Engraving coming out strange.

[Dawn Cortez]

Hi brand new laser owner here. I bought a 50 watt Chinese laser and it arrived two weeks ago. I had never used one before. We are learning a lot from this forum and also youtube. (Thanks to all of you!) I have been making images on shot glasses successfully for the past couple of days. Today this started. I am making Cowboy shot glasses for a friend. Sent over file as normal 1 1/2 inch squared. When it was done it was squished (on left). My brilliant husband then made me a new graphic and compensated by making the second one 1 1/2 by 2 1/2. It worked perfectly. I have been trying to figure out what could have caused the issue in the first place but I'm at a loss. The other design is similar in size and this never occurred.
The rotary I have is the flat box with three silver poles on it. Any help would be very much appreciated. cs issues.jpg

[Mike Null]

Dawn
Welcome to SMC. Part of your issue may be an optical illusion that occurs when doing cylindrical objects. The compensation your husband did is on the right track but still needs a little work.

The other part of your issue is the cone shape of the glass. That will cause the engraving to distort.

I would, 1. reduce the size of the drawing as it is too large for my taste; 2. adjust the drawing along the lines of what your husband did, 3. be very sure that the glass is positioned in the rotary device to be level with the laser head throughout the engraving. That will require that you elevate the end of the device so that the entire top surface of the glass is parallel to the plane of the laser.

Here is a previous discussion regarding the illusion on cylindrical objects. http://www.sawmillcreek.org/showthre...-round-objects

[Dawn Cortez]

We use a padding with a thick rubber band to elevate the bottom of the glasses. Helps to prevent slippage also. I will check out that link. Thank you

[John Kleiber]

What application are you running to upload the job to your laser?

[Dawn Cortez]

Hi John, RDworks that came with the machine.

[John Kleiber]

That does not look like an illusion. Your machine is improperly configured for the circumference of the object.

Select File
Vendor Setting
Input Password
Select Y

Notice the input field entitled Step Length.

That is how the machine understands the circumference of the object.

If that number is incorrect, the laser will skew the image too long or too narrow.

You did manage a work-around by changing the dimensions on screen, however, distorting an image on screen to fix a laser distortion is like fixing a problem by creating another problem.

[Dawn Cortez]

Great thanks John. I will give this a try! Would the input number would be the actual circumference of the thickest part of the glass in millimeters?

[John Kleiber]

Dawn,

No its actually a different method than one would think. Please do not let the following overwhelm you. Just print the instructions out and check them off as you do them. Each step is numbered so do them one by one in the order listed.

Here goes......

1 Turn on Laser

2 Prep item:
Wrap item with a single layer of foil generally around the circumference of the area you wish to engrave.
Place a piece of masking tape to cover the foil with enough tape extended beyond the foil to adhere to the item.
Mount item into your Y axis which should be your roller.

3 The foil will protect the item from laser damage.

4 Open RDworks

5 Draw a square the same dimensions as your star graphic with all sides equal. In this example I will use 10mm. Use whatever is appropriate in your case.

6 Set the square for CUT and lower the power down. You only need enough power to cut the tape.

7 Save the file as whatever name you want. A descriptive name will be easier to correlate the test with the item for future use.

8 Upload the square image to your laser and position it on the item just as you would a real graphic. Make sure the square does not extend beyond the foil.

9 Laser Cut the square.

10 Pull the foil off the item. Maintaining the same orientation, write a "T" for top and a "B" for bottom respective so you will remember. To be clear, when I refer to top and bottom, I mean top as the item is on its side. Not literally the top of the item as it sets upright.

Top

Rollers ------------------------
Item on its side mounted in Y axis rotary
Rollers ------------------------
Rollers ------------------------

Bottom

11 Pull the tape off and place it on a flat surface. Measure the tape from top to bottom.

12 Using my above example of 10mm, measure the square top to bottom with a digital caliper.

13 Note the measurement and write it down. The measurement will either be short of 10mm or over 10mm, that is normal. Lets say the measurement was squeezed in like your star and indicated 7.4mm

14 Select File

15 Select Vendor Settings

16 Input Password

17 Select Y axis very important. Y is the only radio button selected.

18 Select Save to save the current settings. Name it something like "original_software_settings". If things go wrong, you will need this file to get the settings back.

19 Press the Read button and the software will read what the machine has stored.

20 Save that file as "original_machine_settings"

21 Make a note of the number in the Step Length field. This number will change once you do the following;

22 Press the button that has the three dots "..." which is next to Step Length.

23 Input 10mm (or whatever measurement you decided into the Graph Length. In my case I just type 10.

24 In the Measuring length input what the measurement actually was when measured with the caliper on the tape. In this example I input 7.4

25 Press ok

26 Now its time to Write your new setting to the laser firmware, press the Write button.

27 Prep item:
Wrap item with a single layer of foil generally around the circumference of the area you wish to engrave.
Place a piece of masking tape to cover the foil with enough tape extended beyond the foil to adhere to the item.
Mount item into your Y axis which should be your roller.

Cut the square again and measure. Is the square 10mm from top to bottom? or the measurement you are using?

If so great, load your real file and laser away. If not, continue to adjust using steps 21 thru 24 until you get it right.

When you do, Save your settings to your hard drive using descriptive terms like "rotary_shot_glass_settings"

You will only have to deal with this process when you have different diameter items.

Please keep in mind, rotary setting will be different than flatbed settings.

When you decide to run the machine without the rotary, you will go through the same process but the item will be flat.

In short, lay a flat item on the laser bed, place a piece of foil to protect the item and tape it down. If you do not care if the item gets lasered, then just laser a square with settings appropriate to the material.

Once you get that perfectly square, just like you did with the rotary save the settings while in vendor settings Y.

The bed will always be flat so name it "flatbed_settings"

In addition, note that the settings files you are saving have a different extension than "rld". This is normal and allows you to differentiate between a "rld" drawing file and a settings file.

I know it seems like a lot, but its really not. You'll be able to do this in your sleep it will be so easy.

-John

[Brian Book]

Hi John Thank You for the explanation .... will give it a try after I get my Machine all setup

Brian

[Dawn Cortez]

Thanks John, will give this a try tomorrow. I really appreciate the time you took to spell it out for me. Learning it is a challenge but I am looking forward to the awesome things it can create!

[Kev Williams]

I learned a lesson awhile ago about the two basic rotary types, the 'chuck' style and the 'hot dog turner' style.

With a chuck style, you should start with a working area plate height (Y axis) equal to part diameter x pi, as in a 1" diameter part requires a 3.14" plate height.
you must also tell the software the diameter, because a chuck rotary turns from the zero point inside and works outward.
The same 1/2" x 1/2" square on a 1" diameter part eats up 16% of the available "Y" real estate. But on a 2" diameter part it only eats up 2%
So the software needs to compensate by rotating the 1" part much farther to get the same result...
Sidenote, with a chuck rotary, you don't HAVE to have an exact plate height UNLESS your full-circle zero points must match up.
The software will correctly size the engraving regardless, placement is up to the user...

With a hotdog rotary, as with a chuck, you must start with the correct plate height for the diameter of the part-
But a hotdog rotary works outside-in, with friction wheels rotating the part. The friction wheel doesn't know, or care, what the part diameter is-
this is because a 1" move around the circumference of the friction wheel will move the part 1" around its circumference also, regardless of it's diameter.
So "secondary" software diameter adjustments to compensate for diameter aren't needed.
However, the plate height is important because even though the drive wheels rotate all diameter objects equally, larger diameters require more drive wheel revolutions.
--if you tell the machine you're engraving a 2" diameter part that's 1", the results will be squashed just like in the example--
That's my best guess as to what happened

bottom line, with any rotary style, diameter input is critical!

[Doug Fisher]

Hi Kev -

Could you please explain what "plate height" means?

Thanks.

[Kev Williams]

the defined working area has always been called the "plate size" in my engraving life, so simply, X is the plate length, and Y is the plate height--

When working with a cylinder in lasers, the Y axis is almost always the rotary axis. So a cylinder's plate height would the cylinder's diameter x pi (3.1416)...
so if you're engraving a 4" long x 1.5" diameter cylinder, the working area or "plate size" would be 4" x 4.712", and that the top and bottom of the plate will both be the cylinder's "zero" point..

[Erik Goetheer]

John, that looks like a good set of instructions. I received my shot glasses today, so I'll try them out. One thing though, you are telling us to put foil on the glass but I normally use a wet tissue (sofar I only engraved flat glass). Is there an advantage with using foil?

[John Kleiber]

John, that looks like a good set of instructions. I received my shot glasses today, so I'll try them out. One thing though, you are telling us to put foil on the glass but I normally use a wet tissue (sofar I only engraved flat glass). Is there an advantage with using foil?

Erik,

Taping foil to the item is only used to protect the item while testing.
At low power settings, the CO2 laser will cut the tape, leaving the foil to protect the underlying item.
Once your test is complete and settings saved, remove all tape and foil.
From that point, add whatever you normally would, ....wet paper towel for glass, masking tape for wood etc

Here is an example of the foil/tape settings test in progress as I prepare my newly created Yeti and extended chuck rotary fixture for a laser job.
rotary_chuck_settings_01.jpg
-John