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04-04-2003, 12:35 PM #1Bill GGuest
Vacuum Chucks and Solid Spindle Lathes
I just got home from a couple days out of town, and I see that I missed out on a bit of discussion in which I have several interests. I thought I would post a new post instead of putting this at the end of one several days old now. I would also like to say that this is NOT an advertisement of any sort, but rather a discussion of principles of operation and technical problems that need to be overcome for this specific application.
My Poolewood is a world class lathe, but it has one design feature which prevents the use of a conventional vacuum chuck, that being a solid headstock spindle. The VacuuMaster vacuum chuck was developed for me by a woodturning friend of mine who just happens to own a CNC machine shop. As with many things, it is just as easy to make 100 as it is to make one once the setups are established, so once we had the design nailed down, my friend Ron decided to do a short production run so others with solid spindle lathes could take advantage of this item (and make a few bucks for himself of course!)
The design of the chuck is straightforward. All that is needed is something that will hold a vacuum and pull it out at a right angle, all while the lathe is spinning at high rpm. The real big problem is doing it so that it doesn't leak, overheat, or seize up. Through the headstock vacuum adapters do not have this problem, even though the design is essentially the same, because the diameter of the seals are much smaller, and as such do not experience the same amount of friction per rpm.
To make the VacuuMaster work, special construction was required. When I tested the prototype, the vacuum chamber rode on two high temperature O-rings. While it worked to perfection, it got extremely hot, even though it was lubricated with a special goo designed to withstand that temperature. The production unit incorporates ball bearing raceways to cool it down and make the chamber less suceptible to losing vacuum if it is bumped. The chuck has loose bearing in raceways machined at the factory. Off the shelf bearings (cheap ones from China) were $60.00 EACH, and each chuck needs two.
The chuck also has a stop rod to make sure the tubing does not wind up and cause trouble, and it will happen if the rod is not used. I did not tighten the stop rod sufficiently one night. It fell out, the tubing wound up, yanked my pump off the table, and left me with an $80.00 repair bill for the pump. The repair guy told me I got off easy. It would be nice if the rod was not needed, but again, the large diameter of the vacuum chamber necessitates extra measures not found on conventional designs.
I know it ain't cheap. It is, however, comparable dollar for dollar with the system designed by Oneway, and which is very popular with Oneway owners. Part of the price is because of the unusual design, part of it is because they are made in small quantities right now. It is a special design to accomodate my Poolewood. My friend Ron at Sierra Mold decided that since he was building one for me, he would make a bunch and offer them for others. While it is expensive, it is definitely superior to the alternative, which is nothing.
I might also add that once something is done, it is relatively easy for others to knock off the original design, at least in most cases. If I recall correctly, Oneway was one of the first, if not the first to market a vacuum system for woodturning. Their adapter is easy enough to copy, and it has been copied at a much lower price. I don't think that will be the case with the Vacuumaster, at least for a while. It is built to very high standards, with exceptionally high manufacturing tolerances in order for it to function properly, but that's not the reason. The reason is, it is tough to come up with the materials needed and put them together in such a way so that they will work in a robust manner. I have been running my chuck for almost two years now, and it still runs great with no maintenance needed, such as replenishing the lubricating goo.
Again, this is not an advertisement on my part, but I wanted to explaina bit about what went into the design and testing of the unit. If anyone has any questions, I would be glad to try and answer them to the best of my ability.
04-04-2003, 03:36 PM #2dicklaxtGuest
RE: Vacuum Chucks and Solid Spindle Lathes
Thanks for the story Bill, very interesting.I have decided to forgo the vacuum chuck syatem because of cost and look for some other lathe toys that will be more useful to me. If I hit the lottery Saturday night I'll just buy the best lathe available with all the accessories and a new building to put it in.