Hi,
The 60 degree bits mill wider the deeper you let them mill. I
use the Think&Tinker 60 degree copy of the T-Tech. Each bit can mill a
4" X 6" board with lots of traces. The speed rate is .0004" to .0006"
of feed rate for every revolution of the tool. So at 12,000 RPM your
feedrate would be 12,000 X .0005 (Middle number) or a feedrate of 6"
per minute.(Using a Dremel) Rough edges form after the tool is running
for 10 minutes or so. After the board milled sand it with fine emery.
The use on of the toothbushes with steel bristles to clean the tracks.
I have milled hundreds of boards and sold them. I use a homemade Brute
machine that I sell plans for. You only have to isolate the tracks you
don't have to remove all the other copper. In my designs I use the
remaining copper for ground. This allows me to use single sided boards
with just a few jumpers.
John www.kleinbauer.com
--- In Homebrew_PCBs@yahoogroups.com, "Pete" <pegood@i...> wrote:
>
> Hi, Group! I teach at a university which recently bought a T-Tech
> Quick Circuit 5000 for student project fabrication. I'm trying to
> mill a TQFP-100 footprint, which has 0.22 mm (nominal) wide pads
> (approx. 8.7 mils) on 0.5 mm centers. This means removing a 0.28 mm
> (11 mil) wide space between pads, but IsoPRO tells me it needs to
> use a 6-mil tool The reason seems to be that it cuts twice between
> pads, and I wonder if that's really necessary.
>
> I've made one attempt so far, using a T1 pointed tool which has a 60-
> degree point and which T-Tech says will mill 8-12 mil paths. I set
> it for a depth of about 7 mils, which should have made the cut width
> about 5.4 mils on a 1-oz copper board, if I'm not mistaken. I set
> the depth by carefully lowering the tool until it just touches the
> copper surface, then counting clicks. The manual says each click
> lowers the tool by 0.4 mil, but it seems as it may actualy lower it
> a bit more than that.
>
> The results of my first cut were not acceptable. Most of the pads
> appeared to be narrower than 8.7 mils, and pretty ragged. some 10-
> mill traces also looked pretty chewed up.
>
> I'm going to try the following:
>
> 1) run the spindle at top speed (24,000 rpm)
>
> 2) Slow down the rate of head movement
>
> 3) use 1/2 oz copper instead of 1 oz.
>
> 4) use a smaller pointed tool, the T-4 which is supposed to be good
> down to 4 mils.
>
> What is your opinion of these three steps? Am I going in the right
> direction? Is there a way to keep the machine from cutting twice
> between pads, and would that be a good idea?
>
> Thanks,
>
> Pete Goodmann
> Assistant Professor,
> Electrical and Computer Engineering Technology
> Indiana-Purdue University Fort Wayne (IPFW)
>