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I have been having occasional strange behavior making small parts on my
cnc router and think I finally figured out what is causing it. I thought
it was miss-feeds or just about anything else but have almost certainly
determined that there are (fortunately occasional) blocks of wood that
are unbelievably hard, almost impossible to cut. I discovered this today
and am using a SouthEast tool 1/4" down spiral bit that is almost virgin
so it is not the tool.

The spindle boggs down and then all hell breaks loose while moving with
no cutting action. Or at least I think this is what is happening. quick
estopping resetting the machine and starting over confirms that the wood
is in fact very difficult to mill.

I am using an xbox controller that has plenty of spare
buttons so I configured the big 4 way toggle button to be feed hold.
I did not want to use feed hold because I thought there was a warning
about resuming from feed hold. But I tested it and it seems to work correctly

When I get the first indication that a piece of wood is like a stone, I hit
the feed hold button on the xbox, set the feed to 40% and hit run again.
Then before running the next part I set it back to 100%

Wouldn't you know that right after implementing this I ran into a wooden
rock and the method worked.

It has been years since I set up the VFD spindle controller and I sort
of think that I have it halt on overload. Maybe I should turn that
feature off and hope it powers through at a slower speed? Seems like a
pretty awful idea to me?

Any opinions of screwing around with the spindle fault settings?

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I'd guess it's a spindle issue, unless you are making really deep cuts at high speeds. Other than cutting through a know, no sharp 1/4" tool should have trouble cutting through any wood. How powerful is your spindle?

Ger

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the motor is more than adequate, i think it is 2 HP wired with a fairly short proper cable. I should check the connections could have loosened.

I have a big button estop that cuts power to everything but the computer and breakout board and ESS so I am only using the estop on the breakout to not allow the program to run if the motor is not running but this does not work as I would like. I was cautioned to use only NC estop for safety reasons but feel confident that I can us NO as long as I have the mechanical estop. So I am going to change the VFD inverter to? close the relay contacts (unfortunately it only has NO contacts) when it faults or when the motor current overloads.

This wood is really strange, almost all of it cuts just fine. But occasionally when starting into endgrain it provides a lot of resistance. Again 95% of the time it is fine cutting at fairly high speed but just occasionally it it a problem.

I might also experiment with different speeds for the arcs that lead into endgrain. All of my circles and D shaped cuts are made of multiple arcs so this experiment should not be too difficult. However I have found that in general it is not good to vary the speed in a series of arcs.

Wood is definitely a different beast from metal or plastic. Never have any of these problems with other materials.

I'd guess it's a spindle issue, unless you are making really deep cuts at high speeds. Other than cutting through a know, no sharp 1/4" tool should have trouble cutting through any wood. How powerful is your spindle?

Ger

On 2/5/2022 5:11 PM, spencer@... wrote:

I have been having occasional strange behavior making small parts on my
cnc router and think I finally figured out what is causing it. I thought
it was miss-feeds or just about anything else but have almost certainly
determined that there are (fortunately occasional) blocks of wood that
are unbelievably hard, almost impossible to cut. I discovered this today
and am using a SouthEast tool 1/4" down spiral bit that is almost virgin
so it is not the tool.

The spindle boggs down and then all hell breaks loose while moving with
no cutting action. Or at least I think this is what is happening. quick
estopping resetting the machine and starting over confirms that the wood
is in fact very difficult to mill.

I am using an xbox controller that has plenty of spare
buttons so I configured the big 4 way toggle button to be feed hold.
I did not want to use feed hold because I thought there was a warning
about resuming from feed hold. But I tested it and it seems to work correctly

When I get the first indication that a piece of wood is like a stone, I hit
the feed hold button on the xbox, set the feed to 40% and hit run again.
Then before running the next part I set it back to 100%

Wouldn't you know that right after implementing this I ran into a wooden
rock and the method worked.

It has been years since I set up the VFD spindle controller and I sort
of think that I have it halt on overload. Maybe I should turn that
feature off and hope it powers through at a slower speed? Seems like a
pretty awful idea to me?

Any opinions of screwing around with the spindle fault settings?

-- 
Best regards, Spencer Chase
67550 Bell Springs Rd.
Garberville, CA 95542 Postal service only.
Laytonville, CA 95454 UPS only.
Spencer@...


(425) 791-0309

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I have tried every speed and feed combination and almost anything works for 90% or more. It is just that less than 1% where I have to reduce the feed to about 40% and it still chatters.

I tried to make the motor driver fault when the motor is overloaded and can not do it. The minimum max amps is something like 1.9 amps and holding a wooden stick on the spindle nuts until it burns, the motor does not stall or trip the overcurrent so this is not an option.

However I think I finally figured out what the "real" problem is. The motor has plenty of power and the bit can certainly cut through almost anything. I have a forth axis to machine three surfaces of the part. It uses a stepper and a pneumatic that "locks" the forth axis in place. However is is just a block that clamps one of the three surfaces of the pneumatic "vise"

What is actually happening is that when the bit hits the strange hard uneven end grain instead of cutting it moves the part along the third axis tries to climb the block and just plain fucks up. I had noticed the vise moving along the fourth axis (rotary) but never made the connection that this is the beginning of the serious fuckup. If the fourth axis did not budge the bit would probably roughly chew through the tough grain.

So after I get some work done today I am going to make the "lock" a real lock with a pin instead of just a clamp. However when the awful chatter happens it is likely to lose steps so I have to re home the machine but at least I will not break the cutter or run it into the cylinder on the vise or ??? in the next move.

Spencer, you might try reducing your spindle rpm. Hardwoods sometimes burn and form a carbon layer at higher speeds.

-- 
Best regards, Spencer Chase
67550 Bell Springs Rd.
Garberville, CA 95542 Postal service only.
Laytonville, CA 95454 UPS only.
Spencer@...


(425) 791-0309