CNC Holding Tabs

What are CNC holding tabs? Coming from a world of manual machining this is all new to me. However, when you start machining parts from sheet materials you will inevitably end up creating islands. With rotating tool bits these islands don’t just float away.

At first I created these tabs manually by dividing the perimeter of the part into 3 where the ends don’t meet. This is OK, but you need to take into account the size of the tool bit yourself. So, move the ends apart by a distance greater than the diameter of the tool. The downside is the perimeter is now treated as separate parts. Hence, slower with lots of tool lifting and restarting.

In Carbide Create when you select Contour in Toolpath there is an option to add tabs. This is independent of the design so you don’t need to think about it until you get to creating toolpaths.

carbide create adding tabs to a design

Don’t just think about the parts you want. Scrap parts can also come free and ruin your day. By default the scrap should get pinned down by the logic used for the main parts. However, watch for free ends that might jump.

This scrap island has 4 tabs, if it only had 2 it then would have a chance to rotate.

Back to Carbide Create and the tabs. The thickness is specified from the base of the material upwards. The width of the tab is the narrowest point. There is a balance between holding the parts and the amount of final cleaning up required. For the first go I selected 0.8mm thickness and 5mm wide. However, knowing how well these are defined I think I can reduce the width to 3mm next time and 0.6mm thick.

frame for a kant twist clamp

Kant-Twist Clamps

First proper cnc project with a real purpose. This will be a tiny Kant-Twist clamp, but with a maximum opening of 25mm it will be excellent for model making.

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