Beetles

[DLJeffs]

I bought some new resin that is supposed to cure slower, at lower temperature, so less bubble formation. And we're supposed to be in the 80's all this week. The resin says it's best to cast when the resin temperature will be above 70F. So my next project is going to be this. This is a 6 inch long coconut beetle. We caught this checking under the street lights back when I was in high school. I injected it with formaldehyde and pineed it into position on that styrofoa,. It's been in a box ever since.


I figure three layers. The first will be a base, about 75% cured, and then stick the beetle in so it is secure and won't float. I'll paint the underside of the beetle heavily right before sticking it into the resin, and then pour it up to the jaw level. That will cover the underside and hopefully minimize bubbles. Then the last pour will cover the beetle sufficiently to give me room to sand and polish the final. The mold is hand made from 1/16" acrylic plastic. When we did this back when I was in high school we used old aluminium pans. This will be better because I can see through the sides and see what's going on under the beetle, etc. I'll wax the inside of the mold before starting the pour but I fully expect to have to trim it off with my bandsaw, we'll see how it goes.

If this one goes well, I have a matched pair of rhinoceros beetles and a pair of fire beetles to also cast.

 

[DLJeffs]

Started on the coconut beetle today. This is an all day project, once you start you need to be on standby for the next step. I poured about a 3/8" base layer right around two (I had to go get mix cups and measure and mark volume lines on them). Then that had to set a couple hours to (1) set up stiff enough to support the beetle so it wouldn't sink to the bottom, and (2) the instructions said the best way to hide the line between layers is to wait about 4 hours between layers. So around 6pm I went out and mixed a larger batch, painted the bottom of the beetle, set it into the mold, and poured the second layer. Then I found it still wanted to float so I devised a little hold-down that I'll go out and remove in another half hour. The resin will be set up enough to hold the beetle in position.



Then I discovered I had too much leftover resin to waste, so I decided to use it for the base layers for the two smaller fire beetles. I cut the bottom off a feta cheese container for one of them and quickly cut and glued together another acrylic mold for the other. These beetles set on their bellies (the coconut beetle stood on it's legs) so these can go onto the first layer sooner because they float rather than sink.





So far it's looking pretty good. The resin still heats up as it cures but it seems to stay very clear and release bubbles easily. The big concern will come when I completely cover the beetles (which are hollow and filled with air) and as the resin heats up, that air expands and has no where to go except out along the surface of the beetle.

 

[DLJeffs]

Well, so much for that. The final pours turned out more or less just like they always did when I was in high school. The exothermic reaction of the epoxy causes the air inside the beetles to expand and it's forced to find the path of least resistance. From a scientific standpoint, the specimens would still be useful, but from an aesthetic perspective, they're ruined. I guess a pressure pot is the only way to prevent the air from escaping like this and I don't have one of those.

 

[Nubsnstubs]

Well, so much for that. The final pours turned out more or less just like they always did when I was in high school. The exothermic reaction of the epoxy causes the air inside the beetles to expand and it's forced to find the path of least resistance. From a scientific standpoint, the specimens would still be useful, but from an aesthetic perspective, they're ruined. I guess a pressure pot is the only way to prevent the air from escaping like this and I don't have one of those.

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The large beetle looks like it's lungs were crushed, but the other two look like they farted.
That's too bad, especially the coconut beetle as you probably won't ever get another one.
Do you think if you had a pressurized pot, would it have crushed them because of the voids inside the body, or would the pressure have been equalized?.............. Nubs

 

[DLJeffs]

I don't know Jerry. I have never tried one of these in a pressure pot. I think as long as you increased the pressure slowly enough that the pressure inside the beetle's exoskeleton had a chance to equalize with the increased pressure on the outside, it wouldn't damage the beetle. In my experience, these beetles have lots of little holes, some natural and some made by me when I injected them with formaldehyde, for the air to escape. My science teacher in high school, and the guy who got me into collecting and casting these, had a bell jar in his room. I tried for a couple years to figure out a way to cast the beetles inside the bell jar, so we could cast them in a vacuum. Removing the air seems like the best way to prevent it from expanding in the hot epoxy. But being glass, i couldn't figure out a way to get a hose inside to pour in the epoxy. We tried pouring these in an ice bath, experimenting with different ratios of resin and catalyst, etc. I even tried injecting epoxy into a beetle to fill the void with epoxy, but we never solved the problem of expanding air. I think the best solution will be when they develop an epoxy that isn't exothermic. I had high hopes for that coconut beetle too. And you're correct, those are the last ones I have. I have a mated pair of rhinoceros beetles still that haven't been cast but I think I'll wait on them now.

 

[Sprung]

Well, so much for that. The final pours turned out more or less just like they always did when I was in high school. The exothermic reaction of the epoxy causes the air inside the beetles to expand and it's forced to find the path of least resistance. From a scientific standpoint, the specimens would still be useful, but from an aesthetic perspective, they're ruined. I guess a pressure pot is the only way to prevent the air from escaping like this and I don't have one of those.

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An idea to consider trying before considering a total loss - maybe drilling a couple tiny holes on opposite ends of the air bubbles,, and also certainly into the high points as well, into the air bubbles. Put resin into a syringe and force into one hole to fill the air bubble. The other hole(s) lets air out and resin flow and could allow you to fill in the bubble. Never done anything like I've proposed, but could maybe let you save these - or at least try to.

 

[vegas urban lumber]

Well, so much for that. The final pours turned out more or less just like they always did when I was in high school. The exothermic reaction of the epoxy causes the air inside the beetles to expand and it's forced to find the path of least resistance. From a scientific standpoint, the specimens would still be useful, but from an aesthetic perspective, they're ruined. I guess a pressure pot is the only way to prevent the air from escaping like this and I don't have one of those.

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drill a hole in the air bubble, chip the opening larger, then slow pour or syringe in fresh thin epoxy to fill the void
dang sprunger beat me to it

 

[vegas urban lumber]

or do them upside down on a pre set bed of epoxy, then polish the top side as the air would have traveled down (once turned over) if any

 

[DLJeffs]

An idea to consider trying before considering a total loss - maybe drilling a couple tiny holes on opposite ends of the air bubbles,, and also certainly into the high points as well, into the air bubbles. Put resin into a syringe and force into one hole to fill the air bubble. The other hole(s) lets air out and resin flow and could allow you to fill in the bubble. Never done anything like I've proposed, but could maybe let you save these - or at least try to.

Thanks for suggesting ideas. We actually did do this back when I was in high school and it didn't work very well. First, it's hard to get a path that allows the epoxy to flow in and the air to flow out. In the couple instances we were able to inject epoxy, you could still see the inclusions and it really didn't help hide the problem. The way this one failed, I don't see an easy way to drill into the void and avoid the beetle at the same time. It's such a shame, because the rest of the beetle looks awesome, super clear, clean, color looks great... I'm really disappointed.

But... I'll let these finish curing (the instructions say 3 -4 days) and then mess with them. Who knows, maybe something will help. If not, I'm not out anything more than I already am.

 

[DLJeffs]

Matt ( @Sprung ), your idea worked pretty well. I know we had tried this before and it didn't help much. Maybe this epoxy flows better or welds with the existing epoxy better, I don't know. But I drill 1/16" holes into the air pockets. On the big one from the coconut beetle's thorax, it had a path sideways to the outside so I only needed two holes, one in each of the "arms". On the fire beetle I could only drill a single hole and hope I could somehow evacuate the air and replace it with epoxy. Mixed me up a tiny bit of epoxy and got one of my syringes from rod building. I didn't have an actual needle, so I drilled a 3/16" tap hole into the surface of the epoxy. This gave me a nice hole in which to seat the nose of the syringe to better force the epoxy into the air pocket instead of squeezing out around the hole. And it worked pretty well. I could see when the epoxy flowed into the arms of the air pockets, went to the second arm and when both of those were filled, I injected more epoxy forcing the air out the side of the block of epoxy. For the fire beetle, when I injected the epoxy I could feel the syringe get tight as the air inside compressed with epoxy. So I injected a little, then used the syringe to suck out a few air bubbles, and repeated that process a couple of times until it appeared the air pocket was completely filled with epoxy. The repair isn't completely invisible but I think it'll make the final casting very presentable. In the photos, the light reflecting swirls and such are mostly in the surface and will disappear when I get to sanding and polishing. I'm so glad you mentioned that and gave me the incentive to try it again.

 

[Sprung]

Glad to see you seem to have gotten some good results - will look forward to seeing them sanded and polished up!

 

[DLJeffs]

Screwing up my courage to pour this one. Probably one of my best beetles. This rhinoceros male is huge and in perfect condition. Made the mold yesterday. The mold is 7" x 4.5" x 2.5" deep, same mold as the coconut beetle, but I had to repair two of the sides that cracked getting the coconut beetle out.

 

[Webb]

Should it be molded upside down since the shell could act like a dome and trap air?

 

[Nubsnstubs]

Why couldn't you inject resin in the underside of the beetle, then position it in the mold before you filled the mold with resin. I don't know it the stuff is thin enough to go through a needle, but might be worth a try. ............. Nubs

 

[DLJeffs]

Upside down yes, but not so much because of the shape of the carapace. It's easier to ensure the top will be bubble free by positioning it upside down when casting and also by pre-coating the surface of the carapace before setting it into the base layer. The bottom with all the legs etc has many more places to trap bubbles so it's easier to cast it with the belly facing up so I can coax bubbles out with a fine brush. The beetle breathes through spiracles in the abdomen and thorax and those are the primary places where the air inside escapes during pouring - those spiracles as well as the punctures I made when injecting the beetle with formaldehyde. I'm anticipating that the air inside the beetle is going to escape one way or another and hopefully it'll come out in one place so I can repair it like I did the coconut beetle. By casting it upside down, hopefully that air bubble that escapes will be easily accessible by a 1/16" drill bit. And any shadows or micro bubbles that form during the repair will be in the bottom and maybe hidden from view. I also plan to pour this in several thinner layers rather than three like I did the coconut beetle.

I recall we did try to inject resin into the body of a beetle one time in Panama and it was hard to get the resin to flow through a hypo needle. Plus, it appears the resin didn't fill the entire cavity because we still got air bubbles during the pour. I've thought about drilling a 1/16" hole into the belly of the beetle to either facilitate injecting resin into the cavity or to give the escaping air a pre-planned place to exit, which might make it easier to drill and repair later. I've even thought about getting some clear 1/16" acrylic tubing, and inserting a tube into the body cavity during the pour to give the air an easy path to escape, than removing it at the last moment before the epoxy fully sets up - or leaving it in place and just filling the tube with epoxy afterwards. But there's no guarantee the air would all find a path to vent through that tube or a pre-drilled hole and I'd still have air bubbles to deal with. So I think the best course is to not mess with the beetle, pour it in small layer upside down, and deal with the air bubbles afterwards.