Enthousiast beginner with some questions

[Kurt Hamblok]

Hello engravers world-wide!

This will be my first post, so, hello! My name is Kurt and I'm from Belgium. I've been reading in here for quite a while...
I've been interested in laser engraving/cutting for about a year. Together with a friend we've been looking for affordable options and eventually we found a second hand GCC Mercury Pro 30W.
We went to Germany to get it full maintenanced.
- two mirrors and the lens were cracked
- some belts needed changing
- the tube has been changed since it gave fluctuating power (even engineers didn't have any explanation)
- auto-focus-sensor was to contaminated
- alignment of laser
- some minor things

To start, it's real fun to have such a machine! We're having a great time testing and engraving. We've tested some different plastics and glasses (with a super result on the glasses!).
But we came across some problems too...
1) it seems that the laser isn't falling down perpendicular on the table... When engraving PMMA 6mm, two sides parallel with X-axis, both go sideways like this // (well, it's probably with thinner materials too, but clearly visible with the 6mm) . We think that they aligned the laser and checked it with the table up, and focus on top-left and bottom-right, but not checked again with the table down... (although I can't imagine how you would test that without a focus) Is re-alignment from the first mirror starting at the laser (going from bottom to top) necessary? Or would there be a problem with the carriage?
2) although the engineers checked focus top-left and bottom-right, the table itself seems wobly... Is this normal?
3) the rotary-attachement is great for champagne-glasses, but we're having difficulty setting up the driver. Relative/center/without home/offset... We haven't found the 0.0 yet. It's dfficult to predict where the file will be engraved... Has anyone any indication on how to? I guess all drivers are different for different machines so this wouldn't be a straight forwared answer...

Still some more to go, but enough to start.
Thanks in advance for your answers and time!

Greetings.
Kurt

[Riki Potter]

Welcome to the creek Kurt, I can help out with your rotary question as I believe our machines and drivers should be quite similar.
My method goes like this:

- In Corel set the document height to the circumference of the glass, I use a bendy ruler but you can also just measure the diameter as multiply by Pi.

- Set the page width to 200, this can be any size so long as you have enough room for you engraving.

- Now the page effectively represents the whole face of the glass. The topleft corner should match up with a marker on the rubber cone of the rotary attachment, although yours may be different.

- Insert any text or pictures you want and turn it all sideways as this will be the orientation of the glass.

- When you go to print it may ask if you want it to automatically set the page size, say no as we're going to do this now.

- In the driver under "Paper" click the "Rotary Attachment" checkbox, this should give you Paper Size field on "X" and "Diameter". Take the height of your page and divide by Pi (3.14 is fine), that's your diameter, then set X to whatever your page width is.

I just looked at what position mode it's set to and I have it on "Without Home", I've never changed this in the past.

Hope this helps, engraving cylinders takes a bit of practice and figuring out but it's worth it in the long run.

Also your driver and rotary attachment probably differ atleast slightly from mine so this isn't a gospel.

[Kurt Hamblok]

Hi Riki,

thanks for your detailed answer. It nearly matches our procedure, however, in our driver, we can insert die diameter and it automatically gives me te circumference of the glass :)
I have seen the dot on the rubber and wondered what it represents. However, we thought it couldn't be 0.0 since the red beam starts slightly on the black metal box, not above the rubber. Also, the guide of our mercury indicates we have to move the red beam to the startposition of the rubber/glass. On the display, we can then read the X-offset which we need to fill in in the driver. But every setting: home/center(except for relative) makes the carriage bump into the rotary attachement, resulting in an x-axis error. I had quite a heart-ache when this happened the first time, thank god for the rubber :)
So, for now, we use relative, but it's hard to position the carriage on the exact same spot every new glass... I guess it'll be a lot of trial and error to find the right procedure.
Thanks anyhow for your answer!

[Richard Rumancik]

. . . 1) it seems that the laser isn't falling down perpendicular on the table . . .

I would suggest you go through the procedure and recheck the alignment. You need to learn how to do it anyway. Do you have a written procedure?


2) although the engineers checked focus top-left and bottom-right, the table itself seems wobly... Is this normal?

The table is supported on two screws on the left and one on the middle right. Although three-point support is technically a correct way of defining a plane, the problem that this creates is that the back right and front right corners are cantilevered. So if you put pressure on these corners it will tend to rock the table. There is some axial play in the jackscrews so when you push on a corner it is causing another jackscrew to move axially till it hits a hard stop (maybe a few millimeters.) So I doubt there is a problem with the table, it is just a limitation of the design.

[Kurt Hamblok]

Hello Richard,

thank you for your response, I am a little hesitant about fiddling with the alignment, but I am aware there's no other way. I found a fully written and picture enhanced document about aligning and it looks straight forward, so it looks like I'll have to take the plunge. It even seems, that the engineer has forgotten the last step, since it seems that's the one to align perpendicular to the table. I just know I'm going to curse myself if I get it all the way misaligned....
Regarding the table, thanks for the confirmation. I was wondering whether the 3-point support would be the cause... I will up the table and hang the manual focus-tool on the carriage and check across the whole table wether it's equally spaced. If not, then I'll have to start looking for solutions from there... :)

[Rodne Gold]

I Think if you press the Y axis button on the LCD panel , it will rotate the rotary to its "limits" , IE it reaches a stopped position , if you do this before lasering the object and using it as a start point and put the object in the same position there , as far as I remember , you will always be engraving in the same position on the object , its a sort of "home" , I may be wrong as I have not had a Mercury for like 7 ir 8 years.

[Richard Rumancik]

... When engraving PMMA 6mm, two sides parallel with X-axis, both go sideways like this // . . . Kurt

Do you mean when cutting PMMA? If I understand correctly you are saying that the two sides of the rectangle that are parallel to the x axis cut with a similar slant; I am assuming that the two sides that are parallel to the y axis are fine as you did not mention them.

Before you do a full-blown alignment from the laser source, why not just see how centered the beam is as it enters the carriage? Put a piece of masking tape or label material over the hole, go into test mode, activate the laser for one second or so (to make a minimum burn mark on the tape) and see if the burn mark is centered with the round opening. If it is, then I would say your alignment is okay. Also, insert the focus probe and scan over the whole table as you indicated to prove that the table itself is not causing the problem.

If the beam entering the carriage is centered and the table is "level", then it could be a problem with the angle of the last mirror (I think they call this mirror 4 but I don't have my manual handy.) This mirror is in the carriage, and the angle is not adjustable. Suppose that the beam coming from the previous mirror (#3?) is "perfect", in that is is parallel to the table. If the mirror 4 is not oriented at exactly 90 degrees to the incoming beam, it will hit the table at an angle and will show up when cutting in the x direction. In the y direction, you would not notice the fact that the beam was hitting at an angle.

What could cause this? I suppose some error in the the carriage mounting or in the machining itself could cause it. But I have never studied the carriage mounting in detail.

The reason I bring this up as a possibility is that my machine had this problem from day 1. It would cut perpendicular in y but slanted in x, regardless of the alignment. You could not really correct this kind of error with mirror alignment. So one possibility is to shim your last mirror. In my case, I put a .005" thick strip of mylar film between the top of the aluminum mirror backing plate and the thin edge to which it is clamped against (using the set screw at the top). The shim did the job, and seemed to be the least painful and least risky solution.

There might be other ways of fixing the problem, but this worked in my case and I did not investigate further.

[Kurt Hamblok]

Hi Rodne,

I noticed indeed that rolling up the Y-axis does stop at some point. So the 0,0 has probably been found, it's just the 0 on the x-axis that needs to be foudn too :) I figured I'll make a file with several lines on fixed distances, well, one distance should do it, and than I can phisically measure it. I'll have to investigate from there on, but thanks for the tip!

Richard,
I did mean cutting indeed, rushing a post is never good :) Your assumption is right, the both sides along the x-axis are slanted, along the y-axis are both fine.
Yesterday took me a few hours to figure everything out, but I got it re-aligned. The mirrors were a bit off, but I can't say it was a lot. As i recall right, the beam hits the tape spot on in the middle, but I'd have to check again to be sure. However, I did a new test and I had the exact same result, slanted both along the y-axis.
I checked the table with the manual focusing-tool too. Left top and bottom are perfect, middle and right middle are too, but to the right top and bottom there's a problem. Right bottom comes a little up and and right top goes a little down, a little more than a mm maybe. Should I leave it at that or look for a solution? I'm quite picky at such things, it'll bother me everytime I think something might be wrong...
Two days ago, when we noticed the slanting problem, the first thing we did, was looking for a possibility to adjust the carriage, but we couldn't find any. We did notice that fastening or loosening the bearings that drag on top of the guiderail made the carriage rotate along the y-axis noticeably, but when moving, it would return to its previous level.
Your suggestion about fitting something underneath the mirror might indeed be the shortest and simplest solution, I might try that today or tomorrow.
Thanks for your input!

[Richard Rumancik]

. . . I checked the table with the manual focusing-tool too. Left top and bottom are perfect, middle and right middle are too, but to the right top and bottom there's a problem. Right bottom comes a little up and and right top goes a little down, a little more than a mm maybe. Should I leave it at that or look for a solution? . . .

It would seem to me that the table has a bit of a twist to it but as it is just an aluminum plate with a stiffening frame it is not ever going to be rigid like a machine tool bed. The right top and bottom are the "unsupported" corners of the table so are more likely to show some deviation from a flat plane. Looks like they leveled the table the best they could at the three support points. There is no adjustment that will fix the two corners. I don't think there is a "solution" to the table twist - you are not likely to have success in trying to straighten the table and could make it worse. But it might be tolerable as-is - I would say that you should leave it alone for now.

If you see the angled cuts when cutting on the left side then I would tend to think your last mirror is not aiming correctly. But you might have to shim opposite of what I did. In your first post, you said it was cutting with angles like "//". Is that when looking at the front edge of the workpiece? If that is the case then I think the shim needs to be at the bottom of the mirror. I'm not beside my machine but it should be possible to shim the bottom. Think it through and it will probably be obvious to you where you need to add the shim.