Bosch Rotak 32R Lawnmower Pulley/Fan - Version 2.3

by pittance Apr 19, 2015
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You have two versions here now, the single piece, and the two piece attached by 3 bolts. Which one is the preferred one? How did it last, was the June 21 death which version, and how did it die?

Thanks for the work and testing! I don't have any printing capability, but I am interested to test this, would it be feasible when ordering a print...

You need both parts. The pulley is printed separately from the fan and they bolt together with the three M3 bolts. The fixing so the shaft is interference so you have to tap it into place and it won't come off - tolerances on the hole need to be right for that and it will take drilling out to achieve.

The latest version was the one that finally died but I've been through about two previous versions that just wore out. The final end was down to something that might have killed the mower even if it had been the stock pulley (it jammed on a piece of wood and the idler bearing assembly was damaged).

Thank you! Appreciated!

I have had two of these (on separate yards) and had the bearing support damage on one of them. Seems to be even more prone to failure part than the pulley. Subsequently it ate the belt... and spilt it all over the rest of the machinery.
The other one had, due to incorrect fan fitting, touching surfaces heat melting, and finally fan slippage on the axis. That is why I am a bit worried about the 'interference fit' approach.

I know what you mean - I really, really wanted to get away from the interference fit after the first version but none of the clamped ones worked anywhere near as well. I thought about grinding a flat on the shaft and using a screw to hold it but I guessed that might just end up with a groove in the shaft when everything slipped anyway...

I never tried ABS or nylon though and those might have been a better choice in any case

that essentially looks like a washing machine motor , like a `/1 2 or 3/4 hp motor with the plastic enclosure to keep the water out ..
how much u wanna bet maytag bosch and whirlpool all get this motor winding from the same source ?
nice design replacement ! necessity is the mother of invention adn i'll bet u didnt liek the price or shipping time/cost for that new flywheel fan/gear, if it was even orderable .....

Could very well be the same type of motor used elsewhere, I checked other mowers (there are many brands that have essentially the same guts, I discovered) but I never thought to look for other appliances...
I also discovered that you can buy the motor/pulley assembly, from stock, as a spare (free postage too). However when I checked it cost almost exactly twice the price of buying a whole new lawnmower which is stupid and makes me wonder why they bother keeping the stock at all

Thank you, I have the same problem, but it lacks some of the piece in the file ?

You're right, I must have forgotten to upload the fan section. I can't fix it now because I'm away but if you download the. scad file and openScad you might be able to render your own before I get back :) In case that doesn't work for you I'll try to do it after the weekend anyway...

Hmmm, you said you printed this in PLA which doesn't like heat very well so you will probably be lucky if this holds up even after a few uses.

ABS or NYLON would be the way to go.

I know, but I don't have any ABS or Nylon and I had to do something before the lawn got knee deep :)
This was a prototype really, mainly intended to check if the geometry was correct. If it doesn't die after a couple of weeks I'm going to open it up again and see how it's getting on. With the airflow it has going past it I hope it won't get too hot over most of the surface but I could easily see the teeth failing from local friction heating from the belt. To be honest even if it does only hold up for a few uses that is still around a month of use and better than buying a whole new mower; then I'd probably redesign for easy replacement of the part(s) that fail most often...


Thanks for sharing the CAD,
could you tell us how is it doing so far?


Still going; it's done the lawn at the front and back of the house each week since I made it back in April.

I took it apart a few weeks back and found no significant wear, it was oiled with a couple of drops of Teflon bike oil when I installed it and that seems to have either helped or at least not to have made it worse...

It probably won't last very well compared to the original material but I'm already happy with how long it has lasted so far given how expensive the alternative was.

In a way I'm disappointed that it hasn't failed yet as I was hoping to see the failure mode to make it more robust :)