RBnDFW wrote:

Pete C. wrote:
RBnDFW wrote:
Bill McKee wrote:
wrote in message
...
On Apr 21, 6:18 pm, RBnDFW wrote:
A friend is coming over tomorrow night so we can mill some BMW calipers
for his Porsche. Now, I'm no machinist, I guess I'm more of a machine
collector. I just don't want to mess up the calipers, and I'd also like
to not look like a klutz G

So, we need to mill .125" off the mounting ears on these iron calipers.
I'm guess these are some sort of cast steel.
I'll be using most likely a Enco Mill-drill, possibly a Burke MVN if I
can get it wired.
I have a 1.125 indexible face mill, with two triangular carbide inserts.

What speed should I run it at, and what depth of cut?
I checked and it is cast iron. These came off a BMW 320I, std model.

I would probably take a pass at about .070 depth of cut. Then measure
it and make the next cut to get it to size. It sounds as if you have
a very small amount of metal to remove. If that is the case just use
a low speed and do not worry about the optimum speed to do the job in
the least amount of time.

Yes carbide does give you a better surface finish if you have a higher
speed, but he is doing this on a Mill Drill. So I would use a slow
speed.
Still OK with carbide, right?

An 1/8" I would use a grinder or file. Depending if it does not have to be
a precision flat surface.
It does have to be precision. This surface locates the caliper in
relation to the rotor, so it has to be parallel and flat

Be sure to spend the time with a dial indicator to locate the part and
ensure that the existing reference surface is fully in plane before
making any cuts. The cuts will be the easy part, the setup will be the
difficult part.

Good suggestion. I've given that some thought. As far as I know, the
only reference surfaces will be the mounting ears themselves, both
sides. I don't expect there will be much surface area to indicate on.
Now that I think on it, there will also be a surface where the two
caliper halves mate, probably on a difference plane, but parallel. That
might be usable.

The plan is to support both ears (at opposite ends of the part) with
spacers, bolt and Tee-nut through one ear mounting hole, also a clamp on
the body, probably bearing on the bottom of the piston bore hole. I'll
probably also support & shim under the caliper body beneath the clamp
spot, taking care not to distort the body in clamping. I'm sure it's a
super-stiff forging, as calipers have to be inflexible.
We do have a worksheet (below) from an expert who has done this many
times, and this is the recommended setup.
I don't see any way to set this up one time to make both cuts.

Here's the instructions from the expert:

MACHINING THE CALIPERS (FOR LATER 914-4s ONLY)

The 320i caliper does not have the correct flange-to-center dimension
(too small) for the later 914-4 struts, so you will have to machine the
inside face of each mounting flange (not the face on the outside of the
caliper, where the caliper bolt head is seated) to 0.587" +/-0.005"
inches. The flange thickness "out of the box" should measure 0.712" +/-
0.002". This means that 0.125" of material must be removed from the
flange. This will leave the caliper with a flange-to-center distance of
1.025" (this dimension is difficult to measure), matching that of the
original 914-4 caliper. What you’re effectively doing is moving the
center of the caliper away from the strut mounting towards the outside
of the car. Before you have the caliper machined, convince yourself that
machining the outside flange faces would do nothing to re-locate the
calipers properly about the rotor—this way you won’t be confused as to
which flange faces (the inside ones) need to be machined. Your calipers
may have a recognizable casting mark that is just about at 0.125" from
the face to be machined.

NOTE: Before machining the 320i calipers, you should verify (with an
accurate measuring device, e.g. dial caliper or micrometer) that the two
mounting flanges are equally thick. If they are, follow the instructions
below which DO NOT involve "splitting the caliper open." If, on the
other hand, the flanges are not of equal thickness, explain that to your
machinist and he will come up with a method to guarantee that the
caliper flanges are machined to the exact parallel of the center line of
the caliper. One suggested method is to split the calipers open and use
the center half as a clamping point. However, if you choose to use this
method, you will need to replace the fluid O-ring seals between the
halves, and retorque the caliper bolts properly upon reassembly. If you
split the caliper halves and reassemble them you had better know exactly
what you’re doing so as not to compromise your safety.

The recommended machining setup is on a mill, with the caliper’s outside
mounting flanges resting on two (large) gauge blocks on the table, i.e.
with the outside mounting flanges face down, and the inside ones facing
up. Typically one clamp is pressing down on one inside flange, and the
other flange is unobstructed and ready to be machined. Another, much
taller clamp presses down on the caliper near the ends of the bolts that
hold the caliper together on the same side as the flange to be machined.
It is extremely important to ensure that the caliper is being held down
"flat" against the mill table (via its outside flanges and the gauge
blocks), otherwise the caliper will be skewed relative to the rotor when
its mounted to the hub. Considerable clamping pressure is required to
immobilize the caliper. Fill or cover the caliper orifices with
something to prevent metal shavings from entering.

Use a large end mill (e.g. 1 5/16") at very low speed to remove the
proper amount of material from the face of the inside flange. Be sure
your cutter is big enough to maintain the large surface area of the
inside face of the mounting flange. Do your work slowly and check it as
you go. Try for +/-.005" tolerance, but +/- .002" would be better.
Unfortunately each caliper has to be setup twice (once for each flange)
due to the fact that the only place to clamp it to the table is the very
surface you’re trying to machine. The whole job can be done in under an
hour.

Yep, it does sound like a bit of a pain to clamp and indicate properly.