Racks, timing belt or screw, which is the best?

One of the most common questions I get is which drive is the best, let’s look at some pros and cons that hopefully will help you too choose.

Propulsion pros and cons:

Trapezoidal:

trapezoidal

has a low speed and the pitch usually does not exceed more than 4 mm per revolution, ie the motor must rotate once for the machine to move 4mm In this way you can get the machine to go in about 1-2 meters per minute faster than this requires a higher pitch of the screw or more powerful motors. I recommend this variant to machines that don’t need to go fast, and to your machine’s Y-axis (up and down) even if you are running with timing belts or other solutions. With this solution you will have a very low backlash and a relatively inexpensive solution.

Protection against dirt = bad (have the screws on the side or underneath the machine)
Backlash = Good (until it wears)

 

Ball screws:
kulskruv

as above, but much more expensive. A screw can go for several hundreds of Euros and you may need 4 pieces. Here you will gain higher speeds maybe 3-4 meters per minute. And up to 0 in backlash. If you are working with wood or larger pieces this solution is painfully slow, it’s more suitable for small objects like aluminum or engraving jobs. So use this if you require precision and decent speed.

Protection against dirt = Ok (have screws on the side or underneath the machine)
Backlash = Very good, and probably the best option if you need as low backlash as possible

Rack and pinion:
kuggstang

Now we’re talking, a machine with racks has both speed and power as well as low backlash. The problem is that it is harder to design a machine with racks. With racks you will get ridiculous speeds with enormous powers. This is the dream option for you who really want to work with your machine. On our Raw 1.5 machine we have racks as an alternative. To make the construction as cheap as possible, the rack hangs outside the machine and up side down to prevent dirt from getting caught in the teeth. The advantage of this is that we do not need a mechanism that forces the gearwheel against the rod, a Raw uses gravity to handle this for us. Many have questioned this idea, but my tests show that this works ridiculously well and are extremely easy to construct. Check our videos if you are in doubt. One disadvantage of a rack is the sound when you jog the machine back and forth. We do not want to lubricate racks in a dusty environment, so it’s steel against steel, but this does not affect the cutting results.

Protection against dirt = Very good (probably the best solution)
Backlash = Very good (If you find high quality steel Racks)

 

Timing belts:
kugrem

Timing belt can be good or bad depending on how you use them. I have seen many projects that builds CNC machines with a G2 timing belt that is 6mm wide. These are like rubber bands and are only suitable for 3D printers, decal and paper cutting machines. The backlash with a 6mm belt must be brutal. I use timing belts for my machines as well but these are HTD3M belts 15mm wide and with a steel core. These work very well and you can even turn the belt upside down to avoid dirt. I like belts, they are cheap and easy to replace. As with the rack you will get speed and strength and very good accuracy. I recommend you to use belts for your first machine. I recommend using timing belt for your first machine. Belt machines runs smoother than a rack machine and I usually recommend timing belt before racks for machines under 1 meter.

Protection against dirt = Very good
Backlash = Good (with wide belts)

Chain:
kedja

Like timing belt but with much worse backlash. It can be solved if you find a good chain without backlash.

Raw 1.5 can have different options

Our machines are modular, which means you can have several different drives depending on your taste. Raw 1.5 can both have a belt and rack, so if you’re unsure, start with a belt and upgrade to racks if you notice it’s necessary. There are even those who have added ball screws to a Raw and it’s easy, but unfortunately I have no instructions for it, so you have to figure out a solution yourself.