Epoxy Surface Plates

[Mike Mcdermid]

If you cover the underside with ply you get a box. Stiffer then a plate or bowl (the box without it's 6th side inclosed.) You also might want to use dimensionally stable sides and webs, 2x4's are not to stable over time. Andy.

Thorlabs - Honeycomb Optical Breadboards

[Jonathan]

I'm giving it a shot too. Talked to the guy for a while, super helpful! He said that if I frame up some 3/4 plywood with 2x4's like I was making a floor, it should be rock solid. I'm a little paranoid about the wood warping over time and flexing the plate... but it'll be a half inch of epoxy on top and he didn't think it'd be an issue. I'm going to try to put my instinct to worry about everything aside and trust the expert ;-)

Go for it. The only reason I'm using a 350lb piece of steel on a table is so I can cold set against the weight.

[Kumo Cycles]

I discussed this with another builder who had been doing the research.

Bear in mind that when you pour the epoxy there will be a meniscus on the sides where it touches the enclosing material, be it plywood, steel or aluminium.

You will need to cut down the meniscus or just keep in mind that the plate will not be flat around the edges

[prolix21]

I'll probably be trying this in the next few months - just bought a new house where I can finally have a decent shop setup.

[Mark Kelly]

I discussed this with another builder who had been doing the research.

Bear in mind that when you pour the epoxy there will be a meniscus on the sides where it touches the enclosing material, be it plywood, steel or aluminium.

You will need to cut down the meniscus or just keep in mind that the plate will not be flat around the edges

The height of any meniscus is determined by the contact angle between the fluid and the solid, which is a measure of how well the fluid wets the solid. It should be possible to minimise this by treating the inside surface with something which isn't wet effectively by epoxy. PVA (commonly sold as mould release coating) seems like a good candidate.

Keith if you are going to try this I have plenty of PVA, I can give you some.

[Jonathan]

The height of any meniscus is determined by the contact angle between the fluid and the solid, which is a measure of how well the fluid wets the solid. It should be possible to minimise this by treating the inside surface with something which isn't wet effectively by epoxy. PVA (commonly sold as mould release coating) seems like a good candidate.

Keith if you are going to try this I have plenty of PVA, I can give you some.

The epoxy sales guy reccomended Pam, the cooking spray. The lip is rather small anyway and if the plate it big enough you'd never measure on the edge.

[veryredbike]

If you cover the underside with ply you get a box. Stiffer then a plate or bowl (the box without it's 6th side inclosed.) You also might want to use dimensionally stable sides and webs, 2x4's are not to stable over time. Andy.

Oh, good good call... yeah, box makes sense. Dimensionally stable... are we talking hardwood and specific cuts or something like MDF?

[Mark Kelly]

Water is the enemy of dimensional stability in wood.

Normally hardwoods are sold at around 10 -12% moisture content which is in equilibrium with around 60% RH (temperature dependent). If the RH varies and the wood is exposed to this variation, the moisture content of the wood will also vary.

The wood fibres take up the moisture and swell laterally, there's basically no change in length. The seasonal layers (grain) also affect swelling: the swelling across the layers (tangential) is much greater than through the layers (radial), usually about 2:1 though sometimes more.

Net result: to ensure dimensional stability in wood, is must be completely sealed off from humidity variation. Epoxy works well, the thicker the layer the better. For the inside of my tubes where I can't be sure there won't be some condensation or other water ingress I use a layer of 75 GSM glass fibre tissue to bind a nice thick layer of epoxy onto the surface(approx 0.1mm).

[prolix21]

I've been debating using something a bit more substantial for the base, something along the lines of aluminum plate with some sort of grid support underneath to keep it rigid. Overkill?

[Mike Mcdermid]

I've been debating using something a bit more substantial for the base, something along the lines of aluminum plate with some sort of grid support underneath to keep it rigid. Overkill?

if you look at how an optical table is made they do exactly that ,two aluminium plates with honeycomb pressed between them

you can pick an optical table up for less than you think, theres lots of science places going out of buisness and they hold around 0.1 for flatness over a metre squared ,im assuming thats accurate enough ,there was one for sale here in the UK for less than 50 quid you cannot buy the epoxy for that and suffice to say they dont get beet on

just remember don't put anything hot on the epoxy if you go down this route and remember any loose filings or stray microsopic pieces of metal have a certain amount of magnetism towards these things regardless of how carefull you think you are , will embed themselves quite happily into the surface

[veryredbike]

I've decided to simplify. Instead of spending a bunch of cash on epoxy and worrying about wood warping at all and ruining it I'm buying 80/20 and making a frame. Then I'll epoxy thick slate tiles on top and then lay the self-leveling epoxy coat (in a luscious red) over the top. Might be overkill, but I don't want to do this again in two years and I have basically no experience with wood. Stuff should be here pretty shortly. I'll post a photo of the frame when it's together.

[veryredbike]

EDIT: Seems like porcelain tile is harder, cheaper, more uniform and absorbs almost no moisture. Going to go that route for the substrate.

[Mark Kelly]

you can pick an optical table up for less than you think, theres lots of science places going out of buisness and they hold around 0.1 for flatness over a metre squared ,im assuming thats accurate enough ,there was one for sale here in the UK for less than 50 quid you cannot buy the epoxy for that and suffice to say they dont get beet on

Mike, If you come across anything like that, would you be so kind as to send me a message?

These things are as rare as rocking horse shit over here. Shipping won't be cheap but it would be cheaper than a cast iron surface plate.

[Will Neide]

How much heat can an epoxy plate take? I didn't think you could get a torch near it.

[devlin]

Mike, If you come across anything like that, would you be so kind as to send me a message?

These things are as rare as rocking horse shit over here. Shipping won't be cheap but it would be cheaper than a cast iron surface plate.

That's the biggest issue for us colonialists. Finding a surface plate of any description of a decent size is difficult and expensive.

[Mark Kelly]

That's the biggest issue for us colonialists. Finding a surface plate of any description of a decent size is difficult and expensive.

Yeah, I've had a search on Gray's for "surface plate" for the last few months, I check it every week. Not a thing has come up.

[shand]

how about this?

Steel Machined Engineering Surface Table in Melbourne, VIC | eBay

[Mike Mcdermid]

Mike, If you come across anything like that, would you be so kind as to send me a message?

These things are as rare as rocking horse shit over here. Shipping won't be cheap but it would be cheaper than a cast iron surface plate.

aye will do if theres a cheap one comes up tbh new they are not that expensive in terms of it just sits there doing nothing till you need it

Melles Griot Optical Table Work Station Heavy Duty Stainless Steal Welding Table | eBay

[devlin]

how about this?

Steel Machined Engineering Surface Table in Melbourne, VIC | eBay

Not bad. Wouldn't fit in my workspace and would be hideously expensive to get to Brisbane. They are out there just hard to come by here.

[Mike Mcdermid]

Not bad. Wouldn't fit in my workspace and would be hideously expensive to get to Brisbane. They are out there just hard to come by here.

Can you guys in OZ not get hold of tooling plate ?

serious question i just don't know the cost or logistics of material supply down under