Drilling holes on cnc

[m_c]

For general purpose drilling, I'll normally get Cobalt drills. More durable than pure HSS, but typically slightly more brittle (not as brittle as pure carbide though!), and can handle higher speeds than pure HSS (but no where near as high as pure carbide).
Polished ones for aluminium, and suitably coated ones for steel.

Key thing is to ensure you are within the speeds/feeds specs for the drill, and as Chaz/Wal say, with Chinese spindles that can be a problem. You'll likely get better results on larger holes by either pre-drilling then milling to size, or just helix milling.

Spot drilling depends on what you're doing. I generally only use stub drills with split point (or whatever the manufacturer wants to call their self-centring drills), which I'll never spot drill first. However anything I need to use any longer a drill on, I'll generally spot first.

[wiremonkey]

Hello,
Drilling accurately placed holes is not easy. I strongly suggest screw length bits, the shorter the better, to eliminate deflection. I'm fairly new to cnc and posted a video of my experiences drilling holes here: https://www.youtube.com/playlist?lis...jVPFZmTCBEeF2y
I should add that I bought an old 3/8" Jacobs chuck off of ebay and a straight 1/2" shaft for it. I chucked it up in a precision collet on the router and damn if it doesn't work perfectly. For drilling operation, no more changing collets or needing collets for every different size. I highly recommend it. I show it in the video I linked to above.
Cheers, Tyler

[routercnc]

I use a mix of 3mm HSS twist drill in a standard 3mm collet to pilot holes (no spot drill), and then finish on the drill press. Or interpolate holes using a 6mm end mill ideally with a spiral toolpath. Fusion is great for this.

These end up being very accurate although for bolt clearance holes I often go for bolt nominal diameter plus 0.5 mm to give some allowance in assembly.

See examples in my videos here:

4:40 and 10:40
https://www.youtube.com/watch?v=wqff3IZZWvw