Hello! I’m very new to the CNC world and plan, as I’ve seen done, to make signs with MDF. I was wondering if anyone has tips to offer and things to avoid. Specifically, I’m wondering about the following:
What primer do you use?
Are there certain types of pint that work best?
Can you do epoxy fills on MDF?
All I have it that the first coat, primer, or whatever, you will need around twice as much as you think. It is that thirsty.
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Hi Will - welcome to the forums. IME, there are very few upsides of working with MDF. It is generally completely flat, mills easily, and has a super smooth finish if cut properly. MDF is completely unsuitable for any project that will be exposed to the elements, even if it is painted and sealed (IME). They do make moisture resistant MDF, but I’ve never seen it for sale locally, so I’m guessing you will need to special order it at a real lumber store.
As for tips, @Markevans36301 provides some good ones. Having recently completed my ultimate office makeover using MDF, I’ll offer a few more:
1 - sand to 120 grit before painting.
2 - prime the project - two coats might be warranted
-> the internet says use an oil based primer, but I’m not sure that is needed. I’ve done both and haven’t seen an upside of oil-based.
3 - You must use some sort of dust collection and always where a respirator or high quality dusk mask.
4 - never cut MDF indoors - the dust is too fine and will get everywhere, including your lungs
5 - speeds and feeds are similar to plywood or other soft woods such as pine.
6 - always pre-drill any screws - it will split or strip 99% of the time otherwise - guaranteed
7 - you can assemble with nails, but MDF offers little “holding power” for nails. Use a good quality wood glue with nails.
Hope this helps.
-Tom
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Thanks Tom! I’ve noticed that many have built tables for their OneFinity with MDF on the top that they mount the OneFinity to. Should this be primed/painted before using? Note that I’m not referring to the wasteboard, but rather to the surface the wasteboard sits on.
Hi Will - you don’t have to - but if it ever gets wet for any reason, it will swell and deform. Wet here can be water, oil, humidity from the air – any form of anything that is liquid or viscous. I primed and painted my desk surface for that reason. Paint isn’t a perfect protector, but better than nothing IMHO.
-Tom
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Get a proper 3M respirator and cartridges, MDF dust is dusty in any volume.
One huge advantage that @cyberreefguru left out is that it has very uniform density making it great for speaker enclosures.
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Yes, it resonates equally everywhere 
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This is really more in the context of signmaking with MDF, but check out the story highlights on his instagram. He has several in-depth breakdowns on how he primes, paints, glues/assembles his MDF signs. https://www.instagram.com/davetaylors3dwoodart/
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