blind fastening template

[Kevin Jenness]

I was asked by an artist with whom I have worked before to make a base for a sculpture. The underside of the resin casting has four threaded inserts in a random pattern to allow for hidden fastening, and the task was to locate holes correctly in the base.

I first considered using plexiglass but lacked a large enough piece of scrap and was dissuaded when I checked the price of a 2' square sheet. I roughed out a piece of 1/4" melamine coated particleboard and marked two holes on it using trammel points on a beam. From the initial points I picked up distances to the other two holes in the casting and marked where the arcs intersected on the template. I ran fasteners through the template into the casting inserts, marked the casting outline and cut it out with a bandsaw.

The template and casting were reunited and place on the base and precisely located by the artist to get good margins at several points. The template outline was marked on blue tape on the base, then the loose template was replaced on its marks and the hole locations marked with a vix bit.

The inserts were not plumb in the casting, so I indicated the drift direction and angle for each one and drilled through the base with a handheld drill lined up with a protractor. The holes were counterbored in the base and the fastening completed.

I'd be interested to know how others go about this sort of thing.

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[glenn bradley]

I grind a point on pieces of a bolt or threaded rod. Screw them into the subject and set it on the pattern blank. The points act like dowel centers marking the positions for drilling. As to inserts out of plumb; a washer and a slightly oversized through hole in the template and the eventual base solves that for me when attaching.

[Edwin Santos]

Rub some dark chalk or pencil graphite liberally on the inserts, turn the statue right side up and set it down on a piece of cardboard or thick paper. The marks left on the cardboard are your template.

It looks like the inserts are slightly proud, so you'll probably get a clean impression of the insert. If not, use some threaded rod and rub the graphite on it.
If the bottom of the statue were flat enough, I would just lay paper on it and make a rubbing impression.

[Bill McNiel]

I grind a point on pieces of a bolt or threaded rod. Screw them into the subject and set it on the pattern blank. The points act like dowel centers marking the positions for drilling. As to inserts out of plumb; a washer and a slightly oversized through hole in the template and the eventual base solves that for me when attaching.

I like this approach.

[Rob Sack]

I would use pieces of threaded rod or a bolt with the head cut off and screw them into the inserts. Use lipstick to transfer the pattern. I would drill oversize holes in the base and probably use some kind of rubber washer when fastening the piece of art to the base, especially if the inserts are not plumb. Overtightening could crack the resin casting.

[mreza Salav]

put small lump of playdough on the board approximately where the screws would land. Put the object over so that the screws press down on the dough. Clear the excess of the dough and mark and drill.

[Paul Haus]

I've done as both Rob and Bill mentioned, both works. In Rob's process I used allen head screws and put the lipstick on the head.
You have gotten good advice here. Good luck and Merry Christmas.

[Kevin Jenness]

Thanks for the replies. I probably would have used the more direct method of impressions from pointed cutoff screws if the seemingly oddball 12/24 fasteners had been on hand. As it was the trammel method worked perfectly without the effort of cutting anything. One insert was plumb, the others were off by 3, 6 and 10(!) degrees so the angled holes seemed a good idea. I wound up snugging the screws lightly through oversized holes with threadlocker and steel washers over 1/8" crepe rubber cushions to minimize the risk of cracking.