Titivating a Wire EDM Machine

[awemawson]

However if you contrast these two pictures you can see it is progressing

[hermetic]

Thanks for the link to the book Andrew, very interesting, I get it now.
Phil.
No experience with this type of kit, I will continue to follow with great interest.
Learning all ze time!

[micktoon]

Hi Andrew , Interesting post and well explained. It looks like the acid is doing its job, good luck with the project, I will be interested to see it running, I remember seeing skips of the used wire in the scrapyard.
  Cheers Mick.

[awemawson]

A few more hours in the citric acid bath and at last things have come up reasonably clean - certainly enough for me to be able to start dismantling with some confidence of success.

[awemawson]

My main concern was getting the insulators off without cracking them. They are machinable ceramic, so could be re-made, but that stuff is horrendously expensive

[awemawson]

The other metal bits were less of a concern. Amazingly some of the screws actually unscrewed, however several had lost too much material from their heads in the hex socket and had to be carefully drilled out

[awemawson]

The part that holds the bearing for the lower wire pulley will need re-making as it is going to have to hold the new contact electrode as well as the pulley - this is it:

[awemawson]

I seem to remember that I had to replace that shaft that sticks out of it when I re-did the bearings when I got the machine in the first place.

Now to try and remember how they all fit back together 

[awemawson]

A little bit of progress today - mainly taking decisions as to which way to jump.

It would have been much easier to mount the new Tungsten Carbide contact to the outer side of the wire (ie lhs looking at it), this way I could re-use the existing pulley mounting. However it would be in the way when re-threading the wire and make an already tediously hard job harder.

So I decided to let the wire touch the contact tangentially, and  wrap it round the contact by taking the pulley nearer to the machine body - ie to the right as you look at it. However this meant slightly modifying the arm to make room for the pulley

[awemawson]

It was a bit like cutting hard swiss cheese - all very porous.

In the picture below, the two white nylon bars represent where I will mount a delrin insulator onto which the contact will mount using a stainless steel stubby axle. The end of this axle will take the power connection.

Slab of delrin, and a bit of stainless bar to re-make a longer pulley mount are on order, along with numerous stainless cap screws

[awemawson]

Being at that frustrating point of 'waiting for bits to arrive' I've embarked on trying to clean up and restore the concertina 'curtain' arrangement that is suposed to stop water splashing out of the working area of the machine.

When I got my machine the curtains were flapping about, the far one is torn in several places, and the sliding seal mechanism that surrounds the arm and holds the inner end of the curtains is missing

[awemawson]

Now a few years ago I had the opportunity to rescue parts from a 'Model L' Fanuc Tape Cut (mine is a 'Model M') - the 'L' has a smaller operating envelope, so for instance the arm that I'm working on is a smaller cross section.

However I did manage to get the curtains, and although encrusted with detritus it turns out that they are the same size (110 mm tall) as the Model M. So after a week end soak in citric acid they've come out perfectly usable - a result 

[awemawson]

From the donor machine I also got the sliding seal arrangement, and although too small for my arm at least shows me how it's supposed to be. So this also was cleaned up for inspection - all these bits were very heavily encrusted in, presumably, whatever the machine had been cutting, which had then oxidised into a solid mass

[awemawson]

The actual seals are 10 mm square closed cell neoprene foam, which eBay has provided me with  And rather than bend up the complicated shape out of stainless sheet, I'm going to machine a version from 20 mm square stainless bar, with a 10 mm groove to house the seals.

What I hadn't appreciated, when I robbed the donor machine, was that I had obtained a pair of 'grooved ditch' wire guides and their mounting. I frankly hadn't recognised them as what they are. These are a slightly less precise method of location for the wire, but vastly easier to thread. Using them will need quite a bit of adaptation - the upper one will just bolt straight on, but the lower one will need a bit of engineering, and both will need provision for flushing nozzles.

[awemawson]

Note the delicate 'salmon pink' copper deposits - these were covered in crud like everything else, and a dip in the acid bath has cleaned them, but I suspect this machine had been cutting copper, and the copper oxide crud, and the acid has plated the stainless steel ! It'll come off easy enough later.
Fitting these will be another project - they'll be put to one side for now.

When I got access to the 'Model L' it had already been pilfered sadly, but I did manage to get the entire Fanuc 6 cnc control with the exception of it's operator panel and screen as that had already gone. Poor thing was under a tarp in a back alley behind a factory when I got to it, and was in a very sorry state.

[awemawson]

So now to start dismantling the upper and lower runners for the curtain - all pretty fouled with accumulated build up of residues, now caked rock hard.

Starting with the brackets that tether the curtains on the outer edges

[awemawson]

Then remove the 'upper track' - easy so far but this revealed a problem.

Some plonker in the past has mounted the lower track using ordinary HT cap screws, not stainless ones 

[awemawson]

Only two rusted cap screws, but in a confoundedly awkward place. As they are so low down on the base, the tray that surrounds the work space limits access. 

The rear one had entirely rusted the head off, and the front one was so nearly completely gone that there was no chance of gripping it to unscrew, so I ended up grinding the remains away to allow removal of the lower runner

[awemawson]

This has at least given me access to clean the work area up a bit - I'm actually amazed how well it's come up, and I'm not finished yet.
This is the result of the 'first clean'  :

[awemawson]

Now to get at those rusted screws I will almost certainly have to remove the stainless steel 'tray' that surrounds the work area. A pain as I didn't really want to delve in so far, and it's going to need sealing back to prevent leaks.

Meanwhile the runners are soaking in phosphoric acid (running short of citric !)

So how to drill out and re-tap these pesky screw  Any suggestions welcome if they mean I don't have to remove the tray - distinct case of 'scope creep' here 

[awemawson]

The 'curtain rails' have cleaned up really well. It took quite some soaking, and scraping, and certain bits were so caked I had to sand blast them, but the result is more than acceptable. Quite surprising seeing what a state they were in 

[awemawson]

So in the absence of any other ideas I took the bull by the horns and removed the 'tray' that surrounds the work area. 32 screws later it was off giving far better access to the rusted screws

[awemawson]

Fortunately the rubber gaskets that seals the tray to the main base remained stuck firmly on the tray and came away cleanly with it. There is evidence of silicone sealant having been applied previously to this joint and I will probably do the same on re-assembly.

So the next job is to fabricate some sort of drill guiding jig to clamp on to avoid boo-boos.

However I have to stop now as I'm due to collect 'Robert the Boar' from Kent. 'Blossom the Sow' is hopefully coming in to season and needs covering to produce a litter that will be ready to wean in early spring.

[awemawson]

So Robert the Boar is now playing Piggy Back with Blossom and I can return to drilling out rusty screws !

The front screw had just the slightest bit still protruding, so I could use it to centre the jig. Jig comprised a bar, through drilled 5 mm (tapping size for 6 mm) and counter bored 5.8 mm to accept the short screw stub. This I clamped on and drilled through, and eventually it came out nice and concentric,as when I was re-tapping it I could feel I was following the original thread, just clearing it.

I started using my air drill, reasoning that it was more controllable in this confined space, but it didn't have enough umph and the mains electric was called in to help.

[awemawson]

Now the front screw was easy to centre using the jig. Nothing protruding on the rear one, so I had to use my 'Optical Centre Punch'. Not the easiest of places to use it, especially as I had to rig a torch to get enough light into it, but it worked ok

The previous screw had drilled out happily using ordinary HSS jobber drills - not this one. Even a brand new unused drill wouldn't touch it  I ended up taking a trip to our nearest 'tool shop' - really just imported Chinese stuff in the main, and getting a cobalt drill. Out of stock in 5 mm, ended up drilling through at 4.5 mm and then managed to clear the last 1/2 mm with an hss drill.

Again this hole tapped out nicely following the original threads, so a success, but what a palavour just for two rusty screws 

Now I know what I want for Christmas - a set of cobalt drills - went through like butter