Renishaw touch probe bits

[gerry maddenParticipant @gerrymadden53711]

I purchased some setting rings at an auction recently and the lot included a number of bits and pieces. One of these was a small box containing parts of a Renishaw TP20 touch probe from a CMM.

I did think I would attempt to re-sell it but I’m wondering if I can make a edge-finder out of it. There are two small brass contacts on the upper face of the unit, which look like electrical contracts, but these seem to be open-circuit regardless of whether the probe tip is touched or not. So its either broken OR I have no idea what I’m doing!

Can anyone advise me as to how this probe unit indicates to the CMM that its touched something? Reading the booklet in the box that the probe came in, the tip sensitive to 1/2 a micron deflection, so its a pretty clever device 🙂

Gerry

 

[SillyOldDufferModerator @sillyoldduffer]

Could be a strain gauge rather than resistive sensor?  The latter requires a voltage to be applied, and detects a current change on contact. Ohmmeter required.

A strain gauge produces a voltage on contact, so I guess no external power needed unless it contains an amplifier.  Voltmeter required.

Another guess: the resistance change and voltage produced are both tiny, requiring a sensitive multimeter or a scope to see what happens.  The electronics in a CMM are probably more sophisticated than a simple on-off switch detector.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Fuelled by lust and envy … I had a quick dip into the Renishaw site:

https://www.renishaw.com/search/en?term=tp20

looks a good place to start.

MichaelG.

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Edit: __first iidentify what you have

https://www.renishaw.com/cmmsupport/knowledgebase/en/tp20-touch-trigger-probe-kit–13528

[DiogenesParticipant @diogenes]

You could try a thoughtfully worded enquiry to Renishaw themselves, they do take some pride in levels of product support and a lot of pride in their ‘local’ (and national) connections – they still operate (more-or-less) as a family business.

I guess you have visited their website and seen the manual.

They ‘do’ nearly all the relevant trade shows, which might provide an ‘opening,’ or you could try dropping them a line through their support site.

Nothing to lose.

 

[DiogenesParticipant @diogenes]

See ‘Scanning Probe Connector’ below..

https://www.renishaw.com/cmmsupport/knowledgebase/en/connectors-and-signals–13753#:~:text=This%20socket%20is%20intended%20for%20use%20with%20the

 

..search term was ‘Pin outs for Renishaw TP20?’..

I really must go to work..

 

[Michael GilliganParticipant @michaelgilligan61133]

216 patents of potential interest:

https://worldwide.espacenet.com/patent/search/family/027516963/publication/US5505005A?q=nftxt%20%3D%20%22renishaw%22%20AND%20nftxt%20%3D%20%22touch%20probe%22

MichaelG.

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Edit: Not sure if it is directly relevant to what you have, but this one is refreshingly ‘readable’

[Michael GilliganParticipant @michaelgilligan61133]

 

Image credit:

https://2000signs.com/products/under-new-ownership-18×24-store-business-retail-promotion-signs-1

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More to follow in due course

MichaelG.

[Robert Atkinson 2Participant @robertatkinson2]

I missed the start of this thread. I’ve used these probes in custom machines.
They are closed circuit when undisplaced and open circuit when displaced in any direction. If this one is reading open when untouched it is faulty. This couls be due to mechanical displacement or damaged contacts. The contacts are not designed to carry any significant current or voltage but checking with an multimeter on Ohms is OK. Check to see if the probe looks and feels like it seating properly. Also check that the external surface of the rubber bellows is clean and undamaged. They are mounted to the CMM arm or CNC magnetically so that in a crash they are knoked off rather than damaged.

Robert.

[Michael Gilligan]

On Michael Gilligan Said:.

More to follow in due course

I am delighted to say that Gerry has too many other important projects at the moment, and he therefore offered me the opportunity to buy this from him.

In the world of CMM, this little unit is at the thin-end of a very costly wedge … but my ambition is to see what this impecunious amateur can make of it.

Please don’t expect any rapid progress, or any sophisticated machining [a look at my Profile will explain why] but I will be doing what I can, as-and-when.

The patents, and some of Renishaw’s published documents make very interesting reading.

MichaelG.

[Robert Atkinson 2Participant @robertatkinson2]

Hi Michael,

I designed an interface for one of these several years ago. I’ll see if I can dig out the details. It sensed the contact resistance per Renishaw specification, lit the LED on the mount and provided a open collector output.

Robert.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Robert …

I spent a little while last night watching this:

https://youtu.be/m2D4iYep_pQ?feature=shared

which seems to point me in the right general direction … but your advice is always welcome.

MichaelG.

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Must admit, I was very impressed by Renishaw’s throw-away comment here:

[Robert Atkinson 2Participant @robertatkinson2]

It was back in 2016. I can’t find the information at the moment. I did find a note clarifying thet it was a dual comparator design.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks anyway, Robert

As indicated earlier, this is going to be a long, slow, and probably intermittent project for me.

One happy note is that I opened the “cleaning kit” which still contains almost three full strips [it looks like there were originally four] of a white putty that works just like the Rodico that watchmakers use … so a grubby little TP20 looks much better already.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Yes, it’s all a bit obsessive … but when you’re hoping for sub-micron repeatability,it matters !

https://www.renishaw.com/cmmsupport/knowledgebase/en/14906.aspx?srsltid=AfmBOoordl8Ih_e8TXXteOvrxGAV63bqaK4SmFM07zWh8porBcPc06Ts

MichaelG.

[Les RileyParticipant @lesriley75593]

I would love a proper Renshaw unit but couldn’t justify the cost. I ended up making my own.

It works on the three pairs of ball bearings and a tri-lobe centre principle.

I use it for location on my CNC mill via an ad-on wizard for Mach 3.

It is surprisingly accurate for such a crude device.

[ChrisLHParticipant @chrislh]

Les,

Very nice. I’d be very interested to know how you cope with runout of the probe tip. Ignore, adjust mechanically, compensate electronically, etc. ? Do you get more accurate results than are obtainable with a wiggler or edge finder ? I appreciate that there are reasons other than accuracy for using such a probe.

[Michael GilliganParticipant @michaelgilligan61133]

Well done, Les !

MichaelG.

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For anyone interested …these are, I believe, the two most significant patents that cover the switch:

US 5505005 … and specifically the fourth embodiment

US 4153998 … this is the original, By Rolls Royce

[John HaineParticipant @johnhaine32865]

A year or two back a design emerged from China that is widely available on eBay and AliExpress at low price points.  I bought one and it seems well made and accurate.  Like most such designs there are adjusting screws for probe concentricity.  These ones are nice because the shank is 6mm and they don’t take up much height.  I haven’t used it much in anger yet.

Probing is a fascinating topic (which is why Renishaw have made so much money from it over the years).  Their latest probes are wireless and are designed to operate while the spindle is turning at ~1000 rpm!  I have seen mills with auto tool changers where the probes are sitting in the tool magazine so they can be swapped in as needed during a cutting program.

[Les RileyParticipant @lesriley75593]

Chris,

The actual probe tip is a Renshaw one, from a “source”.

The whole centre is held on the three round head philips screws that you see. They are in over size holes to allow for a small amount of adjustment. Also there are three small hex grub screws in the outer rim to push the base about (you can see one of them). I set up the tool in the mill with a DTI against the ruby ball and fiddled about for best position until I got zero movement on the DTI.

Then, in the wizard I use ( https://www.craftycnc.com/probe-it-wizard-mach3/ ), you can do a calibration routine based on a known round object. I used a large ballrace centre.

The unit is then always placed in the same rotational position when probing.

The wizard then allows many different shapes and edges/corners to be probed and fixed as a zero point for the start of an operation.

 

[Michael GilliganParticipant @michaelgilligan61133]

Noting that Les very sensibly used a Renishaw stylus, I have put a copy of their catalogue for same in my ‘Documents Gallery’ … it makes for interesting browsing.

MichaelG.

[mgnbukParticipant @mgnbuk]

One happy note is that I opened the “cleaning kit” which still contains almost three full strips [it looks like there were originally four] of a white putty that works just like the Rodico that watchmakers use

Renishaw used to use BluTack for cleaning magnetic attachments. I used to use a Renishaw Ballball system for doing dynamic checks & calibrations on CNC machines that was held together in operation with magnets – the “cleaning kit” provided with that was a pack of BluTack with a Renishaw part number sticker attached.

Nigel B.

[Michael GilliganParticipant @michaelgilligan61133]

That’s interesting, Nigel

The white material tat came in my box performs MUCH better than regular BluTack

… but it also costs a lot more.

MichaelG.

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Edit: __ Curiously; what they are listing now is said to be Yellow

https://www.renishaw.com/shop/Product.aspx?Product=A-1085-0016

 

[ChrisLHParticipant @chrislh]

Thanks for the explanation Les. I did notice the screws but didn’t put it all together !

Michael, I wonder if your cleaning material is White BluTack. The sample I have is quite a lot stickier than the blue version.

[ChrisLH]

On ChrisLH Said:

Michael, I wonder if your cleaning material is White BluTack. The sample I have is quite a lot stickier than the blue version.

I have no way of knowing, Chris

… from my personal recollection, it seems to handle more like the [Green or White] Rodico material than any of the Bostick products … softer and more malleable, and generally ‘more sophisticated’

MichaelG.

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https://www.cousinsuk.com/product/rodico

 

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[Michael GilliganParticipant @michaelgilligan61133]

For the entertainment of our Electronics enthusiasts …

 

US Patent 5279042 describes the function of the innards of that innocent-looking ‘Probe body’ module to which the trigger probe module attaches.

MichaelG.

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