At the end of this blog series I will post some measurements for those who want to build one and also some more photo details but for now I will go on to an overview of how I built the “works” of the chevalet.
This is my version of a blade clamping mechanism. I have limited metal working tools and capacity here in my AZ. shop so I kept it simple. I started with a piece of 3/8” square bar and a piece of 3/8” square tubing. I drilled and tapped the square tubing for a thumb screw (8-32 I think it was), then over-drilled a recess hole in the bar to keep the pieces together when the screw was loosened. Then by grinding away a little of the bar opposite from the screw, I made room for the blade. Next up I ground the square bar roughly round on the other end by hand on a bench grinder and threaded it for a 3/8” wing nut on one piece and a barrel nut on the other. The barrel nut threads into the handle knob.
Two square holes in the saw frame and you have a cheap simple clamp that works. I did beef up the saw frame arms later as they were too flexible.
On to the sliding mechanism. This is a shot of the adjustment tightener. It’s just a piece of 3/8” rod with it’s ends threaded, run through the center of the carriage base. The dado along the length of the bottom of the base locates it on the support post squarely. Square is very important on these parts if you are going to be able to square the blade to the work.
This is the basic carriage (again, my term) setup. The round bar made alignment a problem and will be refined later. The vertical ends each have a slot for the adjustment rod. The one on the front of the machine is vertical and the one on the back is horizontal. This was an early mock-up using 3/8” steel pipe for bushings.
The small wooden parts clamped to the bar are called “tumblers”. These are probably the most critical parts and are usually machined metal parts, but I’m not a machinist, I’m a wood guy
This is the whole sliding mechanism mocked up with steel bar and pipe from HD. The saw frame is clamped firmly to the shaft and the shaft slides through the tubes. All you have to do to make the chevalet work is to insure perfect alignment of the two bearings. My, that was easy to say! Doing it may prove a little more of a challenge. Once tuned and with a little wax added, this setup actually worked reasonably well. You can also see the vertical adjustment slot in this photo.
When I received my linear motion bushings and precision shaft in the mail things really started to improve. As you assemble this piece and try the sliding motion it becomes very obvious that no wiggle at all is allowable. I started with a clamped together mock up and as I decided on correct positions and glued pieces up, one at a time, I could feel the improvement in sliding smoothness each time a clamp was replaced by glue. I always wondered why these were so massively constructed to do such dainty work. I think this is the answer.
The second last step in achieving the perfect alignment I needed was to make the bushings self aligning. I did this by over-drilling the mounting holes almost to the center but not quite.
Then when I assembled them I shimmed the clamps with washers so as to leave very little pressure on the bushings, allowing them to align with the shaft. The final clamping pressure was actually so light that I used narrow strips of double sided carpet tape to retain the bearings in the tumblers. It works, they align perfectly.
Try not to notice the cracks in the tumblers. ..over tension. The final step in wiggle elimination was to fill the square holes in the tumblers, where they fit over the square tubing with epoxy and reassemble them, square them to the tubing. and let the epoxy set for a rigid fit. I did wax the tubing first so that I can still disassemble it.
Here’s what the final setup looks like. It works just fine and I probably won’t change it because I want to work with the chevalet, not on it. That said it shows signs of being a prototype and could be done, knowing what I know now, a fair bit more tidily. The round rod didn’t give enough alignment control so I slipped a piece of square tubing over it and locked them together the same way as the blade clamps above.
There you go, you too can build a chevalet and have lots of fun making cool stuff with it.
Next entry, as I said above, I’ll try to give you some measurements and tell you what I might do differently if / when I build another one.
Comments and questions welcome.
-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/