how to measure temperature of a rotating drill bit 3

[khalchris]

I am trying to measure the temperature of a drill bit while drilling metals, I intend to pass the thermocouple through the one of its coolant holes , the problem is that the drill will be rotating and the thermocouple should send the temperature reading in a wireless way to the data logger ,is there such wireless method which I can use to capture the temperature while the drill is rotating. or is there any small wireless temperature sensors ?

I don't want to use a thermal/IR camera..

 

[itsmoked]

No there is no way to measure this directly. The direct rubbing, cuttings transport, rotation speed, coolant spray, and changing geometry of the entire system will prevent any success at direct measurement of the drill bit's temperature. Indirect measurement will have Heisenberg all over your ass too.

Why don't you do what everyone else does and just flood the contact area with enough coolant to preclude the drill ever overheating?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Are you at all uncertain about this Keith?? grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

I'm sure NASA or someone insane enough to make their own drill bits could bore-drill them for a TC. Followed by heat treating them, coating them, using them, followed by wondering how the measured temperature equates to the actual cutting edges...

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

What size drill bits???

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

Chuck up the material to be drilled and spin it against a stationary drill bit.

 

[IRstuff]

Unless the TC is located at the tip, you'd only be getting a shadow of the actual temperature. Nonetheless, if you are insane enough to do it, you could possibly wire up a thermistor to a small Arduino with a Bluetooth shield, and lots of silicone to keep it from flying apart.

TTFN
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[VEBill]

Or make the following minor change:

I do n't want to use a thermal/IR camera.

 

[MacGyverS2000]

David is thinking along the correct lines... drilling on a lathe is often spinning material with a stationary bit.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

One other option would be to measure the temperature externally, i.e., move the bit to a fast TC or thermistor, grab the temp and move back. There are/were temp sensors that had response times on the order of a few milliseconds.

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[77JQX]

Could one use the interface between the bit and the drilled material as a thermocouple junction? And measure the voltage from the bit to the drilled metal?

 

[btrueblood]

Had a similar thought, 77JQX. It would have to be calibrated somehow (put a compression-loaded test sample of the two materials into an oven, and measure Seebeck voltage over a big enough temperature range), and the noise of the cutting interface making what is likely intermittent make/break contact would have to be filtered from the signal...but it might work. Passing the voltage across the rotating interface would be a challenge, but there is a simple method. We used this to measure strain gages on parts spinning in a lathe: simply let the leadwire out through the lathe headstock, providing enough length for the wire to twist/wind up and limiting the sample time to a fraction of what it takes to snap the leadwire (then rewinding the wire by reversing the motor between runs).

 

[OperaHouse]

Great idea. I had a similar thought. Any two metals can make voltage. To save space in the cooling hole, only run one one wire down and spot weld it to the tip and calibrate. Of course that all depends on the drill tip being metal.

 

[IRstuff]

However, the problem is going to be that there will be an extremely tenuous electrical contact between the bit and the metal, potentially further compounded by anything like a coolant or lubricant.

Actually, another option is to build a slip ring around the drill head.

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[jraef]

Indirect measurement will have Heisenberg all over your ass too.

This weeks award for obscure humorous physics reference goes to... itsmoked!


"Will work for (the memory of) salami"

 

[MacGyverS2000]

I'm not sure I'd want to be the engineer designing the circuit for such a thermocouple... the noise would be atrocious.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[MikeHalloran]

One off the wall thing I'd like to try; bore a small hole along the drill's path in the test article, and fill it with insulated t/c wire. In the case of an iron article, maybe you could just use constantan. Then the passing drill flute would smear the wire into contact with the test article, however briefly, giving, maybe, a discontinuous thermocouple reading.

... yes, it would be a reading of the bulk test article temperature near the cutting zone, possibly not too different from a measure of the drill flute temperature somewhere near the cutting zone.





Mike Halloran
Pembroke Pines, FL, USA

 

[VEBill]

In theory it would be a thermocouple. In practice it would be an electrically-noisy mess, and then the drill would rip the wire out the hole.

This thread reminds me of The Old Barometer Joke.

 

[MikeHalloran]

I agree that instrumenting a drill fixed in a lathe and rotating the test article is the most likely arrangement to produce usable data.

There are some problems.
Few lathes spin fast enough to get a drill flute up to optimum speed.

So, don't use it as a drill. Put it on the cross-slide, at say 75 degrees behind the axis, and use the instrumented flute to shave the face off a plate. The surface speed goes up as the drill is fed from the center, prebored hole, to the periphery, in a way that's independent of the drill diameter, but it can go fast enough to give data that will represent real drilling conditions with a fast spindle.

That may not give a representative temperature, because it removes friction from the drill's chisel point from the situation, and also whatever heat is associated with dragging the flutes against the drilled surface. ... but maybe you wouldn't want those contributions included anyway.





Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

Not necessarily that noisy. If the OP uses a 100 ohm PRT, that might be pretty reasonable, given that he could filter the signal ad nauseum.

The problem with instrumenting the article is that the article, being metal, is essentially a giant heat sink. It's probably going to be nowhere near the temperature of the bit.

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