Fixing a bow and Preventing a bow question

admin

I am trying to cut 20ft pieces of 3/4x8 flat steel down to 7 1/4 with a torch. On the first 1 The last 2 feet or so bowed out about a half inch, than the next one I cut the whole thing by cutting 6 inchs at a time than going the other end cutting 6 inch an so on. The 2nd time it only bowed out about a quarter inch. What is a good practice to avoid this? I have never actually done this much cutting on one piece of steel so this is the first time I have ran into this. Also is there any good way to get the bow out of the first one. When I saw bow I mean that it bowed across the 8 inch side of the steel, I guess that might be called a crown.
Reply:this is not an easy cut to make freehand. think about setting up a fence and clamping the fence right onto the part to be cut. these cuts are typically made in industry with a rail-type burner thatruns on a track. as you cut, the part will grow lengthwise along the cut edge from thermal expansion so the line you cut must constantly move to adapt to this action or must cut the area that has not been affected by this yet,. if you clamp the fence to the part you can only clamp at one end. if you clamp at both ends the part will grow and stretch or move the clamped fence. typically you would want to burn towards the single clamp so the growth would be behind the cut. beware that the cut part may not return to exactly the same shape as the heat may cause some permanent deforming if the part cannot be cut very quickly. try a test cut on a piece and see what results you get and proceed accordingly. soapstone the line and clamp the fence at one end, then burn as quickly as you can starting from the free end and moving toward the clamp. set up the parts and work zone so you can cut the whole part very quickly at one time if you can.