Arcol blog Just another RepRap weblog

20Nov/13Off

High precision custom pulleys and belts

Why have I decided to manufacture my own pulleys myself?

Grab one here.

Spoiler alert:)
flickr:8693066999

I) Not finished
The stock pulleys have only conical indentation at the end of the pulley, which acts as a starting point for drilling.

flickr:8694286785

Also no M3 grubscrew either.
So basically you need to drill it on a lathe if you want precise work, and this directly affects the precision of the machine.
(Imagine an eccentric pulley).

II) Eccentric

If you make the pulley first, then you drill it even on a lathe, there is no way you can drill an absolutely concentric hole in the middle[1].
I tried to use a 32 teeth pulley once, we drilled on a lathe, and it was a tiny bit of eccentric hole, destroying the print quality immensely.
But if you drill the hole first, and you machine the outside while putting the workpiece onto a shaft, then it will be concentric, and now if you cut the teeth on the outside, then the endresult will be absolutely concentric.

[1]:
In general, you always loose precision if you have to remove the workpiece and put back onto the lathe. There are solutions (4-jaw chuck, collet chuck) for the issue, but you start to tool yourself against this specific problem, which is expensive.

III) Low quality tooth profile

If you want to cut the teeth right, ie. within the tolerance specified in the DIN7721 standard,
then you need different cutting tool for the most popular teeth counts.
Some cheap sources, definietly save on cutting tools, having lower quality tooth profile.

IV) New possibilities

If I self-manufacture the pulleys, then it opens new possibilities, which was unimaginable before.
Just one picture to prove the point:
flickr:8693066999

No more flipping the belts on the bearing end!

V) Less mechanical stress on the belts

With bigger diameter the belt turns on a bigger radius, that means less stress on the belt.
Also with toothed bearing (read below), you can forget about belt flipping.

The problem with belt flipping:

  • unnecessary stress on the belt, especially the steel cords inside. It may break, or delaminates over time.
  • aesthetically unpleasant
  • limited by the belt width (you can not flip a 20mm wide belt).

VI) Different (out of standard) width pulleys

It is just an idea now, but the possibility is there.
We can have 20mm wide pulley, if you are thinking in a really big (above 500mm) machine,
and you are affraid of belt stretch.

Product tour

Let's see what we have here.

I) T2.5@32 pulley

This pulley has 32 teeth, 5mm bore, M3 grubscrew ready to be inserted onto a motor shaft:
flickr:8693988610

Available here.

II) T2.5@16 pulley
This pulley has 16 teeth, 5mm bore, M3 grubscrew ready to be inserted onto a motor shaft:
flickr:8693066029

Available here.

III) 608@T2.5 bearing

This 608 bearing has a ring with T2.5 tooth profile, you can put it onto the other of the belt.
It solves the belt flipping problem.
flickr:8693070715

Available here.

IV) 624@T2.5 bearing

This 624 bearing has a ring with T2.5 tooth profile.
flickr:8693069563

Available here.

V) High quality belt

Maybe you can source elsewhere, but this one is steel reinforced, and known to be working high quality belt.

Available here.

Tolerance and precision

There is no backlash, if you have

  • good enough tooth profile (minimal clearance between the pulley's teeth and belt's one)
  • low weight carriage (under 1.5kg or 3 pounds for american readers:)
  • numerous teeth contact (16 teeth pulleys or more)
  • high enough tension, so the belt does not slip between the belt

Here is how the teeth look like:
flickr:8693068067

And here is with belt applied.
flickr:8694182540

Notice the non-existant or minimal clearance between the belt and pulley's teeth.

Standard flange

It has a flange and a degree between 8 - 20 degree according the DIN7721 standard.
Here is a picture:
flickr:8694177668

Out-of-the-box experience

They are ready to go, you only need to put onto the motor shaft, even the M3 grubscrew is included.
No need hunting for lathe or sourcing small grubscrews or workaround with bigger M3 screws.
flickr:8693063469

The belts fit well around the pulley.
flickr:8694180392

(For closeup picture, please refer to the bearing section.
This one could is not easily photographed because of the metal skirt)

High quality belts

For your convenience, I have sourced high quality belts with steel cords inside.
flickr:8694515575

You can get it here(TODO)

Bearings example assembly

In case of toothed 624 bearing:
M4 Bolt - (M4 washer) - M5 mudguard washer - M4 washer -
- (toothed) 624 bearing -
- M4 washer - M5 mudguard washer - (M4 washer) - machine
flickr:8694935573

The M5 mudguard washer is enough in diameter:
flickr:8694934733

In case of toothed 608 bearing:

M8 Bolt - special M8 washer of >30mm diameter - M8 washer -
- (toothed) 608 bearing -
- M8 washer - special M8 washer of >30mm diameter - machine
flickr:8696058178

I used a special washer, which had 40mm diameter, maybe it is a bit overkill:
flickr:8696057242

Update: I have manufactured special disks, which is only 0.5mm thick, so it does not wear of the belt's edge.
Obligatory picture:
flickr:10974050914

10Feb/11Off

Another planet update (article updated)

I have been working on the planet furiously during the whole week.

17Oct/10Off

Blender broke

I broke my blender, simply filled to the maximum and switched on. The rubber "gear" grinded away:

8Oct/10Off

http://planet.arcol.hu update

Im running the reprap planet since this february.

21Mar/10Off

Worst smelling filament ever (updated again)

I received half kilogramm sample straight from the factory, from India. The cross section is perfect, but the smell...

24Jan/10Off

Going blue

Some diversity or how Latin says: Varietas dēlectat.
But the reason is trivial: I ran out of the white plastic.

26Dec/09Off

It has to start somewhere

"It has to start somewhere
It has to start sometime
What better place than here
What better time than now"

-- Rage Against The Machine
Guerrilla Radio (1999)

This is an upcoming blog about adventures of a reprap enthusiast.