Surfacing Resin?

[ClayM325]

So I am trying my hand at using castable resin making a resin river shelf. The pouring went fine, and after that i wanted to surface both sides to get it perfectly flat and the bit is badly taking chips out of the resin. ANy suggestions? Below if a pic. Bit i was using is amana 2250. thanks!

32221

[bking1836]

Hi, what were your feeds and speeds and pass depth? And did you use all 4 insert knives or just two? Were they the knives made for MDF or the special diamond ones for hardwood?

[ClayM325]

Hi, what were your feeds and speeds and pass depth? And did you use all 4 insert knives or just two? Were they the knives made for MDF or the special diamond ones for hardwood?


I was cutting at 8" a second, tried 12k rpm and 18k rpm same result with both. using 2 of the hardwood cutters.

[bking1836]

I was cutting at 8" a second, tried 12k rpm and 18k rpm same result with both. using 2 of the hardwood cutters.

8ips at what pass depth? That strikes me as fast but I don't know what machine you are using.

[ClayM325]

8ips at what pass depth? That strikes me as fast but I don't know what machine you are using.

.100 inch

Typing more here because it told me my message is too short lol

[bking1836]

Others with more experience will hopefully weigh in, but 8ips with .1" bites seems like too fast and too deep, especially for something hard like resin. When I surface hardwoods with the Amana rc-2551 (similar, just larger), I tend to run 3-4ips at .05" bites. Epoxy is both harder and more brittle...Also, if your spindle is even a little out of square, you're going to end up digging even deeper than your .1" on the edges, and that might account for the chipping pattern that you're experiencing.

[ClayM325]

Others with more experience will hopefully weigh in, but 8ips with .1" bites seems like too fast and too deep, especially for something hard like resin. When I surface hardwoods with the Amana rc-2551 (similar, just larger), I tend to run 3-4ips at .05" bites. Epoxy is both harder and more brittle...Also, if your spindle is even a little out of square, you're going to end up digging even deeper than your .1" on the edges, and that might account for the chipping pattern that you're experiencing.

That would make sense, because the chipping is all occuring on the same side of each cut

[mclimie]

Yeah slow it down - also test climb vs conventional. I surface a lot of resin and never have chip out like that but am moving much slower (I have a very small machine and palm router and use a 3/4 diameter surfacer). You might also try testing it when it's cured enough to cut but not fully. It will gradually get harder over some days or weeks depending on conditions and the resin you use, so the early stages of being solid and in the 60-70D range may be more forgiving.

Also, this is fixable if you clean it up really well of any sawdust and pour the same resin on top of it. Don't make it too smooth - just make sure it's dust-free.

Marc

[ClayM325]

Yeah slow it down - also test climb vs conventional. I surface a lot of resin and never have chip out like that but am moving much slower (I have a very small machine and palm router and use a 3/4 diameter surfacer). You might also try testing it when it's cured enough to cut but not fully. It will gradually get harder over some days or weeks depending on conditions and the resin you use, so the early stages of being solid and in the 60-70D range may be more forgiving.

Also, this is fixable if you clean it up really well of any sawdust and pour the same resin on top of it. Don't make it too smooth - just make sure it's dust-free.

Marc

Slowed it down and took out .030 at a time and got it cleaned up. Thanks for the help everyone.

Marc what brand castable resin do you recommend? for resin river and such? Stuff I'm using seems expensive (Smooth On 690)

[ClayM325]

Considering the bit is 1.5" in diameter, the 12k speed is really, really fast. The tips of those blades might be approaching supersonic! I suggest slowing way down, perhaps 6k and see what that does. The larger bit would also exacerbate any issues with your rig being out of square. Unless you have a real reason to use such a large bit, I'd suggest using a 2 flute 1/2" end mill running 12k with no more than 6ips.

I will look into that bit next time, The 1.5" amana is all I had other than 3/8" and smaller compressions. thanks!

[bking1836]

Marc what brand castable resin do you recommend? for resin river and such? Stuff I'm using seems expensive (Smooth On 690)

It's all expensive. Take a look at Total Boat.

[Brady Watson]

FYI - When I did the 6' dia brass floor inlay (1/2" thick Naval Brass) for Christopher Newport University, I used SmoothOn Smooth Cast 325 and tinted it black using their So-Strong dye. I undercut the pocketed lettering with a Dremel by hand (so they wouldn't pop out), pre-heated the metal using a space heater and heat box (DIY Celotex/foam box) and then poured it in using a thin stream...Then post cured it @ 130F for 4 hours to make sure it was all good. This was in February...and even with the heat on 70F it was still too cold to do without preheating.

Even though I took classes @ SmoothOn & Polytech over the years, I still called up their engineering dept to make a recommendation. I would encourage you to do the same so you get the right product for the job. ALL of the polyurethanes look like a donkey's butt when you machine them...some are slightly better than others, but they all swirl with tool marks and if you use anything but really sharp tools and adequate RPM, they can chip.

I over-filled the letters with 325 and then machined them within about .01" from the face of the brass (to prevent gouging). IIRC I just used a sharp solid carbide 2-flute end mill and essentially just Zzeroed on the face of the brass, then stepped it up .01 and then ZZ'd again. Then just re-ran the pocketing routine but offset to the outside a bit. There were lines from the raster, but since I didn't go right flush with the top, I was able to easily get it flat using various grits with an orbital sander. I think I started @ 220 since I already took the brass from 36 all the way up to 400 grit...and I didn't want to undo my work. After all was flat, an automotive clear was added. From what I hear, it still looks good and is holding up great with foot traffic on it every day.

More info & pics of the project from the archives here (http://www.talkshopbot.com/forum/showthread.php?945-Christopher-Newport-University-Brass-Project&highlight=newport+university) - Hopefully it helps you out some.

[mclimie]

It's all expensive. Take a look at Total Boat.

Absolute truth. There is no cheap alternative in cast-able if you want quality, whether it's epoxy, urethane or silicone.

I use 690 as well, but I'm populating very small molds and need the thin viscosity and the work time, which I just turn around and put in my curing oven, I mean repurposed dishwasher. :)

Check out also BJB, Polytek, Alumilite and ArtResin. As far as I know, ArtResin are the only ones using HALS UV stabilization, which would appear superior according to the tests. I've tried it and cant use it - too thick and doesn't degas very easily in a vacuum chamber (among the worst I've ever tried), but it's used for your type of application a lot I think - if you are open-pouring it degasses on its own with maybe some help from a heat gun or torch here and there. I think they are also FDA food-safe.

Forget about using any sort of urethane resin matched with wood unless you can achieve zero moisture content in the wood. The aliphatic (water clear) urethanes are sensitizers anyway, so if you can avoid using them, you are better off.

Marc