Modifying the X-Carve - Part 1 Adding more Z-Depth

In recent weeks I've become more interested in milling three dimensional molds Using Fusion 360.  At Hammerspace I have access to two 3 axis mills, my personal 1 meter square Inventables X-Carve, and a 8 foot by 10 foot frankenstein of a machine that I've taken to calling 'The Beast'.  

 'The Beast' in action at Hammerspace.  This CNC is so big and heavy, they had to build an extension to the workshop around it.

'The Beast' in action at Hammerspace.  This CNC is so big and heavy, they had to build an extension to the workshop around it.

The Beast had a cutting area of approximately 10 feet x 8 feet x 2.5 inches deep. It is really more of what is called a 2.5D CNC machine, intended for cutting slots and tabs in sheet material like plywood and aluminum.  This machine had been lobotomized and rebuilt around a Mach3 controller, so it is capable running G-Code directly from Fusion 360.  I'm going to use The Beast for some of my experiments, but to mill anything more then 2.5" tall, I'll need a different tool.

The X-Carve is an inexpensive tabletop CNC carver intended for enthusiast and light duty work. It's working area is 3.2 feet x 3.2 feet x 2.75". The X-Carve has its quirks, but i've had good luck running 3 dimensional G-Code exported from Fusion 360 on it.  Like The Beast, this machine is intended to be a 2.5D carver, but with a few advantages.  This is my personal machine, so I can freely make modifications to it, and the X-Carve is open source, so all the files and drawings for it are available on Inventables GrabCAD page.

For the first stage of the Modifications to this machine, I'm going to add more z-clearance between the bottom of the X-Carve's gantry and its spoil board.

The easiest way to do this, is to replace the four corner brackets at that connect the Makerslide rails to the spoilboard's frame with taller one.  I downloaded the drawings for the original brackets from GrabCAD, and added three inches to their height in Fusion 360. The new brackets were cut out of 1/4 inch thick aluminum plate on The Beast. If you'd like to create your own extra tall brackets, you can download the DXF files for them HERE

 The new X-Carve Brackets add 3 inches to the Z-Height of the gantry.

The new X-Carve Brackets add 3 inches to the Z-Height of the gantry.

 A Big Thanks to Tom Newell of Sainsmart and Oni Technologies for doing the cutting for me! Cutting plate aluminum is still a bit out of my wheelhouse.

To tell the story of installing this modification, I've made a short youtube video to take you through the steps.


Until next time, when we'll adjust the reach of the Z-Axis to take advantage of all that newly added depth.

Thanks for Reading!


Fixing the SketchUp Involute Gear Plugin

Long ago, there was a simple plugin for SketchUp that would make Involute Gears quickly and easily. Called 'gear.3.rb' I used it on countless simple mechanical projects.

 The SketchUp Involute Gear Plugin in operation after some quick repairs to its Ruby script

The SketchUp Involute Gear Plugin in operation after some quick repairs to its Ruby script

Recently I wanted to revisit one of those projects, and found that the original download site for the plugin was gone. So I dug the script out of one of my old SketchUp installs and discovered that it won't load into SketchUp 2015. It looks like there is an error in how the plugin adds itself to the menu system. 

After adding the script to my sketchup plugins folder, it failed to load do to a missing 'GetString' Method in the script. 

I pulled the Ruby script open in TextWrangler, and found the UI section.  It looks like the code is using and out of date function to add itself to a UI menu that doesn't exist in newer versions of SketchUp...  

The Offending Section of the Ruby Script that was keeping the Gear.3.rb plugin from loading into Sketchup 2015

A quick search of the SketchUp Ruby resources led me to the documentation of the Menu Class. It looks like the class was simplified at some point, and this plugin never got rewritten to use the new tools. 

Screenshot from the documentation of the updated Menu Class in the Sketchup Ruby Documentation

The Fix to get gear.3.rb working again seemed straightforward. Rework the items in the plugin's Ruby script to match the strucure of the updated commands. To keep things simple, i'm just going to add the two commands from the Involute Gear plugin to SketchUp 2015's 'Tools' menu, and add a menu separator to make them easier to find.  Based on the Ruby documentation, the changes were straightforward.   

The Modified UI section of the gear.3.rb plugin's Ruby Script

Nothing left now but to Save the script, reload SketchUp, and check the Tools menu...

The Two commands from the gears.s.rb script added to SketchUp 2015's Tools menu, with there own menu separator.

Holy Shit... It worked.  

Did I mention I have never written or modified a Ruby script before in my life?  

You can download the repaired SketchUp Involute Gear Plugin gears.3a.rb here.  You'll need to follow these instructions to get it installed.

A big thanks to Doug Herrmann, the original author of this plugin.  I don't know where he is now or why his site is gone, but I'm happy I've found a way to keep the tool he created running.


Aliens M41A Pulse Rifle - The Stock

The stock of the Pulse Rifle is, at its core, a piece of metal u-channel with a slot pattern cut into it. The stock extends forward under the rifle's body work and it's mounted to the top of the Thompson's upper receiver.

It took me a little while to realize the slots in the stock are not purely ornamental. The slots on the top are close to lining up with the holes where the Thompsons rear sight use to be attached. Our Stock will be designed to be bolted to the Thompson through these holes.

 Reference model on the left. Measured model of the back of the Thompson on the right.

Reference model on the left. Measured model of the back of the Thompson on the right.

To verify my measurements of the Thompson, I printed the test objects I created in the last step and fitted them onto the gun's body. I had to modify the 3d model a bit and reprint a few times to get the fit I wanted. It was time well spent, now I know my 3d model is accurate and how much allowance I need to incorporate between the Thompson and the final printed parts.

I doubled the thickness of the stock's walls in comparison to what's in the reference model. The extra thickness will add strength to the stock and make it less brittle, a critical improvement for a part 3d printed out of PLA. The cutout in the right front of the stock lets the Thompson's charging lever move freely. The inside of the stock, the part that touches the Thompson, is shaped to match the geometry of the test piece I printed earlier, so I know it will fit in place properly.

Screen Shot 2015-07-06 at 3.03.20 PM.png

The final part is a 278mm long and will barely fit onto the 285mm x 153mm build area of my MakerBot Replicator 2. To add strength to the finished part I set it to print with 4 outer shells and 50% infill.  I also turned the stock to print at a slight diagonal, so that the layer lines on the flat surfaces wouldn't be running parallel to the direction of force.

The final printed stock fits marvelously. Its not so tight that its deforming the plastic of the Thompson, but there is good surface contact on all sides. Ther charging lever can move freely into the slot without any problems and the higher print density made the part really strong.

For now, i just used two bolts to hold the stock in place. They pass through the slots, through the sight mounting holes, and into the upper receiver where nuts hold them in place. There are many advantages to this over just glueing the stock on.  I can adjust its location, remove it for sanding and painting, and easily replace the stock if it gets broken.

Next up, The hard part, building the primary body components!



Aliens M41A Pulse Rifle - Measuring the Thompson.

Before proceeding with the rest of the pulse Rifle, I'll need to spend time looking closely at the Airsoft Tommy gun I'm using as the base. 

To start I'll need to remove the Thompson's stock, foregrip and rear sight.

The Stock and Foregrip are each held on by 2 screws.  Unscrew them and the parts pull right off. The gun's battery is normally housed in the stock, so i'll have to reroute those wires and create a new battery holder somewhere in the rifle.

Removing the rear sight was a bit more tricky, involving removing the upper receiver and unscrewing four small interior screws. With the grenade launcher and the reference model, we can start to see the basic shape of the pulse rifle.

I need an accurate digital representation of the Thompson to work around as I model the body of the pulse rifle. With calipers and a bit of patience, I reconstructed the Tommy Gun inside sketchup.

I didn't bother measuring and modeling the pistol grip, because there is no part of the Pulse Rifle body that touches that area. No need to waste time accurately creating something I won't need. 

The most important parts of my digital reconstruction are the places where the Pulse Rifle body will touch the Thompson. To confirm the accuracy of those areas, I created test geometries to 3D print and fit onto my real world Thompson. If the parts fit, my measurements are accurate, and I can get started on the hard part.

Aliens M41A Pulse Rifle - The Grenade Launcher

In the original Pulse Rifle the underbarrel grenade launcher is a shortened, repurposed pump action shotgun. To simplify this project, and because airsoft pump action shotguns are surprisingly expensive, we going to use the Launcher from the Thingiverse 3d Model as a substitute.

I adjusted the Pulse Rifle 3d Model to the correct scale using measurements from the Airsoft Tommy Gun and cut the launcher away from the rest of the rifle. A little clean up work later and we have the launcher as a single solid object.

To fit the 350mm long Launcher into my 150mm tall MakerBot Replicator it has to be cut into 3 parts using SketchUp. I also added attachment pegs to each section to simplify reassembly.

Front and Rear sections of the launcher are easy to print, but the center section will need support material. MakerBot Desktop’s supports are a pain in the ass, so instead I'll use Meshmixer. Meshmixer lets you create minimal supports only where you needed them. They work great, are easy to remove, and are much more efficient.

Estimated Print Time with Makerbot supports, 11 hours.  

Estimated Print Time with Meshmixer supports, 6 hours. 

The finished launcher looks great.  A little modeling putty and some sanding will have it ready for paint in no time. Unfortunately, something is off. Look closely at the small reference model I printed on my Form 1+.

The Thomson's barrel is about 30mm too short. Damn.  

After rechecking my measurements, I have to conclude the original Pulse Rifle didn't use the stock Thomson barrel.  I'll have to look into ways to fix this.   

Aliens M41A Pulse Rifle - Getting Started

There are dozens of Pulse Rifle kits available and sections of the Replica Prop Forum dedicated to building them properly. I however, being a bit of a design masochist, am going to build it my own way. I'm not breaking any new ground, every conceivable permutation of Pulse Rifle has already been done, but this project is just for fun.

From my research, I know the original Pulse Rifles were made from World War 2 era Thompson submachine guns. If you look closely at the gun Ripley is holding in the screenshot, you can see the charging handle, ejection port, upper receiver, and barrel.  

Or you can just trust me... Its in there.

I’m going to start my build from an Airsoft replica of a WWII M1A1 Thompson. Starting here will simplify my build by giving me something with known dimensions to work around. As a bonus, the final creation will fire Airsoft BB's. I'm also going to use this 3d model of a Pulse Rifle from Thingiverse as a guide. It’s the same 3d model Freeside used to print their rifle, and it will save me a lot of time working out the weapon’s proportions.