I haven’t used a laser. I don’t know how hard it is to focus, but I would assume I would need to focus it for each thing I was lasering. I was thinking a thumb screw would work to get it focused, and then a lock screw to keep it still, instead of using another motor/driver/dealing with CAM. Seems like it would work for engraving, but not for cutting. Since the Core XY only uses 2 motors, it would be yet another motor off the top. Seems like an OK idea to me.
For me it is pretty hard to get it super focused, that is how I ended up with that script. Then I realized for engraving it doesn’t really matter so much but like David says for cutting, it really changes the strength. If I remeber right the power of the dot is exponential so a little bigger radius means a lot less power (although it is really a tiny rectangle). Hard by hand but super easy with the script.
David I got my parts in!!! We’ll see what come out if I can free up some time soon.
1 Like
With my laser I do adjust the Z for focus - but I don’t usually adjust it during a process. Basically I adjust the focus collar on my laser so it’s focused at a certain distance - then have a cheater stick I use to manually adjust the Z so the laser is always that height above the surface.
I’ve experimented with adjusting the Z on multiple passes for thick materials, but haven’t really seen any benefit to doing so, in fact in most tests I’ve seen worse results from doing that for some reason.
So a powered Z isn’t really needed, but an adjustable Z is very helpful.
I did use Ryan’s focus script to get the initial focus dialed in…and for a bit did use it to try and fine tune for each operation. But found that for my uses that wasn’t really necessary and just using the height gauge method was accurate enough.
Here’s what I do with the little Makeblock machine… and it works fine. Two or three millimeters either side of absolute best focus is generally fine for engraving…
[attachment file=36402]
[attachment file=36401]
Beyond that, however, I still have visions (hallucinations?) of hanging something other than a laser on this thing… a pen, a drag-knife, a hot-wire bow, or ???. And beyond that, I think herringbone gears (or r&p) are fun to play with and it gives me a chance to use my new Prusa printer. Beyond that, it’s just plain sexy – and at my age…
=8^)
About focus… it’s crucial for clean cuts in thicker materials. I have successfully cut 4.75mm luan plywood with my laser on the MPCNC (where I have a fully-implemented Z, of course)… 5 passes, full-power, 100 mm/min, constant focus on top of material. I don’t remember whether I had the air-assist active at the time or not…
[attachment file=36407]
[attachment file=36412]
[attachment file=36408]
[attachment file=36409]
[attachment file=36410]
[attachment file=36411]
GremlinRC (Dave from Dublin), in my FT thread, later substantiated the importance of focus as well… cutting in a single pass material that had been taking multiple passes. We also investigated “air-assist” and found that it can be a great help as well when cutting thick materials.
I’m still not entirely clear as to why keeping focus at the top of the material for all passes seems to work best for me. Many feel that you need to lower the Z-axis – and focus – with each pass, to cut thicker material. I tried it but was never able to get it to work. This diagram shows the idea… though the depth should probably increment with each pass rather than “reciprocate”:
[attachment file=36413]
Any ideas?
– David
1 Like
About materials…
Here’s what I do to set up for cutting any material… here, corrugated cardboard.
First, I run the Ryan’s focus script and then lower Z back down to best focus on the top of the material… here about 16mm… and leave it there.
[attachment file=36424]
Then I run a series of 10 lines… full-power, starting at 1000 mm/min feedrate, down to 100 mm/min.
[attachment file=36425]
Flip the test piece and find where the earliest, cleanest through-cut occurs… here, 200 mm/min might work but 100 mm/min will insure through-cuts…
[attachment file=36426]
Then cut the parts. These all look nice and fall out on their own. There’s a slight crown in this piece of cardboard that I usually can just ignore (focus is reasonably good over range of 6mm or so) if it’s not too severe or abrupt…
[attachment file=36427]
[attachment file=36428]
[attachment file=36429]
[attachment file=36430]
– David
1 Like
That looks cooler in cardboard than in wood!!! To the Gallery it goes!
1 Like
If you think about power, then if it’s perfectly focused on the top, then all the power is going down into the hole. If it’s focused 15mm lower, then a lot of the power is still on the surface. The amount that ends up in the hole is probably pretty close to the amount if it was focused 15mm off.
It seems like the cut would be slightly larger as it went further down, and then it would end up spreading out again, and get out of focus again, but focusing lower without widening the hole wouldn’t get any more power down in the hole.
I wonder if you could make cuts wider at the top, before focusing lower. If you could consistently cut 4mm thick with it focused on the top, I wonder if you could cut to 8mm or more if you made the first 4mm double wide, and then cut in the middle of those two paths after 4mm deep. I don’t know a good way to do that in CAM, but it would be easy to make some manual gcode to test it. If it worked, we could try to find a way. Actually, I wonder if the tricoidal milling would do that.
1 Like
I think you are right, Jeff. Good call.
While best focus certainly concentrates the power at the surface, makes the narrowest kerf, and maximizes penetration, it leaves an “aperture” too narrow for a now-“defocused” beam, on successive passes, to pass through. Intentionally widening the kerf at the surface, as you suggest, makes sense then… purposefully creating sufficient “aperture” for the beam’s energy to pass through on successive passes. Not a problem with a collimated beam certainly… but definitely a problem with the focused beam we have here.
Thanks! I think that explains what I’ve been seeing quite well.
– David
That makes a lot of sense.
What I tried with “descending focus” was doing more or less what David does to find optimal cutting…except I wasn’t trying to get a full cut - I was looking for the cleanest cut and sharpest line. Then I’d run my test cuts off the edge of the material and measured how deep it cut.
I then tried doing multiple passes dropping the Z in various amounts - full depth of initial cut, half depth of initial cut, 1/4 depth…but none of them seemed to help and just leaving the Z constant seemed to result in equally deep additional passes as additional passes with the Z dropped.
The beam width description certainly makes sense as to why that would be since I was looking for the cleanest (hence smallest) cut at the top of the surface.
I really need to pickup a three element lens…I went with the G2 on mine (I’m using the “standard $100 2.8w laser”) since I wanted to cut balsa and figured the more efficient lens would help. But it sure seems everyone I know running the three element lens gets noticeable better cutting performance at the same power levels. So it seems the higher efficiency of the G2 isn’t enough to make up for the larger spot size. Kind of like how a good antenna is better than more power in radio - tight focus is better than more power with a laser 
Though until I remember to pickup a three element for myself to test with and compare the same laser/driver/power setup with both lenses this is just speculation - even if it makes sense 
You were serious about editing the Wikipedia page for “152”!!!
How cool is that???
Thanks,
David
[citation needed]
Sheesh, citation added. 
2 Likes
Hilarious!
An update on my MPCNC-inspired CoreXY laser engraver… still a work in progress but moving once again!
Please recognize that this machine is too large/heavy/clunky for best corexy operation and is NOT a general-purpose CNC machine or MPCNC replacement – but as a dedicated laser-toting machine, with no real tool-forces to deal with, this machine seems to operate quite well. It’s been a fun project… and I’m quite pleased with the result. Development began about the same time, or slightly before, as the ZenXY project and we’ve all learned a lot about CoreXY since – so please don’t be too hard on me… =8^)
This project has sat idle for several months and I’ve had some difficulty locating all the original STL files – some were done in Tinkercad originally and the rest were done in Onshape – but I’ve rounded up most of the parts needed to build the MPCNC-inspired CoreXY laser engraver and uploaded/published it to Thingiverse
https://www.thingiverse.com/thing:2375050
I had to regenerate several STL’s (I haven’t sliced/printed these exact model files) but I think these should be usable. The videos are showing the original configuration but operation hasn’t changed. Several parts are stock MPCNC/LowRider parts or mods thereof… the NEMA17 corner motor mounts are stock LowRider parts IIRC and the bottom-most three corner parts are stock MPCNC parts (Thanks, Ryan!). The Marlin firmware (and the stock MPCNC and LowRider parts) are from this site and only a few lines in the Configuration.h file need modification to get CoreXY operation and proper steps per mm on each axis.
The Z-axis linear slide assembly shown mounted on the tool-plate is found at https://www.thingiverse.com/thing:2813896. Thanks to John Mulac (3DPRINTINGWORLD) for a really nifty mechanism!
– David
2 Likes
Thanks a lot for posting your progress, very interesting and super helpful as I begin tackling adding a laser to my machine. I’ll be hitting you up for advice - looks like you know what you’re talking about!
Thanks… but looks can be deceiving =;^)
Actually, since I’ve been away from this for a while – long enough to forget a lot of stuff – I’m just trying to get my creative juices flowing again. I was never happy with the big, clunky Z-axis I’d made so I’ve reworked the X-carriage and am trying a couple of ideas for modest Z-lift, a couple of inches or so. Don’t really need it for laser but it is helpful for finding best focus and testing materials for engraving/cutting. I’ve just fired up a brand new Banggood 3.5 watt laser and am testing it now. I hope to retrace my steps described earlier in this thread and get it operationally equivalent to the MPCNC I’ve got set up as a laser engraver, complete with Jeff’s v1pi image running on a Pi ZeroW. The timelapse video functionality is a lot of fun…
Get going on your laser setup and keep us posted on your progress. – David
1 Like
Don’t know who gets these but I got an email this morning… Banggood Mid-year sale until 6/25. Same 3.5 watt laser for $70 and free shipping… just had to have another one so ordered it just now. Spare… or another machine?
3 Likes
Thank you very much! Got a laser and an applicable pair of safety glasses. Some protection ought to be better than none. They at least match the wavelength range. If I can get a camera set up to watch it, then there wouldn’t be much reason to actually stand and watch it directly.
While I do agree with that sentiment to some extent, I believe it is something to be wary of in this scenario. Depending on the optical density (OD) of the glasses, they could reduce the beam output enough that you feel comfortable looking at the beam spot, but damage is still being done to your eyes. Also, the blue diode lasers often put out IR light in dangerous amounts if they aren’t properly filtered, and I never trust that these Chinese lasers are properly anything at first use. Once you get your glasses, if they aren’t marked on the frames or lenses with their protection rating, I wouldn’t put too much trust in them. There was another thread on the forums here about laser glasses from survival laser and I picked up a pair, and they are very nice for the price.