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dratkinson

Snowthrower: Maximum Speed?

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dratkinson
All, I have a question. Baseline information and the genesis of the idea. There did not seem to be that much wind coming off of my snowthrower auger. My little Sears 2-stage snowblower seems to be moving much more wind than this 1-stage snowthrower. So, since I've been sitting around here with these idle hands, waiting for some measurable snow, and was just wondering what would happen if...I took my baby Alice (B-206, 10 hp b&S i/c, 32" no-name snowthrower) and ... I've been seeing a lot of posts talking about changing pulley sizes and how to compute the new belt size required. I ocurred to me that if I used the same pulleys...but in a different order..., then the belt sizes should stay the same. So..., I swapped the 3" drive pulley and 5" driven pulley on my no-name snowthrower....to be now 5" drive and 3" driven. Should spin a little faster now. When I fired it up to try it...it really screamed! No, really...the chain drive from the right-angle drive (3" sprocket on the shaft) to the auger (5" sprocket on auger) was really making a loud noise. So I measured all the sizes of all the pulleys and sprockets, dropped them into a spreadsheet and asked the question: "..if the input engine speed is 3600 rpm, what is the effective pulley ratio, and what is the new auger rpm?". Answers. The effective combined pulley/sprocket ratio is now 1:1, so the auger is turning at 3600 rpm, and the right-angle drive output shaft is turning at about 6000 rpm (5/3 * 3600). Hmm... So the noise from this combination.... 1. Is there a maximum chain speed law...that I may be violating? Honest (club) officer, I didn't see the sign. 2. Will this combination quieten down when it is full of snow? 3. Should I wear earplug? 4. Is there something I have overlooked? Or should I put some kind of schrapnel shield around the snowthrower? Oh, just for grins, I computed the original auger speed...it was about 1297 rpms. I was figuring that if the 3" pulley was driving a 4" pulley (not 5"), the auger would run at close to 2000 rpms. 5. Is there a maximum safe speed for a snowthrower? Could you all send me some snow so I'll have something to play with? Surely you could spare just one little 12" storm...you would never miss that little bit...you have so much... Really do enjoy all your pictures of the boys and toys playing in the snow. /r David Denver

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Kent
Well, the specs for an original snowblower showed 1250 RPM max, assuming all of the Simplicity single belt blowers are essentially the same... http://www.simpletractors.com/attachments/snowthrower_specs.htm Sounds VERY dangerous to me....

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Agricola
I think you are right on that being dangerous. Let me do some quick math. 3600 RPM * 5" gives you about 4710 feet of chain per minute That would be about 53.5 MPH of chain speed. That doesn't sound too bad but consider the auger itself. If that has a diameter of 20 inches or so then the speed it fires out a rock would be over 214 mph. I don't think I would want to be hit by that. Here is my math... RPM *2PI * radius divided by 12 for feet divided by 5280 for miles times 60 for hours. Did I do the math correctly?

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PatrickE
Yup, way to fast for a chain, have to switch it to a belt and pulleys, might as well put some good heavy duty roller bearings on the auger shaft too! I also agree, you could take out a neighbors window from 200 yards! You need to make sure that you are actually turning 3600RPM, when I bought my Broadmoor, the way they had the throttle cable it was only running 2700RPM max. I wish I had some snow to send you, we finally got 2 inches this winter.

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maxtorman1234
quote:
If that has a diameter of 20 inches or so then the speed it fires out a rock would be over 214 mph. I don't think I would want to be hit by that.
I dont think I would want to be hit with that either, that could easily take out a window and seriously hurt someone. Im guessing 2000 would be decent looking at previous posts.

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BillC
I would assume the snowblower 1250 max. RPM is calculated when the engine speed is at 3600 max. RPM. The original pulley ratio is 0.60:1, 3"/5". By changing the pulleys around the ratio was changed to 1.67:1, 5"/3", increasing the snowblower max. speed from 1250 RPM to 3480 RPM, 2.78 times. If you were to change the 3" pulley to 4", the ratio would be 1.25:1, 5"/4", and the snowblower max. speed would be 2604 RPM. If you were to use both 3" pulleys, the ratio would be 1.00:1, with a max. speed of 2083 RPM.

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Agricola
Remember to silicone the chute and blades and the snow should just fly through the blower as designed by the engineers. I agree that the engineers can often make small mistakes and when I was a mechanic, I often had a chance to "tune" those mistakes. But one has to be careful when speeding things up beyond their designed ratings.

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MPH
Really think your looking for personnel injury speeding a snowblower up that much. They're not machined that finely or balanced for such high speed. Look at how a crankshaft is made and compare it with your auger. That auger is pretty crude. Besides, I think you's have more snow being thrown out the front with more speed. MPH

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acjohn
Been there, done that. In theory, you will get that auger speed. In reality, the engine won't handle the inertia load. Once you put snow in it, the engine will bog down. I have a 410S with a 42" 700 series blower. I changed sprocket ratios to increase auger speed. Threw snow great if there was no more than 1" or 2". This fall I backed it down from a 22T on the auger to 18T. It will handle 8" of snow in 2nd gear without bogging the engine. I think I have it pretty close now.

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BillC
To answer your original question regarding belt and chain drive speeds. In general, belt drives are applied where the rotational speeds are relatively high, as on the first stage of speed reduction from a motor or engine. The linear speed of a belt is usually 2500 to 7000 ft/min. A speed of 4000 ft/min is generally ideal. Chain drives are typically applied at lower speeds, with the consequent higher torques.

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