Re: milling circuit boards

Bill, this is what I would suggest for drilling printed circuit
boards with small drills.

I wrote this up before, but will repeat it again for this
appplication. By the way - responses to my post showed that X axis
displacement is not lost with the KDN Tool solution. Just extend
the table in the direction of the offset. You'll see what I mean
when you read the post and visit the KDN Tool website to see the
solution.

Here is my previous write up.
Looking for an affordable high speed spindle for your SIEG X1, X2,
or X3 - or for any bench milling machine? I've been looking for one
for over a year, and finally found one at KDN Tool.

I first looked at the NSK Astro-E 250, which sells for over $2,000.
I can buy 18 of the KDN Tool high speed spindles for the price of
one NSK Astro-E 250. The solutions I found on ebay, the internet,
and in the discussions on Yahoo CAD-CAM-EDM-DRO group, DIY-CNC
group, hf47158toCNC group, Irk-torquemax group, X-Series-Mills
group, and CNCzone came close, but not quite close enough in price,
power, number of collet sizes, reliable collet chuck design for
small end mill shanks, air cooling, variable spindle speed,
commercial designed spindle nose bearings, low spindle run out,
quiet running, and a fairly good duty cycle for long jobs.

I've got it on order - 5,000 to 20,000 rpm with six collets 1/32" to
1/8" - for $170, which includes the mounting bracket for the SIEG
X2. You will find it on www.kdntool.com

Finding the KDN Tool spindle has been quite an adventure. When I
first got into CNC, I determined that I would not be primarily
making conventional machine parts, but would be engraving, and
sculpting plastic, aluminum, and brass. I was surprised to learn
that I would need a high speed spindle, for the same reason that PWB
drilling, and engraving applications demand. The very small diameter
end mills require the high speed. My stock SIEG X2 at 2,500 rpm
needed to be stretched up to 20,000 rpm. No way. I looked at high
speed routers (collet limited to one size), air driven spindle
motors (too noisy), hand pieces for manual grinding, engraving,
sculpting (not enough power or too expensive), and die grinders (one
speed).

The breakthrough for me was when I found an article by Paul
Frederickson and David Grimes of The Precise
Corporation, "Increasing Torque For A High Speed Spindle", in MMS
Online. They published a formula to determine the cutting torque
required, and a Power equation. The cutting torque equation is:
Torque (N-m)= Depth of cut (mm) x Width of cut (mm) x Feed rate ( mm
per tooth ) x Number of teeth per revolution x Machinability Torque
Factor

Machinability Torque Factor – aluminum (0.145), brass (0.29), and
steel (0.435).
I wrote Paul Frederickson and he graciously told me the process for
determining the Feed rate ( mm per tooth ), and told me the factor
for brass. He said that, "a good rule of thumb to start with is 1%
of tool diameter per tooth".

So a 1/32" ( 0.794 mm ) dia end mill, 0.4 mm deep cut, 0.008 mm feed
rate per tooth, and 2 teeth results in Torque ( N-m ) of 0.0007
aluminum, 0.0015 brass, and 0.0022 steel. The power in watts for the
KDN Tool spindle at 20,000 rpm is 1.5 aluminum, 3.0 brass, and 4.6
steel. The KDN Tool spindle has a 100 watt capability. So it will
cut through these speed and feeds like butter. If you've never seen
such high rpms before, it's because it involves the breakthroughs
from High Speed Machining technology. Engraving machines have been
running at those rpms for decades, and so have PWB drills. Small end
mills / drills, small chip loads, and high rpm.

For a 1/8" ( 3.175 mm ) dia end mill, 1.6 mm deep cut, 0.032 mm feed
rate per tooth, and 2 teeth results in Torque (N-m) of 0.046
aluminum, 0.093 brass, and 0.139 steel. The power in watts for the
KDN Tool spindle at 20,000 rpm is 97.2 aluminum, 194.4 brass, and
291.6 steel. So for brass and steel either the depth of cut needs to
be reduced, or the speed needs to be decreased to 10,289 rpm for
brass, and 6,859 rpm for steel.
Power ( kw ) = ( Torque (N-m) x rpm ) / 9,550

When I tried to adapt some of the other solutions to my SIEG X2 I
was stunned to find out that it is a major production to remove
the "Spindle box" casting part # 49 from the "Spindle box seat"
casting part # 63, which rides the column Z axis vee way. Part #49
is bolted through the back of part # 63, and you can't see the bolt
heads, because the are covered by the Z axis column vee way. Aggghhh!

Wait till you see KDN Tool's solution. It's just right for me, I
don't need all of the X axis travel. When you get to the web site
scroll down past "It's Alive", and past "Just Born" to "Our Latest
Innovations" - "High Speed Spindle Attachment For The X2 Mini Mill",
click on CLICK HERE for more information.

If you don't own a CNC Mill and want to get one for small hobby work
or jewelry making take a look at "Just Born" - full CNC conversion
of the Proxxon MF70 micro mill, with stepping motors and full
electronics, and it comes with a Proxxon high speed spindle.

If you are looking at the SIEG X2 then you may want to look at "It's
Alive" XJ-95 alternative to the SIEG X2 - with Y axis travel of 6.3"
vs SIEG X2 3.94". I sometimes wish I had the extra 2.3", oh well it
wasn't around when I was looking.

With the KDN Tool, SIEG X2 High Speed Spindle and adapter, I'll be
able to finally start me sculpting, and engraving.

God bless you.

Bill Perun


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "wdavis364" <wdavis@...>
wrote:

>
> Shopping around for a router, Some router have 1/4 collets and

some

> have 1/4 collets and 1/8 collets. Not knowing much about this,

what

> size collet will I would most likely to be using in milling

circuit

> boards. Will 1/4 collets handle the very small size drill bits

(1/32)?

> Thanks for any advice on this.
> bill
>