Laser cut tab advice?

I've got all these laser cutter template drawings for the Mo'Best, and I'm told I need to modify them with "cut tabs". These are little breaks in the laser cuts which prevent the cut part from falling completely out of the sheet after the laser cutting.

Can anyone give me any recommendations for the length and locations for such cuts?

Thanks kindly!

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"If you don't have time to do it right you must have time to do it over." -anonymous

I've built DARE Sparthawk laser-cut kit. Here's how they have them:

1) All tabs were about 1/8-3/32 wide
2) There were four tabs per rib half way between the spar cut and front and rear edge
3) Rudder, elevator and stab cutouts were about 3" apart going aroung the part perimeter
4) There were no tabs within 1 inch of any corner except for the two tabs near the leading edge of the rib parts.

Hope this helps.

Larry,

Personally, I just love parts which fall out. If I can get them that way, they are ready to use. Kyle obviously would rather not have all the small jig and lightening holes falling into his cutter support grid. We sorta compromise. We use masking tape to secure most of the small stuff before lifting the part sheet from the cutter and I occasionally dump his grid to clean out the small trash collection. If you are going to sell something, I suppose that tabs are more professional, but loose parts sure are nice. In any case, I'd let the cutter add tabs as he thinks necessary. He will know what is best, and would probably prefer to do it anyway.

I have worked with a laser cutter on one rib design so my experience is limited. The reason I did most of the requested work like drawing in the cut tabs and resizing for the spar cut lines was simply to save money. The cut tabs make the laser job go faster because the parts don't fall out and have to be picked up by the person running the laser. Time is money and somebody has to pay one way or the other.

Now if I had Al's money I would just buy my own laser cutter and not worry about tabs

I also feel like I'd like to take care of my own CAD drawings where possible. In addition to saving setup expense.

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Here's an example of what I am trying. The blue dots are 1/8" tab areas (blue dot is NOT a cut..). Now, there are still some holes that are not tabbed and will probably fall out.

Will the laser cutter guy still be upset at me? Should I tab ALL parts?

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"A pessimist is one who has been intimately acquainted with an optimist." - Elbert Hubbard

Larry,

Tab if you like, but let me offer a suggestion. Don't tab in a spar or leading edge cutout. One of the great features of laser cutting is slots and cutouts accurate enough to hold fast to spars, leading edges, landing gear blocks and etc tight enough to pick up parts without adhesive. Also, it creates the need for judgment in cutting out the slots. I suggest tabs, as much as possible, on long straight stretches where a straight edge can be used for a precision cuts.

Larry,

Use 1/8" tabs on sections parallel to the wood grain. That way they will snap right out when you want them. With the ribs I've had cut the 1/8" tabs have rarely broken out on their own before I put a little pressure on them.

As for spar holes, the solution I've settled on is to leave about a .010-.013 gap at one corner of the hole, on a side of the hole parallel to the grain. The kerf on lasers is usually less than that, so just a little nib stays to hold the piece until the sheet is out of the tray. I stumbled on that idea when I noticed that if I wasn't careful with the corners on my drawing objects, the laser would occasionaly leave a hair of wood there. I went back to the original and zoomed in on the offending spaot to find I had left a little gap that wouldn't show on the hardcopy version. Now I zoom every corner to 5000% and overlap the lines a few thousandths.

I too prefer, by far, to do my own drawings. Sure it saves money, but I also know exactly where to adjust the kerf to put a little squeeze for tighter joints (for thin CA), or leave a little play to allow angled fits.

By the way, you probably already know to minimize the nodes on curves for lower laser costs, but be careful if your drawing program has an automatic node reduction feature. Mine will occasionally alter an airfoil curve by as much as .007". Not much, but the errors can accumulate and for some of my free flight airfoils I shoot for better accuracy than that. I'm leaving the image of the drawing below(for a limited production kit rib of a vintage combat model) large enough to show the gaps I use. It also shows the rib support that holds every rib, the LE and TE in position during assembly. This entire model can be assembled in place on a flat surface without glue, then quickly fastened together as fast as you can wick the CA into the joints:

Thanks! To everyone.

I was trying to keep the tabs on straight sections as much as possible and accessible for an Exacto blade. But I see the value of putting them in line with the grain.

Al, I've already taken into account the laser cutting thickness, to get that tight fit you are referring to. Precision is where it's at with CAD and lasers.

I'm learning!

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"Progress is not created by contented people." -Frank Tyger

>
>Al, I've already taken into account the laser cutting
>thickness, to get that tight fit you are referring to.
>Precision is where it's at with CAD and lasers.
>

Not to mention repeatability... .

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