How long before delrin linear wheels start to wear down?

I noticed that everyone fastens their delrin wheels to the v-slot extrusion in a fixed fashion, with two wheels snugged using eccentric nuts. I'm wondering how long before the wheels wear down, introducing slack in the linear system. I was thinking about designing a special tensioning system, but if the wheels take forever to wear down there wouldnt be a need for it.

Also, I noticed that everyone likes using the wheels in groups of 4. Why not 3? Any reason?

Thanks.

I did not experience wear, but wheels on two axis on one of my Ordbots deformed slightly, flattened on one side, and lead to artifacts and noise.

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

People use 4 wheels instead of 3 for the same reason they use 4 leveling screws on the bed instead of 3.

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

That's interesting because I thought it was better to only use 3 leveling screws instead of 4. I'm going to use 4 leveling screws regardless.

Quote
CVRIV
That's interesting because I thought it was better to only use 3 leveling screws instead of 4. I'm going to use 4 leveling screws regardless.

Are you kidding ?

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Quote
MKSA

Quote
CVRIV
That's interesting because I thought it was better to only use 3 leveling screws instead of 4. I'm going to use 4 leveling screws regardless.

Are you kidding ?

No.



Edited 2 time(s). Last edit at 11/22/2019 12:17PM by CVRIV.

[drmrehorst.blogspot.com]

Actually I think I will do the 3 point leveling method. Makes more sense after reading that.

Maybe I should have been more direct...

People use 4 wheels (4 leveling screws) because the carriages (printer beds) are generally made rectangular and rectangles have 4 corners.

Two wheels (screws) on one side of the rail (one axis of the bed) provide guidance (pitch adjustment) along the rail (axis). A third wheel (screw) on the opposite side of the rail (bed) provides stability (roll adjustment).

A fourth wheel (screw) provides...?

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
Maybe I should have been more direct...

People use 4 wheels (4 leveling screws) because the carriages (printer beds) are generally made rectangular and rectangles have 4 corners.

Two wheels (screws) on one side of the rail (one axis of the bed) provide guidance (pitch adjustment) along the rail (axis). A third wheel (screw) on the opposite side of the rail (bed) provides stability (roll adjustment).

A fourth wheel (screw) provides...?

It's provides you with nothing, except maybe the ability to carry more weight evenly throughout the bed etc. I completely understand what you mean now. It's those 4 corners that makes it so hard to not use four screws. LOL.

It was a rethorical question !

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Before I used a 3-wheel config on my CoreXY printer, now I changed that to 4-wheel carriages and I have seen a dramatic decrease in deflection of the moving X-rail. Also the X-carriage itself now is more stable. I think that 3-wheels would be enough, but I'm using it in a pen plotter and therefor the lines need to be just super precise.

Just to add, I did make sure that the string-tension (I'm using strings instead of belts) was the same in both configurations and I spent about an hour to get the carriages correctly tightened on the rails.

The frame was squared after constructing both 3 and 4 wheel types.

I honestly feel that 4 wheels is better, however it adds more weight.

---

http://www.marinusdebeer.nl/

I didn't find any wear with the delrin wheels, but I've heard that not all black wheels are really delrin--some are nylon fwiw.
I currently use the PC wheels from Openbuilds, and they show no wear in almost 3 years on an enclosed machine.

As for 3 .vs 4, I use 4 because I've had a hard time keeping the eccentric nuts tight on a 3 wheel setup. There seems to be just enough wiggle to wedge them into a looser adjustment. With 4 it's been set and forget.

I had Chinese black vwheels. They were fairly soft and I tend to run higher belt tension. I ended up switching to the clear poly carbonate wheels. With the black wheels I had squish in the wheels, uneven wear and issues with x-y deflection at moderate speeds. Switching to the clear wheels alleviated all of it. I currently use a 4 wheel pattern out of convenience. But have been working on a 3 wheel version because it will be more optimal.

if the 3 wheels are placed properly the rail will be constrained to only direction in 1 axis. there is nothing that specifies only to use 3 it just is all that is normally required,

and if unworn out the three 3 should constrain the system as accurate as 4 would as the main deviation of the axis would come from flection and the run out of the bearings so i would minimize the diameter as much as possible but bearings are usually quite precise. over time the bearings should be allowed to wear slightly. if significant wear, then too much load is on the axis for the current design. in this case 4 would help.

but if they are loose fitting then using 4, or a wider separation between the 3 will reduce wobble and further constrain an axis.

for example i would only use 4 if i had a limited space to put the 3 wheels, or bearings in, and i would probably spring load the single wheel to maintain tightness over time. but this is reprap so i would go with perl slogan, more than one way to get things done....

so if 4 rails seem to help then the system is being overloaded, or there is too much flection in parts or there is poor precision in the bearings at some point in the mechanism (bearings, sleeve, ect)

and in this case your hunch is correct, it would be far easier to change setup to use 4 as the machine would more than likely otherwise need a redesign to allow for 3 to be spaced wider to accommodate the higher loads on the machine for the flection that occurs.

and as for the Delrin wearing down, it should wear slightly, but not enough to allow for slop, it should just wear to fit. so it could be a design flaw, or the system is overloaded. i can see this being much more of an issue on core x-y machines as they are on constaint high tention. so 4 might be a reasonable solution to accommodate the load of the machine and allow for minimum flection, or the system should be designed with a lot wider placement of the 3 roller guides.

Edited 3 time(s). Last edit at 11/25/2019 03:06PM by jamesdanielv.