I’m looking for a suitable needle to poke tiny holes of varying size into paper. The needle should be less than 0.1mm at the tip and gradualy increase in diameter, so that the further you poke it through the paper, the larger the hole gets.
So far i have looked at hand sewing needles, which are a bit too big, machine sewing needles, which have a consistant diameter, and medical needles, which also have a consistant diameter.
If anyone can point me in the right direction I would appreciate it very much
What I plan to do is this:
The tiny holes are used as “pixels”, when the paper is held against a light source an image will become visible. The smaller the holes I can make the better it would look, on a paper with something printed on it the image becomes virtually invisible until you hold it against the light.
On the first page of the swiss passport your photo is engraved in this way, and I would love to recreate this effect
At my last job we did some experiments with a highspeed galvo lasercutter, but the smallest holes we could achieve were about 0.2mm, clearly visible.I’m hoping to have more success with the needle approach
Do you know how far you have to push the needle to get it to puncture the paper? The paper is going to give a bit as the needle encounters it. I suppose you could put it up against a hard backing, but then you will end up dulling the needle.
This isn’t answering your question. But for cutting and perforating foam boards, model RC folks use a “needle cutter”. They just attach a motor to a very thin wire and then use the cnc to move it around. Their intention is to cut through the whole foam, or just the top layer of paper.
I can imagine using that. But moving around in a helical pattern to increase the diameter.
At any rate, they have learned a lot about what works and there are several designs for hardware to do this. They are all built with easy to find materials. I think putting some cheap foam behind the paper is probably a good choice, because it will give but hold.
The “needles” used in the cutters @jeffeb3 is referring to are made by the owners of the cutter from solid music wire. You could choose wire of the diameter equal to the largest hole you wanted and by controlling the angle when grinding the point you may be able to achieve repeatable diameter at a given depth from one needle to the next. I don’t know that I’ve got that level of grinding skill but it should be possible.
Cork or a self-healing cutting mat as backing material might last longer than insulation foam or foamboard (with paper on either side).
Yeah I thought about using styrofoam or something else as a backing, something that doesn’t give, but lets the needle pass through. I’m not sure if I could grind the music wire precise enough.
The increase in thickness of the needle should be linear, so that a nice greyscale effect can be achieved.
I’ll do some experiments with the finest hand sewing needles I have around, their diameter ranges from about 0.15 to about 0.55mm. It won’t be invisible, but a good first test
I think it will be hard to get an accurate Z when also poking through a soft material. I expect it will give more or less and that will affect the width if you’re using a tapered needle.
Although, I’m not sure how to get the CAM to do what I was suggesting, where darker areas are wider because of more punching of the same size.
I can’t imagine doing this with a simple needle cutter as these usually are just free-running and independent of the feedrate… and generally are used to leave a line of overlapping perforations that effectively cut shapes in the material.
A laser would be far easier to control using dithering, such as “halftone” or “newsprint”, and is easily achieved with Lightburn or similar.
Can you tell me how they are measured? I just ordered one that is 0.4mm, but honestly I have no idea what that means ^^’ I hope it’s the diameter of the needle, and the tip goes down to 0
Ok, so I’ll have to wait and see if it’s going to work. In the meantime I can get started on the software side
From the laser experiments I already have code that converts pixels to vector circles with varying diameter, I think I can easily adapt that to output gcode
