reducing "stepping" on sides

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reducing "stepping" on sides

Postby letterman7 » Thu Oct 06, 2016 2:46 am

Hi all,
I don't visit here much so bear with me. I primarily use Photocrv to do small items for myself and the occasional background textures for signage. I have in house a fairly large signage project for a client that I thought would lend itself perfectly to the program. Starting with a greyscale of his logo, I was able to manipulate it enough to have the contrast I wanted and the dimensions for carving. It's carved in Signfoam, using a 3/16" ballnose, with 10% overlap. Both pieces are 27" round (they are sort of family crests). The total carve time was 27 hours...

In the end, it turned out pretty much the way I wanted it to, except for the sides of the cuts, which exhibit the stepping. The cuts are about 3/4" deep, and since it's foam I can easily sand them out, but I'm wondering if there is a way to minimize or eliminate the jagginess. Any ideas?

Rick
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Re: reducing "stepping" on sides

Postby FixitMike » Thu Oct 06, 2016 3:06 am

Does the stepping show in the preview?

If so, it is something you are doing in PhotoVCarve. If not, it is a machine or machine driver problem. I would suspect an acceleration setting, but that is just a guess.
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Re: reducing "stepping" on sides

Postby letterman7 » Thu Oct 06, 2016 3:31 am

Yes it does, Mike. There is stepping in the preview.. I put that off to low resolution. Not quite sure what to do about that. Maybe the image is too low a resolution, though it's close to 300dpi at size. Good for printing, maybe not so good for carving!
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Re: reducing "stepping" on sides

Postby FixitMike » Thu Oct 06, 2016 3:42 am

Obviously not low resolution, since it shows up on the job. I am not real familiar with PhotoVCarve, so I can't offer any advice, other than to say that I have seen posts about a similar problem with 3D carvings in Aspire. In those cases, it was what happens when there is a vertical surface in a 3D carving.

Are you using PhotoVCarve? Even though you posted in that forum, the pictures look more like something carved from Aspire.
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Re: reducing "stepping" on sides

Postby letterman7 » Thu Oct 06, 2016 12:21 pm

Yep, Photo VCarve. I haven't upgraded to Aspire as I don't spend the time with the router that I should!
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Re: reducing "stepping" on sides

Postby adze_cnc » Thu Oct 06, 2016 5:36 pm

Everything in the picture is what I would expect from a raster cutting with a high step-over size (low detail resolution) meeting a vertical plane (as FixitMike pointed out).

letterman7 wrote:using a 3/16" ballnose, with 10% overlap


Be careful of your terminology with this. If the tool moves 0.01875" (10% of its diameter) from pass to pass then the overlap is 90%. For a 10% overlap the tool would be moving over 0.16875" pass to pass.

Steven
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Re: reducing "stepping" on sides

Postby letterman7 » Thu Oct 06, 2016 7:14 pm

You may be absolutely correct, Steven. My terminology isn't correct; when I calculated the paths, I set the line spacing to 10%, which gave me decent (what I thought) resolution. Being an exported image at 300dpi I thought that would have sufficed, but apparently not. Just for an experiment, I resent the logo at 600dpi at size as both a .jpg, .tif and .png, and all had the same results with the same jagged edge. Even reducing the line spacing to 1% still resulted in the exact same thing, so I'm guessing this is just the nature of the beast. I could do an inside vector sweep, but there would be no way to calculate the rise and fall of the different planes, so the overall look would be compromised. I have another to do for this client at three times the size, so I'll have to split up the file and assemble it in pieces... just trying to see if there was a way to get around sanding all the verticals.
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Re: reducing "stepping" on sides

Postby adze_cnc » Thu Oct 06, 2016 10:38 pm

letterman7,

Attached is an image of a recent project cut in VCarve. The wood is about 11.5" x 8". It was cut with a 1/8" ball nose (1 degree taper) bit with a step-over of 0.025". Notice that the nose, eyes, and mouth have "stair-stepping".

Steven

artifacts.jpg
Artifacts of the cutting process.
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Re: reducing "stepping" on sides

Postby letterman7 » Thu Oct 06, 2016 11:06 pm

Ok, so how can we minimize this, if not eliminate it? Or is that just not possible in Photocarve?

Rick
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Re: reducing "stepping" on sides

Postby adze_cnc » Fri Oct 07, 2016 6:08 pm

Rick,

I don't have PhotoVCarve (PVC) but from what I understand of it the size of your material and the resolution of the source image determines what 100% line-spacing is:

e.g. If you are cutting using a 0-deg angle (horizontal), your material is 12 inches, and your image has 240 lines then your line-spacing at 100% is 0.05 inches.

Increasing the percentage of line-spacing also increases that step-over size. So, at 120% line-spacing my step-over is 0.06 inches. I save time in cutting (fewer passes) but at the expense of resolution.

So, unless PVC can do less than 100% line-spacing, to reduce the step-over from 0.05 inches I can do one or both of two things: 1. increase number of lines in my source image; 2. decrease my material size.

I take it your material size is constant, in this case, so you'd be looking at increasing the resolution of the source image.

Since you are using a sign foam can you get a bit more aggressive with you Z step-down? Maybe increasing it closer to the limit of the tool's cutting edge length?

Steven (middle name Richard)
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Re: reducing "stepping" on sides

Postby letterman7 » Fri Oct 07, 2016 6:44 pm

Hmm, yeah, tried both those things. PhotoVC can go as low as 1% line spacing, and I've tested that with a 600dpi at size image and the resulting preview image looks the same (jagged). One of my initial routs of this job was using 100% line space with a 300dpi image at size, and the results were so sloppy I had to do it again, and these photos are from that second go-round. I'm half thinking the ball-nose bit that I was using, being a 3/16" bit, has a slight taper to it as it goes up the shank to 1/4". On the next part of this job I'm going to try a 1/4" round nose to see if the lack of taper has an effect. On the preview there appears to be stepping, but that might be the resolution of the preview...

Thanks for the input Steven!
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Re: reducing "stepping" on sides

Postby martin54 » Fri Oct 07, 2016 6:55 pm

I've not picked pvc up again to try some of the things I have read about on the forum so can't really help with advice on settings but would like to ask what sort of size & file format your original photo was at 300 dpi & how you increased the size to 600 dpi.
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Re: reducing "stepping" on sides

Postby letterman7 » Fri Oct 07, 2016 7:02 pm

Hi Martin,
I design in CorelDraw, the image was created as a vector initially at size, then converted to a bitmap through Corel. I can set any conversion dpi I wish, so I started with 300dpi. With the 600dpi, I simply resampled the image and resaved it as a 600dpi image.
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Re: reducing "stepping" on sides

Postby martin54 » Fri Oct 07, 2016 9:51 pm

OK so you know what you are doing, I only asked because I work as a signmaker & image size & resolution is something that a lot of my customers don't really understand :lol: :lol: , I have people who give me a 72dpi image the size of a postage stamp & ask me to print it to fit an 8' x 4' board :lol: :lol: :lol:
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Re: reducing "stepping" on sides

Postby letterman7 » Fri Oct 07, 2016 10:02 pm

:lol: Yep, I'm a signmaker as well. I don't utilize the ShopBot as much as I'd like, but for items like this where it'll run for 20 hours unimpeded, it's pretty nice. And much cheaper than subbing it out to another company!
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