Dealing with cast iron / stress?

[Highpower]

Venturing into another new area for me...

I have an iron casting here (camel back straight edge) that I want to attempt to turn into a usable tool.

The raw casting has been fully annealed so that it will be machinable. After it is rough machined how does one determine if the casting needs to be thermally stress relieved? Or is that a given?

I would hate to spend months hand scraping this thing only to have it twist into a pretzel later. Anyone been there / done that?

[PixMan]

In a perfect world, you would rough machine it then set it out in the elements to natually age and stress relieve itself. When I worked for a machine tool builder in my youth, they let the rough machined casting age outside in the New England weather for between 6 months and 2 years.

[Highpower]

(01-23-2013, 10:23 PM)PixMan Wrote: In a perfect world, you would rough machine it then set it out in the elements to natually age and stress relieve itself. When I worked for a machine tool builder in my youth, they let the rough machined casting age outside in the New England weather for between 6 months and 2 years.

Ken, what did they do, if after 2 years the casting shifted or warped?
Re-machine it and let it sit another 2 years, or did they just run with it as is and put a final finish on it?

I think I'll have to call around town and see if I can even find a place that I can take it to, and what the cost might be. Most likely there will be a minimum charge that is 3 times what the casting is worth...
That would definitely pronounce the idea D.O.A.

[Tony Wells]

How big is it?

[Highpower]

It's just a baby Tony, 18 inches. That's why I have a feeling any heat treating places won't want to even bother with it, unless they charge me for tonnage.

My main concern is the bottom is going to need a LOT of clean up to get it flat. Granted there is plenty of extra material there, but what is going to happen when I remove it? There is also a good sized divot (void) in the back edge of the base, which looks like I would need to cut at least 1/8" - 3/16" off to get it flat.

Or is it too small to even worry about it?

Obviously I don't have a clue since I'm a first timer.

[PixMan]

After two years they simply finish machined it and all was good.

[Tony Wells]

You can't really artificially age the material short of paying the heat treaters, but if you're friendly with them, they might do it reasonable. Otherwise, it's called "seasoning" kind of like firewood. Just takes time. If you've already got it roughed out to within 1/16" or so, it may have moved all (nearly) it will. Depends on how "seasoned" it was before you roughed it out.

One method you might consider, if available, is shot peening for stress relief.

You may want to take a few skim cuts after you evaluate just how distorted it is, and wait a while and check it again to see if it i stable. I don't think your home oven will help, btw. Temps need to be upwards of 1200-1300 °f to properly relieve gray cast. That's why you might want to consult a heat treater to see if you can get it in with a batch of someone else's parts.

[Highpower]

I just got the casting the other day, so I haven't done anything with it yet. I guess I'll see what the heat treat gurus say first, if I can find one locally. The kitchen oven is definitely OUT.

I might just end up roughing it out and then bead blast it. That's the closest thing I have to shot peening since it won't fit in my tumbler.
Let it sit for awhile and see what happens....

[claudef]

Many years ago (20), I was in England at a machine rebuilder. They had an old large planer and were machining the ways for a machine they were rebuilding. My first observation was, if they are so good a machine rebuilding, why would they not have a nice gantry mill for this type of machining. After voicing my opinion they explained that any type of milling operation naturally induced stress into the material surface. Planers, on the other hand, remove a small amount of material on the full length of the part in minuscule steps and does not induce stress. Take this for what it’s worth but if you have access to a planner, I would plane the surfaces then do your scraping.
Claude

[Sunset Machine]

Gotta love 'em. I barely have this thing working and have zero experience running it, else I'd volunteer...