Self-stopping drill depth?
Self-stopping drill depth?
(OP)
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!
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!





RE: Self-stopping drill depth?
What are the differences in hardness?
What thicknesses are involved?
RE: Self-stopping drill depth?
RE: Self-stopping drill depth?
The depth is the variable, the only sure thing is that the far end of the hole will have a harder, denser, stiffer material than the rest of the shaft.
I'm about where you are MintJulep - nothing simple comes to mind.
Thanks for the help!
RE: Self-stopping drill depth?
Here is one that encompasses all aspects of drilling which might be a little much for your application. I will look around for additional types such as the ones used on commercial routers.
www.ovationengineering.com/compensatordatasht.pdf
RE: Self-stopping drill depth?
RE: Self-stopping drill depth?
RE: Self-stopping drill depth?
How thick is the base layer?
What is the allowable depth tolerance?
Any dielectric constant difference?
Any optical transmission difference?
Not that this would result in anything simple...
If there was something optical, one could potentially create, effectively, an optical depgth gauge.
Likewise, if there were some dielectric constant difference, one might be able to create an electronic depth gauge.
If the base layer is conductive but the epi is not, then a simple conductivity sensor might work.
TTFN
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RE: Self-stopping drill depth?
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Self-stopping drill depth?
My goal was to geometrically limit the drill shape to prevent puncturing the far cortex of a bone. The tolerance is a few millimeters, but going too long is not an option, only stopping short. (+ 0/- 2mm). Electrical and optical methods may be out just due to cost and complexity (and sterility).
Doesn't a paper drill require a pretty significant amount of force? What would stop it from breaking through something hard on the bottom side?
RE: Self-stopping drill depth?
How is the depth controlled when operatiing done on the skull?
RE: Self-stopping drill depth?
Mike Halloran
Pembroke Pines, FL, USA
RE: Self-stopping drill depth?
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Self-stopping drill depth?
What is the hole size.
As I understand it you want to drill perpendicular to a somewhat round object with unknown wall thickness to a set distance.
How about a fluoroscope?
My wife has a broken back,no T8 vertebra, and receives monthly injections of pain medication. The doctor uses a fluoroscope to position the point of the injection needle as close to the spine as possible.
I also just had a stent installed and the fluoroscope they used was impressive as to the detail on screen.
RE: Self-stopping drill depth?
If you wanted a round hole I'm pretty sure it wouldn't be difficult to make the same tool with a round tube around it that is sharpened appropriately. The blade acts as a safety stop because it will not pass through the bone so stops the drill from piercing it. (OK I'm guessing at this but it sounds feasible to me!!)
RE: Self-stopping drill depth?
Sounds like DEXA might do the job: ht
h
TTFN
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RE: Self-stopping drill depth?
There may be some possibility of running a flatter bit with just a small point and running it high speed to get through the first cortical layer, and then dropping the speed way down going through the spongy bone. As the bit gets to the far side cortical layer, it won't be going fast enough to drill through, and it'll be scraping the inside surface, which might be detectable as a sound or vibration change in the drill.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Self-stopping drill depth?
RE: Self-stopping drill depth?
I think for cranial screws they use something more like a burr to remove material slowly - although I did find this patent:
http://www
which seems to only apply if you know the depth ahead of time.
Power source is usually electric. My holes can be 2 to 4mm, depending on the type of screw.
We're not drilling through flesh or muscle, that has all been resected above our bone and we're trying to prevent the drill ever touching the anatomy below the bone. IRstuff has it right for the boundaries - but we're not under any computer control, just surgeon brainpower.
I'll ask around about a flat bit / zero lip relief angle. Unfortunately our drill materials are pretty tightly defined by FDA regs.
Thank you all for the great brainstorm!
RE: Self-stopping drill depth?
Pretty cool device, seems to do almost what I wanted, although theirs are only used for skull thicknesses, I don't see why you couldn't adapt it for a more variable depth.
RE: Self-stopping drill depth?
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
RE: Self-stopping drill depth?
RE: Self-stopping drill depth?
RE: Self-stopping drill depth?
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.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.Drill-N-Tap.com
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