lithos with black subjects

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Xxray
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lithos with black subjects

Post by Xxray »

Got a buddy who wants me to do a litho of MLK, am trying to spin it around my head how its going to turn out. Pic posted below is the one he wants but of course another more suitable could be used. A black guy with a white shirt against a black background ,,, On the other hand, most of his face is highlighted decently.
What do you guys think, any reason why this would not be suitable for a litho ?
I also want to do one of Jimi Hendrix and another of a black and tan german shep, so I'm trying to figure out a strategy for darker subjects. For instance, would I still invert the colors ?
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Re: lithos with black subjects

Post by tonydude919 »

Here is one I did a year ago or so. It came out better than I thought it would. I used a .0625 ball nose on it.

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Re: lithos with black subjects

Post by ssflyer »

That should actually come out much better than your first attempt - way better contrast. I did one of BB King I took in a dark venue, lit only with the stage lights, and it actually came out pretty well.
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Re: lithos with black subjects

Post by Xxray »

Great, I'll give it a shot and post back with the results.
The guy is a good friend of mine, he is black and runs a laser craft booth, doing all sorts of things. He saw the Marilyn Monroe I did and was blown away ,,, He says he often has problems with darker skin tones with his laser work.
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Re: lithos with black subjects

Post by pops1964 »

Xray, Thiis is Jeff I've asked you a couple questions on the shopbot forum. I was looking around and thought i seen you saying the machine time on one of your lithos was just a few hours. I'am just curious I've been doing them about a year now and have never talked to anyone about them before . I'am getting great quality I try to stay in the 7'X 9" up to 10"x 12" seems to get best quality and seems that for best in the faces I zoom and crop to mostly a portrait look. and the way I program it I can do them in either 8hrs. or 12hrs. depending on how busy I am and the quality of the picture I have to work with. I just joined this forum and posted a few litho's under POPS1964 thanks
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Re: lithos with black subjects

Post by Xxray »

Forgot to post back did this a couple weeks ago, no problems with black subjects.
This is about 8x10" and took about 2.5 hours with a .125 ballnose, 8% line spacing.

8-12 hours seems quite excessive, unless you are going for ultra detail with a 1/32 bit or something.
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2.jpg
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Re: lithos with black subjects

Post by pops1964 »

Xray when i run my lithos I do two pass's roughing and a finish rough with a 1/8" ball nose , finish with a 1/16" taper ball nose .

Roughing Carving max depth - .18 Finish .2
Line spacing - 50 % Finish 1 %
Number of Lines - 206 Finish 5145
Distance between - .063 Finish .003
Number of pass's in Z -3 (,063 Finish 1 (.200
Line angle -30 Finish -30
Check invert light/darkness box Finish same
contrast 25% Finish 25%
Rapid clearance .06 Finish .06
1hr. 20 min. 12 hr. 12 min.
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Re: lithos with black subjects

Post by Xxray »

I run without a need for roughing, and also 8-10% line spacing - I think your 1% surely should be jacked up a bit, I can see why it takes so long.
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Re: lithos with black subjects

Post by scottp55 »

Doug, Is line spacing the same as stepover?

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Re: lithos with black subjects

Post by Xxray »

Not sure, I would think the 2 sprang from the same concept.
There is a point of diminishing returns where all you are doing is increasing machine time without any greater detail, not sure where that point is I would guess somewhere between 5-10%.
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Re: lithos with black subjects

Post by scottp55 »

Thanks Doug, I don't do lithos so was just wondering. I forget whats the stepover in your plexis? Jeff, 1 % does seem extreme if line spacing is the same or similar as stepover, can you try a small one at say 5-6% zoom in on preview and then redo at say 3-5% and watch preview closely to see if quality improves sufficiently to merit the time? With Partworks 3D that's how some people find their sweet spot. I know nothing about the program as I told you but may be worth a shot?

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Re: lithos with black subjects

Post by Xxray »

Put it this way - The 5,145 lines at 1% would be more like 1,200 or so at 8% and under 1,000 at 10%, and I really doubt if there would be an appreciable difference in quality if any.
That and depth, not sure but multiple passes might be unnecessarily made further increasing cut time.
If my max depth is say .21, I will set that depth in tool properties, therebye insuring you only have to make 1 pass per line.

I have found roughing unnecessary, bits chew through corain pretty easily - You do want a 45 angle though to greatly reduce stress on the bit. Exception might be .5 corian, in that case I'd mill it down to .25 before starting, milling is quick at 50% stepover/line spacing.
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Re: lithos with black subjects

Post by PaulRowntree »

Xxray wrote: You do want a 45 angle though to greatly reduce stress on the bit.
XXray, how is the stress affected by toolpath angle wrt the X or Y axes?
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Re: lithos with black subjects

Post by Xxray »

PaulRowntree wrote:
Xxray wrote: You do want a 45 angle though to greatly reduce stress on the bit.
XXray, how is the stress affected by toolpath angle wrt the X or Y axes?
If you were to go 0 or 90 angle, the tool would do a full line of fresh cutting on both sides of the bit the length of the workpiece, putting a lot of stress on both the bit and the workpiece. 45 angle eases you into it a little bit at a time as much as possible starting from a corner. If you got through the very first pass with low or no angle with no problems then you are out of the woods, as the rest of the passes will not be cutting on both sides of the bit ... But every time I have had a mishap using no or low angles, it is on the 1st pass.

I have a beauty of a tapered bit that for some reason cuts more aggressively than others, it will easily fracture .25 or even .5 plexi or corian with no angle, cuts like butter with a 45 angle. Just one of those things some costly trial & error has taught me.
[The above doesn't necessarily hold true when doing a roughing pass, which by default greatly eases the job of the finish cutter. I tend to skip roughing as much as possible to save on cutting time, thus the 45 angle for me is not an option, it is critical].

I do alot of 3d work in thick plexi, for that I don't skip roughing and then I don't have to consider angle.
Doug

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