Adrian's Rocking Tombstone

Make your foam tombstone even creepier by having it slowly rock back and forth, as if the body below is fighting to resurface.


Prices are approximate for my area at the time of writing. Links to sources are not endorsements or recommendations or affiliates. I'm just trying to help you find what you need.

1 foam tombstone (1″ to 2″ deep) varies
1 1/2″ inner diameter schedule 40 PVC pipe $2.31
1 Gorilla glue or foam board adhesive $5.47 HD
1 1″×10″ board, a few inches wider than the tombstone
1 Simpson Strong-Tie 20-gauge 12-13/16″ strap tie (ST2122) $1.97 HD
1 1/2″-13 × 4-1/2″ hex bolt $1.08 HD
1 1/2″-13 nut $0.28
2 1/2″ washers $0.78 (for 3)
7 #6×1/2″ wood screws $3.82 (for 100)
1 “reindeer” motor $12.00–$16.00 MG FP Kindy's
2 Simpson Strong-Tie 20-gauge 16-5/16″ strap tie (ST2115) $1.37 HD
1 1/2″ diameter wood dowel
1 #4×1/2″ round or pan-head sheet metal screw $1.18 (for 16) HD
2 #4 metal washer
2 #4 nylon washers HD
1 or 2 cable ties
1 or 2 cable tie mounts
several small wood dowels
Note: As of the time of this writing, and are shipping identical models of these motors, and that's the model shown in the photos below. The model has a slightly different crank arm and a different style of power cord. If you get the Kindy's motor, be prepared to improvise a bit on the linkage.

If your tombstone is less than 2″ thick but tall or heavy, you might also want to have these extra bits.

2–3 foam or plywood scraps approximately 2″×2″
4–8 #6×1″ wood screws

And finally, you might also want to pick up some spare M4×12mm machine screws in case you lose the hub screw that comes with your reindeer motor. That's a metric screw, so it'll be in a different, smaller section at one of your U.S. hardware stores. At Home Depot, for example, look for the drawers in the fasteners aisle.



Part I - modify your tombstone

Whether your tombstone is finished or not, start by making these modifications. Starting with this will give the glue some time to set while you complete the mechanism.

Using the 3/4″ spade bit, drill a hole through the tombstone (front to back) 2″ up from the bottom at the centerline. Keep the hole as perpendicular to the face of the tombstone as possible. Go slowly to avoid tearing away too much foam. Do not overdrill, we want a snug fit.

If your tombstone is thin (e.g., less than 2″ thick) and tall, cut one or two scraps of foam or plywood into 2″×2″ squares. Through each square, drill a 3/4″ hole to match the hole in the tombstone. Using a length of PVC as an alignment guide, glue the squares to the front and back faces of the tombstone (sandwiching the tombstone). Use some #6×1″ wood screws through the squares and into the tombstone to hold it secure while the glue sets. The thickness at the reinforced part of the tombstone must not exceed 2-1/4″.

Cut a 2-1/2″ length of the PVC pipe. Glue it into the pivot hole. This will act as a sleeve bearing (bushing) for the pivot. It should be as perpendicular to the tombstone as possible. It should protrude beyond the front and back faces of the tombstone at least a little bit—don't make it completely flush. Be aware that Gorilla glue is an expanding foam, so check that the PVC sleeve remains perpendicular to the face of the tombstone as the glue sets. You can shim it with toothpicks if it starts going awry.

the tombstone laid flat with the 3-inch length of PVC pipe being glued in perpendicular to the face of the tombstone

Use the linkage arm (one of the skinny steel straps) to figure out where it will join with the back of the tombstone. With the tombstone face down, hold the arm parallel to the long edge of the tombstone, so that the bottom of strap is even with the bottom of the tombstone, and in an the outer edge by an inch or two. Mark where the top hole in the linkage arm touches the tombstone.

the linkage arm is temporarily laid on the back of tombstone to find and mark the location of the coupling

Carefully drill a 3/4″-diameter hole in the back of the tombstone. This one must not go all the way through like the pivot hole. Between 1/4″ and 1/2″ deep is ideal.

If you have a very thin tombstone, you might want to glue a scrap square of foam or plywood to the back first, and drill into that.

Glue a 1″ piece of PVC into this hole. As before, make sure it stays perpendicular to the back of the tombstone as the glue expands and sets.

a 1-inch length of 1/2-inch PVC is glued into place in to act as a coupling for the linkage

Part II - the pivot

Find the center of the wide strap tie, and mark a line 1-1/4″ to either side of it. These lines should be perpendicular to the length of the strap.

the wide strap tie is marked with the locations for bending it into the U-bracket

Bend the strap on the two lines to make a U-shape. You can use using a bench-top vise and hammer. If you don't have a vise, you can clamp the piece to the edge of your workbench. I first clamped some angle aluminum to protect the workbench.

check the alignment with a right angle when clamping the strap tie into the vise for bending

The bends should be straight across the tie. Use a right-angle to check before bending. The base of the U should be 2-1/2″ (to match the length of the PVC sleeve).

When done, the base should be flat and the large holes in the strap tie should be aligned. Test the fit with the 1/2″ bolt and nut.

the pivot bracked with the bolt in place to check the alignment

Cut a 1″×10″ board so that it's 4 or more inches longer than the tombstone is wide. This will be the base.

a 1 by 10-inch board being measured to create a base that's several inches wider than the tombstone

You'll want to paint the board, especially the bottom and the edges, with exterior latex paint in order to protect it from moisture. You can do this now or afterwards.

Screw the base of the U-shaped bracket to the board with #6×1/2″ screws. The bracket should be in the center of the length of the board and 2″ from one of the long edges. This long edge will be the “front” of your prop. The bracket should be oriented so that the bolt runs perpendicular to the length of the board.

the U-bracket is secured to the base board with wood screws

Part III - the motor mount

Mark the following bend lines on one of the narrow strap ties starting from one end: 2-1/2″, then 4-1/2″, then 1-3/4″, and then 4-1/2″.

the remaining strap tie is marked for bending

Bend the strap tie into a motor mount per the picture. Once again, make sure the bends are perpendicular to the length of the strap tie. It's easiest to start with the inner two bends and finish with the outer two.

the motor mounted to the base board with one of the strap ties

Four of the screws around the perimeter of the deer motor are flush with the top of the motor. (The other six screws on the motor hold the two-part case together.) Unscrew one of the flush screws and reattach it through an appropriate hole in the motor mount strap tie.

On the opposite side of the motor, another of the flush screws will pass near the strap but won't actually align with one of the holes in the strap. Remove that screw and reattach it through a flat washer, pinching the strap between the washer and the face of the motor case. Now the motor should be firmly attached to the motor bracket.

the motor mounted to the base board with one of the strap ties

Part IV - complete the linkage

Using a #6×1/2″ wood screw, attach a 1-1/2″ length of the dowel into the last hole on the remaining strap.

the linkage arm shown with the dowel attached at the end

Using a #4×1/2″ sheet metal screw, two nylon washers and a metal washer, attach the linkage arm to the crank on the motor. The linkage arm should be sandwiched between the nylon washers. Tighten it enough to hold without too much wobble but loose enough that the arm can rotate freely.

the linkage arm is attached to the crank on the motor with a sheet metal screw and washers

Part V - assembly

Check that the glue holding the PVC pieces in the tombstone has set. Temporarily attach the tombstone to the pivot. Recall that we mounted the U-bracket closer to one edge than the other. That closer edge will be the front. Mount the tombstone to the U-bracket by feeding the bolt from the front side so that the nut is on the back. From front to back, you should have:

Don't overtighten the nut. Check the rocking motion of the tombstone. Does it rock smoothly, within a plane that's parallel to the length of the board? It doesn't have to be perfect, but if it's way off, take a moment to do whatever you need to make it as smooth and orthogonal as possible. For example, perhaps you have to twist the U-bracket a little, or even remount it at an angle to compensate for an imperfect bend.

the stone attached to the pivot bracket with the bolt, washers, and a nut

Now slip the linkage dowel in to the coupling, hold the motor mount to the base board, and power up.

the linkage arm dowel fits into the PVC coupling on the back of the tombstone

Slide the motor around to find the ideal spot for the motion. The tombstone should rock back and forth without banging a bottom corner into the base board. There should be a little tension in the linkage arm to ensure the dowel remains in the coupling. Nothing should bind.

holding the motor mount to the board, find the best position for the rocking motion

When you think you've found the right spot, hold it there for two full rotations of the motor just to be sure.

Mark where you'll need to screw the mount into the board, and then disconnect the power. Attach the motor mount to the marked locations with #6×1/2″ wood screws. Note that you may have to temporarily remove the tombstone in order to screw down the front part of the motor mount.

If a bit of the motor mount extends beyond the base board, you can bend it over or down with a pair of pliers and a hammer. If you prefer to trim the excess with a power tool like an angle grinder, make sure you take the appropriate precautions and remember to file down the cut edge.

TODO: Need photo

Using cable ties and mounts, anchor the power cord to the base board, taking care not to break the insulation or over stress it. The intent to make sure the power cord cannot get tangled up in the moving parts and to protect the motor if the cord is accidentally yanked.

TODO: Need photo

Part VI - build up the base

Your restless tombstone will need a base that hides the mechanism. Depending on viewing conditions and how much effort you want to put in, there are a couple of approaches.

The sophisticated approach is to make a box, using the board as the bottom and 1″ thick foam for the sides and top. The top will need a slit to accommodate the tombstone. I assemble boxes like this using foam glue and wood screws. The foam can then be carved and painted to coordinate with the look of your tombstone. Drill holes in the board where the edges of the box will be. Glue dowels into the holes. Carefully press the box into place so that the dowels make indentations in the bottom of the foam. Hollow out the foam where the dowels made the indentations until the box fits snuggly in place. Being able to lift the base off the dowels will allow you to remove the box to access the mechanism for repairs and changes.

The simpler approach, illustrated below, is to use two lengths of 2″-thick foam to sandwich the mechanism. Start with two lengths that are (at least) 5-1/2″ high and the same length as the board. The 5-1/2″ minimum ensures that the base will hide the pivot bracket.

TODO: Need photo

Use hook-and-loop fasteners to attach one of them to the board. You may need to hollow out a small part of the back to accommodate the head of the pivot bolt. You can do this with a utility knife or use your 3/4″ spade bit.

TODO: Need photo

Hold the second length of foam along the back edge and mark where the motor meets. Cut the foam into three sections and throw away the middle section to make a gap for the motor. Attach the remaining sections to the board with dowels as described above

TODO: Need photo

© 2018-2019 Adrian McCarthy. All rights reserved. Last updated 19-MAY-2019.