Which drill sizes to stock?

[Lomax]

I've finally broken down and bought a CNC router, and now I need to get some PCB (tungsten carbide) drills for it. I'm pretty confused about drill sizes though - since there is a significant discount for packs of 10 (~£1 each instead of ~£1.50 when bought singly) - and since I'm sure I will be snapping them very frequently - I'd rather get 10 each of the most used sizes, but which are they? I know 0.8mm is very common, so that's a given, but should I get 1mm or 1.1mm for the next up? 1.2mm or 1.3mm? 1.5mm I think is also a given, but then what about screw holes; 2.1mm or 2.2mm for M2? 2.6mm or 2.7mm for M2.5? 3.1mm or 3.2mm for M3? What say the experts?

[Lomax]

In my cart, ready to check out, I currently have ten each of

• 0.8mm
• 1.0mm
• 1.3mm
• 1.5mm
• 2.1mm
• 2.6mm
• 3.1mm

But I've got a feeling this might not be a good selection... What should I change?

[mikeselectricstuff]

Depends on what sort of jobs you do.
10 each 0.8 and 1.0 definitely, others probably not as many as you won't use them as much and they're harder to break. I'd say 1.2, 1.5 and one or two each of a few sizes above that

[Lomax]

Thanks. So you reckon 1.2mm rather than 1.3mm?

[mikeselectricstuff]

Thanks. So you reckon 1.2mm rather than 1.3mm?

Really depends on what sort of stuff you need to fit. Compared to 1.0 and 0.8 it's a miniscule fraction of usage

[Lomax]

Thanks. Here's what I did in the end:

10x   0.6mm      PCB
10x   0.8mm      PCB
10x   1.0mm      PCB
10x   1.2mm      PCB
10x   1.5mm      PCB / M2 tap (maybe)
 5x   1.8mm      PCB / M2 tap (maybe)
 5x   2.1mm      M2 clear / M2.5 tap
 5x   2.6mm      M2.5 clear / M3 tap
 5x   3.175mm    M3 clear

They're all Kemmer Präzision tungsten carbide coated 1/8" shank drills, and the larger ones have a working length of 10.5mm. Should be good for clearance and tapping holes in acrylic, and probably aluminium, as well. Total cost ~£80 delivered.

Edit: In hindsight, this should probably have been posted in the "beginners" forum instead. Mods?

[mikeselectricstuff]

Thanks. Here's what I did in the end:

10x   0.6mm      PCB
10x   0.8mm      PCB
10x   1.0mm      PCB
10x   1.2mm      PCB
10x   1.5mm      PCB / M2 tap (maybe)
 5x   1.8mm      PCB / M2 tap (maybe)
 5x   2.1mm      M2 clear / M2.5 tap
 5x   2.6mm      M2.5 clear / M3 tap
 5x   3.175mm    M3 clear

They're all Kemmer Präzision tungsten carbide coated 1/8" shank drills, and the larger ones have a working length of 10.5mm. Should be good for clearance and tapping holes in acrylic, and probably aluminium, as well. Total cost ~£80 delivered.

Where from?

[nctnico]

Why buy so many? For creating a PCB every now and then you can use one drill for decades.

[Lomax]

Where from?

TME

Why buy so many? For creating a PCB every now and then you can use one drill for decades.

Maybe. Making PCBs is a new thing - I haven't had the equipment for it before - but I do go through a lot of drill bits for other things. The M2/2.5/3 drills will see other uses, and the thin ones I'm sure I'm going to snap at a high rate. Last job I did I snapped all the 1mm drills we had (3) in short order and ended up having to go buy more. And the stuff you can get in shops tends to be very poor quality; you have to order and wait if you want decent drills. There is also the volume (and shipping) discount; buy a couple here, a couple there, you end up spending way more. I'm also one of those people who likes having things to hand. I hope you're right and these will last me a very long time. To me that would only be a good thing.

Edit: I should perhaps point out that this is a business expense. I can see how spending £80 on drill bits might seem insane from a hobbyist perspective.

[mikeselectricstuff]

Carbide drills snap easily when used by hand, also occasionally in a stand, but should last a lot longer if CNCing at the right feed rate

[mikeselectricstuff]

Edit: I should perhaps point out that this is a business expense. I can see how spending £80 on drill bits might seem insane from a hobbyist perspective.

And of course it's not just the cost of the  item you need to consider, but the cost of not having it when you need it.

[Lomax]

at the right feed rate

And that's the rub. Although I used to work as an industrial automation engineer, that mostly involved programming robots and PLCs - I have zero experience of operating a CNC router/mill. I fully expect to break every single tool I fit it with for the next few months...

[Lomax]

And of course it's not just the cost of the  item you need to consider, but the cost of not having it when you need it.

Absolutely. Since I work a lot on site (exhibition electronics / embedded systems) I know only too well how important it is to have the right equipment to hand. I ran out of Dupont crimps last time, despite having brought along a new pack of 200 (I blame the Pi for everything having bloody pin headers these days) and in desperation had to hand solder a lot of the wiring. Not only did it cost me time; I know this will come back to bite me when it's time to service stuff.

[nctnico]

Edit: I should perhaps point out that this is a business expense. I can see how spending £80 on drill bits might seem insane from a hobbyist perspective.

Even as a business expense it is a rather large amount to spend on low cost drills which may low quality. I rather buy a few expensive drills which don't snap so easely. If you snap a lot of drill bits a good drill stand may be a better investment because at one point you'll run out of drill bits. Also the problem with stocking a lot of items is that you'll need to store it in a sensible way otherwise it will get lost which is just as bad as having no stock on hand.

[Mattylad]

What size would you make vias? They can be far less than 0.8mm

[nctnico]

I use a 0.6mm drill for that (and thin wire).

[jpanhalt]

For vias in some DIY boards, I have been using a #75 drill (0.021" or about 0.55 mm) and 24 AWG tinned copper wire.   The 24 AWG is about 0.020" or a little more and makes a nice fit.  Any burr or flattening keeps them from falling out during soldering. 

John   

[mikeselectricstuff]

For vias in some DIY boards, I have been using a #75 drill (0.021" or about 0.55 mm) and 24 AWG tinned copper wire.   The 24 AWG is about 0.020" or a little more and makes a nice fit.  Any burr or flattening keeps them from falling out during soldering. 

John

The trick to stopping them falling out is to bend the wire into a U shape, insert the ends through two holes , solder, then cut

[nctnico]

That is one way. Another is to raise the PCB slightly (a few mm), stick the wire in a via, cut it and repeat until all vias have a wire. Now solder all the wires, turn the PCB over to solder the other side and cut the excess wires. This works pretty quick. In the past I put the PCB on styrofoam but that way took a much longer length of wire.

[Lomax]

Even as a business expense it is a rather large amount to spend on low cost drills which may low quality.

http://hartmetallwerkzeuge.kemmer-praezision.com/de/Micro-Bohrer/SM32M

 

[westfw]

I end up using 0.6, 0.8, and 1.0mm drills for vias, component leads, and 25mil header pins, respectively.
2mm routing bit for cutting, and most bigger holes...  (as a hobbyist.  I might get more serious about mounting holes if I were more professional.)

[Mechatrommer]

Why buy so many? For creating a PCB every now and then you can use one drill for decades.

i broke a number of 0.6mm and smaller bits already. 0.3 or 0.4mm bit can break at an instant esp if one is dont have multimillion drill cnc machine like me, so an excess in stock should be wise.. i would say 0.7 or 0.8mm is good general purpose pcb drill, good for most dip chip and have acceptable strength to withstand slight vibration from cheapo diy drill machine, but i will usually find them too big for th passives components. For larger bits i dont care since they can be get easy few km away from local hardware stores and possibilty of breaking them is miniscule.