pcb guillotine blades

A few months ago I made a guillotine for cutting fibreglass pcb boards, based on a commercial design I saw pictures of on the web. It consists of a straight blade at a shallow angle cutting against a bottom fixed blade. I was delighted when I tested it on a sheet of paper and obtained a perfect clean cut.

When I tried it out on a piece of pcb material, things went downhill rapidly, the force needed to cut the board was much too high causing all sorts of problems. When I made the guillotine I made an attempt to measure the slicing angle between the two blades from a picture I printed out, but realised this was a bit suspect.

If anyone has access to a pcb guillotine (or even a sheet metal one) I would love to know what angle they use beween the two blades as I suspect I made the angle too shallow in my design.

Doug

Hi Douglas,

Years ago I tried a guillotine for 1/16 FR4 PCB's with no luck.

Then I spoke to a PCB firm and they recommended either routing a series of holes and slots on the break lines, or a score-and snap-method. For s-and-s, score both sides of the pcb as deeply as possible in a couple of passes with a HSS lathe tool ground to a V point of 10-20 degree included angle. The PCB will snap cleanly along the line with little force. Keep all component holes back .080-.090" from the edge to avoid breakouts from edge to hole.

The PCB firm had a scoring device like an X Y plotter that could rotate the scoring tool 0-360 degrees in 90 degree increments. They scored the PCB's after drilling and other routing.

I've done them using the mentioned lathe tool clamped to a paper cutter device that has a board and a guided X Y cutter on rails. The paper cutting wheel was removed, the tool clamped up, and the PCB secured to the table, then scored.

Hope this info helps.

JD

Hi Douglas,

I use an old fashioned bench shear (ungeared) to cut my boards and it works well, The cutting edge of the top blade is an arc of a large radius circle and the fixed blade is straight along its cutting edge and the angle of attack is about 20 degrees all along the cut. If a straight top blade is used then the angle of attack reduces as the blade cuts. I hope that make sense.

I'll try and make a sketch to explain the principle better and post it later.

Best regards

Terry

Hi Jeff,

The scoring idea sounds interesting, I must give it a try .I suppose a stanley knife might even be worth a try.

Hi Terry,

I see what you mean about the attack angle reducing with a straight upper blade if the upper blade is pivoted at one end. In my design the upper blade is held at a fixed angle and is guided vertically (as in the head chopping guillotine the French were so fond of) so the attack angle stays the same throughout the cut.

I hope somebody can provide me with the attack angle used on commercial guillotines.

Doug

Doug,

One of these, from Olfa, would probably handle better than a regular Stanley Knife.

MichaelG.

I have a big cast iron guillotine, the type we used to have in schools before H&S.

Big heavy thing. I use it for cutting shim steel up to 1/2mm and PCB's, no problems at all. Goes thru both like butter.

Hi John,

Thats the same as mine, bought it for a song from a school that was throwing a couple away. I bought both and gave one away to a mate. As you say they are effective, it hardly notices pcbs.

Hi Michael,

you could always buy a carbide engraving bit or small slot drill and machine through with the milling machine, or even a router with a simple fence - use a sacrificial base of say, scrap mdf and stick the pcb down with double sided tape. I'm about to try milling PCBs on a small CNC milling machine,

Best Regards

Terry

Quite so Terry; that is exactly what I would do

I was just discouraging the use of a regular Stanley Knife for the "quick job" ... because there are much better scribing/scoring blades around. Aside from the Olfa, there are several carbide-tipped tools available; designed for laminates or ceramic tiles but also good for GRP. [ I have one by Cintride, that is excellent ] ... This style

MichaelG.

Edited By Michael Gilligan on 20/11/2012 09:23:52

Terry,

Milling works OK but you have to use isolation milling or you will be there all day.

Vee cutter works best.

When I started down the route of cutting pcb material I did think of a paper cutting guillotine and looked at some modern ones and quickly realised they were too flimsy for the task. I have been looking ever since for a good old fashioned one at my local auction house, but no joy there.

My main reason for wanting to use a guillotine was to avoid producing fibreglass dust, which is not good for the lungs. Scoring the board should be ok from the dust point of view but I would not like to start milling the stuff or using a bandsaw.

I am still hoping to get an answer to my original question about the attack angle between the guillotine blades.

Doug

Hi Doug

I just measured our commercial PCB guillotine which has a 320mm wide cut with one end of the moving blade 17mm clear when the other end is touching. This gives an approx 3 degree angle. The guillotine is a toggle action with the end of the actuating arm moving approx 300 mm for a 17 mm movement of the blade. Mechnical advantage about 18 to 1. We drill board using a high speed PCB drilling machine with solid tungston carbide drills. To avoid dust we have arraged a vacuum cleaner hose mounted near the drill which successfully cleards all the dust. No reason why you should not do similar on a mill. The dust and chippings are very light and eay to entrain in an air flow and so remove. Hope this helps.

regards Martin

You can get for a reasonable price , a carbide tipped hand tool for scribing ceramic tiles for breaking them, I was looking at one the other day thinking it might work as a lathe tool. Ian S C

My 3 in 1 metal mangler is OK with fibreglass board.

Hi John,

what program do you use for the code to drive the milling machine. Your example is exactly how I intended to do the job but have only got as far as designing my circuits using Eagle files.

Best regards

Terry

I use photo etch, but I understand a vacuum chuck works well for milling PCBs. especially if working to tight (smt) tolerances.

I use a hacksaw to cut up PCBs.

Neil

If you do a search on ebay for ' vintage + guillotine' there's a few for sale. . some silly prices, others not !

W.

Actually, there was a thread about this when Doug first broached the project — see here:

Old Thread

In that thread I referenced a U-Tube video in which a Chinese guy used what appeared to be an Olfa cutter together with a simple scribing frame to cut board quite easily. I later got hold of an Olfa and rigged up an impromptu frame but my experience with this technique was less happy. I used standard 1.6mm g/f board and found that I had to make many passes on each side of the board to make a real impression (glass-fibre doesn't cut like glass!). If the scribing wasn't deep enough , when breaking, the board tended to delaminate and leave a ragged edge. I was left wondering whether he had used one of the thinner spec boards. Apart from that, the blades seemed to be of the same quality steel as used for Stanley blades, fine for card and maybe Plasticard, but not up to cutting glass-fibre. Maybe one of the laminate cutters using a tungsten carbide blade would fare better.

Joe

Hi Martin,

Thanks for your input, you provided exactly the information I was looking for. My guillotine used an angle of 2.5 degrees which is only slightly less than the figure you quoted so perhaps my problem lies elsewhere in the design. I found that there was a springy feel when the top blade started to cut the board which suggested a lack of rigidity in the toggle mechanism, so I must look at this point first.

Hi Joe,

Oh my goodness, I have just used your link to go back to the post I made when I first thought of this project and was horrified to see how long ago it was.Where on earth does the time go? I have done a quick try with a Stanley knife and found it does work, but it is a slow business. If the first cut is made on the copper side it is easy to see the line of the cut from the other side of the board.

Doug

Hi

I have Model 45 from Mega-UK

**LINK**

The blade rise at an angle of 10mm to 135mm. It has served me well for 16 years in cutting pcb, brass and alu.

Terje

Hi Terje,

The guillotine you have is the exact one I tried to make a copy of, using a couple of photographs found on a website. If you have time could you possibly make a few measurements which would assist me in making my one work. The main dimensions I would like to have are these:-

(1) diameter of the two vertical pillars

(2) diameter of the horizontal bar that the handle is fixed to

(3) the centre to centre distance of one of the links connecting the horizontal bar to the top of the upper blade carrier

(4) the same dimension for one of the links connecting the end of the horizontal bar to the block at the top of the vertical pillar

(5) the distance from the centre of a vertical pillar to the centre of where the previous link pivots

If you can oblige I will be most grateful,

Doug