[Gallchobhair]

Hello everyone.

My question concerns making multiple cuts. If I am engraving in plexi at say .002 and decide that I want to go a little deeper. I want to use the same tool path but say add .002 to the cut. What would be easier. Move the tool to zero then raise the Z enough to move off the piece note the number for Z and add .002 and call this my new zero. If I make say in Bobcad 3 engraving features each one being .002 and .004 and last .006 and post each as a separate NC. If I run the first one it will be .002 deep and if I run the second one it will be .004 deep or will it be .006. Or could I save them and have Mach3 think it is waiting for a tool change even if I don't specify a different tool. Then if I like what I see at .002 I stop if I want .002 more I just hit start from here. will I get a total of .004 or .006 deep because it it will cut 4 starting at the bottom of 2. I hope this makes sense. If it makes sense to me I know everyone else will be confused LoL ???

Don

[jrmach]

With plexi I would probably want to make some test cuts on scrap 1st.Hopefully the thickness does not vary too much on the plexi.

[mcphill]

I would use one toolpath. Use Z0 at top of stock for the first pass. If you want it deeper, go to Z0, and call it Z0.002 (or stay where you are, say Z1.000, and add 0.002 to the value, or 1.002). Rerun the same toolpath (it will cut 0.002 deeper, at a depth of 0.004). Repeat as necessary to reach the final depth you like.

[rfenn]

If you are using a basic profile or engraving, the Z value will likely only be in a couple of places in the G-code. For this, I just manually edit the G-code and increase the Z depth. You can use Notepad to do a global replace of Z-.02. Just make sure you understand your code and there are no other similar strings you might confuse. Make sure to find "Z-.02" and not just "-.02". I have left out the decimal point accidentally - thank goodness for soft limits! Of course, if this is more complicated with lots of Z depths in the G-code, don't do this. My only other alternative (besides redoing the toolpath), as stated previously, is to lower Z0 height reference after moving off of the piece.

Just update "Z-.02" with "Z-.04"
N286 G01 Z-.02 F60.

[Ben S]

The way I accomplish this kind of thing is by always using a tool length offset. I can then just adjust the offset in my controller by how much deeper I want to go. No need to change the program or jog the tool to a new Z position. Changing the program can be just as easy, provided it is a simple program, as rfenn said.

[mmoe]

I think it should be done with multiple depths of cut. If you re-zero the tool and re-run the program, it's possible that you could drag the tool across the stock surface. IMHO, the top of stock should never be above the zero position unless you are programming with the bottom of stock at Z=0. While a few thousandths probably won't be a problem, it's just not a good habit to get into. Just make copies of the engraving toolpath and change them to greater depth of cut, but the Z0 and rapid positions will remain the same, helping to ensure there isn't a rapid move through the stock.

If you are happy after a specific point in the program and don't need the final pass, you can just use the "feed hold" and then "stop" functions in Mach 3 to intervene before the last pass is made. It should have to rapid back to the start point, so you should have some time to feed hold. Be sure not to hit stop directly, just use stop after feed hold.

[Gallchobhair]

Thank you for all the replies. I have a lot to ponder. My basic question and maybe I asked it wrong is how do I get a wider line with. The tool I am using is a floating drag cutter. It is spring loaded so lowering the thing does not give me a wider line just better contact with the surface. I think I need to go to a regular V-Cutter. So a 120% V-bIT AT .005 will give me a wider line then a 60% V-bIT AT .005. Here is a picture of a test Litho I just finished. Yes I did stop and restart and it did drag the bit.Another learning experience LoL. I now need to make a light box. Anyone have a simple but nice design they would like to share. I think I am getting the hang of this stuff.

Thank You
Don

[rfenn]

If you want the drag bit to effectively cut wider, you will need to make your lines be an enclosed area (ie the finite width line has edges defined by lines) and pocket them. When I do these, I do an engraving toolpath and then I select the areas that I want to fill in. For those areas, I define my tool to be .04" but then adjust my stepover to say 50% so that there are pocket cuts every .02". For smaller detail, you can define .01" diameter and then make the stepover some percent of that.

I use the 90 deg diamond drag bit but also have the 120 deg one I haven't used. From the one experience I heard regarding the 120 deg bit on plexi, they were not happy with those results. Vbit should work fine if you can avoid melting and make sure your table is perfectly flat, otherwise line width will vary.

One more thing, if you are edge lighting this, make sure to do a reverse image on the back of the acrylic, otherwise you will get a reflection and image won't be quite as bright. I had mentioned this in an earlier thread here regarding Plexi.

Are you looking for a light box or just a base to stick it in? If you are doing a base and a single color LED and your plexi is wider than .25", then pretty simple. I use 3/4" material and cut a 3/8" slot and then within that slot, cut a 1/4" profile to fit the single color LED strip (LED strip width is about .25". You will need to either profile a groove or manually drill a hole in the side to run the power wire. The RGB lights are .4" wide, so this doesn't work as well. I have a somewhat complicated base design that encloses the electronics. Since I friction fit the acrylic and the width varies, I have to custom cut the slot to each lot of acrylic. This entails having a jig and flipping the top part. I recently designed a backlit, non-rectangular shape for LEDs but it is with a client at the moment being evaluated, so I don't have pictures of the internals. I showed a picture of the two part base design in a previous Plexi thread.

I started working on a frame design yesterday that would have an LED strip and pockets for housing RGB remote control electronics but I'm still working that out and only have sketches.

[Gallchobhair]

I do use mirror image and cut from the back. The picture I posted is Mirrored Plexiglass. I will try doing the pocket in areas that I find need it.

The lighting you mention I would like to see examples. You mention edge lighting and also a light box. You also mention backlit system. I would like to see these and how they work. Right now I just do the edge lighting.I am not doing color or remote control lighting. That will will come later. One step at a time. LoL

Thank You
Don

[rfenn]

Here is my back lit box (not rectangular) that is really using LEDs along the edge but below the top piece - hence not on direct edge of top piece. This is two pieces of 1/2" MDF put together and there is a .25" lip on the top piece holding a piece of 1/4" corian and there is a similar lip on the lower MDF piece along which a single color LED strip is held. I made it so that you could not see the LED directly since you would have bright spots. The lip on the top piece blocks direct light from the LEDs in the lower piece. To make this work, you also need a reflective backing - for this I used a 1/4" piece of mirrored acrylic that is inserted and does not have a lip to set on. Later I plan to use 1/8" mirrored acrylic and put it on a small lip so it will stay together better.

This is my first prototype for proof of concept - you can see I didn't even sand out the tabs and the pieces are held together with scotch tape. I was attempting to try and use LEDs instead of fluorescents since there is much more flexibility on the shape with LEDs.

Note the yellow color of the 2nd photo is an artifact from the digital photo - the first photo more realistically represents the actual item color.

[Gallchobhair]

Will the Corian have a design on it. That is very cool and outside the box thinking. LoL

Don

[rfenn]

If this project is approved the corian would probably be replaced with 3/16 translucent lexan which should brighten it up a bit. This is smallest of three pieces, which when laid out, form a company logo that will be used at an interior front entrance. Initially I didn't plan on any design on this section of corian but you can put a photograph in here by laminating a print on top of translucent lexan, so you can really do some interesting stuff. If it is to remain plain, then I'll get orange lexan with white lights - this mock up has red LEDs with white corian which is almost orange. I still have some challenges as far as making the front and back pieces connect and to be disassembled if wiring fails. Also, the wiring would need to be routed through the back onto some other back board that will also require some type of design. The MDF edges have to be primed well before they will take paint, so that is a definite pain. I likely will use a metallic paint to make it look like an aluminum frame.

I think this same design has potential for lithophanes - I just don't know if the LEDs are light enough along the edge. The other option is to make the design deeper and lay the LEDs along the back and put some type of diffusion over the lights to you don't see individual light sources.