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Building a Pointing Machine

You can build a much better pointing machine in the studio than you can buy commercially. The machine shown below is easy to make in the studio workshop. It is pictured being taking a measurement from a plaster model fixed to a plywood board. This is a common strategy for copying things that are small or fragile, or sometimes for originals, where making a plaster cast is not practical. Numerous measurements have already been taken, as can be seen from the pencil dots on the model. Note the pasteboard spacer, which insures that the pointer is always set to the same distance from the model, in this case, about 1/32 inch. (When removing the heavy overburden of stone, go down to roughly 1/4 inch first, and take points only at the high spots. This leaves only a small amount of stone to go through at the more exacting final pointing level.)

Most of the manufactured machines available are delicate, and can be used for measurement only. The studio-built machine described here will measure just as accurately as a manufactured machine, but has the advantage that it is tough enough to serve as a guide for a drill bit. This can be a tremendous time saver52. The machine is very simple and can be made entirely with a drill press and some hand tools.

The pointing frame mounted on a board holding an original.

The stock dimensions are not critical--the sizes for this machine were chosen because the steel happened to be available free. This example machine can handle bars big enough for life-sized or larger carvings, but larger or smaller machines may be scaled to suit your needs or to accommodate the available metal stock.

The long elements of the frame are five-eighths inch shaft stock. The joints are machined from one-and-one-quarter inch cold-rolled square bar stock. Cold-rolled refers to the process by which it is formed at the mill, which gives it a smooth finish that looks almost machined. You can substitute ordinary mild steel for either or both, but you will want to drill a test hole to be sure that you can match the bar stock to a drill bit. For big frames, using aluminum bars instead of steel would save a lot of weight. (You'd probably still want to use steel for the joint blocks.)

The mounting pins and the point are cut from three-eighths inch rod of unknown provenance.

The essential tools are a vice, drill press, hack-saw, carpenter's or machinist's try-square, taps and a tap-wrench, and drill bits to match the shaft stock. You will also need drill bit that match the taps. More on this below. Use high-speed steel drill bits for all the holes, not all-purpose carbide.

An electric grinder or a single-cut mill bastard file can be used to clean up and remove sharp edges. A reciprocal hack saw or cut-off saw is nice, but not necessary, for cutting hte bar stock.

Marking and Drilling the Connectors

There are three kinds of connector blocks used:

  • The connectors for the main members have holes for two five-eighths inch bars drilled through adjacent sides of the block for joining bars at ninety degree angles. You need at four or five of these.
  • The connectors for the three mounting pins are similar, but have one five-eights inch hole and one three-eights inch hole, again, at right angles in the block. You need exactly three.
  • There is a unique terminating block for the armature that has two three-eights inch holes drilled at right angles, and one five-eights inch hole drilled in from the end. The big hole is for attaching the block to the armature. This is the block that holds the pointer.

The connector blocks are 2 1/8 inches long.2 1/8 inches long. You can do most of the drilling and tapping before sawing them to length.

Make a test cut with your hacksaw or cutoff saw to find out how big the saw kerf is. Use a try square and a scratch awl to inscribe cut lines all the way around the bar for each piece to be cut, allowing an extra amount for the saw kerf. If your saw kerf is 1/16th inch, the first piece will be 2 1/8, and the rest will be 1/16 longer.

The three blocks for the fixed pins that hold the frame to the model or the work piece are 1 3/4 inches long. The unique piece that holds the pointer is also 1 3/4.

The holes should all be marked along the center line, which should be scratched on two adjacent sides. They should be in from the ends 1/2 the diameter of the bar on one side of the line you will later saw (in this case, 5/8 inch). On the other side of the line, they should be 5/8 plus the width of the saw kerf, of course.

Using a machinists's punch, dimple each of the locations you've marked for the holes. To do this, place the tip of the punch precisely on your mark, and with the punch held perpendicularly to the steel, rap it once with a hammer. You don't have to hit it very hard. The dimple will center the drill bit when you start the holes--without the dimple, there's a tendency for the drill to walk around on the surface before biting in.

It will not be possible to mark for the holes to be drilled on the ends until the blocks have been cut apart, but for both safety and ease of working, it is best to do as much drilling as possible before actually cutting the blocks apart.

Drill five-eighths inch holes first. You must use a drill press for this. Do not drill pilot holes--go straight in with the full size drill. A word of warning: large drill-bits can easily fling the steel if you lose control of the work-piece.

Drill against a pine or plywood backing for two reasons: first, you need not worry about accidentally drilling into the drill press table if you don't have the drill centered over a hole in the table, and second, the undrilled dimples on the other side sink into the wood, rather than causing the bar to wobble. You can fix the wood to the table with two C clamps--these will stay in place until you are finished all the drilling. Clamp the work to the plywood table with another C clamp. Set the clamp up to hold the steel to the table loosely, start the hole (just touch the drill to the dimpled mark to ensure that it's in exactly the right position), then tighten the clamp to hold it in position.

Drill the holes for the tightening screws next. These will be used to lock the long bars into position. If you're using the recommended three-eights inch screws, us a #16 high-speed steel drill, not a 3/8 bit--the #16 is specifically designed to leave enough steel to cut the threads from. If you have already made this mistake, simply go to the next larger tap size and the appropriate drill. My machine has holes are drilled on all sides for convenience--only one screw per bar is actually needed when tightening the armature.

When drilling steel, you want to keep the speed of decent of the drill constant, not the amount of pressure. If you merely apply uniform pressure, the drill will tend to suddenly bite too much steel as it pushes through the other side, and may either break, stop the drill press, or even fling the work-piece. At the very last moment of drilling through, you will be actually holding the drill back for an instant as it tries to pull ahead. This effect is more pronounced with larger drills, and worse when intersecting another hole, as we are doing here. To minimize this effect, drill the large holes first, then the small ones. Use drilling fluid or oil while drilling, and cool the steel in water after each hole or two. You can buy special oil for this purpose, but Three-In-One oil works fine, and even cooking oil will work. The oil keeps cuts down friction and dissipates heat so you don't de-temper the drill tip.

The holes in the terminating block of the armature should be 3/8, not #16, because they will not be threaded. Drill one in each direction to get full use from a block--the holes will wear eventually if used with a drill. You could even drill two in each direction, but they won't be on the center line.

Threading the Set Screw Holes

It's easiest to thread the holes before cutting the blocks apart. You can purchase at the hardware store individual taps and matched drills for threading the lock screw holes. If you opt for a different size set screw, make sure to get the matching tap and drill. For this design, it's a 3/8 inch tap and a #16 drill.

A tap-wrench is a T-shaped holder that fits a range of tap sizes. Lock the tap in the wrench, oil it lightly, and start screwing it into the hole as if you were opening a bottle of wine. Hold it as perfectly in line with the hole as possible.

Cutting the threads with a tap and tap-wrench.

You may feel it bind when some chips have been produced. When it binds, back off a quarter turn and twist again to let the chips fall free. Excessive force will break the tap.

When the hole is fully threaded, the tap should spin freely all the way in and out like a bolt. Oil is not necessary for cooling, but keeping the tap lightly oiled is helpful; too much oil tends to keep the metal chips in the hole.

Cutting the Blocks to Length

It's hard to get a square cut from one side using a hand-held hacksaw. To get square cuts, lock the bar in a vice and use a 24 teeth-per-inch hacksaw to cut a 1/16 inch deep slot on the first side, using your thumb to position the blade on the scratch line.

Use the first cut as a guide to start the second, and so on around the bar.

Using two shallow cuts act as guides, alternately cut at a low angle to each to get a perfectly square cut started on the corner. Once you've gone in a little way the cut will be self-guiding. Use long strokes.

With square cuts started on all corners, cut all the way through with the blade firmly held straight. Little pressure is necessary. Each cut takes about ten or fifteen minutes.

Alternatively, an iron works or machine shop may be willing to cut the bars apart for you with their stationary reciprocal hacksaw. Ask for a test cut first to ensure that the saw is well-adjusted. If it's sloppy, it can run out of square just like a hand saw. A stationary hacks saw will make a clean cut in less than a minute.

Clean up the rough surfaces left by the saw with a metal-grinding wheel on an angle grinder. Lock the work-piece in a vice and check often with a square to make sure you are keeping it square. Even a small amount of grinding will make it very hot--don't get burned.

When the piece is smooth on the face, make a quick pass on the edges at a forty-five degree angle to soften the edges and the corners. You can also do this with a file, a coarse sharpening stone or a sanding wheel on the angle grinder.

While the piece is in the vice, mark and dimple the hole to be drilled in the end, if any, for the second round of drilling and tapping.

Cutting the Long Pieces

Next, cut the five-eighths inch bars to length with the hacksaw. The lengths you choose are a function of the size of the pieces you anticipate executing. An eighteen inch length for the base, twenty four inches for the upright, and two or three pieces eight to twelve inches long for the arm should provide enough flexibility for a bust. You can always cut more as needed. Square them off neatly, and twirl them lightly against a grinding wheel to smooth and bevel the corner.

Cut a piece of three-eights inch stock about fourteen inches long for the top mounting pin. Put the bottom one inch in the steel vice and heat the steel an inch above the vice to cherry red with a propane torch. Keep the hot spot as narrow as possible by not moving the torch. When its glowing brightly, bend it over to a right angle and let it cool. Don't cool it in water until it is no longer glowing--you don't want to harden it.

Cut two equal length pieces of the three-eighths inch bar stock, about four inches long for the bottom mounting pins, and finish both ends of each square and neatly beveled using a stationary grinder.

Cut a piece about a foot long for the probe pin. Square one end, and sharpen the other end to a pencil-point with slightly softened end.


You can buy ready made drill-stops that work perfectly for the locking collar, but they usually available only in sets, which include one for every size of masonry drill. Alternatively, you can drill and tap a short section of bar stock, which is what is shown here. Drill and tap before cutting the stop off the main bar. A screw with a wing-head obviates the need for a screwdriver when setting it.

The end holes must still be drilled. Because of the small size of the work-piece, it is absolutely critical to lock them firmly in a vice, lest they be thrown by the drill. A wooden two-handled carpenters clamp is good for this. Clamp it to the table with a C clamp.

A Dremel-tool with a conical stone can be used to de-burr the outer edges of the holes. One light pass should be sufficient. Where holes intersect inside the blocks may also have burrs that interfere with the smooth sliding of the bars. Running the drill through them up and down should loosen them up.

If the bars don't slide easily enough in a block, chill the blocks ice cold, and re-drill with the press on low speed. Chilling shrinks the steel by a tiny amount, letting the drill take a few thousandths of an inch more metal, so when they return to room temperature, the holes will be a little bigger. Run the drill in and out of the hole a couple of times. This will polish the hole and enlarge it minutely. Blow the holes clean with compressed air, or clean them with a bottle brush.

Stiffness in the threaded holes will loosen up with use. When you're finished, spray everything with WD-40 and wipe clean with a piece of T shirt. The coating is for rust proofing, not lubrication. You won't want it slippery or greasy in use.

Notice that the pointer illustrated here is discolored on the pointed end. After grinding the point, it was heat treated to make it very hard. This allows the pointer to be tapped against the stone to mark the spot, and leave a small dimple to keep the drill from wandering.

The full kit made from 100% from recycled junk, except for the machine screws.