Can casting resin be used to create a custom mortise routing template?
I am wondering if casting resin can be used to create a custom mortise router template? As some background, I have a slab table that to be “reverse engineered”. Let me further explain. I recently made a Nakashima inspired coffee table using Japanese joinery. Unfortunately, I want to remove the slab top because it was too small.
I am going to use a router to remove material close to the tenons that are sticking through the top of the table, and then carefully pare back to the tenons with a chisel. Once the slab is off, I will need to route a mortise in the new (larger) slab to exactly match the custom tenons, like I did in the first place. However, I will no longer have access to the router mortise template when I built the table.
I have been trying to determine if I could pour casting resin over the exposed (after I route down say 3/4” into the slab and chisel) tenons to produce a “negative”, which I could then use as a mortise (router) template using a pattern bit?
I will attach a few pictures to give you a better mental picture than my words can describe.
Thanks for your input!!
Replies
I think you could do this. I assume that the template you make would bea single piece for all four legs of the tenons, so that it would look like the plywood one shown in the pictures. One problem would be shrinkage. Most casting resins shrink when they set. Generally the package will tell you what percentage of shrinkage to expect. The guys I use for resins are here: https://www.smooth-on.com/ They are very helpful online and in person, and can guide you as to the right resin to use for minimum shrinkage. Since you are going to have to remove the tenons from the top anyway, why not just use the tenons to mark another piece of plywood, and make a template like the one you used the first time? You could fit the template to the tenons for a nice sliding fit, so it is accurate, and not have to worry about shrinkage. Another alternative would be to just call it a bench instead of a coffee table, and make another coffee table. 😁 Question- what kind of wood is the leg with tenons made of? Looks really nice.
Thanks for the suggestion. Species is Black Walnut.
Oh, and make sure to use a good release agent if you decide to cast a template!
Ouch. This is a very difficult proposition. Are the legs that precious? I'd sell the table and make a new one. It's good enough to be worth money.
I think you will really struggle with the release though and the chance of success is not high. You don't have anything to lose though if it does not work, but as I said, I'm not optimistic.
I've never done this, but based on casting experience:
Make sure the legs are crisp and clean. Any shreds will make it hold in the mould firmly.
Cut a bit deeper than you intend to make your template and pour in some molten wax to make an easy release base.
Include some fibreglass in the resin to encourage it to stay in one piece.
FWIIW I recommend you go with the make a new template option - it'll save you cash and angst.
All good advice! I especially liked the idea of pouring wax into the mold. Gonna use that one!
Remember that thick resin gets hot and may melt your wax - either pour in thin layers or use a very slow setting thick pour resin.
For what it's worth, I would make a small plywood template for each tenon, slide them on each one, and fasten them to a larger piece. It should be easier than trying to make a wooden template that encompasses all four in one go.
Paring those tenons perfectly down their entire length seems unrealistic, and even if you did, they are already saturated with glue.
Make a new template with the tenons slightly smaller than the originals and recut both sides. You have already tested your process and it worked, use that to your advantage.
Good one.
Thank to everyone for the wonderful suggestions! Part of the challenge is not having enough room (from underneath) to use the existing tenons to trace out a new template, after I have "released" the old top.
The legs and post design are all black walnut and were custom cut using a Japanese pull saw, requiring hours of detailed work. That is why I am trying to "re-use" the tenons instead of sacrificing them.
I will give you all a follow-up when I get the new slab top in place. Thanks again!
Peace
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