For turning black bar free cutting mild steel is better than bright drawn. I understand this is down to it cooling naturally so there is less stress. Bright drawn is then processed cold which will add stress and it varies. Machinists did have a term for the bad stuff – park railings. From WWII when they were melting anything that could be found. I have had a supplier wait for some "good stuff" to come in. He cut hexagon disks for me from plate. I expected cut bar. Only ever happened once and it turned rather well. Some doesn't.

I have no information on annealing it other than red heat and slow cooling. Castings are much the same except lathe manufacturers traditionally leave their castings lying around for a very long time before doing anything to them. This is why some people prefer to fabricate rather than buy castings especially for tooling. It also suggests that at least in this case heat treatment isn't the best way to go about it.

John

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A simple solution to this issue that I use occasionally (originally not with raw material – but with a large work piece that needed to be "repaired" by welding) is to stick it in the bonfire – or in my case – my garden incinerator.

After I screwed up some milling work on a large piece of block steel, I had to fill an unwanted deep 'groove' with some built up weld, I was worried about distortion and wanted to relieve any stresses before I finished re-machining the work. My solution was to stick it my garden incinerator once I got a good bed of hot ashes going in the bottom of it. I then kept the fire going with the rest of the wooden garden waste through the evening and then let it burn all night with the lid on. The ashes (and steel part) were all still very hot the next morning. I was able to trim off the excess weld and re-machine the surface without any distortion later. It wasn't a perfect finish but it also happened to be in an area that wasn't normally visible once assembled.

My garden generates lots of wood the local council won't take away in our brown bin, so I have incinerator bonfires several times a year. Since the original welded steel piece, I've dumped several small brazed fabrications in there, as well as a few (part machined) steel bits from the scrap bin that I was worried might distort. Whether my fears were well founded (or not) I don't really know but I can say that they all behaved themselves perfectly afterwards. I most certainly have had work that has bent like a banana after machining, so better safe than sorry…

Regards,

IanT

Edited By IanT on 20/07/2015 12:25:12

Machine a light skim off one side. Allow to bend. Turn over and machine a light skin of the other side. Now you can machine both sides and they should remain flat. If you do heat treat it do not bend it afterwards or you will introduce more stress.

Edited By David Clark 1 on 20/07/2015 13:05:02