Turning cast iron brake disc.

[Alan Reynolds]

Hi, hope you can assist me here. I've been asked to reduce the diameter of a vented and drilled brake disc to enable it to fit the brake pads better. It's a bespoke system so all a bit experimental.

I need to remove about 1/2" from the diameter.

It's too big to go in my Myford ML7 but I've got access to a 12" Harrison. (If I can work out what all the buttons and levers do!)

I only use 1/4" tool steel in my Myford so my question is, will it be ok on the cast iron and any tips on tool angles.

I might have a bit of 3/8 tool steel if that's better.

Cheers for any guidance chaps.

 

[Seadog]

You'd be better of with a brazed carbide tool. The disc will probably have a surface that's glass-hard.

 

[Alan Reynolds]

Thanks Seadog. The disc is brand new so hasn't been subjected to any heat or polishing from brake pads, it's virgin metal. Would that make it easier?

 

[Seadog]

I've never tried turning a new disc so I can't say for sure. All you can do is to give it a go. Don't pussyfoot around though, or you could end up work hardening the surface.

 

[hotponyshoes]

If it's a drilled disc I would see how far the holes are from the outer edge at the moment and check you are still going to have the same sort of distance after machining otherwise they will be liable to crack.

I have reduced them on a lathe using indexable insert tooling with a tip for cast iron before.
Have also done them on a rotary table on a mill by taking a full depth pass on the side of a carbide cutter. Take about .5mm at once (so shrinks the disc by 1mm each pass. My rotary table is manually wound so couldn't guess at what the feed rate was but there is only one speed that it cuts cleanly and it's a bit faster than I though it would be if that helps!

 

[gaz1]

you can do it with a shaper

or a naughty way

 

[piman]

Hello ALan,

I don't think you'll have any problem turning it down from the point of the tools you want to use. It will be machined all over so there won't be any hard skin and cast iron is very nice, albeit dirty, to turn.

Holding it is a bigger problem. The easiest and least effective is holding it by the bore. If you have the capacity, using outside jaws and gripping it on the bell is better. However this may be as cast and may not run true. You need to assess what means you have. A faceplate would be a good option?

Alec

 

[merryman]

Did one last week, though a stainless steel disc. No problem with a standard HSS tool. Had to get a bit close to the holes, but had done another last year without any issues. Reason for doing it, Suzuki 700 King Quad discs available as pattern parts, Suzuki 500 King Quad discs, manufacturer only. Identical bikes, identical pads, identical hubs, but smaller discs, and no, the calipers wouldn't go on with the slightly bigger discs fitted.

 

[Alan Reynolds]

Well, managed to do them. Tool steel worked but I had to try and take a generous cut without lubricant. That just killed the edge completely. Taking a light cut resulted in sparks and a blued tool and worn off tip. Had to guess at the tool profile though. How do you get to grips with all the different carbide tips and profiles? They seem to be a complete jungle so I would appreciate any guidance as I'd like to buy a proper tool to use in this wonderful 12" Harrison I've got access to. Just wish it had a user manual.

 

[brightspark]

a slow speed and a reasonable cut using decent ground hss tools should have no problem on a new disk. its only old overheated disks that have hard spots that need carbide . and if they were that bad I wouldn't bother

 

[Bill Edwards]

Well, managed to do them. Tool steel worked but I had to try and take a generous cut without lubricant. That just killed the edge completely. Taking a light cut resulted in sparks and a blued tool and worn off tip. Had to guess at the tool profile though. How do you get to grips with all the different carbide tips and profiles? They seem to be a complete jungle so I would appreciate any guidance as I'd like to buy a proper tool to use in this wonderful 12" Harrison I've got access to. Just wish it had a user manual.

Most turning work tends to be done with a right hand tool (which I think should be called left hand, but that's how it it). But if you can I'd buy a cheap set of indexible tooling which will have all the different types of tool that you are likely to need, and ideally where they all use the same tip which means that you only have to have one type, as it's the inserts that cost money.
Then forget about the cheap inserts and buy decent ones - there are some threads on here with them explained and if you need more help just start a post asking for a good tip for your usual work.

Then you're good to go about turning work without the faff of grinding HSS, which is not only time wasted but also requires some understanding of cutting angles as well.


Oh and although I've not used a 12" Harrison make lovely machines.

 

[Alan Reynolds]

Yes, this Harrison is quite nice. Coolant pumps, a tool post at the 'back' of the saddle, long bed. I'll take the advice and get some indexable tools for when I get to use it. Thanks folks!

 

[james butler]

Did one last week, though a stainless steel disc. No problem with a standard HSS tool. Had to get a bit close to the holes, but had done another last year without any issues. Reason for doing it, Suzuki 700 King Quad discs available as pattern parts, Suzuki 500 King Quad discs, manufacturer only. Identical bikes, identical pads, identical hubs, but smaller discs, and no, the calipers wouldn't go on with the slightly bigger discs fitted.

wouldnt it be easier to space the caliper or fit the caliper and carrier from the bigger one? then you would have had better brakes and easier to replace

 

[wookie]

wouldnt it be easier to space the caliper or fit the caliper and carrier from the bigger one? then you would have had better brakes and easier to replace

I'm betting there isn't enough space inside the wheel for bigger discs.

 

[merryman]

wouldnt it be easier to space the caliper or fit the caliper and carrier from the bigger one? then you would have had better brakes and easier to replace

No, it wouldn't be easier to start altering caliper mountings than to mount the disc in the four jaws, centralise it, and take 1/8" off. Took less than 30 min in total.

Had the same problem on a Honda 420 on Thursday, when I compared the worn out ones on the 2015 bike against a set of pre 2014 Honda 420 discs we had in stock, they have altered the OD slightly, but also the PCD of the mounting holes by a couple of mm. Again, you can't get pattern parts, so it is genuine Honda at £84 each this time.

 

[james butler]

No, it wouldn't be easier to start altering caliper mountings than to mount the disc in the four jaws, centralise it, and take 1/8" off. Took less than 30 min in total.

Had the same problem on a Honda 420 on Thursday, when I compared the worn out ones on the 2015 bike against a set of pre 2014 Honda 420 discs we had in stock, they have altered the OD slightly, but also the PCD of the mounting holes by a couple of mm. Again, you can't get pattern parts, so it is genuine Honda at £84 each this time.

altering? i thought you said Identical bikes, identical pads, identical hubs so all you need is the caliper carrier from the suzuki 700?

I'm betting there isn't enough space inside the wheel for bigger discs.

probably correct on a car but on a quad there is usually one disk in the centre of the axle so you have plenty of space.
you can still get disks skimmed so it should be possible to turn them down to size bearing in mind the issues others have mentioned about putting too much heat into them.

 

[merryman]

i thought you said Identical bikes, identical pads, identical hubs

Problem is, the Japanese alter things slightly, why not use the same discs on all the 450 to 750 King Quad range? I have found out the hard way that the two bikes have different front A arms, and that the discs won't fit un-modified, so either the steel caliper slider assemblies, or what we call the "knuckle assemblies" must be different. I was referring to the wheel hubs in the previous post, the parts that carry the discs and wheel studs. Suzuki parts are eye-wateringly expensive, which is why we use pattern parts when we can. For example, genuine reversing lamp, which looks like a £5 accessory shop item, £54 from Suzuki.