> On 2018-Sep-10, at 18:02, Chris Albertson <albertson.ch...@gmail.com
> <mailto:albertson.ch...@gmail.com>> wrote:
>
> You can actually make good measurements with a larger spot. This assumes
> you are using software and not just eyeball estimates. Typically you can
> do about 1/10th pixels position estimates. With micro-meter scale pixels
> this become way-overkill for machine work. I would not bother to do more
> then roughly align the laser.
>
> Yes you need a sensor. A $10 webcam with the lens replaced by a welding
> glass filter would work but you'd need to experiment with different filter
> and laser power.
>
Alternately you could use a quad optical diode array and read the currents
through the four diodes:
https://www.mouser.com/datasheet/2/414/OPR5911_RevD-1145186.pdf
<https://www.mouser.com/datasheet/2/414/OPR5911_RevD-1145186.pdf>
Years ago I built a rig to measure the spacing of dots on a slide using a HeNe
laser and an optical diode array like that and was able to get sub-micron
precision doing so.
> I would not adjust anything r "zero". between measurements. leave the
> target and laser bolted down solid. Just record the numbers and when you
> are done cal the smallest number "zero"
>
> To get the center point, just use the "centroid" the same math if looking
> for the balance point of the laser spot.
>
> You should be able to make a measurement at least once per lead screw
> revolution, maybe many times more per revolution.
>
> On Mon, Sep 10, 2018 at 12:09 PM Gregg Eshelman via Emc-users <
> emc-users@lists.sourceforge.net <mailto:emc-users@lists.sourceforge.net>>
> wrote:
>
>> I have a LASER that is made to mount in a chuck or collet. It has
>> alignment screws and adjustable focus. Aim it at a wall far away and adjust
>> the focus for as small a dot as possible.
>> Make a target to mount on the carriage, chuck and center the body of the
>> LASER then use the alignment screws and adjusting the target and rotating
>> the spindle until the spot no longer describes a circle when the spindle is
>> rotated.
>>
>> Move the carriage to the right end as far as possible. Move the cross
>> slide intil the dot is on the target. There's your zero. Advance the
>> carriage toward the bed until the dot moves off the target. Adjust the
>> carriage until the dot is back on target, at least in the X axis. A really
>> good way to map the bed would be to have a sensor as the target so the
>> carriage could be moved by the control and read a continuous stream of how
>> far off X it gets. Barring that, stop every X distance then adjust to
>> re-zero and interpolate slopes between adjustment points.
>> If you put the target on a vertical slide to re-zero Y at each stop, the
>> error map (with appropriate math) could compensate for that too. Perfectly
>> straight cutting even with a very worn bed, as long as the vertical error
>> doesn't drop the cutting tools too low.
>>
>> On Monday, September 10, 2018, 1:55:36 AM MDT, Chris Albertson <
>> albertson.ch...@gmail.com <mailto:albertson.ch...@gmail.com>> wrote:
>> The lasers are easy to find on Amazon but be warned the laser is not
>> perfectly aligned with the housing. But as I said, this does not matter
>> if you spin the spindle.
>>
>> I think a laser is the only option. If you are measuring the bed your
>> reference needs to be at least 10X straighter then the bed. Precsion rods
>> are not good enough but a $20 laser is literally perfect (as long as you
>> rotate the spindle.)
>>
>> With effort you can use the same laser to measure the error with the lead
>> screw pitch. Use it as a laser range finder or laser inferometer
>>
>> But all this measurement may be moot if the lathe is not reputable. The
>> error might be random. Maybe the carriage moves like a tuck on a dirt
>> road?
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>
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
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