This will document the construction of a Helios (see photos of completed Helios at http://www.solarfire.org/Helios,36 ) in Lytton Springs, Texas (just a bit less than 30 degrees N. Latitude). Since the first construction article for the Helios was written in French, I ran the article through a translation program, saved it, and printed it so I could convert the measurements for materials into American units of thicknesses, widths, and lengths that I could purchase at a local steel supply yard. (Discount Door and Metal L.L.C 2 at 1083 Highway 71 West, in Bastrop, Texas 78602) Then, I obtained a printed price list from them, and made a list of what I wanted, and hooked up my 12 foot long cattle trailer to my diesel truck and drove the 20 miles to the supply yard. Loading the 24 feet long 11 gauge (heavy duty) square tubing into the 12 foot trailer left me with a good bit angled up into the air over the bed of the truck. With luck, I managed to clear all the low hanging power and telephone lines on the way home. The first photo shows the material and prices I picked up on that trip. Then using the pictorial Helios construction plans put together by Marie Testud (GUIDE DE CONSTRUCTION FOUR HELIOS) I began using a hacksaw and a 14" metal chop saw to cut metal. To cut the 3" wide 1/8" thick material that the 12" mirror tiles are glued to, I used the chop saw to cut two at once. Put them on edge, measure carefully (These need to be square 3" by 3") and lower the grinding disk. Works great! Then clean up the edges on the bench grinder. The smaller pieces for the spider were cut in a bench vise using some old hacksaws, mostly to save on material, because the chop saw takes at least 1/8" of material for each cut. However, the chop saw does cut at pretty close to 90 degrees each time.
Mirrors were purchased from Lowes Home Center for $1.40 each. They were available in boxes of six tiles. I bought all they had (8 boxes) using a ten dollar discount coupon, plus my cash. Two days ago, they sent me another ten dollar discount coupon, so it is time to drive there and buy more mirrors, and some polyurethane adhesive. Lowes and Home Depot are our two large chain building supply and home repair stores. Eerik says in Canada, they use Lepage Bulldog industrial adhesive. A google search yields no availability in the U.S., but did say that Henkel purchased all or part of Lepage. Lowes has plenty of Henkel glue products..Gorilla glue might work, but I certainly don’t want the mirrors falling off the steel plate.
Nuts and bolts: I priced the metric threaded items, and decided to use a 1/4-20 size bolt which is a very common size here. The eight bolts pressing on the mirrors need to have threads from the top of the bolt to the bottom, so you have to order a TAP BOLT. I ordered 1/4-20 x 2" Tap Bolts grade A, Zinc for less than a nickel each from WholesaleBolts.com. They were ordered at 2 P.M., and showed up the next morning at 8:30 A.M. I also ordered some lock nuts, and shorter 5/8" grade Hex bolts (1/4-20) to attach the spiders to the tabs on the square tubing.
I’m welding these spiders using a Miller Synchrowave 250 TIG welder with Argon Gas and RG-60 welding rod. There was a label on the square tubing indicating it was made in Mexico. The square tubing looks very strong, and the 24 foot length is heavy. The 1/2 strap steel used for the spiders is not very strong, (I guess I should say it is very soft steel) but it is light weight, and I believe it is going to do the job. When welding it, I’ve noticed parts here and there that don’t seem to be real pure steel. (i.e. not like aircraft grade 4130.) Well, yesterday I added a few more spiders to the pile and today I need to cut out some more materials, and possibly get a few more made.
- Materials with prices to begin construction. Not sure if it is complete, but should be enough for spiders and frame.
- Shows progress on the spiders and bolts.
Thanks to my neighbor (Dave), I bought a trailer for a small boat and I hope to be able to modify it to hold the array so I can move it into the barn during a storm or hurricane. Also, the two tires hold air, and would simplify movement of the array so it can track the sun.
For the interior of the oven, I’ve stripped a discarded dishwasher of all electrical, rubber, and plastic parts and now have a steel box with a door and a large round hole. A round microwave clear glass turntable might work as a porthole to let the energy into the oven. (I now have two of those, for FREE, but I have no idea whether or not they will work, as the glass is thick.)
Making the 90 degree bends (about 500 of them) for the spiders. I’ve been hacksawing these in my basement using large vise and a couple of CFL lamps. Earliler, I had made some templates out of light cardboard from a cereal box. Next, I carefully cut out some "Go-By" pieces, and marked them using a ring of duct tape. These are my reference pieces for the three different sizes of legs for the spiders. Place the steel in the vise with the wide side up, so you get a 90 degree cut (no slants). After cutting a large stack, lay one of them on the anvil part of the vise, and determine which end is going to have the hole (save the perfectly perpendicular end for the weld joint.) and lay an old hacksaw blade over the end of the piece and use the hole in the end of it to locate the position of the center punch mark. Give it a good whack with a hammer, and inspect. If it isn’t in the center, turn the piece over and try again. (Put this piece in your pocket, so you know it has marks on both sides.) Set up your drill press with a slow speed and using a #7 wire drill size or a 13/64th fractional drill size drill the holes. I like to keep the drill bit cool by using a little acid brush dipped into used motor oil. The one bit should be able to drill 500 holes if it never gets overheated. (The steel cuts like butter.) A photo shows the nice spirals coming out of the hole.
After drilling a bunch of them, take them back to that big vise and clean the chips from around the hole with a large coarse file. Insert the metal piece into the vise so the end of the metal is exactly even with the lower edge of the jaw. (Otherwise, you can build those little boxes that Marie shows on her plans.) (see photo)
Now, drop the large nuts (together these are 3/4" high) over the end of the steel and use a large adjustable (Cresent) wrench to twist the steel 90 degrees. Remove the steel from the vise, and insert it horizontally in preparation for the threading operation. First, examine the twist and see if everything is straight. If not, lightly hit it with the hammer, or twist it a bit more with the wrench. Run the tap in the hole, backing it out to remove the chips, and then going forward. Insert one of those 2" 1/4-20 bolts and see if you can put it in with your fingers. (No wrenches here!) If not, run the tap into the hole again. I have an old toothbrush that I use to clean the chips from the Tap each time I use it, and then put a drop of oil on it. This seems to reduce the number of times I have to re-insert the tap in the hole so I can easily turn the bolt with my fingers. BTW, when you buy taps, I would recommend getting at least three, because I’ve already had two break...maybe because I dropped them on the concrete floor?? There are different types of taps. One type has a long taper. The other type has a blunt end, probably for tapping holes in solid blocks. I’m using what I found in the drawer in my shop, but if you need to purchase them, the tapered type is what you should buy
After taking all these little pieces to the steel welding table, and creating a stack of spiders, you should return to the big vise again. Clamp a large C-Clamp (mine is a 7" labelled "malleable" - I think it came from Sears.) Put a spider into the C-Clamp, one leg at a time, held near the 90 degree bend. Examine the bolt to see if it is straight up and down, and if not, bend it with the large adjustable wrench. (Tweak it!) Also inspect all of the welding, and if something doesn’t look good enough, tag it for re-work.