Newbie Question about workpiece holding

[Faust]

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]

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]

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.

[Geoff57]

do you have a vice if so you could mill soft jaws to hold on the dia.

[RobC]

I do quite a lot of milling wood, composite woods and hardwoods. Most of the time you need not bother if you are working with mdf or an engineered one as they are perfectly flat most times. Raw unfinished wood, so band sawn or rough sawn generally yes face them either side if you are wanting clean finishes on either side. Generally when I do my hold down which I use 20mm x 50mm x 10mm aluminium bolt down clamps I milled I will mark out on my work piece the dimensions and then give myself a good 3 or 4 mm to spare. Being aluminium you can get away with the odd scrape instead of steel where you get no chance of getting away with such. My clamps are all sorts of shapes on the tips :whistle:

Be it a messy setup, it works flawlessly so i never changed it. 28417

Regards to the last cutting, I tend to leave that specific task for the cutting of the very final edge before it would disconnect from the main body that is clamped down. Ensure you have triangular tabs. Most times with wood I'll let it drop down to the bed once its been cut free as there is normally sawdust within the slot which acts as quite a good temporary restriction to stop it moving sideways.

[Faust]

No but I can always get one. Will look into small vices for T-beds.

[AndyUK]

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

!!!

[JAZZCNC]

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.

[Faust]

If removing all the outer stock then buy your self some Mitee bite low profile clamps.
Thankyou, I think this is exactly what I need!

*EDIT* Not that I can find anywhere that's SELLING them. Typical!

[JAZZCNC]

Thankyou, I think this is exactly what I need!

*EDIT* Not that I can find anywhere that's SELLING them. Typical!

https://www.mscdirect.co.uk/CGI/INSRCH?No=10&N=4294966260

[Kitwn]

If the disk is to have any holes in it you can clamp the blank, drill the holes and screw it down through those. Remove the outer clamps and away you go.

[Kitwn]

!!!

Precisely!

[cropwell]

I generally use a pocket on a spoil board like wot Jazz said, but I also have 3D printed some plastic 2-4-8 blocks with M6 threads in them and clamp these onto the T slots and use grub screws or long nylon cap head screws in the horizontal threaded hole to apply clamping force. That way no steel to chew the cutter.

Aren't those Mitee Bites expensive !

[the great waldo]

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

I'm not sure if i'm missing something, but couldn't you just fix the block of wood to the spoil board with double sided tape and machine it. The tape usually holds well. A vacuum holder I would imagine would work but be expensive.
Cheers
Andrew

[cropwell]

I'm not sure if i'm missing something, but couldn't you just fix the block of wood to the spoil board with double sided tape and machine it. The tape usually holds well. A vacuum holder I would imagine would work but be expensive.
Cheers
Andrew

Double sided tape is OK if you have a large contact area, but the efficacy diminishes rapidly on small bits. It also doesn't do well with aggressive machining.

[Kitwn]

Slightly off from what you need, but I made these cam clamps on Sunday just to try out the idea. They are based on a design from Marius Hornberger on YouTube but I'll design my own if I decide to mass-produce them. To make sure they dont slip I fix them to the base with an M8 bolt, just loose enough to turn then lock them down once in place. Worked OK holding the test piece for surface skimming with a 22mm tool and being quick and easy to make from scraps of wood they can be treated as sacrificial.
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