In this installment, 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 want 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. (see below)
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
I understand that not everyone has a lot of CAD or has access to a CNC, so I am offering a set of printed frame templates.
The templates are printed on 8-1/2" x 11" paper, and need to be assembled to make full sized templates.
You can get the frame templates here:
Let’s take a little close look at each of the components and how to use the templates.
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.
On the templates you will notice there are sides that say "Cut" and "Dont Cut".
Shown here is the "Frame Side Upper" template and the "Frame Side Lower Rear" template.
Use a ruler to slice the side that is to be cut. Set the ruler so that it splits the cut line (dotted), then use a razor knife to cut the line while firmly holding the ruler against the template.
Note that you can use scissors, just make sure you are extra careful around the small square tabs, as they are used for alignment.
Once you make the cut, align the small square tabs and secure with tape. You can use a ruler to help maker sure the line running down the outside edges is aligned properly.
Attach the "Frame Lower Front" template to the "Frame Lower Rear" template just like you did above.
Once the three templates are combined, you need to trim the outside edges. Again, this is best done with a ruler and a razor knife.
At this point you will ignore the don't cut lines.
The inside corner has fillet. You will need to cut this free hand or use scissors.
Tape your completed template to the stock as shown here. Align the outside corner with one of the corners of the stock.
If you stock is already cut to 19" x 18", then align three corners to the stock then tape in place.
With the template secured to your stock, mark all your holes with a punch.
Trace any edges that need to be cut. Once your holes and edges are marked. Remove the template. You will be using it to mark the left frame side.
Probably the easiest way to cut the stock is with a jig saw. You can also use a band saw if you have one.
To make all the holes, I recommend a drill press. It does not have to be a big one. A small 9" or larger bench top model will work. You can drill the holes by hand but you need to make sure you keep the drill perpendicular to the stock.
To cut the large holes you can use a hole saw if you have one, A jig saw can also be used. The cuts are not critical. Just make sure you completely cutout the circle. If you do decide to use a jig saw, you will need to mark the cut line.
When marking the frame right side the template goes on the outside of the stock. When marking the frame left side the template goes on the inside of the stock. This is important if you have a preference as to which face is on the inside or outside of the CNC, otherwise it does not matter.
The drill size is listed on each hole of the template.
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 front brace template consists of to parts. They must be assembled exactly like the side template. You will need to cutout the two interior rectangles.
I recommend the stock be cut to 16" x 7" so that the template fits perfectly over the stock.
Attach the template to the stock and mark your holes and cutouts, just like you did earlier.
You will have to use a jig saw to cut out the inside rectangles. Drill some small holes to give you a place to start your cuts.
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 rear brace is done exactly like the front brace, except for the large rectangle cutout.
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.
The top brace is done like the front and rear brace. You will have to separate the two templates first, by cutting down the middle as shown here.
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 cleat template goes together like the top brace. Be extra careful with this template when removing from the stock as you will need to mark four pieces.
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.
Having used the KReduCNC for over a year now, I have found access to the controller board underneath the machine to be cumbersome if you plan on experimenting with the machine. I plan on doing a DIN rail electronics hookup in the future.
All that said, you may still want to add the cleats and a platform. The ability to place some items, like wrenches and cutters inside the CNC to be convenient.
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.