This page shows the upgrades/changes made on my CNC Mk2 design. Which are the following:
- The linear guide based on V-groove bearings has been replaced with LM8UU bearings on 8mm steel rods (taken from the photocopier I disassembled).
- The control board is also replaced with the latest design of my FlexNC control board, which resolves some overheating issues.
- I got a new spindle to replace the Dremel.
I started the upgrades by designing a holder for the 8mm steel rods. My aim is to try and “streamline” the design a little bit and have as fewer unique components as possible. So this particular component is going to be unique for all axis.
Here is the holder. I made it out of a 15x15mm solid square aluminum profile, which was cut into pieces, then drilled and taped. The cuts were done with a handsaw. The holes were drilled initially using a Dremel router base (poor quality and precision). The 8mm hole for the steel rod was drilled successively at 3mm/4mm using the Dremel, then at 5mm/6.5mm/8mm using a hand drill. I believe that given the poor tools I have the result was quite satisfying.
The holders have been secured on the basic frame of the CNC and the 8mm steel rods have been secured on them. I have removed the “bridge” part of the frame for now, as it will be added when it is time to modify it too.
One of the difficulties I had, was how to attach the LM8UU bearings on the carriage. Initially I was thinking to use a 3D printed part, similar to the ones used for the same reason on many 3D printer designs. But I had no access to a working 3D printer. Luckily, I found an aluminum profile for that too! Cutting it to length and drilling two holes was all that was needed and the 15mm outside diameter of the LM8UU fits perfectly inside it. For the Y-axis I only used one of them for each linear bearing which was pressing the LM8UU against a piece of wood. But as you will see later on, for X-axis and Z-axis I used two of these to hold the linear bearing from both sides.
A wooden slab was added, that will serve as the holder for the material to be milled. That was a good time also to make any adjustments to the steel rods and their holders, in order to make them perfectly parallel and the slab to be perfectly level.
And here you can see the two carriages of the X-axis. Hopefully they will be found together and they will not be moving in relation to each other, after I make and install the Z-axis guide rods. You might also notice in this picture the old control board, hanging from the side of the CNC. It was previously fixed on the back of the X-axis guides, which is not possible any more. I will think of a way to fix this later on though. It’s not something important. After all this particular one will be scrapped, as soon as the new version of the control board gets fabricated.
I started making the Z-axis by attaching these LM8UU holders on the spindle mount, using a clamp. I then drilled a 6mm hole using the existing hole of the spindle mount as a guide. As soon as this was done, I have inserted the M6 screw that tightens the spindle mount and secured it with a nut. The clamp was then removed (because the screw was now holding the LM8UU holder in place and I drilled the other hole, by using again the existing hole of the spindle mount as a guide.
For the other half of the LM8UU holder, I inserted 2 LM8UU bearings and inserted through them a piece of 8mm rod, to hold them in place. then I added the other half of the LM8UU holder and clamped it in place. I then drilled the first hole and repeated the previous procedure. I finished the Z-axis carriage, by inserting the right length 8mm rods through the LM8UU bearings on either side of the spindle. I then fitted the 8mm rod holders I previously made (you can see details here) and I cut and fitted two horizontal aluminum brackets to connect the holders together.
With the carriage and Z-axis guides finished, I could then assemble the whole thing on the X-axis carriages. I aligned them and clamped them together, in order to make the first hole, then secured them together initially with one screw and then removed the clamp to drill the second hole too.
At this stage the CNC is almost complete. The missing parts right now are the X-axis and Z-axis drives and the electronics. The X-axis drive mechanism was the easy part, because it was pretty much the same as before, so I just re-assembled it with some small modifications in the mounting brackets.
At this stage I decided to align/calibrate the Y-axis and make sure it is perfectly level with the basic frame. After the initial measurements it looks like the 4 “corners” have a variation of about 0.35mm. This is mainly because the 8mm holes of the 8mm rod holders are not all perfectly centered on the aluminum piece from which I made the holders. But the variation is quite small. I decided to sand the bottom surface of the holders appropriately in order to make the Y-axis assembly level to less than 0.01mm. Which worked nicely.
The next step was to create the Z-axis drive mechanism, which is going to use a M4 threaded rod attached axially to the Z-axis motor. I started making it, by making 2 L-brakets that will support the weight of the Z-axis drive mechanism and the spindle.
The threaded rod is mounted on the L-brackets with two small bearings (courtesy of the disassembled photocopier).
I then decided to combine the two separate carriages of the Z-axis, in order to have a solid interface where the spindle is attached, which will not need alignment every time the spindle is removed. I combined the carriages using two flat bars of aluminum, with thickness of 4mm. The way they were mounted leave a horizontal gap between them, which will serve another purpose as we will see in the following pictures.
The horizontal gap is roughly 4mm and I used a small piece of a 4mm thick flat bar in order to make a captive nut which will be set inside the gap. As soon as the spindle is in place, the captive nut will be fixed in place and move the carriage along the Z-axis. In the picture on the right you can see the captive nut I made, but it is not in it’s final place yet. It will go a bit lower between the two horizontal aluminum flat bars.
The final step was to connect the electronics. Unfortunately using the old version of the control board, which will be replaced later on (possibly I will make the new version of the controller using this CNC 🙂 ). The spindle is 48V DC and draws about 450Watt. So I got a 500Watt PSU which was mounted on the side. The new step motors are 12V DC so I also got a 48V to 12V DC-DC converter in order to power them. The AVR processor is powered over the USB, so we don’t need anything else. With the wiring done this way I only have 2 cables to connect to the CNC (AC in and USB to a computer) and I am ready to work. It is important to have as few as possible cables to connect when you want to use a machine. It greatly reduces the setup time.