Newbie- Longer Z axis builds?

[rbs]

Hi Guys,


After years of dwindling I'm going to save and spend the money on making a decent 3 axis CNC machine.

proposed budget $1500

I've taken the common advice and done some research and I'm a good way along understanding "what you need " to start in this game.

I'd rather build an 8020 Aluminum machine first for the following reasons that I would like to jump straight into the high end DIY 3 axis CNC machining, so I can start on some of my high end ideas.

I can model my designs in Autodesks Maya (learning rhino) then concert to Nurbs and output as dxf.

I have been considering MDF and have seen good results but many have said that spending out on 8020 with good ball screws etc. will in ensure good or better accuracies .

I'm looking to build a large machine 40" 30", and something like a 12" or more Z axis.

My question which I can't seem to find any info on is, I would like a longer
Z axis so I can cut larger items or carve deeper into foam core etc.

Are there any 8020 or even MDF build that's have more than 6" on the Z axis.

[FandZ]

Originally Posted by rbs Hi Guys, After years of dwindling I'm going to save and spend the money on making a decent 3 axis CNC machine. proposed budget $1500 I've taken the common advice and done some research and I'm a good way along understanding "what you need " to start in this game. I'd rather build an 8020 Aluminum machine first for the following reasons that I would like to jump straight into the high end DIY 3 axis CNC machining, so I can start on some of my high end ideas. I can model my designs in Autodesks Maya (learning rhino) then concert to Nurbs and output as dxf. I have been considering MDF and have seen good results but many have said that spending out on 8020 with good ball screws etc. will in ensure good or better accuracies . I'm looking to build a large machine 40" 30", and something like a 12" or more Z axis. My question which I can't seem to find any info on is, I would like a longer Z axis so I can cut larger items or carve deeper into foam core etc. Are there any 8020 or even MDF build that's have more than 6" on the Z axis.

Most of the ones with the really long Z axis are mill type(where the table moves the stock back and forth) rather than the gantry type. But since you are working on foam I don't think it is as big of a deal.

[High Seas]

Greetings rbs -- and thanks for doing a bit of research. WELCOME ABOARD!

My SYSTEM2 is an 8020 system with "right at" 12 inches of usable Z. (Go to the Member Gallery - search SYSTEM2 -- or High Seas)

Mind you, I have 18" rails on the Z and about 6 inches are taken up in the "stack up" of attachments, fittings, carriage, etc.

The Challenge with a tall Z; is how to account for racking. The racking will come not so much from milling FOAM, but the torque generated by the weight of the spindle/router. The racking will be exaggerated as the router moves down to the work surface and affect your system's resolution, repeatability, and ultimately accuracy/precision.

I used a Bridge approach, dual 8020 rails on the Y axis and then mounted the Z between. The images ought to help clarify.

The next challenge is; will you be able to get the spindle (and the Z axis) down into the working plane to mill the foam without impacting the material? This can be solved by using LONG router bits - available -- but not Cheap. Or by using a technique called "slabbing." Thats where you mill the project in several layers and then assemble them (vertically) to have the finished product. Foam does well this way and your CAD can help you with the model - else there are CAM programs to help by generating a solution - ie STLWork2. A tall Z axis seems like a natural to convert into a 5/6 axis machine.

OK - hope that gives you some grist to mill.
Cheers - Jim