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ksangeelee
08-06-2010, 10:31 PM
Hi,

I've decided that I need a CNC machine to mill and drill double-sided PCBs (0.4mm track size would be ok). I'll also want to cut fascias in FR4, mill custom PCB mountings (POM or ABS), and engrave casing for prototyping and maybe initial low-volume manufacturing.

The best combination I can find for my money is a Merchant Dice A4 ballscrew machine kit with 800W Kress spindle, combined with Motion Control 3-Axis Driver Kit-1 from Zapp Ltd (3Nm SY60STH86-3008 motors, PM752 drivers), and Mach3. This appears to be adequate and upgradeable, and will cost me around 1500.

I'm just looking for a sanity-check. Am I over-optimistic in thinking that a CNC machine costing that amount can give the repeatability and linearity to do double sided PCBs? (layer misalignment over 0.1mm can ruin the board)

Are there better options for similar amounts of money that I've missed? I'd prefer to buy from UK suppliers. All advice and opinions gratefully received.

Regards,

Kevin

irving2008
08-06-2010, 10:45 PM
Firstly, welcome.

A good CNC machine should be able to hold an accuracy much better than 0.1mm but you'l need to work on the ballscrew nuts to get down to low levels of backlash to get the repeatability you need, but its certainly feasible The trick with double sided anything is the jig you need to ensure the part is exactly in the right place when flipped. The simple solution is a hard edge to push the board against, the difficulty is getting repeatability as the slightest dirt or swarf will give an offset. The best solution is a 2-part frame into which the board is placed which has locating pins that guarantee the registration from either side. This could be made from engineering plastics (delrin, HDPE) on the machine itself.

I cant comment on the MD A4 kit as I've never seen one, however I have heard some 'less than complimentary' views. I'd have a think about the Kress spindle, it will certainly do, but runout can be an issue. I beleive there are some simple bearing upgrades to improve it. The 3Nm motors are a bit overkill for an A4 ballscrew machine but will serve for a bigger machine later.

ksangeelee
09-06-2010, 12:10 AM
Hi Irving,

Thanks for your welcome and reply.

I had in my mind that I'd use two holes on the board for registration, either drilled just for that purpose, or possibly making use of diagonally opposite pads. However, I expect the custom holder with registration pins will be a much better option. I'm assuming that CAM software such as Mach3 will naturally handle the recalculation of relative co-ordinates.

Spindle runout may be an issue - it would seem daft going to some lengths for repeatability just to consistently gouge furrows out of the board. The Kress datasheets don't specify runout, and I can't find any reference to people who have measured it. Can you suggest an entry-level spindle that might do as an alternative?

I've also found it difficult to find any other UK manufacturers of entry-level XYZ tables. I've read mixed opinions on the Merchant Dice kit, but that mix includes positive reports too. If I didn't need relatively accurate PCB tracks, I probably wouldn't think so hard about this - nothing else I need requires much precision. I just want to be sure I don't have copper remaining at one end of an isolation path, or wiggly diagonal tracks, for example.

I'm realistic about what I might expect from a 1500 machine - as long as I can get milled and drilled double-sided boards that are as good as I get with single-sided toner-transfer and manual drilling, then I'd be more than happy.

Robin Hewitt
09-06-2010, 12:59 AM
I'm just looking for a sanity-check.

Okay, sanity check... 1500 would buy you fifty 160x100mm DS, PTH, gold plated PCB's with 2 resist and legend masks, all different and guillotined to size from Olimex with no alignment problems to worry about.

Presume you want it to do something else or think it looks like fun :naughty:

Run out in the chuck is not a problem because it still cuts round but oversize. Simply lie to Mach about how big the tool is to compensate.

leadinglights
09-06-2010, 09:46 AM
Look carefully at what you want it to do. If you want to do any production PCBs - even for very short runs, then pCB milling is a non starter. If you are doing prototypes and you can afford to wait a week or two, then again it isn't worth it. If you are doing prototyping at low speds it is better to use Veroboard or similar techinques.

Where PCB milling scores is where you need a prototype within hours, or perhaps days but the components are not available in non-SMT, or where you want to investigate high frequency layouts - such as switch mode PSUs, BLDC controllers etc..

ksangeelee
09-06-2010, 10:15 AM
Okay, sanity check... 1500 would buy you fifty 160x100mm DS, PTH, gold plated PCB's with 2 resist and legend masks, all different and guillotined to size from Olimex with no alignment problems to worry about.

Twenty-five boards when you add express shipping, but still respectable. Turnaround time is one reason that I chose not to use a fab-house - I'd need to allow at least one week per iteration, which I could otherwise do in a morning.


Presume you want it to do something else or think it looks like fun :naughty: Both! I'll confess there is something a little 'Christmas Morning' about CNC machines.

John S
09-06-2010, 10:40 AM
2259

This was done on a KX1 mill as a test for someone who wanted to do roughly the same prototype boards with no lead time.

Not knowing sod all about PCB's, only JCB's, I asked for a file, this was code generated direct from one of the PCB software packages.
On the left is the code as sent but the tool depth was too deep so it was edited and the one on the right run again.
You may recognised the pad layouts but as scale the holes which were in the scrap sample board are 3mm.

A Krees spindle will cut these tracks with no problems, no bearing update needed, I do finer work than this with no problems.

.

ksangeelee
09-06-2010, 11:26 AM
2259

This was done on a KX1 mill as a test for someone who wanted to do roughly the same prototype boards with no lead time. ..... You may recognised the pad layouts but as scale the holes which were in the scrap sample board are 3mm.

Looks like 2.54mm pitch through-hole, and 1.27mm SMD. The job on the right is close to what I need. Do you happen to remember what tool you used to mill this?

Just looked at KX1 specs - shame about the exchange-rate, because that would otherwise have been an option for me. The stated linearity and repeatability are well within my needs, and 180mm z-axis travel would be really useful.

John S
09-06-2010, 12:56 PM
Just a vee shaped engraving tool with 30 degrees included angle, good for PCB's because the less you go the finer the cut and it's not so prone to breaking like a 10 thou cutter.

leadinglights
09-06-2010, 02:35 PM
I tried standard engraving tools from suppliers in U.K., Poland and China in various angles from 30 degrees to 60 degrees, but were unable to get the 0.25mm traces and 0.25mm isolation that I wanted. 60 degrees was better than 30 degrees - cleaner edges and fewer burrs.

I came across spade mills on CNCZONE a couple of years ago and have not used anything else since - there is little burring at 20,000RPM and the life is about twice the standard type. I can easily get 0.25/0.25mm and have got 0.17mm track and 0.13mm isolation in trials - but not used on working PCB.

You can get them now from :- http://www.drewtronics.net/

Mike

ksangeelee
09-06-2010, 03:46 PM
Look carefully at what you want it to do. If you want to do any production PCBs - even for very short runs, then pCB milling is a non starter. If you are doing prototypes and you can afford to wait a week or two, then again it isn't worth it. If you are doing prototyping at low speds it is better to use Veroboard or similar techinques.

I want to produce prototypes and one-off units for pilot installations. Thereafter, a fab shop will make the boards in larger quantities. Waiting even a week per iteration could easily become difficult to plan for. Leaving aside design-errors and oversights, even a change in the enclosure choice, or the fascia layout, could require moving PCB connectors or mounting holes.

The boards typically incorporate RF comms and ADCs, so breadboards/veroboard only go so far (though this is where I always begin).

ksangeelee
09-06-2010, 04:06 PM
Hi Mike,


I came across spade mills on CNCZONE a couple of years ago and have not used anything else since - there is little burring at 20,000RPM and the life is about twice the standard type. I can easily get 0.25/0.25mm and have got 0.17mm track and 0.13mm isolation in trials - but not used on working PCB.

Thanks for the info, that looks like what I need - the milled boards shown are quite impressive. Can I ask why (in your previous post) you're reticent to advocate milling boards for prototypes, given that you can get 0.25mm tracks and better?

Kevin

leadinglights
09-06-2010, 05:19 PM
Hi Kevin,

I am not so much reticent as a bit choosy where I would use it; my main problem is that it takes quite a large investment in time. Boards to be milled have to be planned for in the layout stage and there is an extra step in converting Gerber files to G code (Coppercam or similar). The board then has to be milled - which normally has problems such as short circuits caused by copper swarf (not to mention operator error), as well as the extra steps of fitting shorting pins to replace the vias. The completed board has to be treated with extra care as there is no solder resist.

A simple PCB may take 4 hours of your time to make - compared with about 40 from PCB-Pool. Except for the time from dispatch to recieving the goods the commercial process is cheaper and better in every way.

Having said that, I routinely use PCB milling if it is for my hobby - and would at least consider using it if time is particularly critical.

Mike

saxonhawthorn
09-03-2012, 03:11 PM
I came across spade mills on CNCZONE a couple of years ago and have not used anything else since - there is little burring at 20,000RPM and the life is about twice the standard type. I can easily get 0.25/0.25mm....

Thank you for this helpful information Mike. I'm about to start making PCBs again after a break of a few years and all my past experience was wet and messy. What you have written MAY just persuade me to move across into using a CNC mill to make my boards instead of ferric chloride. But... in view of the cost of making a decent mill, can I ask if you have had any reason to change your advice since you wrote the above? It's the LQFP100 chips that bother me. I know I can etch them chemically; I'm just not sure whether I could trust a milling process to cut all those tiny 0.25mm inter-track slots repeatably? And also, roughly how many hours or metres do you get out of a spade mill before you bin it? (hand-waving figure good enough). Thanks in advance for any advice.

Regards,
Ian

leadinglights
10-03-2012, 10:45 PM
Hi Ian,

Since I wrote that I have had occasion to make a PCB with very fine gaps and tracks. In this case it was a 10 pin DNF switch mode regulator IC with pads on 0.4mm pitch - the little Proxxon acquited itself admirably, although I did fit long springs to bias the X and Y axis and reduce backlash.

One point to note with the spade bits is that the 60 degree angle means that the cut width is very depth sensitive, you should ensure that the bed that you mount the PCB on is as true as you can get it or the variation in the cut width may make the job impossible. Outside of that, I think a LPFP100 should not be a problem.

As far as bit life goes, I could no more than hazard a guess that it is about twice the life of the common 30 degree engraving bits (sucks end of thumb possibly 10 meters with 0.2mm width)

Mike

saxonhawthorn
11-03-2012, 12:42 PM
Hi Mike,

That's very encouraging to hear. Many thanks for your quick and helpful reply.

I was thinking more in terms of building a 3-axis mill from scratch, but I must confess that finding a spindle with a runout spec suficiently good has been a problem. The Kress spec doesn't look as though it quite cuts the mustard for fine PCB work (unless somebody here has contrary experience?) In PCB we seem to be working at the bleeding edge of what's achievable. I have a cheap and Chinky 3.5" lathe and was thinking of having to make my own spindle.

But I confess I simply hadn't thought of using a Proxxon mill. It's true that their stuff is solidly made, and if it's as good as you say it may be a route to go. Which model do you have? (Have you posted piccys anywhere? It's always stimulating to gawp at other peoples' kit. :eek: ) I had set myself a design goal of milling Eurocard size boards (160 mm x 100 mm) but more from habit than actual need. Most of the PCBs I actually deal with these days are much smaller than that and could probably be milled at least four-up on a Eurocard.

Regards,

Ian

HankMcSpank
11-03-2012, 01:14 PM
I've spent the guts a few a months trying to get consistent pcb milling for reasonably fine pitch SMD....I actually only go need down to SOT23-6 compoinent size (which is about 0.6mm space between pins). I've got there in the end, but not without an astonishing amount of hair pulling & frustration.

Here's my general musings...

1. Level the machine bed - if you don't have a level bed, then you are up against it from the start - forget a V cutter unless your bed is level (in which case go with a small endmill instead)

2. Choose the right V bit for the board - for example if you intend going really fine - it likely has to be 20 degree V bit....careful though, these tips snap like buggery & are expensive!

3. All V bits are depth sensitive - the wider the angle, the more robust the tip is(less prone to snappig the tip), but with wider angle V bit, just taking the bit down a little in depth really make the milled cut a lot wider - personally I'd never now use anything wider angle tha a 45 deg.

4. Calibration, calibration calibration - eliminate backlash from your Z - I knocked up a simple g-code file to raise/lower the Z axis about 30 times....and made sure at the end of it my dial meter still showed 0.01mm or less error after 30 Z ascents/descents. Also, missed steps are the scourge of pcb milling (where incredible amounts of accuracy are needed - so make sure that your axis consistently move the distance they are meant to ie use a dial meter again)

5. If you are going really fine pitch, then seriously consider some form of Z autoleveller program- (this is where you first probe your copper board to pick up the height irreguarities (even if your bed is level, just clamping the copper down will raise the board slightly in the middle region) ...and then apply the probed Z inconsistencies into your g-code Z info prior to the cutting run. You can get a free autoleveller in pcb-gcode (an eagle plugin), but I went the way of CNC-USB which has this feature integrated (it's called warp - http://www.youtube.com/watch?v=0jGY92S8bxM )

6. Use a CAM program that imports gerbers...then you can really fine tune your V bit tip offset to suit...and see the projected cut before you go near the machine itself . I use CAMBAM (so create pcb in eagle ,export tracks as a gerber, import gerber into Cambam...group select all the pcb track outlines in there, tweak your machining parameters to suit....some say you should use an engrave mop for milling the tracks ...this is wrong...if you do, there is no offset applied (it cuts along the pcb track outlin line...and therefore you lose PCB track width = the radius width of the V tip at the actual cut depth ...you need to select a 'profile' cut (which then allows you to apply an offset away from te pcb outline- you want the maximum offset possible but without fear of then cutting into a neighbour pad when milling your finest pads - you can see the visulaizations within cambam - the trial is free )

it's been a long journey, but worth it....being able to knock out a consistently good proto pcb in short order...epanelled, mount holes in the right places etc (vs chemical etching) is a major win for me.

saxonhawthorn
11-03-2012, 01:58 PM
Hank, that's very helpful. Z-axis resolution and accuracy have been bugging me a lot for the very reason you say. In a previous incarnation I was Chief Calibration Engineer of an MoD Main Contractor in gas detection where we cut big gas-tight threads in some of the nastiest stainless steels I never want to encounter again, and I don't believe ANY instrumentation - period! (I sometimes had to go back in after hours and check the measurements my staff were making during the day, which was a good test of the repeatability of the kit as well as the competence of the staff. Both passed I'm glad to say). We used a Mitutoyo Low Voltage Differential Transformer (LVDT) probe for examining the wear on thread gauges, and it was very sensitive and repeatable, so I have had it in mind to use LVDTs on each axis for absolute positioning, and to incorporate their signals into the controller before each cut.

Yes <sigh> I was afraid of narrow carbide bits snapping. I think I'd rather spend the money on getting good positioning accuracy in the first place, but in real life some wastage can't be avoided.

I hadn't even thought of missed steps being a problem! But as I'm actually a software engineer rather than a mechanical man I should be able to write some code which eliminates missed steps. And again, the feedback of an LVDT on each axis should help to eliminate that problem. And measuring the warp before each cut is a useful thought. Thank you.

Your point 6 is also a good one, and taken.

Like many of us in engineering, I'm a perfectionist; which means I go through many iterations of software and prototype PCBs before I'm satisfied that I've got something I can release. That's the main reason for needing to do PCBs myself rather than just sending the artwork off to Olimex or whoever, and I must have a system which turns out reliable boards quickly. I'm grateful for the benefit of the experience of all here.

Ian

russell
11-03-2012, 05:47 PM
If you want really quick prototype PCBs why not use the Press-n-Peel / etching method. You can easily get 10 thou tracks and spaces. You can then use cnc to drill the holes from your Excellon files.

Russell.

HankMcSpank
11-03-2012, 06:11 PM
If you want really quick prototype PCBs why not use the Press-n-Peel / etching method. You can easily get 10 thou tracks and spaces. You can then use cnc to drill the holes from your Excellon files.


Well I look at it like this ...I already have a CNC machine - and CNC machines can mill PCBs, so better to have it earns its keep than shell out for press n' peel (that stuff isn't particularly cheap!). But actually this is more about saving time and getting consistent results more than saving a couple of quid.

What I found with chemical etching...it was a real chore, massive time sump, got erratic results (unless you use fresh batches of developer & ferric chloride each time - but then that starts getting expensive) then there's the temperature variations....make a chemically etched PCB on a cold day...you'll get differing results vs a chemically etched pcb on a warm day (my point being lots of variables) & fraught with problem getting the alignment right (oh what joy to see 1.5 hours chemically ecthing wasted because the CNC machine wasn't aligned 'quite' right when drilling holes out or cutting the board outline) ...and wait there a minute, if we are going to use the CNC to drill out the holes, we may as well get it to isolate the tracks in the first place!

Your mileage may vary, but I need rather intricate shaped PCBs...and therefore for me at least it's better just to run the whole sequence on the machine...at least this way you can be assured of everything being aligned.

My next target now is - after the tracks have been milled on my CNC machine - to get my CNC machine to dispense solder paste on all the track pads (I have all the 'process elements' in place...I'm just waiting on some solder paste of the right viscousity to arrive) ....another huge time win (because for protos, it's not worth making a solder stencil, and it's a real chore dispensing solder paste by hand each time!)

saxonhawthorn
11-03-2012, 06:17 PM
Russel, thanks for the suggestion. I have admittedly never tried Press-n-Peel, but as far as I can see it goes most of the way back to chemical etching. It still needs ferric chloride (which has ruined more pairs of jeans than I care to remember) and still needs the intermediate stage of plotting/printing artwork. The only process it seems to avoid is UV exposure, which is actually the least messy part of what I do now, and not a problem anyway.

And I'm not sure that double-sided image location would not be tricky with Press-n-Peel. Double-sided is admittedly tricky with any system, but at least with both UV and milling it's possible to get precision - with care!

Milling appeals to me on two counts (well, three if you include having a new toy to play with) - (1) Not having to worry about slippage in a laser printer, or less-than-black inkjet printing, and of course (2) No messy bubble tanks. Not to mention the accumulated guilt of years pouring spent ferric chloride down the drain ("What me, gov? Nah, it's ketchup.").

Ian

saxonhawthorn
11-03-2012, 06:32 PM
Hank, you're right on all counts. Fresh developer each day is a must (prepared the night before to stabilise), though I've found I can usually go on using ferric chloride until it's spent. But temperature control is very critical, and it took me a lot of experimentation to get it right. I was making boards for production then, not just prototyping, and scrap costs money.

Another nice thing about milling has just ocured to me: there's a big price difference between plain copper boards and pre-sprayed photo-sensitive boards (NB to anybody thinking of doing it: use Fotoboard 2. Don't even think about spraying your own photo-sensitive stuff on. You've got to spray it evenly with no missed bits, bake it dry at the right temperature, and never let it see daylight until you use it. You really don't want to go there).

A pick-and-place m/c for SMD is next on my list after PCB-making. Sounds as though you and I are travelling the same road. Are you using an "Archimedes Screw" device to dispense solder?

Ian

HankMcSpank
11-03-2012, 08:28 PM
Another nice thing about milling has just ocured to me: there's a big price difference between plain copper boards and pre-sprayed photo-sensitive boards (NB to anybody thinking of doing it: use Fotoboard 2. Don't even think about spraying your own photo-sensitive stuff on. You've got to spray it evenly with no missed bits, bake it dry at the right temperature, and never let it see daylight until you use it. You really don't want to go there).


I use from SRBP copper boards (not so much nasty glass fibre dust in the air, they're easier on the tools & they're fine for protos)...

http://www.rapidonline.com/Tools-Equipment/Low-cost-copper-clad-board-32634/?sid=9b9e283b-5737-4305-bd1f-e2e6ffd711d1

....for 100pcs it works out about 36p inc vat & delivery for a 6" x 4 board" (cheapest I know of but I'm happy to be corrected!) ....the cheapest fotoboard of the same size I was ever able to source worked out at about 2.00 delivered per board, so yes a lot cheaper! (and the board I'm milling with are so cheap that it doesn't ruin your day if you screw up!)

re your comment...


2. Don't even think about spraying your own photo-sensitive stuff on. You've got to spray it evenly with no missed bits, bake it dry at the right temperature, and never let it see daylight until you use it. You really don't want to go there).



been there done that...bought some foto spray from Farnell & was appalled that they could even sell this stuff - complained to Farnell "This stuff truly sucks & you should remove it from your product range asap" ...they re-credited me for it!

Still got the can - doub't I'll ever use it....it's twatful stuff.

saxonhawthorn
11-03-2012, 09:12 PM
Still got the can - doub't I'll ever use it....it's twatful stuff.

Maybe it works as fly spray?

I'd be interested in details of your solder paste dispenser (apologies if you have already posted them somewhere - I've been away from this site for quite a while). What air pressure do you use? Is the amount dispensed repeatably accurate? I admit to a prejudice against pneumatic control of such small amounts of thick and gooey (and expensive if lead-free) stuff, but I'd be very happy to be proved wrong.

Ian

saxonhawthorn
12-03-2012, 02:56 PM
Grateful thanks to Mike for steering me towards a Proxxon mill. Their new KT150 compound table is the perfect size for milling my PCBs, and looks sturdy enough to hold the work properly. I have settled on:- a KT150 table, BFB 2000 Mill/Drill Stand, and BFW 40/E Mill/Drill Motor and Controller, all at http://www.proxxon-direct.com/index.html .

And to Hank for advice about leveling, calibration, cutters, and warping. All greatly appreciated.

I'll do the CNC conversion myself, and I should be able to machine the stepper motor mounting plates on the mill. Then I'll make a cabinet with extractor to keep the dust under control. So I now have an enjoyable summer ahead, and I'll post the results here when I have something to show.

Thanks again to all for your very helpful advice.

Ian

HankMcSpank
12-03-2012, 06:57 PM
Grateful thanks to Mike for steering me towards a Proxxon mill. Their new KT150 compound table is the perfect size for milling my PCBs, and looks sturdy enough to hold the work properly. I have settled on:- a KT150 table, BFB 2000 Mill/Drill Stand, and BFW 40/E Mill/Drill Motor and Controller, all at http://www.proxxon-direct.com/index.html .

And to Hank for advice about leveling, calibration, cutters, and warping. All greatly appreciated.

I'll do the CNC conversion myself, and I should be able to machine the stepper motor mounting plates on the mill. Then I'll make a cabinet with extractor to keep the dust under control. So I now have an enjoyable summer ahead, and I'll post the results here when I have something to show.

Thanks again to all for your very helpful advice.

Ian

As it goes it's the Proxxon BFW/40E that I useas a spindle a nice solid quietish spindle (albeit a bit chunky & low RPMishh) ...I trialled AudioAndy's before buying it....in facr I think Andy had it up for sale a few weeks ago on here for a good price (though probably too late for you now!)

Jonathan
12-03-2012, 07:02 PM
I also use that cheap PCB from rapid, but tend to need the bigger sheets.

Have you considered toner transfer, where you print the mirrored artwork off using a laser printer onto the correct type of paper, place it over the bare board, iron it on then etch as normal? I've used it quite a lot and you can do very accurate boards with a bit care. The best paper is the type that sticky labels peel off as the toner doesn't stick very well to it. The finest I did was an 80-pin TQFP as a test. PCB was fine but I couldn't solder it!

Anyway, clearly milling PCBs is superior. Whilst selecting the track outlines and offsetting them to create the toolpaths works, if you're trying to make fine board it can be difficult to ensure pieces don't overlap. So instead I convert the tracks to the minimum required lines to isolate each connection.

From this:
(drawn with funny pads/track widths to make conversion easier)
5467

To this:

5468
Unless you're doing fancy RF stuff the odd shape tracks shouldn't be a problem. It's also less cutting, so clearly tools last longer and it doesn't take as long to cut. The latter isn't really an advantage unless you're making several of the same as it takes a while to redraw it.

As long as you don't skimp on the stepper motor and drivers there's no reason to expect long term problems with missed steps. This is particularly important since you seem to have chosen a relatively heavy machine bed with dovetail slides, not rolling balls, so the total force required by the stepper motors (F=uC+ma) will be high compared to a moving gantry router if you want to get decent acceleration and speed, which you do for PCBs since they have a lot of short moves and changes of direction.

HankMcSpank
12-03-2012, 08:10 PM
Re what you've done to minimize thecut lines...there's a free app out there called visolate - it's basically a midline voronoi region generator ...it takes a gerber as an input file & creates an NC file. It's poorly supported & the documentation sucks, but it does work ok (you just need java loaded on your PC with JAva's 3D libraries loaded too, it's explained a little better here...

http://blog.makezine.com/2010/07/26/voronoi-mapped-pcbs-using-visolate/


Terrible stray capacitance though so forget it for anything over 1khz or so!

(I'm also in email contact with a chap who after a bit of communication to/fro, is soon about to lauunch a web portal where you upload a dxf & it'll generate the voronoi midlines & give you the file back with the midlines done for you)

Re worring about offsets.....in cambam you can import a gerber, fine tune the offset & see the cut width onscreen...the trick is to get the offset so that the midlines of ajacent pins of your smallest IC pitch so they almost share the same path. Difficult to explain, but look here...

http://img694.imageshack.us/img694/3982/isolate.jpg (http://imageshack.us/photo/my-images/694/isolate.jpg/)

the IC pads are black, the tool cut width is turquoise & the midline for the toolpath is the dark blue thin line in the middle ....it's important to set your offset to get these midlines to almost kiss, but not go over, else you'll be unintentionally cutting into the neigbouring pad.

saxonhawthorn
12-03-2012, 08:27 PM
Andy had it up for sale a few weeks ago on here for a good price (though probably too late for you now!)

Story of my life!

Ian

saxonhawthorn
12-03-2012, 08:53 PM
Thank you Jonathan. Yes, I'll make sure the steppers and drivers are beefy enough. I haven't done any CNC yet, but I used to plot PCB artwork on a Roland plotter and I know what you mean about all the stops and starts and changes of direction. Dovetails have more friction than ball bearings, but unless there's a similarly solid XY table out there with ball bearings, my guess is that it's easier to compensate for high friction by beefing up the steppers, than it is to compensate for a less-than-rigid (aluminium) ball bearing table of the kind I have seen being offered by the oriental suppliers, some of which look a bit flimsy to me. But I confess to a total lack of experience.

I hadn't even got as far as worrying about minimising toolpaths, and I'm going to have to print off your two examples and lay them side-by-side to ponder them. Obviously there are things to learn about this CNC business! Is there a good book out there which deals with subjects like toolpath optimisation?

Ian

saxonhawthorn
12-03-2012, 08:59 PM
http://blog.makezine.com/2010/07/26/voronoi-mapped-pcbs-using-visolate/

Terrible stray capacitance though so forget it for anything over 1khz or so!

Re worring about offsets.....in cambam you can import a gerber, fine tune the offset & see the cut width onscreen...

Well I think it's a safe bet that I'll be going quite a bit over 1 kHz, and I can do without yet more stray capacitance problems, so perhaps I'll give VISOLATE a miss.

But I take the point, and your pic is helpful. CamBam has probably got to go on the shopping list.

Ian

John S
12-03-2012, 10:03 PM
I wish someone had told me how hard it was to do circuit boards before I ran the last batch of 20 off this weekend without any glitches.

HankMcSpank
12-03-2012, 11:49 PM
I wish someone had told me how hard it was to do circuit boards before I ran the last batch of 20 off this weekend without any glitches.

Yeah, that happened to me when I first started pcb milling too .....but next I had to make a pcb with something more than just two very large through hole components on it!

John S
13-03-2012, 12:06 AM
5474

That's about 80 x 80 mm.

Jonathan
13-03-2012, 12:28 AM
That's a large track width, all through hole and no tracks between the pins - I'd have been amazed if anyone had problems with that. A lot of SMT IC's have a quarter the pin spacing of DIL, which is when it gets more difficult.

If it's a circuit which is running at relatively high frequencies I do engrave it in the 'normal' way or etch it.

I cut plenty of PCBs on the Roland PNC2300A (same as one John S has) at school with a V-cutter. It's a very weak machine, yet did what I needed at the time (up to SOIC). So you don't need a massively rigid machine for PCBs, since the cutting force is minuscule, however if you're happy with the travel on the table and expect to use it for other things then clearly rigidity is good.

HankMcSpank
13-03-2012, 12:41 AM
Exactly....anything through hole like that, feels like groping "Dawn French" after Kylie ....Dawn might have a welcoming large warm bosom to nestle in but not many want to go that way nowadays.

(nice board though)

ecat
13-03-2012, 11:10 AM
Curiously enough I've spent two weeks trying to coax 0.4mm tracks and 0.3mm isolation out of my little X1 - quite the experience for the reasons mentioned previously in this thread. I agree with the statement, if the machine is going to do the drilling it may as well do the milling, especially for double sided boards, and wanted to see if the X1 could hold the resolution before I spent any real money or even bought a 'real' CNC machine.

The results are looking quite promising atm, I think the next issue to address is spindle speed - 2,000 rpm does not make for a happy experience. I'm reluctant to add any additional weight to the X1's already over stretched arrangement but I reckon I can drop a 50mm spindle directly into the existing spindle hole. This looked just the job, ESX16 collet, 28,000rpm http://www.ebay.co.uk/itm/230755919387?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 but worried about its age and condition I was out bid :( If any of you fine gentlemen know of a suitable substitute I'd be most grateful.

Looking at 'real' CNC machines for the first time in quite a while I see the UK hobby market remains in a dismal state and the UK DIY/kit market practically non-existent.
Strike CNC routers looks promising, if expensive, I'm not convinced by CNCDudze and I refuse to roll with Dice. Reading the Chinese threads make the machines sound a bit of a lottery, even with a little reinforcement and upgraded linears there is still the question of the ballscrews and I've not seen any actual measurements. I took a look at the Zen Toolworks machine, could be ok in a light breeze ;) and spent an entertaining afternoon reading the XZero threads on the zone!

Anyway, it's been a while. Nice to see some of the old faces again and good to see some new ones. Time for more coffee and low fat procrastination.

... Oh, John, when they asked for a PCB with a bus I don't think they meant the #47 to New Street Road End ;) Joking aside, nice board John, smooth, good definition and more consistent isolation than I've managed to date.

HankMcSpank
13-03-2012, 03:04 PM
Having got off to a bad start with my little machine...it's actually come though all this with its reputation in tact (my problems were to do with everything else!), so I can certainly recommend it for pcb work....

http://www.ebay.co.uk/sch/i.html?_nkw=sable+cnc+&_cqr=true&_nkwusc=sabel+cnc&_rdc=1 (mine is identical to those ones, just mine is called a panther vs a sable) ...I'd stay clear of the controller & spindle (bought my frame on its own)

it only uses 1.5mm pitch threaded rod, but I'm getting very good accuracy with it.

I agree by & large with your sentiment re the CNC machine market...componded by the fact that I prefer a moving table to a moving gantry design, but there's very little moving table designs out there that are up to it IMHO.

saxonhawthorn
13-03-2012, 03:56 PM
What spindle do you use Hank?

HankMcSpank
13-03-2012, 04:11 PM
What spindle do you use Hank?

The same one you ordered .... A Proxxon BFW 40/E Mill/Drill Motor and Controller ...which is riducously out of proportion for that machine, but it's quite low noise (neighbours!) & has low runout.....the RPM is a bit low (at something link700rpm maxed out), but nevertheless I get good results with it.

saxonhawthorn
13-03-2012, 04:30 PM
Hank,

I haven't actually ordered anything yet. A Chinese gentleman is still making overtures for my custom (and offering to teach me Chinese), and I normally like to let purchase decisions rest a while anyway in case I change my mind. But at least having made a choice gives me a starting point for comparisons instead of wandering around in a mental fog.

I do remember seeing those Sable / Panther machines from a couple of years ago, and thinking they looked nice and workmanlike. My instincts agree with yours about moving the table rather than the gantry, but I expect it's a case of horses for courses. I'm not thinking of sculpting a new set of lions for Traffalgar Square, just flat PCBs.

But I haven't thought either about the pros and cons of moving the table in just one horizontal axis, as yours does. There's probably something to be said for keeping only one dimension variable. I need to do some back-of-envelope calcs on tolerances.

And I'm casting glances as I write at my trusty 125W rotary tool, which claims to do 20,000 rpm (a cheapo imitation of a Dremel). I've never measured it, nor have I any idea what its runout may be? But the shaft power should be adequate for milling off a thin sliver of copper. Has anybody tried using something like this for milling?

Ian

HankMcSpank
13-03-2012, 04:59 PM
Hank,

I haven't actually ordered anything yet.

It was probably this bit that threw me yesterday...


I have settled on:- a KT150 table, BFB 2000 Mill/Drill Stand, and BFW 40/E Mill/Drill Motor and Controller, all at http://www.proxxon-direct.com/index.html .

If you've not bought a spindle, you could do worse than buying AudioAndy's (if it's still available)....

http://www.mycncuk.com/forums/showthread.php/3821-Proxxon-BWF40-E-Spindle?p=24773#post24773 ....80 + delivery is a decent price for a decent low noise spindle (heavy at 4.2kg though!)

Any dremel knock off (dremel's are bad...knockoffs are wose, save for proxxon), is gonna suck wolf's cookies for milling pcbs.

Jonathan
13-03-2012, 05:46 PM
Have you considered making your own spindle?

http://www.mycncuk.com/forums/showthread.php/3096-Using-RC-Brushless-motors-as-spindle

saxonhawthorn
13-03-2012, 05:59 PM
Have you considered making your own spindle?

http://www.mycncuk.com/forums/showthread.php/3096-Using-RC-Brushless-motors-as-spindle

Yes. In fact, that's where I started. I bought Harprit Sandhu's good little book on Spindles (No. 27 in the Workshop Practice series) and it got me motivated-up. Then family matters intervened (two girls at Uni to support) and things got put on hold.

I could still be tempted. ATM I'm mostly hampered by lack of working space (electronic gear, woodworking, metalworking, and book printing & binding stuff all pushing for space). Too many irons in a small fire.

Ian

("I used to be indecisive, but now I'm not so sure!")

saxonhawthorn
13-03-2012, 06:45 PM
Any dremel knock off (dremel's are bad...knockoffs are wose, save for proxxon), is gonna suck wolf's cookies for milling pcbs.

Sorry, I didn't express myself well. I was thinking more in terms of using the motor guts with some better bearings, etc, to make a spindle of my own.

And yet another worthless idea from a CNC ignoramus:- Has anybody experimented with dental turbines for PCB milling? They're light and fast and cheap from HK suppliers on eBay, and high-class dental labs work to tenth-of-a-thou standards (or so they tell me).

Ian

Jonathan
13-03-2012, 07:25 PM
cheap from HK suppliers on eBay, and high-class dental labs work to tenth-of-a-thou standards

But do the high-class labs buy them from cheap HK suppliers?

saxonhawthorn
13-03-2012, 07:32 PM
But do the high-class labs buy them from cheap HK suppliers?

I've no idea, but I could ask tomorrow. A turbine would get the heavy power source off the mill, which in itself sounds an attractive proposition. Sort of thing I'd like to experiment with. But I don't know if it's been tried.

Ian

Swarfing
13-03-2012, 10:22 PM
http://www.dieselrc.com/projects/cncspindle/

ecat
14-03-2012, 12:45 AM
The Sable machine looks sweet, all aluminium and quite solid. HankMcSpank, did you get stung for duty and shipping?

It looks like you can buy them direct from Holland http://www.cnc-sable.nl/sable-2015-p-21.html , 655 euro including tax for just the base machine + steppers, about 550.00, I don't know if this includes delivery.
N.B. It's best to view the site in Dutch, their English translations are missing some bits.

The home made spindles look beautiful but impossible for those without a lathe. Two complete units I've been looking at are http://www.cnconabudget.com/ - the site looks dodgy but I believe the guy is trustworthy and still in business (info from cnczone), and http://www.wolfgangengineering.com/Home.php . Both of these have fixed 1/8" collets so not quite ideal for me.

Jonathan
14-03-2012, 01:46 AM
I wouldn't call a machine that uses unsupported rails 'quite solid', more like quite flimsy espectially since the spacing of the Z-bearings is tiny. Also it appears to only use standard M10 threaded rod for the leadscrews, so you wont reliably get very low backlash which is clearly important for very fine PCBs. Also the steppers are uses are very small, which combined with the low efficiency (compared to ballscrews) of using M10 rod will ensure you can only get low feedrates...

They should not anodise it and use the money saved to improve the machine.

' It can be use for ... litle aluminium work.'

False advertising, as is so often the case. Not very fair on the people who make machines which can cut aluminium at proper speeds.

If you buy that I bet you'll end up replacing most of it.

One way to make a spindle without the lathe is to find a brushless outrunner with a 1/8" shaft and simply replace the shaft with a V-cutter of the same diameter. Not tried it so can't comment on the rutout, and clearly it's hard to change cutters ... but it would be very cheap and very high speed with sufficient cooling. I'm sure blackburn_mark will comment on that as I believe he did it.

HankMcSpank
14-03-2012, 09:16 AM
For milling pcbs, the sabel is just dandy......re the lack of supported rails - the machine's working area is only 20 x 18cm, so for me at least, this is of little concern (I only mill acrylic & pcbs)


To put this into some context ...it cost me about 440 delivered for the frame/motors only (including import duties/taxes, you might want to drop the seller an email - http://myworld.ebay.com/motorstar01/?_trksid=p4340.l2559 ...if he can still surce them, you'll save about 100 vs buing in europe) ....sure I could have likely built a machine with supported rails for that....but I needed to crack on and get milling.

HankMcSpank
16-03-2012, 10:37 AM
Probably not gonna cut anything stromger than warm butter & the odd pcb, but rather cheap...

http://www.ebay.co.uk/itm/CNC-milling-drilling-machine-router-kit-with-motors-controlling-board-etc-/180840111357?pt=LH_DefaultDomain_0&hash=item2a1ae91cfd (looks like an ok spindle)

Edit: just seen the postage ....160!!! Ouch

saxonhawthorn
16-03-2012, 11:20 AM
Probably not gonna cut anything stromger than warm butter & the odd pcb, but rather cheap...

http://www.ebay.co.uk/itm/CNC-milling-drilling-machine-router-kit-with-motors-controlling-board-etc-/180840111357?pt=LH_DefaultDomain_0&hash=item2a1ae91cfd (looks like an ok spindle)

Edit: just seen the postage ....160!!! Ouch

I think I'd have preferred 10mm Dural to 10mm PVC. Otherwise it's fine. :(

Swarfing
16-03-2012, 01:22 PM
Hank that is a Zenworks CNC

http://www.zentoolworks.com/

saxonhawthorn
16-03-2012, 01:52 PM
FWIW this Sable seller on eBay
http://www.ebay.co.uk/itm/190643190988?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
has just offered me the machine for USD 600 including shipping to my address. No drivers or spindle, but not a bad price methinks.

Ian

HankMcSpank
16-03-2012, 01:57 PM
FWIW this Sable seller on eBay
http://www.ebay.co.uk/itm/190643190988?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
has just offered me the machine for USD 600 including shipping to my address. No drivers or spindle, but not a bad price methinks.

Ian

That's about what I paid...you need to add on about 50-60ish for import duties (assuming you can persuade the seller to massage the [delared ..cough...value] a little!), so about 450 through your door.