Drilling holes cause breakage

I’m trying to drill holes into laminated wood boards using the millone, however when drilling some holes the whole thing goes “pop” and I notice the motor slows down and the finish looks like the hole on top, but other times the finish is good like the hole on bottom. I tried 100 as the feed rate and 25 as the feed rate but both have the same issue. What am I doing wrong? The drill bit is 1/4"

@zhumxcq Welcome to the group.

Are you using a drill bit or an end mill? What make is your router? At what speed are you running the router?

What software are you using to generate the Gcode?

Finally, when you mention feedrate, are you running metric or imperial?

Lots of questions with no answers, I realize. But with the answers, I’m sure we can help you out.

Thanks for the reply, I’m using 1/4" end mill but I notice similar things using a drill bit as well. The router is Makita and I have speed set to “2” on the router. I wrote the Gcode manually myself, currently using
G0 X0Y0Z0
G1 X0Y0Z-20F20
G0 X0Y0Z0
All units including feedrate is in metric MM. I use GRBL Panel to run the GCode

@zhumxcq It’s not clear to me what the F20 means. That is, I know that it is the plunge rate, but I don’t know enough g code to know what measure it refers to and what interval. Is that 20mm/sec, 20mm/min. You’ve said that you are in metric, but I don’t see an indication of that. So, to me, in my ignorance, this could be 20in/sec or 20 in/min.

All that said, you don’t say if you are using a downcut or an upcut mill. Looking at the pic showing the blow out, I would guess that you are using a downcut bit and plunging too quickly. Are you getting a clean cut on the top of the material?

Now that I think about it, it is 20mm/min, as it is very slow when plunging downwards. It is originally set to 100mm/min. The blow out are happening on both sides, I’m not too sure if it downcut or upcut, I can take a look tomorrow. This blow out is also happening with 1/4" drill bits as well.

I think the problem is heat. Going down 20mm in one pass that slow will cause the chips (or dust) to stuck onto the mill and not to come out of the hole. The glue will enforce this. Try to go in more passes like:
G90G1 X0Y0Z-5F50
G1 X0Y0Z2F100
G1 X0Y0Z-10F50
G1 X0Y0Z2F100
G1 X0Y0Z-15F50
G1 X0Y0Z2F100
G1 X0Y0Z-20F50

Btw, I think 50mm/min is still too conservative, could/should be me much higher.