This is a HOW-TO from a newbie to a newbie, so all you pro's out there bear this in mind :)
Gap construction: In this instance I must admit to having no knowledge on building one of these so I took the liberty of following my very good friend Stefan. His instructions and concepts certainly are worth bearing in mind and I find his webby one of the most informative and concise pages on the net. As in all things I tried to follow the instructions but found that given sizes over here (UK) don't always agree with the author's location so its time to improvise. Don't you just love that word :) This is where you put into the project a little bit of yourself.
Now I am lucky in one respect in that the place I work as available a wide range of talents and skills and always on the look out, I made the most of these. However there is know reason why one could not achieve the same success by doing this alone..
OK, start time. I visited a pipe engineer and asked him for a off cut off 6" dia pipe. He handed me a 8ft length of 160mm saying will this do.. I only want 5" I replied. Anyway orf I toddle with me pipe. You don't half get some funny looks round here. Next stop was the chippy, smiling sweetly I ask if he can cut this pipe into 2 x 5" lengths and 1 4ft length (always thinking ahead, MKII). Thankfully he obliges, so I return the unused portion. Next port of call is the coil shop, in there I ask for 15" of 2" diameter copper pipe, alas they only have 42mm, (do wish they'd keep to english), Thanking them, I again head for my next port. The tool maker, he's sweet, I ask him if he can cut the copper pipe into 2" sections and also square the edges on the PVC pipe, being a bit cheeky I also ask if he can drill 2 holes into each copper section 0.5" from each end..
Following day I collect my machined parts :) all polished and deburred. Cant wait to get home now :) Looking at the PVC pipe I see no problem in fitting the first tube section, this is to be positioned in the center of the PVC pipe wall, however, positioning the 2nd and 3rd etc proves to be difficult. Quick revise on Stefans page, h'mm they have to be 0.028 apart, pipes 42mm dia, wall is approx 1mm, how do you calculate the distance apart on a curve??? After many hours I concede defeat on this one, so by girlspower I align the 2nd tube up, mark the hole position and drill two obrounds (there oval holes ) offering the 2nd tube in place along side the first one I proceed to set the gap at 0.028. Now to save face I use a compass to set the distance between each centre bolt then rotate 180deg on a pre marked center line and it gives me the next hole position and with the obrounds I have a little to play with.... Each copper pipe is secured by 2 M5 brass bolts with star washers There the little serrated ones :) These effectively locks the nuts in place (I hope). Isn't technology wonderful :) Work to date
So its back to Stefans page for more instructions, I will emphasise you cant ever read to much, after all there is no point in re-inventing the wheel. Now seeing I have 7 copper tubes fixed it seems I need to separate No1 and 7 by some insulating material. At hand I have mackrolon but I guess any perspex type would do. This is secured in place with araldite (2 part epoxy resin). I seem to remember reading about air flow, quick recap..... Back to the pipe place and I again ask for a 50-60mm off cut. this time I get a 6ft length. Not wanting to appear cheeky I decide to cut this myself. Now the gap housing is 5" long and according to instructions (Stefans page) I need at least 3-4" at the bottom for air flow. So with this in mind I cut a 8" length. Next I need a way of mounting the gap 4" of the table.. Back to work there I find some Plexiglas rod (wooden dowel would do), armed with this I head back to the tool man. There he cuts this down into 4x5" length and taps a hole (M3) 0.5" from one end into each one. These are then secured to the bottom part of the large PVC pipe 90deg spacing and provide the required distance from the table, (they also look kinda sexy as well). Next I place the 60mm pipe in the center and araldite it to the mackrolon spacer. Assembly so far
This is where I deviate slightly from instructions, I intend to mount my fan on the top, blowing down, and require as much air flow around the copper tubes as possible. so with this in mind I make a cone out of some thin clear plastic. This is glued to the top of the 60mm pipe and its apex is just under the center fan. I found that opening the fixing holes on the fan to M5 and using M5 self tapping screws it produces a tight secure fit on the 160mm pipe. Another rummage in the kitchen produces some tupper ware containers and by carefully cutting the lids along there edge in a curve shape produce a section that butts against the fan and outside edge of the 160mm PVC pipe. These are held in place by my trusty araldite. Only thing left is to tidy the mains/fan lead and secure it with some adhesive cable tie bases, wallooo job complete & side view