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Best setup for probing a trumpet mouthpiece
« on: August 26, 2015, 05:39:48 AM »
Hello!
I'm into the mouthpiece business and I have made many so far using mach 3 with a couple of lathes.
Now I bought a 4 axis mill that I'm using for engravings and light 2.5 sculpting on brass plates.
From time to time I have customers asking to copy their mouthpieces and most of the times I ask a friend of mine to make scans with a "arm"specifically made for this kind of jobs.
Unfortunately he lives far away and timing can be an issue for some customer.
I then thought to make it on the mill or on the lathe.
Can mach 3 do a scan of a curved shape?
What probe is best for this job?
Since a mouthpiece is a simple Mix of curves revolved on one axis I need the probe to scan only on two axis: let's say I want to measure the width at different depth values.
Can I then obtain a cloud of points that I can then transform into a complex curve?
The minimum diameter is 3.5mm.
Can the program compensate for the probing tip diameter?
Thanks!


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Offline RICH

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Re: Best setup for probing a trumpet mouthpiece
« Reply #1 on: August 26, 2015, 08:55:17 AM »
From a Trumpet player ........... :o

In my lathe screen I created some buttons that will capture the manually probed X and Z points and then can create a version 12 DXF
file from the points or draw the lines. Using CAD you can create curves based on the points. Mouthpiece exterior profile is easy.
The rim and end edge contours require more attention to duplicate.

So it's  manual probing. I use axis MPG's to assist in touch off along with a light indicating probe. This allows control over
accuracy and location of the points ( +-0.0002" repeatability). Plus I can make custom probe tips and no compensation is
required. If auto probing is used, ie; G31 then a very slow probe rate is required ...like 1 or less ipm. Thus manual probing as it's quick and easy.

Just a thought... maybe make custom visualizers such that they match the mouthpiece being used! ;)

I researched probing for the lathe and not much out there or you get high end and it's expensive.

Just some thought's,
RICH

 
 

Offline BR549

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Re: Best setup for probing a trumpet mouthpiece
« Reply #2 on: August 26, 2015, 02:54:00 PM »
RICH I have what you need to do auto 2d probing for turn. No point in doing it manually when you can push a button and watch with a cup of Joe in your hand.

It can be done in XZ linear fashion or a XZ Radial approach that is tunable so you could probe around a corner very easily. Do it all from one setup.  

Linear probing of curves is not that accurate due to tangent error of the tip and approach angle. You can ether do all the math to corrct OR  work smart and avoid the needed corrections.

Just a  thought, (;-) TP
« Last Edit: August 26, 2015, 02:57:30 PM by BR549 »
Re: Best setup for probing a trumpet mouthpiece
« Reply #3 on: August 26, 2015, 03:45:45 PM »
Hello, today me and Richard spoke a while on Skype about probing manually or automatically. He also pointed me to the lathe probing wizard you uploaded to the forum (thank you BR549!!!).
It took me a while to understand why I couldn't write the data to a file but finally I made it!
Since I don't have a probe yet I switched the spindle index interrupt to the probe one and make a few tests faking contacts by manually moving the spindle. It worked and now I can easily get data if I buy or make a probe.
The kind of shape I need tip scan brings me to the next problem: is there a way for Mach3 or any other software to CORRECT my cloud of points taking into account the tip reasons of the probe?
The other option would be to use a tip so small to almost eliminate the problem mechanically but it would be sharp and I can't scratch Mouthpieces that cost up to 400$...

Offline BR549

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Re: Best setup for probing a trumpet mouthpiece
« Reply #4 on: August 27, 2015, 02:38:16 PM »
IF you use a small spherical tip made of polished RUBY you should NOT have a scratching problem. Tip size around .050"/1mm. Even that small you wiil get tangent tip error BUT they will be very small. IF you are referring to tip radius comp Mach3 has that built in. But it only accounts for tip radius NOT tangent error.

(;-) TP
Re: Best setup for probing a trumpet mouthpiece
« Reply #5 on: August 27, 2015, 04:23:46 PM »
Hello!
Unfortunately my products need to be insanely precise and I can't exceed one or two hundredths of a mm.
Another option is to use a VERY thin internal grooving insert. Due to the shape I need to scan I just need one corner of the insert to touch the surface and, maybe, it just takes the insert to be gold plated and wired so that when it touches the silver/good surface I scan the contact will be closed.
Does it make sense?

Offline BR549

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Re: Best setup for probing a trumpet mouthpiece
« Reply #6 on: August 27, 2015, 06:03:35 PM »
IF you are talking .01-.02 mm (.0004-.0008) then you are NEVER going to get that from Mach3 probing a shape such as that. And without temp compensation you will never cut or measure it accurately.

Just a thought, (;-) TP
Re: Best setup for probing a trumpet mouthpiece
« Reply #7 on: August 27, 2015, 06:05:59 PM »
You mean the probing routine can't obtain such a precision or the progress aren't that precise?

Offline RICH

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Re: Best setup for probing a trumpet mouthpiece
« Reply #8 on: August 27, 2015, 07:39:34 PM »
I always say that accuracy will only be as good as the machine " system ".

By that I am meaning:
How repeatable is the machine ( it cannot be as good as the calculated resolution)?
How repeatable is the probe?
How repeatable is actual cutting?

SO
Any movement, sensitivity of a probe, and any actual machining, etc, etc will influence /  determine how accurate the information will be.
Thus it's all that makes up the routine / process.

RICH




Re: Best setup for probing a trumpet mouthpiece
« Reply #9 on: August 28, 2015, 06:57:57 AM »
The lathe consistently cuts with one thousand of a mm precision, servo motors and zero backlash bell screw. It's insanely precise, beyond what I expected!
I can't say for the probe, I still have to buy it.
I spent the morning with that wizard for lathe and, in fact, is very easy to use and seems to compensate correctly for the tip radius!
Can't wait to have a real probe to test precision and repeatability.