need to determine distance to steel

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kinneplastics
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need to determine distance to steel

Post by kinneplastics » Wed Mar 23, 2005 4:56 am

Anyone know a way to determine how far a cutting head is from steel? The steel is imbedded in a substace that is not metalic which I need to peal off to expose the steel without cutting into it, I would like to stop the cutting head perhaps .003" to .006" from the steel, the closer the better. My idea would be a reading head that rubbed against the surface to be cut away and have a PIC control the cutting depth. I do not want or need to make one deep cut, I would be working down slowly to the steel, perhaps cutting off just a few (10) thousands at a time.

terri
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Re: need to determine distance to steel

Post by terri » Thu Mar 24, 2005 9:48 pm

What might be helpful to know and possible techniques:<p>0. How big is the part? How deep or wide (kerf) a cut can be made? Is it a highway bridge or can it be held with tweezers?<p>1. Can an electrical connexion to the embedded steel be made elsewhere on the part? Is it exposed anyplace else besides where the cut is being made? That is, can an electrical contact between the cutter and the embedded steel be used to sense contact? Can a HiPot measurement* be used to sense the proximity of the cutter to the embedded steel?<p>2. What is the nature of the encapsulating (non-metallic) substance in which the steel is embedded? Is it conductive? Is it thermoplastic? Can it be melted --that is, can one melt one's way to the embedded steel rather than cutting one's way to it? How hard is it? Can you use a cutter which is softer than the embedded steel, but which will still cut the encapsulating material --like a bronze or copper or aluminum cutting head? Can you abrade the encapsulating material away with a soft wheel or a cloth wheel charged with a mild abrasive? Can a wire (bronze or soft steel) wheel be used?<p>3. How many of these parts are to be processed? On a onesey-twosey basis, can successive "tenth" cuts be made, the tool withdrawn, and progress observed?<p>4. How critical is it that the embedded steel be unblemished at the end of the operation? Is a one-tenth "nick" in its surface tolerable?<p>5. Can the part be molded so that the steel is exposed in the first place?<p>---
* HiPot measurements involve placing a very high impedance high voltage (high potential, hence "HiPot") between two parts (one of them usually ground) to determine the electrical leakage between the two parts. Used to determine the insulation quality of the device, usually for safety reasons. The voltage ("potential") involved is very high, but the current is limited to a low value (high impedance), so the process is pretty safe. No worse than getting a shock from walking across the carpet and touching a light switch --"surprising," but not life-threatening.<p>[ March 24, 2005: Message edited by: terri ]</p>
terri wd0edw

kinneplastics
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Re: need to determine distance to steel

Post by kinneplastics » Fri Mar 25, 2005 8:50 am

0 - The surface to be removed is about tree square feet<p>1 - There are reasons this would not be doable.<p>2 - it is non matalic, non conductive, it can not be melted. The cutter will not conduct. Our cutter is our great idea and can not be changed, it's what makes this idea work, the cutting width is about one foot.<p>3 - thousands<p>4 - Coming into contact with the steel with the cutter is not wanted<p>5 - no<p>I was really hoping for some type of IC chip radar, for measuring small distances, the coating to remove is less than one inch thick with only a few exceptions, then never more than three inches thick. the system would resemble a lathe and the cutter could be lowered a few thousands at a time until the senser told us we were at out limit. I do not know if there is anything like this out there, perhaps a micro metal detector??? Can one be that sensitive and that accurate?<p>Thank you very much for your response,
Wayne

rshayes
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Re: need to determine distance to steel

Post by rshayes » Fri Mar 25, 2005 11:13 am

A capacitance probe of some type should work if the metal is close to the surface. As the material over the metal is thinned, the capacitance will increase. By making a series of measurements as the embedding material is cut down, it should be possible to steadily refine the thickness estimate.<p>Another possibility is to use a gauge based on eddy currents. This may be better for long ranges where the changes in capacitance would be small. I would expect a capacitance measurement to be more accurate for distances of a few thousandths of an inch, but less so at distances of about an inch.<p>Commercial instruments are probably in the industrial instrumemtation area.

kinneplastics
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Re: need to determine distance to steel

Post by kinneplastics » Fri Mar 25, 2005 12:22 pm

I would like to thank Lothar for sending me an email of a circut using a hall effect transister, right out of a Raido Shack experaminters book! Looks like it should work great, Honeywell says it should be good to .002"<p>Thanks all, problem solved!
Wayne

terri
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Re: need to determine distance to steel

Post by terri » Fri Mar 25, 2005 3:21 pm

In only five posts? Imposserous!
terri wd0edw

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