Newbie Question about workpiece holding

**Faust** · 18-06-2020

Hi there! I'm strictly a hobbyist here and, although I'm trained in the programming of the machines, a lot of the hardware is new to me and I don't know a lot of the terminology required, so please bare with me!

Let's say for sake of argument that I want to use a small home CNC 3-axis mill to create a thickish disk from a rectangular block of wood of similar diameter. I'm assuming to mill the edges correctly I'd need to do the top half, then flip it over and do the bottom. Ignoring issues with setting datum for the cylinder for now, how would I clamp the circular half down securely so that the still-rectangular bottom half could be carved safely?

Sorry if this is a really silly question, but I've searched around for CNC specific clamps and can only find hold-down and stepper clamps, which would block tooling on the sides or parts of the sides, and I don't like the idea of trying to mill around the clamps. I'm sure some suitable equipment should exist for this but I either don't know the name or how to use it! D:

-F

**Kitwn** · 18-06-2020

I think most people would cut it without turning it over. You just need a long enough tool and depth increments suitable for your machine.

Kit

PS I don't know you well enough to bare with you but I will bear with anyone who is willing to learn!

**Faust** · 18-06-2020

Originally Posted by Kitwn

I think most people would cut it without turning it over. You just need a long enough tool and depth increments suitable for your machine.

So clamp from the top, cut in between the clamps, then move them around and cut the bits that were covered? This seems prone to error and it's what I want to avoid. Or do you mean cutting the perimeter last and trusting the newly-disconnected piece not to chip or go flying off?

Besides, I'll have to turn it over sooner or later as there will be designs on both the upper and lower face.

**AndyUK** · 18-06-2020

Originally Posted by Kitwn

I don't know you well enough to bare with you

!!!

**JAZZCNC** · 18-06-2020

Depends on how you want to tackle it and remove stock.
If removing all the outer stock then buy your self some Mitee bite low profile clamps. These will clamp it so you can machine away most of the material, then turn it over reclamp on the edges and remove the remaining stock.
Or if you want a cheap dirty method then machine a pocket in some scrap just slightly smaller diameter than your circle so it's a tight fit and tap the cut part into the hole. Take light cuts on the remaining stock and you won't have any issues.

However, seen as your using a rectangular piece of stock then just do a profile pass and leave tabs to hold the part or very thin onion skin. Screw the parts down in the corners of the rectangle.