Drill bit settings

Looking for information on tool database settings for drills. I’m a new CNC hobbyist so I’m learning, but I am also a design engineer. I’m using Vcarve. What useful information I have found varies widely. My drills are number size stub length M42 carbide split point. Here are parameters that I have:

6000 Min RPM machine limit
Hole sizes from 1/4 down to .104 thru holes in 3/4 curly maple Janka 1450
SFM 300-400 for wood from a chart.

I have information that recommends speeds of 1500-3000 RPM that I would figure is meant for drill press. I have a chart that shows speeds for wood within the limits of the machine for the size ranges I am dealing with. I can make the calculations if I get some good advice from someone with some experience.
Anybody out there?

Hi Philip,

Congratulations on entering the CNC world! There is lots to learn about tools and the operations they can perform. Twist drills require much slower speeds than mills, and figuring out what works on your setup, in your particular material of choice, is a learning process.

You can bet that you’ll be breaking at least one drill in your CNC router as a result of learning.

In general, the smaller the tool diameter, the faster you can turn it. But remember, taking lots of little ‘bites’ on each revolution means that you cannot travel very fast (feed rate).

Most speeds and feeds charts are calculated for metal, meaning that they feed much more conservatively than what you would want for wood. They also have much higher rpm suggestions than what you want for wood. This makes sense when you consider how much more dense metals are than woods.

The moral of the story is that you want to turn far less than 6000 rpms for number drills, maybe more like in the hundreds of rpms. This takes router motors out the realm of possibility. A proper spindle is what you will need. Do you have a spindle or a router motor?

Hi Phlip,

You can use twist bits on the CNC router, with some caveats. You have to get your router running a bit slower. I have over ridden the min speed on min so I can run down to 500 rpm. If you run at 6k rpm, especially on bits >0.25" you will likely burn the holes. I am told the newer frequency drive that comes with the new Hiteco spindles won’t go down to lower speeds, but I can’t verify that. If you can get it down to 2k, you will probably be ok for most small bits. You have to take it easy with long thin twist bits because they want to deflect when starting (you can always start them with an endmil and come back and drill). Using peck drilling to keep the chips cleaned out is a must as well. Here is a video I did last year on the topic. Drilling with standard twist bits on an AVID CNC Router - YouTube
jim

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