TIL: BR85HB-SR Edition!

AKA. The First Mistakes Post of Many!


I was just reflecting on some of the things I’ll be doing differently on future builds and/or kits, and realised that it might make an interesting post. Currently I’m in the unique position of being still just about post-first-build, and therefore the things I’m reflecting on now are likely to be “obvious”, overlooked by builders further on in their pursuits.

Here’s the top five that I think about regularly:

1) Building Reality

Mating parts should, y’know, mate. I found that this goes away when you do one of two things. One, you’re working from blueprints or a 3D model and you build part of your piece. You then build the next piece from the original measurements rather than from the piece of model you already completed. Unless you perfectly nailed the first piece, the second piece isn’t going to fit- and still may not even if the two pieces both perfectly match the plans. Remember, it’s not the plans that have to go together in the end, it’s you’re actual pieces of build. So allow for minor and cumulative errors when you’re doing a multi-piece build.

2) Clear Coat Is Not Your Friend

Two, your finishing work can obliterate all your careful measurements and test fitting to make sure pieces mate perfectly. Don’t use clear coat on anything other than one-part masters! It goes on far too thick to maintain mechanical clearance. Don’t use it on one-part masters either, actually, because the slight dimpling of planes and rounding of edges that it creates completely ruin all those hours of careful wet sanding. It’s just bad news except for sealing in final paint jobs, and silicone has no problem with auto primer. If you have to polish up with something, stick with floor polish (specifically Future Shine, or “Pledge Floor Care Multi-Surface Finish” as it’s called now).

3) Slinging Goop

More is better. Thin walls need more support and will deform more in one of two ways; either they’ll blow out, and you’ll have a big dome on your casting that should be a flat plane, or they’ll shear past each other and you’ll get a step at the seam. That’s bad, since it needs a bunch of sanding and filling.

If you can’t afford to make block molds of the required volume compared to your part (ie. substantially larger in all directions), then go with a brush-on mold (eg. Rebound 25) and fiberglass or plaster bandages for the mother mold, both of which are substantially cheaper than RTV silicone. Just make sure to get your fiberglass supplies from an eBay marine supplier rather than a DIY store so that you pay normal prices rather than “hobbyist” prices.

4) Kits Take Time

Or, more specifically, complex kits (ie. actual “kits”) take time. If you’re just making one- or two-part casts you can crank them out and print money, for sure. However, if you’re actually producing genuine kits, where there’s a parts list and build process rather than simply paintable parts, don’t underestimate how much time it’s going to take you to put together the whole thing.

I’ve switched from using Smooth-Cast 305 (30 min demold) to Smooth-Cast 320 (10 min demold) and it makes a significant difference, though that may be at the expense of my moulds thanks to thermal breakdown, only time will tell. But know going in that if you have a “real life”, kit-making is going to take a huge chunk of time out of that and get not-very-fun, faster than you think.

5) Kits Take Money

If you’re trying to offer kits as a method of breaking even, quadruple your sales requirements or double your prices. Resin’s expensive, getting a dehumidifier for your shop to reduce bubbles in solid cast parts is expensive, and the time it’s taking away from your other projects is (or should be) expensive.

Strangers admiring your work enough to give you money for it is always gratifying, but the practicalities work out a fair bit less in your favour. You hear established builders saying not to get into propmaking if you’re planning on making money on a regular basis. Yeah… The margins are very slim, even when you have a home shop.


And there they are! I hope that these points clear some things up for at least a few people, and save some ill-fated money for someone who couldn’t afford to lose it! I know I’ll be taking them to heart over the next few months- in fact, I already have a Rebound 25 sample kit and some Home Depot fiberglass supplies to go with it. I’ll be putting two and two together on the Halo 4 combat knife that I built, and taking those lessons into larger projects in future.

Any other hindsight-is-20-20 lessons you’ve learned?


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