Laser Build (Based on 2.x)

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Re: Laser Build (Based on 2.x)

Postby cvoinescu » Tue Sep 01, 2015 12:12 pm

I don't know the answers to the other questions, but the unipolar motor is fine: it's 6-wire unipolar, so it can be wired as bipolar simply by ignoring the center taps of the windings (typically white and yellow wires). FYI, 4-wire bipolar, and 6-wire and 8-wire unipolar, work; only 5-wire unipolar doesn't. Also, are you sure it's the Z axis motor? I vaguely remember the Y axis being a dual-shaft motor, to drive both sides of the gantry.
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Re: Laser Build (Based on 2.x)

Postby karsten » Wed Sep 09, 2015 9:31 pm

You are right cvoinescu its the Y axis, sorry :P

I started purchasing some pieces, waiting to arrive :)
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Re: Laser Build (Based on 2.x)

Postby _ID_ » Fri Sep 11, 2015 6:14 am

Regarding the belt length. You can go in one loop around all 4 screws or with 3 shorter belts (1 longer on x axis and two shorter ones on each side of the y axis).

Mirror diameter- more is better-it's easier to to aim the bigger "target".
Lens diameter- the same as for the mirror.

Diameter of lens/mirror does not affect the laser beam quality.

Focal length-more is better. At focusing the beam you have the hot spot, witch is the sharpest point in the cone of the beam. After that point the beam starts to expand again and loses its power. So longer the focal length less steep the angle of the cone is. Result is better cut-you have less angle on the edge of the cut.
Attachments
Laser focus.jpg
focal length
belts 3x.jpg
belts
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Re: Laser Build (Based on 2.x)

Postby cvoinescu » Sat Sep 12, 2015 9:43 pm

_ID_ wrote:Focal length-more is better. At focusing the beam you have the hot spot, witch is the sharpest point in the cone of the beam. After that point the beam starts to expand again and loses its power. So longer the focal length less steep the angle of the cone is. Result is better cut-you have less angle on the edge of the cut.

While that is partly true, mother nature isn't quite that helpful here. If optics would follow geometry perfectly, you'd be exactly right. However, diffraction makes the spot wider and fuzzier than pure geometry would have it. Instead of a double cone, the beam never focuses to a point. Instead, it just goes thin then wide again, like the pinched part of a hourglass -- only fuzzy on top of that too. The carbon dioxide laser has a very long wavelength, so the effect is a significant limitation. For the same diameter lens, a short focal length would have a higher numeric aperture and hence less diffraction, so the beam would get fairly close to a point in the focal plane. A long focal length would have a large depth of field, yes, but its smaller numeric aperture would cause the beam to be much more dispersed even at the exact focal plane. For cutting thin materials and engraving flat objects, then, a short focal length is much better.

_ID_ wrote:Diameter of lens/mirror does not affect the laser beam quality.

The beam width makes a difference, though. For the same focal length, a wider beam focuses closer to a point (higher numeric aperture, lower diffraction), but has a shallower depth of field (wider cones). Unfortunately, the beam width is set by the construction of the laser tube. (Beam expanders exist, but I don't know whether they improve diffraction the same way as a laser with that native beam width; they do make the depth of field shallower, as you would expect.)

Typical focal lengths for small lasers are 25 mm (for fast, precision cuts with small kerf in flat, thin media), 100 mm (for slow, wide kerf cuts in thick materials), and 50 mm (a reasonable all-round compromise, and the best choice for medium-thickness materials).
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Re: Laser Build (Based on 2.x)

Postby karsten » Fri Jun 17, 2016 4:53 am

good day members of this forum!

I almost finished the machine, but i have a problem with one of the Motors/Drivers

I am using this for the Y axis

Motor:.9deg Nema 17 Unipolar 12V 0.4A 32Ncm Double Shaft 17HM19-0406D
Info(http://www.omc-stepperonline.com/9deg-n ... p-121.html)

Driver: Bipolar Stepper Motor Driver Max 3A Current 128 High Subdivision ST-7128
Info(http://www.omc-stepperonline.com/bipola ... p-244.html)

Its connected as bipolar ignoring the 2 cables as is described in the diagram, the motor works but it does a bit of noise, more than enough for notice, i think the problem is the current, but im not sure, can you tell me? and if its possible recommend a replacement how works fine?
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