Author Topic: One for the machinists (Read 3861 times)

bwaller · « **on:** May 02, 2011, 04:01:46 PM »

I have two brake discs and each vary in thickness 0.0015" around their circumference. I need to reduce that thickness variation to 0.0005 or less. Not very much to remove, just a lick....but what tonque? $:-\$

Any bright ideas?

I would like to make a track day Monday, the engine top end is in pieces while I wait for some sealant and there is too much pulsation through the brake lever. I'd like to resolve the brake issue too so I can go get some practise before the first race.

Jim F · « **Reply #1 on:** May 02, 2011, 04:52:41 PM »

be very careful when you indicate the ID of the rotors (The part that locates on the Hub)
That lone could cause much more run out than just measuring the OD
then use a tool post grinder and skim the OD and measure

A .0015 difference is not a lot

Good luck

754 · « **Reply #2 on:** May 02, 2011, 07:24:54 PM »

BW, I cant anwer pM's on here larely.

I would indicate the discs, mounted on the wheel, if there is more than you mentioned take diosc off try turning or swapping, or filing , to reduce runout.
Assuming one side of each disc is true or within 1/2 thou, I would try to block sand out the difference.. ir should work but may take a while. It is certainly worth a try..
Taking them off, getting them recut or ground, is going to get pricey fast..

FunJimmy · « **Reply #3 on:** May 02, 2011, 07:50:09 PM »

Contact Chris Schumann at Portland Engine Rebuilders, (503) 230-1276.
He does cross drilling and precision surface grinding.
Should be able to get those disc spot on..

scottly · « **Reply #4 on:** May 02, 2011, 08:05:04 PM »

It took days for me to resurface a Kawa disc on a lathe with a tool-post grinder, and even then, despite my all my efforts, the results were far from perfect.
You might try mounting the discs on the wheel with the thin spots 180 degrees apart; this might reduce the pulsation in the lever.

754 · « **Reply #5 on:** May 02, 2011, 08:11:21 PM »

He needs it this weekend.. 1 1/2 thou, got to be able to get that off with a block..

bwaller · « **Reply #6 on:** May 02, 2011, 08:19:03 PM »

Chris did these to begin with. I'm sure with stock Honda calipers you wouldn't feel a thing. TG sent me an article that describes my problem to a tee. Runout doesn't appear to be the issue but thickness variation. It is true that this is a small amount and maybe I can make it better by mounting changes. I'll also think about how best to block sand Frank.

What a friggin nuissance.

Thanks guys

turboguzzi · « **Reply #7 on:** May 03, 2011, 09:51:49 AM »

hei brent

how about a closeup shot of those discs

might help....

simon#42 · « **Reply #8 on:** May 03, 2011, 09:56:38 AM »

i would advise against block sanding disks , your chances of getting it right are none existent , your chances of making a complete dogs breakfast of it are pretty good . take them to any good machine shop that can plough grind them . shouldn't be expensive or take too long

turboguzzi · « **Reply #9 on:** May 03, 2011, 12:13:40 PM »

just seen the pic of the discs in the build thread and they are riveted to carrier, so guess plough / flat grinding is no go....

Brent, cant you use just for this emergency stock discs or GS discs? or the Brembo's are too narrow for them to fit?

simon#42 · « **Reply #10 on:** May 03, 2011, 01:14:33 PM »

they look to have already been ground [ to reduce thickness ? ] if so i would check the mounting flange again [ as big jim suggested ] or as tg has said fit some more for the time being [ spare discs should be part of your spares package anyway ] and send the discs back to be re checked .

754 · « **Reply #11 on:** May 03, 2011, 07:45:56 PM »

Simon, he has to take off HALF the thickness of a hair..not sure how rapid you envision sanding to be, but its a slow process.. not like grinding..
As for redoing them it is time consuming.. anyone that runs machine tools will tell you its probably harder to re-grind a minimal amount than it was to do it originally.
I guess it boils down to wether you can do fine work, and have a micrometer..

And he cant just send them back, he wants to race this weelend, and he is around 2500 miles from the place that did the work..

bwaller · « **Reply #12 on:** May 04, 2011, 09:29:30 AM »

The track time on Monday is not possible now anyway. After spending more time measuring the discs there is no way hand work would be possible.

Chris has stepped up & offered to re-do. I'll hold my breath until their perfect and back in my hands.

simon#42 · « **Reply #13 on:** May 04, 2011, 10:59:50 AM »

754 he has to take off half the thickness of a hair in the right place , i guess it boils down to wether you want to spend all that time and money building a nice bike , and then make some half arsed job of the brakes

bwaller · « **Reply #14 on:** May 04, 2011, 12:48:51 PM »

Those discs were thinned then finish ground to 5mm. I slotted and drilled and removed more weight after. They are on the way back to Chris and hopefully will be perfect after.

I set up and indicated both hub faces and although not dead perfect are not a cause of the problem. I have a set of thin Suzuki discs that I mounted last night but need to re-space the calipers a tad to use them. I'm just not able to make the track time Monday but would like to get it running again this weekend anyway.

Thanks for the advice guys, I'll let everyone know how it turns out.

754 · « **Reply #15 on:** May 05, 2011, 08:43:06 AM »

Simon, sometimes things are done out of necessity..

There is a lot of your so-called half arsed jobs being performed in the pits, motel parking lots.. all around the world.. and then winning.. you should see some of the half arsed work performed and Bonneville and the wonderfull results.

Sometimes you got to ask yourself, do you want to really be there, and make it work..

Myself, I have a thinned disc that was not right. I carefully made a mounting fixture, to correct it. The harmonics of the lathe were such that, I could not turn the disc at even the lowest steady speed.. I ended up using the jog button to finish off the cut.. about a hundred times of nearly stop, and then go again. I did take off about 6 or 8 thou.. that would be about 6 or 8 on the fat side but only 1 or 2 on the thinner side, on a now slightly work hardedned surface. Grinding would have been better, but I am not set up for it. I still am out abot the same amount as bwaller on that disc. I will not try to turn it anymore, disc it already thin.. I will just do it with a block when I take it off.

simon#42 · « **Reply #16 on:** May 05, 2011, 12:04:07 PM »

yes you are right sometimes things are done out of necessity , and i have performed some spectacular mechanical butchery in the pits when required . its just that if you dont have to then dont ! . i also suppose it depends where you live , i am spoilt in that there are 3 good machine shops within a couple of miles of my garage that would regrind a disc in half an hour so the thought of finishing one by hand did seem a little unnecessary to say the least .

754 · « **Reply #17 on:** May 05, 2011, 09:28:25 PM »

I am not sure wether you were thinking, sanding while disc is turning, or taking off the high spot with the disc on the bench?

simon#42 · « **Reply #18 on:** May 06, 2011, 11:09:22 AM »

i was thinking about taking off the high spot with the disc on the bench. i wonder where the distortion has come from ? i think bwaller has gone about this the wrong way round . a better idea might have been to drill and slot the discs first and then have them ground , assuming they where ground right [ and its an easy process that was done by a professional so they probably were ]
the distortion must have occurred latter .

simon#42 · « **Reply #19 on:** May 06, 2011, 01:18:23 PM »

just to add to my last post , i dont think bwaller did anything wrong with his work . i just think it may have released a stress in the disc which has caused the distortion

haill · « **Reply #20 on:** May 10, 2011, 04:36:49 PM »

Would it be possible to replace the brake pad with a cut file welded to a old set of brake pads then place them in the caliper, using the action of the brakes itself to take the high spot off the rotor as the bike slowly moved along under it's own power? That could get you some MacGyver points... or over the bars and in the hospital or screw your brakes completely up and wondering why you didn't just take up wood carving instead... Your could be less of a man and walk beside the bike, while this was being tried....

bwaller · « **Reply #21 on:** May 10, 2011, 07:48:28 PM »

Simon, I slotted the rotors after having them ground to further remove weight and I wondered about the stress issue. It would have been better to grind last. However they were tapered as well as variable in thickness. More than a stress problem.

I think the only way to dress them is to grind a lick off them and that is being done.

turboguzzi · « **Reply #22 on:** May 10, 2011, 09:12:02 PM »

Brent, down to how many mm's have you grinded them down to?

reason i am asking is that getting off weight is definitely not everything in life

In heavy braking tracks you just NEED weight in the discs to act as a heat sink. I am facing such issues now with the new bike. when I took the original discs for grinding the very knowledgeable shop guy told me to not even think of further drilling as he got them thin enough and they would over heat. he was spot on. They are ok-ish on light braking tracks, got fade and overheating in one track that is nasty in terms thermal load on discs.

leave the heavy drilling to the cafe racer kids

bwaller · « **Reply #23 on:** May 11, 2011, 04:25:20 AM »

I understand TG, and my original thinking when looking at modern disc thickness was that at or around 5mm should be safe even mounted solid. I decided to slot them in the area where the pads don't contact anyway. At 146kg plus fluids it's still heavy for a little race bike so time will tell if they overheat.

Chris phoned last night and he needed to remove only 0.005" total to flatten. There were other issues but he felt there definitely was some stress relief issues when I slotted them. Hopefully this solves my pulsing problem, because as it turns out one of my spare Suzuki discs is warped. That'll get dealt with another time.

FunJimmy · « **Reply #24 on:** May 11, 2011, 08:42:11 AM »

Quote from: bwaller on May 11, 2011, 04:25:20 AM

Chris phoned last night and he needed to remove only 0.005" total to flatten. There were other issues but he felt there definitely was some stress relief issues when I slotted them. Hopefully this solves my pulsing problem, because as it turns out one of my spare Suzuki discs is warped. That'll get dealt with another time.

Brent

Sounds like you might have that Gremlin sorted out.
Let's hope it stays out!

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Author Topic: One for the machinists (Read 3861 times)