Timing belt as a rack?

[jacampb2]

I am new here, and I apologize if this has been considered before, but a search did not turn up any info, so here is my question, and a little background on the thought.

I am starting my first two CNC projects, the first will be just a small PCB router of a standard gantry mill design like is all over the interweb, and the second is going to be a CNC plasma table for my Hypertherm Powermax 1000.

My question came about from researching drive systems on this site. The PCB router I am making will just be a standard lead screw design, but for the larger plasma table, I am wondering if anyone has tried to use a larger timing belt as a rack, and the timing pulley as a pinion. I have seen the designs that use an endless belt drive, but this would be a bit different in that the belt would be mounted to a solid bar to form a rack. The timing pulley could be clamped to the rack via an idler bearing running on the bottom side of the improvised rack. I am thinking that it would be an inexpensive way to generate any length rack you could want. The only concern I would have is weather the timing belt would hold up if used in this manner. It seems to me that the forces it will see are not going to be any different than the belt would see in an ordinary installation, but I am just guessing. I guess it would not self clean as well as a driven belt design, but if used for plasma, it is not going to see any swarf or tailings.

What do you all think? Like I say, it is just a thought, and may not be feasible at all.

BTW, I have to say this is an awesome site. I have just been reading and reading for days. I am excited to get started on my projects.

Later,
Jason

[Gear head]

Originally Posted by jacampb2 I am new here, and I apologize if this has been considered before, but a search did not turn up any info, so here is my question, and a little background on the thought. I am starting my first two CNC projects, the first will be just a small PCB router of a standard gantry mill design like is all over the interweb, and the second is going to be a CNC plasma table for my Hypertherm Powermax 1000. My question came about from researching drive systems on this site. The PCB router I am making will just be a standard lead screw design, but for the larger plasma table, I am wondering if anyone has tried to use a larger timing belt as a rack, and the timing pulley as a pinion. I have seen the designs that use an endless belt drive, but this would be a bit different in that the belt would be mounted to a solid bar to form a rack. The timing pulley could be clamped to the rack via an idler bearing running on the bottom side of the improvised rack. I am thinking that it would be an inexpensive way to generate any length rack you could want. The only concern I would have is weather the timing belt would hold up if used in this manner. It seems to me that the forces it will see are not going to be any different than the belt would see in an ordinary installation, but I am just guessing. I guess it would not self clean as well as a driven belt design, but if used for plasma, it is not going to see any swarf or tailings. What do you all think? Like I say, it is just a thought, and may not be feasible at all. BTW, I have to say this is an awesome site. I have just been reading and reading for days. I am excited to get started on my projects. Later, Jason

Hi Jason,
We keep gear racks in stock. Imagine that one of our mild steel racks would be cheaper.
Just PM me if you want more info.
Thanks
Bill

[andy_ck87028]

Using timing belts as racks are very effective and cheap. (Stretched and anchored at both ends with belt looped around the pulley and two pinions to hold in place)

There are a number of these in Australia .... me, ynneb, Apples (I think) and others.

There is a lot written about the subject within this forum. Check ynneb's log as a starter.

I'm sure I have asked questions about the same in my earlier posts.

The precision is not as good as a acme or ball screw but there again who would want to control whip on an 8 foot ballscrew?

Whether more cost effective than a rack, I don't know for sure but in Oz sourcing parts is a problem.

My machine is still not finished but I am content I made the right decision for the right reason.

Andy

[jacampb2]

I looked up his threads, and this is indeed the idea I was having, although a bit different.

I am sure you can imagine the results I pulled up by searching this site for both "timing belt" and "rack"...

Do you have a link to the build thread of your machine?

TIA,
Jason

[andy_ck87028]

Hi Jason

Not sure that my log will help. (http://www.cnczone.com/forums/showthread.php?t=13456).

It is very out of date and a quick flick through does not reveal much about timing belts.

I do need to update it!!

Andy

[harryn]

Most of the belt drive setups I have seen so far use a fixed belt and the motor drive is a "trolley", as opposed to a real "rack". The main reasons (I think) have to do with some assumptions about tooth strength and the typical methods of dealing with it.

I have a thread over in the wood machines build area where I am still trying to figure out what I am doing, and one of the ideas is to use the belt teeth as the rack. It might just be a good idea, but I have not actually found a build log with someone doing it yet. Maybe we can be first.

As you read through my log, you can see the painful growth of dead ends and sensitive areas to making this whole concept work well. I think it can be done, but there are some unique sensitivities to alignment, and it needs fairly strong motors. I am hoping to pull it off, but don't hold your breath waiting for me.

[vmax549]

Jason the problem you will run into is that you will not have enough tooth engagement and it will tend to strip out the rubber teeth. You could something similar. But you will need to use two idlers to allow the belt to form a half loop around the drive gears. the bar running under the belt will help to prevent sagging. (;-) TP