Impressive $20 brake rotor for tramming the mill

[nheng]

Although I have a garage full of old brake rotors, I hate to machine CI in the shop. Stopped at Autozone this evening and had the girl grab any small (thin) rotor off the shelf. She looked up the price and it was $20. I forget what car it was for but here are some very careful measurements ... quite impressive.

Rotor thickness variation measured at 4 quadrants, at 2 diameters:

+/- 0.00005"

Height from outer face (at wheel hole pattern) to rotor surface (also 4 quadrants):

+/- 0.0001"

In short, these Chinese rotors are on a par with the best quality parallels !

Of course, they are soft and they have a fine turned, not ground finish and these accuracies are only possible because the faces of the mics ride on (and integrate) the surface peaks.

Still darned good for $20 and it let me tram the mill within 0.0005" across about 8" in 5 minutes. A large diameter ball or roller contact point would allow the DTI to see close to the accuracies listed above.

Den

[Chipslinger]

Yep been doing that for Oh, 15 years now.


Brilliant Idea.

[nheng]

The point of the post was the somewhat incredible precision in the dirt cheap Asian rotor ... a product of which I am not fond.

A noobie may not have heard of this method of tramming yet or even know what tramming is. Last time I checked, noobies were still welcome at this forum.

Has something changed ??

[lazlo]

Yeah Den, I'm really surprised too at the precision of that rotor. What brand did you ask for at Autozone?

I never understood why folks don't like to use the mill's table directly: if you bend the DTI needle in the direction you're sweeping, the T-slots don't hurt the gage, but heck, it's nice to know that you can buy a "precision flat" for $20 at your local AutoZone.

[nheng]

Lazlo, It's their own Duralast brand, part number 34144 (may need a GA 81601 prefix). I don't know what it fits but the OD of the disk is 9.1" and the hub is 5.3"

[quasi]

فou should sell them on Ebay as "Tram-A-Rounds" for $60.00 each!

[clutch]

My tram ring. Race from a CNC spindle at work



Set it in the kurt vise, tram away.

Clutch

[A.K. Boomer]

I never understood why folks don't like to use the mill's table directly

That's what I also wonder, go directly to the horses mouth and eliminate error (dont have to worry about crumbs between the two surfaces or if the second surface is precision enough)
All mill tables iv ever seen have a hefty chamfer, the only way to get in trouble is to go too deep with the indicator needle so just dont do it, I just skim aprox. .010" --- Lazlo throws in another failsafe with his paying attention to the direction of which way the needle is dragging (not pushing) Set your mill up to its rough alignment degree marks first, if they dont match up then either make them or mark them so you know when its very close, that way you wont lose your indicator ball below its radius --- So you have an old mill with tons of dummy marks in the table?, take a putty knife fill them all with JB weld let harden and stone them in, it should be done anyways to keep chips out so you can install your vise and RT table and other stuff without dredging up swarf between the two surfaces...
If your mills table has jewling or etching then just stop the needle on a flat

[Carld]

I sweep my head in like Boomer does it. I don't like anything between the indicator and the table surface.

[wierdscience]

One more time-

If your working on the table tram to the table

If your working on the vise tram to the vise

If your working on the RT tram to the RT.


In other words tram to whatever surface your using for refrence for the particular job.

The accuracy of the Chinese rotor doesn't suprise me,both faces are machined at the same time.

What would suprise me is if they have improved the quality of the cast iron.Used to the first time you stopped hard the rotors warped and that was the end of that.

I've used brake rotors,bearing races,plate glass and most recently a two-groove vee-belt pulley that I surface ground.Whatever floats your boat.

Oh and I would add that a coaxial indicator running on a mill spindle at speed and temp will tram in closer than a idle spindle with a DTI.

[lazlo]

If your working on the table tram to the table

Yeah, I don't know why folks go through hoops with 1-2-3 blocks, tram rings, TramARounds, ... I'm guessing they see those T-slot and assume it's going to crash their Tesa DTI

The accuracy of the Chinese rotor doesn't suprise me,both faces are machined at the same time.

Judging by the circular grind marks, I'd have guessed that they're Blanchard ground, one side at a time.

[nheng]

The Autozone has what appears to be a high speed turned finish. Better grade ones that I've bought in the past were Blanchard ground.

Weird, That's quite true about the dynamic vs static testing. Same as checking TIR on a machine spindle. Next best thing is to run it a while for lube and temp at least.

Lazlo, Interapid (but got em cheap)

[Chipslinger]

One more time-

If your working on the table tram to the table

If your working on the vise tram to the vise

If your working on the RT tram to the RT.


In other words tram to whatever surface your using for refrence for the particular job.

The accuracy of the Chinese rotor doesn't suprise me,both faces are machined at the same time.

What would suprise me is if they have improved the quality of the cast iron.Used to the first time you stopped hard the rotors warped and that was the end of that.

I've used brake rotors,bearing races,plate glass and most recently a two-groove vee-belt pulley that I surface ground.Whatever floats your boat.

Oh and I would add that a coxial indicator running on a mill spindle at speed and temp will tram in closer than a idle spindle with a DTI.

Very true, thanx Wierd.

[A.K. Boomer]

One more time-

If your working on the table tram to the table

If your working on the vise tram to the vise

If your working on the RT tram to the RT.

I respectfully disagree --- I have my vise AND RT table bolted to the mills table most of the time, They both are very stable and tested to good precision - I only do the mills table and then everything else is as good as it gets and by far good enough for 99%, If it wasnt it would be stoned in to be good as I need, or I might re-tram for a very very special occasion.
I dont have time to go tramming everytime I switch from vise to RT table and such as sometimes this would require 5 trams in a couple hours --- since compound errors would have the chance of increasing if say I trammed to the RT table and then used the vise without tramming (I.E. two segregated pieces attached to a common) then the only real logical solution is to eliminate a compound and start with the common (the table) since I already know the deviances (or lack there of) of both my RT table - its taper mounted three jaw and my Kurt vise I make the assumption that i can pretty much count on everything being within a pre-determined range --- So far - so good

If your really having that much deviation from RT table to vise ect. enough to have to re-tram every time then I would check into better quality bolt ons or bring them around somehow - or stop working on space shuttle stuff in your home shop

[nheng]

Speaking of tramming to the vise, I got quite the surprise a few days ago when I put a seldom used Grizzly 5" mill vise into use on the BPT. The jaws are parallel to the table to within 0.001" but the "slides" (if that's what they're called) have a whopping 0.008" across the vise width. Bummer ... it looked precise