Stump grinder questions

[Mysfyt]

Would like to build a stump grinder for my tractor and if I do, it will be the first stump grinder I've ever operated. So there will be a lot of basic questions to ask.

The first question is, why don't any of them (as far as I've researched) have a telescoping boom to advance the cutting wheel. They always have the tractor itself advance, which must be kind of a pain to reset on bigger stumps.

Does a larger wheel 'bounce' less? Seems this way on the videos.

For the sake of something to go off of, how many teeth should there be on a 22" wheel? Is it beneficial to have some teeth lower down on the wheel?

I believe my tractor has 27HP at the PTO. Would a 22" wheel be too big?

Looking forward to your replies and there will be more questions as we go.

 

[Jim Timber]

The larger the wheel the more mass (good), the more leverage it has against the grinder frame too (not so good). No free lunch!

I'm actually going to be running mine some more in the next couple days, so I'll try to get more video on it and explain some of the design characteristics I used.

Without power down-force, the grinder will lift when enough resistance is met. Weight in your frame is a benefit. The more the better.

I thought about doing power extend-retract and having a splined shaft to power the head, but the added cost and how I had no idea how my grinder would perform precluded my doing it. There are commercial grinders which have this feature. Repositioning on stumps isn't that big of deal.

I'll answer any questions you have.

This video is uncut. 6 minutes for a 16" DBH red oak stump (fresh), and when I get my hydraulics installed for real, I'll have more depth available by tilting the grinder downward. As things are now, I use my single rear SCV to power a twin spool valve to run my grinder. I'll be plumbing that valve into the tractor permanently and also adding another valve for my top/tilt so I'll have more functionality.

 

[dickfoster]

Would like to build a stump grinder for my tractor and if I do, it will be the first stump grinder I've ever operated. So there will be a lot of basic questions to ask.

The first question is, why don't any of them (as far as I've researched) have a telescoping boom to advance the cutting wheel. They always have the tractor itself advance, which must be kind of a pain to reset on bigger stumps.

Does a larger wheel 'bounce' less? Seems this way on the videos.

For the sake of something to go off of, how many teeth should there be on a 22" wheel? Is it beneficial to have some teeth lower down on the wheel?

I believe my tractor has 27HP at the PTO. Would a 22" wheel be too big?

Looking forward to your replies and there will be more questions as we go.

The reason they don't telescope is because they are PTO driven and the PTO shaft can't stretch.

 

[Jim Timber]

The reason they don't telescope is because they are PTO driven and the PTO shaft can't stretch.

The PTO to implement geometry is limited, but there are ways around that.

 

[Mysfyt]

Hey Jim! Was hoping you would chime in on this.
What is the diameter of your wheel and how many teeth do you have on it? How long does the boom extend from your 3PH? I've watched some videos of stump grinders and some of them will do a nasty 'dance' if you over feed them, which would be hard on the tractor. I like how smooth yours operates!

 

[Mysfyt]

The reason they don't telescope is because they are PTO driven and the PTO shaft can't stretch.

I have a connection with a company that builds drive shafts, so I think I can work around this.

 

[Jim Timber]

I have a connection with a company that builds drive shafts, so I think I can work around this.

By any chance, could you source a H yoke for a series 7 cross bearing? I'm pretty close to making one out of two inner yokes back to back, but if I could just buy it, that'd be better. I have some vibration at max travel to the left side of the tractor that I want to resolve (too cheap to buy a CV joint for it).

My wheel is 22" iirc. It's 3/4" plate and has the leading hole of the pockets set on 24 degrees from each other; with the exception of the inner-most 4th tooth because those were too crowded for my liking, so I pushed them over one bolt spacing.

The toplink geometry on my grinder isn't standard. I intended for the grinder to be pulling on the link when trying to raise itself. The I-beam feet are another stability enhancement. More leverage to hold against twisting when the cutting head "bucks."

I'll take some measurements for you when I get out there. I'd spent a few months watching all the viedos I could find on grinders and still screwed up. Were I to build another, I'd have it cut so chips are pulled towards the tractor. Much smoother operation that way.

Mine's smooth because of a steady hand. If I feed it too hard it'll shake the tractor too.

24 teeth

 

[Mysfyt]

Good info!

I'll forward your request on to the engineer.

 

[dickfoster]

The PTO to implement geometry is limited, but there are ways around that.

Would it be a better design to go with a hydraulic motor rather than a PTO mechanical drive. Or maybe a PTO pump driving a motor which drives the cutter. That way you'd have total freedom of movement. I know slip splined shafts tend to wear like erasers the more they are extended and off hand it
seems like you'd get the gearbox back in the trade anyway. Not much but it's better than nothing.

I'm still trying to figure out why these things cost so stinkin much. They cost like backhoes but do so much less and are so much less complicated. Is it just marketing and economy of scale?

 

[Mysfyt]

Would it be a better design to go with a hydraulic motor rather than a PTO mechanical drive. Or maybe a PTO pump driving a motor which drives the cutter. That way you'd have total freedom of movement. I know slip splined shafts tend to wear like erasers the more they are extended and off hand it
seems like you'd get the gearbox back in the trade anyway. Not much but it's better than nothing.

I'm still trying to figure out why these things cost so stinkin much. They cost like backhoes but do so much less and are so much less complicated. Is it just marketing and economy of scale?

I'm open to the idea. Going to need some help with sizing the pump and motor, unless the tractor hydraulics would have enough GPM to run it. Next question: would I need a cooler for the hydraulic fluid?

I'll take a guess that the liability to manufacture and sell these to the public is included in the price.

 

[Fallon]

Hydraulics are less efficient than a PTO shaft & more expensive. Most tractors top out at around 10gpm @ 2,500psi, which translates into a little over 17hp. So most tractors don't have enough flow, which means needing a PTO powered hydraulic pack, which is $1-2k.

 

[Jim Timber]

The problem with hydraulic rotation is flow. I have 17hp at full pressure, but only 11gpm of flow. As soon as you want to move the cutter, you're peeling off flow from the teeth and losing power in the cut.

With PTO power, I have 58hp at the teeth, and I have full motion control over it. An add-on hydraulic pump off the PTO was another consideration, but then you're talking about several gallons of fluid, another cooler, and you still have the same available power at the teeth.

I have $500 in teeth and pockets.

 

[dickfoster]

Hydraulics are less efficient than a PTO shaft & more expensive. Most tractors top out at around 10gpm @ 2,500psi, which translates into a little over 17hp. So most tractors don't have enough flow, which means needing a PTO powered hydraulic pack, which is $1-2k.

Well for the huge price tags you'd think there is plenty of room in the budget for that. Especially if you're building more than onesies and twosies. So far they look like the highest cost implements going with the least utility.
As far as liability aspects as one said, no more than a backhoe or anything else you stick on a tractor.

Perhaps I'm overlooking an opportunity? Nah don't go there, I'm retired and intend to stay retired.

 

[Jim Timber]

Small market, high materials cost, and slow moving once built.

My friends asked if I was going to start making these for sale; Nope, I'm going to start grinding stumps for hire.

 

[dickfoster]

The problem with hydraulic rotation is flow. I have 17hp at full pressure, but only 11gpm of flow. As soon as you want to move the cutter, you're peeling off flow from the teeth and losing power in the cut.

With PTO power, I have 58hp at the teeth, and I have full motion control over it. An add-on hydraulic pump off the PTO was another consideration, but then you're talking about several gallons of fluid, another cooler, and you still have the same available power at the teeth.

I have $500 in teeth and pockets.

Yeah no matter what you have only the power out that you have going in minus a bit. Simple physics and no math required.

They say the smaller Worksaver can work with PTO power as low as 22HP. Still it's $4700. A Woods TGS50 is supposed to work on even smaller tractors but still costs about $3600. I assume the smaller units take much longer to do the same work. The larger ones take more PTO power and cost more too, much more in most cases. Your's would likely retail in the 5 to 6 grand range. For such simple machines with so few parts it just seems too high to me.

I know you must have knocked yourself out building your very nice unit, Jim. However if these things cost what they should, I expect you would likely have plunked down your money and bought one.

I expected them to cost pretty much what a brush hog does plus maybe the cost of the swing cylinder. What else is there? There must be something I'm not seeing, as you've built one, maybe you know. Are they charging a premium simply because stumps are so ornery?

I wish for the days of good ole dynamite that you got at your local hardware store.

 

[dickfoster]

Small market, high materials cost, and slow moving once built.

My friends asked if I was going to start making these for sale; Nope, I'm going to start grinding stumps for hire.

Well I'd hire ya and pay in beer but you're too far away. LOL

I thought stumps were one of those universal markets. Well I guess you wouldn't expect to sell many in the antarctic but everywhere else has trees and trees make stumps.

 

[Mysfyt]

I was thinking along the lines of a boom that would extend 12". Having never operated one, would this be significant enough to mess with?

 

[Jim Timber]

Beer doesn't pay the mortgage, and my beer is $2 a bottle. I wouldn't load the tractor for less than $250.

I have under $2k in my grinder, and it was a fun build. I don't think I'd buy one if I were to do it over.

 

[dickfoster]

Beer doesn't pay the mortgage, and my beer is $2 a bottle. I wouldn't load the tractor for less than $250.

I have under $2k in my grinder, and it was a fun build. I don't think I'd buy one if I were to do it over.

I said beer not pee in a bottle.:laughing:
Still you'd lose money getting here even at $250. Nice trip though. Lots of people come here and spend their vacations.

 

[Jim Timber]

$250's to get me to leave the property. You'd be better off buying the grinder for $6K. I have a CA environmental surcharge of $20k.