DIY CNC Build in Switzerland - Building the motor mount, gear box and belt drive for Y Axis

I have been searching for options to build the linear motion drive either with lead screws or belt drive. In Switzerland, building a CNC with lead screws (or even ball screws) is incredibly expensive. This is my first try so I did not want to invest a lot:) I decided to use belt drive for all axis. Belt drive is not also cheap when you consider the pulley and belt price. Usually for CNCs 12 mm width (or more) belt is used but the pulleys and belts are expensive again. So I decided to try something: use two 6 mm GT2 belt pulley system in each axis. A short summary of belts systems for you(from RepRap wiki):

T5

These are asynchronous metric timing belts. They have trapezoidal teeth and deliberate backlash to reduce belt wear and noise for uni-directional applications. They are difficult to get in North America. The pulleys themselves though can be printed. Using a printed pulley will give you approximately the same results as if you use an MXL pulley/belt combination with the wrong bore size.

T2.5

Like the T5 these are asynchronous metric belt/pulley combinations. These have a 2.5mm (.098") pitch and are printable. With the same diameter pulleys there is a better grip (compared to t5) on the belt and will give a better result. The best results are with metal pulleys due to the fine tooth profile.

MXL

This stands for "mini extra-light". These belts have been around since the 1940s. Like T5 & T2.5, these are also asynchronous timing belts but they are common in North America because they use imperial sizes. The distance between teeth is 0.08" and the teeth are trapezoidal. You *may* be able to find pulleys that have a 5mm bore but it seems difficult. Most stepper motors have spindles that are 5mm in diameter.

HTD

This stands for "high torque drive" and was introduced by Gates in 1971. These belts have less backlash than MXL and T5 belts because the teeth are deeper and are rounded. These belts were originally patented by Gates but the Patent has since expired.

GT2

These are Gates PowerGrip® GT®2 industrial synchronous timing belts. GT stands for "Gates Tooth". GT2 came about because the HTD patents ran out and they needed a new tooth profile that was not public domain. Gates says the GT2 belts will run OK on HTD pulleys but not the other way around. GT2 belts are stronger than HTD belts, but they need the GT2 tooth profile on the pulleys to achieve their ultimate strength advantage over HTD. These may be more difficult to find everywhere.

Spectra

Spectra fiber braided fishing line is quickly becoming a popular choice to replace belts in many applications after its first implementation in Tantillus and then in many Delta printers. It is cheap and available in most cities around the world. Once tightened correctly it has almost no backlash and provides very smooth movement due to the lack of bumpy teeth and its incredibly small bend radius allowing high steps per mm.

In summary, for best performance at least 6 teeth must be in contact with the pulley at any given time. That minimizes the chance of the belt slipping, and helps reduce backlash even further.Beyond that minimum, fewer teeth are generally better than more teeth, since a smaller pulley gives both more torque and more resolution. So I bought GT2 belt and pulleys for $40 in total:)

Lets start building the motor mount:

For the motor mount I have tried to use Acrylic plate but I could not find a plate of 10 mm thickness as this was required to embed the bearings. So I decided to use MDF. If you have access to HDF, use it as it is stronger. And a tip for you never drill MDF from the side(10 mm side). MDF is built in factories by pressing layers of wood particles. So it is strong from the faces not from the side

 

I marked the motor mounting points so I could use a threaded rod to mount all three plates around the motor.

I have got Nema 24(Yes:) that is 24 not 23). This motor has 485oz/inc torque. The top of the motor has a 37 mm circle bevel so I needed to use the fly cutter to cut a deep groove in the MDF.

I could have directly mount the belt to the motor as it is strong enough, but I would like to mill mild steel as well at the end so I decided to use around 1/7 gear reduction. As you may see in youtube or on web, reduction on belt drive systems are done again with pulleys and belts, which is too expensive for me to invest:) So I decided to build my gear box on top of the motor. I found matching gears and just drilled them to 8mms which is the size of the motor shaft.

For mounting the gear, I decided to use set screws, I have unfortunately M3 taper smallest. So I decided to use M3 as set screw size.

 

 

The ball bearing will be the shaft for the big gear. I needed to embed it into MDF. I used the fly cutter to cut 7mm deep grove and pushed the bearing inside.

The motor mount was not tapped but the width was perfect for M5. So I tapped it:)

 When all the pieces were ready as shows above, I started assembly.

 
Next is mounting it to gantry. To mount the block to gantry, I drilled holes into sides of MDF and drilled a hole on the face and pushed a nut there. If you use wood screws on MDF it may break, be careful. So I solved it like below.

Here is a video of testing motor block only.

 Here is a very very very:) primitive test with clamps holding the belt in place.