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Off Topic Hobbies => Mechanical Engineering => Topic started by: coppercone2 on March 19, 2021, 07:41:22 am

Title: tips for machining graphite sheet
Post by: coppercone2 on March 19, 2021, 07:41:22 am
So I need to replace a graphite gasket on my solder pump, the kit was ridiculously priced and the quote people are not responding so I bought a graphite plate.

I need to drill a few screw holes in it and cut a graphite sheet to a 5 inch circle. It does not look like the dimensions are critical, so I was going to do the layout with drafting tools. I am pretty sure its some what porous anyway, so I think it just needs to be bigger then the pump body.

I am not sure about how to go about cutting a circle, How does a band saw sound? It can be oversized or not exactly a circle because its just a gasket, so long the bolts are correct perhaps I can cut a square, or some kind of many sided shape, if the circle is deemed too hard.

The holes are like 1/4 inch.

Any tips for doing this? Can it be done on a mini drill press? I saw something on applied science but he used a router IRRC, my proxxon mill is too small.

I am going to only have 1 or 2 shots at this before I run out of material, but on the bright side it looks like a repair with epoxy or super glue is acceptable from what I have seen, so long its not in the very middle, where the rotor touches it.
Title: Re: tips for machining graphite sheet
Post by: Ian.M on March 19, 2021, 08:08:29 am
Did you google: machining graphite (https://www.google.com/search?q=machining+graphite)

Graphite is *EXTREMELY* nasty to machine, and even working it with hand tools is unpleasant.   Apart from being very brittle, if you use any coolant it is likely to form an abrasive slurry which destroys tooling and if it gets in the ways, spindle bearings etc. wrecks your mill or other machine.  Dry, its still very hard on tooling - even carbide will wear quickly - and the dust is a severe respiratory hazard, and a potential explosion hazard.
Title: Re: tips for machining graphite sheet
Post by: coppercone2 on March 19, 2021, 08:31:36 am
I watched a video a little while ago where the applied science guy said it was pretty easy just messy with dust

Can I drill it under water using a diamond mini hole saw on a drill press like I do to tiles? I think the 1/4 inch tile hole saw is the right size for the holes.

Any since it seems like the circle is out of the picture, can I some how make a 5x5 inch square cut out?

I just need a plate with a bunch of holes in it. A square with mitered sides should fit into the machine. The google results are a bit too advanced for my application. Again so long its big enough I don't care, I was hoping there is a trick with this, like snap and score, or various things like cutting glass with scissors under water, or something else.

I forgot to mention, its only 2 or 3mm thick. I am not trying to do something crazy here. Worst case I think I can drill holes in a circle to make a flower shaped thing?

The part is called a wear plate, bolts go through it to clamp it to the pump under the back plate of the pump so the rotor can rub against it. Maybe if I drill a few holes I can just snap it?
Title: Re: tips for machining graphite sheet
Post by: Ian.M on March 19, 2021, 09:32:34 am
See page 40 onwards of https://www.osti.gov/servlets/purl/4284913 (https://www.osti.gov/servlets/purl/4284913)

You should be able to use a fly cutter to get your circular disk.  Fixturing it may be problematic - I'd be inclined to try sticking it onto a MDF backing board with hot wax, so its fully supported then clamping it with padded toggles screwed down at the corners of the blank, then drilling the smaller holes, and adding clamping screws with rubber and plain washers under their heads through the holes, then finally fly cutting the outer circle.


Caution: vacuuming graphite dust needs a fully grounded vacuum system, with special filters.  A vacuum rated for copier toner should be suitable.
Title: Re: tips for machining graphite sheet
Post by: helius on March 19, 2021, 08:54:54 pm
I picked up a new Atrix Express copier vacuum for $20 a couple of years ago. It's incredibly loud (small motor) but a nice bit of kit.
Title: Re: tips for machining graphite sheet
Post by: coppercone2 on March 19, 2021, 11:58:01 pm
I do not have a machine that can use a fly cutter or own a fly cutter

I think I have something that can fit a boring bar but it would need to be put into a drill press and I think you would need to replace the boring bar with some kind of scribe tool
it sounds like a bad idea to try to do that