GearHeads Corner

When I create a box with tabs and then cut it out with me CNC machine, the "fingers" are too tight. We need the ability to cut them just a bit more loose, so that they will fit together.

Thanks and I enjoy your product a great deal!

Duit:

  Good point, I hadnt considered  it. Added to my list.

Art

Could you fake it by setting the cutter size slightly smaller than it actually is?

Kirk

Thanks for your suggestion. When I tried to use the advice (fake it with the smaller bit diameter), the whole box was then cut to a different dimension. I would like for just the fingers to shrink size in the width dimension, not the whole part. The fingers are just too tight. I appreciate your help, though.  :)

I have the opposite problem, my tabs are a bit too loose.  I suspect it's because the only option I have for laser cutting DXFs (chinese low budget controller with proprietary low budget software) will follow the center of the lines so there's a gap the size of the cut.  Perhaps what it needs is a tab size percentage that can be tweaked.  Acrylic cement (supposedly, not here yet) takes tight tolerances to work since it's a thin solvent and not a gap filling glue.  Certainly not as important as Auggie (and when should the controller boards be ordered to beat the rush?  Group buy?).

Also, interestingly, I've been making long narrow plates so most of the gear is exposed, with plates on the narrow ends.  I have to set the tab count quite high (think 20s or 30s for the two gear project) to get any tabs.  My guess is the tab count is based on the longest side so it take a high count to get tiny tabs.  Not a problem, just took some experimentation to figure it out.

Kirk

Kirk:

Ill consider this in the fall, I hadnt had that trouble, my laser made pretty tight tabs when in focus so the solvent works fine, but i can see where with certain focus's ( focii?), the tabs could be trouble. Ill look at an offset allowance in the fall.  As to controllers, I wouldnt rush, lets see how testing and development go, I dont want anyone stuck with hardware they dont need.  This controller will be specifically dedicated to weirdo machines so general cncer's may not find iot all that appealing except perhaps for a wizarding program or simple ( well, not too simple) cnc use.  ( Though Pokeys do work on Mach3 and 4 as well which is a good thing.).

Art

Thanks guys!

As to the "too loose" scenario that you are having, I believe a "slop" button or a "reduce finger width" (or widen finger socket) button would solve your issue too. Of course, it would be a button to REDUCE slop. Lets just cross our fingers and hope that the Magical Artmiester can perform a miracle (AS IF.. what he has done already.. isn't enough  :D)
I really appreciate all the feed back that I have received from y'all. I enjoy working with your product, Art. I will continue to recommend it to my fellow "makers", whenever I can.

Thanks Duit:

:)

It will be an interesting season..

Art

ArtF wrote:It will be an interesting season..

It's always an interesting season, in ways we never expect :)

Is the weirdo you're referring to the machine or the operator?  I've got the latter down.

I was thinking on the long drive to town today, always dangerous for multiple reasons, including missing the moose standing in the road.  You've already got logic for offsetting the cut path based on cutter diameter, so perhaps an option to offset dxfs based on a supplied beam (or cutter) size might be a general solution in the laser cutter case (in the low priority section of the infinite list).  My cut width is very small, the thickness of a piece of paper or less, but still enough that the box tabs aren't a gapless fit.  Don't know how much of that is user error/ignorance, or how prevalent center following laser software is, but won't the cut width always be non-zero and potentially cause a problem with materials using thin solvent-type glue?  Or am I just inhaling too many of those fumes?

This doesn't solve Duit's tight tab issue or the desirability of tab size adjustment, of course.

Kirk

Well, its never a zero kerf.. but results vary from person to person, when I cut acrylic, the pieces have to be pressed out, they are well tight enough for
solvents to work, but it depends on several factors from material to laser focal length and such. About the only solution I see is to make the tool pull away
a smidgen when its actually in a tab.. one of them anyway.. I expect theres no perfect all round solution..

Art

The answer may be in your CAM program. I use Sheetcam, a very basic CAM program. Sheetcam, and I assume others, allow you to factor in a Finishing Allowance so that you cut a part slightly larger and then do a finishing, cleanup pass down to designed dimension. When I want a part ever so slightly smaller, I input a negative finishing allowance. This can be done for whatever part of the drawing is on that layer. So, if I was milling a gear, I put the  center hole on one layer and the outline on another. That way, the center hole is cut as designed. The outline could then be cut with the negative finishing allowance giving the looser fit that you're after.

Hope that makes sense.

David Morrow wrote: The answer may be in your CAM program.

That's a good option, but calling LaserDRW/CorelDraw a CAM program might be an overstatement.  It's pretty basic, but in it's defense it's a minimal proprietary driver for a proprietary (undocumented interface) controller tacked on a drawing program.  No other choice unless I try reverse engineering it's protocol or replace the controller.  While it will somewhat vary the cut order (inside first so parts don't fall out by cutting the outside first) there's no provision to compensate for the tool (or laser beam) width, at least that I can find.  Hmm, Inkscape has an offset tool, perhaps Corel has one too; that might do it.

If Art can get cuts so tight they have to be pressed out perhaps I need to realign again and maybe look at a better quality lens.  Cutting up a slope (to find the best focus distance) shows I'm pretty close, but these are about the cheapest possible optics - about what you'd expect from a sub $400 delivered (rounded up to) 40W CO2 machine.

I found some gap filling acrylic glue (SciGrip 16, good except in California where it apparently causes cancer) that worked for my project.

Kirk

>>If Art can get cuts so tight they have to be pressed out perhaps I ne

  I find in acrylic I usually have to press out the part, or the air assist sometimes blows it out, but its usually a pretty tight fit. Air assist IS VERY important though and I blow a few psi at the cut...

Art