Calibrating and adjusting for accuracy

While building the pantorouter, I made a few test joints. The mortise and tenon joint at left worked out perfectly, but the multiple mortise and tenon joint at right didn't fit as well as it should.

The spacing between the tenons is a bit smaller than that of the mortises, and I had to cut the joint with some slack (using a smaller follower) to be able to assemble it at all. The distortions would, to some extent, be the same for both sides of the joint, except that I cut the tenon piece lying flat on the table (with the tenons oriented vertically), whereas the mortises were oriented horizontally. So it appears there is some distortion introduced by the pantograph.

I hadn't individually checked the pantograph parts for accuracy, so I suspected some might be a bit off. But before taking it apart, I figured I should check how the router aligns with the table. I mounted a piece of 1/4" steel rod in the router.

The rod rested flat on the table along the full width of the table, so it appears that aspect is accurate.

But checking with a square, I could tell that it was not square to the edge of the table. Also, plunging in and out, I could see the shaft moved to the side a little bit as the router moved forward and back, so the router axis was also not parallel to the plunge.

Time to take the pantograph out of the machine. Pulling the shafts out is difficult. I used the clamps from the plunge stops to grab the shafts as I pulled them out.

Using another shaft, and a mallet to drive the first shaft out works too. Push the shaft half way through, then pull both shafts out from either side.

Then checking the links for length and twist.

Twist is easy to check. With pins in the holes, I rest the links on some straight pieces of wood on a flat surface. If it rocks back and forth (like a wobbly chair), then the link has a twist.

I measured about 0.010" (about 0.25 mm) of rocking on the long link.

I measured the spacing between the shafts by hooking a tape measure on one shaft, then measuring to the near edge of the other shaft. Should be 36 cm to the near edge for the long link. This one is spot on.

One side of the short link was nearly half a millimeter too long, but it also had some twist. The dial indicator showed 0.015" (0.3 mm) of rocking. Given that it's a short link, that was a bit much.

The biggest inaccuracy I found was the length of the router mount link. The shafts were a full 1.5 mm too far apart! That probably accounts for most of the inaccuracy.

Rather than make the part again, I figured I should try to "fix" it. First I cut a section of 3/16" x 3/16" maple square on the table saw. Then I whittled it to an octagonal shape using a small hand plane.

I used the octagonal piece as a dowel to plug the holes that needed to be changed.

Driving a peg into the pantograph link's hole. I gave the glue a day to dry before re-drilling.

Then carefully measuring where the hole actuallyneeds to be. I used an awl to punch a divot in the new hole position. But now, how to drill this without allowing the drill to wander?

So I drilled a hole in another piece of hardwood with the drill I wanted to use. I then stuck the drill bit in that hole, with just the middle of the drill's points protruding, and placed that point in the divot. I then firmly clamped the piece of wood in place.

With the clamped on piece of wood guiding the drill, I was able to re-drill a new, overlapping hole. It worked out ok, so I didn't need to make a new piece.

I wasn't sure whether the error in the short link was worth fixing, but I figured while I'm at it, I might as well try. I glued a piece of dowel in the hole and gave that a day to dry.

The twist that I was trying to correct was really quite small, so I have to be very accurate about marking to get it more accurate than it was. With the piece supported on the shafts in the other three positions, I used the point of a 3/16" drill bit to scratch the center line of where the hole should be and carefully measured the distance to the other shaft.

I then use the same technique as with the router mount link to make sure the hole went in the right place.

The operating handle link had quite a bit of twist to it.

But I also had the hole for the follower slightly crooked, the long part of the link wasn't stiff enough to resist twist flexing where the follower mounts. So I redesigned the operator handle link (drawing on the workbench) and started building a new one.

Making the new operator handle link.

If you build a pantorouter XL from my plans, you will of course have the improved design to begin with, so hopefully, you will not need to rebuild yours.

This time, I put glue on the first joint (instead of doing it dry initially), which sped things up a bit. Though I still waited for the glue to dry before gluing on the other rail so I could focus on aligning one joint at a time.

Checking the plunge sled accuracy. The main pivot for the pantograph was not perpendicular to the table edge, nor was it parallel to the plunge direction. I checked it by measuring sideways movement with a dial indicator while moving the plunge sled in and out.

My procedure to make sure the rails were parallel to each other did not include making sure the plunge sled was aligned with the rails. I also only used two screws instead of four on each rail, so I had quite a bit of slack, and, though parallel, the rails were not square to the wood when I tightened the nuts.

So I loosened the nuts, adjusted it, and retightened. After that, everything was aligned.

Next: Final assembly

Back to Pantoruter XL main page 

Pantorouter plunge controls and router springs Making the plunge lever Having built the pantograph, plunge sled with drawer glides, table, and template holder, the pantorouter XL is basically operational, but it's not very convenient to use. The shape of the lever is simple enough that I can transfer the measurements onto a piece of wood rather than paste the template on. I made the cuts parallel with the wood on the table saw, then cut the rest on the bandsaw. A series of holes needs to be drilled in the end of the lever, to allow me to mount it slightly further out if I want to later. I just mark the holes off the 1:1 drawing, then drill and countersink them on the drill press. Next the operating handle. I round the edges of the handle part of the lever. The other end needs to have a notch cut out of it to couple with the link I just built. The operating lever couples to the link as shown. For the lever's main pivot, I'm using a #10 wood screw, which screws into the template holder. The hinge with the link could be a piece of steel rod or a wood screw. I'm using part of a knock-down fastener screw. I like the large head on it, and the smooth shank will make a nice pivot. I cut the screw to length, then chamfer the ends to make it easier to screw into a slightly undersized hole. The screw threads end up engaging only the other side of the operating lever, allowing the link in the middle to pivot freely around the smooth part of the screw's shank. The lever and link mount on the pantorouter right here, but I will leave them off for now so I can work on the plunge depth stops. Making the plunge depth stops The depth stop mechanism is made from four blocks of wood. I cut the basic rectangular shape of these on the table saw, and here I'm checking the size against the 1:1 drawings. Three of the blocks get a hole the same size as the shaft, but the largest gets a hole slightly larger so that the shaft will slide freely in the hole. The holes get a slot cut into them to allow the block to clamp down on the shaft. Also, a few other bits are cut off to shape the blocks This is how the plunge stops fit on the pantorouter. The block at left secures the shaft to the sled. The large block at right is screwed to the table, and the two small blocks clamp onto the shaft to provide depth stops. In the plans, I have a 1/4" (M6) carriage bolt and threaded knob to clamp the blocks onto the shaft, similar to the one shown at left. But I have these screw knobs that I have been meaning to use for something. They are a bit too short to use with a nut on the other side, but a T-nut extends them enough to be just right. Unfortunately, the knobs have an M6 thread, and the closest I have is 1/4" T-nuts. The T-nut almost fits. So I ran an M6 thread tap into the T-nuts, and now the metric threaded knob screws in just fine. I place the T-nut over the hole, then tap it with a hammer to mark where the prongs end up, then drill holes for the prongs, large enough for the prongs to loosely fit into. T-nut and knob mounted on the block. The block that holds the shaft is screwed to the plunge sled, and the other block to the table. The hole in this block is larger so that the shaft can slide freely. The small blocks are then clamped to the shaft to serve as stops. And the plunge lever can now be mounted right above the depth stops. Router weight compensation Gravity always pulls the router down. Though the operating lever provides a 2:1 advantage, lifting up the router by the operating lever is still tiring over time. To help lift the router up, I'll be adding springs that push the two pantograph links up, which in turn lifts up the router. Two cam-shapes for a string to wrap around are cut from Baltic birch, using 1:1 templates, on the bandsaw. A screw on the inside corner of these will allow a loop of string to hook onto them. One of these spring cams mounts to the front. It goes on the main shaft and also screws onto the long link. The other cam just slides onto the shafts of the pantograph. The holes in the cams are slightly arger than the shafts to let them slide on easily. The springs I bought at Lowes are slightly too long, so instead of using the loops at the end, I'm bending the last loop to the side on the vise, using a piece of wood and a hammer, then cutting off the original end loop. The sideways-bent loop screws to the edge of the plywood. And some string (sash cord) ties the spring to the screw on the cam. With the link pivoted all the way to the other side, the spring has quite a bit of stretch to it. Imagine the long link held in a fixed position, this spring will effectively pull the short link to lift up the router. The other spring cam is on the front. The spring needs to go under the shaft for the plunge depth stops. I hadn't drawn how the spring attaches on that end yet, and the spring is long enough that it needs to go under this shaft. I had to carve out a notch to make room for it. I moved the shaft for the depth stops a bit higher in the plans, so you shouldn't need to carve a notch to make room for the spring. The springs aren't strong enough to counteract the full weight of the router. Even though it's a smaller router, it probably isn't any lighter than the motor-only unit of a full-sized interchangeable base router that I used on my other machine. And another minor touch, a piece of dowel as an operator handle. Ready for some more testing. Here cutting a tenon. A sizable tenon for such a small router, but I can take it in steps. And the corresponding mortise cut. Makes a nice pop when the tenon is pulled out of the mortise quickly. Back to the Pantorouter XL