Tabs in tight object arrays

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PLLman
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Model of CNC Machine: Shopbot 4 x 4
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Tabs in tight object arrays

Post by PLLman »

I have to cut out two different sets of 70 objects that fit into a 2" x 2" space. I can get good layout density with seven rows of 10 parts on 1/4" plywood. The problem is holding the parts in the stock during cutting. We have used double sided tape, put that tends to creep with a lot of milling. Tabs are better, but I'm not experienced with them, especially in such an array. I cannot seem to find any rules, guidelines, or suggestions on how much wood has to be around the part to which the tab is attached. There is enough wood to screw down the sheet at 6" intervals, so that seems okay to me.

So, with the best part array density, a row of 10 parts fit across a 24" sheet with only cut lines between parts. Can I attach parts within a row with a tab? (Think of it as joined nose to tail.) The sides would be attached to a strip between each row of parts. Every other one of these strips could be screwed down to the spoil board. Any suggestions, guidelines as to the width of this strip or general methods?

If there are guidelines out there for tabs in an array already, I'd appreciate a pointer to them.

Lastly, in a related topic, can you array parts with tab positions defined, so that I don't have to move the tabs that don't go where I want them to on 150 parts.

Thanks.

tomgardiner
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Re: Tabs in tight object arrays

Post by tomgardiner »

If you create one iteration of your part(s) then toolpath it and place your tabs where you want then go back and array the part. Your tabs will be created in the same place.
I can't remember whether it is necessary to associate vectors with the toolpath (Vector Selection) but I would for any complex layout. When you recalculate toolpath the tabs should all be in the same place.

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adze_cnc
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Re: Tabs in tight object arrays

Post by adze_cnc »

PLLman wrote:70 objects that fit into a 2" x 2" space. I can get good layout density with seven rows of 10
Four square inches for 70 objects?---I'm impressed. I'd 3D-print them instead. Or is this a "Spinal Tap" 18-inch tall instead of an 18-foot tall Stonehenge model moment?

LittleGreyMan
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Re: Tabs in tight object arrays

Post by LittleGreyMan »

Steven,

That's what I read the first time. But it seems it is the size of one part as the op writes "a row of 10 parts fit across a 24" sheet".
Best regards

Didier

W7 - Aspire 8.517

PLLman
Posts: 11
Joined: Mon Sep 21, 2015 12:26 am
Model of CNC Machine: Shopbot 4 x 4
Location: Granite Bay, CA

Re: Tabs in tight object arrays

Post by PLLman »

Yes, the individual part is 2" x 2".

Thanks, tomgardiner. Your trick worked a charm. I can set the tabs on one part and then array it and keep the tabs where they were placed on the single part.

Now all I need is some direction on how small the "web" of wood can be around an array and if parts can be tabs to other parts, at least on one direction.

tomgardiner
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Re: Tabs in tight object arrays

Post by tomgardiner »

You may not need to leave a web between parts, only around perimeter. If you place your tabs so their position is the same left/right and top/bottom then you might be able to array your parts only a small amount larger than your bit diameter. I nest at a .40" for a 3/8" bit. If the tabs are side by side cutting one part will not obliterate the tabs of others. Selection order may be important to reduce the stress on the complete sheet.

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