Advice on milling slots in 1mm pcbs

Hi all,
I need to mill a dozen slots in about 40 1 mm PCB panels.
The slots are 1.2mm wide and about 20mm in length. The slots are full depth of the PCB. The panels are around 160mm x 120mm.

I’m planning to use a 1.2mm burr style mill. I also have access to 1mm 2 flute slot mills. Both are carbide.

Has anyone had experience with this type of milling? I’m particularly interested in the speeds and feeds to use. As I’ve seen conflicting advice.

Also I plan to make a fixture to hold the PCBs as the position of the slot is critical.
The panel has four 1.5mm diameter locating holes on the panel. One option is to use 2 1.5mm dowel pins on diagonal holes to locate the PCB, then clamp it with a couple of strap clamps. I can’t find the dowel pins from a supplier that can provide them quickly, but I can be used the shafts from some 1.5mm drill bits. I also have some 1.5mm spring steel that I can use in a pinch. This method allows me to stack a number of PCBs if I’m game. ????

The other option is to cut a relief into the fixture that is made out of Corian. The relief would be 0.8mm deep to allow for the strap clamps.

I’m not sure which way to go. I leaning towards the first method with the locating pins. One reason is that I can sandwich the board to be cut under a cut one if the top edge of the cut is not clean.

I can try both fixture methods if necessary but am mostly concerned with the speeds and feeds along with the depth of cut as the cutters are quite easy to snap. Also I plan to use air to cool the bit and remove the swarf.

Any advice is welcome.

Cheers

Peter.

Hi Peter,
easy. I use 1.5mm four flute endmills to cut the outline, and mill features into PCBs all the time.

I have a range of small endmills down to 0.5mm, and they handle the copper/fibreglass no sweat.

I spin the endmill at 24000rpm and usually have 600mm/min feed-rate, but in truth you could probably push that out to 2500mm/min if you spin at 24000rpm with a low
runout spindle. I couldn't do that with 0.8mm or 0.5mm tools, they are too tender, and in these smaller sizes are two flute and not as strong as four flute.
I'm not in that much of a hurry. I don't break these endmills but rather throw them out as blunt after countless dozens of boards.

I have attached a pic of a board that I make regularly. The outline is cut as a slot at full depth (plus 0.2mm to ensure a through cut). But the holes (larger than 1.55mm anyway) are
all routed using circular interpolation. It saves having to fit multiple drills, I have a manual tool change spindle and the less tool changes I have to do the better.

I use 1.5mm pins to align the PCB blank, particularly because these boards are double-sided and alignment pins are the easy way to do that. Searching around for precision pins....no bloody way!!
I use 1.5mm diameter bronze welding wire cut into 1 cm lengths. They are not precision ground but I easily achieve 0.02mm repeatability and that's entirely good enough. Precision pins.....don't be a plonker,there are much easier
and cheaper ways!

I get Kyocera Tycom tools from the US, have done for over ten years. They are sold especially into the PCB industry. Cheap as chips and good quality. All 1/8th shank with depth rings preset,
whats not to like?

https://www.ebay.com/str/carbideplus....m47492.l74602

Craig

Hi Peter,
I've just paid my property tax bill for the year and am feeling 'money deprived' but over the next fortnight to month I need to make another order on the US supplier.
I need more 1/16th four flute, I want some 1/16th two flute but x10 length, some more 60 degree PCB engraving tools, and as many 1/8th Destiny Tools Raptors
(four flute AlTiN coated, just the bees knees for steel and stainless) as I can afford. I usually buy about $200USD-$250USD worth at a time. If you want some sing out and I'll get
whatever you want....I seem to recall that I owe you a favor over a deal that you gave me on an ESS. Many thanks.

Craig

Hi,
do these look suitable?
Note the price is for five endmills.

Craig

Hi Craig,
Thanks for the replies. It’s just what I need. I bought a PCB spindle years ago with good runout. I was made by a hobbyist manufacturer in the USA. I’m not sure of the top speed but I can measure it.
I also have a Chinese HS 800w spindle I could also use.

The bits I have are these as they were the only one I could get next day.

Yakamoz 10 PCS Titanium Coat... https://www.amazon.com.au/dp/B098T3B432

I also have some 1mm 2 flute ones with 1mm shaft but the flutes look too long. I could try putting the flutes in the collet but I’d expect that may cause runout.

Thanks for the links to the PCB mills. I think I’ll order some 1, 1.2 and 1.5mm ones.


Sent from my iPhone using Tapatalk Pro

Hi Peter,
my preference is stub (1.5x diameter)or standard (3x-5x diameter) length tools, and four flute, just because of the greater core strength. I have 0.8mm four flute tools which get used occasionally,
but the 0.5mm and 0.4mm endmills are two flute and are pretty tender. Mostly I use 1.5mm (x3) four flute for PCB milling.

Believe it or not milling PCBs is easy, easier say than the same thickness aluminum. You always battling with chip evacuation with aluminum to prevent the chips from welding together and sticking to the tool.
FR4 PCBs are a delight by comparison, they produce very fine chips, just a fluffy white powder in effect. Certainly not recommended to breathe it, but for the tiny quantities that you'll produce its a no
issue. Having said that I might try feeding some to my mother-in-law.....

I use the 1.5mm four flute tools for months at a time. They usually get thrown out when I find that they are just not good enough to do a decent job in plastics, aluminum or steel any more. Having said that
they are not great in steel, but they do work with plenty of flood cooling. By-and-large I use them for softer materials.

Craig

PS joking about the mother-in-law thing,I don't even have a mother-in-law, and if I did I would use arsenic, however if you've ever read Madame Bovary by Flaubert, it will put you off
arsenic for life, Flaubert sure managed to wring the horror out of it.

So, the job went fine in the end. The fixture took a bit of time as it was made on the TM20VL, then transferred to the Taig that I put the High speed PCB spindle on. I ran it at 30,000rpm.
I put a fence on the underside of the fixture that I could put in the center T-slot on both mills to assure alignment.
https://uploads.tapatalk-cdn.com/202...d6b3f3e08c.jpg
https://uploads.tapatalk-cdn.com/202...3f799bba03.jpg


Sent from my iPhone using Tapatalk Pro

The finished fixture.
https://uploads.tapatalk-cdn.com/202...ed89c2626d.jpg


Sent from my iPhone using Tapatalk Pro

Hear are a few more pics showing a few shots of the fixture being made and the milling of the slots in the PCB. After the first panel was milled, I did them 2 at a time.
The fixture has a 1.7mm recess that the boards fitted into. I also put pins (1.5mm drill bits) into the panel and had the 4 clamps to hold them in place. They weren't going to move.

The slots are 1.3mm wide and I only had 0.1mm either side to play width.

In the end it all went well so I was very happy.

And thanks to Craig for your advice and guidance.

Cheers,

Peter

Hi Peter,
kool.

Milling FR4 is not to bad, its abrasive so will dull tools, but it does form chips and so mills pretty well.

I don't use clamps, I've tried in the past with bad results. No matter how good the clamps are and how well you place them they always pull some warp or bow into the board.
When isolation routing you want the PCB blank as flat as possible, 10um or better. I use double-sided tape to hold the PCB down and 1.5mm pins for alignment.
The spoil bard is plain 10mm acrylic. After 50 to 75 boards the surface of the acrylic becomes so scarified that the tape does not adhere well and I replace the acrylic

The real game changer is a freeware software utility called Autoleveller. With it you probe the PCB blank and the resultant data will be used the moderate the Z axis depth.
5um 'not deep enough' means that the copper is not cleared and your board is a failure, 5um 'too deep' and the engraving tool is cutting into the FRP under the copper,
while the angle of the engraving bit reduces the target width of the trace. To maintain 10um without the use of levelling software is just not practical. Even a brand-new seeming
flat piece of PCB will have 100um of warp over 100mm or so. With Autoleveller I get 98% success rates, and I shudder to think what I'd get without...20%????

Craig

I use a vacuum table for PCBs. I can shave the surface before I start so it is FLAT. I start with a thick top!
Some vacuum tables have holes everywhere. That is unnecessary and expensive.
A single central hole and a surface which is NOT ultra-smooth is all you need. Plus cheap tape around the edges to improve the vacuum.

Attachment 498434

I did try very narrow cutters, but they left raggy edges and too many copper whiskers. Now I mostly use a 1.0 mm carbide end mill.
Ah yes: then I check over all the bit of copper with a multimeter, looking for shorts.

Cheers
Roger