Steel Tape transmission - increasing friction

[fkaCarel]

I will try to explain. Your sprocket wheels are 25mm. 1 revolution gives a travelled distance of 25 * pi (pi simplified to 3.14) = 78.5 mm.

The sprocket + 2 * tape diameter = 25.3 mm.
The transporting diameter = (25.3 + 25) / 2 = 25.15 mm (neutral line). Transported tape at 1 revolution 25.15 * Pi = 78.971. This is 1.006% more than if you expect the tape to roll over the pulley.

I see now that you will have to rethink your sprocket, there is no multitude of the 10mm pitch. Let's assume it 8-ball. Neutral line transport = 80 mm. 80 / Pi = 25.48.
25.48 - 0.15 = 25.33 mm. Transport per step at 1200 step/rev: 0.066 mm

The same things you will see in timing belts, the neutral line outside of the sprocket. You will also see the need for the number of tooth in contact, to distribute power. This almost prohibits a flexible coating, because the more precise the pulley, the better the load is distributed over the tooth.

I hope you understand this explanation from a linguistic challenged person.

[greybeard]

Quote
< Let's assume it 8-ball. Neutral line transport = 80 mm. 80 - 0.15 = 79.85.
<
Unquote

Is this correct??? You appear to have deducted the thickness of the tape from the length of 8 holes length of tape.


If we assume that I use 8 balls then the length of the neutral line is 80mm.
This would give a diameter of the neutral line of 80/pi = 25.46mm.

But if the tape is 0.15mm thick I must reduce the sprocket wheel diameter by 0.15mm, making it 25.31mm.

This is not a problem, nor is the new stepping distance that it would give.

Unless, of course, the balls are the wrong size anyway.

[fkaCarel]

No, it is not correct, I deducted tape thickness from diameter * Pi ! Stupid, Stupid.
This was because I lined out the calculation and found your diameter did'nt match and had to go in reverse. I will also edit the original.

[greybeard]

I think you use a more accurate value of pi, but now we agree on the diameter.
The size of the hole is 2.5mm so I can proceed.
Now I will see if I can come up with an assembly method which does not require the sprocket wheel to be turned to such an accuracy while I wait for the delivery of the balls !

John

[fkaCarel]

Tonight I remembered I made such a thing more than 20 years ago to transport thermal paper. I used needles from a needle bearing because it's easy to make a press-fit for these. From my FAG catalogue the shortest 2.5 mm is 7.8 mm (NRO.B2,5x7,8G2).

[greybeard]

"FAG catalogue" ? more info please fka.
John

[fkaCarel]

FAG catalogue is nothing more than a standard bearing catalogue, in this case from FAG. Find out which brand your local supplier is associated with, get such a "bible" and order from the catalogue. Be amazed at what you can get. The needle bearing supplier of origin is INA.

[Colin31]

Greybeard, try these people
http://www.chronos.ltd.uk/acatalog/i...ml&CatalogBody

http://www.hpceurope.com/index.html

Colin.

[greybeard]

fka - many thanks. This aged person needs all the help he can get.

Thanks Colin - look very interesting and have bookmarked both.

As soon as the balls arrive, I'll start adding drawings/photos of progress.
John