Precision

With the start of school, I won't be able to do as much with my CNC, but I'll still be able to do less time consuming projects on the weekend. This labor day weekend I decided to redo the walls of the gantry so the router didn't stick so far forward.

Yesterday I attempted to cut out the new sides but failed all three times I tried. The first one looked fine but when I cut out a second, I noticed they didn't line up. The back of the second one was missing about a 1/8 on an inch. I tried a third time (and failed) before realizing that the wood I thought was 12 inches wide — the width of the gantry sides— was actually 11 and 7/8 inches. I would not be able to get identical sides without perfect alignment of the cutting material. I decided to stop there and get some wider planks of wood the next day.

Today, my dad and I went to Home Depot and got 4'x8'x3/4" piece of fairly nice plywood. We also picked up a wet/dry vacuum that attached to a bucket (used for the dust collection). The plywood was cut into 16 inch wide planks, which is wide enough for the gantry sides.

A little tweaking to the CAD drawing (to fix the upper corners; I forgot to readjust the diameter of the bearing mount but I don't use it anyways) and several dusty minutes later, the two new sides were cut out. They were a 1/8" short but I expected that. The entire gantry bends back as the router plunges into the wood and the cutting forces push and pull the bit off center. It's relatively accurate for now, but I'll definitely need to tighten up the y-axis or rebuild the lower axis to use supported bearings.

Old CAD drawing

New drawing.

It was fairly easy to disassemble the gantry and drill the holes into the new sides because we could use the old sides as templates. We did have a little confusion when we forgot which pipe mounting block went where but with a little trial and error and looking at pictures we got all of them in the right place.

Old.

New.

Vacuum is pretty good for the price; just need a way to mount it and to add a dust boot.

Now the gantry looks a lot cleaner and cooler. I tightened up the y-axis and added super glue to the thread to keep them from stripping. Tomorrow I'll cut out the back of the gantry as the old one doesn't line up anymore.

Router Clamps

It turns out that my initial tool paths for the router clamp were calculated incorrectly because I accidentally doubled the width of my end mill in VCarve (5/8 instead of 5/16). After adding a line in the CAD file where the clamp tightens and recalculating the tool paths, I was ready to cut out two new router clamps. The first one went rather smoothly but when cutting out the second one, the z-axis coupler slipped off. A slight re-tightening fixed the problem and the second clamp came out nicely.

You can see a partially completed clamp on the left (the one where the z-axis fell).

First Cuts

With the router mounted yesterday, I was ready to make my first actual cuts with the CNC. I designed the new router clamp in AutoCAD and used VCarve to generate the toolpaths and g-code.

AutoCAD drawing.

I flipped the y-axis direction in stepconf to fix the problem from yesterday and opened up the g-code in LinuxCNC. It looked good and the router clamp felt fairly tight so I felt ready to begin cutting. I used the smallest router bit (not exactly a "true" end mill) I had to cut this part out, which was 5/8 of an inch. With all my safety equipment on, I hit run.

Woops.

I immediately hit several problems and stopped the machine. The clamp was actually slightly loose and router could wobble back and forth. The router also flexed and jerked in the clamp quite significantly in all directions under the load. To make the clamp tighter, I just used several layers of duct tape to fill in the gap between the router and the clamp. It worked like a charm and held the router very tightly.

Duct tape solves everything.

In VCarve, I recalculated the tools paths so they only took out one hundred thousands (1/10") of an inch and slowed down the feed rate to about forty-five inches per minute.

This resulted in a successful cut. It isn't the most accurate cutout (there are visible defects on the edges) but it's pretty nice for a first attempt.

In the middle of cutting.	LinuxCNC running the machine.
Done cutting!	Not bad.

This machine makes a mess when cutting. I'll definitely need a vacuum.

Here's a list of tasks I need to do to make the CNC better:

• Make a second router clamp and replace the old clamp
• Buy a shopvac (or other dust collector) and make an attachment for it so it sucks up the dust right at the router
• Soundproof the shed (sorry to the neighbors that I might have annoyed at night)
• Add in the limit switches and the e-stop
• Build a clear barrier around the entire table (to catch residual dust and stop any flying chips)
• Buy smaller end mills (including ball mills, v-bits, etc.)
• Buy a variable speed router/spindle with less runout
• Buy a solid state relay to control the spindle
• Make the whole machine more rigid

Plotting

I was able to finally run a legitimate test of the CNC today. I didn't cut anything yet, but I was able to plot the LinuxCNC default code with a Sharpie. It was flipped (because I had the axis direction flipped) but turned out okay. The errors in the test were from pen deflection. There wasn't enough grip to hold the pen perfectly in place, and as a result, caused the tip to wiggle back and forth as it dragged on the paper.

First plot.

To reach this point, I had to put the table and its torsion box on and mount the router. The table was relatively easy and I put it on last Sunday. I just had to glue the torsion box to the table top and then bolt that to the side walls.

Table mounted.

How not to use a jigsaw.

Mounting the router was a considerably more difficult challenge that I tackled this night. I drafted out dimensions for a router clamp and drew the lines to cut on the wood. I had only used a jigsaw maybe three times before and my inexperience showed in cutting the clamp out. I was surprised that the router sat pretty snugly in the mount. It's ugly, but it did the job.

Split wood.

I need to learn how not to split wood. And use cutting tools. (I should find time to practice.)

Router mounted.

The first thing I'll be cutting out on the CNC will be two new clamps for the router. Two are needed to prevent the router from deflecting. You can even see the router sagging inwards with my single clamp. I just hope my crude clamp (which I will likely need two of) will survive a couple of cuts so I can replace them.

Clamps

Since the last post, I've gotten the ends of the CNC bolted to the lower torsion box. I just glued on the top layer of that torsion box and am now waiting for it to dry. I always knew that you could never have enough clamps, but today I learned this firsthand. There weren't enough clamps to hold down the top of the torsion box. We had to use the heaviest things we could find in the shed to weigh the top down.

Putting the glue on.

Weighing down the top panel.

All I have left to do is to attach the upper torsion box, cutting surface, and the router.

I also was able to get some cheap plastic from TAP Plastic's scraps. The bottom-most piece is 8.5 inches by 11 inches.

Seven decently sized pieces of plastic for $7.00.

CNC Almost Done

Two days ago my dad and I built a table for the CNC to sit on and moved it into the dedicated CNC shed. Just last night we moved the gantry into the shed and attached the Y-axis anti-backlash nut to the gantry. The final leadscrew was also cut to length. We still need to align the end blocks and get them bolted to the torsion boxes. The machine looks really good and I hope to complete it this week.

The shed.

Table in assembly.

Me working on the table.

The CNC machine, almost complete.

CNC Update

I've finished the X and Z axes on the CNC and was able to jog them back and forth. I'm using LinuxCNC on an old desktop to run the whole system. All I need to do now is move the gantry outside and mount it, along with the motor, leadscrew, and nut, onto the Y axis. I should be able to run test cuts very soon.

On another note, I spent the last month at COSMOS, a summer science program. Here's a link to my team's final project (a kinetic sculpture): https://sites.google.com/a/eng.ucsd.edu/2014-team-6/