New Machine Build- First CNC Build - 19"x19"x5.5"

[Cosworth]

This is my first time building a CNC machine, and after over a year of starting to try various ideas, thinking of designs, and even just ignoring the project, I've finally started down a path with a design I feel is solid (or at least much much more so than my previous starts).
First thing I'll say, is that in building this, I wish I had a CNC machine to help make the pieces accurately, but I seem to be running into a chicken-and-the-egg scenario. Luckily, there is a place near where I live that provides metal for big projects and cuts it to whatever specification, and they have a ton of scrap pieces that they don't have a ton of use for. So, I was able to get a single piece of steel from them to join my Y and Z axes. Soon after getting it, I set to work with a tsquare, ruler, compass, and pencil mapping out on the metal where to drill. Unfortunately, the holes I ended up drilling weren't quite parallel. Annoyed, I tried to figure out how to right my wrong, and eventually thought to print out some graph paper, tape it to the metal, and drill based upon that. After filling in the misaligned holes with welds and grinding it smooth, I redrilled the steel and came up with a nice, parallel result (though a couple holes are still off a little).
Yesterday, I used the graph paper method and started to make either a template for or the start of the mount for the Z axis.

YZ plate



Z plate


My X and Y are 25" 20mm rails, and then I have 13" rails for my Z.
http://www.glacern.com/sbr
I should be getting some 25-2550 and 25-5050 aluminum within the next week to help build the frame of my Y axis.

And to those without very accurate tools to build a machine with, custom graph paper from any number of sites is a wonderfully simple yet GREAT tool.

[Cosworth]

My 80/20 came today and I started to work out just how I want to line everything up for the frame, but I have a question I was wondering about. My screws are 3/8" acme screws, and I was wondering how I should go about mounting them to the frame. I'm thinking something like this would work, but I'm not positive. Any suggestions?

[Telly]

Nice idea with the printout! I'm watching this one.

[Cosworth]

As the ideas and plans take shape with the materials I'm getting, a machine is starting to form. I've moved from a moving gantry to a moving table for my X axis, but I think it may work out better for my first machine. Unfortunately, my workspace has moved from about 19x19 to about 16x19.

There WILL be some triangular support brackets in this design to add strength, but I don't have them yet, nor do I have the bolts to hold much of anything together yet. I do, however, have everything in this Pro/E model apart from the plate with the holes drilled and tapped in a 40 mm grid. As for the size of the main plate, it is larger than the cutting area, which is shown here by 1mm shaved off of the top an bottom. In order to maximize the workspace without sacrificing strength, I moved the bearing blocks in from the edges of the workspace by 75mm along the X axis.

EDIT: On a side note, does anyone know how to make a threaded rod in Pro/E?

[Cosworth]

I've been working on my machine a bit more, and it's starting to look like an actual mill now.
The vertical extrusions will be cut down quite a bit before it's done

[Cosworth]

I haven't been happy with the overall feel of my machine's structure. It seemed too spread out. I went back to the drawing board to come up with something whose parts are a bit more compact.


This will have a screw above each Y rail and one between the Z rails. Currently, there will be one screw above the upper X rail, though I'm unsure if I like that placement. Most of it will be made of 30-6060 extrusions. I've not yet drawn in any of the supports to stiffen the frame, though they will be in the final design.

Any suggestions, thoughts, or criticisms are welcomed.

[Truss-rod]

Back to the drawing board = back to the wallet. I like the your new design cause it offers space for oversized parts to hang off in either direction. Your first design would be a little less spread out if you flipped the table's rails upside down. Just throwing it out there.

[Cosworth]

I've been tweaking the design a bit and adding some more detail.

Due to the design, I'm going to have two motors for my main axis. How would these two get hooked up to the controller board? Is there a way to program it so that two outputs correspond to the same axis, or could two motors be wired to the same channel?

[Dman65]

I believe the two safest options for driving two motors are:

1. Connect the parallel port output that is to be duplicated to two different controllers or to two different inputs on the same controller if you are using a multi-controller board.

2. Your software may support sending the same signals to two different ports, in which case you would just connect those two ports to two drivers and the drivers to the motors as usual.

[Senna]

Well... I only use Mach3... and in Mach3 you just need to check the SLAVE axis box on the config page... simple as that.

Senna

[RomanLini]

Cosworth- I think your new design in post #6 looks much better then the one on post #8.

The #8 design has an issue where the drive screws are very high above the table, so if the cutting force is at the table (like with flat sheet ie 90% of cutting jobs) there is a lot of leverage there that will cause flex and possibly bind.

Ideally if you can get the gantry lower near to the cutting point and especially the X and Y drive screws you can get a much better rigidity and accuracy.

[Cosworth]

Originally Posted by RomanLini Cosworth- I think your new design in post #6 looks much better then the one on post #8. The #8 design has an issue where the drive screws are very high above the table, so if the cutting force is at the table (like with flat sheet ie 90% of cutting jobs) there is a lot of leverage there that will cause flex and possibly bind. Ideally if you can get the gantry lower near to the cutting point and especially the X and Y drive screws you can get a much better rigidity and accuracy.

I'd moved the table down when I added my dummy spindle (I have no clue what I'll be getting yet), and I suppose I put it too far down, as the bits wouldn't even reach the table.
I'll try to mount the X screw a bit lower, though I won't be able to get it too low, otherwise I'll start hitting my vertical supports.