We left off in the last oven related post having arrived at the dimensions for the pizza oven and cutting a template from 3/4″ plywood to use to assist in laying out the sheets and later on in forming them to the appropriate curve.
So really the key peace is the curved segment you form – the arc with the inner radius of 13 1/2″ and the outer arc 16 1/2″.
The first step is to trace out the parts for the inner back of the oven. I had one piece upon which I could trace the form and allow for a 1″ tab all around the outside of the form. After positioning the pattern I traced out the outer curve and followed it up by using a ruler to mark our a new curve 1″ further out from the first one based on the pattern.
So now to cut the steel to shape along the outermost curve you’ve drawn out. For the curved segments I used a good quality metal cutting blades on the jigsaw. I grabbed two sets of blades to trial from two quality brands (Bosch and Vermont American) – one coarser and one set that was finer. I suspected the finer blades would be by far the better choice on the thin sheet metal. As it turns out, the coarser blades were more effective, and the Bosch beat out the Vermont American by a consider margin in longevity. That said “longevity” is a relative thing… even the coarse Bosch blades were given to stripped teeth and eventual breakage. For the project as a whole I needed nearly ten blades!
Much more effective was the use of the angle grinder with a 1/16″ thin kerf metal cutting disk mounted. It raced through the stainless steel sheet with what seemed to be no difference in progress or wear than with regular carbon steel. Of course, the angle grinder is really only suited to straight cuts, so as easy a solution as the grinder proved for the straight cuts the jigsaw remains necessary for curved cuts.
The 1″ section that lies outside of the patterned curve is intended to be used to form tabs so that we can bend inward so that we can create parallel surfaces to join the assemblies by spot-welding. Another benefit of the tabs is that they will add three dimensional rigidity to the forms.
Mark out the locations for the cuts to form the tabs – approximately 1″ apart. The slots between the tabs can be cut easily with the angle grinder – making the cut just so deep that you contact the inner line that was traced from the pattern.
Once the tabs are cut clamp the steel sheet to the form making sure that it lines up with the original inner curve you traced out.
Your next step is to bend the tabs inward overtop of the plywood form. Use a ball peen hammer to tap them over. Once the tabs are all bent over – and you may need to shift your clamps around before the process is completed – use the hammer to make sure the tabs follow the contour of the plywood form – rather than simply being bent over at 90 degrees from the original sheet.
You’ll now want to take a file and remove any rough edges that may be left. That finishes up the inner back segment of the build.
Our next steps will include the building of the outer back piece and the front curved segment.