In this instalment, I will show you how to assemble the frame components. You will need the means to cutout the components. This will vary depending on the materials used. In my case I used a table saw to cut out the parts and a jig saw to cut out the larger holes. I used a portable drill to make all the holes. At the end of the article, I will provide a link for you to download the drawing files in both eps and pdf form.
The frame can be made from any 3/4" stock. In my case I used melamine coated particle board. Both plywood and plastic could also be used. I would not use metal as it would make the machine too heavy and difficult to transport.
The inside area of the frame is 16" x 16", while the footprint is 17.5" x 18". These dimensions were chosen to accommodate 16" long 8mm steel rods and flanged supports for both the X and Y axis.
The frame consists of five components. Two sides, a front brace, a rear brace and a top brace. Holes have also been provided for mounting a 3/4" cleat. This cleat may be desired if you wanted to mount a shelf inside the frame to hold some of the electronic components.
It is important that the holes drilled into the frame components be placed as accurate as possible. Having dealt with various CNC builds in the past, I have found that using templates is the best way to achieve that. I will be offering a set of templates that can be placed over your stock to allow you to easily mark the points to drill the various holes.
The frame components are cut from 3/4" stock. Melamine coated particle board or some other suitable stock.
- 2, sides cut to 18" x 19"
- 2, braces (front and rear) cut to 16" x 7"
- 1, top brace cut to 16" x 3"
- 4, cleats cut to 3/4
Let’s take a little close look at each of these components.
There are two side components used on the frame. They are identical with all the holes drilled through. Each one is cut from a piece of stock 19” high by 18” wide. A 12” x 12” section is cut out so that the side piece forms an L shape. You can fillet the inside corner or make it a 90 degree angle.
The sides contain the holes used to mount the motors, bearings, and rods for the X-axis. The large holes on the bottom are for optional fans or vents.
The front brace is positioned between the two sides. It has the holes for mounting the bearing block and rods. The square holes on the bottom are for eventually mounting plates that may contain holes for various controls, such as an E-stop or power switch. Even if you won’t be using these holes, I suggest you cut them anyway for future upgrades.
The rear brace is much like the front brace. Instead of the bearing block, a motor will be mounted. The holes for this are identical to the front brace. A large slot has been cut into the bottom of the brace for access to various connections to the CNC.
The top brace (Figure 4) is used to help stiffen the frame. It is placed between the two sides near the top of the CNC. This brace can also be used to anchor cables or hoses.
In addition to the frame components listed above, the following hardware fasteners were used to hold the components together:
- 12, 1/4-20 Cross Dowels
- 12, 1/4-20 x 2” hex bolts
- 12, 1/4 washers
The 1/4-20 cross dowels can be purchased here: Cross Dowels
To assemble the frame, cross dowels are inserted into the face mounting holes of the front, rear, and top braces.
The cross dowels are designed to fit into a 1/2" hole in the face as shown Figure 5.
A 1/4-20 x 2” bolt with washer is then inserted into the face of the sides and then into the appropriate cross dowel access hole as shown in Figure 6.
The exploded view (Figure 7) shows each of the 12 cross dowel connection points. Once assembled and tightened the frame is very rigid. When assembling the frame, make sure the bottom is sitting firmly on a flat surface. This is important to keep the linear rods lined up correctly.
Cross Dowel Jig
In order to accurately drill the access holes in the edges of the braces, I created a small cross dowel jig, shown in Figure 8. The jig kit is available on the KronosRobotics website. It is assembled by slipping the two sides over the three guide plates and held in place with two screws shown in Figure 9.
The jig is slipped over the edge of the brace and the 1/2” hole in the jig is centered over a cross dowel hole on the face of the brace, as shown in Figure 10.
A 1/2" bolt can be placed into the hole to help secure the jig to the brace, as shown in Figure 11. A 1/8” drill bit is then used to drill a pilot hole into the edge. Once the pilot is drilled, remove the jig and use a 5/16” drill bit to enlarge the hole. When drilling the access holes, make sure you drill them past the cross dowel hole in the face. This is done to give you some space for the bolt as it exits the cross dowel.
The four cleats are provided to mount a shelf. This will allow you to place some of the electronics inside the frame. While the cleats can be made from particle board or other engineered material, I recommend a quality plywood like baltic birch. A solid wood like pine will also work well. The shelf will be attached to the cleats with wood screws later in this project.
The cleats are secured to the frame using the following hardware:
- 12, #6-32 x 2” machine screws
- 12, #6-32 hex nuts
- 12, #6 lock washers
- 12, #6 flat washers
Figures 12 and 13 show how the cleat is attached to the frame. Even if you don’t plan on adding a shelf to mount some of your electronics, I still recommend installing the cleats. It is much easier to add them now than it is later after the Y-axis has been installed.
This completes the KReduCNC frame assembly. If you are building along with me, your machine should look like the one shown here.
The drawing files for the frame components can be downloaded here:
Please note that these files are subject to change. You will need some sort of CAD software that can import eps or pdf files to use them. They are raw 2D drawing files without annotations. Near the end of this series I will offer a complete set of annotated drawing files and/or templates.