Milling / drilling PC boards on home shop CNC equipment.
Posted by
Larry Edington
on 2001-07-23 14:18:35 UTC
I've been using my 2' x 3' CNC router table to make PC boards for years. It
uses McMaster 5/8 ball screws and nuts. It's plenty accurate enough for
drilling and milling PC boards. You don't need micron accuracy to do
standard 10 mil trace / 10 mill spacing PC boards. Make the traces and
spaces larger and your accuracy requirements go down further.
Dremels are also good enough. I've used the cheap ones up to the new digital
speed control model as well as the Dremel flex shaft. I have seen NO issues
concerning Dremel bearings causing routing or drilling errors.
I do prefer the air grinders. I paid $50 for mine. It looks like a Dremel
flex shaft hand tool. I've got a large compressor so it's no problem to run
it for long cutting sessions. My next favorite is the digital control
version of the Dremel. You want the highest speed you can get for the
cleanest cut.
The most important thing for isolation milling is a floating head. You want
the head to move down and put pressure on the PC board blank to help keep it
flat. Or to at least contact the board to ensure the bit penetrates into the
blank the same amount each time.
For this I use a small slide that the lead screw has been removed and a
return spring is attached. I mount this slide to my normal Z axis slide. The
router head ( a dremel or air grinder ) is attached to the small slide. The
small slide has a 'foot' that is attached with a threaded screw. The bottom
of the foot has a Teflon pad glued to it. When the Z axis moves down, the
foot contacts the PC board and does not allow the bit to penetrate any
further. More downward movement of the Z axis just results in the upward
movement of the small spring loaded slide. There are many ways to accomplish
this. You can do this fancy or simple.
You adjust trace isolation width by adjusting the depth of the bit via the
screw on the foot. Even if your PC board is not flat the floating head will
ensure an even depth of cut.
Get drill bits that have the plastic depth collars on them or add them with
1/8 ID wheel collars from a local hobby shop. Build a fixture you can drop a
new bit into and then place the wheel collar on the bit. This way when you
change tools, they are all the same distance from the dremel or grinder's
chuck and your depths remain constant.
Think & Tinker sells 60 degree carbide isolation bits. That's what I use. I
set my depth for a .010 inch wide isolation path and set the board clearance
rules accordingly. For wider isolation I use .032 carbide end mills. I don't
use these often.
Another option is an array of holes drilled for a vacuum hold down plate.
This would hold the PC board as flat as your MDF surface. But would be
dependent on perfect axis alignment and perfect flatness of your table. The
floating head eliminates a lot of potential errors.
The perfect solution would be a floating head with vacuum hold down. That
way you can eliminate the double sided tape.
Side to side alignment is no problem.
After you have finished laying out the board, place two .125 holes exactly
in the center of the board, but one at each end of the board.
Cad tools make this easy. The holes should be placed left to right exactly
the same distance from the center of the board horizontally and in the exact
Y axis centerline vertically.
Order your excellon drill file so that these two 1/8 inch holes are drilled
first.
You'll need something you can drill into under the board. I use 1/2" MDF
stuck to the aluminum surface of my router table with double sided tape. I
also stick the PC board blank down to the MDF with double sided tape.
Your first two holes should drill 1/2 way down into the MDF after going
through the copper clad blank. Now insert two 1/8" pins ( old broken bits
are perfect ) into these holes. These are your locator pins. Make sure they
don't project up above the PC blank far enough to allow the drill or router
bits to hit it or your depth foot to contact a locating pin.
Now drill the board and mill the top side's isolation paths.
If your drill speed is high enough, you won't need centering holes drilled
in the board blank. The carbide bits won't wander all that much before they
break. If they are sharp they will go right into the copper dead center
perfect every time.
Next flip the board left to right and place back on the pins. By the way,
the gerber file for your bottom side must be mirrored for this to work.
Now mill your bottom side which is now facing up.
It's as easy as that. It'll take some work getting your cad software
procedures figured out and getting the the hardware setup on your router or
mill to do this. The floating head is the hardest part.
Print some gerber files out on transparency plastic to get the board
flipping figured out.
Once you are done you can go from board design to a finished board in under
an hour. That beats a 3 day wait from the board shop.
Kellycam now has Gerber isolation paths working in his cnc software. It
works fine for generating the isolation paths but Master5Cnc is much better
for running the stepper motors to cut the paths. You won't likely find an
isolation program for $125 anywhere else. Isolator Pro from T-Tech is $1995.
Ztrace which in my opinion is a worthless piece of junk is $320. Eagle PC
layout software generates isolation paths as does a couple of programs from
Germany. Kellycam is the cheapest simplest solution I've seen so far.
I use Protel and Pads PCB layout software. This is what works for me. Your
mileage may vary.
later,
Larry E.
uses McMaster 5/8 ball screws and nuts. It's plenty accurate enough for
drilling and milling PC boards. You don't need micron accuracy to do
standard 10 mil trace / 10 mill spacing PC boards. Make the traces and
spaces larger and your accuracy requirements go down further.
Dremels are also good enough. I've used the cheap ones up to the new digital
speed control model as well as the Dremel flex shaft. I have seen NO issues
concerning Dremel bearings causing routing or drilling errors.
I do prefer the air grinders. I paid $50 for mine. It looks like a Dremel
flex shaft hand tool. I've got a large compressor so it's no problem to run
it for long cutting sessions. My next favorite is the digital control
version of the Dremel. You want the highest speed you can get for the
cleanest cut.
The most important thing for isolation milling is a floating head. You want
the head to move down and put pressure on the PC board blank to help keep it
flat. Or to at least contact the board to ensure the bit penetrates into the
blank the same amount each time.
For this I use a small slide that the lead screw has been removed and a
return spring is attached. I mount this slide to my normal Z axis slide. The
router head ( a dremel or air grinder ) is attached to the small slide. The
small slide has a 'foot' that is attached with a threaded screw. The bottom
of the foot has a Teflon pad glued to it. When the Z axis moves down, the
foot contacts the PC board and does not allow the bit to penetrate any
further. More downward movement of the Z axis just results in the upward
movement of the small spring loaded slide. There are many ways to accomplish
this. You can do this fancy or simple.
You adjust trace isolation width by adjusting the depth of the bit via the
screw on the foot. Even if your PC board is not flat the floating head will
ensure an even depth of cut.
Get drill bits that have the plastic depth collars on them or add them with
1/8 ID wheel collars from a local hobby shop. Build a fixture you can drop a
new bit into and then place the wheel collar on the bit. This way when you
change tools, they are all the same distance from the dremel or grinder's
chuck and your depths remain constant.
Think & Tinker sells 60 degree carbide isolation bits. That's what I use. I
set my depth for a .010 inch wide isolation path and set the board clearance
rules accordingly. For wider isolation I use .032 carbide end mills. I don't
use these often.
Another option is an array of holes drilled for a vacuum hold down plate.
This would hold the PC board as flat as your MDF surface. But would be
dependent on perfect axis alignment and perfect flatness of your table. The
floating head eliminates a lot of potential errors.
The perfect solution would be a floating head with vacuum hold down. That
way you can eliminate the double sided tape.
Side to side alignment is no problem.
After you have finished laying out the board, place two .125 holes exactly
in the center of the board, but one at each end of the board.
Cad tools make this easy. The holes should be placed left to right exactly
the same distance from the center of the board horizontally and in the exact
Y axis centerline vertically.
Order your excellon drill file so that these two 1/8 inch holes are drilled
first.
You'll need something you can drill into under the board. I use 1/2" MDF
stuck to the aluminum surface of my router table with double sided tape. I
also stick the PC board blank down to the MDF with double sided tape.
Your first two holes should drill 1/2 way down into the MDF after going
through the copper clad blank. Now insert two 1/8" pins ( old broken bits
are perfect ) into these holes. These are your locator pins. Make sure they
don't project up above the PC blank far enough to allow the drill or router
bits to hit it or your depth foot to contact a locating pin.
Now drill the board and mill the top side's isolation paths.
If your drill speed is high enough, you won't need centering holes drilled
in the board blank. The carbide bits won't wander all that much before they
break. If they are sharp they will go right into the copper dead center
perfect every time.
Next flip the board left to right and place back on the pins. By the way,
the gerber file for your bottom side must be mirrored for this to work.
Now mill your bottom side which is now facing up.
It's as easy as that. It'll take some work getting your cad software
procedures figured out and getting the the hardware setup on your router or
mill to do this. The floating head is the hardest part.
Print some gerber files out on transparency plastic to get the board
flipping figured out.
Once you are done you can go from board design to a finished board in under
an hour. That beats a 3 day wait from the board shop.
Kellycam now has Gerber isolation paths working in his cnc software. It
works fine for generating the isolation paths but Master5Cnc is much better
for running the stepper motors to cut the paths. You won't likely find an
isolation program for $125 anywhere else. Isolator Pro from T-Tech is $1995.
Ztrace which in my opinion is a worthless piece of junk is $320. Eagle PC
layout software generates isolation paths as does a couple of programs from
Germany. Kellycam is the cheapest simplest solution I've seen so far.
I use Protel and Pads PCB layout software. This is what works for me. Your
mileage may vary.
later,
Larry E.
----- Original Message -----
From: "Alan Marconett KM6VV" <KM6VV@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, July 23, 2001 12:24 PM
Subject: Re: [CAD_CAM_EDM_DRO] Leadscrews, PCB router experiment
> Hi Jon,
>
> Yes, I take your point. I'm hoping for simple PCB's, designed with
> "relaxed rules", and less stringent requirements. Side alignment WILL
> be a problem. Then again, it can be a learning experience!
>
> Alan KM6VV
>
>
> Jon Elson wrote:
> >
> > Alan Marconett KM6VV wrote:
> >
> > > Hi Jon,
> > >
> > > I have a 3/8" slab of aluminum, that might have to do for my base. I
> > > want to do more then drilling, I want to be able to mill traces as
> > > well. I'm planing on using a dremel tool.
> >
> > We've gone around with this a few times. I don't think the standard
> > Dremel moto-tool spindle is good enough for PC board drilling.
> > The problem is that you have to hit the 'target' quite accurately, or
the
> > hole will cut through the side of the pad, rather than through the
> > middle, leaving a complete ring of copper around the hole. I even
> > have problems on my system, with the air bearing spindle motor,
> > high precision ground ballscrews, encoders delivering resolution
> > of .00005" (yes that's 50 uInches) and the physical stability of a
> > Bridgeport. If you mill the board, then the holes should at least
> > line up with the copper, but you still have to deal with alignment on
> > the other side, if you do 2-sided boards.
> >
> > Jon
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
> > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> >
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> > List Manager
> >
> >
> >
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