New Machine Build- 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.
http://www.cnczone.com/forums/showpo...8&postcount=14

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