Topics

cutting stencils w/router - code #eagle #pcbgcode


John Ferguson
 

I have SheetCAM for use with my Sherline 2000 mill and Chinese 6040 router. SheetCAM costs 110 pounds and is downloadable from their web-site.  It uses DXF files as input and lets you set up your tools, cuts, drills, etc, runs an animation of what the g-code it has generated will do, and then outputs an ngc file (or whatever you want to call it). I've used it a lot to cut single sided boards, as well as ribs and bulkheads for R/C aircraft.

I've found it easier to generate perimeters for my boards using DXF files from AutoCAD since I can precisely control dimensions and mounting hole locations.  When I run a one-sided board, I drill bottom holes, then bottom etch, then cut the perimeter leaving tabs so the board won't come loose when the perimeter cut is complete. I remove them later with a saw.

Now that I'm getting into SMD, I decided to do reflow soldering. I converted a Black and Decker toaster oven to a temp-controlled reflow oven (kit from Whizoo).

Cutting stencils looked like it might be a problem which could be solved by converting the Gerber file to DXF, but that required buying more software.

After the usual google quest, I found https://github.com/SWITCHSCIENCE/eagle-cream-dxf.

This is a very simple ULP which writes a dxf file of the solder pads. You can control the offset so that your bit will cut to the outside perimeter,or increase the offset to make the solder aperture a bit smaller than the pads.  It works perfectly, every time.

It does both top and bottom as separate files.  I load the one I want in SheetCAM, tell SheetCAM tool size and desired Gcode parameters, and generate the Gcode to run my router.

Mind you, I haven't done all of this yet, but should have done one by end of weekend.

I have a fixture for the router which holds a 2 3/4 x 4 board using 6-32 nylon socket head cap screws. I've only cut one double sided board to date and so haven't yet had to deal with alignment. I'm going to add two .250 HDPE dowels to the fixture and cut holes for them ibn the boards as well as for the 6-32 hold-down screws.

The dowels will be at each end of board outside the circuit perimeter and should make it easier to get perfect (?) alignment when i flip board to cut the back.

I have a drill jig for getting the 4 6-32 holes in the correct place on the boards. I will add the .250 holes to this for the alignment dowel holes. I plan to use same jig to cut holes in mylar for stencil and then I will make another fixture for applying solder paste using the stencil.

I have project ready for all this and should have it running by end of weekend.

I'll let you guys know how all of this works out.

John Ferguson


kcress1x@sbcglobal.net
 

Hey John;  How are you physically cutting the stencils?  I picture trying to route thin stainless and envisioning horror scenes.

Kapton tape?  What tool if not a laser?

Thanks,
---Keith---


John Ferguson
 

I'm going to try to cut mylar.  I did some large stencils this way to use for painting morse code oh a carry-on bag for airport identification.  the characters were about an inch high, but the quality of the cuts was very good.  Maybe this won't work this small.

I'll k ow on a couple of days.  stencil doesn;t need to be that durable because I'm onluy going tro make a couple of boards with each one.

john

On 8/21/20 5:02 AM, kcress1x@... wrote:
Hey John;  How are you physically cutting the stencils?  I picture trying to route thin stainless and envisioning horror scenes.

Kapton tape?  What tool if not a laser?

Thanks,
---Keith---


peterg1000
 
Edited

Hi John,

I've cut stencils from 0.2mm mylar with good results.  The 30degree engraving bit I use for the pcb's did a neat job.  It was cutting at 18000rpm, 750mm/min at a depth of 0.25mm, so only one pass was required. I used the "stencil" file that pcb2gcode generates and had added some alignment holes to the board for good measure. Not yet used it in anger, but dont see why it shouldn't do the job OK.

I did try using 0.25mm brass sheet - big mistake!!   I managed to trash a 0.3mm end mill whilst on the second of three passes!!   Expensive lesson.

I've some pics to show if only I could fathom how to get them onto the forum!!

Peter


John Ferguson
 

Hi Peter,

I bought a roll of "Mylar" intended for use in a hobby knife stencil cutter for the luggage stencils. I did try cutting some tiny rectangles with it while I was doing the morse and they just popped out.  I'm turning the alignment dowels for the fixture from HDPE.  They will protrude into the plane, but not the area of the circuit.  I use plastic for this in case of a cnc runaway, not metal to destroy a bit.

john


joeaverage
 

Hi,

' I'm turning the alignment dowels for the fixture from HDPE.'  

I bought a length of 1.5mm bronze welding wire and cut 15mm lengths. They make great
alignment pins, and cheap as chips! 

I use a 1.5mm endmill to mill the perimeter of my boards and so is almost always still in the machine from the
last session. I use it to make the holes required for the alignment pins, no tool changing, loading boring
programs......thirty second to one minute to zero the machine, drill the 0,0 hole, MDI the 69mm (eg) to the
other end of the board and drill the second hole 69,0, alignment holes done....too easy!!

If you have a runaway you'll will almost certainly break a bit whether you impact plastic or metal. The trick is
to avoid runaways.....not trying to make everything soft enough to accommodate such an event.

What makes a ship safe is not the lifeboats, what makes a ship safe is doing the right things making sure the
bastard doesn't sink.....then no need for the lifeboats.

Craig


From: pcbgcode@groups.io <pcbgcode@groups.io> on behalf of John Ferguson via groups.io <jferg977@...>
Sent: Friday, 21 August 2020 11:51 PM
To: pcbgcode@groups.io <pcbgcode@groups.io>
Subject: Re: [pcbgcode] cutting stencils w/router - code #EAGLE #PCBGCODE
 
Hi Peter,

I bought a roll of "Mylar" intended for use in a hobby knife stencil
cutter for the luggage stencils. I did try cutting some tiny rectangles
with it while I was doing the morse and they just popped out.  I'm
turning the alignment dowels for the fixture from HDPE.  They will
protrude into the plane, but not the area of the circuit.  I use plastic
for this in case of a cnc runaway, not metal to destroy a bit.

john






John Ferguson
 

Hi Craig,


You are right, of course about the lifeboats, but.


I'm the guy who yesterday poured a cup of water onto the lid of the coffee-maker.


What material is your board sitting on when you frill through it for the dowels?  Is this material changed for each board?  I use an HDPE fixture which I level with a flycutter when i install it on the 6040 although this is often only once a year if I don't need to use the 6040 for something else.  so this means that I would be re-drilling into the hdpe when I do the alignment holes in a new board, and for me, I would expect the hole in the hdpe to enlarge a little from running a number of boards.


I made an aluminum drill guide to drill the four 6-32 hold-down screw holes and am adding the .25 holes for the alignment dowels in the milling fixture.  I should be able to do this today.


john

On 8/22/20 2:18 AM, joeaverage wrote:
Hi,

'I'mturning the alignment dowels for the fixture from HDPE.'

I bought a length of 1.5mm bronze welding wire and cut 15mm lengths. They make great
alignment pins, and cheap as chips!

I use a 1.5mm endmill to mill the perimeter of my boards and so is almost always still in the machine from the
last session. I use it to make the holes required for the alignment pins, no tool changing, loading boring
programs......thirty second to one minute to zero the machine, drill the 0,0 hole, MDI the 69mm (eg) to the
other end of the board and drill the second hole 69,0, alignment holes done....too easy!!

If you have a runaway you'll will almost certainly break a bit whether you impact plastic or metal. The trick is
to avoid runaways.....not trying to make everything soft enough to accommodate such an event.

What makes a ship safe is not the lifeboats, what makes a ship safe is doing the right things making sure the
bastard doesn't sink.....then no need for the lifeboats.

Craig

------------------------------------------------------------------------
*From:* pcbgcode@groups.io <pcbgcode@groups.io> on behalf of John Ferguson via groups.io <jferg977=aol.com@groups.io>
*Sent:* Friday, 21 August 2020 11:51 PM
*To:* pcbgcode@groups.io <pcbgcode@groups.io>
*Subject:* Re: [pcbgcode] cutting stencils w/router - code #EAGLE #PCBGCODE
Hi Peter,

I bought a roll of "Mylar" intended for use in a hobby knife stencil
cutter for the luggage stencils. I did try cutting some tiny rectangles
with it while I was doing the morse and they just popped out.  I'm
turning the alignment dowels for the fixture from HDPE. They will
protrude into the plane, but not the area of the circuit.  I use plastic
for this in case of a cnc runaway, not metal to destroy a bit.

john






John Ferguson
 

Hi Peter,

I've added the .250 alignment holes to my drill jig such that the pcb blank sits in a recess in the lower piece atop the mylar, then the top is screwed down and the 6-32 clearance holes are drilled through both pcb and mylar, followed by the two .250 alignment holes.  The results using the "CriCut" stencil material look good.  This stencil material has a backing sheet and is sticky with the backing removed.

Mylar thickness alone  is .004 -.0045 and with the paper backing about .008.  I suppose I can just cut a few of these and see how they work, but it would seem that the thickness of the solder paste will wind up a function of the stencil thickness.

.004 seems to be contemplated in some of the notes I found online.  What do you think?

best,

john ferguson

_._,_._,_


joeaverage
 

Hi,
the baseboard is a piece of 10mm Lexan. The holes obviously penetrate the baseboard, as do the hole drills when
drilling through holes and end up with grooves being cut in its surface when milling through the board around its
periphery.

I do not resurface the Lexan base board between PCBs. I use Autoleveller and any small deviation in the height
of the PCB due to warp or bow and/or any variation in height across the baseboard is easily accommodated
by Autoleveller.

I hold the PCB blank down to the baseboard with double sided tape. Eventually the upper surface of the baseboard
becomes that scarred that the tape loses its ability to secure the blank. Then it's necessary to resurface, or easiest replace it.
I typically get about 75 boards from one piece of Lexan. The Lexan itself is bolted to a piece of steel which is in turn 
clamped in the vice which is permanently attached to the table.

The stops on the steel bar mean that I can remove the whole base board/PCB combination from the machine, flip the blank
say, and reinstall it in the machine with no loss of alignment, and all within seconds.....repeatably.

I make that many one-off boards its necessary that I have a process that is fast and accurate, fly cutting the surface of the
base board is just too slow, and with my process not required.

Craig


From: pcbgcode@groups.io <pcbgcode@groups.io> on behalf of John Ferguson via groups.io <jferg977@...>
Sent: Sunday, 23 August 2020 12:03 AM
To: pcbgcode@groups.io <pcbgcode@groups.io>
Subject: Re: [pcbgcode] cutting stencils w/router - code #EAGLE #PCBGCODE
 
Hi Craig,


You are right, of course about the lifeboats, but.


I'm the guy who yesterday poured a cup of water onto the lid of the
coffee-maker.


What material is your board sitting on when you frill through it for the
dowels?  Is this material changed for each board?  I use an HDPE fixture
which I level with a flycutter when i install it on the 6040 although
this is often only once a year if I don't need to use the 6040 for
something else.  so this means that I would be re-drilling into the hdpe
when I do the alignment holes in a new board, and for me, I would expect
the hole in the hdpe to enlarge a little from running a number of boards.


I made an aluminum drill guide to drill the four 6-32 hold-down screw
holes and am adding the .25 holes for the alignment dowels in the
milling fixture.  I should be able to do this today.


john



On 8/22/20 2:18 AM, joeaverage wrote:
> Hi,
>
> 'I'mturning the alignment dowels for the fixture from HDPE.'
>
> I bought a length of 1.5mm bronze welding wire and cut 15mm lengths.
> They make great
> alignment pins, and cheap as chips!
>
> I use a 1.5mm endmill to mill the perimeter of my boards and so is
> almost always still in the machine from the
> last session. I use it to make the holes required for the alignment
> pins, no tool changing, loading boring
> programs......thirty second to one minute to zero the machine, drill
> the 0,0 hole, MDI the 69mm (eg) to the
> other end of the board and drill the second hole 69,0, alignment holes
> done....too easy!!
>
> If you have a runaway you'll will almost certainly break a bit whether
> you impact plastic or metal. The trick is
> to avoid runaways.....not trying to make everything soft enough to
> accommodate such an event.
>
> What makes a ship safe is not the lifeboats, what makes a ship safe is
> doing the right things making sure the
> bastard doesn't sink.....then no need for the lifeboats.
>
> Craig
>
> ------------------------------------------------------------------------
> *From:* pcbgcode@groups.io <pcbgcode@groups.io> on behalf of John
> Ferguson via groups.io <jferg977@...>
> *Sent:* Friday, 21 August 2020 11:51 PM
> *To:* pcbgcode@groups.io <pcbgcode@groups.io>
> *Subject:* Re: [pcbgcode] cutting stencils w/router - code #EAGLE
> #PCBGCODE
> Hi Peter,
>
> I bought a roll of "Mylar" intended for use in a hobby knife stencil
> cutter for the luggage stencils. I did try cutting some tiny rectangles
> with it while I was doing the morse and they just popped out.  I'm
> turning the alignment dowels for the fixture from HDPE. They will
> protrude into the plane, but not the area of the circuit.  I use plastic
> for this in case of a cnc runaway, not metal to destroy a bit.
>
> john
>
>
>
>
>
>





John Ferguson
 

HI Craig,

what machine are you doing this on?

john


joeaverage
 

Hi John,
it's my home made mini CNC mill. Machining extents are 180mm x 180mm x 180mm, cast iron axis
beds, 75 x75 solid steel column, C5 ground ballscrews, 15mm linear rails/cars, 5 phase Vexta steppers/drivers
with 10:1 low lash (<2 arc min) planetary reductions.

Craig


From: pcbgcode@groups.io <pcbgcode@groups.io> on behalf of John Ferguson via groups.io <jferg977@...>
Sent: Sunday, 23 August 2020 8:53 AM
To: pcbgcode@groups.io <pcbgcode@groups.io>
Subject: Re: [pcbgcode] cutting stencils w/router - code #EAGLE #PCBGCODE
 
HI Craig,

what machine are you doing this on?

john






John Ferguson
 

sounds really substantial.

john

On 8/22/20 8:28 PM, joeaverage wrote:
Hi John,
it's my home made mini CNC mill. Machining extents are 180mm x 180mm x 180mm, cast iron axis
beds, 75 x75 solid steel column, C5 ground ballscrews, 15mm linear rails/cars, 5 phase Vexta steppers/drivers
with 10:1 low lash (<2 arc min) planetary reductions.

Craig

------------------------------------------------------------------------
*From:* pcbgcode@groups.io <pcbgcode@groups.io> on behalf of John Ferguson via groups.io <jferg977=aol.com@groups.io>
*Sent:* Sunday, 23 August 2020 8:53 AM
*To:* pcbgcode@groups.io <pcbgcode@groups.io>
*Subject:* Re: [pcbgcode] cutting stencils w/router - code #EAGLE #PCBGCODE
HI Craig,

what machine are you doing this on?

john






joeaverage
 


Hi John,
it started out just as a machine to do PCB's but then I decided I wanted it to be more capable, not larger but
a whole lot more rigid so I could cut metals, steel and stainless in particular.

It is those later materials that determine the required rigidity and what appeared to be a simple decision
turns out to have major ramifications regarding cost/weight/time/energy etc.

Having actually made the machine I find I use it increasingly...and not just for PCB's.

I have started on a new build, much bigger, rigid and powerful. Machine travels 350mm x 350mm x 350mm.
Total weight approx 750kg.

750W Delta B2 series (160,000 cpr encoder) servos driving 32mm diameter C5 ground double-nut THK ballscrews
in 115kg cast iron axis beds on new-old-stock 20mm HSR (by THK) linear rails/cars. The rail/cars/ballscrews/servos I have in hand.
I've had the beds cast already and being machined/ground at the moment. I propose to cast the machine frame in 275kg of
SG iron.....assuming my budget holds out.

I am going to run out of budget to get a new spindle so I will continue to use my existing two spindles, one a 750W 24000 rpm
asynchronous spindle by Mechatron Gmbh and a home made manual change (ER25) spindle based on a recycled 1.8kW Allen Bradley
AC servo and drive, 6Nm continuous at 3500rpm rated make short work of steel.

I really want a 2.5kW 42000rpm with HSK tool changing by Mechatron Gmbh, but at over 5000 Euro it'll have to wait!!!
I might be able to afford a Jianken 3.2kW 24000 rpm with ISO30 toolchanging at about $1500USD.

Craig


From: pcbgcode@groups.io <pcbgcode@groups.io> on behalf of John Ferguson via groups.io <jferg977@...>
Sent: Sunday, 23 August 2020 2:33 PM
To: pcbgcode@groups.io <pcbgcode@groups.io>
Subject: Re: [pcbgcode] cutting stencils w/router - code #EAGLE #PCBGCODE
 
sounds really substantial.

john

On 8/22/20 8:28 PM, joeaverage wrote:
> Hi John,
> it's my home made mini CNC mill. Machining extents are 180mm x 180mm x
> 180mm, cast iron axis
> beds, 75 x75 solid steel column, C5 ground ballscrews, 15mm linear
> rails/cars, 5 phase Vexta steppers/drivers
> with 10:1 low lash (<2 arc min) planetary reductions.
>
> Craig
>
> ------------------------------------------------------------------------
> *From:* pcbgcode@groups.io <pcbgcode@groups.io> on behalf of John
> Ferguson via groups.io <jferg977@...>
> *Sent:* Sunday, 23 August 2020 8:53 AM
> *To:* pcbgcode@groups.io <pcbgcode@groups.io>
> *Subject:* Re: [pcbgcode] cutting stencils w/router - code #EAGLE
> #PCBGCODE
> HI Craig,
>
> what machine are you doing this on?
>
> john
>
>
>
>
>
>




sdmonaco
 

Hi John,

I don't do a lot of surface mount but when I do I found a useful way to generate solder mask stencils on my CNC machine.  What I do is hide all layers except for 17 (pads) in eagle.  I then export the file in png format (default for eagle 5.11).  I then use Convertio — File Converter to convert the file to svg format which is the input format for Easel the online CAD program that I use.  Using the Easel input porting function I select the cut depth and outside shape path.  To generate my g-code I select machine then advanced settings.  Click on generate g-code and it produces mach3 compatible code.

Hope that helps!

Sam





Jerry Lee Marcel
 

On Mon, Aug 24, 2020 at 09:49 PM, sdmonaco wrote:
What I do is hide all layers except for 17 (pads) in eagle. 
Actually you should use the tstop or bstop layers, where the islands are usually slightly larger than the pads.