I cannot be the only one......

[Kishmul]

.....unless I am very smart or, more likely, very dumb.
Half way through a long cut the bit breaks or wears down such that it does not cut.
I need to stop the cycle, up the spindle, replace the bit, zero Z, return to last position (preferably a few lines of Gcode earlier) and restart the cycle.
Anyone got a work around for this issue?
For the moment I am making beautifully shaped, expensive firewood and I'd rather not!
Thanks in advance.

[ger21]

What type of machine do you have, and what type of bits are you using?
It sounds like you are cutting too slowly, with the RPM too high.

[thegreatwaldo]

Hi Gerry

I think this is a rhetorical question by Kishmul.

regards

Andrew

[A_Camera]

Anyone got a work around for this issue?

Surely the issue must have to do with the machine, material, tool, spindle, feedrate, spindle speed... and so on, so the workaround is to set up everything right. You must list/show more data before anyone can give you the right answer. At least a picture of your machine and a short list of current setup would help analysing your problems.

[Kishmul]

Thanks for the replies.
Stepcraft V1 420, HF350 spindle, 1mm ball nose. Step over 10%. spindle speed 15000 rpm, feed 15mm/sec, plunge 10mm/sec.
Material is a hardwood from Mozambique known as "brown ivory" noted for its blunting effect on tools. Job size is 130mm dia.
Roughing cut with 3mm end mill.
From the attached you can see, the overall job, the excellent finish that is achieved around the antlers, and (around two hours into the cut) that the finish is deteriorating on the Celtic knots just before the job was aborted.

[ger21]

Increase your feedrate 4x-5x, if your machine is capable of doing it. That should increase tool life proportionally.

However, many woods can contain silica, and other minerals, which can be very hard on tools. If that's the case, there's not a lot you can do to extend tool life.

[A_Camera]

Increase your feedrate 4x-5x, if your machine is capable of doing it. That should increase tool life proportionally.

However, many woods can contain silica, and other minerals, which can be very hard on tools. If that's the case, there's not a lot you can do to extend tool life.

...but he is using 1mm ball nose... so to be honest, I think that the speed he has can not be increased. 900mm/min may not be very fast but with such small cutter I think it should be OK. Also, "ball nose" doesn't really say everything. We don't know the number of flutes... we also have no idea about the depth of cut. If too deep it can break the tool if too narrow it can burn it...

[ger21]

If it's a finishing pass, following a roughing pass, it can certainly cut much faster. I've used a 1/32" bit (0.8mm) at 175ipm.

[thegreatwaldo]

Push up your rev per min rate to as fast as possible. Small cutters need a very high rpm rate so set it as high as possible 24.000 + would not be bad according to which router / spindle you have.

cheers

Andrew

[ger21]

Higher rpm will make things worse, unless he drastically increases the feedrate.