My first custom building block mold

I’ve made lots of molds in the past year or so, since I started really getting involved with plaster and resin. I’ve made molds for miniatures, terrain, building blocks, etc.

But up until now my molds have really fallen into three categories:
1. Miniatures (I’ve probably got about ten miniature molds)
2. Non-standard terrain (Only a few of these, one for a wall, one for a column, one for some rocks)
3. Hirst block assemblies (These are all floor elements that are intended to make it fast and easy to make modular elements for dungeons. This also makes for much stronger floors than just gluing individual blocks together).

What I have not made, up until now, is any sort of custom mold which duplicates the function of the Hirst molds, but with my own sculpted blocks.

Now I have one. Basically I wanted a 4″ diameter fieldstone tower mold and didn’t have one. So I sculpted the individual blocks and then created a mold that lets me cast sets of blocks which I can then assemble into towers, etc.

I’ll try to take a photo tonight. I made the mold Monday night (during the football game) and it took 24 hours to fully cure (which means I probably didn’t get the catalyst exactly right in spite of using a postal scale to measure the amounts “precisely” – sigh). So last night I started casting some blocks using the new custom mold. I was able to cast five sets of blocks, which was enough to create a four block high “tower”. Tonight I’m going to cast more blocks, hopefully enough to have a high enough tower that it can actually be used in a game. Then I can paint and seal it.

But just based on the dry-fit four block high “tower” I did last night, I am fairly pleased with the results. The blocks fit together pretty well even without any sanding, meaning I got the sizes close enough that they fit together without any horrible gaps or unevenness or bubbles, etc. I believe the result would be a perfectly usable tower.

It will take a few days for me to make the blocks needed even for a prototype tower and they will need 48 hours to dry enough to glue and paint, so it will be Friday at the earliest before I have anything to take a photo of, and it will probably be more likely to be a weekend activity.


One thought on “My first custom building block mold

  1. By the way, for those that are interested, the basic technique for making my custom blocks is as follows. I use the cut block mold to cast some “blanks”. That ensures that I get teh right dimensions and shape for the blocks. Then I sand them down lightly to remove the “look” of the cut blocks. Yes, this does change the dimensions slightly,but at this time I can live with that. Eventually I want to create a pure blank mold that allows me to cast blocks that are exactly the right size with no design at all. But the cut stone blocks are very close to that already.

    OK, so once I have a “blank” I get out a pencil and draw the basic design of my “fieldstone” pattern. That’s just done freehand and I almost deliberately do not try to be very precise. I kind of want some randomness in the result so that it looks like the blocks are truly random. This is hard. Very hard. This is one area where I have gained some real appreciation for the sculptors who do this sort of thing. There is a surprising amount of artistry in this so that the result is sort of random, but also provides enough of a consistent look that the blocks “mesh” together. In my first attempt I have one of my blocks that doesn’t quite fit with the others. I dont’ think it’s very noticeable, but it is noticeable enough that it bugs me now that I’m casting them. I hope that painting the blocks reduces those differences instead of enhancing them. Time will tell.

    So, after drawing the basic design the rest is pretty straightforward. I get out my rotary tool and use three different bits. I first use a course cutting bit and just go over the pencil marks, doing my best to have a consistent depth of cut. Considering these blocks are all less than a cubic inch, that’s pretty detailed work. I use reading glasses to allow the control I need. This “roughs out” the block design. But the result doesn’t really look like stacked stones, it looks more like a block which has been gouged.

    Next I get a fine cutting bit and cut a deeper channel down the middle of the wider channel I just created. This is when I try to define the outline of the actual stones. The result is surprisingly nice looking. Something about the dual cut approach really makes the individual stones seem to stand out.

    Finally I get a rough elliptical sanding stone and sand down most (but not all!) of the corners. At this point I also use that stone to give the individual “stones” some definition and shaping so that they approximate the organic shape of actual individual stones. Then I use a very fine grit sandpaper to just go over the block and smooth it over because I want the stones to be smooth stones. In a future design I might want sharper stones. If I do another one.

    Anyway, that’s the process for creating these blocks.

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