DIY Fellerbuncher

[northforker]

Thanks Snowstorm. I'll look into the Rexroth valve. The saw seems to have plenty of power. Bear in mind that I'm not cutting down 20" hardwood or anything, just up to about 14" softwood. The aux. high-flow hydraulics on my machine are rated for 3000 PSI, but I'm sure I never get close to that. The saw is designed to cut mostly with angular momentum, just a disc weighing a couple of hundred pounds spinning at nearly 1000 rpm. By the time the disc start to lose momentum, I'm already through the tree. I use small teeth (1-1/8") for a relatively narrow kerf too which cuts down on the power requirements.

rexroth made load sensing pressure compensatered valves  valmet used them. with an open center gear pump. am surprised you have power enought with only 25gpm. what psi are you at?

[customsawyer]

Nice looking work. You certainly do fine on the fab work IMHO.

[sjfarkas]

Nice job.  I like your ingenuity.  I wish I had time to build attachments for skid steers.  A bar saw would be cool too.

[John Mc]

rexroth made load sensing pressure compensatered valves  valmet used them. with an open center gear pump. am surprised you have power enought with only 25gpm. what psi are you at?

Wouldn't the flow rate just affect the speed? I'd guess the torque would be more a function of pressure.

[snowstorm]

rexroth made load sensing pressure compensatered valves  valmet used them. with an open center gear pump. am surprised you have power enought with only 25gpm. what psi are you at?

Wouldn't the flow rate just affect the speed? I'd guess the torque would be more a function of pressure.

well sort of. on a cyl. the more the gpm then it should be faster. with a hydr. motor a little different. lets say you have a pulp loader with a 25gpm pump 2100psi. the main boom will lift a lot. but the bucket rotator dose not have a lot of turn power. most full size hot saws run what 70gpm??? at 4500psi???. at one time i had a morbark shear 14" rapid buncher it stood up well worked good and was happy with 25gpm. there used to be quite a few around here

[northforker]

well sort of. on a cyl. the more the gpm then it should be faster. with a hydr. motor a little different. lets say you have a pulp loader with a 25gpm pump 2100psi. the main boom will lift a lot. but the bucket rotator dose not have a lot of turn power. most full size hot saws run what 70gpm??? at 4500psi???. at one time i had a morbark shear 14" rapid buncher it stood up well worked good and was happy with 25gpm. there used to be quite a few around here

It's all a matter of scale. Let's look at it this way, a Quadco C series 52" disk (their smallest) weight with teeth and holders is 604 lbs. My 36" disk with teeth is ~ 200 lbs. We can calculate the moment of inertia (discs' resistance to change in rotation) with the formula 1/2*mass*r^2. The Quadco's moment of inertia works out to be ~1409 lbft^2 whereas my disc's moment is only 225 lbft^2. The Quadco disc's moment is 6.26 times greater than mine. Now, given that torque=moment of inertia*acceleration, it follows that to accelerate either disc to any equal speed requires the motor driving the Quadco disc to supply 6.26 as much torque as my motor, and that much more torque to keep the disc spinning at a constant speed when encountering any resistance during cutting. So the big hotsaws require much more power and torque just to get them up to speed compared with mine, this is before anything is cut.

Obviously, the moment of inertia works in the larger saws favor as once that sucker is spinning, it's going to take that much more cutting resistance to slow it down. Once my little saw starts bogging down, it will rely more on the torque of the motor as opposed to disc momentum. That's why if I scaled it to cut let's say 20" trees it probably would not work well - I wouldn't be through the cut before the disc lost momentum. I would probably have to stop halfway through to let the blade speed up again. However, for the small timber I'm working with, softwood up to 14" or so, this hasn't been an issue so far.

Thanks again to everybody for the comments. Have a Merry Christmas and Happy sawdust-filled New Year!

[snowstorm]

all the math makwes my head hurt. i know the vp at quadco. interesting guy

[northforker]

Yeah, mine too. I was hoping someone would check it for me! What a cool job it would be to work at a place like Quadco. Imagine getting paid to do this stuff.

all the math makwes my head hurt. i know the vp at quadco. interesting guy

[John Mc]

Northforker -

I believe those moment of inertia formulas only work if all of the mass is concentrated right at the rim of the disk. To find the true moment, you have to do integration (integrate as r goes from 0 to 26" for the Quadco disk). It's been too long since I've had to do that to even attempt it.

Also, you may be missing a time variable in your torque calculations: "to accelerate either disc to any equal speed" in the same amount of time...
With identical torque, if you were willing to wait a whole lot longer for the Quadco disk to come up to speed.

The last time I dealt with this stuff was a couple years out of college (and I probably had to look it up then), so I may be all wet on this...

[northforker]

 Thanks for checking John! Nope, it's not that complicated. Start here. Moment of inertia for a point mass is just the mass multiplied by the distance between the point and the rotational axis squared, that is to say I=M*r². The same equation can be used for an infinitely thin hollow cylinder with mass M with radius r, no? Okay, one step further. Let's suppose we have a hollow cylinder with a finite thickness rotating about its axis. It's moment of inertia will be the mass of the cylinder multiplied by the radius of the average thickness of the cylinder or I=1/2M*(cylinder's inside radius² + cylinder's outside radius²) or I=1/2M*(ri²+ro²). Okay? Now last step, let's look at a solid cylinder (a disc in our case). Let's take the last formula and substitute "0" for r_i since our cylinder is no longer hollow. That leaves us with I=1/2M*(0+r_o²) or as I put it earlier I=1/2M*r²  .

Yes, you are exactly right about the time variable that is what I meant to imply "in the same amount of time." There's no doubt that I could get the Quadco disc up to speed eventually, but life is short. Plus, what would I do once I cut through a 20" tree grasped by my little ASV loader... ? Okay, enough geek stuff for 2011 already.

[Ron Scott]

Northforker: Are you located near Polebridge, MT?

[northforker]

Yes Ron, pretty close. My home is south of P'bridge and have a cabin north of there. Are you familiar with the area?

Northforker: Are you located near Polebridge, MT?

[barbender]

Wow, you fellas get talking about moment of inertia and all, I have to tap out My wife and I went to NW Montana on our honeymoon back in '98. We stayed at a B n B in Eureka. I was amazed at all the logging and mills out there at that time.

[northforker]

You'll see a lot less logging and mills up there if you were to see it now. Stimson pulled out of the old Libby Mill in 2003 I think. What was left burned to the ground in 2010. Owens and Hurst in Eureka closed some time ago as well. The area ran out of timber sales and trucking in trees from Idaho was too expensive. The American mill in Olney shut down too as did Trout Creek over in Thompson Falls. I'm sure there are others that I forgot about but needless to say there's hard times for Lincoln County now.

Wow, you fellas get talking about moment of inertia and all, I have to tap out My wife and I went to NW Montana on our honeymoon back in '98. We stayed at a B n B in Eureka. I was amazed at all the logging and mills out there at that time.

[Ron Scott]

Yes Ron, pretty close. My home is south of P'bridge and have a cabin north of there. Are you familiar with the area?

Northforker: Are you located near Polebridge, MT?

I've been to Polebridge a few times and out to Bowman Lake, etc.so know the area some. A neat place. There have been several forest fires in the area and my son Todd lived in Whitefish as a fishing and rafting guide on the Flathead and worked at Big Mountain. I also have some good  friends that live in Whitefish and Kalispell.

My son Todd and his wife live in Bozeman now. He and his wife were here over Chritmas and just left here today.

[northforker]

Ron, Your son did a fine job of pairing his interests with geography. Smart kid. We had big fires up here in 2001 (Moose) and 2003 (Wedge,Robert). 2003 was a bad year for us but could have been a lot worse, The Wedge fire started a few miles from our cabin and was about a mile away when we went up and evacuated what we could and brought it home and put the stuff in the garage. Five days later, the Robert fire started and came within 1/4 mi. from our house on its initial run. We had to evac in a hurry. It's not a good feeling looking in the rearview mirror and wondering if your house was up in that cloud of smoke. Tough summer as the fires started early and burned nearby for a couple of months. Both our home and cabin survived thanks to the work of the firefighters and a little luck in wind direction.

Give me a holler if you make it out this way again.