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### Author Topic: Mirror probing  (Read 1978 times)

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#### joeaverage

• 6,387
##### Re: Mirror probing
« Reply #20 on: April 01, 2019, 05:35:19 PM »
Hi MN300,

Quote
There are other potential problems with the 3 probe method too

Yes you are correct. I have some ideas about how the 'translation' would occur. I think in terms of Lua and have
some success in manipulating probe data files to achieve a specific goal. It is none-the-less a programming
problem, ie it costs nothing but time and effort.

I'm just wondering how it is you propose to mount a rifle (4 or 5 or 6 feet long?) and rotate it? Its not
a regular shape and would also require a big machine, may be bigger, even much bigger than Don has got.

Craig
My wife left with my best friend...
and I miss him!

#### MN300

• 243
##### Re: Mirror probing
« Reply #21 on: April 01, 2019, 05:59:43 PM »
I am not proposing to physically rotate the rifle. Once you have the measurements down the center line the rest of the measurements would be calculated for different angles. It's just simple trigonometry. It would take a fair amount of custom programming to make G code or a file that could be used to make G code.
A person experienced with CAD could use the initial set of measurements to create a cross section and rotate it into the full profile. The CAD program would do the rest of the work and generate the G code.

#### joeaverage

• 6,387
##### Re: Mirror probing
« Reply #22 on: April 01, 2019, 06:08:21 PM »
Hi,
the problem occurs at the flanks of the barrel where the surface is vertical, you lose precision, badly if
probing vertically. If you had an omnidirectional probe yes that would work, but as you know they cost a bomb.

Craig
My wife left with my best friend...
and I miss him!

#### joeaverage

• 6,387
My wife left with my best friend...
and I miss him!

#### MN300

• 243
##### Re: Mirror probing
« Reply #24 on: April 01, 2019, 07:11:17 PM »
Hi Craig,

I think you may be misunderstanding what I suggested. One line of measurements taken along the X axis would give you the radius of the barrel at many points. To do this you would setup the center line of the rifle to be in line with the X axis.

Regardless of how you get the measurements you would eventually need to know where the center line is, either by measurement or calculation, to make the G code. This is because you need to consider the radius of the probe and the tool and the angle to the center line. If you measure with a thin probe in line with the center line of the barrel the probe radius could be considered to be zero. This allows the use of a simple probe like you have described earlier.

John

#### joeaverage

• 6,387
##### Re: Mirror probing
« Reply #25 on: April 01, 2019, 07:15:54 PM »
Hi,
but Don has told us that the barrel is not round, or at least perfectly so.

https://www.machsupport.com/forum/index.php?topic=39769.msg266789#msg266789

Craig
My wife left with my best friend...
and I miss him!

#### MN300

• 243
##### Re: Mirror probing
« Reply #26 on: April 01, 2019, 07:45:33 PM »
I  interpreted Don's comment to mean the diameter is not consistent. If the barrel is not round then my suggestion doesn't apply. The geometry problems involved in converting the measurements still apply.
I'm curious to know how you would generate G code.

#### joeaverage

• 6,387
##### Re: Mirror probing
« Reply #27 on: April 01, 2019, 08:14:54 PM »
Hi,

Quote
The geometry problems involved in converting the measurements still apply.
I'm curious to know how you would generate G code.

All good questions......we'll have to wait until Don replies and can give us a bit more to go on.

Craig
My wife left with my best friend...
and I miss him!

• 4,908
##### Re: Mirror probing
« Reply #28 on: April 01, 2019, 09:19:16 PM »
Hi,
but Don has told us that the barrel is not round, or at least perfectly so.

https://www.machsupport.com/forum/index.php?topic=39769.msg266789#msg266789
Craig

I think what Don meant is that the "contour" can end up anywhere.
The way the barrel blank is turned, lathe contoured and then spun sanded an polished all results in any cross section of the barrel perpendicular to the bore is a perfect circle. (near enough for practical purposes, anyway) I've done a few barrels and this was the case in my experience. I would think that all you would need to do is probe in the X down each side at centerline Z height in the area needed to determine the dia. at whatever interval you desire. The concentric circles could be easily drawn and connected in 3d, then sliced to leave the desired segment of the contoured cylinder. Cam the rest.
If it is truly round, would you need anything more than the dia. at intervals ?

#### RICH

• 7,419
##### Re: Mirror probing
« Reply #29 on: April 02, 2019, 06:03:08 AM »
Probing function is easy and  accurate. The point accuracy will only be as accurate as your set-up
and machines capability. Only you can define just how acurate the probing needs to be and how
automated you want the actual probe process to be.

I took a practical approach to the matter in that i wanted to be able to convinently and quickly
probe a piece to duplicate it or find dimensional information. If it is not easy and convient to do
you will not use it. Complex becomes a PITA also, so KISS applies, be pracatical for your intended
use.

I created a probing page / wizard for both the lathe and mill. A detachable index ring on the lathe
chucks allow for accurate indexing. As Russ replied, the barrel, for practical  purposes, is symetrical
about the  center line. If  mounted in a  lathe,you could probably take 30 probes on the top at 0 degrees,
15 probes at 90, 180, and 270.

The probed point data is is used by CAD to actualy draw the probe profile or just just show points.
In cad you could easily compare the probing at 90, 180, and 270 for any shape variation.

I must say thanks to Terry for the point conversion into CAD. In the end I still had to read a CAD manual
to get it to work in two different programs.

In summary here is what I do and works for me:
1. Set up work on lathe, mill, what ever.
2. Acquire point data
3. Have CAD draw the point data
4. Save as a dxf file
5. Use file in CAM or whatever program to get the GCODE.

No fancy probes and only one which allows side and point contact required ( make you owne for \$1).
Make a visual one for realy fast and easy point collection, look into  camera / optical techiniques.
A lot of options for doing things and YOU DON'T HAVE  TO SPEND  MUCH MONEY!

Note that electronic probing doesn't work on non- metallic material so you need options.

FWIW,

RICH
« Last Edit: April 02, 2019, 06:06:33 AM by RICH »