View Full Version : thin cast iron plate

03-21-2004, 11:42 AM
Anyone know a source for 3/16" thick cast iron plates? Need pieces about 12" square for some brake rotors. Tried all the usual online suppliers but came up dry.



Bruce Griffing
03-21-2004, 11:49 AM
Cast iron is just that-cast. It is expensive to make sheet stock because it must be sawn from a large cast boule. You can buy sawn bar stock, but it is rough and expensive. There is a product called Dura-bar. I don't recall the sizes, but you might check into that.

Forrest Addy
03-21-2004, 12:10 PM
Bruce has it. Check into your local durabar dealers. They will supply you with oversize sawn plates but it's up to you to get it machined/Blanchard ground/whatever to thickness.

Rich Carlstedt
03-21-2004, 03:09 PM
WOW,I also needed 3/16 CI Sheet 3 years ago for a project. Needed 3 sq feet and never found it.
The thinnest I found was 1/2 inch.
As I recall, Mc Master Carr has some (1/4?)
Anyway, figure on 50 bucks a sq ft and then the machining time to get it to size..

Rich Carlstedt
03-21-2004, 03:13 PM
Wait a minute !
I just reread your post..
You want round plate..
I found that.. Its used for cams for screw machines..found 3/16 and 1/4 thick 9 inch dia with 1 inch holes as i recall, but that did not cut it for me.. no holes !
Check out some old screw machines shops.
The source I had is now gone..they were closing down when a friend told me..
Good Luck

Paul Alciatore
03-21-2004, 06:45 PM
I don't know about their suitability for brake rotors but cast iron skillets come to mind. Get a big one and turn or saw the sides and handle off. Dare I say Wal-Mart?

As I said, I don't kow about their suitability for brakes. Please don't laugh me off the board.

Paul A.

03-21-2004, 08:23 PM
But, but...what about Thruds barbell weight idea. He might know if it's good enough quality for this. BTW...what are the brakes for?
Paul...great idea...stomp on the brakes REALLY hard, heat up frying pan brake... tip car on side...fry bacon and eggs for breakfast!

[This message has been edited by torker (edited 03-21-2004).]

Paul Alciatore
03-21-2004, 09:19 PM
Hey, can't be any worse than some military vehicles I've driven.

Paul A.

03-22-2004, 12:20 AM
The brakes are for a university built Formula SAE car. This is a design event where engineering students design and build open wheel, open cockpit racecars. Here we do 100% of our welding and about 80% of the machining. The only jobs we send out are things we don't have the equipment for...like the splined shafts I've brought up in other posts. Great experience.

As far as the plate goes, I've got requests for quotes in for durabar at a couple of companies. The barbell idea has occured to me, and Paul was not the first person to recomend a skillet. Another painfully obvious idea was to get old car rotors from a junkyard and turn them to size. We'll see how it goes.

Looking forward to anymore ideas!

03-22-2004, 12:44 AM
JDF...what about some of the new composite rotors that some of the newer cars are using? I'm going to put some on my car soon. They are a lot lighter. You're makin me drool building that car. I spent a whole day climbing under and over David Empringhams Formula car several years ago. Fantastic engineering! Stole lots of ideas for the race stuff I build.

03-22-2004, 01:05 AM
I think using OEM rotors is probably the best and safest way to go about this. If you give us the final dimension and mounting provision you're looking for perhaps one of us has experience with a rotor that is already near net.

If you have a website to validate your FSAE involvment perhaps you could ask someone in the business to help steer you in the right direction. Here's some interesting links.




03-22-2004, 03:16 AM
Yikes, for that kind of money you can buy ready made brake rotors in sizes from 7" up to 14". Better yet, go to an auto salvage yard and pick up some re-grindables for a few bucks a piece.

3/16 CI is mighty thin for brake rotors. After the first couple of turns, I think you'll end up with BOWLS.

Peter S
03-22-2004, 07:27 AM
I wonder if you could just use steel plate?

My guess is that cast iron is used because it can be cast with ventilation slots, maybe it offers some other benefits like quieter braking (guessing), but I wouldn't be happy with 3/16" cast iron, especially not if made from weights etc!!

You could get them laser cut from steel with all the groovy curved slots, holes etc you need.

This is just an idea, I am no brake expert, but my guess is that motorcycle rotors are steel??

03-22-2004, 09:44 AM
I'd love to find some production rotors that would fit the application but time is limited (2 weeks) and weight would be a problem. Our car will weigh around 600 pounds with driver, and be braking from speeds typically no greater than 70 MPH. Its a tight course to keep speeds down. 3/16 is a typical thickness for rotors in this competition. Some go even thinner with no problem.

I am not opposed to using steel. We went with stainless the last two years, but weight and machinability were a problem. The real problem is I don't have enough time left to really look into different options. Basically, I've seen 3/16 cast rotors work, so that was what we were going to shoot for...no way to solve an engineering problem, but saves a hell of a lot of time.

Any recomendations for steel if I go that route?


J Tiers
03-22-2004, 10:03 AM
Dunno about types, but steel looks like it would be:

easier to get

much more consistent

much less likely to have "break-in-half" type defects hidden in it.

03-22-2004, 11:06 AM
I have 4 rotors that I was planning on bringing to the jnk yard, they are a bit rusty, but you can have them for shipping if you want, can ship them this afternoon. They are a bit smaller then you wanted, two @ 11 inches and two at 9.5 inches.


03-22-2004, 03:31 PM
my 82 vw scirocco had non-vented rotors which were pretty thin, probably $20 or so at the parts store
also check out www.colemanracing.com (http://www.colemanracing.com) they have 3/8s rotors of many diameters

Some of the sprint cars use aluminum. I heard they dont wear well, but for Fsae you should be OK I think wilwood makes them. Perhaps you could use their designs for inspiration

Paul Alciatore
03-22-2004, 03:48 PM
Well, the frying pan idea was probably due to being hit over the head with one too often.

Why are brade disks made from CI? Is it a special grade of CI?

In your situation, I think I would go to a goood junk yard and look for something a bit oversized to turn down. Much more likely to get something that will work well. Take advantage of the engineering knowledge that went into selecting the material for a production car.

Paul A.

Randy M
03-22-2004, 04:27 PM
Why don't you look at a motor cycle disk.
They would be thin and light weight.


03-22-2004, 04:35 PM
Ya...what Randy said. I had an old Honda 750 Four that would have had that size of rotor. All you'd have to do is adapt a mounting hat.

03-22-2004, 05:57 PM
merf, I'll check on the VW rotors.
Mike, will keep your rotors in mind.

I've looked into most of the aftermarket racing brands and cost is going to be prohibitive. Right now my basis for using 3/16 CI is based on computer braking simulations using a particular pad on an iron rotor. I hate basing anything off of pure calculations, but it is the best starting point we have. The aluminum stuff from Wilwood is pretty nice, but doesn't give near the stopping power of the pad/rotor combination selected. Also, the suspension upright/caliper mount is already under construction, so changing rotor diameter is no option. Probably could have found a motorcycle rotor in a good enough size a month ago, but its too late now.

I'm still looking for the best source for durabar, and am keeping old auto rotors in mind. Right now we have three weeks left to get the car rolling and only about five weeks worth to do, so everything is basically right on track.

03-22-2004, 11:13 PM
Do you want the old rotors/carriers off my FZR600? They're just at the limit of spec, and should still be safe. E-mail me and we'll work out the details.

Rich Carlstedt
03-22-2004, 11:15 PM
If You want Dura-Bar
why not ask them ?

03-23-2004, 02:03 AM
Abn, just sent you an email.
Rich, thanks for the suggestion. Have emails off to several distributors, but never thought of going to the source. I'll give them a call tommorow.

Peter S
03-23-2004, 02:34 AM
I would not trust a disc of 3/16" cast iron for a brake rotor, why not try a disc of mild steel, cut out of plate, much stronger and more simple all round.

03-23-2004, 03:07 PM
Durabar is donating everything we need. Their sending 1/2" slabs of barstock so I'll have some thickness to work with. In the meantime we'll do a little math on this end to see if 3/16 is pushing it or not on reliability.

Thanks for all the suggestions!