still kicking

[rweigel]

pictures of flex shafts and controller

 

[Sinterklaas]

I stand corrected.
I guess I at least got the bit about the unruliness of a flexshaft right..

I am curious, if the slower RPM and higher torque is more manageable for cutting stone seats, how does a micro-motor perform when cutting other more brittle mediums? such as glass, eggshell, mother of pearl, or abalone?
This may be a unusual question, but have you ever used it to try and remove a broken screw or tap from a hole? I'm curious of other advantages of the torque over RPM and if, with appropriate technique, there is any true benefit to higher RPM..

For brittle stuff it works also. At low speeds. But then I would use diamond burrs. They have no teeth so they won't really start to run off on you.
I have also used either carbid or diamond burrs to remove broken burrs and taps. It work well. Just go slow so the tool will stay cool. And will keep its cutting properties much longer.

Dentist use high rpm tools. But they are always watercooled. The dental machines all have a water jet shooting at the burr to keep it cool and maybe to prevent dust that is breathable.

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Dani, Another problem might be how you hold the tool.
If you hold the motor to far back it will run off.

I hold the micromotor at its very tip. Just like a pen. And I even have 1 finger against the shaft of the burr. And an other finger on the metal. So I have good control close to the cutting action.

 

[Meshach]

For stone setting I use only flexible shaft tools at low speed. Position of the stone marked with a deep dot from a scriber, I drill first a 0.5 mm hole through the metal with a spiral drill. For the rest of the work I use round dentaI reverse the direction of rotation. Build a special controller for this, with a selector switch for my 5 flex shafts. The burr will still remove material if rotated in the wrong direction, but much slower and without chatter. I set down the burr on the metal and start rotation slowly with the foot pedal. Thanks to Ganoksin for the “reverse rotation” idea…
...
I mounted 5 flex shafts (4 of them light and small like the Dremel flex shaft) onto DC motors with different max. speeds, which I control all with one foot pedal with selector switch.

Reverse direction.. .. at first I missed the part about having mounted the flex shafts to dc motors and was dumbfounded how this could be done but upon checking the 2 foredoms I have access to I found that one is indeed AC 120 but low and behold the other is a 120v DC motor .. I believe this could be adapted for reverse with a simple pigtail with an inverted plug at the footcontroll... And after reading the post in this thread, perhaps I will be starting down another rabbit hole of tools..
This .470 inch (12mm) flex shaft still seems less than optimal for handling with fine inlays, perhaps I just need to 'relocate' it to the engraving bench to try some finer work with it.. the picture you provided appears to have different sizes of flex shafts, is that just an optical illusion or are there indeed various sizes (diameter) available?