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The DILAGON: a DIY laser goniometer
(07-05-2018, 01:35 AM)Jan Wrote: Mr. Cyrano, in my understanding the angles shown in your straight scale by green lines are 2*alfa (double the bevel angle) while in the semi-circular DILAGON scale the figures are bevel angles alfa in degrees.


Thanks! I've corrected the diagram for the straight scale example.
Very interesting Cyrano and Jan. Our hat is off to your ingenuity. We've had a fair amount of past experience in laser matters so this thread really captures our interest. We owned a division that dealt with laser alignment tools. This division (BearmerLine) dealt with products that ranged from laser levels to bore sights for .50 Caliber machine guns. In the final analysis we sold the division and the buyers turned our technology into a perimeter swimming pool alarm system. We manufactured our own laser modules in this division because commercially available modules were not acceptable for our purposes for a number of reasons. Please keep in mind though that this was 15 years ago. In our experience then, the devil was not in the electronics but in the mechanics. Everything was terribly heat sensitive and when dealing with collimating optic focal lengths of around a single mm, a lateral shift of .001" in the optical housing arrangement was devastating. If the product contained other mechanical elements i.e. bases, clamps, adjustment screws etc., those became potential sources of error as well. Which brings us to our question for you;

Calibration adjustment before each use was often the bail-out for many of our products. A calibration option for your bevel angle instrument seems obvious and simple to us as well but only if one assumes that the bevel angles on each side of the edge are equal. One would just adjust the knife/laser position until the reflected angles were equal and Voila!, the answer. If it cannot be assumed that the bevel angles are equal then this calibration technique is out the window.

Things have advanced in 15 years and likely our thoughts are mired in the laser stoneage so perhaps this is not a problem at all for you or you have skinned the cat in a better way. In any case, we would be interested in your thoughts as to whether or not you regard any of this is an issue for you and your devices.

I wouldn't make a general assumption that any blade's bevel angles are equal. An assumption that a blade's primary grind angles are equal seems more sound, but I still wouldn't count on it for critical applications.

To my mind, an ideal laser goniometer would include a method to hold the knife which meets these criteria:

(1) The position of the knife edge projected onto the X-Y plane, its pitch, and its roll, are all fixed. These are all enforced by a static mechanical fixture or jig.

(2) The yaw of the knife blade is adjustable. Adjustments are done via rotation around an axis passing through the apex of the blade edge, so as to preserve the parameters noted in item (1), above. The mechanism controlling yaw allows adjustments which are quick, precise, and stable.

I second Rupert Lucius' suggestion that you consider bringing a reasonably-priced laser goniometer to market. Based on the design elegance of the PT50A, I'm certain you'd knock it out of the park.
Thank you for your response to our question Cyrano and thank you for your confidence in our manufacturing acumen. We agree, you have to listen when Rupert speaks.
Thanks for your interest, Mr. EOU. Smile 

My goniometer was inspired by a book written by prof. Verhoeven and also by handbooks to Catra goniometers which Mr. Wootz pointed out to me.

I do not have a sophisticated calibration procedure. In my goniometer the blade is mounted in a small vise which allows sideways movement of the blade. I assume that (at least) the blade is symmetrical and try to adjust the centre of the shadow cast by the blade on the division 0° of the scale. Adjustment accuracy is circa 1°. This approach allows me to measure asymmetrical bevel angles also.


Thanks Jan. 1° is plenty close enough for me or, as I overheard my great uncle Jake ask my grandfather August as he finished hanging another piece of sheetrock in a rental house they owned together many, many years ago. "Was denken sie, August?" to which grandpa replied "Das ist gut genug, Jacob."
Wow guys, this is pretty cool stuff. Got my brain going for a while now.
I wish I had the time to build one now! But other priorities are taking the lead.

One thought that kept coming to mind was rotating the whole apparatus.
If the semi-circle were rotated 90 degrees to the 'floor' with the laser pointing through a small hole at the zero mark, gravity could be used to rest the blade on a jig. This would also allow a fixed point for the collimation of the beam.

A centering mechanism would be needed to assist in the roll on the X axis. But that does not seem to be much of a challenge.
It removes the floating blade aspect.
The yaw is mostly gone except that which is caused by blade geometry.

Not sure if any of that makes sense, if it sparks some interest, I will try to find some time to draw it up.

Great work gentlemen!
I present the DILAGON 2.0, with a linear scale and no assembly required -- just print and fold:

[Image: i-jKbvbw3-L.jpg]

Attached Files
.pdf   DILAGON 2.0.pdf (Size: 26.66 KB / Downloads: 92)
For whatever it's worth: 
I'm using a Bosch distance meter; the laser isn't anything to write home about but I already own it, and having an angle finder, distance finder and laser source in one device makes it quite convenient.

I've been using the gaps between sections in an expanding-type dining room table to hold kitchen knives for measurement. Not perfect, but alignment is good and it's handy the have the laser just sitting there. My table is circular with a split at the diameter when you take the leaf out, so measuring and printing a scale to attach to the edge was very simple (though the radius is enough that I need two sheets of paper to measure useful angles.)

Making a pinhole or slit aperture out of cardstock cuts down on noise from the outer lens cover on my laser, though it hasn't been a real problem either.
Mr. Cyrano... Thanks a lot for sharing this!

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