Z Axis Continued, Torsion Box Intro

Here is the Z axis carriage after unclamping from the glue-up and giving it a light sanding. I am using aluminum bar stock to mount the profile rails. I chose this method in case I wanted to mill a perfectly flat surface on these or to mill shoulders (the preferred mounting method for HIWIN rails). At this point the bar stock is just positioned for a test fit. They will be epoxied in place after drilling and tapping the rail mounting holes.

Z Axis with Al bar stock

After making this first piece for the Z axis, I noticed it had a very slight warp to it. I don’t think it will be a problem, since I can lay the bar stock on a flat surface, coat the carriage with a thick epoxy, and lay it on top of the bar stock, so that the rail mounts will remain perfectly flat and in the same plane. The epoxy should take up any space due to the slight twist.

I now realize that I will need a perfectly flat work surface to make the remaining parts on. I also will need a perfectly flat base for the machine, so I decided to go ahead and build up the torsion box base at this point. The machine base will serve as my assembly table for the rest of the build.

To build a perfectly flat torsion box, you need to start with a perfectly flat surface. Inspired by this article on popularwoodworking.com, I made two small torsion box beams. This allowed me to practice the techniques for making a torsion box, and then I could use these to create a flat work surface for building the torsion box machine base. You will see later what I mean. Here is a picture of the two torsion box beams being constructed.

Torsion Box Beams Clamped

Start CNC Router Build – Z Axis

I started with the Z axis since the parts are small and if I make any mistakes, it will be easier to redo with less wasted material. Working with the dimensions and images from my solid model, I started by cutting all the pieces out of a sheet of birch plywood to make up the Z axis carriage, laid them out for a test fit, then glued and clamped them together.

This is the Z Axis design:

CNC Router Z Axis Solid Model

Gluing up the first pieces:

Z Axis frame clamped together.

It is starting to look just like the model :-).  It is fun to see something come to life that you have been working on designing for so long!

Close up of Z axis wood frame

Lots of clamps:

Top view of clamped z axis

My table saw left some burn marks on the wood. They will get sanded down later to make it look nicer. After these cuts I spent some time tuning up the table saw to align everything properly. Perhaps a new blade would help as well.

CNC Router Design Overview

Here are the major components, with the wood frame design as seen in the image below. I am using Fusion 360 for the modeling and design simulations. I’m very impressed with the capabilities of Fusion 360, being that it is free for hobby use. I do run into quite a few bugs, but I can’t complain for the price I’m paying! Also, they are continuously improving, rolling out updates, and they respond in a timely manner to inquiries on their support forums.

  • HIWIN HGR15 linear profile rails (X=1200mm, Y=800mm, Z=350mm)
  • HIWIN HGH15CAZAH bearing blocks on Y axis
  • HIWIN HGW15CCZAH bearing blocks on X and Z axis
  • Ballscrews: 1204 on Z Axis, 1610 on X and Y axis
  • BK/BF 10/12 supports for all screws
  • NEMA23 381 oz-in stepper motors (4 total, 2 on X-axis)
  • Gecko G540 stepper drivers
  • 48 vdc power supply
  • Mounts for DeWalt DWP611 (shown) and DW618 routers
  • Linux CNC control software

The frame components and the machine base use a torsion box design and will be made from birch plywood and MDF webs.

DIY CNC Router Prototype

Goals for the CNC Router Build

I was not happy with the performance of any of the CNC router plans currently available, nor with the prices of kits and commercial machines. So I decided to come up with my own design. Not to mention, it is more fun to design and build your own, right?

I laid out a set of performance and cost goals and then designed a machine to meet those goals. However, this series of posts is not about that exact machine. I am first building a proof-of-concept machine that is lower cost and easy to build (therefore the wood frame). This will allow me to learn and flush out any issues with the design before building a more expensive and time consuming version of it. I did however attempt to design the wood frame to be as strong as possible so that it will have enough performance to make parts for the originally designed machine.

My rough goals for this wood framed version of the machine:

  1. Working area of 37″ x 25″ x 6″ (940 mm x 635 mm x 150 mm).
  2. Accuracy and precision in the ballpark of 0.001″ over 12″.
  3. Performance – will leave this for later discussion.
  4. Learn and test the concepts needed to build my originally designed machine.
  5. Have a machine to start making parts for the next machine.
  6. Have fun!

I will give some design details in my next post.

Introduction to CNC Router Project

Intro

I have always enjoyed learning new things and thinking about innovative solutions to a wide array of problems I encounter in life.  Many of the ideas and subsequent solutions have seemed viable, but would require resources that were not available to me to implement the idea.

In the back of my mind, I’ve always been intrigued by the thought of having a CNC machine at my disposal. This would help me to bring my ideas to life.  Seeing stories of other people building their own low-cost machines tempted me over the years to do the same.

After years of reading/dreaming about it and gradually learning, one day I decided to seriously research the options.  I looked at buying one of the hobby machines that have been popping up on the market in recent years, buying a diy kit, buying plans, or following one of the free open source projects to build my own CNC router.

In usual fashion, I spent a few months studying all of the specs, pricing out each option, and reading hundreds of forum threads, articles, and reviews.  It was quickly apparent that I could not afford to buy a machine, or at least a machine that had the performance I required.  Kits and open-source machines were not much better for affordability, but plans offered a lot of bang for the buck.

Researching CNC Router Plans

Quite a few plans were available, so I dug in to comparing them all.  In the process, I read many accounts of people who built machines based on the plans, those who modified the plans and those who upgraded their machines after not being satisfied with the initial results.  In addition, I happened upon people who designed their own machines altogether, which planted an idea in the back of my mind.

Once I had gained enough knowledge to evaluate different designs, features, and the resulting performance, I realized that none of the plans would satisfy my needs as-is.  However, they could probably be modified to do what I wanted at an acceptable price point.  After a lot more research (see the trend here?) I got to the point of feeling comfortable looking at any CNC machine, including the commercial models, and evaluating the design decisions and understanding their weaknesses.  It was then that I realized I could design my own machine and probably end up with a better product than anything currently available at a given price point.

A New CNC Router Design is Born

To confirm my thoughts, I made up a quick Bill of Materials and researched the prices of all the individual parts and raw materials that would be required.  This further cemented the idea that I could design and build a machine that would come in at the right cost, and likely with great performance too.

For the next 3 months, I researched CNC design, studied mechanical engineering, compared products, part manufacturers, parts suppliers, and started formulating a design.  I also knew that once I had a working CNC machine, I would have to learn CAD software to create the designs that the machine would produce.  I decided to jump in and learn solid modeling to design the CNC machine.  I compared all the CAD options and settled on Autodesk’s cloud based Fusion 360 software.  It was offered free to hobbyists and small businesses, and has comparable functionality (at least from a beginners view) to the industry standard SolidWorks, which I couldn’t afford.

In December 2015, I installed Autodesk Fusion 360.  Through reading the educational materials and following the tutorials I was able to quickly learn the software.  By the end of the month I had a rough conceptual model of a CNC machine, rendered beautifully and quickly in the cloud by Autodesk’s servers.  Over the following 6 months I went through many iterations of the design, gradually refining it and converging on an optimal solution to match my budget and performance requirements.

Once I felt the design was getting close, I learned to use the Simulation functions in Fusion 360 to perform stress analyses and deformation tests in order to find the weak points of my design.  It was a relief to see that the results of the stress analysis and cutter deflection simulations were in line with the calculations I performed during the initial design stages.  A few more tweaks to the frame components yielded a design that should meet the design goals and performance requirements.