PTO speed at low engine RPM

[lostcause]

I'm trying to figure out what my PTO speed is when the tractor's engine is running at near idle. My main question is whether PTO speed is linear with the engine speed. If my tractor (JD 770) is rated for 540 PTO RPM at 2600 engine RPM, can I assume that with the engine at near idle (800-1000 RPM) the PTO speed will be about 165-200 RPM?

What I'm doing is reworking an old cement mixer that is going to be run off the tractor PTO. My tractor is supposed to be about 20HP at the PTO, and I can't see the sense of running the tractor at full throttle when I should be able to accomplish the task with far less power. Since I have a belt drive between the gearbox and the ring gear, I can easily adjust speeds once I figure out the tractor PTO speed.

I am also wondering what the rotational speed of a cement mixer drum should be, if anyone knows.

Thanks.

 

[rambler]

Leave things the way they are, and run your tractor at idle. They already set the pto mixers up to be run at tractor idle as is. At 560rpm, you won't get any mixing done, the cement will be held on the outside of the drum!!!!

--->Paul

 

[lostcause]

Leave things the way they are, and run your tractor at idle. They already set the pto mixers up to be run at tractor idle as is. At 560rpm, you won't get any mixing done, the cement will be held on the outside of the drum!!!!

--->Paul

all that would imply that i have a functional mixer to start with, which i don't. it's been hacked apart, cobbled together, poorly repaired, and generally mistreated. the pulleys on it don't resemble anything you would see on a commercially made mixer, so i'm confident that one or both have been replaced, and i can't guarantee they were replaced with the correct size.

the mixer may also have been powered by a much older tractor that didn't have a 540 rpm pto, so they could have been changed to compensate for that. also, there is an idler/tensioner from a 1970's european car attached to part of a 4-way tire wrench welded to the frame to keep the belt tight. i don't know if this is because the belt they had on hand was too large, or whether the pulley sizes were changed.

the machine is disassembled and being changed over from a towed axle to a 3 point hitch configuration, so testing is out of the question. i figured it would be simple to get an answer as to what the rough pto speed of a tractor at idle was, but it doesn't seem to be that way. i also figured someone would know the rough speed a cement mixer drum was supposed to rotate at. wrong again i guess.

as it sat, the pto drove a 1:1 ratio gearbox which turned a 3" pulley. the 3" pulley drove a 4" pulley via the belt. the 4" pulley turned an 8 tooth pinion which spun an 81 tooth ring gear. in theory, if i turned the tractor pto at the full 540 rpm, reduced by the 3:4 pulleys and the 8:81 gears, the drum would rotate at 40 rpm. if my pto speed at idle was sub-200, i'd be looking at the drum turning about 12-14 rpm. i'm going to take a guess that a mixer drum should run somewhere between 15 and 50 rpm, but that's a lot of pulley sizes and tractor speeds inbetween.

i have to fabricate a belt guard and install a functional idler, not to mention buy a new belt. even if it was together to test out it wouldn't matter. i mix concrete so infrequently that i'm not a good judge of what speed it's supposed to be done at. i hope to get it right the first time, since re-fabricating costs time and money.

 

[Soundguy]

to answer the question.. yes.. pto speed is locked to engine rpm via ratio.

look at engine rpm when you are at marked pto speed on the tach.. now do the ratio math to find the pto speed at a reduced rpm.

soundguy

 

[lostcause]

to answer the question.. yes.. pto speed is locked to engine rpm via ratio.

look at engine rpm when you are at marked pto speed on the tach.. now do the ratio math to find the pto speed at a reduced rpm.

soundguy

Thanks, I kind of figured it was linear, but I wanted to hear it from someone else. I've been figuring on building it around a 200 RPM PTO speed, which would be about 1000 RPM on the engine. By going just a little above idle it will allow me to tune the speed down slightly if I ever need (165 PTO @ 800 engine) while not having to run the tractor full bore for a trivial task.

 

[rambler]

Just replied to your other thread on this, I got a 'factory made' pto cement mixer, think it was designed for an N, will be late Friday or Saturday before I get to it during daylingt tho.

Every tractor idles different speed, so it's hard to answer your speeds question _exactly_. Getting the pulley & cogs count from mine might help you tho.

Mixed up a fair amount of mud to fix cracks in my rock barn wall foundation. Worked well.

--->Paul

 

[bcp]

Bunches of mixers at 32 rpm:
Concrete Mixer

24 to 27 rpm:
Concrete Mixers | Mobile Concrete Mixer | Portable Concrete Mixer | Small Concrete Mixer | Cement Concrete Mixers

20 to 22 rpm:
http://www.shriconstructionequipments.com/concrete-mixers.html




78 rpm:
[ame]http://www.youtube.com/watch?v=bSOn5gQFDpE[/ame]

Harbor Freight 20-36 rpm:

 

[Baby Grand]

Way to post, bcp!
Just awesome.

 

[RaydaKub]

It's been a long time since we used a mixer (maybe 35 years?), but I would have guessed that each revolution would have been 1 1/2 to 3 seconds long, so that would mean 20-30rpm. That matches the advertisements bpc posted.
If it goes too fast, you won't get any mixing action at all, just stationary mud that rides along the outside.

However 78 rpm might be an exception to that rule. :thumbsup:

 

[rambler]

My pto mixer has the 1-1 gearbox, then a 5 inch to 8 inch veebelt pulley, and the cogs is a 8 cog to 95 cog rim.

--->Paul

 

[Jerry/MT]

I'm trying to figure out what my PTO speed is when the tractor's engine is running at near idle. My main question is whether PTO speed is linear with the engine speed. If my tractor (JD 770) is rated for 540 PTO RPM at 2600 engine RPM, can I assume that with the engine at near idle (800-1000 RPM) the PTO speed will be about 165-200 RPM?

What I'm doing is reworking an old cement mixer that is going to be run off the tractor PTO. My tractor is supposed to be about 20HP at the PTO, and I can't see the sense of running the tractor at full throttle when I should be able to accomplish the task with far less power. Since I have a belt drive between the gearbox and the ring gear, I can easily adjust speeds once I figure out the tractor PTO speed.

I am also wondering what the rotational speed of a cement mixer drum should be, if anyone knows.

Thanks.

There is a fixed ratio between engine speed and the pto speed.

 

[SSdoxie]

I have never measured my electric mixer but reading this post I was guessing it ran about 30 RPM, which BCP verified in his post. Your PTO ratio of 540 @ 2600 is .207:1 so at 1000 RPM figure about 7 to 1 PTO to drum ratio to get 30RPM drum at 1000 engine RPM. May want to go slower ratio yet then have availblity to rev the engine if more speed is desired. As stated earlier too high of RPM it won't fix, won't fall off the padels at top of the rotation. Too slow will still mix just take longer to mix up good.

 

[zzvyb6]

If you are going to hang the mixer off of the 3pt hitch, be sure to add a LOT of weight to the tractor's front weight bar, better if you have a full loader bucket. My 1070 equiped with a 1/3 yard mixer and a full load of concrete and water will bounce the front wheels off the ground when traveliing to a site. Its good to start the mix off at idle because the powder will flop around and can choke you. But when you are all filled and want a good mix and no lumps, I run it at full rpm. You will also want it moving very slowly when dumping the cement otherwise it will fly all over the place.

Hydraulic dump is VERY handy. I use one side of the loader's curl circuit to run the dump cylinder. Concrete is FUN to work with. I make up a new slab, sidewalk or planter base at every opportunity. I don't bother with the separate gravel, cement and water mix anymore, either. I get the 50 or 80 lb Just-Add-Water bags, dump in a full bucket of water and head out to the form(s). Use all my old crappy cheap tools for reinforcement bar. Even my dogs love to walk across fresh cement !:laughing:

 

[RaydaKub]

Even my dogs love to walk across fresh cement !:laughing:

Oh man, please don't let them do that. A good friend of ours is the resident expert on treating burns at the Mayo Clinic. She had a patient a few years ago who worked in concrete all day long. I just recalled now that he had been kneeling in the wet concrete most of the day troweling it off. He was in for 3rd degree chemical burns. The dogs don't know any better.

But now you do.

 

[zzvyb6]

Thank you for that good advice. I never would have guessed it, but they (as well as YOU) can get a nasty alkaline burn (treat with mild vinegar). In the dogs case, they could rub their paws near their eyes and ears and then you have a serious chemical burn problem on your hands with a very poor outcome.

 

[lostcause]

Thanks for the input everyone. Based on what bcp posted, it looks like low 20's to low 30's is a good rpm range. Since I'm hoping to run mine at around 1000 rpm on the tractor, which should equate to just over 200 rpm at the pto, the original pulley ratio of 3":4" would have yielded 15 rpm, which looks to be a little too slow. If I flip the pulleys and go with a 4:3 ratio the drum speed should be just over 27 rpm, which looks to be in range. Idling the tractor at 800 rpm would put the drum speed at about 22 rpm, so I think I have my starting point for the gearing.

Thanks again everyone. I'm going to abandon this thread, but if anyone is interested in seeing the project as it progresses, I'm going to be updating the thread in the build it yourself section of the forums.