Rabbit Laser Machine Testing -Warning Large Images

[Travis Reese]

Just curious to hear thoughts on these tests. I finally got my machine up and running and figuring out the basics of how to use it. I did some tests in cast acrylic. The image below is a close up of an engraved rectangle that is 3.5mm wide with a scan gap of .254 or 100 dpi. It appears that there is a very slight amount of backlash in the machine on the x axis. Each line is slightly staggered. A measurement of each line leads me to believe the spot size of the laser is about .1mm or .004".

1.jpg

If I turned off the bidirectional option I got the following where the staggering disappeared...

Screenshot 2016-01-01 17.14.01.jpg


Here is a more zoomed out image of the first picture...

Screenshot 2016-01-01 17.21.45.jpg


This is the test image I used. The rectangle above is right next to it.

Screenshot 2016-01-01 17.22.46.jpg


And here's an overview. The image above and the one below were both done with a .07 scan gap. I just used the .254 scan gap earlier to put some space between the scan lines. At a normal viewing distance it looks ok. But I'm wondering if I should be able to achieve better.

EDIT... thanks for helping me figure out the upload. It says "Upload files..." but it definitely doesn't look like a button!

[Scott Shepherd]

Travis, please upload those images to the site. Linking photos like that isn't allowed. What happens is your great photos end up gone from the location 6 months or a year from now, so it'll be a bunch of broken links, which will be meaningless to someone looking at this years from now. If you upload them to this site, then they'll stay up and it keeps the data all in tact.

Please fix that.

That's a very natural issue that you have documented. Most lasers have the ability to adjust that in the software. I'm not sure how Rabbit does it.

[Kev Williams]

Yes, it will do better. And it's just my opinion, but I never run any laser job that I consider 'high quality' at anything less than 500 lines or dots per inch. Anything less and the detail suffers. Your .07 gap works out to 364 lines per inch, .05 gap works out to 510 lines per inch. I pretty much default my Chinese Triumph at an .05 gap...

Somewhere in your software you should have a backlash adjustment. In the PHCad software for my Triumph, it's called "carving backlash". The faster the machine runs, the higher the backlash entry must be. I have a different backlash setting in 50mm/sec increments from 200 thru 800 mm per second speeds. And it took quite awhile to fine tune the settings, but even though this thing is a large "cutting" laser (51" x 35"), my engraving results down to .060" lettering will hold their own against any western machine...

Bert or a few other Rabbit owners should know the procedure to fine tune your machine.

[Travis Reese]

I've actually tried. Using both Firefox and Microsoft edge it doesn't seem to work. I click on the image upload link and select from computer. I'm able to select my file, but there's no button to actually upload the file.

[Keith Winter]

It's a bit hidden after you select you file directly below the file name is some text that says upload file, click that. If it fails it's because your image is too large, I think the limit is 2 or 4mb on here.

[Art Mann]

You won't be able to upload really high resolution images because it takes up too much room on the server. I upload images at 1024 pixels horizontally and let the resizing software choose the vertical resolution to keep the aspect ratio the same. 1024 pixels shows up very nicely on a normal 24 inch computer monitor. There are lots of ways to resize using different programs but I find Faststone Photo Resizer (free) to be very easy to use on a Windows based computer.

[Dave Sheldrake]

Backlash can be made better by ensure belt tension is spot on but sadly it's the nature of toothed belts/no compensator/no ball screws/steppers with no linear encoder that causes it.

Reducing engraving speed will also help

[Kev Williams]

To upload files to the board:

First, at the bottom-right of the reply screen, click on "Go Advanced"
ppic1.jpg

Then, click on 'manage attachments'
ppic2.jpg


This dialog box will come up. When you click "add files"--
ppic3.jpg

--the browse-upload option appears. Click 'browse', then locate the file on your computer...
ppic4.jpg

Once you choose it, the filename will appear, now click "upload".
ppic4a.jpg

The pic you chose will upload and appear in the "attachments" box. You can continue to upload pics if you want. When you're done, click "insert inline", and the pics will be put into your reply screen. You can move pics where ever you want, by dragging or using the mouse cursor.
ppic5.jpg

Note that all pics you upload will be saved into your own "home" folder. You can drag and drop and insert any saved pics the same way.

I'm sure there's a file size limit to the pics that can be uploaded, so resizing pics down a bit may be necessary

[Gary Hair]

Backlash can be made better by ensure belt tension is spot on but sadly it's the nature of toothed belts/no compensator/no ball screws/steppers with no linear encoder that causes it.

Reducing engraving speed will also help

Just beware that too tight is probably as bad as too loose. I know that's what you meant by "spot on" but I thought I'd expand a bit. I had some strange alignment issues with my previous laser that cropped up after I adjusted the belts. Somehow I didn't correlate the two and fought with the problem for a while until I went back to square one and loosened the belts and saw the problem go away. I'm sure there is a tension tool to ensure consistency but not having one I just adjusted them until they were even and the alignment wasn't affected any longer.

[Travis Reese]

Kev, thanks for the info. I've poked through settings in LaserCut 5.3 and don't see a backlash compensation anywhere. Anyone here know where to find it?

[Scott Shepherd]

Just a reference, I was incorrect in my previous post. You are free to post images from outside sources. It's discouraged, but it is allowed. There used to be a file size limit, something like 150Kb per image. I'm not sure if that's what it still is or not. I do know if your images are large, they won't upload.

Sorry for the confusion, my misunderstanding of the rules.

[Dave Sheldrake]

Just beware that too tight is probably as bad as too loose. I know that's what you meant by "spot on" but I thought I'd expand a bit. I had some strange alignment issues with my previous laser that cropped up after I adjusted the belts. Somehow I didn't correlate the two and fought with the problem for a while until I went back to square one and loosened the belts and saw the problem go away. I'm sure there is a tension tool to ensure consistency but not having one I just adjusted them until they were even and the alignment wasn't affected any longer.

Requoted as Gaz's information is very important and I neglected to mention it... too tight can be worse than too loose

[Bert Kemp]

Travis what speed did you run your test at. Try slowing it down .I don't really do a lot of high res engraving, mostly vector engrave. and seldom do acrylic and really don't change my settings that much. My machine seems to produce good quality images at the settings suggested in my manual. if you tell me your settings and speed I'll see what mine does.

[Travis Reese]

Travis what speed did you run your test at. Try slowing it down .I don't really do a lot of high res engraving, mostly vector engrave. and seldom do acrylic and really don't change my settings that much. My machine seems to produce good quality images at the settings suggested in my manual. if you tell me your settings and speed I'll see what mine does.

I'm running at 300 mm/s with a scan gap of .07 on those tests I posted.

[Kev Williams]

I had some strange alignment issues with my previous laser that cropped up after I adjusted the belts. Somehow I didn't correlate the two and fought with the problem for a while until I went back to square one and loosened the belts and saw the problem go away.

-- Part of the problem with your previous laser was the X belt was (is) wearing out. Right now it's doing what my LS900 does (11 years old and on its original belt): When engraving thru the first few inches from home-position to the right, it results in 'fat' engraving, particularly noticeable with text. Since 95% of all engraving is done in the top-left corner and much of it is 6" long or less, those first few inches is where all the belt tooth wear happens, and results in backlash that only a new belt can fix.

This became noticeable on my LS900 maybe 3 years ago. My bandaid has been to start any and all engraving (if possible) 4" from left (and 2" down for good measure. I have a new belt for it, one of these days I'll actually put it on!

For now I'm doing the same thing with the GCC until I get a new belt, as everything 4" from normal left engraves perfectly!