Grad student 4'x8' ambitious build!

[HenryK]

Hello cnczone!

My name's Hank, and I've been lurking around these forums (learning and admiring) for about a year now. My friend and I are both architecture graduate students, and we've decided to move forward with an ambitious build. We've built a handful of commissioned furniture using large 4/5 axis machines at a shop that we had a connection to. Our "friend discount" has slowly disappeared, and we've decided to take the next step in our venture by bringing the machinery in-house. We'd like to begin building by December, giving us a little time to work out some bugs in the design.

The design is currently on it's second draft; revisions were made after meeting with and consulting "lunchtrayrider" who coincidently has his machine located a few blocks from my house (thanks aaron!)

I've attached a few images of the structure, but if you have sketchup on your computer, I can email you the 12.0MP file so you can wander around the drawing yourself!

A few key notes:

Table
- The table structure is 8" hot-rolled steel channel.
- Corners are braced with 1.5" slices of 4x4 steel bar-stock cut diagonally.
- Table is squared using cables tensioned diagonally between the braces.
- X-axis rails are .25 x 1.5 cold rolled steel (adjustable)
- The 49x97 MDF substrate is supported by interlocked 3/4"plywood.

Gantry
- The gantry structure is a combination of aluminum channel and aluminum tubing
- The ganry has 3 height settings, increasing rigidity and reducing distance from bearing to bit when cutting ply.
- Height settings offer 3", 7", 10" of clearance between top of substrate and lowest point on gantry
- Y-axis rails are .25 x 2 cold rolled steel (adjustable)

Z-axis
- The Z-axis structure is a combination of cold-rolled steel, aluminum tubing, and machined aluminum plate
- The Z-axis is centered on the gantry limiting any torque from moment stresses
- The Z-axis has a range of motion that allows a 1" bit to reach the substrate from full gantry height, and allow a 2" bit to raise high enough to clear the lowest point on the gantry. 10"+ of travel
- The router drawn is a Milwaukee 5625 3.5HP router to demonstrate the capability to upgrade. I plan on starting with a Hitachi M12VC.

Drive System
- Linear carriages and countless other parts will be sourced from cncrouterparts.com (what an incredible resource!)
- The X and Y axes will be driven by rack and pinion system. I'll be using all of the parts from Ahren's NEMA 23 R&P system, except I'll be using a custom aluminum plate to suit my needs.
- The Z axis will be driven by a 5-start ACME screw.
- I am planning on using Ahren's 4-axis complete electronics kit, but am a little concerned it may be underpowered. I'll be starting a seperate thread to discuss motors and electronics, and would rather focus on structure in this thread.
- The motors drawn are NEMA 34, to demonstrate the capability to upgrade.

Because of the scale of our projects, anything less than a 4'x8' cutting area will handicap our design. (Luckily we have a full stall in a large 2-car garage to work with). As drawn, the cutting area is 49.5" x 99" (from bit-center, allowing 1/4" clearance from any "hard stop").

All metal will sourced from discount steel, convieniently located a mile from home.
Current budget is 3000-4000. The most recent estimate, including all structural material (including cutting, but not machining or drilling), all electronics (assuming Ahren's 4-axis package), and the Hitachi router is $2300. This leaves a small cushion for some machining (most of which will be done taking advantage of Harvards waterjet/milling machines).

So, I guess that's enough info for one post! I know a lot of you wandering the forums have years of experience and a number of builds under your belt, and I'd love to hear your thoughts on the direction I'm headed! Thanks!

Hank

[ger21]

Table
- Corners are braced with 1.5" slices of 4x4 steel bar-stock cut diagonally.
- Table is squared using cables tensioned diagonally between the braces.
.............................
- The 49x97 MDF substrate is supported by interlocked 3/4"plywood.

Cables can flex, and those small corner blocks aren't really enough, or you wouldn't have added the cables. You might want to get some 1/4" plate, maybe 18"x18" triangles, and bolt them on with angles? You can add epoxy similar to this method.
My First Router, Built in Steel

The plywood ribs aren't nearly enough to support that. You need to make it a torsion box, with both a top and bottom skin, glued in place. I'd probably use 1/2" MDF on both top and bottom, then add another 3/4" sheet for a spoilboard. Unlesss you have another plan for work holding.

- The ganry has 3 height settings, increasing rigidity and reducing distance from bearing to bit when cutting ply.
- Height settings offer 3", 7", 10" of clearance between top of substrate and lowest point on gantry

By making it adjustable, you're probably making it less rigid, but I guess it depends on the design. But I think changing the height will be a hassle.

Z-axis
- The Z-axis has a range of motion that allows a 1" bit to reach the substrate from full gantry height, and allow a 2" bit to raise high enough to clear the lowest point on the gantry. 10"+ of travel

Why do you need 10" of travel with a 2" bit?? Not sure if I've seen anyone with a high gantry actually use it.




Imo, you should shoot for a minimum of 3:1 gear reduction. 4:1 is better. It looks like you have much less?

And if you're going for 49.5" of cutting area, add another 1-1/2" or so. A lot of sheet goods come 49", and you might want to be able to use a larger tool on both edges. And adding another 2" should cost anything more.

[HenryK]

Hi Gerry! I was excited to get a response from someone that's already provided so much of my learning material

I'll start fiddling around different diagonal bracing/larger corner brackets. The whole point of using steel channels for the frame is to make it beefy, so there's no excuse for giving it any slack.

I like the idea of a torsion box, and I think if I arrange the parts correctly, I can even widen the gantry another 2" without requiring significantly more material! I just needed that little spark of inspiration How's that for two birds with one stone?

The reason the gantry height is adjustable is that I predict it will be set up at the lowest height (for better rigidity, less cantilevering) 90% of the time, in order to cut plywood. The extra material required to allow raising of the gantry costs less than $100, and it would be a shame to limit my flexibility for that little. I get the strength and stability of a low-slung gantry, with the ability cut widely varying pieces (site models for architecture school?) if the need arises.

Lastly, I'm planning on using the 3:1 gear reduction from Ahren's R&P system. I'm interested in, but not yet sold on, his 4-axis system with 380oz motors. I'm actually looking for input on electronics in the following thread if you have any thoughts!

http://www.cnczone.com/forums/showth...084#post810084

Thanks again gerry