Bought new laser, few questions

[John Blazy]

Thanks to this forum, I bought a laser from Rabbit - real pleased so far. I mastered most of the basics pretty quickly, but I have a few puzzles. The pic attached has three issues in one pic - from left to right - too much burn in a laminate of PET / Vinyl / epoxy bonded to .25 Duron, middle shows a warped laminate of acrylic, and need tips on holding down and flattening warped panels, and far right shows burned egg crate - need tips on different material that wont catch fire under the pc to be cut.

So the first issue is that the individual laminates can be cut well, but I was hoping that a finished laminate on 1/4" Duron (HDF) would be cut all at once, but even 3mm / sec @ 95 - 100% power is burning too much (I can sand the char off later, but would like to avoid that) . Question is - is it better cut in multiple passes at higher speeds, or one slow pass? I did multiple passes at 20mm/s/100% but it appears that the carbon build up in the kerf is blocking further penetration. I plan to order some 6mm Baltic birch, and maybe that will make a big difference. I tried several heights with no difference (focus at top plane, focus .060 below face, etc). Cutting with a 63mm lens - optimally focused and centered within the tube - clean mirrors etc). May switch back to my 53mm lens?

Next is cutting through warped material, pressed down with weight / and or magnets. Space under the 63 mm lens allows 1/2" steel weight plates positioned out of cutting path, and is lower than the laser head, but still need better ideas for hold down. The high hold magnets are great, but not enough steel in the honeycomb to grab. Need to make a custom steel grid from .090 steel bars, tops ground into "V"s for magnets to hold. Any other better ideas? I cut it fine with slower speed since it did not press fully flat enough, so that might be the best answer.

Next is I need non flam egg crate, but if I commit to welding a steel grid, that may solve the issue.

So any tips on grid plate design would be appreciated.

Thanks to all you members in advance !!! Been great help so far!

[David Somers]

John,

I can't speak about your laminate materials. Never worked with it. Hopefully someone else can offer help.

Regarding work holding though, I use N52 Neodymium magnets to hold things flat to my steel honeycomb. I can easily use a 1/2" x 1/2" x 2 or 4" magnet to bring bowed 1/8" and 1/4" Baltic Birch down to the table. Obviously I need to account for the position of the magnet in my cutting or engraving design. I usually do that by making a fast engraving job with the size of my material and a lightly engraved rectangle of the size of my magnet. I build that into my final job so I can account for that rectangle in my design. I run that, I dont care how good the engraving is, just using the job to mark the wood for the position of the magnet. Then I place the magnet and run the real job minus the rectangle.

If you bought your magnets from a local hardware store or big box those are usually N40 magnets. Made of Neodymium and decently strong, but not nearly as strong as an N52 neodymium magnet. If you need a vendor I use KJ Magnetics at kjmagnetics.com. You can order all their N52 into one list and each one will show you its holding power in lbs for easy comparison.

Another thought might be to use a thin nut, bolt and wide washer passed up through the honeycomb (bolt head and washer located below the honeycomb....bolt length JUST long enough to do the job without interfering with your laser head) through a hole cut in the center of your workpiece. Be gentle so you dont mess up your honeycomb, but use that to bring the workpiece down flat to the table. And of course, like above, cut the hole with the laser and have that built into your main job so you can account for the hole in your design.

You might also ask Ray at Rabbit if he has any thoughts. He is very helpful.

Dave

[Mike Null]

John

I think you may have used a polystyrene grid which will melt and burn quite readily. An acrylic grid--also made for fluorescent lights --will work much better and give you longer life. Still, it has to be considered disposable.

Dave's fender washer and bolt idea may work if you have space for them on your work.

[John Blazy]

Yep, I was thinking of mechanically fastening the panel with a wire through the honeycomb, and didn't want to add the extra time (in my old mindset, I thought that I had to drill it manually) but the idea of lasing a quick hole is great, then your bolt idea made me think of a simple "T" or "L" headed bolt passing though the top, because I didn't want to have to reach under the table to fiddle with a bolt.

I bought Neodymium magnets from McMaster Carr, and they scare the pants off me every time I set them down - snapping themselves onto anything metal with a serious bang, until I get used to them. The honeycomb doesn't have enough steel to really grab, so maybe I will just cut slots into it, and mount just a few steel bars for magnet holds. Thanks a ton for the source for magnets - need to get bigger ones.


My grid is definitely polystyrene. Will make the switch - thanks, Mike.

[David Somers]

John,

Not just bigger magnets, but stronger if you are not already using the N52 magnets rather than N42. For example, an N52 magnet with the dimensions .5"x.5"x2" will have a pull of 67.4 lbs. The same size in an N42 has a pull of 54lbs. And there are lots of sizes as well. I use the .5"x.5" size since I know it will clear my 2" (50.8mm) lens.

Here is a thought for you to increase the pull of a magnet.

Measure the size of your honeycomb comb holes. KJ Magnetics has N52 magnets with countersunk holes in them. Insert one that fits well into a honeycomb hole with a fender washer below so it can't possibly be pulled up above the level of the honeycomb top. Use a bolt that fits the countersunk hole and a nut and set it in that honeycomb hole. Like my other suggestion, make note of of its position and create a layer in your graphics program where you can place the outline of a magnet for placement.

Put your material over the honeycomb, lightly engrave the shape of your magnet shape. And then place another N52 magnet on your material. It will now have a very strong pull down to the honeycomb with one magnet pulling towards the other, but the magnet in the honeycomb unable to ride up under any circumstances because of the nut/bolt/fender washer. Your N52 magnet in the honeycomb wont have to be removed because it does not come above the level of the honeycomb table top so it is ready anytime you want it. You have a layer ready in Corel that has a rectangle drawn on it to quickly mark its location on your material.

A cheaper alternative would be to get a hunk of steel and place it in a honeycomb hole and again, prevent its being drawn up with a recessed nut/bolt/fender washer. Use a Cyanoacrylic glue or epoxy to lock it in place into the hole so it cant fall through the hole. Everything above is the same, but you have not had to buy 2 N52 magnets.

And cheaper still. place what is called a coupling nut into a honeycomb hold. Superglue it into place. Make sure it stays below the top of the honeycomb surface so it doesnt interfere with anything laid on the honeycomb. Mark its location in a Corel file and make a hole cut in the file. When you need to hold down some ornery item cut a hole in the material with that file, and use that file as a layer in your final document so you can avoid the hole in your design. Just like before. Then use a short bolt to screw through the hole into the nut embedded in the honeycomb and pull down just enough to flatten your bowed material. Now you are down to pennies worth of cost because you havent had to buy any magnets at all.

One thing. Your honeycomb table needs to be setup in a way that permits it to be fixed securely in place so the location of your hole in the Corel file is always accurate. And you would be well served if you setup the honeycomb so it can easily be removed, worked on (for cleaning for example) and replaced exactly where you took it from.

See if any of those ideas help you!

Dave

[Rich Harman]

I also use the 1/2 x 1/2 x 2" neodymium magnets. They work great for flattening warped ply wood. So well in fact that the magnets will pull the honeycomb out of shape as is fights to flatten the wood. I solved this by building an egg crate style structure that goes beneath the honeycomb out of 1/4" MDF, about 4" tall. The honeycomb is lashed to the structure using SS safety wire in several places. It has the added advantage of reducing flashback on the underside of the parts. It's been in use for years now and is due to be replaced. It lasted far longer than I expected though.

I very rarely make any sort of pattern or template to locate the magnets. I just place them where I know there will be no cutting, or I move them around as needed during the cut.

[Gary Hair]

I very rarely make any sort of pattern or template to locate the magnets. I just place them where I know there will be no cutting, or I move them around as needed during the cut.

One of the things I love about JobControl is that I can turn on WYSIWYG and move the cursor around the drawing to open areas and place a magnet where needed. No templates or guesswork needed! That saved me a few weeks ago lasering half-hides - they were nowhere near flat and would have been almost impossible to do otherwise given the complexity of the graphic I was lasering.

[Mike Null]

No help for cutting materials but for engraving I made a platform about 7 inches high out of wood and mdf. One side is nearly the size of my table, the other quite a bit smaller. I am able to clamp the edges of materials--leather, plywood, plastic, etc. to the mdf and keep it in focus. On the smaller side I am able to clamp baseball gloves and other unusual shapes.

[David Somers]

Mike,

Didnt you post earlier about a Corian table you use or was that someone else. It looked like a great idea if it was you and you can share the link to the post.

Dave

[Mike Null]

Dave

That was Keith's invention.

[Kev Williams]

...Next is cutting through warped material, pressed down with weight / and or magnets. Space under the 63 mm lens allows 1/2" steel weight plates positioned out of cutting path, and is lower than the laser head, but still need better ideas for hold down.
No, you don't... If your lens clears the weights, and you can keep them out of the engraving path, you're golden. ;)

During 13 years of trying to figure out how to hold stuff down, I always ended up finding something heavy to use. So finally I had a customer make me up a dozen 1/2" x 1" x 12" steel bars, and a dozen 3/4" x 2" x 12" bars. I use them with nearly every job in every laser. They keep SS from warping, and they're great for keeping leather from puckering. If I'm not holding edges down with them, I'm setting them against items to insure they don't move around. They also make great spacers, as they're EXACTLY 1" and 2".

[Kel Kodama]

Sorry if I misunderstood the laminate material composition, but I hope you aren't cutting PVC vinyl in your laser cutter.

[John Blazy]

Super awesome ideas everyone!!! Now I am going to make an MDF grid - super idea. Thanks a ton Rich, for the info about reduced flashback. I think I will lase out 1/8" Duron, or even order flame resistant MDF and a make a grid about 3" high or so, with 3/4" or 1" spacing. Then glue in some 1/4" DIA steel rods about 1/2" below the surface for the magnets to grab. I am planning some methods to eliminate the warped acrylic altogether anyway.


So yeah, Kel, good point on not lasing PVC, but the laminate isn't exactly PVC, although may be just as bad since it has a different type of vinyl component. I never cut without the exhaust going. I heard that vinyls will corrode the coatings on lenses and oxide the mechanical parts, so I am keeping watch for all that. So far so good though. I cut a ton of the laminate yesterday and the lens was a little dirty, but it cleaned up fine.

[David Somers]

Thanks Mike! And apologies to Kev!

Dave

[Rich Harman]

MDF and a make a grid about 3" high or so, with 3/4" or 1" spacing. Then glue in some 1/4" DIA steel rods about 1/2" below the surface for the magnets to grab. I am planning some methods to eliminate the warped acrylic altogether anyway.

Intersting idea. My grid has about 6" spacing - but it is only a support for the honeycomb.

[David Somers]

Rich,

On my Chinese laser I have both the knife edge table slats and the Honeycomb. I leveled all my knife edge slats to the gantry. Then I used some locktite to lock the adjusting screws in place so they wont wander over time. Then I placed the honeycomb on that and verified that it was also level to the gantry, which it was, and setup so that I can place the honeycomb onto the slats and get the same position everytime. Then I setup a way to lock the honeycomb in place so it doesnt wander unless I want it to. And after that I lay down some stainless rulers onto the honeycomb that are square to the gantry X and Y axis giving me a known corner in each corner of the honeycomb table so I can easily repeat operations. All that took a few hours to do, and now that it is done setting up for a job is quick and repeatable. Even dissembling things for cleaning is fast since I can put the honeycomb and guides back right where they came from.

This was one thing I never understood on the Chinese setup. Their setup didnt make repeat operations easy like you see on the western machines like Epi or Trotec or ULS. And they didn't seem to understand why I would want that ability. What I gleaned from them is they put down oversized materials, roughly align it and cut it and toss out the waste. Repeatability and being square to anything is not an issue with this approach. I think my woodworking and lathe background makes that offensive to me. I like repeatability.

For what that is worth.

Dave