Monday, April 18, 2016

Weapons Manufacturing

9:08 AM Comments 0

My wife teaches 10th grade humanities at a classical Christian school, the Ambrose School, which means their focus is on the ancient era, mostly Greece and Rome. The 10th grade has not had any regularly planned field trip as part of the curriculum, so she asked if we could plan some kind of trip out to the shop. Her goal was to get the kids into a space completely different from their normal environment, and to have them work on a project that reflected the era they have been studying.

My wife and I brainstormed ideas for a while and finally settled on making a weapon of some type. After all, who doesn’t like a good old-fashioned weapon making? I immediately began researching and narrowed it down to three potential candidates, the Gladius, the Pugio, and the Makhara.

AS1

The Gladius is the short sword and the Pugio is the dagger worn by Roman soldiers in battle. The Makhara is lesser known, but was a short sword created by the ancient Greeks, with graceful curves and a sweet looking handle. The picture above shows the templates I made for each of the weapons, and the Makhara I cut out, wrapped, and painted for my wife’s classroom.

The students were only going to be at the shop for 1.5 hours, and I wanted them to be able to take home a completed weapon, so we would not be cutting any sword, just decorating them. Plus, the last thing I wanted were 34 students anywhere near spinning blades. We settled on making the Gladius because it was of substantial size and did not have any difficult curves that the students would have to deal with, like on the Makhara.

The task before me was to figure out how to make 36 swords in an efficient manner. The old stand-by was to make a pattern, trace it onto the material of choice, cut it out on the band saw, and either sand to the line with a spindle sander or, using a router with a flush trim bit, cut it out using double stick tape a the initial pattern. The manual method was going to take a monumental amount of time…time I did not have!

Many of you may be asking why I wasn’t going to just use that gigantic CNC machine sitting in the corner of my shop? I really wanted to, but I was nowhere proficient enough with the software that came with the machine to program the toolpath for the Gladius, so I figured I was stuck with the old school route. I struggled with this issue for several days, before finally realizing that I could design the sword in SketchUp and export the .dxf file. Unfortunately, the basic version of SketchUp does not include a way to export a .dxf file, but, using the oracle of all knowledge (Google), I was able to find a free plug-in to accomplish what I was after.

SketchUp

Usually, I use SketchUp for its 3D rendering power, but for this project, I would only be using 2 dimensions, the X and Y planes. The Z plane would be programmed later. For this project, SketchUp would only be used as a quick and easy way to create the tool path, or, in other words, the outline of the sword. I began by creating a layer named “Sheet”, which would refer to the raw material the swords would be cut out from. Next, I drew out a sword, making it a separate layer named “Gladius”, and copied and pasted it on top of the sheet, making sure there was at least 7/16″ of space between all the swords. With that accomplished, I exported the .dxf file and opened it up in a program called DraftSight.

DraftSight

In DraftSight, I opened up the layers tab and renamed the layers so the CNC machine would know how to interpret the tool path. I could have done the final layer naming in SketchUp, but given that this was my first time, I tried to keep it as simple as possible, and followed the method I was familiar with.

A little background on the layer naming nomenclature:

“DIM” simply tells the machine that that specific layer is the substrate from which all the parts will be cut out. The next layer is the one for the swords and is a bit more complicated.

MILLT2001Z-19.2C2E1L50I0

The “MILLT2001″ tells the machine which cutter head to pick up. In this case, the 2001 cutter head is a 3/8” diameter compression bit.

The “Z-19.2″ tells the machine to cut 19.2 mm down into the material, which is about a 1/64th deeper than the 3/4” MDF.

The “C2” tells the machine to cut on the outside of the tool path versus cutting on the center or the inside of the line.

The “E1” and “L50” tells the machine to enter the material in a down angled fashion and reach full depth within 50mm.

I just realized that I have no idea what the last part of the code refers to, the “I0” part. I guess I better figure that out.

TPA CAD

After renaming the layer, I opened up the file in the CNC program, double checked all the parameters, and saved the file.

TPA CAD Timing

When you save the file, the program makes sure that you have not asked it to do something stupid, incorrect, or incoherent. It also tells you exactly how long it will take to accomplish all that you asked. In this case, it was going to take the machine 844.571 seconds to cut out all 36 swords!

AS2

After making a few test samples, we had the pattern dialed in. I cut the swords out of 3/4″ MDF, which we had plenty of in the scrap bin. MDF was the perfect material because it cuts very easily, both by the CNC and by the hand-held router, and gives a nice smooth substrate for the aluminum tape and the vinyl grips.

On small parts, if the CNC is programmed to cut all the way through the material, there is a very high likelihood that things will move and ruin the part or break the router bit. In order to prevent this, I programmed the 3/8″ compression bit to cut only .74″ into the MDF, leaving a .01″ “onion skin”. The swords stayed put through the entire operation, and it was very easy to cut them out with a knife and lightly sand the edge.

AS3

After the machine had cut out all the swords, I needed to add an angled edge to the blade.

AS4

The blade was so skinny that I was having a hard time keeping the router from tipping and digging into the edge of the sword, so I made myself a makeshift router table. It was not the prettiest thing, but it did the trick. Without having to worry about holding the router steady, I was able to more quickly and accurately chamfer the edges of the 36 swords.

AS5

Here is the pile of finished swords, just waiting for the 32 students to show up…which they did, about 1 hour after this picture was taken.

Students 1

The field trip began with me explaining to the students what the CNC machine was, how I used it for this particular project, and how it was different from the other methods available. I then cut out a few sample swords to demonstrate how the CNC machine worked, and then we handed out the finished swords. We wrapped the blades in aluminum tape, found in the HVAC section of any big box store, and the handles in black vinyl. The vinyl was adhered using contact cement, since it would create an immediate bond. The students also painted the hilt and pommel in colors and patterns that would make ancient Roman soldiers proud!

Students 2

It was a whirlwind of activity for 90 minutes, and the shop was a disaster when everyone left, but it was well worth it, and if the pictures are any indication, fun was had by all!