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MDF as milling backer?

J

JustaDB

Ultra Member
I seem to recall watching a video where somebody was through milling a chunk of metal & had used MDF as a backer. Is there any demand for this sort of thing? I have access to 4x8 cover sheets (some damage on the edges) which are probably 3/8" or 1/2" thick. I could bring some up to the Calgary meet later this spring if there is (or p/u local to Lethbridge). Cut into, say, 2'x4' sheets? 5 bucks?
 
I've used the 1/4" handy panels from HD as sacrificial backers for milling sheet quite a few times before. Works great, but as David says be mindful of the swelling issues. In my case it didn't matter, as it was all through cuts. I just left holding tabs where needed, and zipped them off afterwards.
 
Same for me, use it quite often as a flat-ish backing board material like drilling through or machining edges where the EM extends through a bit. I even made a mockup fixture plate from MDF but it was for a small part & low quantity. But you need to use metal blind nuts or threaded inserts, the wood (well sawdust + glue) itself has no real strength for threads. I've even glued finicky thin metal stock directly to the MDF, done the machining & then de-bond the adhesive. As mentioned, liquids will swell it so you will loose dimensional stability. Not just water, any liquid, but oil seems to be just a bit slower. So when I tapped holes I used one of the creams instead of oils. But basically the MDF is a low cost disposable item.
 
I scored a quantity of 7x24x5/8 MDF scraps from HomeDepot several years ago so a perfect size to fit my mill's table. As others have noted it works well as backing when drilling or finishing the edges of stock. I've also used it with double sided tape (https://www.amazon.ca/dp/B000QC48UU) to cut thin plastic and metal parts.

Liquid coolant is a complete no-no!
 
You just reminded me @Tom O I have a few chunks I grabbed as samples from some lumber/flooring place. I wondered out loud if swelling might be minimized or mitigated because its obviously weatherproof. This particular sample has kind of embossed fake wood grain, but its still reasonably flat. You are kind of limited by size, guessing maybe 4-6" wide 'boards' vs. what could be cut from sheet stock of wood products. But it might be handy. Material prices are crazy these days & probably lots of volatility with recent news, one has to think outside the box.
 
True they do have some pattern on them but you could also machine them to use as a indexed fixture when making multiple parts
 
I'll take a look again & maybe varies by manufacturer. Seems to me they have kind of a skin layer & a core, so might be limited what you can skim off. Mine looked flat with embossed grain, presumably through the rollers, so I don't think would be a problem from that standpoint. Actually what I learned with gluing parts onto sacrificial board (especially CA glue) is grooves can actually assist, it gives the glue somewhere to migrate to & kind of anchors in the grooves. I think these products are largely vinyl based + wood but plastics vary all over the map. I may not do as well under any kind of sustained cutting tool heat but I'm guessing as a simple backing board probably fine.

Just as aside, MDF also has density difference too as a function of roll/press manufacturing. Probably varies but I've heard as much as 50% lower density in core vs outer skin surface. It does make dust & shavings that can turn into some unwanted paste mung when soaking up any oil especially on ways so be mindful of that.
 
Dollarama here sells 8”x8” and 12”x12” 5mm MDF panels as art supplies, usually about $4 for four sheets. Make great spoilboards for my engravers, and perfect for test engravings before I slap down expensive real materials.

My laser engraver has one of the 12” MDF panels taped down to the engraver platen. MDF is engraved with a 10mm x 10mm grid pattern. Works great for quickly locating workpieces, and when I screw up and overshoot the workpiece the platen doesn’t get marked. Too many screwups means it’s time to flip the MDF panel and use the second side.
 
If anyone in the Niagara area wants off cuts or spoil boards, I can save my protection sheets here. We get at least one per lift, not always MDF but frequently. I had one guy line his entire cottage up north with random protection boards instead of drywall or OSB.

MDF is great on CNC machines for a spoil board. The vacuum sucks thru and holds parts down.
Waterproof MDF is saturated with linseed oil in the resin and is not affected by moisture or oil. We use it frequently here for toe kicks or outdoor projects. Over a hundred a sheet for 4x8 though and you can get it up to16’ long.
Martin
 
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