Ideal diesel running speed?

JRWoodchuck · February 05, 2016, 02:47:16 PM

I am using a Kubota D662 engine to power my mill. At 3600 RPM is produces 19.2 hp and at 2700 RPM it produces 30ft/lbs of torque if I understand the spec sheet properly. What should I be aiming for with my RPM's? Talking to other people those RPM's seem high. Pretty new to this whole game and curious what your guys thoughts are on it.
Thanks!

JustinW_NZ · February 05, 2016, 03:27:17 PM

Quote from: JRWoodchuck on February 05, 2016, 02:47:16 PM
I am using a Kubota D662 engine to power my mill. At 3600 RPM is produces 19.2 hp and at 2700 RPM it produces 30ft/lbs of torque if I understand the spec sheet properly. What should I be aiming for with my RPM's? Talking to other people those RPM's seem high. Pretty new to this whole game and curious what your guys thoughts are on it.
Thanks!

The small diesels usually rev higher.
I would just follow the factory settings for idle etc..

Cheers
Justin

Ox · February 05, 2016, 06:56:43 PM

Yep, the newer smaller diesels are spun right up there and that's where they're happy. The engine manual will likely tell you that the max speed, which is governed speed, is where to set your machine at. 3600 rpm - which is the standard for many of these engines and machinery. The highest torque rating is usually somewhere in the rpm range where it sounds like it's lugging and you'll see black smoke, if this is a mechanical engine (as opposed to electrical with brains and computers) and not turbo.

bkaimwood · February 05, 2016, 07:19:43 PM

I would be shooting for 2700 RPM... Doesn't make it right, but in many applications, horsepower means squat, torque gets the job done...so I'd be shooting for the RPM that max torque is made...the lower rpm also saves incredible amounts of fuel on diesels...

dgdrls · February 05, 2016, 07:44:13 PM

Hey JR,

see if the motor has a continuous rating spec
then tune your pulley size from there to achieve the RPM you need to drive your blade/band at its required speed
with just a small increase above that to allow a small drop in RPM when sawing.

If no continuous spec I would tune just a bit higher than max torque RPM, again, to allow a bit of RPM drop
when sawing,

Dan

Magicman · February 05, 2016, 08:22:13 PM

What sawmill do you have? (Adding it to your profile helps with questions.) What does the sawmill manufacturer list for the proper RPM for sawing?

JRWoodchuck · February 05, 2016, 08:45:57 PM

Building a mill at the moment. Picked the motor up off craigslist.

sawguy21 · February 05, 2016, 10:42:00 PM

I would run it at 3600 or close to that for maximum efficiency and cooling.

Oak hound · February 06, 2016, 04:14:14 AM

Cooks has a good bit of information about band speed on their web site. If you down load their catalog, they have written a couple pages for reading about this. They also provide you with a formula for figuring your band speed. I hope that helps.

JRWoodchuck · February 09, 2016, 01:51:46 PM

I am running 18.75" band wheels with 158" cooks blades. Optimal band speed is 1020rpm if I have done my math right. So I will have to gear my motor down. Just trying to get an idea on ideal motor speed not band speed. The motor has a 6.75" pulley on the flywheel which is where I will drive my cutting head off of. So my plan is to order another 18.75" pulley for the drive side. Which will reduce my running speed 2.77 to 1. So if I run anywhere from 2800 to 3200 I'll be in the ballpark of ideal blade speed. I had just heard that diesels run at lower RPM's than that typically so I wanted to make sure that I wasn't miss reading the actual specs on the motor. I really appreciate everyones input!

Kbeitz · February 09, 2016, 03:53:21 PM

This might help you...

sandsawmill14 · February 09, 2016, 04:45:24 PM

Quote from: bkaimwood on February 05, 2016, 07:19:43 PM
I would be shooting for 2700 RPM... Doesn't make it right, but in many applications, horsepower means squat, torque gets the job done...so I'd be shooting for the RPM that max torque is made...the lower rpm also saves incredible amounts of fuel on diesels...

i was always taught that torque started the load and hp pulled it ??? :P

if it is a governed engine i would run it at wot as thats where its designed to run if you drop the rpm by roughly 1/3 (2700rpm) it will run hot if try to run at full load. if you run at wot hp is higher and torque is lower and then the load will try to slow engine down making the torque come up then the governor takes over more fuel more hp more rpm till it hit setpoint and is constantly changing to keep it right. is that little kubota water or air cooled ???

Kbeitz · February 09, 2016, 05:11:41 PM

The best way to look at torque is that it's kinetic energy stored up in a heavy flywheel.
It's a measure of the turning force on an object.
It take Hp to do that and it take HP to keep it there. Old hit and miss engines had lot of torque
because they had huge flywheels. This is one reason people liked the older garden tractor engines.
They had really heavy flywheels. Today HP is rated different than the old days. They run the engine WOT
and slam it to a stop to rate the hp. It's not continues HP. Diesel's work with higher compression
so they have a stronger rod push or more torque. The longer your tool handle the more the torque.
HP is an amount of work done in a certain amout of time. One horsepower equals 33,000 foot-pounds
of work per minute.

redprospector · February 10, 2016, 12:19:28 AM

Kbeitz, the second formula in your post seems a bit odd to me.
You said;

To find the RPM of "B"
Diameter of "A" times RPM of "B"
Divided by diameter of "B"
8x200/16=200

What seems odd to me is...If you know the RPM of "B", as indicated in the 2nd line of the equation...why are you trying to find the RPM of B? :D And the correct answer to the problem is 100. ;)

I'm not really trying to be picky, but at least you know I read your posts. ;D

Kbeitz · February 10, 2016, 02:10:05 AM

Quote from: redprospector on February 10, 2016, 12:19:28 AM
Kbeitz, the second formula in your post seems a bit odd to me.
You said;

To find the RPM of "B"
Diameter of "A" times RPM of "B"
Divided by diameter of "B"
8x200/16=200

What seems odd to me is...If you know the RPM of "B", as indicated in the 2nd line of the equation...why are you trying to find the RPM of B? :D And the correct answer to the problem is 100. ;)

I'm not really trying to be picky, but at least you know I read your posts. ;D

Wow... your right... almost... My drawing was wrong...
The right answer was to be 50 not your 100 or my 200.
You have (8x200/16=200) should be (8x100/16=50)
I've had this drawing for many years and I guess I never checked it.
I went back and fixed it.

Thanks so much for lookin into this. I'm sorry if I confused anyone.
Thats the last thing I want to do.

Ox · February 10, 2016, 06:49:05 AM

Murphy will get ya every time. I'm gonna find that sonuvagun one of these days...

It sounds like your diesel will be in its torque curve with your band in the speet spot for speed. Only way to know for sure is to try it at the ideal blade speed, then go to wide open and see if the engine likes one better than the other or if it just doesn't seem to care. These smaller diesels can be very different. I had an older Yanmar 22hp 3 cylinder diesel and it was just as happy at half throttle as full throttle. Course it was over 20 years old, the newer smaller diesels may not like that as much.

sandsawmill14 · February 10, 2016, 07:38:36 AM

my comment was based on the ford ag/industrial engines back in the early 90s when i worked for them we had to keep governors set at +/- 10% for them to cover warranty work these were 3 cylinder water cooled engines from from around 20 hp up to about 45-50 hp i dont remember the exact hp ratings but they all had the same rules. the 4-6 cyl were lower rpm but had the same governor rule so i figured the kubota engines would be about the same. but with 19 hp he is gonna need every bit of it

jrwoodchuck you said your band speed would be 1020 rpm is that the speed of bandwheel ??? if it is the rpm of the band that would be over 13000 ft per min

terrifictimbersllc · February 10, 2016, 07:55:00 AM

Quote from: Kbeitz on February 10, 2016, 02:10:05 AM

Belt needs a bit more tension :D

JRWoodchuck · February 10, 2016, 02:27:26 PM

With a 18.75" pulley that gives you roughly 5' circumference. Which in turn would be that the blade is traveling 5' per revolution. 5' x 1020rpm gives me 5100' band speed I do believe. Please correct me if my math is not correct!

ladylake · February 10, 2016, 02:54:50 PM

Your math is correct, I might shoot for 4500 fpm on the band with 19hp. you'll have more torque at the band. I'm not a fan of running a engine wide open either maybe 3200 to 3300 RPM on that engine. Steve

JRWoodchuck · February 10, 2016, 03:48:14 PM

Will do thanks!

Ox · February 10, 2016, 05:15:03 PM

Yes, I agree. 4500 is a good number to shoot for.

bkaimwood · February 10, 2016, 06:57:30 PM

I must interject with an earlier post made by sawguy21, as max rpm being the most efficient and best cooling... In lamens terms, engine efficiency is defined as an engine producing the most power required to do the job at the least amount of rpm's. Similar to what ox said about a piece of equipment he has that is rated to run at max rpm, but does the same job at half throttle. My experience has been the same, for most of my diesel equipment... It does the job at peak torque, lower rpm, and the only thing accomplished by running at full throttle is unnecessary fuel consumption... And it's significant. One of the few times it makes sense to run an engine over it job doing rpm is solely when rpm matter, like running a hydraulic pump, where increased rpm means stuff spins faster, more FLOW... Just make sure whatever your final decision is as right as it can be on your first effort, as, obviously, engine rpm has everything to do with the remaining calculations discussed...

Brucer · February 11, 2016, 01:21:15 AM

I agree.

Here's the physics.
- Force is what pulls the blade through the wood.
- Torque is the rotating equivalent for Force.
- Horsepower is Torque multiplied by Speed.

Remember, saws are designed to run at a constant speed, and there is an optimum speed for any particular type of saw. If you run a band saw too slowly, it will make waves. Run it too fast and you will dull your blades more quickly but you won't cut any faster.

So, figure out what speed you have to run your blade. Then size your drive so when the motor is producing maximum torque, it is driving your blade at the optimum speed.

That gives you the maximum cutting force at the proper cutting speed.

gms1911 · February 11, 2016, 07:37:05 AM

Brand new here. I also just picked up a kubota d662 off craigslist. Out of a Jacobson tricking mower. Water cooled 3 cylinder. If yours is water cooled then I wouldn't think it would matter what rpm you run at. I plan on running for max torque. My kubota tractor never runs hot when I plow and I am only running in the neighborhood of 2000 rpm.

When I was trying to figure my drive pulley size I found a online pulley calculator. Here's a link. You might have to copy and paste. Hope that helps.

http://www.blocklayer.com/pulley-belteng.aspx