Friday, August 10, 2012

Harsh Easel project part 2

After playing around with the commercial counterbalances I started thinking about systems with long travel that use springs. One of the systems most of us have seen are garage door openers. The type I'm talking about are the hinge type with the big scary extension springs. These springs are manufactured by the boatload and are readily available and cheap. The question was how to apply them to my problem. What do you do when you don't know? You hit the shop of course. Orchard Supply hardware supplied the test spring and I supplied the elbow grease. The first question that I wanted an answer to was would one of these springs have the necessary travel for the easel range of motion. After a quick shop test it was obvious that it had more than enough travel and probably had enough force. I could only estimate the load at this point since the rest of the easel wasn't fully designed. Remember I just needed a good direction to head for my power source for the counterbalance.
After fussing around with the design a bit I settled on a dual spring system that travels one half the distance the painting support frame travels. The load of the spring changes less because of the shorter stroke and the spring is less extended at the extreme ends of the travel. Because of the Gun Tackle type cable system I chose the working end of the cable was offset from the center line of the easel.
It would have functioned as intended but it bugged me from a design elegance perspective. I solved the problem with a little cable re-router device. As you can see in this little study drawing I like to start on paper then move to the more sophisticated electronic design tools. For this project I never had the thought of perfect documentation since it would only be seen by me. Looking back its a combination of hand sketches and loose electronic layouts.
This is the cable re-router designed and built just so the cable came out on center on the front of the easel. Hey I really thought it would look crappy coming down off center on the side you see all the time.

Here are a couple of shots of the lower area of the easel. The column tilting adjuster and the lower spring anchor can be seen in the right hand image. In the left hand picture it shows the main guide rollers, the locking mechanism and the track that the main easel frame runs on.
In these pictures you can see one of the major design features requested by Bill. He uses a special board material to tack up his storyboard sketches when he is developing a painting. He wanted the ability to mount this board to the back side of the working surface of the easel. essentially a dual working surface easel. This added to the load the counterbalance mechanism had to deal with. The left hand image shows the main surface in the "compressed" condition. Another requirement was that he be able to work really large.
Here you start to get an impression of just how big a painting you can fit on this easel. The side frames are extended and the top clamps are at full range.

Next up delivery day and the FAT (factory acceptance test).