a shipping address and an open cheque and I'll send you one 

Here's one for you :

http://www.larchwoodltd.co.uk/machine.asp?id=840

Andrew