Seal MDF spoilboard?

[analogman]

I am machinging aluminum sheet metal. I am using a bit of spray cooling, and this wrecks the MDF spoil board quickly. Anybody ever seal their spoilboard after surfacing to prevent it from soaking up coolant?

thanks

[CarveOne]

I am machinging aluminum sheet metal. I am using a bit of spray cooling, and this wrecks the MDF spoil board quickly. Anybody ever seal their spoilboard after surfacing to prevent it from soaking up coolant?

thanks

Even if you seal it, you will defeat the seal where the bit cuts into the MDF during cutting operations. Coolant will just soak into the MDF anyway, but it will take a little longer to get completely soggy.

If your machine is not so large, maybe a sheet of Lexan would work ok without prohibitive expense if you use it only when cutting aluminum. Or if it is a large machine, cover the MDF spoil board with polyethylene sheeting and use a Lexan sheet on top of the MDF spoil board only where you are cutting the aluminum.

CarveOne

[martinw]

Dear analogman,

I would say that CarveOne is absolutely correct, and bang on the button. MDF, even the water/weatherproof stuff is lousy at resisting water if it comes into the core from cut surfaces, or from an edge. It always acts like blotting paper. Always.

Best wishes,

Martin

[analogman]

Sure, makes sense. Thanks for the help.

[CarveOne]

Sure, makes sense. Thanks for the help.

Even your clamping fixtures will need to be sealed from seepage where they attach to the MDF through the polyethylene sheeting. Plumbers putty or caulking cord weatherstripping may work ok for this, as it can be removed relatively easily. You just want to put a "dam" at the places where fluids can get through the plastic sheeting.

I haven't done this myself yet, but have already been thinking of a way to do something like it in the future when my second build machine is completed.

CarveOne

[sonicwonder2000]

Okay, this is totally a shot in the dark, but here is an old boat-maker's trick: how about sealing the mdf with epoxy thinned heavily with acetone? This is sometimes used to seal rotting wood from further soaking up water and continuing to deteriorate. The epoxy should soak into the mdf and thereby even if the top layer is punctured, the remaining epoxy will still prevent the mdf from soaking up the coolant.

[CarveOne]

Okay, this is totally a shot in the dark, but here is an old boat-maker's trick: how about sealing the mdf with epoxy thinned heavily with acetone? This is sometimes used to seal rotting wood from further soaking up water and continuing to deteriorate. The epoxy should soak into the mdf and thereby even if the top layer is punctured, the remaining epoxy will still prevent the mdf from soaking up the coolant.

West Systems laminating epoxy (105 resin, 206 hardener) is thin enough for brushing and rolling, but it is not cheap. Using acetone will thin it further and it will cure, but it won't get as hard when it cures as their non-diluted laminating epoxy will. The West Systems web site has some details about this. It will make it more water resistant though.

The question is how deep will the thinned epoxy soak in without putting the MDF in a vacuum chamber. I have over-cut into the MDF by 1/8" when I had a Z axis problem like a slipping coupler.

CarveOne

[analogman]

As you alluded to earlier, maybe it will require a different spoil board material. MDF is great, cheap, surfaces OK and doesn't melt with fast spinning bits. I wonder is there another material with similar qualities that is somewhat fluid resistant?

[martinw]

Dear analogman,

IMVVHO, why not dodge the problem? Instead of using water based coolants, you might be OK using a wax cutting paste. They make them specifically for cutting aluminium . Just a wild thought...

Best wishes,

Martin

[ger21]

The question is how deep will the thinned epoxy soak in without putting the MDF in a vacuum chamber. I have over-cut into the MDF by 1/8" when I had a Z axis problem like a slipping coupler.

CarveOne

Don't thin it, just warm it with a heat gun (low setting) or hair dryer. Warming it thins it and allows it to penetrate deeper. If you skim cut the surface off, it'll probably soak in as much as you put on, when warmed up. A cheaper alternative to West System is US composites 635 thin epoxy. You get 3 quarts for $36, vs $35 for 1 Qt, 6 oz of West System. I used it last week, and seems very comparable to West Systems.

http://www.shopmaninc.com/epoxy.html

[CarveOne]

Don't thin it, just warm it with a heat gun (low setting) or hair dryer. Warming it thins it and allows it to penetrate deeper. If you skim cut the surface off, it'll probably soak in as much as you put on, when warmed up. A cheaper alternative to West System is US composites 635 thin epoxy. You get 3 quarts for $36, vs $35 for 1 Qt, 6 oz of West System. I used it last week, and seems very comparable to West Systems.

http://www.shopmaninc.com/epoxy.html

Warming it will also accelerate the cure time, but you're right about making it soak in faster. I haven't used this epoxy at work since the boss won't use anything but West System for our projects. I may get some of the US Composites 635 to use on home projects when my quart can of West System runs out.

Thanks ger21,

CarveOne

[martinw]

If you skim cut the surface off, it'll probably soak in as much as you put on, ]

Absolutely right.

MDF has a surface layer of dense material, and a core of mush. The "waterproof" versions have greater resistance to moisture in the surface layer, but the core is still blotting paper. Given that your spoil board is going to be cut into when you use it, you have to protect the core. To impregnate the core, with whatever brew you choose, cut into the surface before application.

(If you apply a paint finish to the edge of MDF, you may be surprised how fast the finish gets sucked in. I once put three coats of toluene based paint into the edge of 18mm MDF before getting a good surface finish),

My guess is that if you rout a 2" square grid with an 1/8" cutter through the surface of the MDF (say 1/16" deep), any impregrating brew will soak the core entirely.

Will it work? Make a small sample, spray it with coolant, and find out.

The alternatives are..

1) Paste wax

2) A plastic spoil board, but that depends on plastic prices in your area, and how big the board needs to be.

Just my two cents,

Best wishes,

Martin