Longest x axis

Terr · May 21, 2024

Guss said: ↑

Is there anyone here that attempted a 2.1m x-axis?

Use case: Engraving and routing on a standard 1080 x 900 mm solid door panel.

I read the articles on long runs, where timing belts slip, about pinion and rack methods, double belts, etc.
My humble opinion is that if I just use a deeper tooth (GT3) 6mm wide, and control the surface area on the pulley, it should not slip.

Example: If the pulley and belt only have a 1/3 surface contact with the surface, it will slip under load. The real surface is even less, because the outer teeth are already leaving the groove.

I'm not an engineer, but here is my logic:

Figure 1 is issue, too little surface area for long runs and where the combination of stretch and torque worsen the problem exactly where the belt make contact with the pulley (Entry point - let call it A). Though, in real example, it will be applied like in Figure 1B, which reduce the problem somewhat. (still and issue, cause of the slag that exist at idler A.

Figure 2, better, but the surface contact area is still less than 50% (in the sketch its 50%, but teeth to groove, is less because the entry and departing contact is not 100%. Still and issue, cause the torque will "lift" the belt at entry point A. (all the slag over the whole length of the belt manifest itself at A, making it worse the longer you go or the less tension you have on the belt.

Figure 3. my first choice. This is not just idlers to increase the surface contact area, but dynamic tensioners. Off course they will catch the "slag" as it occurs, and on top of it, it ensure full surface contact all the time. I will guess, that in practice, there will be 100% surface contact over 50% of the radius. (in the 2D drawing, its at 66%)

Figure 4 is another way of looking at it, but this time its higher up, but with less friction on the belt (less radiuses for belt to pass through). I did not put more thought into it, whether this will just be idlers ensuring contact of the belt with the drive pulley, or just tensioners.

That leaves an open question, what effect the tensioner will have on the departure point B of the belt? If it does, then Figure 3 is the worst scenario for departure and Fig 4 is better. Maybe with the smaller rollers even linear to the centre of the pulley.

What else: This could be little bearings mounted to the mounting plate itself, or something more complicated as dynamic tensioners (rollers pulling to each other, and the belt's own tension pulling them apart)

I think it is feasible. Will people with experience in such use cases please comment.
There must be a solution to the issue of belts slipping on long runs without going to expensive linear guides and modifying v-rail profiles, and bolting metal racks to the rail.

I also would like to make contact with people with axises that is 1500 mm and longer and with builders doing >= 400 mm z-axises, and 4th axis with rotating beds.
Click to expand...

I just bought 4*2 = 8 meters of SBR16UU rail. I will run into the same issue. My rail is bare. I need to add the lead screw and for now the Tr8*8

Down the track: ball screw.

There are motors out of China which I can import which are hollow shaft. (I am in Calgary & my company is an importer/exporter)

...Terr

Terr · May 21, 2024

I think I know a way to accomplish very long axis drivers.

1) hollow shaft motor. Problem is picking up the thrust. I know a manufacturer in China & I can bring them in.

2) use the motor to rotate a nut. The nut then carries the thrust bearing. This should be pretty easy to do. Then the lead screw ends up stationary and can be placed under tension.

In my case the X0 axis is 6 meters. Offset (Y-axis) is arbitrary. Parallel is the X1 axis which in my case is 2 meters. I don't need 2 meters. 1 meter is fine so I will simply use a standard 1050 mm lead screw drive.

I need to find a way to mount on an SBR16UU rail instead of V-Slot. If I can't find it I will make it. I have run a lathe. A mill should not be hard to learn.

By doing this I can put TWO (2) router tables side by side. Likely I will want this.

So: hollow shaft -or- rotating nut on a fixed lead screw & this provides 1 or more routers side by side. Cheap. Simply add another motor and Y-axis.

------ what if we want say 6 meters? ------

3) Airplane cable.

Here is the problem: each rotation of the drive spool will cause an offset equal to the diameter of the cable.

This causes a *REAL PROBLEM*. The solution is to put the drive motor on a slide. So a small secondary motor is required to slide the main motor left & right. Else it's a gearing problem.

Since the airplane cable cannot slip on the pickup/feed spools the accuracy should match the 1050 mm lead screw over the full 6 meters.

Furthermore it should be reasonably cheap because we don't need the lead screw any more.

Protospace is available to me here in Calgary. I figure there just might be interest. A NEMA 17 or smaller on a SBR8UU rail system should work.

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