I've used a similar tactic, making the base of my STM style vertical unit out of garden variety (literally!) 8" x16" x2" concrete stepping stones. I used three, cut one in half, and made a 24" long base out of two layers of 1 + 1/2 pieces. I used "liquid nails" as an adhesive and it works great. For fasteners, I mostly used "T-nuts" epoxied into holes in the concrete which I made with ordinary masonry drill bits. I chose mostly #8 hardware, and it turned out that a 1/4" drill bit was just about perfect to drill a hole to glue the T-nut into. I found that the drill bit wants to wander as you drill, so I shoot for a slightly sloppy fit. Then, I fill the holes about half way with epoxy and set the entire assembly to be attached, with the t-nuts threaded on, right into the holes. I use wax paper to make sure only the t-nuts get epoxied to the base. In five minutes, the epoxy is set and I back out the screws and remove the assembly. I usually clean up the epoxy overflow with an exacto knife, and wait a full day before putting any real strain on the fitting. It makes the base heavy, but extremely heavy! One other note. Concrete is porous, so before final assembly, I coated the entire base with a high quality sealer/primer paint. It has the benefit of making the base a nice neat white color. Good Luck, Keith Payea ChrisAtUpw@....... wrote: > In a message dated 13/01/00 09:23:33 GMT Standard Time, twleiper@........ > writes: > > >> My daughter's Lehman is on a pier cast atop what is either an immovable > huge bolder or exposed bedrock in the root / wine cellar. It is a very stable > environment with natural temperature control and the seismo is made from > thermally stable materials, such as a granite tool and die makers slab for a > base. With a natural period of 50 seconds it only needs seasonal centering > adjustment.... > > Dear Mr.Leiper, > > This all sounds great, but what is the price of granite engineering slabs > and how do you go about boring holes in them? I read through your account of > the construction of the original seismograph with interest. > > I have been trying to think of a relatively cheap, heavy and robust base > material for a seismograph. I noted that people who used plate Aluminium > seemed to have put weights on them, so presumably, some weight can be an > advantage. > > I was driving past some roadworks yesterday, when I had a bright idea. > You can get 2" thick paving slabs made out of high density 'vibrated' > concrete, with a reasonably flat finish on both sides. The workmen were > cutting 3' x 2' slabs to size with a disk as I passed and I wondered if > anyone had thought of using part of one for a seis base? You could probably > stick flat metal base plates onto the concrete with epoxy. The smallest > diamond core drill that I can hire is 1/2", which seems a bit too big. I > haven't yet tried drilling a slab with a hammer drill and a carbide bit, but > from past experience, high silica aggregates are quite drill resistant. > > Do you know if anyone has used a paving slab and if so, were there any > problems? The price and weight seem about right. Can you comment, please, in > comparison the granite block? > > Regards, Chris Chapman > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@.............. with the body of the > message: leave PSN-L _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>