Up or down cut leveling epoxy resin?

I’ve done several projects with epoxy resin and just used the McFly to level them off with good results, but I’ve got some new projects on deck that have a little more detail in them that’s causing me to reconsider my approach.

My thought is to be less aggressive and use 1\4” endmill but not sure if an up or down cut would be better.

Secondary thoughts on what number of flutes would be appropriate.

As always, suggestions and info appreciated.


I believe that downcut bits leave a better surface on the top and upcut bits leave a better surface on the bottom.

Be cautious using a down cut on epoxy, it’s just plastic and will melt! I’ve used an up cut and many projects with a coat of polyurethane (also plastic) for a nice smooth, shine, with most importantly, very little sanding required.


Very good, 1/4” up cut it is. Thank you!

Any recommendations on the number of flutes, 2, 3, 4?

My thinking is, more flutes means smaller cuts and less stress on the epoxy, but could also cause more abrasions and a less clean surface.

If you are going to buy a new one… look for an “O flute”
(normallly used for polycarbonate, but also great for epoxy)

Edit: O flutes are not as strong as “normal” endmills (e.g. not designed for fast cutting in wood), but this is because they have a bigger hollow shape for the flute, which helps a lot with chip evacuation. When cutting plastics/polycarbonate/epoxy but also aluminum, your biggest enemy is re-cutting of chips (that causes friction, which causes heat, which melts the material, which then becomes the big glob of gunk on your endmill and ruins the finish)… the O flute shape is optimized for evacuation of chips reducing this problem enormously.


That’s my plan, so thank you for the suggestion!

Great info, thank you!

I guess my next question is how to manage speed/feed with an O flute to avoid chip melt and/or tear out (or any other unwanted finish)?

When adding a new tool to the library I generally copy an existing tool that’s most similar to the new one and modify the available attributes to fit the new tool. 1/4” end mill seems like the foundation to use for an O flute and dial it back.

To avoid melting, you want BIG chips. So, fewer flutes, low RPMs and high feedrate. DOC is usually then set experimentally, pretty much as “As deep as doesn’t cause the machine to complain.”.

Also, epoxy takes a surprisingly long time to come to full strength (a.k.a. full hardness). If it’s a project in progress that you don’t want to put aside for a couple of weeks, the epoxy is likely softer than you think it is.


Very helpful, thank you!

When adding a new tool I generally dial-back the feed/speed from the one I’m copying until I see how the new one performs and change as everything tolerates.

When working with resin I always give it 72 hours or more to harden before cutting it, but with this project I’d have no problem letting it sit for a couple of weeks.

Thanks again!

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I’ve used both the 1/8" 102 and 1/4" 201 to cut epoxy resin. I used the stock speeds and feeds and they both worked flawlessly. I also cut plexiglass backers for projects we both do with the same results. My wife goes through a half gallon of resin and hardener weekly in her business and has me cut for her regularly.


Wow! There appear to be a lot of layers/pours there. I don’t even know what to ask. LOL It looks really cool!

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