Cutting PCBs, please show your method. - Page 1
Forum section: electronics / projects

author: moffy
author_rank: Super Contributor
timestamp: September 04, 2021, 04:38:43 am
content: I recently had to make 3 small PCBs with cuts/outline accurate to at least 0.5mm or better. I had a battery powered tile cutter left over from a previous job round the house and some scrap board and aluminum. I came up with the following, which is compromised for cutting size by the mounts, but was large enough for the current job and was very precise.Would like to see what you guys use.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 04, 2021, 07:03:00 am
content: OK, but do it outside and wear a mask against that fiberglass dust generated by power tools. Not good to the lungs, and the effects are visible only much later, decades later.If you do PCB cuttings often, better use a guillotine, or big scissors, or some other method that does not use power tools, the power tools usually produce and spray cutting dust, in this case microscopic fiberglass needles dust.

author: Gyro
author_rank: Super Contributor
timestamp: September 04, 2021, 09:19:22 am
content: A tile cutting wheel is a good choice (wear wise) for surprisingly abrasive FR4 PCB.Personally I use a cheap table type tile cutter - basically the same thing but inverted and with water cooling. The water captures the dust nicely.Here are a few previous threads on the subject...https://www.eevblog.com/forum/beginners/is-this-a-good-(or-overkill)-pcb-guillotine/https://www.eevblog.com/forum/reviews/mini-table-saw-for-pcb-cutting-worth-buying-from-china/https://www.eevblog.com/forum/eda/clean-way-to-cut-fr4-pcb/https://www.eevblog.com/forum/manufacture/cutting-fr4-boards/(I'm sure there are more if you try a few search term variations.)

author: Psi
author_rank: Super Contributor
timestamp: September 04, 2021, 09:52:16 am
content: I've used the drop/mitre saw before.But one word of warning,It goes without saying to not hold the PCB with your hand anywhere near the blades in case it kicks the PCB back and pulls your fingers into the blade.Note that there is often a ~2mm gap at the rear of the cutting areaunder the back-stopand it can rip the PCB into this gap violently! So, if yours has a gap there, cut on top of some wood or something.Also your edge quality will depend on the cutting blade you have installed.But it is easy to get your desired width by cutting oversize and then slowly trimming down a tiny bit at a time until you get what you need.

author: kripton2035
author_rank: Super Contributor
timestamp: September 04, 2021, 10:20:12 am
content: I use a small band saw with a blade designed for metal cutting (small teeths) . works nice for the (very) small qty of pcb I do.Now I make them at chinese factory, you have to wait 15 days to get them but it's so much better quality than mine !

author: 2N3055
author_rank: Super Contributor
timestamp: September 04, 2021, 11:49:33 am
content: Quote from: RoGeorge on September 04, 2021, 07:03:00 amThis !!Absolutely guillotine type cutter. Do not saw it, crushed fiberglass fabric is nasty, asbestos kind of nasty...

author: Mark
author_rank: Frequent Contributor
timestamp: September 04, 2021, 01:27:45 pm
content: For long stright edges I use a guillotine. For any fancy cut-outs or rounded corners I program the CNC machine.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: September 04, 2021, 01:42:36 pm
content: I use a Proxxon circular bench saw, but the stock circular blade coming with the saw is not intended for PCBs, either you have to use a hard-metal circular blade or diamond

author: tooki
author_rank: Super Contributor
timestamp: September 04, 2021, 02:32:03 pm
content: Quote from: HB9EVI on September 04, 2021, 01:42:36 pmFYI, “Hartmetall” translates to “carbide”. (“Hard metal” is not a term used in English, so people won’t know what you mean.)

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 04, 2021, 02:42:28 pm
content: Quote from: tooki on September 04, 2021, 02:32:03 pm

author: David Hess
author_rank: Super Contributor
timestamp: September 04, 2021, 03:52:58 pm
content: Notching shear - but I have been thinking of making an sliding saw using a Dremel for precise and clean linear cuts using abrasive disks.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: September 04, 2021, 03:56:33 pm
content: sure, thanks Tooki; I should have known it, but obviously the 'mechanical' part of the english language left me for an instant, I'm not much into the mechanical world after all

author: richnormand
author_rank: Unknown
timestamp: September 04, 2021, 07:46:38 pm
content: @moffy,similar idea as your setup but upside down.I modified a low speed diamond wafering saw to cut small pcb with a good precision.The rotating blade is under the platform and is exposed like a table saw. The through under is filled with water and the bottom of the blade dips in it.This cools/lubricates the blade and takes care in controlling the sawing debris.Works extremely well either with x-y micrometer control or freehand with a 90 degrees machinist square edge.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 04, 2021, 08:01:58 pm
content: If I need it precise? CNC mill. You know, the same ones the fabs use? Yeah, I just let them figure it out.For protos? Nothing anyone would really want. Hand shears or hacksaw to get rough shape, wet sanding to get smooth edges and final shape. Indeed, the dust isn't the most pleasant thing, definitely use wet cutting or low-dust methods where possible (hacksaws aren't terribly aggressive tools, but the sawdust can be kicked up). Works fine for sticking together bits into shell housings and stuff, I've made a few neat enclosures over the years this way -- but it's rather tedious, setting up a bunch of slots for things to slide together or pin/locate on.I still think doing this with copper clad is less work than carving up most (prefab) enclosures, and you can solder to it. But not much less, and I do use those from time to time as well.Tim

author: David Hess
author_rank: Super Contributor
timestamp: September 05, 2021, 12:02:28 am
content: Quote from: T3sl4co1l on September 04, 2021, 08:01:58 pmWith a precise saw, strips of copper clad can be cut to make instant controlled impedance microstrips for prototyping over a ground plane.

author: moffy
author_rank: Super Contributor
timestamp: September 05, 2021, 01:48:20 am
content: Thanks so much for all the info and sharing of experience. I do cut the PCBs outside, the smell apart from the dust is atrocious. The vinyl tile cutter sounds like a good idea too.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 05, 2021, 06:12:52 pm
content: For prototyping, snapping the PCB after V-scoring is the least troublesome, if the cuts are straight. Of course it's not 100% failsafe, so better do this before populating the PCB than after.

author: t1d
author_rank: Super Contributor
timestamp: September 06, 2021, 04:20:16 am
content: I DIY'd a tile saw... The cheap, black, plastic one from Harbor Freight. I added a slide table. Cuts are accurate and fast.

author: james_s
author_rank: Super Contributor
timestamp: September 06, 2021, 05:18:34 am
content: If I'm going to cut a few of them I go to my friend's shop and use the large foot operated shear they have. If I just want to cut a quick one at home I clamp it against a scrap of 1/4" aluminum in my bench vice and using the aluminum as a straight edge I cut it with a hacksaw.

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 06, 2021, 08:54:40 am
content: I order in a quick proto lab near, so have etched and drilled boards next day deliveredAnd they use a big shear cutter

author: m3vuv
author_rank: Super Contributor
timestamp: September 06, 2021, 07:48:16 pm
content: I have a bench grinder with a thin 1mm cutting disk on one end of it,the thin netal cutting disks meant for a 4" angle grinder,its dodgy to use tho but i dont cut many boards but beats a hacksaw.

author: Buriedcode
author_rank: Super Contributor
timestamp: September 06, 2021, 08:16:20 pm
content: I really haven't found anything I would consider easy. But scoring 3-4 times both sides with a craft knife or knife cuttoff blades with a steel rule, and then just snapping. Then a couple of runs along the edges with either "cheap" needle files (I say cheap because with FR4 they wear quickly) or 600 grit wetdry. Cheap, but hard on the hands.Bare in mind, I really haven't done regular DIY PCB's in a few years due to how incredibly cheap it is to get them made - even odd shapes. So I never reached the point where I would invest any real time/effort/money into finding a more convenient solution to the many problems DIYing PCB's can have - cutting material, drilling, rivets fro TH etc..edit: typos

author: moffy
author_rank: Super Contributor
timestamp: September 07, 2021, 01:55:32 am
content: Here is a picture of one of the boards cut, populated and interfaced to a DM556T stepper driver. I used a 16 pin IDC cable to carry the power, gnd, step(x-z), dir(x-z) and enable to the boards. You then set 2 or 3 jumpers to select X, Y or Z (all the boards are identical) and or Enable. The drive signals (3.3v CMOS in this case) then drive the appropriate resistor/transistor which then drives the opto input of the DM556T. Keeps wiring to a minimum, especially as my controller board has the same 16 pin connector.I also added the Schematic for the board as it is a better description than my words.

author: Buriedcode
author_rank: Super Contributor
timestamp: September 07, 2021, 05:59:54 pm
content: Nice. I would recommend SMT - purely because it saves drilling so many holes. It's obviously not always ideal, sometimes parts are much cheaper, but for passives you generally deal with 100-5k at a time, and of course, power parts are easier with TH, for mounting heatsinks (SMT requires good ground plane. vias etc..). I use SMT where-ever possible for DIY boards, often leaving the only holes being pin headers or connectors.

author: ajb
author_rank: Super Contributor
timestamp: September 07, 2021, 07:57:03 pm
content: Quote from: T3sl4co1l on September 04, 2021, 08:01:58 pmWell, they use routers, which are kinda the same thing in the way that a bulldog is the same thing as a greyhound, but yeah, letting the fab figure out is the best way.That said, I have use a CNC mill to carve up panels full of prototypes before (IIRC it made sense in terms of price/specs/lead times that I could get at the time and just being a fun experiment). The big problem with using a typical mill in lieu of a purpose-built router is spindle speed. Cutting tools work best at a particular surface speed, which is the linear speed that the cutting edge moves through the material. Small tools at 1-2mm like you typically want for PCB routing, where the cutting edge sweeps a very small circumference need high rotational speeds to get the desired surface speed, so it's not uncommon to see things like PCB routers with 60,000rpm spindles, or sometimes even faster. Cutting tools also have a defined chip load, which is the amount of material removed by each pass of each cutting edge, which sets your feed rate as a function of RPM, so there again small tools with small chip loads need high rotation speeds to cut efficiently.I was using a Tormach PCNC 1100 with a ~5,000rpm top speed, so performance on a 1.6mm tool was far from optimal, but it got the job done. I threw a chunk of thick acrylic from the scrap rack in the machine, drilled tooling holes and made threaded hold-down holes in the acrylic in place, and milled relief channels in the plastic to clear where the tip of the tool would pass while milling the boards. For the actual milling I used a drill-point carbide burr, which worked pretty well. The drill point allowed it to pierce very effectively, and the burr left a pretty good edge finish despite the non-ideal cutting parameters, maybe just a bit less nice than what you'd get from the fab. The clearance channels in the fixture weren't strictly necessary, but burrs don't clear swarf as effectively as helical tools so some extra space there was helpful, and drill points aren't meant to cut sideways so it would have been kinda gross. The cutting was kind of slow due to the limited spindle speed, but the great thing about CNC machines is that you can press Cycle Start and then walk away from them.Of course dust control is important, as with any time you cut materials like this. I wouldn't do it on a machine that wasn't fully enclosed or equipped with really good dust collection. I also wouldn't do it on a machine set up for flood coolant unless it had REALLY good filtration, otherwise the fine abrasive particles produced by cutting FR4 are liable to cause increased wear and tear on the machine and cutting tools down the line. Well, really, I wouldn't do it at all because it's just a whole lot easier to have the fab that has the fancy routers with high speed spindles and fancy dust shoes do it, like Tim said in the first place!

author: moffy
author_rank: Super Contributor
timestamp: September 07, 2021, 11:45:00 pm
content: Buriedcode: I don't tend to use surface mount mainly because my eyesight is getting a bit blurry. I agree the holes are a pain and I have magnifiers and even a surface scope(unused), I just find it easier and more familiar.Ajb: That info is very interesting for us CNC newbies. So what would you suggest as the best routing bit for a 5000 RPM spindle CNC? Just so happens that is what my little boards are for.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 08, 2021, 01:04:43 am
content: Quote from: David Hess on September 05, 2021, 12:02:28 amWouldn't it be simpler to buy copper foil or adhesive copper tape in a roll?

author: ajb
author_rank: Super Contributor
timestamp: September 08, 2021, 04:52:30 am
content: Quote from: moffy on September 07, 2021, 01:55:32 amThat's a really nice solution!Quote from: moffy on September 07, 2021, 11:45:00 pmDepends a lot on what you're doing. For FR4 or similar fiberglass-type materials I would probably go with adiamond-pattern burr. I suspect that's what the PCB fabs use. You can use standard end mills as well, but anything with a high positive rake angle is going to wear very quickly. (Positiverakemeans the leading face of the cutting edge leans away from the surface being cut, so a high positive rake means the cutting edge is very acute, which makes for low cutting forces, but also a thin, sharp edge that is more subject to chipping and just wearing away.) Either way it should be carbide. Really, if you're not doing production you don't have to worry that much about wear on cutting tools. Honestly, in general it takes a fair bit of practice to get to the point where you can wear tools out before you break them anyway!*For wood, you can use standard wood router bits, but also solid carbide ones, which opens up a lot of possibilities. Spiral upcutting bits will clear chips better than standard straight flute bits, downcutting or compression bits (which have up-cutting flutes on the bottom and down-cutting flutes on the top) can help avoid chipping out the top of the material. For plastics or aluminum, you want a sharp tool. In plastics that reduces friction and gives a good surface finish, in aluminum it keeps the cutting forces low. We used to have a big router we did lots of aluminum panels on, and we used a lot of Onsrud single 'O' flute bits for that. They have one, big, round flute with a polished surface that works really well for cutting aluminum dry. Really there are a ton of options, but if you're just getting started then I wouldn't worry too much about the details. Getting the machine set up properly and figuring out the right machining strategies are more important. On small/light machines like most hobby/DIY routers you're going to be limited by the power and rigidity/damping of the machine more than the tooling.If you've only got 5000 rpm, you're just going to be limited on how well small tools are going to perform, there's not really a way around that. You can still get decent results, it's just going to take longer to get them, but if you're not trying to make money with it that's not that big a deal. In the world of bigger CNC machines, you can fit a 'speeder', which mounts in the spindle like a regular tool but either has a set of multiplying gears driven by the spindle or has an air turbine or electric motor to run small tools at higher speeds. They're expensive, but then so are the machines, so it's worth the cost if it makes the machine more productive.* In our machining area at work we have two jars. One has a small and slowly growing handful of tools that we've managed to wear out, that's the well-earned retirement jar. The other has a few thousand dollars worth of broken carbide, broken work probe tips, and at least one chewed up parallel, that one is labeled "Tuition". We don't mind too much if you break something as long as you learn from it. Next time try to break it a different way so you can learn something else!

author: moffy
author_rank: Super Contributor
timestamp: September 08, 2021, 06:56:50 am
content: Ajb: Thanks very much for the info, I shall ponder it.