Carve went ok. How to finish?

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Re: Carve went ok. How to finish?

Postby sirkossorg » Thu Jul 07, 2011 5:03 am

jeffD wrote:Chris,

Just a pic would be appreciated. My ugly dirt cheap scratch built mill is more accurate but slower than the fancy $$ Taig. No $$ and go really cheap, more $$ and tax deduct it quick. :mrgreen:

I'd love to see if you have made something even more ugly. Somewhere on my site
< http://users.gmavt.net/jdemand/mill.html > is a pic of the cheap mill

jeffD


Well Jeff, I think that is beautiful. I see a little of the Tom McWire style that inspired my machine.

Here's a pic.
Attachments
Bumblebee2.JPG
Bumblebee2.JPG (115.27 KiB) Viewed 5015 times
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Re: Carve went ok. How to finish?

Postby AdPrinter » Tue Aug 16, 2011 5:03 am

Hi Chris,
Very nice work on the lithophane. Could you please share with us, the following specifics:
1-Number of colors used (or shades of greyscale)
2-Depth settings you used for each color
3-How you determined the depth settings for each of the colors
The reason I ask for all of this, is because I have done some carvings with MeshCAM Art, but they were basic vector graphics using solid colors, and MC Art's various shaping functions (Round, Add, etc.)
Did you basically just make an assumption on the depths, based on things like background, midground, foreground, and highlight areas of the bitmap image? What I am after here, is a general "rule of thumb" like:
Number of colors used=6
Darkest areas (Blackest, in a Greyscale image for example) = say 0.01"
Dark Grey areas (Slightly lighter than solid black in our example) = say 0.02"
Mid Grey areas (Slightly lighter than Dark Grey areas in our example)= say 0.03"
Light Grey areas (Slightly lighter than Mid Grey areas in our example)= say 0.04"
Grey areas (Slightly lighter than Light Grey areas in our example)= say 0.05"
White areas (Highlight areas in our example)= say 0.06"
My understanding of lithophanes in general, are that the darkest image areas are carved with the shallowest depth of cut into the material, while the lightest image areas are carved with the deepest depth of cut into the material. Also, what size cutter did you use on your lithophane? I have tried to do a couple, using a Dremel V-Bit engraver, but the results were terrible. I do not have the ability to control the spindle speed, so the tests I tried were at full speed (30,000 RPM) on sheets of white nylon. Which resulted in a blob of molten plastic on the cutter after a very short time, followed by a broken bit. What were your feedrates set to on yours?
Sorry for the BOOK of questions, but I would really like to figure this out! Thanks, -Michael
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Re: Carve went ok. How to finish?

Postby Randy » Fri Aug 19, 2011 6:04 pm

Michael, Chris will need to answer about his machining parameters, but you don't need to use Art to do lithophanes. Basic MeshCAM will let you do lithophanes from grayscale images. I described how I did my first in http://www.grzsoftware.com/forum/viewtopic.php?f=4&t=446 .

1/4" thick Corian (used for the backsplashes when people get Corian countertops) is a popular material for lithophanes. People sell pieces on eBay, or you might be able to get offcuts from a local countertop store. It's nice because the pigmentation in it makes it dense which gives a good contrast to the lithophane.

You are correct in your understanding of thicker/darker since the carved sheet is variably blocking the backlight.

Randy
All opinions in this post are mine alone. I am not a MeshCAM employee, I do not have a financial interest in MeshCAM, nor do I speak for MeshCAM. MeshCAM user since Beta 5 in 2003. viewtopic.php?f=11&t=15333 :ugeek:
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Re: Carve went ok. How to finish?

Postby AdPrinter » Mon Aug 29, 2011 2:46 am

Randy,
I read the post you referenced:

My first experimental piece is made from 6mm ("1/4-inch") white acrylic, which is .236" thick. I cropped the picture I was working from to a 4:3 aspect ratio and converted it to an 8-bit grayscale. I imported it into MC and sized it for 4x3 inches and kept the .100" depth range. I kept the material size the same X and Y dimensions as the image, but set the thickness to .236" and set the top margin to .100". This meant that the machining would be from Z-.100" thru Z-.200".

My actual blank was 4.5 x 3.5 inches, so I set the machine origin to X-.250, Y-.250 and the top of the material. I made two "finishing" passes. The first used a .125" ball-end mill with a .040" stepover, X passes only. That was my roughing step. The actual finish pass used a .031" ball-end mill with .007" stepover, X passes only. "Roughing" took about 25 minutes at 12ipm and finishing took a little under 4 hours at 8ipm.

"This meant that the machining would be from Z-.100" thru Z-.200"
Shouldn't that be Z+0.100" thru Z-0.200"?
The very biggest thing I struggle with in MeshCAM, is setting everything up to happen relative to the top of stock (which I always set to Zero in Mach3 by jogging the tool down to just touching a sheet of paper placed on the top of my stock). I have spent many HOURS in MeshCAM, trying to get a negative Z toolpath generated which will run in Mach3. Only to find, that the G code generated by MeshCAM contains only positive Z movements. The confusing point in MeshCAM is the "Center Z" - Try as it might, my router simply will NOT ADD material to the top of the stock. It can only remove material (by locating the tool path to a NEGATIVE Z coordinate). There are so many variables in MeshCAM, that I get confused, at subsequent attempts to go back and try again! Set Tool Zero in particular. And if importing a bitmap to work with, whether or not to set Black as +Z or -Z. I have actually broken bits, which plunged full-depth into the material (after experimenting with MeshCAM's Tool Zero settings in particular). In an effort to wrap my head around this issue. Could you offer any guidelines in this area?
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Re: Carve went ok. How to finish?

Postby Randy » Mon Aug 29, 2011 5:49 am

Michael,

MeshCAM is actually very easy to use once you get your head around it. :) "Program zero" is the key to the whole thing.

Here is a little bracket I made a while back, just brought into MeshCAM for 3-axis machining:
bracket01.gif
bracket01.gif (20.11 KiB) Viewed 4744 times

The part is 2.94" x 2.60" x .375" thick.

And here is the Define Stock dialog before I have changed anything:
stock01.gif
stock01.gif (12.15 KiB) Viewed 4744 times

You can see that the stock is "shrink-wrapped" to the bracket geometry, and the Program Zero, defining the output gcode coordinate system, is in the "top southwest" corner of the stock. The part geometry zero that I used when CAD'ing the part, is irrelevant at this point. MeshCAM always uses Program Zero as the basis of its coordinates.

Now I've gotten a block of rawstock that is 4.00 x 3.60 x 1.00 inches and introduced it to MeshCAM:
stock02.gif
stock02.gif (12.12 KiB) Viewed 4744 times

I've let MeshCAM center the workpiece, so there is rawstock all around the geometry:
bracket02.gif
bracket02.gif (20.37 KiB) Viewed 4744 times

The Program Zero follows the rawstock, so it is still at the top southwest corner of the rawstock. The program zero has moved relative to the part zero, but that doesn't matter.

Now I've decided I want the Program Zero in the top northwest corner of the rawstock:
zero01.gif
zero01.gif (7.45 KiB) Viewed 4744 times

And here it is onscreen:
bracket03.gif
bracket03.gif (25.11 KiB) Viewed 4744 times

When I put the block of rawstock in my mill vise, I will touch off zero for Mach3 on the top, rear, and left surfaces of the block. All of MeshCAM's gcode will be relative to that point. All rapid moves will have a positive Z (which will be the Z I define as Retract Height), and all cutting moves will have a negative Z. Maximum cutting depth defaults to the bottom of the rawstock (which in this case will be Z-1.000), until I redefine it.

On my lithophane, the cutting range was .100" in Z from shallowest to deepest points (i.e. my "part" was .100" thick). But I embedded the top of that .100" range, .100" deep into the rawstock. So in Program (machine, i.e. gcode) terms, the cutting depth was from Z-.100" to Z-.200". The bottom of my carving was .036" up from the bottom of the rawstock, which was .236" thick. Therefore the lightest points of my lithophane were .036" thick and the darkest points were .136" thick.

Does that help?

Randy
All opinions in this post are mine alone. I am not a MeshCAM employee, I do not have a financial interest in MeshCAM, nor do I speak for MeshCAM. MeshCAM user since Beta 5 in 2003. viewtopic.php?f=11&t=15333 :ugeek:
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Re: Carve went ok. How to finish?

Postby sirkossorg » Tue Sep 06, 2011 7:53 pm

Michael,

I apologize for not responding. I hadn't checked the forum in a while.

The reason I like MC Art is because I really don't have to do much to cut something like that litho (maybe normal MC is the same, I don't know). I convert to greyscale and edit the picture using GIMP (wish I hadn't made the noses/lips darker), and bring it straight in. I set the x and y limits, set the material thickness to be however deep I want it to go and set the top of part to zero. Smooth it a little and pretty much go. I'm guessing the software divides the total cut depth by 256 and assigns Z coordinates accordingly.

For this one, I roughed with a 1/8" straight upcut bit and used a 1/16" 2-flute endmill for the finish. I use a router with no speed control, but I bought an external speed controller for $20 at Harbor Freight and it slows the router down pretty well.

My feedrate is 10ipm with .03 stepover. X-only.

Randy is also right about sourcing Corian.

Chris
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Re: Carve went ok. How to finish?

Postby AdPrinter » Wed Oct 19, 2011 1:35 am

Chris,
Thanks for the details on the lithophane. I have a single piece of Corian, and just wanted to make sure that I got everything set up correctly on the FIRST try.
Randy,
I appreciate the graphic illustration you posted. It really helps in understanding. (I apologize for taking so long to respond, but I have been busy churning out a lot of wood carvings and haven't been on the website for awhile). It is important to note, that I am working with MeshCAM Art (using PNG bitmaps created in CorelDRAW, and opened into MeshCAM- NOT traditional CAD DXF files). What I wound up doing, was changed the import Black to -Z and then GIVING UP! (I.E. -I stopped fighting with MeshCAM, and just accepted the defaults in Program Zero). So far, it has worked almost flawlessly. There was this one carving though, that involved a 70 degree Round surface on a circle (dome-shape) that I set up with No Limit on Height. It actually extended 0.08" above the surface of the stock. When I started the cut and saw that the top of the dome was not removed on the first pass of the Roughing cut, I stopped the program, returned to Zero in Mach3. I then started the spindle, and manually jogged the Z to -0.08" and reset Z Zero in Mach3, regenerated toolpath and then restarted the program run.
This particular carving is of the U.S. Marines logo (Eagle, Globe, and Anchor). Obviously, the Globe was the "Dome" shape in this carving. I used a 1/4" end mill for the Roughing cut, and a 1/8" end mill for the Finishing cut. It did not turn out as detailed as I would have liked, so I finished it up by hand with a Dremel. I will post pix later when my daughter brings our camera back home. Again, THANKS for the help!
-Michael
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Re: Carve went ok. How to finish?

Postby Randy » Wed Oct 19, 2011 3:28 pm

Michael, I'm sorry if I assumed too much. MeshCAM's coordinate system behavior is the same with STL and bitmap import, and I assumed it would be the same with Art.

Randy
All opinions in this post are mine alone. I am not a MeshCAM employee, I do not have a financial interest in MeshCAM, nor do I speak for MeshCAM. MeshCAM user since Beta 5 in 2003. viewtopic.php?f=11&t=15333 :ugeek:
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Re: Carve went ok. How to finish?

Postby osprey » Sun Oct 07, 2012 9:14 pm

Your Lithophane is great! Mine have not turned out as well. How about posting your workflow from beginning (manipulating the photo to the milling?
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