Forum Home
PC World Chat
Thread ID: 65593	2006-01-23 21:39:00	car brake disks.....	drcspy (146)	PC World Chat

Post ID	Timestamp	Content	User
423703	2006-01-25 05:55:00	When I got a reading of 3/10s of a thou is when I started lightly tapping the gauge to make sure it wasn't sticking :) It is rather good, next I'll have to check the other front wheel. 0.003" is the typical maximum lateral run out allowed according to various websites, including this one already mentioned: www.brakeinfo.com So to measure runout up to that sort of level with any certainty implies having a dial indicator with a resolution of at least 10 times less, ie about 0.0001" per division, but certainly not more than 0.0005" per division. Such small measurements means that the set up must not creep or move as the rotor is turned. That's not so easy to achieve.	Terry Porritt (14)
423704	2006-01-25 23:06:00	Haven't you got a laser interferometer yet, Terry? I designed one as I rode into town today. Just a bit of optics and a bit of software. :D I might even build it, one day. Of course, however good the measuring tool is, giving it a place to stand is the difficult place. It still needs a rigid mount on the bit of the car which holds the wheel bearing.	Graham L (2)
423705	2006-01-26 01:22:00	Haven't you got a laser interferometer yet, Terry? I designed one as I rode into town today. Just a bit of optics and a bit of software. :D I might even build it, one day. Of course, however good the measuring tool is, giving it a place to stand is the difficult place. It still needs a rigid mount on the bit of the car which holds the wheel bearing. I think it'd be better to get a helium light source and use quartz plates to check the angstrom light rings for concentricity. Keeping with one or two rings might be good enough. Lasers are dangerous in non-professional useage.	SurferJoe46 (51)
423706	2006-01-26 01:55:00	Can you drive through the judder, eg. is it still there at 120km, 130km, if so I would suspect the breaks otherwise just get all 4 wheels balanced, even 10g could give you a shake or judder.	Rob99 (151)
423707	2006-01-26 03:01:00	... Lasers are dangerous in non-professional useage.It seems disk lathes are dangerous in professional hands. I'm talking about an interferometer working over inches, not laser machining. The optics, and the laser, from a CD player look to be very tempting. There's even a photodiode detector array. CI brake disks don't need to be optically flat. They need to be running true. Quartz flats? And a helium source? You must be rich. I've got some pieces of 1" thick float plate glass for my optical flats. I think they were within one fringe of sodium light .	Graham L (2)
423708	2006-01-26 04:11:00	Haven't you got a laser interferometer yet, Terry? I designed one as I rode into town today . Just a bit of optics and a bit of software . :D I might even build it, one day . Of course, however good the measuring tool is, giving it a place to stand is the difficult place . It still needs a rigid mount on the bit of the car which holds the wheel bearing . No, I haven't got around to it yet :rolleyes: I used to use an HP laser interferometer for machine tool calibration, 3D measuring machine calibration and long length gauge measurement, but some how I doubt a reflection could be obtained from a grotty CI disk . A bog standard dial gauge is good enough for the job ! If anyone wants to read up more on rotor runout, this Google has some useful sites . . google . co . nz/search?q=measure+rotor+runout&hl=en&lr=&start=10&sa=N" target="_blank">www . google . co . nz I still dont know why Joe finds measurements to 0 . 0001" so remarkable, that's every day normal engineering stuff, dont take my word for it, it is what is every article on rotor runout says . In machine tool manufacture, we go up an order of magnitude in precision over and above the automotive parts industry, and when we calibrate measuring instruments we go up yet another order of magnitude . For example, the runout of a precise high speed grinding spindle nose would normally be within about 0 . 000 02", I'd start to get really worried if it was around 0 . 0001" . The runout of the axis of a precise air bearing rotary table at the table surface would be expected to be less than 0 . 000 002" (2 millionths of an inch, or 0 . 05um) . It's horses for courses .	Terry Porritt (14)
423709	2006-01-26 04:22:00	I think the CI would reflect IR quite well. And of course, IR is what you get from a CD laser. Heavy averaging would be needed to get the runout, rather than a measure of the roughness. I suppose by keeping more of the electronics you might get music from the disk. :D It would probably be as good as most modern pop.	Graham L (2)
423710	2006-01-26 04:49:00	On the subject of precision I was making a lot of measurements to 1 part in a million this morning. The last digit is probably reliable. My frequency counter's crystal is at least that good. I don't think the (Tek) oscilloscope's digital timebase is quite as good. The calibration I'm doing will satisfy me if it's to one part in 10^3.	Graham L (2)
423711	2006-01-26 18:48:00	It seems disk lathes are dangerous in professional hands . I'm talking about an interferometer working over inches, not laser machining . The optics, and the laser, from a CD player look to be very tempting . There's even a photodiode detector array . CI brake disks don't need to be optically flat . They need to be running true . Quartz flats? And a helium source? You must be rich . I've got some pieces of 1" thick float plate glass for my optical flats . I think they were within one fringe of sodium light . I was being . . . . er . . . pendant* *Definitions of pendant on the Web: ~ an adornment that hangs from a piece of jewelry (necklace or earring) chandelier: branched lighting fixture; often ornate; hangs from the ceiling ~ pendent: supported from above; "a pendant bunch of grapes" wordnet . princeton . edu/perl/webwn ~ A pendant (from Old French) is a hanging object, generally attached to a necklace or an earring . The use of pendants has several purposes; ornamentation is only one of them; pendants are also used for identification (i . e . religious symbols, sexual symbols (This might fit well), symbols of rock bands), protection (i . e . amulets, religious symbols), self-affirmation (i . e . initials, names), ostentation (i . e . jewels) . Of course these purposes can be combined (i . e . a richly jewelled symbol) . en . wikipedia . org/wiki/Pendant BTW: I Wicki'd the word "pendent" too and got the same results . . . is that a NZ or American-English usage? Either way, I was perhaps OTH'ing (and speaking sarcastically) the whole idea of worrying about such small, miniscule measurements and their non-necessity in disc brake rotors . If parallelism# and runout are within designed limits and the calipers themselves are free to float for any other irregularities, then there isn't going to be much deleterious effect to the driver via the brakes . # The condition of a surface, line, or axis equidistant at all points from a datum plane or axis . www . ticms . com/wizard/glossary . htm	SurferJoe46 (51)
423712	2006-01-26 18:59:00	and to Terry: your: "I still dont know why Joe finds measurements to 0 . 0001" so remarkable, that's every day normal engineering stuff, dont take my word for it, it is what is every article on rotor runout says . " . . . . . . . . . . . . . is all well and good, but those tolerances have no practical use in the world of disc brakes . Don't get me wrong . . . I love the feel of a very well made (and engineered) product, but the real effectiveness of brakes is not so cut and dried . If shops were to have to keep to such close tolerances I suggest that no-one could afford to (without altruistic ideals here) pay for the labor (no "u") to have even the most mundane services performed . Shops cannot afford to have clean rooms with . 01 micron air purification to keep cleanliness standards . Cars aren't NASA prototypes, nor are they huge bridges either . They fall somewhat in middle turf . C'mon, there are even torque values to installing oil pan drain plugs . My (tongue-in-cheek) evaluation of such trivia in the real world is this: "The most dangerous person in a repair shop is an engineer with a micrometer and an idea" . Engineers do not good mechanics make . . . . . . . . the sound of sobbing is disturbing to those with the wrenches .	SurferJoe46 (51)
1 2 3 4 5