Sunday, February 26, 2012

Chevalet Mechanic Tips






I love fast cars and I love fast chevalets. I am fortunate to own a fast car and I am also fortunate to have a stable of chevalets. The primary difference is that I pay a mechanic to work on my car, but I am the mechanic for the chevalets. That is probably because the car is German and the chevalets are French. This seems weird to me today, as I reflect on my life, since I passed my language proficiency in college in German, and never took a class in French in my life. However, my French is much better than my German (unless you ask my partner, Patrice, what he thinks...something I usually avoid.)


Back to the point. Owning a few marquetry cutting tools requires a bit of normal maintenance. Now that others in this country are discovering the advantages of this unique tool, it might be instructive to pass on some tips for the owner/user to make their experience more enjoyable. When I have classes, I spend a bit of my time adjusting these tools for the students, and there are some normal things to consider to keep them working properly.

The first question is: does the size of the chevalet fit the worker? Traditionally, the worker would build his own tool, so it would be built to fit his sitting height, and whether he was right or left handed. The height (or size) of the chevalet is measured in metric centimeters from the top of the seat to the blade, when the saw is resting in the chops. In the school I have 6 different sizes, from 54cm (the size illustrated in Pierre's book) to the largest which is 61cm. That is about a 3" difference in height. The best height for a worker is determined by where the saw sits relative to the body, when the worker is sitting normally on the bench. The saw should be at about the same height as the base of the neck, or the collar bone. The reason is that to adjust the saw blade tension the worker pulls the frame together with his arm, pressing the knob of the saw against his shoulder. Thus, it should be low enough for that to be comfortable. At the same time, it needs to be high enough for the worker to see the blade in front of his eyes when sawing.

If the tool is not the right size, then it is often possible to replace the wood jaws of the clamp to better fit the worker.

The next step is to determine if the saw is cutting exactly perpendicular to the work. That test is done from time to time, or when it seems that the tool is no longer cutting properly. Use a piece of wood about 1/2" thick, and I prefer tulip poplar, since it is easy to cut. Mark the piece "front" and cut a keyhole test. Pierre describes this test in his book on page 207. The test cut should pass easily in and out of the wood from either side. If the top edge is not parallel, then an adjustment is made to the horizontal support for the saw carriage. If the cylinder is cone shaped then the adjustment is to the vertical. Note that there is a relationship between both the vertical and horizontal adjustment. Usually, it is mostly one and a little of the other. Continue cutting test pieces until it works properly. Another tip: using a very small blade makes this adjustment more accurate, before using a larger blade to cut the project.

When the tool is new, it is normal for the saw frame to work properly in a horizontal plane. Over time it is common for the saw frame to warp or the chevalet arm to bend slightly. It doesn't take much deflection to change the accuracy of the cut. That is why older chevalets have a saw carriage tilted up on the vertical adjustment, which you would think is bad. Not so. The only thing that matters is if the test cut is proper at the face of the jaws.

There is another adjustment that I make from time to time. Since the packet is manipulated around the saw blade, it is important that the chops or clamps press only in the center, where the blade is cutting. If the clamps grab the packet on the edges, then the pivot point is moved away from the blade and it is more difficult to get a smooth cut. Thus, I take a piece of paper (see photo above) and put it only in the center of the jaws and clamp it shut with my feet. It should grab. Then I test the paper on the edges of the jaws and it should pass freely. To make this work, I use sandpaper or a rasp to remove some wood from the jaws on the edges, so they only press in the center.

Finally, when I sit down to cut, there is usually dust on the sliding rod for the saw carriage. I wipe it clean with a rag and add a small drop of oil to the bushing. I also add a drop to the pivots at each end of the carriage which allow it to operate smoothly. These pivots should not be tight. There should be a little "end play" in the pivots to allow the carriage to swing easily.

Following these tips should make the driving experience more enjoyable. Remember, speed counts, but don't go so fast that you go off the line and crash the project.

I'm thinking of either a seat belt or air bags for my chevalet??

7 comments:

Chuck said...

Gee Patrick, I did not expect such an elegant discussion in response to my question about the saw angle. Was not aware of the changes wrought by time and usage to the chevalet. You more than covered a number of items of interest and yes, I use the keyhole test you taught me to verify squareness of my "portable" chevalet. My saw has an idiosyncrasy so it is necessary to mount the blade high in one clamp and low in the other to get it square within the frame adjustments. That coupled with other amateurish construction attempts helps to make it an alignment challenge.

Thanks for the interesting and enlightening post!

Chuck

Anonymous said...

I want one for the cool object factor alone.

To further heighten my driving experience I exchanged the computer chip in my Audi to boost the turbos....added 57 horsepower. Any place for that in the Chevalet?

SFPaul

W. Patrick Edwards said...

If you add a cup holder and fill the cup with Peet's coffee, it will add a boost to your cutting...

I measure my coffee by octane.

Frank Strazza said...

It is wonderful to have such a knowledgeable craftsman such as Patrick to share all of this wonderful information. All of this could be lost if someone did not take the time to write it all down. Thank you Pat!

I do have a question regarding the clamp adjustment. On mine it only pinches along the top, how far down the jaw should it pinch? in other words how far down should the jaws be parallel? I hope this makes sense.

Thank you again.

Frank

W. Patrick Edwards said...

Frank

When viewed from the side, the two jaws of the wood clamp are not parallel. They taper in towards the top edge where the packet is held. When doing the paper test I described in the post, pressure should only be pressed on the paper around the "V" notch in the clamps. The area of pressure should be about 1-2 inches in diameter, max.

The lower part of the jaws should not be touching, since many packets have elements which would catch on the jaws as you manipulate them.

The concept is to have only pressure where you need it and as much clearance as possible where you don't.

Hope this answers your question.

SpunkWOOD Aga said...

Hello!
Where i could buy chevalet?....If i have enough money :)

W. Patrick Edwards said...

You can order the hardware kit from me, with blueprints, for $500 plus shipping. If you check out the most recent post, you can see that I am working with Mark Hicks to produce the wood kit, but I do not know what that price will be yet.

In the past I have bought and sold complete chevalets and the price averages $2500.