How Large A Circle?

[Joe Wood]

How large a diameter of a circle can a CNC cut with a 4' x 10' table? Is it limited to 4' or can you move it on the table after doing 1/2 of it? I'm hoping to have some 6' to 7' diameter circles cut.


I had these smaller circles cut but my CNC guy is out of town for another week so I can't ask him.

[Brian Lamb]

As long as you or he are willing to fixture the parts, yes, you can cut larger than the machines smaller stroke. It usually involves some extra holes located in areas that will be waste later on and a sub plate that has pins sticking up or holes to drop pins in to register the parts.

I have done this on my CNC mill when I needed something larger than the 16" y axis stroke I have.

[Josh Molaver]

Depending on the software yes; Vectric lets you "tile toolpath" which lets you move your workpiece and continue machining it.

See http://support.vectric.com/aspire-qu...-cnc-work-area

I've done this several times with excellent results, using steel pins to register my work

[Jerome Stanek]

Can you laminate the pieces together

[Kevin Jenness]

I've used tiling to cut pieces longer than my machine bed but I don't see how to cut a path wider than the space between the gantry supports, such as a 6' circle on a 4' wide machine. Certainly parts such as the pictured window frame could be done in sections.

[Joe Wood]

I wish I could understand what you're all saying about tiling. The way I made the two smaller circles (not the moon gate entry which was laminated) was to build a segmented octagon using 2x8, with splines at the joints. Could you tile something like that??

Sounds like I'll probably need to laminate this new one the same way I did the large moon entry.

[Brad Shipton]

Tiling simply means adding registration points in the first cut that can be used in the second. The trick with moving the parts between cut routines is getting the stock exactly aligned. One cannot simply measure a distance of 6'-0" for example to a degree of accuracy of 0.010", but the machine will cut the part where ever you fixture it down, and we all can feel a misalignment of 0.01" with our fingers. A CNC machine is dumb unless it is given gcode. It knows nothing where things are on the table, and it is up to the operator to place them precisely and tell the machine how to cut the part to achieve what you want. That is not always easy. A four sided cut routine is much easier, but it would be difficult to fixture your parts strictly from the bottom of the parts using vacuum.

You will need an industrial CNC to cut 3.5" + thick material. The guys on the woodweb where you have your other post will be better at answering. Here is a video how some do their windows using a CNC. https://www.youtube.com/watch?v=zdlWuofwRyY The video does not get that interesting until about 3min in. I realize you are not building anything nearly as complex, but it still shows the general gist. Your parts would only need the perimeter sizing from what I can gather from your drawings. This is not a machine any of us own, but there are a couple that run them at their workplaces. Could we flip the stock and cut the parts in multiple routines on our smaller machines? Likely, but it will not be a cost effective solution when one considers the number of steps and part movements.

David Sochar and Joe Calhoon have posted quite a few images on the woodweb over the years how they makes these large elliptical or circular parts on a shaper. They make the blanks, cut them on the shaper, then precisely clamp them up into their final shape. That is likely how I would do it. You might find a shop in San Diego that will do a one off for you on their CNC, but you might need to do some searching. The machine in that video is in the realm of $250k.

Out of curiosity I checked to see what cut length I could find for my machine. I could buy a 3/4" diameter x 4 1/2" bit for $300 that will allow me to cut 2 1/2" deep. https://www.vortextool.com/index.cfm...F1B0E13454809C It would take some trial and error to see how well it might cut. The longer the bit cut, the stiffer your machine needs to be.

[Jerome Stanek]

I cut sections like what you are showing and then gluing them together on some real large ones we cut 2 full circles that had 6 sections and laminated them overlapping the joints.

[Joe Wood]

OK looks like I can't do this by CNC, darn, they come out so perfect. Have to build another laminating jig and go to it!

[Brad Shipton]

I believe Jerome is one of the guys that runs an industrial machine (Biesse I recall) at his work. You might want to try extracting some ideas from him. Most of the others here have flat table machines mainly used to build boxes and smaller parts. While cutting the completed circle will not work, the CNC may still save you some time and it will come out perfect if you put it together perfect. I do not have access to a larger machine anywhere nearby, but I am very sure you do. I looked at your website and you seem to have a nice product line (very nice stuff by the way) where you could use a CNC at some point. You could talk to a Biesse salesman, CR Onsrud, or any other of the big name guys and I bet they will help find someone. Good luck either way.

[Joe Wood]

Brad something clicked, I could still build the octagon frame but without splines in two opposite corners! Have the two half circles cut, and spline 'em together!