Engraving coconuts

[Scott Marquez]

I'm continually amazed by your ingenuity Kev! Very clever way to hold those!

I think if he used the same cup design as the top, on the bottom it would take the "off centered" base out of the picture and it might spin pretty true.
???
Scott

[Kev Williams]

Keith, thanks, but don't blame me, blame good equipment! Great cylinder unit, comes with lots of accessories.
And it works with all the newer Gravograph machines, I can use the same unit on my IS400 and IS7000 tool machines

Scott, I tried using a cone on the cup-top and a 'dish' on the bottom, doesn't make much difference!
But I got to thinking about what I said above, that the cup ENDS are relatively flat to each other, so,
I turned around the big dish, AND my small cone (the groove in the back of the big cone is in the way),
so I can hold it flat-to-flat.

!DSC04278.jpgDSC04279.jpg

Once I find a relatively evenly round section of the side to start from, I can look straight down and
eyeball side-to-side center, then close the clamp. Might take a few extra seconds to load, but
I should make that time back in less stops to refocus...

(Mike, sorry for the hijack! )

[Keith Outten]

Mike,

Can you grab the inside of the cup with the chuck on your rotary?

If you don't have enough reach from the chuck jaws you can turn an ID / OD disk on your wood lathe and cut it into segments to extend your chuck jaws. Make sure that you cut a groove in the disk so you can use a rubber band to hold the segments to the chuck jaws.

[Mike Null]

Guys, thank you all for your suggestions. Kev, you didn't hijack the thread, your ideas are relevant. My NH has a very similar rotary device to yours and I'm quite sure I can route them using cutters like these. http://www.antaresinc.net/EngSTD.html This process will be slower, more expensive and will probably entail more breakage.

Dave, your idea is a good one and similar to what Kev is doing except he put the cylinder on the other end. I should be able to find a cup around the shop that will work--if not I can turn it on my lathe. (actually I'm going to use a piece of pvc pipe taped to one of my cones.)

Keith, I believe you're referring to a rotary device for my laser which I do not have.

[Kev Williams]

Hey Mike, I was assuming you had a rotary for your laser, my apologies!

I'm not sure what holding jigs you have for your NH, but assuming you have a self-centering clamp and no issues holding the top of the coconut, to get around the issue of the cup's base, could you make from wood another v-cup, with the center hollowed out to clear the base? It would take a good size chunk of wood, but I'm sure that's not a problem!

this way it'll support the cup and the base will be untouched. This assumes you'll have enough engraving area remaining after you size it to work...

cuptail2.jpg

[Joe Hillmann]

Does it have to be laser engraved? Due to the curve in both directions as well as slight inconsistencies in shape and size I think pad printing would be the best way to go with that or depending on the size of the image maybe loose screen printing.

[Keith Outten]

Mike,

I knew that you didn't have a rotary for your laser engraver but I thought you had a 3 jaw chuck for your NH rotary. Most 3 jaw chucks can be used to hold objects from the inside diameter or the outside by reversing the jaws.
.

[Mike Null]

Keith

You are right but my chuck is relatively small and I doubt that I can hold the nut securely enough to rout. I may pad the fingers with some sponge or rubber for better grip. I'm thinking I'll have to make a .010" deep cut to be enough to give me an outline for a freehand fill.

Joe, I think pad printing might be the answer also. The concerns are the course texture of the nut and the irregularity of the shapes. I don't know how much texture can be handled with pad printing. Everything I can recall seeing has been on a smooth surface.

[Kev Williams]

I'm finally putting a laser beam to these coconuts--

My setup is as described above, except that I turned the tailstock cone around so the narrow end fits inside the cup bottom. Turns out many of the bottoms are too big for the flat side of the cone, and this is working out nicely.

Note the lens setup- I'm using a 4" lens installed in one of my Triumph lens holders. The lens and holder is on the machine upside down, the lens is just under the mirror at the clamp. To get the clamp to hold I had to wrap a couple of layers of tape around the tube end. Hey, it works! The other thing I did was make a new auto-focus plunger rod out of some delriin. It works too!

The 4" lens is the saving grace on this job! As noted above, I just find a relatively consistent 3" sweep area on the coconut, put the starting point straight up, then eyeball the side-to-side center as best I can- They're running flawlessly, no stops, and the engraving looks great, very consistent- even with the lens upside down! (I swear, with certain materials and jobs I get better results with an upside down lens).

-I'll show the engraving if I get permission to...

[Joe Hillmann]

How far + & - out of focus can you be with that 4 inch lens and still get good results?

[Kev Williams]

I haven't tested it, but according to this webpage: (which has some cool laser & lens info, check it out!)
http://www.parallax-tech.com/faq.htm

--the depth of field of a 4" lens is .200" (5.6mm), which is quite a bit. This means from dead-center of the lens's focal length, the work can be nearly 1/8" closer OR farther away and still get pretty good results! The trade-off is the beam's spot size is bigger, so that has to be taken into account. But hey, I'm engraving coconuts! Spot size isn't really an issue!

This is a table from the website, showing the beam spot size and depth of field for different focal length lenses...

[Mike Null]

Just a quick update. I was able to get a good quality engraving using my Trotec and two focus settings. Even though the engraving is good I can't figure how to colorfill without getting paint outside the engraved area. Masking is not possible due to the rough surface and I've tried a paint pen and a small brush. A syringe might work but it's too tedious for 1600 pieces.

I think I'm going to tell my customer no fill is available.

[Bert Kemp]

Mike how bout a liquid mask would that work?Plastic dip or something like it?

[Mike Null]

Bert

These are in their natural state and so rough that no mask can be used, The liquid would work up to the point you tried to remove it then it would be too time consuming.

One of my customers is a promotional products company and I am going to consult with them today. If they have a solution I'll turn the job over to them.

[David Somers]

Mike,

This is a silly question. But have these cups with the rough coconut husk exterior actually been made yet? Or are you dealing with a few prototypes? If the latter, can you explain to the potential client that a smooth coconut would be doable but a rough coconut would be better left unadorned?

Another silly thought just came to me. If they are rough husk exterior I assume they were not meant to be used with any frequency, if at all? Display items only in other words? If that is the case, how about not actually engraving them but cutting fully through the shell to the interior? Just a wild thought. Not sure that would have any bearing on the design. Just brain storming.

Dave