PDA

View Full Version : Cast or Steel



Chip_er
11-02-2006, 10:50 AM
Hi, This could be a crazy question on metalology (if spelled right) I,ve all-ways been fasinated in flying red hot molten metal. Building stuff out of metal. The thing I don't understand is, can a person make his own parts in respect to a cross feed milling table (small one). Does it have to be made out of cast iron or could I make one out of regular steel and tempered it a bit. yes I do realise I could buy one and get it over with, but trying to be a machinest with time to spare, wouldn't it be fezable to try such a project.

Changing the subject, this week-end I'll be picking up an old 9 foot long Reed Lathe. Quite large compaired to my 8 foot Sebastian I got last month. I was just thinking "another conehead". What I like about this old lathes are they haven't been used very much, very little wear. The contraptions people build to replace the overhead belt systems is what I think gets people fustrated and then buy a newer machine leaving the conehead in the corner thinking no one would buy that old thing! Good for me thow!

pcarpenter
11-02-2006, 11:10 AM
Unless I am naive, the word you were looking for was metallurgy :D

Cast iron tends to be easier to make stable (less prone to warpage) by normalizing. That and the fact that it scrapes *far* better (scraping as a flattening and fitting process) than steel are some of the reasons it is used in machine tools. I won't say you can't do what you are after, but since you can buy cast iron, there is no reason you cannot use it, either. For something you are going to mill from an existing billet of raw material, you can still choose your material.

Durabar is in the business of making what is known as "continuous cast" iron bars. You can buy gray iron as well as malleable iron. I recently bought a small bar to make a scraping straightedge, but ended up finding a straightedge from Kap Pullen before heading into that project.

www.durabar.com (http://www.durabar.com)

Paul

SGW
11-02-2006, 11:41 AM
Sure, you could use steel. If 'twere me making a cross feed table, I would probably build it up out of low carbon ground stock, pinned/screwed together. Or, if I were feeling rich (not likely, but a miracle might occur), I might use 4142 pre-hardened ground stock.

I think Paul is correct that cast iron would make a better job of it, though. The Durabar Paul talks about is really nice stuff to work with.
It would just involve a lot more machining, and cast iron plate is expensive to buy, far more so than cast iron bar stock.

www.mcmaster.com is a good place to get small quantities of raw materials.

J Tiers
11-02-2006, 12:55 PM
It would just involve a lot more machining, and cast iron plate is expensive to buy, far more so than cast iron bar stock.



Not to mention the incredible mess it makes over all the machines (and you) when you mill or turn away much CI material........ and the nicer the CI is to machine the dirtier it seems to be.

pcarpenter
11-02-2006, 01:01 PM
I wish I could remember the name of the Durabar distributor (Wisconsin as I recall) who I ordered from via the phone. They were very helpful even with my small order. I almost gave up on buying a piece of cast iron bar because prior to finding them, all I had was McMaster. Their pricing was *far* higher than the Durabar distributor. Don't get me wrong, I like McMaster-Carr....but they are not the place to buy steel etc, unless you have no choice.

Paul

lazlo
11-02-2006, 02:01 PM
Cast iron tends to be easier to make stable (less prone to warpage) by normalizing. That and the fact that it scrapes *far* better (scraping as a flattening and fitting process) than steel are some of the reasons it is used in machine tools.

Gray Cast iron is most often used for machine tools, because the flake graphite in the iron matrix absorbs vibration. Grey cast iron has a relative damping capacity 4 - 5 times higher than ductile cast iron (which is stronger), and 10 times higher than steel.

When I was at the Dura-Bar dealer in Dallas two weeks ago, he was describing a demonstration that the Dura-Bar techs do: they hang a piece of steel, a piece of aluminum and a piece of Dura-Bar, and ping them with a ball-peen hammer.

The Aluminum and the steel plates ring. The Dura-Bar plate just "thuds."

I would recommend cast iron for your table if you can: it's a little bit more expensive than mild steel (about $1.30/lb), but if you make your table out of steel, you either have to used cold-rolled, and the plate will warp when you mill it, or use hot-rolled steel, and deal with the mill scale.

lazlo
11-02-2006, 02:06 PM
I wish I could remember the name of the Durabar distributor (Wisconsin as I recall) who I ordered from via the phone. They were very helpful even with my small order.

You're probably thinking of the Racine, Wisconsin outlet for MetalExpress -- they carry Dura-bar:

http://www.metalexpress.net/

pcarpenter
11-02-2006, 03:35 PM
Nahh...although I did hit that web site when I was shopping. I should have done this before...I found my original post about making a scraping straightedge.

www.versa-bar.com (http://www.versa-bar.com) is the URL for American Iron and Alloys. They had the best prices I found when doing my research, but you have to call them for pricing. I had that confused with dura-bar. Same principle though...it is what they call "continuously cast" which resembles extrusion if you ask me. Anyhow, it is nice stuff with no casting "nubbies" on the outside. It looks more like an extrusion. You still have an outer crust that should be cut through and is likely harder than the rest of the bar, but it is much less rough on the outside than say a cast iron ingot.

Thanks for the information on the relative damping abilites of the products. It is interesting to note that plain old gray iron has some actual advantages over ductile iron.

paul

lazlo
11-02-2006, 04:06 PM
www.versa-bar.com (http://www.versa-bar.com) is the URL for American Iron and Alloys. They had the best prices I found when doing my research, but you have to call them for pricing.

Does Versa-Bar sell direct? As far as I can tell, it's the exact same stuff as Dura-Bar.



Same principle though...it is what they call "continuously cast" which resembles extrusion if you ask me. Anyhow, it is nice stuff with no casting "nubbies" on the outside. It looks more like an extrusion. You still have an outer crust that should be cut through and is likely harder than the rest of the bar, but it is much less rough on the outside than say a cast iron ingot.

The slick part about continuously-cast cast iron is that when it's extruded, the core is molten, and after the bar is pulled through the die, the inner core melts the hard crust. The end result is that there's no skin stress on the final product, like you have with cold rolled steel. So you don't need to stress relieve Versa-Bar or Dura-Bar, like you have to do with mold-cast irons.

Also, someone made a comment about Versa-Bar and Dura-Bar not being available in plate -- it is. The Lokey Metals guy in Dallas took me out into their storage yard and showed me the "bars" that Dura-Bar is shipped in: I'm guessing they were 3 feet by 3 feet by 12 feet long. So when you ask for plate, they literally saw off a piece to your dimensions. So on the Dura-Bar plate I bought, they have one "rough" side and 3 saw-cut sides.

pcarpenter
11-02-2006, 04:21 PM
Yeah, I almost wondered if Versa-bar was the same stuff as Dura-Bar and perhaps Versa-bar was just some sort of reseller, but the company name is American Forge and Foundry and I think they are really a manufacturer of this stuff and that is the trade name for their competitive product.

They do sell direct and I bought a piece maybe as small as 3.25x1.25x28" or there abouts. When I called, I got transfered to sales and started off by apologizing and admitting that I was just a home shop guy and did not want a large lot and didn't even know if they would sell direct. The guy indicated that was no problem, asked for my dimensions, checked inventory and found a piece already cut that was close enough and I think I paid $50 instead of nearly $90 it was going to cost me from McMaster-Carr. I had it the next day here in IL and they only charged me actual shipping.

I sort of presumed the stuff was sold in these odd dimesions to allow for cleanup of the outer layer, but it sounds like that is just not necessary. I appreciate that tidbit of info. I think I might still tend to want to normalize it in some fashion to reduce dimensional change when machining, but I have not had a chance to test to see if that is really necessary. The bars do have what is maybe a 1/4" radius on the edges which may be why they come over-dimension so you can still get a full 3" after machining it away.

I am toying in my case with making some Aloris type tool holders with the bar I no longer need for a straightedge as it is about the right dimensions. Not sure if this is a good application since these have a deep dovetail on one side and not much material between that and the tool holding groove, but it may be that incorrect assumptions about cast iron being too weak is clouding my thinking here.

You are correct in pointing out that it is available in some large sizes that would be fine for an application like a machine table or cross slide as in the original question.

Paul

lazlo
11-02-2006, 04:21 PM
Does Versa-Bar sell direct? As far as I can tell, it's the exact same stuff as Dura-Bar.

Answering my own question: I just called Versa-Bar in Wisconsin, and they do sell direct -- there's a $50 minimum charge. Really nice folks.

Their prices are good too -- about $1.50/lb including the cut charge (since your piece is coming off huge bar stock).

lazlo
11-02-2006, 04:28 PM
I sort of presumed the stuff was sold in these odd dimesions to allow for cleanup of the outer layer, but it sounds like that is just not necessary.

On the Dura-Bar web page, they list the stock sizes (actual size), and the finished (machined) sizes seperately.

I don't see a similar table for Versa-Bar, but the Versa-Bar rep told me that the standard square/rectangles started at 1 1/4" and moved up in 1" increments. I'd want to talk to a rep and have them tell me what the finished sizes would end up like...

The Versa-Bar foundry bars are apparently a little smaller than Dura-Bars -- Brian told me the largest dimension you could order was 14" x 22" (up to 72"), which must be the size of the raw bar they ship to the distributors.

pcarpenter
11-02-2006, 04:34 PM
14x22x72....heh heh...I am guessing that one is over the UPS'able weight limit :D

You could buy a chunk like that and carve a good size lathe bed out of it though!

No cut charge is good.... I can't imagine a big piece like that cuts very slowly and could otherwise incur a big charge. The piece that I got looked like it might have been somehow sheared, or perhaps that end was the end that got pinched as it was being extruded.

Paul

Mcgyver
11-02-2006, 09:06 PM
........ and the nicer the CI is to machine the dirtier it seems to be.

but it does machine oh so nicely.

you've been given a lot of good reasons why CI is the right material for the job, but i didn't see mentioned that its also very good bearing material. its perfectly acceptable to have mating CI ways where as you could not do that with steel, well you could, but it would work or last very well. The cost of large chunks of any metal, exp CI, is yet another good reason to start with an old machine and rebuild.

ligito
11-03-2006, 08:23 AM
They cut it with a real big Iron worker. I think he has a blue ox named Babe.:D

pcarpenter
11-03-2006, 10:12 AM
McGyver-- you raised a very important point. I have been being mentored by what today might be called a machinery mechanic. He spent years scraping in machinery for Caterpillar and his second career has been with a company that deals with big machines. He still does some scraping work, but often they are working on larger stuff and doing modifications and retrofits. He does a lot of mechanical troubleshooting of machinery and knows quite a bit about machine geometry. I tell you all that because it has been a really neat experience to learn far more than just the art of the scraping process.

One of the things this fellow (Gary) pointed out to me as I queried why such soft iron was used for machine ways and he reminded me that they ride on an oil film if properly lubricated and contact is minimal. Cast iron will slide on itself without galling. Not true for steel. Steel on cast iron is even OK as McGyver implied, but steel on steel is a recipie for problems.

Cast iron is porus relative to steel at the microscopic level with the voids containing some graphite. The porus nature also makes it better at "carrying" oil.

Paul

Chip_er
11-03-2006, 11:01 AM
Very good point Pcarpenter, I never thaught that is the reason why most engines have cast iron bores, any why small commerical gas engines have them all so in aluminum blocks. The ability to retain some oil in a metal keeping two meterials apart reduces wear, I like that! One more thing, I din't know a person could buy CI bar stock as if you would steel. I'm going to look into this.
Thanks Room!