Author Topic: Best setup for probing a trumpet mouthpiece  (Read 10180 times)

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Offline resonance

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Best setup for probing a trumpet mouthpiece
« Reply #10 on: November 17, 2015, 10:41:10 AM »
Update: probe arrived, connection made, stylus installed (Renishaw, 15mm long, 1.5mm ball).
I had to install ProbeIt Turn (30 dollars VERY well spent!).

Here are the problems I had to solve: the software can't handle both big diameter ruby tips. 3mm with a step over of 0.5mm won't happen.
If you need a small step over like 0.2 or 0.3mm you need a 1.5 or 1.0 ruby tip.
The software is very easy to use but it needs many points and very close together to behave in a reliable way.
Export is both points and lines Ina DXF file, easily imported into any cad program.

Installation is very easy if you know how to solder two wires and how electricity works... I don't so I asked a friend and watched him doing it. It was easy...

You have to map one of the input channels to Digitize. The probe is always short circuited unless you open it by pressing the probe. This is for safety, makes sense...

The logic of the ProbeIt Turn is simple and clever: you first touch off the piece telling the wizard how big is the radius it's touching. Then you tell it how to move (clock or counter-clock wise) and then it will start probing. Every touch it makes it will move further on the side. If it senses the surface is curving it will try to guess the corner radius and thus it will make a "side step" that will follow the surface to be always square to it.

Problems: the stylus is always prone to some bending when it touches the surface, this depends on the stylus length, thickness, probing feed and probe sensitivity.

All of this can be solved by a little bit of math: you prove an external diameter, then an internal diameter. You calculate how smaller the distance is and this is the error. Divide it by two and make an offset of the scanned profile. Then simply translate the profile towards the center by that amount.

If you have backlash just enable the correction under Mach3, it will be cured properly.

The final test was to cut a mouthpiece with my lathe and then immediately scanning it.
I made a few cross checks and the measures are off by less than 1/100th of a mm!

There won't be many trumpet players here but this procedure can be useful for other purposes as well.

Have a good day!


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Offline RICH

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Re: Best setup for probing a trumpet mouthpiece
« Reply #11 on: November 18, 2015, 08:53:46 AM »
Thanks for the update. Was wondering how things were going.

Did they fix the problem with the new lathe and is that what you used?

I downloaded ProbeIt but have not tried it. It will not work with my new  screen set and have not contacted them to see if I would be able / allowed  to change the scripting
if purchased.

You can do some calc's to find how much over travel post probe touch off due to Debounce and Deceleration.
I use a slow federate of 1 IPM for probing and based on that the calculated overtravel into the material is 0.0000390" and  repeatability here is +- 0.0002" with
a "fixed probe". The probe I had for years just is not as repeatable and accurate as the fixed probe, and on the small lathe, the probe needs to be re-positioned.

I'll send you info, from my screen manual, via Skype for doing the calc's.

BTW,
Can you make a custom mouthpiece such that I don't need to practice, don't have to expend much energy to play those double high C's, and sound like Maurice
Andre? :D

RICH :)


Offline resonance

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Best setup for probing a trumpet mouthpiece
« Reply #12 on: November 18, 2015, 11:22:08 AM »
Regarding precision: a trumpet mouthpiece is between 5 and 15 arcs depending on complexity so, in the end, you don't need so many points to infer what's the shape you are copying. What's more important is the offset derived by how much the stylus bends before you have a contact.
This, as you wrote, takes a bit of calculation but it's not that hard.
Let's meet on skype, thanks!

Mouthpiece: I had it, then I exchanged it for a new lathe from Germany that is still not working... I'm am pissed of, badly.


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Offline eabrust

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Re: Best setup for probing a trumpet mouthpiece
« Reply #13 on: November 18, 2015, 06:29:08 PM »


Here are the problems I had to solve: the software can't handle both big diameter ruby tips. 3mm with a step over of 0.5mm won't happen.
If you need a small step over like 0.2 or 0.3mm you need a 1.5 or 1.0 ruby tip.

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Tony,

Glad you got all sorted and are making useful measurements!  You are correct about the probe ball size relative to stepover... but the issue is really just trigonometry related.  As the ball becomes large compared to the stepover, any 'error' in how squarely the probe hit occurred relative to the surface of the part translates into large relative error of where the touch is calculated to have happened.  That error then compounds in the following moves.  Thank you for reporting out your results and feedback.

You're also right that deflection errors can be calculated out.  The 'mill' version of ProbeIt can take it out by probing a ring gauge, but not the 'lathe' version.  Main reason is that you can really only hold the probe one way in a mill, but you can orient a probe in several different ways on the lathe... tip along x, tip along z, held at an angle, etc...  so I didn't want to add an additional complication on the lathe version (which was really just an experiment)

Rich,
Any easy workaround to a screenset conflict is to just make a new profile by duplicating your existing profile, and revert that copied profile to a standard screen set and radius mode (if diameter mode is your standard work enviornment).  You can then use the wizard from that profile without issue.

regards,
Eric Brust / CraftyCNC
 

Offline garyhlucas

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Re: Best setup for probing a trumpet mouthpiece
« Reply #14 on: November 18, 2015, 06:54:18 PM »
Your lathe may be able to make a cut that accurately, but one minute later holding the part in you hand where it warms up all bets are off. I'd spend my time finding out the limits of accuracy required, in other words what the customer could detect, then work from there.  In the real world accuracy is seldom the issue, and repeatability is much more important.

Offline resonance

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Best setup for probing a trumpet mouthpiece
« Reply #15 on: November 19, 2015, 03:59:55 AM »
Thanks Eric! I think I might achieve even better results with the mill version of your wizard. Mill unfortunately is out of order at the moment so that's why I've resorted to the lathe.
Gary: in my. Business the amount of material you take away during the final polishing is more than the precision I get while making the measure so there is no big concern. But yes, the better the measure the better the result. :)


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Offline BR549

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Re: Best setup for probing a trumpet mouthpiece
« Reply #16 on: November 19, 2015, 11:22:16 PM »
To measure and cut exactly teh same probe and cut with the same radius tip. IF you are measuring with a 3mm probe tip then cut with a 3mm radius cutter. NO trig involved (;-)

(;-) TP

Offline resonance

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Best setup for probing a trumpet mouthpiece
« Reply #17 on: November 20, 2015, 04:07:50 AM »
Eheh, unfortunately i need to use a 0.2 or 0.4mm radius tip for cutting. :)


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