A question for the sign makers - Sealing MDF edges inside small cut letters

I’ve not used MDF for much except waste boards so, ignorant of finishing strategies for inside edges of letters. We all know MDF edges suck up paint, my question is how do I seal the edges prior to paint?

An example of what I’m talking about:

My first choice would be some sort of quick drying spray. None of what I’ve tried works.

Thanks

A high solids primer is gonna be your best bet. If you are looking for spray can, I would try Rustoleum’s auto body primer or Zinnser’s shellac base primer. I have used both with pretty decent results. Super super light coats to prevent more sanding. Word of warning on the shellac primer, the nozzles tend to get clogged easily and spit globs of paint if you don’t shake the absolute crap out of it and religiously clean the nozzle after spraying.

edit: not a professional sign guy by any means…
edit 2: I have gotten so tired of sanding and spraying mdf that I now use “sacrificial” cheap cutters that I run at too low of a chipload, essentially burnishing/polishing the edges to help cut down on the amount of sanding.

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Thanks Scott, I’ll check those out.

edit 2: I have gotten so tired of sanding and spraying mdf that I now use “sacrificial” cheap cutters that I run at too low of a chipload, essentially burnishing/polishing the edges to help cut down on the amount of sanding.

Good tip, I’m cutting all these things with a cheapo 30 deg v-bit. I’ll try a final “polishing” path.

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123 I use for light paints 2 coats sanding each coat. It white

The Rustoleum I use of top coat will be darker paints cause it’s Gray

Nothing I’ve found comes close or works better!
In MDF OR WOOD

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ZINNSER 123​:+1::+1::+1:
2coats sanding each coat for lighter color finishes White Base color

And for darker paints I use RUSTOLEUM
FILLER SANDING primer. Which the base color is Gray

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I tried the 1,2,3 per your recommendation, better results.

Problem is, I can’t/ don’t want to sand inside little letters, not productive. Instead, I’m working to improve tool path finishing strategies to minimize side grain MDF fuzzies.

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And there I am, immediately picturing the silly idea of wrapping sandpaper in a cone shape around a Vbit, and rerunning the toolpath at a slightly higher Z zero :crazy_face:

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Ha, tried that, sort of, with a chineseium diamond 30 degree “cone-bit” I have for stone. Just loaded up.

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I’ve found that setting my can of spray paint in a container of hot faucet water will make the juices flow a bit better for painting and less gobbing/spatter .

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I recently found myself in your position @Griff. After much frustration like yours, I reached out to @Microwave_Monkey. I eventually settled on using a foam brush with a few light coats of a good primer. Anything I sprayed made a mess. After the primer had good coverage, I sprayed with the final coat.

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