Wednesday, August 15, 2012

Spent the Day in the Machine shop

Finally I got to spend a little time in the machine shop today. Last couple of weeks have been pretty busy with work in other areas. A few months ago during the assembly of one of our large superconducting dipole magnets I noticed a couple of the technicians had to take some rather awkward measurements. They were trying to use some old vernier calipers and some loose parallels to take a precision measurement. They were using these ancient old calipers because they had the longest jaws of any of the tools available to them. Imagine a large square block around fourteen inches square and you need to measure somewhere near the midpoint of the square. You need a deep throat measuring tool to reach to the middle. Micrometers in this size range have a pretty decent throat but the shape of the frame limits how far you can reach. There was a genuine need for a specialized gage to reach the center. In my spare time, whatever that means, I managed to put a little design work toward a custom deep throat coil pack measuring gage. The main shop waterjet cut the frame profiles for me saving quite a bit of machine work. A few parts piggybacked on a several McMaster Carr orders and I was ready to make something. All I needed was a little time. The hardest part.
I didn't take any pictures of the early blank parts but you will get the general idea. The aluminum profiles were waterjet cut out of 1.5 inch thick aluminum plate. The silver bar at the top of the picture is hollow Thompson linear bearing shaft. I like to use this for shafting I don't need to modify much. It has a nice hard surface and is smooth for sliding fits. This allows items like the aluminum beams of the gage you see here to move easily when you need to make large size adjustments. On the right the weird shaped profile you see is where the dial indicator will be mounted. The odd profile is just meant to protect the electronic indicator from getting smashed or bumped. Waterjetting the profiles is a cheap way to add simple functionality for not a lot of extra work. If you had to machine all that then it wouldn't even be there. Bottom line is the waterjet is a great value added tool and technique. Like all things you need to understand its limitations. Read a little more about Waterjets here.
Above the indicator housing there is a simple parallel flexure device. I added this so the gage could be quickly and easily calibrated using a length standard between the gage tips. Instead of trying to position the bars super accurately in tiny increments sliding on the Thompson shaft, you just dial a set screw to move the indicator in relation to the standard to calibrate the reference point. The flexure membranes are made out of .063 thick blue tempered steel shim stock and waterjet cut right to net shape and size, no machining. Everything you see so far came from McMaster Carr. The indicator, the flexure material, the Thompson shaft and the gage tips which you will see later. My motto is, "If you cant find what you need in McMaster Carr then you need to re-design"
 In this shot I have the indicator housing and flexure assembly in the vise to see what kind of adjustment resolution I have for the calibration. The screw is hidden behind the flexure where you see the Allen wrench going in to prevent unwanted twiddling after calibration. The test indicator shows me how the adjuster tracks and repeats. I had some worry that it might not be stable enough but it looks pretty good after trying it out. The flexure is pretty stiff with the short membranes.

To be continued.

No comments:

Post a Comment