Type of iron in tool table tops

[DaffyJeffy]

Hi all. Got a question that may or may not have an easy answer. I do a lot of tool/machine restoration in my shop. By "restoration" I mean mechanical restoration (as opposed to cosmetic restoration). I make my living with my tools and need reliable, functional tools. Anyway I currently have a bunch of projects I'm working on: 70s' era Craftsman jointer, 40s'(?) era Dunlap tablesaw, Dunlap jigsaw, and a 30s' era Partington Red Fox planer. I've done a 50's era Craftsman band saw and an 80s' era Craftsman radial arm saw.

Something I've noticed about old tools is that some cast iron table tops seem to resist rust much more than others. Are all tool table tops "grey iron" or are other types of cast iron used. The Red Fox planed and Dunlap tablesaw seem to be virtually rust resistant; they have mild orange hue but not flaky, pitted rust that seems to form so much quicker on other tools. They were both neglected and out of use for decades. I actually got the Dunlap saw for free out of a basement a guy hired me to clean out. The other part of the job was looking at the water issues in his basement. This tool sat in a damp, sometimes-flooded basement for years and the tabletop just needs a light cleaning! I was hoping someone has some insight into this or have noticed this same phenomenon. I'm mainly just curious. THANKS!

 

[jallyn]

I'm willing to wager the ones in good condition had a quality varnish or even oil film to protect them. They would all be cast "grey iron" you mentioned...there is no such thing as stainless cast iron.

 

[Maui]

They could be manufactured from ductile iron. This type of cast iron has corrosion resistance that is equal to or better than gray iron castings.

Maui

 

[DaffyJeffy]

Perhaps, since all metals are porous, they were just more oil-saturated? I'd be surprised if they coated these old tool (1930s and 40s) with any kind of film.

Ductile iron, yeah I wondered about that (but I really don't know the difference). Someone was once telling me how rust resistant grey-iron is. I said "really?" and he said "yeah, have you ever seen a rusty manhole cover?" A rather weak argument but I always though grey-iron was somewhat resistant to rust.

 

[jallyn]

There has been extensive research on the corrosion resistance of certain materials as there is so much buried pipe we depend on for potable water, etc. Regarding cast pipe and underground corrosion... gray iron, ductile iron, and carbon steels are all similar in their corrosion resistanace. From the website (http://www.angelfire.com/pop/myfile/EXTDIPhtml.htm) comparing the three materials...

"The results of both experimental researches and practical case histories have concluded that ductile iron does not possess superior corrosion resistance to other pipe materials such as gray cast iron or carbon steel..."

 

[SVS]

John Oder on Practical Machinist has suggested that machine tool elements cast from raw feed stock as opposed to re-processed scrap with steel content "weathers better". Older the machine, the less likely steel was part of the melt.

I never would have thought of it, but my experiences agree.

 

[Maui]

Jallyn, check out the iron pillar of Delhi:

https://en.m.wikipedia.org/wiki/Iron_pillar_of_Delhi


Maui

 

[DaffyJeffy]

I should really post questions on here more often, the responses are always fascinating. Thanks so much for the responses. Don't think we have a conclusive answer but there is certainly some interesting possibilities! I plan on documenting my tool restos with pics and video and perhaps I'll share them here (under vintage tools). I've done so many projects and I always kick myself that I didn't document them. Have a good day guys and gals.