Skis under the magnifying glass
This is a followup to the comment I made on the "skis" thread. So, here it goes.
First, I have to address another issue that has bothered me for some time.
Take a look at the first pictures and you'll see a 1/2" bit, the collet and a plumbing washer. Obviously the bit fits in the collet. But in earlier threads there was some discussion about bottoming out the bit in the collet. Part of the resolution was to put an "O" ring or a plumbing washer in the bottom of the collet. I went through my collection of "O" rings and couldn't find one that would fit properly. Alternatively, I went through my more extensive collection of plumbing washers and came up with a perfect fit.
Captions for Pictures
#1 - this shows the bit, washer and collet
#2 - this shows the washer inserted. The first time I put the collet in the chuck and the bit in the collet, the washer fell to the bottom of the chuck. When I went to tighten the collet, there was some resistance from the washer as I tightened the collet chuck.
#3 - shows the correct location of the washer. In this instance I made sure to bottom out the collet before inserting the bit and tightening it. This time it stayed put.
The objective in all of this is repeatability. If you make a series of cuts with one bit and then another and you want to repeat the first operation, it helps when the bit is installed exactly the same as the first time. The washer will help insure this. It is also supposed to absorb any dimensional variance of the bit caused by heat.
Working under a Magnifying Glass:
The objective of this thread is to use a router freehand but with great precision, something that is only possible, I believe, with skis.
In order to increase the visibility of the cuts, I used a piece of scrap with a saw kerf in it. On the right side of the kerf is a mark made by the striking knife but the bevel is on the wrong side. On the left side of the kerf is the bevel on the correct side.
There is another element involved in this and that is the location of the router on the rods. In this instance, I have the router shifted over to the right. I can't go all the way because the clamps are in the way holding the workpiece to the table.
Lastly, the setup was made with LeeValley setup blocks. These are similar to OakPark's but come with a 3-2-1 block as well. In this instance, I set the rod height to 2 1/2" from the table surface. The workpiece is about 1 3/4" thick. I set the rods on the left, then the right, back to the left and finally, back to the right. That set the height of the router. Note, there is no baseplate. Also note the tie-wrap is being used to stabilize the left side of the router. I have to also mention that holes in the routerbase that the rods go through are not round. They are hexagonal in shape. The router is almost perfectly perpendicular to the rods. However, the baseplate insert that you see in the picture is not perfectly flush with the surface of the table so there is a variation that shows in the cut.
The magnifying glass is necessary when working at this close a tolerance.
Now, to the operation. The objective is to cut as closely as possible to the flat side of the cut made by the striking knife. If I put the router in the middle of the rods and controlled the router with both hands, it would certainly work but my experience says that it isn't precise enough. The alternative (and the purpose of these experiments) is to fix the right side of the skis with the heel of my hand on the table and carefully move the left ski. Approximately 3" of movement of the left ski will move the bit about 1/2" when used this way. This gives you excellent control over the cut.
My biggest problem is getting the magnifying glass into a position that I can clearly see what's going on. I found that I can control the bit very precisely if I can see clearly what I'm doing.
Take a look at the second picture of the cut. You'll see the knife cut on the right (wrong bevel) and the knife cut on the left (correct bevel). This picture is magnified about 3x. What you're seeing is how close to the cut you can get using this method. You will also see the curve as I moved the bit into, then away from, the cut. The router was brought to the knife cut in arcs. Each arc got a little bit closer to the knife cut.