Why Cast Iron?

H

HBilly1022

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I'm thinking of making the end mill flute sharpening jig in one of Harold Halls books and in it he calls for using cast iron for the bearings. Everywhere else he suggests using 230M07 ( I think that is what he called for) which I think is a free machining steel. I'm wondering why he suggests cast iron for the bearings. I also note that a lot of people use cast iron for backing plates.

I generally use mystery steel from the scrap yard for pretty much all of my projects as there are no steel supply places near me and I don't want to order a bunch of different stock materials and sizes considering I'm only doing this for fun. Most of my projects are for things to maintain tools or to make tools. Not really an end project. So would mystery steel be good enough for the bearings or should I try to get some cast iron?

Here's a link to his site, showing the end mill holder. http://www.homews.co.uk/page236.html
 
Gray cast iron is a common material used in various machinery as bushings or plain bearings. In my experience, it is generally used in low load, low RPM situations. I believe it is used because of it's inherent stability and relatively high carbon/graphite content (as compared to many steel alloys) which provides a relatively low coefficient of friction.

Ted
 
Cast iron of certain alloys and manufacturing processes will maintain size and shape after machining and has excellent vibration dampening properties (alloys used for this purpose), depending on the alloy it may also exhibit excellent wear resistance, also the process of manufacture may cause some particular products to be extremely hard and abrasive.

Cast iron is an alloy of iron and carbon with a carbon content above about 2%, steel is an iron/carbon alloy containing less the 2% or so carbon. All steels (by definition all steels are alloys) are often considered "alloy" steels with when they contain elements beyond carbon and iron which would encompass pretty much every steel used today.
 
Most engine blocks and the myriad of castings we see in use today are gray. It is high in silicone and carbon and has high wear resistance. The difference in gray and white cast iron is white has less carbon and silicon and is usually referred to as cast steel. A hardened steel end mill on a gray cast iron bearing would have a smooth, free movement. Cast iron being one of the earliest metals made from iron ore, had high carbon content due to the smelting process.
 
woochucker said:
Graphite content.. Aside from what everyone already said, it has good lubricity.
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I strongly suspect that is the reason he spec'd it for the bearings. I might just run with my scrap yard mystery steel anyways and if I find it doesn't work well then get my hands on some cast iron and make new ones. Learning something new every day.:)

The end mills do not ride on the bearings, they are held fast in a collet, in a holder and the holder slides on the bearings.
 
HBilly1022 said:
The end mills do not ride on the bearings, they are held fast in a collet, in a holder and the holder slides on the bearings.
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When I stated end mill riding on the cast iron bearing I had not viewed the project you had linked, but my focus was the cast iron paired to any steel, hardened or otherwise it moves freely. I think another angle on his approach is KISS (Keep it Simple Stupid) and there's no extra parts or pieces to complicate things for the home shop hobbyist.
 
I'd expect the cast iron would be less lightly to gall with the grinding dust. Steel on steel with grit wouldn't be a good combo.

Greg
 
Rustrp said:
When I stated end mill riding on the cast iron bearing I had not viewed the project you had linked, but my focus was the cast iron paired to any steel, hardened or otherwise it moves freely. I think another angle on his approach is KISS (Keep it Simple Stupid) and there's no extra parts or pieces to complicate things for the home shop hobbyist.
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I'm not following your KISS approach. Do you have an idea to simplify the build? If so, I'm all ears (or eyes, since I would be reading it). I plan on making some other changes to the design anyways. I plan on making the collet holder for R8 collets that I already have for the end mills I use. That way I don't need to make a bunch of new collets. I did the same thing with the end mill end sharpening block I made before and that worked well.

f350ca said:
I'd expect the cast iron would be less lightly to gall with the grinding dust. Steel on steel with grit wouldn't be a good combo.

Greg
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Looks like I better rethink using steel. I would hate to go through all of this and find it doesn't work well or galling starts and then I have to make more new parts. Better to do it right the first time. Guess I'll stop by one of the machine shops in the City next time I go in and see if I can scrounge some small cast iron pieces.

Thanks for all the feedback. It sure pays to ask questions and have a support team to help out with answers.
 
Send him an email. He usually responds to me within a day or so.
 
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