Laser Setup Question - How Critical Is Height Above Work Piece

Just installed a J-Tech 2.8 on my X-Carve and am messing around with it - very impressed so far. This is my first laser so a lot to learn. The new magnetic mount and shroud J-Tech has available is a nice addition. But the shroud does make it harder to set the height above the work surface if I try to use the suggested heat sink as the reference point. I have interpolated the height to use the bottom of the shroud but I question the total accuracy.

So the question is - How critical is this measurement. Are we talking within three decimal places like we set the Z on a bit? (I’m working in inches) I have varied it up and down a .01" or .02" and really can’t see much difference in the burn line. I certainly would see this difference with a bit.

Been thinking about rigging up way to use the probe to set this right on the money but wondering if it is necessary. I “pretty close” good enough?

Photo of the shroud.

The height changes the focus point size of the laser. The more focused the point, the finer the detail you can get.

I understand that to be the case but just questioning to what degree. It seems the way you manually focus the beam is not highly exact. You are looking at a dot .009 in diameter and trying to see a change. When bumping it up or down .01" really doesn’t seem to change it. OR are my eyes just not good enough?

450 nm :grinning:

It’s like using a V-bit. You can use the focus as an integral part of your artwork.

Since the laser diode is a rectangle you want the long edge of the rectangle to be lined up with the long side at a 45 degree angle . What this does is to make the horizontal and vertical component of the beam to be equal length when moving the laser horizontally or vertically so that you have more uniform lines rather than thin lines moving one way and thick lines moving the other way.

Many of the raster imaging laser programs allow you to select a 45 degree left or right movement to smooth the image.

If you are looking at a dot , then it’s not focused.

Really, though it’s a matter of taste. You can raise your feed rate if you can get the focus right.

I have both fiber and co2 and in my experience focus is critical

OK, I am officially confused. I thought setting the power at 10% and then adjusting until you get the smallest dot possible is how you focused. J-Tech states that should be about .009 with the 2.8 watt. What am I missing?

A distorted sense of humor. (I really shouldn’t post to the board when I’m tired).

Most of the inexpensive laser diodes I have worked with have a rectangular laser cavity. If such a laser is focused you get a fairly uniform rectangle of light output, For some things it doesn’t matter, but if you are trying to get a circular dot from such a laser the technique is to de-focus the laser. You still don’t get a perfect circle but you do get an ellipse that is close to a circle.

My apologies.

My comment about orientation of the “rectangle” with respect to the X and Y axis applies if you have the laser focused well and you would like to have nice lines in small engravings.

For those who try to cut with a laser diode you want to go with the sharpest focus you can obtain as that gives you the highest power in the smallest area. With this type of focus you can use small movements of the Z axis to maintain power density as you “cut” the material.

Focus is key with lasers.

That said, I use a little block of wood that is exactly sized to fit between my laser head and the stock for optimal focus distance. Just jog until it is snug. Imo that is as close as it needs to be, considering very few use perfectly dimensioned wood to begin with

Or if you want a round dot you can change the lens like I did. Better for engraving, not as good for cutting.

OK, I have had time to experiment with my new 2.8 J-Tech. Set up a burn that repeatedly made a 2" line dropping down .01" each time. Started .125" above what I had set as my ZERO and ended .125 below it. Here are photos of the result.

Looking at them I have a hard time seeing much difference. Maybe the bottom is a little wider but if it is it is really minimal. Below that photo is a close-up of the first 1/8" worth of drops. Am I missing something? Just doesn’t seem to be a marked difference in any of these. On J-Tech website they suggest this test moving 1mm at a time and picking the narrowest line. That means they are looking at within roughly .04" is acceptable tolerance.

Printed some text which is .045 high and it was very readable so I guess I have it close enough. Please correct me if I have screw something up here and am looking at this wrong.

BUT, I have added a working “Probe” on the side of the laser’s shroud. I can use it manually by just sticking my touch plate under it and slowly lowering OR attach the wires and do the full automated probe.

1 Like

Did you make the working probe or did Charley come up with that?

It’s nothing special, I just scrapped it together. A little flat piece of steel with two holes drilled. I did stick it in a vice and bent the one edge over a little to better hole the rod in place. It would not need to be that big if you weren’t going to attach the magnetic contact to it.

The rod is just a piece of gas welding rod cut to the right length. Any somewhat stiff wire would work but the welding rod was shiny and I liked that! :grinning:


I had this huge post typed up and realized it could turn into a book, so I condensed it down to this:

This is an ongoing endeavor. There are so many things that come into play that you will need to constantly keep experimenting to find what works best for you.

1 Like

Larry, I appreciate the reply and the advice. One of the things I find most enjoyable about the X-Carve is the continual learning experience. So the experimenting will continue and I hope you don’t mind the future questions that are sure to come.

Be glad to help, as long as I can.