Car brake rotors and drums

[MikeKParticipant @mikek40713]

From time to time I see car brake rotors and drums set out for trash pickup day and always feel like I should snatch them.  Are these worthwhile sources of material?  Two shop projects I’m considering are another surface gauge (but this one with my own name on it) and a micrometer stand.

Has anyone experience machining these brake parts?  I assume rotors and drums are cast iron.

Mike

 

[DiogenesParticipant @diogenes]

They are, but whether there’s actually much useable metal in the ones that you see put out for trash is another matter – modern drums and rotors are as thin as the manufacturers can make ’em, and modern pad material seems to give them a proper ‘cooking’ and they are usually pretty glazed and horrible.

I frequently use and retain scrap for projects, but the last brake components I replaced (Honda Jazz) went straight into the skip at the tip – there’s just no ‘meat’ on them.

As they used to say in old Mushroom-picking guides “edible, but not worthwhile”

Kitchen and trade weights, and ‘Home gym’ equipment can be much better source of iron.

You can pick up nice material relatively cheaply from M-Machine’s Ebay store.

[bernard towersParticipant @bernardtowers37738]

Light commercials have a fair bit on them especially if they are solids plus they have been heat treated!!!!!!!

[MikeKParticipant @mikek40713]

Yeah, I wasn’t sure if the parts had enough meat to make anything meaningful.  The drums looked like I could have made some plates out of the tops, but then I’d be stuck with figuring out what I could do with those thin plates.

I did find a solid iron dumbbell on one of last week’s walks around the neighborhood.  Might actually be thick enough for a mic stand, but definitely the bearings from Harold Hall’s end mill sharpening accessory in “Tool and Cutter Sharpening”.

[Mark RandParticipant @markrand96270]

I’ve got the two ventilated brake disks that I replaced on the Dacia Sandero waiting in the projects list. The intended use is to make another couple of diamond lapping plates for sharpening scraper blades, kitchen knives and ceramics on the lathe or SWMBO’s pottery wheels, so I can use different grits without having to turn the old one off (tends to wear out the tools rather promptly 😀 ).

The current lapping disk is an ex-Aldi 10kg dumbbell weight. That was a lot closer to cast steel than cast iron and I suspect that the brake disks might be similar.

Apologies for the tortuous Sentence!

[Robert Atkinson 2Participant @robertatkinson2]

New brake disks are probably a better option. Fairly low cost, machined flat and not full of cracks….
The completely flat ones have been used as reference surfaces for tramming mills.

[Mark RandParticipant @markrand96270]

I use a new, ventilated, disk for tramming the mill. Because of the way they are turned, they are incredibly flat and parallel (better than I can measure with tenth’s gauges and a grade A surface table). Typical motor car disks (not used for record breaking attempts 🙂 ) won’t have cracks in them, just unworn/rusty ridges and glazed surfaces. They can be faced without issue if they’ll fit in the lathe.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, brake discs can make useful display stands.

Even ventilated ones can look good.

Regards Nick.

[Bo’sunParticipant @bosun58570]

If my memory serves, brake drums and discs are cast from SG Iron.  If that’s any help?

[Howard LewisParticipant @howardlewis46836]

If not cracked or crazed beyond skimming, can be useful as a Base for some project.

Not a usede brake disk, but the base for my Comparator is a hefty piece of cast iron.

SG iron is good stuff. (The new cylinders for 71000, Duke of Gloucester were made of SG iron)

Lots of it used for things like main bearing caps in vehicle engines.

Howard

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I don’t know why my ventilated disc photo doesn’t show in my post above, but here’s a different view of it.

Regards Nick.

[Rod RenshawParticipant @rodrenshaw28584]

I would like to try using a “completely flat” brake or clutch disc, as described in several posts above, for tramming my VMC mill.  I feel a heavy soild disc would be more likely to stay in place when in use than a more lightweight ventilated disc. Can anyone suggest a Make and Model of vehicle for which a suitable new disc, perhaps about 8-9inches diameter, is likely to be available at reasonable cost?

Thanks

Rod

[SillyOldDufferModerator @sillyoldduffer]

I’m extra wary of scrap because it caused so much trouble when I was a complete beginner.    Knowing I was going to make mistakes, I assembled a collection of scrap metal because it was cheap.  Caused a host of problems, to the point I decided my new mini-lathe was  useless, as were most of my drills, files, and saws!

Not so at all, by sheer bad luck, all my scrap was horribly difficult to machine, and this was compounded by various bits of DIY Store metal that also turned out to be nasty.   I was struggling soft, sticky Aluminium that tore, gritty steel, work-hardening stainless, an awkward Brass, and some Induction hardened rod.

Thing is, when a designer chooses a metal, he usually goes with the lowest cost combination of material and manufacturing method that meets his requirements.  As a general rule, processes other than machining are cheaper – casting, rolling, stamping, welding, grinding, laser and gas cutting etc.  Many alloys don’t machine well, and there’s a strong move to thin out or replace metal with composites, plastics and concrete! In short, industrial designers don’t cater for hobbyists.    Bought some weight-lifting lumps a few years ago at a car-boot  hoping to get cast-iron.   Nope, steel swarf compacted in resin.  Never found an old sash-weight that wasn’t nasty too.

Took me a while to realise what my problem was.  Then I did the unthinkable and flashed the cash necessary to buy known metal specifically meant to be machined.   The difference was chalk and cheese – suddenly tools and techniques worked as expected, and I made rapid progress.

Bo’sun mentions Brake Drums being made of SG Cast-Iron, and that’s quite likely, especially old ones. Or, this being 2024, have Brake Drums been redesigned to improve performance or reduce weight or cost etc? Trouble is no-one knows for sure, and that’s a big problem – not having a specification means the metal’s suitability is a matter of luck, not judgement.

Mileage varies!  Not much commercial machining done in my rural part of the world.   Scrap might all be wonderful in Birmingham!

No problem with anyone experimenting with scrap, just be wide-awake to the possibility it’s unsuitable.  If it works, you won.  If not, buy the real thing.

Dave

 

[Rod Renshaw]

On Rod Renshaw Said:

I would like to try using a “completely flat” brake or clutch disc, as described in several posts above, for tramming my VMC mill.  I feel a heavy soild disc would be more likely to stay in place when in use than a more lightweight ventilated disc. Can anyone suggest a Make and Model of vehicle for which a suitable new disc, perhaps about 8-9inches diameter, is likely to be available at reasonable cost?

 

That’s a very small disc for modern cars; later disc-braked Rover Minis used only 8.4″ diameter discs as they were the biggest to fit under 12″ wheels. Even a cheap, small 240mm diameter disc as used on MGFs is going to be nearly £20, so its worth would need to be certain before buying one just for this purpose. If you know someone who will be fitting new brake discs soon, perhaps you could borrow one to make that determination?

I find the idea of a ventilated disc being lighter than a solid one a bit odd, as they’re basically two solid discs spaced apart with webs connecting them.

As for used discs being a viable source of cheap material, I think the actual parts you could get out of them, for the hassle involved, is a non-starter. They’re only good for a couple of pad changes before being too worn, warped or rusty to still be serviceable. The remaining surface tend to be really hard too.

[Rod RenshawParticipant @rodrenshaw28584]

Thanks for the response Nick.

Running a rule over the VMC mill sugggests that an 11″ or even an 11.5″ disc would not be too large, my previous thought of 8-9 ” was just a guess, and if ventilated discs tend towards the weight of solid ones then a ventilated one would do just as well. Does this revised specification suggest a Make and Model to anyone?

I take the point about being sure it would do before ordering one but if the discs are as flat as suggested in previous posts I could always use it as a marking out surface, and who knows, the supplier might even take it back and refund me if I speak nicely to them!

Rod

[Nicholas FarrParticipant @nicholasfarr14254]

Worn brake disc haven’t been any trouble for me to skim and make into a tramming plate, the one below is a nine inch one, I just parted the hub bit off as close as I could get, face off that side, and then the other side, after making sure the first faced side was running true, then just skimmed the outside and inside edges, just to tidy it up a bit, and de-burred all the corners. There wasn’t that much work involved really, and its thickness is close enough overall to be near perfect for my milling machines, this is a ventilated one, and it doesn’t move while tramming, but I’m sure you could clamp one down with a couple of small clamp that you could make, that would fit into the vents, if you find one a problem with movement.

Regards Nick.

[ZanParticipant @zan]

I used a pair of brake drums to make the brake drums for my 3 “ Atkinson tractor

parted them off in the Colchester, then machined them to about 4 mm section x 20 mm “ circular angle”.  They work a treat and for just a few quid rather than using new material   Machined beautifully!

 

[Mark RandParticipant @markrand96270]

Think of the ventilated discs in the same way as camel back straight edges compared with solid ones. They are heavier than the non ventilated ones, they’re also much more rigid.

The reason new ones are good is that the lathes they’re turned on use two tools, to face the front and the back side in a single pass. Helps to stop the brakes from drumming. 🙂

When I got the new one for tramming the mill, I just went into the local motorist centre and asked for what they had in approx 10″ ventilated disks and they rooted through the stock until they found one that looked right.

[Nigel Graham 2Participant @nigelgraham2]

I carved up two scrap, ventilated discs to make the firebars for my steam-wagon, and a former for flanging the ash-pan top and floor, in 1mm thick steel sheet (ex-domestic appliance panel!).

The discs were free – I just asked in a garage for some – and the iron machined without problems, but by the time I’d cut them up and made the bars it would have quicker, easier and possibly cheaper to have bought the material in better stock forms!

For things like bases though, the ventilated types would be fine.

 

[Rod RenshawParticipant @rodrenshaw28584]

Mark and Nick

Thanks for thoughts on just walking into a suitable car-parts supplier and describing what I wanted. I was thinking I would have to order one on-line and would need full details of the vehicle for which a suitable disc was being sold as a spare, I will try my luck at the weekend.

Rod

[MikeKParticipant @mikek40713]

Another thing occurred to me today…What about brake drum material for cast iron model engine piston rings?  The material of brake rotors might not be good, but the cast iron of the brake drums might be usable?  Is this the wrong type of cast iron?  Thoughts?

Mike

 

[HopperParticipant @hopper]

More hassle that it is worth. Brake drums are a thin flatish section, most of it curved. To make piston rings you are better off to start with round bar. Plus the exact material and state of workhardness and heat treatment are unknowns with old brake drums.

[duncan webster 1Participant @duncanwebster1]

Not worth risking wasting your time, just buy some known material. I wrecked a milling cutter last week trying to cut some unknown bar I’d picked up somewhere, I keep telling myself not to, but can’t resist the temptation.

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