Author Topic: Slippy clutch material? (Read 10960 times)

AdeV · « **on:** February 25, 2015, 06:31:41 AM »

As you may recall, I recently bought an EDM spark eroder. It's quite an old machine, and I'm guessing it hasn't been stored in a heated workshop of late; but for whatever reason, it's destroyed its friction clutch.

The idea is, the head descends under motor power, then moves up & down (under motor power); but one can manually wind the electrode back off the work piece (or wind it down into the work piece when you first switch it on). That's where the slippy clutch comes in, it allows you to wind the electrode up or down without affecting the motor. The clutch appears to have been some kind of fibre disc, maybe some kind of bakelite material, with a fairly shiny side which is obviously designed to slip under higher torques. The other side has a pin, obviously to hold it in place, but as a result now that the disc has disintegrated, the pin engages in a hole in the driven side, so it can't be wound up or down by hand (because you're trying to drive a motor through a 100s:1 reduction gearbox.

The manufacturer (Wickman) have acted exactly like I would expect any British company to react (that machine is obsolete, we deny all knowledge it ever existed).

So..... after that ramble.... what material should I make the clutch out of? It's compressed by quite a sturdy looking spring, so it shouldn't need too much sticktion, but it does need to survive being wound backwards against a metal plate turning in the opposite direction...

awemawson · « **Reply #1 on:** February 25, 2015, 06:42:46 AM »

How thick, what diameter?

Several possible materials on that link posted in Rob Wilson's insulation thread this morning.

micktoon · « **Reply #2 on:** February 25, 2015, 06:43:55 AM »

Hi Ade, sorry I can't help with the clutch , but your comment of the companys response made me laugh, you would think they would pride themselves in helping owners of there old machines out rather than deny it had anything to do with them, ..................ln a ' not me mate , I think you have the wrong bloke ' type way

Cheers Mick

AdeV · « **Reply #3 on:** February 25, 2015, 07:00:51 AM »

Andrew- diameter is about 2", the pin is maybe 1/8" and offset from the centre. I can't remember how it holds itself in position radially, I assume there's either 2 pins, or a central hole as well. Thickness - I don't know, but at least 1/8", more like 1/4" at a guess. All I found was one face and some powder in the machine, it had completely disintegrated.

Mick - yeah, it's pretty common these days

Mind you, I can sort of see why - we have an old product which we no longer develop or actively support, which is kind of tough on people who already have it & don't want to upgrade to the new version. Our problem is the team is too small to actively support the old product AND develop the new product; and since the old product no longer earns any money.... So I can sort of understand it, but it's still frustrating as someone who can't afford (or justify) buying new kit.

PekkaNF · « **Reply #4 on:** February 25, 2015, 08:07:02 AM »

Does it looks like a pertinax washer?
http://uk.rs-online.com/web/p/bonded-washers/1360842/
http://uk.rs-online.com/web/c/fasteners-fixings/nuts-washers/bonded-washers/

That is a bad picture but in real life it looks a lot like old printed circuit board material.

I have seen some clutch designs and there seems to be least two approaches:
* Use bearing materials like POM or Teflon (usually solid)
* Use friction pad material (usually has a backing or support disk/structure)

All depends how much load you are transmitting, how much slip and how much you must disipate energy.

Probably original maker used whatever they had in inventory and was reasonable enough.

Pekka

awemawson · « **Reply #5 on:** February 25, 2015, 09:40:08 AM »

I'd try a bit of Paxolin or Carp - srbp (synthetic resin bonded paper) and see how it performs

Manxmodder · « **Reply #6 on:** February 25, 2015, 09:48:08 AM »

Ade,you say it looks to be some type of fibre material,if it is a brown colour it may be Tufnol which is fibres bonded with resin and pressed and baked to make a solid material. I think it is still available......OZ.

Edit to add: Andrew,your post came in while I was typing. Isn't Paxolin similar stuff to Tufnol?

polecat · « **Reply #7 on:** February 25, 2015, 10:05:48 AM »

yes paxolin and tufnol as well as holoplast all the same stuff
polecat

AdeV · « **Reply #8 on:** February 25, 2015, 10:09:53 AM »

Thanks for all the replies chaps - it does look a bit like old resin circuit board, so that's a great idea to start with, ta

I'm not sure how much force is transmitted; the drive plate is a relatively smooth steel item, the clutch is then pressed against this by quite a powerful spring. It has to hold the weight of the electrode & supporting column, which isn't exactly light, probably 20lbs at a guess, and to lift it back out of the work piece via the motor. On the other hand, it has to be slippy enough that I can grab the fairly small manual handle, to wind the electrode + column back up.

If I get a chance at the weekend, I'll take some pictures so you can see what I'm talking about...

There is another option - do away with the clutch entirely, clamp the two parts together, then add a 3-way 4-pole switch to reverse the current going into the motor; instead of winding the electrode out of the workpiece, use the motor instead.... The centre position is needed so the motor doesn't try to wind the electrode out of the top of the unit - as it doesn't have any limit switch on upward travel... This would be the quickest option to get the machine up & running again, except for the fact I'm not sure what the current draw on the motor is, and the voltage is over 100vdc which rules out any switches I've got...

Bluechip · « **Reply #9 on:** February 25, 2015, 11:45:03 AM »

Tufnol & Paxolin are/were manufacturers. Tufnol make both SRBP & SRBF.

http://www.tufnol.com/materials-full/paper-laminates-full.aspx

http://www.tufnol.com/materials-full/fabric_laminates.aspx

Dave

tekfab · « **Reply #10 on:** February 25, 2015, 02:06:24 PM »

Hi Ade. I used this company for a re-lined brake shoe for my lathe. Might be worth a shot.

http://www.industrialfriction.com/

Mike

hermetic · « **Reply #11 on:** February 25, 2015, 02:46:57 PM »

+1 for SRBP, I have seen this type of clutch with a single plate and nearly always they use an SRBP plate. If you take a bit of it to a supplier, or post a pic I am sure someone will be able to identify what it is. Trouble with Wickmans is that they are an umbrella group for a lot of manufacturers, many of whom simply no longer exist. They actually bought Covmac, whe were a Machine tool maker, and made nut and bolt machinery under the Covmac name.
Phil

petertheterrible · « **Reply #12 on:** February 25, 2015, 03:35:25 PM »

As this will be my first post on this forum I do not know what to expect.

The plate you describe sounds similar to the slipper clutches used on PTO drives of tractors. These clutch pads are readily available at the local farmers supply. The pads are just large round flat rings made from composites. These are made of different types of fiber and range from soft to hard grades. I have used these types of pads (round donuts) on different machines retrofitting them. They are torque regulating and protect the machine from self destructing. I hope this helps, but it is difficult to say with no size comparison. An alternative is the synthetic clutches fitted to some ride-on lawn mowers. If in doubt visit the local break an clutch guy, they usually know a thing or two about weird composites. Once has a lathe using the same brakes as a Thames Trader, so their usually is a chance that the parts you are looking for had other destinations as well.

AdeV · « **Reply #13 on:** February 25, 2015, 06:21:11 PM »

Quote from: petertheterrible on February 25, 2015, 03:35:25 PM

As this will be my first post on this forum I do not know what to expect.

The plate you describe sounds similar to the slipper clutches used on PTO drives of tractors. These clutch pads are readily available at the local farmers supply. The pads are just large round flat rings made from composites. These are made of different types of fiber and range from soft to hard grades. I have used these types of pads (round donuts) on different machines retrofitting them. They are torque regulating and protect the machine from self destructing. I hope this helps, but it is difficult to say with no size comparison. An alternative is the synthetic clutches fitted to some ride-on lawn mowers. If in doubt visit the local break an clutch guy, they usually know a thing or two about weird composites. Once has a lathe using the same brakes as a Thames Trader, so their usually is a chance that the parts you are looking for had other destinations as well.

Hi Peter,

Well - first, welcome to the forum! It's a great place, you should pop over to Introductions and tell us a bit about yourself & your projects. Nothing too mad for this place!

Re PTO clutches - I suspect they may be a bit "meaty" for this application, the clutch has to be overridden with just normal hand force, but I think we're definitely on the right track (aha - a PCB joke

).

hermetic - unfortunately, all that's left is some dust, and the thinnest wafer of the remainder of it (and I think that's fallen to bits). I have some old red circuit board knocking about, I may try cutting a disk of that & seeing how it goes. If it works(ish), then I'll get some proper stuff.

geoff_p · « **Reply #14 on:** February 26, 2015, 02:17:14 AM »

Daft as it it sounds - what about a piece of plywood? At least for starters.

Geoff
Thailand

AdeV · « **Reply #15 on:** February 26, 2015, 09:08:23 AM »

Quote from: geoff_p on February 26, 2015, 02:17:14 AM

Daft as it it sounds - what about a piece of plywood? At least for starters.

Geoff
Thailand

Doesn't sound daft at all Geoff!

I'll be in the workshop tomorrow, so I'll certainly be trying some of these suggestions out. I've only used the machine to test out some different electrode shapes, but I love it already

I'd like to see how big an electrode I can use and still get a decent rate of removal - any old excuse for a play

wgw · « **Reply #16 on:** March 08, 2015, 07:39:46 AM »

Old girder forked motor bikes have friction damping, use discs just like you are describing, also older 2CV's. Look on vintage m/c suppliers.

AdeV · « **Reply #17 on:** March 09, 2015, 02:45:11 PM »

I've managed to get the old girl back in action - just cut a disc out of some thin plywood, the pilot hole was exactly the right size for the mounting shaft, and the disk was exactly the right size to replace the clutch plate. Screwed the thing in reasonably tight, and she's off and running! I've no idea how long it'll hold out, but even if it only lasts a few cutting hours, it'll cost pennies to replace again & again.

I've actually got a proper job in it at the moment, pictures to follow.

petertheterrible · « **Reply #18 on:** March 09, 2015, 05:23:28 PM »

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Author Topic: Slippy clutch material? (Read 10960 times)