Self-stopping drill depth?

[Jabberwocky]

Hey all, I have a question which seems to be best-suited for this particular forum.

I want to drill through a relatively soft material, and once I reach a change in material density/hardness I want the drill to stop itself at that depth. I don't expect a screeching halt, but a general stoppage in depth. Is there any sort of drill tip geometry that would support this maneuver? I'm thinking something like an endmill or a ball-tip which would be able to cut the soft stuff but not penetrate the hard.

Thanks for the help!

 

[BiPolarMoment]

Hi Matt.

Is it required that the same instrument is used for perforating the near side cortical bone and drilling? If not, would simply blunting the ever living heck out of a typical drill style (118/120 deg) work? The cutting edges should be held proud of the cortical bone once it gets there and just spin on the tip (I think ). I assume you'd be doing some cadaver testing at which point you'd verify it one way or the other.

 

[Bribyk]

Assuming you're going through hard then soft and then want to stop at another hard surface, could you capture the piece of hard material in the tip (kinda like a hole saw does) so that it'll just stop cutting and rotate? Sounds tricky to get right but that's my outside-the-box thought for the day.

 

[Bribyk]

Or, you could set the feed rate of the drill, spring load the tip and measure the spring force or displacement. Then you'd know you'd hit something harder.

 

[AutoDrill]

Seems the issue here is removing the margin of error from the surgeon's hands, right? I mean, if they feel the difference in density, then they should know to stop but you want to guarantee that if they do not stop for some reason, the tool forces the procedure to halt?

With an automatic unit, we would do something like this with a linear measuring device as the feed rate through the harder material would be slower than through the softer material. Once a speed increase was measured, a PLC would look for a speed reduction again and know that it was time to cut power to the "spin" of the machine, etc...

I'm not sure if a rig or fixture could me used to set up a unit like this, and I'm sure there may be much more simple ideas out there, but this is how it would possibly be done in the automatic or production drilling world.

Make sure to post what you eventually find works so we can all learn something we will probably never use.

Regards,
Joe Agro, Jr.
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01.908.542.0244
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