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Errol
07-18-2004, 12:55 AM
Oh, the other photo that I intended to show you somehow did not go through. Here's the other photo of some friction welded junk on my new rotor.
http://img45.photobucket.com/albums/v139/RedEyes/Rotor0018.jpg

Feedback appreciated. Thanks Errol

G.A. Ewen
07-18-2004, 07:56 AM
What material did you use to make the rotor?

http://bbs.homeshopmachinist.net//redface.gif Opps just read your other thread. I don't know much about stainless steel but I wonder if you buff it vigorously with a buffing wheel on an angle grinder, will it work-harden the surface and thus prevent the gauling?

Some of the scrap stainless steel that I have tried to use seems to work-harden with the smallest amount of heat and friction.

[This message has been edited by G.A. Ewen (edited 07-18-2004).]

topct
07-18-2004, 10:18 AM
You might try refacing the rotor again, but instead of the metalic pads try some kevlar ones. Personaly I would not have used 304, something in the 400 series. It can be hardened and ground. Just like the original.

Errol
07-18-2004, 07:27 PM
topct, How machineable is the 400 series? Machining this Type 304 was difficult for me. Carbide didn't seem to work at all, especially the facing work. I ended up using hss with a tiny radius to kill the chatter, and my experience was.. well, can I say.... a long evening ... 70rpm at .010 doc.

Also, wierd, in hindsight, I should have put on carbon friction pads for the breakin, before switching to metallic pads.

I have since talked to a machinist biker buddy of mine, and he said he went through stainless steel woes as well and ended up making his out of Type 4140 steel, and work great. So perhaps next time I'll try that.

C. Tate
07-19-2004, 09:23 AM
The manufacturers use some grade of 400 series stainless. They are very machinable if you are careful. They will be similar to A-2 or one of the other tough tool steels. 400 series stainless can be heat treated and then ground and chromed if you like.

CT

topct
07-19-2004, 09:34 AM
It would probably depend on what it's number actually is. The alloys designated with a F behind it indicated "free machining". The trouble might be finding the stuff in a form (plate) that you could use. Since you already have the one made from 304 you might, as I said, try refacing it. I have resleeved lot's of English motorcycle carbs (Amal), they made the slide out of the same crap metal they made the bodies out of and would wear themselves out rapidly. I would install a sleeve of 304 on the slide, and turn it to fit a bored out carb body. I tried all kinds of carbide and different shapes without success. What worked the best was an M2 HSS bit that I ground at about 90 degrees with a sharp point. Here's the hard part, you have to take a light enough cut to remove metal and it must be kept moving. A powered crossfeed for the facing would be very helpful, a slow and very constant motion must be used. Also what I did was to not back the tool off to change direction, I would try for about 1 to 2 thou on each pass and again do not stop, the tool seems to want to dig in and leave a line on the work.
Good luck with your experiment. Just curious, but what does KTM get for a replacement?

Errol
07-19-2004, 06:23 PM
topct, thanks for your advice on using hss for tooling for Type 304. By trial and error, I found a small radius tool seemed to work better, but didn't try a 90 degree tool angle with a sharp point. I will try that next time for sure. And yes, I found light doc's seemed to work better.
KTM replacements are only $170.00, but they have fancy laser cut patterns on them which kills the brake pads in muddy conditions.

mbensema
07-19-2004, 07:07 PM
Austinetic stainless steels are very prone to galling and not a good choice for this application. You can only work harden the material by machining, but that will quickly be worn away by the galling. The only case hardening process I have found for these grades of stainless is this http://www.kolsterising.bodycote.com/

The other problem you have with 300 series steels is chloride stress corrosion. If you live near an ocean or in the north, the chlorine will attack the material and pit it. The pittings will be much deeper then they look and small cracks will develope over time, which can fail before you expect.

A little research found 420 to be what's used for brake rotors.

Errol
07-20-2004, 01:33 AM
thanks mbensema! I will order up some Type 420 next time I pass by the stainless steel shop.

Forrest Addy
07-20-2004, 03:16 AM
Nickel bearing stainless is the last stuff to use for a friction usrface given its propensity to weld to practically anything that rubs against it.

Are you using stainless as a brake disk for appearance's sake. If so, I'd give up appearance for performance especially where braking reliability is a safety matter touching on the life of the rider.

Brake materials are closely match to the friction surface they're intended to run against. I suggest you use the shoe and friction surface materials as they're intended by the manufacturer.

RobDee
07-20-2004, 07:07 AM
When I have a tough piece of stainless or 'gummy' metal to machine I use a wax based cutting cream and smear it over the surface to be cut. It takes the galling out. Tapmatic makes a good product. Incidentally I also use it for tapping brass.
Most of my work is done with carbide inserts, on stainless I use a 1/32 radius, M7.
Cutting disks can cause chatter especially if they are thin, sometimes a large rubber band on the outside of the disk helps.