Inconsistent cut results

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Parry Palmer
Posts: 42
Joined: Wed Oct 26, 2016 1:20 am
Location: Melbourne - Australia

Re: Inconsistent cut results

Post by Parry Palmer » Wed Jan 04, 2017 1:27 am

Keith,
I have re-run the test in individual cuts, adjusting the power (MIN and MAX this time, 0.2 difference between the 2 numbers) from the LCD every time.
I have reattached a pic of the new results.
In brief, all tests are at 10mm/sec:
10% power = 1mm depth
15% power = 4mm depth
20% power = 5.5mm depth
25% power = 6mm depth
30% power = 6mm depth
35% power = 6mm depth
40% power = 6.5mm depth
45% power = 6.5mm depth

Don, Yes the bed is perfectly levelled (it was off like your when it was delivered)
Chris, All tests are done within 5 minutes (enough time to make the changes on the LCD), so no substantial change in the temperature/environment. Cut file is 25mm long and the acrylic sheet is 6 mm, so plenty of time to ramp up the power before start cutting.

BTW- The speed on the LCD (top right) regulates the speed of the head, while adjusting the location of the head on the table, not the actual speed whilst cutting/engraving.
test2.jpg
test2.jpg (202.62 KiB) Viewed 150 times
Parry
60W 700mm x 500mm Ke Hui KH-7050
TR - 2"FL - mAmeter -
RDWorks 8.01.18 - Win10 via USB key

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Gene Uselman
Posts: 1202
Joined: Thu Jul 07, 2016 3:18 pm
Location: Suburban Minneapolis, Minnesota, US
Country: USA
Nickname: Gene
Laser Machine Make or Type: QC1390
Laser Power: 130W EFR
Laser Bed Size: 36x49
Home Position: TR
RDWorks Version: V8.01.19 LO
Accessories: I have a combining lens, pin tables [homebuilt], honeycomb table [LightObject], wireless remote on the way [crossed fingers]
Windows Version: Win 7 Pro

Re: Inconsistent cut results

Post by Gene Uselman » Wed Jan 04, 2017 10:14 am

Are you sure that the top laser power is not happening at 25% power? Do you have mA readings? On my 130w I hit full military power at 45% for instance, Gene

Chris Berry
Posts: 18
Joined: Mon Jan 02, 2017 1:58 pm
Location: Crete, Greece

Re: Inconsistent cut results

Post by Chris Berry » Wed Jan 04, 2017 1:18 pm

Parry,
I think it would help if you described what we are looking at. The shot of RDworks I can't 100% figure out what we are looking at.
The cut that I'm looking at in the image below also has several widths - again hard to make out the problem.
Is it inconsistent? Hard to say unless I know what I'm looking at.
It's certainly non-linear - but that's to be expected.
Energy density plots on a laser that's just too close to the material first rise with distance and then fall (inverse square). So one could explain the rapid increase in depth from 10-15% right there. That could also be your optimal distance for cutting but would be slightly too broad for the highest resolution surface etch. I haven't seen a plot of actual laser output v % power (rated) to guestimate whether this is normal.
I suspect that your test is lasering the edge of acrylic to determine the cut depth and what I'm seeing is the result of vibration from acceleration settings slightly too high for what the laser can handle (fix these in user settings or find a way to tighten up the tolerances).
To test for this, (which is independent of laser power) try a 1cm square, speed 50 scan at 10% x unilateral, y unilateral, x swing, y swing, 0.5mm interval. You could also try this at 10mm/s where this is appearing.
--------
Chris
--------

Weike 130 x 90 100W RECI Laser TR
Windows 7, RDWORKS V8.01.10

Parry Palmer
Posts: 42
Joined: Wed Oct 26, 2016 1:20 am
Location: Melbourne - Australia

Re: Inconsistent cut results

Post by Parry Palmer » Wed Jan 04, 2017 3:32 pm

Hi Gene,
Will re-run the test today taking note of the mA readings (from previous work I have done, it was pretty progressive though).

Chris,
Yes. The above picture was a rudimentary test to measure cut depth through an edge of acrylic, at different power settings. The image is taken with the acrylic on a slight angle to be able to see the depth. I am not too worried at this stage about the vibration part: can fix that later. My priority at this stage is to plot laser power vs depth of different materials to create a matrix I can use going forward to avoid wasting material.
Parry
60W 700mm x 500mm Ke Hui KH-7050
TR - 2"FL - mAmeter -
RDWorks 8.01.18 - Win10 via USB key

Parry Palmer
Posts: 42
Joined: Wed Oct 26, 2016 1:20 am
Location: Melbourne - Australia

Re: Inconsistent cut results

Post by Parry Palmer » Wed Jan 04, 2017 7:00 pm

Gene,
Just rerun test, this time running the cut a little bit longer in a rectangular shape (50mm x25mm), half on the acrylic, half off (the first portion of the cut off, just to get the laser at full power whilst on the acrylic).
These are the mA readings.

10% - 4mA
15% - 7mA
20% - 10mA
25% - 12mA
30% - 14mA
35% - 15mA
40% - 17mA
45% - 18mA

I didn't go over 45% as it reaches 20mA at 55% (maximum for the tube), but the cut is not any deeper over 45%.

I am really puzzled how there is no relativity between cut depth and amperage.
Parry
60W 700mm x 500mm Ke Hui KH-7050
TR - 2"FL - mAmeter -
RDWorks 8.01.18 - Win10 via USB key

User avatar
Gene Uselman
Posts: 1202
Joined: Thu Jul 07, 2016 3:18 pm
Location: Suburban Minneapolis, Minnesota, US
Country: USA
Nickname: Gene
Laser Machine Make or Type: QC1390
Laser Power: 130W EFR
Laser Bed Size: 36x49
Home Position: TR
RDWorks Version: V8.01.19 LO
Accessories: I have a combining lens, pin tables [homebuilt], honeycomb table [LightObject], wireless remote on the way [crossed fingers]
Windows Version: Win 7 Pro

Re: Inconsistent cut results

Post by Gene Uselman » Thu Jan 05, 2017 7:49 am

OK- then I got nothing- very curious as you say. Gene

Chris Berry
Posts: 18
Joined: Mon Jan 02, 2017 1:58 pm
Location: Crete, Greece

Re: Inconsistent cut results

Post by Chris Berry » Fri Jan 06, 2017 1:49 am

Raise your bed by 2mm and re-run the test.
Laser cut depth/focus distance is an S curve - chance is your focus distance is on the right hand side of the S.
If this is the case, then you should now have greater depth control - although you'll loose a little energy density at 10%.

Unless your bed was even further away. The difference between 6mm and 6.5mm from optimal focus is 17% power.
I tried to find a good fit to the figures that you've posted and it looks like you may be 2.5-3mm too far.
Test the hypothesis!
--------
Chris
--------

Weike 130 x 90 100W RECI Laser TR
Windows 7, RDWORKS V8.01.10

Parry Palmer
Posts: 42
Joined: Wed Oct 26, 2016 1:20 am
Location: Melbourne - Australia

Re: Inconsistent cut results

Post by Parry Palmer » Fri Jan 06, 2017 2:35 am

Hi Chris,
Thank you for the feedback.
Will try tomorrow morning as soon as up. Hopefully it should be a little cooler than now - 35° C at 7.30 pm
Parry
60W 700mm x 500mm Ke Hui KH-7050
TR - 2"FL - mAmeter -
RDWorks 8.01.18 - Win10 via USB key

Chris Berry
Posts: 18
Joined: Mon Jan 02, 2017 1:58 pm
Location: Crete, Greece

Re: Inconsistent cut results

Post by Chris Berry » Fri Jan 06, 2017 12:05 pm

Stumbles on a trotec article - then lost it which says that on thicker acrylic, you should focus 1/3 of the way into the material - hence you may want to bring the table 4mm closer as well.
Also, you don't mention your lens's focal length. That would also play a huge role in maximum energy density and roll-off. a 63.5mm lens is probably ideal for your tests. While it has a larger waist, the energy density remains higher than for a 50.8mm over a greater depth.
--------
Chris
--------

Weike 130 x 90 100W RECI Laser TR
Windows 7, RDWORKS V8.01.10

Parry Palmer
Posts: 42
Joined: Wed Oct 26, 2016 1:20 am
Location: Melbourne - Australia

Re: Inconsistent cut results

Post by Parry Palmer » Fri Jan 06, 2017 8:40 pm

Chris,
redone the test, with head 3mm closer to the material.
There is a little bit more progression, but the depth of cut has substantially reduced:

10% - <1mm
15% - 2.5mm
20% - 3mm
25% - 4mm
30% - 4mm
35% - 4.5mm
40% - 4.5mm
45% - 4.5 mm

BTW. My machine has a 2" FL.
Parry
60W 700mm x 500mm Ke Hui KH-7050
TR - 2"FL - mAmeter -
RDWorks 8.01.18 - Win10 via USB key

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