Honeycomb epoxy trivet

Julien · November 17, 2020, 10:19pm

Someone (I can’t seem to find the post just now, sorry, @Moded1952 maybe?) recently posted a link to that (fantastic) Youtube video : “Hexagons are the Bestagons”

And of course I just had to make SOMETHING with hexagons after that. I stumbled upon this hexagon trivet project from Fernando Romero (yes, I am aware this is a link to Inventables), and thought this was a great piece so I tried to create my take on this.

This is when I discovered that creating a ~10x10 array of hexagons in a Fusion360 sketch made my PC spill its guts and surrender (!?), as in, near the end every operation freezed the interface for a good 1 minute (i.e. I have a love/hat relationship with F360). I’m not quite sure how I managed to not rage-quit (stubbornness I presume), but I finally completed that sketch and extruded it.

I created an adaptive clearing toolpath using a 6mm 2FL square endmill, leaving about 1mm at the bottom:

And used rest machining to come back and mill the “corners” using a 1/8" 2FL downcut in all pockets:

Here’s the cut after the adaptive roughing (this is heat-treated ash)

And here it is after the finishing pass with the 1/8" downcut (cleeean, I like downcuts for this):

I prepared the piece with a little dam for epoxy,

And tried to mix mica powders I had to create a honey-ish texture and color:

then poured the epoxy (video just because it was a satisfying moment)

and let it harden for 24h:

Those mica pigments made for some interesting clouds in the pockets (unfortunately, this does not show up much in the final result):

I then surfaced the epoxy,

flipped the piece,

and removed the extra 1mm of wood to reveal the epoxy from that side too:

Which after sanding down to 3000 grit and oiling gave the final piece:

Not quite as nice as I hoped it would turn out, but still an interesting look. And hexagons are most definitely the bestagons !

p.s. : do I have trivet addiction? Maybe I do…

fenrus · November 17, 2020, 10:35pm

you;re making me want to do more epoxy projects

… but the temperature here in PNW(USA) has gone past the epoxy point

LiamN · November 17, 2020, 11:13pm

Not wishing to give you more excuses for long toolpaths removing most of the stock but…

If you stopped at the wood with pockets all all different depths you would have an audio diffuser panel.

MikeG · November 18, 2020, 1:39am

Super cool! I thought I might have been about finished making epoxy coasters, but now you’ve done it! I can see clearly that hexagon coasters will be the bestagone coasters, so I’ll be making more, sigh.

A couple of questions though:

What is heat treated ash, is it the same as what we on the side of the pond Lindbergh started from call kill dried? It does look great!
Wiki says that a trivet is " usually to protect the table from heat damage"
So what kind of epoxy are you using and what is the temperature rating?

WillAdams · November 18, 2020, 2:19am

Usually HT (heat treated) wood is a less expensive product where the treatment was more about elimination of pests than preparing the wood properly — c.f., KD (kiln dried)

Julien · November 18, 2020, 6:54am

“Heat treated” is the closest translation for the French name that literally translates to “heated” ash, but “smoked” would maybe be a better name, given the very strong smell, and kiln dried as Will mentions is probably the most accurate. It is apparently intended for outdoor use, e.g decks.

That’s very good point, and one I was concerned about back when I did this other epoxy trivet, but it has now been “in use” at my inlaws for a year and no report from damaging/melting it (though I think they tend to use other trivets for the boiling hot pans, or maybe they don’t use it at all and just pull it out of the drawer when we’re there! ). I honestly did not check the temperature limit for the specific epoxy brand I used, I hear basic epoxy is ok to about 150°C/300°F, while “heat resistant” epoxy used for kitchen countertops can take up to 315°C/600°F.

WillAdams · November 18, 2020, 12:54pm

In that case, it’s more likely a level of wood treatment beyond the traditional kiln drying and is an alternative to the traditional PT (pressure treated) — there was an article on it in Wood magazine a while back — a process known as “torrefaction”:

https://www.airex-industries.com/en/products/thermal-process/heat-treated-wood-kiln

also known as “roasted wood”:

other names include: thermally treated, tempered vulcanized or torrefied.

Julien · November 18, 2020, 12:56pm

“Roasted wood”, that’s more like it, and it matches perfectly with the smell! Thanks

MikeG · November 18, 2020, 3:02pm

That explains the beautiful color that is so appealing, IMO. For guitar makers out there, the roasted Birdseye Maple in @WillAdams link would probably make a real showpiece!

I’m sure that “other” trivet is displayed proudly, even when you’re not there

stutaylo · November 18, 2020, 9:09pm

Very cool, I’m seeing so many epoxy projects lately I am so keen to give it a try!

Fusion360 hates complex sketches, I’ve seen it bog down on computers that could render 5x Solidworks assemblies at once…

as much as possible try and create the extrude and pattern the feature, rather than having the pattern in the sketch, it seems to run much better that way

ctdodge · November 19, 2020, 12:33am

That’s really cool looking @Julien! I might have to give something like that a shot. How thick was your stock - 20mm? What size are the hexagons?

Edit: never mind, I see they are 26mm point to point.

Julien · November 19, 2020, 6:43am

The stock was about 3/4" thick originally, and ended up being ~0.08" thinner in the end after surfacing both sides

ericlin · November 20, 2020, 12:18am

Did/do you use any sealer to prevent the epoxy from bleeding into the wood?

LiamN · November 20, 2020, 1:15am

Yep, the way Fusion evaluates a sketch seems to be to try to find a solution that matches all the constraints in a sketch. The more elements in the sketch, especially if they have relationships like distances, parallel, coincident etc. then the more computationally intensive it becomes to evaluate. The compute load of this type of task grows in a non-linear way, which is why drawing complex things can make it non-responsive pretty easily. If you watch the CPU and memory load this also seems to be single threaded (which is not surprising for this approach) so a machine with more CPU cores or RAM is not likely to go any faster.

As Stu says, using body, face or feature level tools in the main history line to mirror, pattern or otherwise modify the bodies seems to be closer to linear in terms of the compute load. Quite a few times I’ve initially used patterns in the sketch then seen the performance hit and deleted all but a few in the sketch to pattern them as features instead.

Julien · November 20, 2020, 6:48am

I usually apply a coat of clear epoxy with a brush, and let it dry completely, to seal the wood before the main pour and avoid bubbles. This time around I didn’t (which was a mistake, there are some micro bubbles left, they are barely visible since the epoxy has that glitter/powder in it anyway, but still, could have been cleaner)

Julien · November 20, 2020, 12:12pm

@stutaylo and @LiamN: thanks for the tip about keeping sketches as simple as possible, and manipulate/clone the extruded objects instead.

It makes me wonder why they would offer a (super nice) grid/circular array feature in the Sketches if the sketch crumbles under its own weight when using it for anything more complex than a 3x3 array…sigh. Those guys have about 1 billion instructions per second horsepower on hand, and somehow they end up using 60 billion CPU cycles to verify the constraints on that moderately complex sketch ? Yes, I like to rant for no good reason as much as the next guy [still love Fusion360 though]

LiamN · November 20, 2020, 2:08pm

In all fairness to the Fusion team…

The user feature of “express constraints and let the machine work it out” is fantastic, not having to do any trigenometry to make measurements and angles work etc. is excellent.

However, in order to make this magic work for the user you end up having to write a rendering process which has geometric growth in complexity as you add sketch items, measurements and constraints.

It is similar to saying “here is a page with dots on it, for every dot, draw a line to every other dot”. This is dead easy at 4 or 5 dots, for a computer it’s easy at a few hundred dots, go much beyond that and you start to run out atoms and time in the known universe or needing a quantum computer.

EDIT - what’s missing is the user help / info that says “sketches get slow when you fill them with stuff, please use the other features” it shouldn’t be hard to detect long compute times for the sketch render and pop a dialog to say “take some junk out of your sketch”

stutaylo · November 21, 2020, 1:46am

All I will say is: if Solidworks can do it, Fusion should be able to.

@Julien nice tip with painting on clear epoxy first, I’ve not heard that one before! I can’t get over how good it looks! Is epoxy ok with the temps you’d see putting a hot pan on top?

Julien · November 21, 2020, 9:27am

@stutaylo: regular epoxy is only good to about 150°C, so I wouldn’t put a really hot pan on it. I would have had to use special countertop-grade epoxy to make it heat resistant. This one is likely to join the pile of things collecting dust on the top of my enclosure

MikeG · November 21, 2020, 3:15pm

I used to do some work with a cabinet maker that also did Corian countertops, which is basically a high-strength/temp plastic. He shared horror stories about pans being set directly on the counter and deformation occurring or on a joint and like a gun shot, the joint separating. I don’t think these countertops are very popular these days…at least not like Julien’s trivets.