Hi,
I am in the planning stages of a rather large piece of epoxy wall art. (36"x36"x3") I want it to be the shape of a clover leaf when it is said and done.
Any advice on cutting a 3-3.5" thick piece of epoxy?
Do they make cutting bits that long? What are they?
Any links to bits or advice on what to look out for when cutting this thick would be appreciated.
Thanks
The longer the end mill the less rigid it will be. Also the less force it takes to break and the more ringing will affect surface finish. Full length side cutting will be a challenge on our machines at 3 inches.
MSC Direct and McMaster-Carr both have them in stock for cutting resin and wood.
When I need to make really deep cuts in acrylic on the router, I do it in 3/8in deep passes. Any more than that and I find it is hard to get enough heat out of the cut to keep the materail from melting onto the cutter. (This is with continuous air blast to clear the cut) I do have one of those old hot/cold air seperators, I’ve never tried it on the router. I typically just make a bunch of passes. Deepest I’ve gone is ~1in., in acrylic so nothing even close to what you are talking about here. I’m guessing air assist will be a must down in that deep. If this is periphery cut only (not slotting to that depth) then that is a totally different answer…
Would programming a 1 inch at a time with a .010 last pass help dissipate the heat? Cutting wider than the bit to reduce friction. It will be 36" across, I want to avoid jig saw or band saw (Bandsaw not big enough anyhow) because the cleanup in the sharp angles will be to difficult. I will round over and flood coat to finish. So I am hoping the CNC pass will be all that is needed, possibly light sanding. Any tips to pull this off are welcome.
Vortex cooler is what you are referring to.
You know me, Mr. Pedantic. 
Definitely use it with mostly dry aluminum and plastics. Not only does it clear chips but it keeps the work piece nice and cold.
To counter act the tool deflection discussed, could you feasibly flip the part on registration pins? 1.5” DOC would be a lot less for you machine to wrestle with.
You could do tests in the waste to see whether chatter marks from a full-height or near-full-height pass are better or worse than the step-down marks.
If the step-down marks are better, then ideally I would want a large diameter shank and small cutter height for stiffness and a slightly larger cutter diameter than shank diameter to prevent friction above the cutter. I don’t know whether this unicorn exists.
A card or carbide scraper could speed the final cleanup.
The wonderful thing about owning your own machine is you get to experiment and learn.
What’s the saying, “more than one way to skin a cat?”
But deflection and ringing will be your biggest problems. Kind of the bane of gantry machines.
Thanks for the tips so far, I was considering making the mold the same shape as the piece but about .5 over to save epoxy. Then cnc down to the final clean size.
Are you making a mold or cutting it out of a larger piece of poured epoxy. You might want to try making it in 4 pieces, the 3 heart shaped pieces and the stem. I haven’t tried glueing epoxy but I’ve glued 2" thick acrylic with great results. It would also make sharper intersecting corners. Another thing that works great on acrylic (not sure about epoxy) is flame polishing the machined edges. It takes a bit of practice but if you run a flame from a torch quickly over an area you can get a pretty decent finish. I used a oxy-hydrogen torch but I’m sure propane would work just as well. Don’t use a oxy-acetylene torch as it makes to much soot and may be to hot. Just my 2 cents.
Conveniently, epoxy is glue, and sticks to itself very well.
Do two-sided machining. It’s easy to do a 1.5" Depth of Cut with a 3" bit that has 2" of flute length. Pick any one out there. 2L, amana, etc.
Cut half the depth on one side. Cut some alignment holes outside your shape. Cut the mirrored holes in your spoilboard (use 3). Flip it over and use some downs to align it. Finish the cut; include tabs.
Corbin
EDIT: pketcham said the same thing…sorry to repeat it, but it is a good idea!
Thanks for the Suggestions, Can’t make in 4 pieces, It will have bar taps cast inside shape.
As far as 2 sided machining, that is likely the best option. Although, I was going to make the mold on a sheet with the clover protruding out of the plywood base. so when flipped it would not have the plywood touching anymore it would be raised off table by 3". I guess I could build the edges up 3" to put the reg dowels into. that would work. But now I have to cut through the base of the mold as well making it thicker. But still les than 3" cut. 1.75"