I hope there is someone here who can help my company out on machining issue. We priced out some cylinder cams with some fairly large machine shops, and when the quotes came back my boss almost had a heart attack. We are in desperate need to apply reciprocal motion to a slide. The tolerance for the motion must be held within .005". The range of motion can be anything from 1/4" to 3". If there is anyone here with knowlege of cylinder cams, (or barrel cams), your response would be most welcome. Mike
Mike, First thing that you should know is that anything relative to a helicoil shape, involves a lot of time, which of course translates into high cost. Secondly, you are not commited to a cylindrical cam in the first place to accomplish what you are looking for, linkage governed by an excentric cam is almost as effective as a cylindrical, or barrel cam. If the quotes that you received are unusually high, you were probably being quoted on a cylindrical cam being machined from a solid block. The only machine shops that can do this are the larger companies that are equipped with machining centers. These larger job shops, with machining centers have no choice but to bill our their machine time at $175.00 per hour plus. In this machine and tool climate, such as it is, you may be much better off finding a shop that can fabricate the cam from two components, the cost of which will be much less prohibitive, and equally as effective. I personally have made these fabricated cams and used them for years without any problems whatsoever. They are traditionally made from oil-hard tool steel, and heat treated to a
58-59c Rockwell, and with proper lubrication, will last a lifetime. The accuracy of your throw, (you require .005" repeatablility), is accomplished by your slide hitting an adjustable dead stop, which will give you repeatability in the .001" range. The equipment needed to make this type of cam is a vertical milling machine, equipped with a dividing head that is ratio geared to the traverse screw, needed to machine the helicoil profile. I have published to my website some photographs of the cam that you are looking for. Feel free to download them and give them to your vendors for quote. You can substitute your own dimensions as your needs require.
Mike, I have made the model for the fabricated cam that you need to submit to the Rapid Prototype Co, or a Machine Shop, suitable for quote. If you need a sketch of the linkage and mechanical stop used along with this type of cam, get back to me and I can provide it. Bear in mind that the metal that you will ultimately receive your prototype in is on the order of cast zinc or an alloy, and therefore not very durable for industrial use or continuous duty. Also, the process is not cheap. The design offered by the tutorial of Dr. Mather, is of course Classic and a very excellent design, but there again, this is a design that a machine shop would have no choice, but to machine from a solid cylinder of steel, and you would in the same fiscal situation that you were in originally. Whatever you decide, I have published all the files that belong with the assembly for the cam that I propose on my website. Here is the link.
They're usually not that hard to machine using "A" axis mapping (axis substitution), hold better tolerances too. I've done several of them myself. You want to model the cylinder using sheet metal functions so you can unwrap it into a flat pattern. The contours are programmed in the flat state, and wrapped onto a cylinder using a single line of code in the program. Actually very easy. What is it made of and how big is it ??
It sounds to me like the shops you got quotes from didn't know how to do it, and subed it out to someone that did.