Inconsistent cut results

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Parry Palmer
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Inconsistent cut results

Post by Parry Palmer » Sun Jan 01, 2017 2:12 am

With a few days off I have tried to do a bit more tests on the newly delivered machine and discovered some inconsistencies.
On a cold start, I have performed a cut on 4.5 mm acrylic (approx 100mm x 45). Perfect clean cut - Less than 1 minute run (50% power=19MAh @12mm/sec)
Retried the same job, 2 minutes later, same position, and many parts of the artwork were deeply scored but not cut through. Tried another time, but same on/off cutting.

I then performed a power/speed test on some clear 6mm acrilic, vertically, to measure depth of cut against different levels of power and speed combination. The results are really weird: of the 3 speed options (8mm/s. 10mm/s and 20mm/s) the depth of cut is pretty much the same irrespectively of power (for the same speed). In some cases, actually, the 35% power cuts slightly deeper than 50% (hard to see in the picture, but in the 10mm/sec 35% is marginally deeper).

Any idea of what could it be?
test.jpg
test.jpg (225.47 KiB) Viewed 366 times
Parry
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Keith Sherwin
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Re: Inconsistent cut results

Post by Keith Sherwin » Sun Jan 01, 2017 9:07 am

Looks like you might have Default checked for the layer and thus using the setting on your LCD.
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Parry Palmer
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Re: Inconsistent cut results

Post by Parry Palmer » Sun Jan 01, 2017 5:34 pm

That is exactly what I thought, but I have rechecked everything and Default is not thicked. I have just recreated another test from scratch and I get exactly the same results. No difference in depth irrespectively of power.
Is there anything on the engraver control that can default to a standard power?
Parry
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fred ungewitter
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Re: Inconsistent cut results

Post by fred ungewitter » Sun Jan 01, 2017 6:36 pm

a couple of thoughts tossed out in the breeze here,

is your lens positioned inside the nozzle so the flat surface is pointing at the work? There is some scattering of the beam when the direction is improperly reversed.

Are your power settings for min and max power identical? The min power setting allows ramp up and ramp down when the nozzle is changing speed.

Consider to perform the focus ramp test http://rdworkslab.com/viewtopic.php?f=6&t=936 to check the range of power versus depth for your configuration. The link points to the file download, but you would want to search the forum for "focus ramp" to get more insight, or watch the appropriate Russ video.
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Dustin Hawkinson
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Re: Inconsistent cut results

Post by Dustin Hawkinson » Sun Jan 01, 2017 7:16 pm

One other thing to consider is that all of these tubes have a consistency rating of 10%. I see power vary pretty dramatically (within about 10%) when testing and the output power seems to depend a lot on what the last thing the tube was doing.

There is a thread on shapes being cut off in the beginning of a job (most noticeable on the rotary) that is solved by firing the tube at a % below what creates an actual output just before the leading edge of the shape. I've also noticed different power outputs when testing 5% power setting increments with a DoHickey when I test 10%, 15%, 20%, etc then when I start at the high end 75%, 70%, 65% etc. I don't know why this is, but the inconsistency is frustrating.
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Parry Palmer
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Location: Melbourne - Australia

Re: Inconsistent cut results

Post by Parry Palmer » Mon Jan 02, 2017 12:17 am

fred ungewitter wrote: is your lens positioned inside the nozzle so the flat surface is pointing at the work?

YES

Are your power settings for min and max power identical?

For this test yes as the cuts are individually set so I don't want any ramping of power up or down.
Parry
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Doug Fisher
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Re: Inconsistent cut results

Post by Doug Fisher » Mon Jan 02, 2017 2:29 pm

I think Fred has pointed out your potential issue if you are keeping min and max power at the same level. Don't forget to do any changes so that they take effect both in the software and within the internal machine settings themselves.
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Keith Sherwin
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Re: Inconsistent cut results

Post by Keith Sherwin » Mon Jan 02, 2017 2:39 pm

Parry, Please do one more test.
Same as before, BUT, make sure the LCD MIN/MAX power is set to the same as your test file for EACH different power level. Split your program into the 3 power levels and run each separately. Wondering if it will change the results or stay the same.
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Don Flynn
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Re: Inconsistent cut results

Post by Don Flynn » Tue Jan 03, 2017 10:32 pm

Is your bed level? I know when I received my machine I had one corner off by 4.5mm. That can change your beam focus a lot and give you inconsistent cutting.
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Chris Berry
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Re: Inconsistent cut results

Post by Chris Berry » Wed Jan 04, 2017 12:20 am

Could be a power variation or a power intensity variation.
All things being equal, the test should produce the same result so what can we rule out? was there a difference in focus depth? a change in temperature? A loose optical component? or were you right on the edge of the cut and consistency got you?
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