The Shop > Tools
Anybody build Dan Gelbart angled laser centre finder?
spuddevans:
--- Quote from: Arbalist on April 16, 2015, 05:55:47 PM ---Is there a safe way of testing if the body is live without damaging the unit? I have a small test meter.
I can insulate the unit if I need to but I'd rather dispense with it if I can.
--- End quote ---
With your test meter set on DC volts (20V selection if not auto-ranging), connect black lead to your negative end of the battery, and connect the red lead to the laser body. If your meter reads the same volts as your battery then your body is "live"
The same can be achieved by using the Ohms test facility, but this time connect one test lead to the laser body and the other to the positive lead of the laser (doesn't really matter which lead is connected to which, but just make sure that the laser is not powered up). You may find that the laser body is connected to the Negative lead of the laser.
Tim
Tim
vtsteam:
If you make the fixture an aluminum sheet box section you'll get stiffness with reduced mass. Reducing the imbalance of spinning around on the arbor without a counterweight. Therefore less vibration and deflection, and again a thinner and more distinct line.
Arbalist:
Thanks Tim. Not sure of construction details yet but something alloy no doubt.
:update:
The ND4 filter arrived today so I continued the experiment.
Photo one shows the setup. I drilled a blind flat bottomed hole in some PVC rod for the module. The remaining 3mm thick material was drilled with the smallest drill bit I have, a .75mm.
I cut a small piece of the ND4 and turned a small disc to fit in the fixture. This is the result.
This is the effect with another piece of ND4 held under the laser.
Looks quite promising. I tried to lock the lens on the Laser module in place with some stud lock but so far it's not done the trick so it may need something like super glue. It would be nice if I could get a lower power Laser module with a nice round dot but as an inexpensive option this setup should work I think once it's mounted.
PekkaNF:
--- Quote from: spuddevans on April 16, 2015, 06:24:23 PM ---
--- Quote from: Arbalist on April 16, 2015, 05:55:47 PM ---Is there a safe way of testing if the body is live without damaging the unit? I have a small test meter.
I can insulate the unit if I need to but I'd rather dispense with it if I can.
--- End quote ---
With your test meter set on DC volts (20V selection if not auto-ranging), connect black lead to your negative end of the battery, and connect the red lead to the laser body. If your meter reads the same volts as your battery then your body is "live"
The same can be achieved by using the Ohms test facility, but this time connect one test lead to the laser body and the other to the positive lead of the laser (doesn't really matter which lead is connected to which, but just make sure that the laser is not powered up). You may find that the laser body is connected to the Negative lead of the laser.
Tim
Tim
--- End quote ---
I measured my laser module. Body was connected haed to positive (red) wire. On battery operated device this is of little consequence, just usefull to know.
Pekka
Almost OT:
https://astrophotovideo.wordpress.com/building-a-laser-collimator-for-newtonian-telescope/
http://www.withoutlenses.com/articles/how-to/drill-your-own-precision-pinhole-apertures
Some more reading and a little more experimentation to do.
Arbalist:
I had another look at Pekka's original post and saw this:
Hi Folks:
For all of you building a laser center finder, here are some notes:
1. The laser has to be focussed to a very fine spot (under 0.1mm) so a regular laser pointer is useless. Focus it to a minimum spot about 150 mm away. Since the spot is oval, orient oval spot with long dimension tangential to the circle created to get a finer line. You can buy a laser module that can be focussed on Ebay for a few bucks, for example: 2pcs Focusable 3 5V 650nm 5mW Red Laser Dot Diode Module 12x35mm | eBay
2. The tilt of the beam has to be adjustable by tilting the module or a small mirror. A fixed angle is a poor choice. I posted a link to a fully detailed design on the YouTube video where I show the device.
3. Note that the posted design slips over the chuck or toolholder, so you don't have to remove tool to check centering.
4. Make sure design is balanced so you can use it at high speed. Design and test it to withstand much higher speeds as the highest used.
5. You can easily get 25um (0.001") and even better by using some simple tricks. For example, to center a hole on a bar or shaft place piece of paper under shaft and adjust height or beam angle till you just see two tiny spots of light on paper, each one on one side of shaft (e.g. shaft blocking almost the whole circle). This will give you accuracies down to a few microns in a dim room.
6. For all of those who felt sorry for me because of my choice in a milling machine:
The machine shown (Jet) is what I use as a drill press. I have a Makino KE55 CNC mill , Moore jig borer and other fancy machines. This video is part of a course to teach students so I chose machines they will be familiar with. I don't show any of the fancy machines (like a 1um accuracy aerostatic lathe/grinder) in these videos.
Cheers,
Dan Gelbart
Several things come to mind after reading this and looking at the video again.
Dan provides a link to a Laser module that looks exactly the same as the one Pekka and I have bought.
He says the Laser needs to be focussed to a spot smaller than .1mm which is I think highly unlikely with the module I have.
It seems like the spot in the video is nowhere near as small as .1mm either.
He notes the ovality of the spot but just suggests "orient oval spot with long dimension tangential to the circle created to get a finer line".
There was also a link to Dan's design but the drawing is no longer avalable.
Interesting ...
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