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

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!

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.

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

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.

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

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

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!

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.

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.

Never had any problems in machining brake drums or discs . Providing they are compatible for what you are making, then go ahead and use them! The real problem is if they don’t fit well with what you want to make.

Andrew.