Dave Hinz wrote:
On Tue, 5 Jul 2005 17:08:53 -0400, Robin S. wrote:

"Dave Hinz" wrote in message
...


I thought of that...right after I drilled & tapped the first two holes.


While I have no further insight into your hole circle problem, I have a
suggestion.
You should consider writting out work plans for your projects, before you
begin them. While this sounds like a waste of time and a lot of work, I
gaurentee you'll have to think about all the processes in the work plan
while you're at the machine (whether you've done a work plan or not).


Well, I work in I.T., and when I'm doing something complicated with
dependancies like this, I do that. This was actually more of a "feature
creep" thing though - the tool I made is to turn a brake piston back
into the caliper - it has 4 holes in the face of it, and needs to be
turned in clockwise to retract it for the new pads. I made this out of
a disk of 1.45" diameter and 0.250" thick, drilled & tapped a bolt in
the center of it, and then these holes. Made it initially with just two
drive pins (grub screws in this case), but it "rocked" because it was
bottoming out in the holes. So, I figured adding 2 more pins in the
right place would give it a solid location without the rocking. I
probably would have thought about it more if the second pair of holes
hadn't been a later modification to the original design.


The bolt-hole circle is a good example of why work plans are a good idea.
You've probably painted yourself into a corner from which you will not
easily emerge (at least with the original piece of material).


That's OK, I don't mind time in the shop. And this tool meets a need
that a lot of folks with 70's and 80's Saabs (at least, and probably
more, as they're Girling brakes) share, so maybe I'll just run a batch
of 'em. Once it's set up, making extra ones isn't that much effort.
I could probably unload a dozen of 'em without trying, and if I can make
someone a gift for a buck worth of parts, that is a tool that they'll
use and appreciate, well, that solves several problems. Not looking to
go commercial with it by any means.


At work I see this a lot, although simple mistakes like yours could quickly
cost tens of thousands of dollars to repair as well as threatening the
safety of people on the floor.


Well, sense of perspective and all that...I see the first one as my
prototype, found that the plan didn't meet the needs, and revised the
design, trying to refit my changes to the prototype. Since the new
design needs skills I haven't yet mastered, I'm asking how to do it.


Just my $0.02 worth...


Thanks,
Dave Hinz

If you work in IT, the quick and dirty way is to do a quick actual size CAD plot
and glue the paper to the workpiece as a template. "Good enough" in many cases.