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Wheel diameter/teeth for stump grinder
<SLJ Pat>
Well to make a long story short, I am making a stump grinder. Going to be running about 80-90 Hp. Makign this machine is easy enough except for one thing...

...What size do I make the wheel? What brand type of teeth to use? How many teeth? And at what RPM should the edge of the wheel be moving at (currently believe 600 rpms give or take a little)?

Currently planning on using a 24" dia 1" thickness wheel. But still not sure on tooth combinations. I have talked with one tooth manufacturer and we came to the conclusion a 32 tooth pattern would be best. Anything is do able with this. I have a full size milling machine, CNC metal lathe and numerous other metal working equipment on hand so anything is do able.

All comments welcome and allow me to thank you ahead of time

- Patrick Dowling
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<SLJ Pat>
Ok well I am going to go with a wheel speed I found on the internet. Long story short it essentially tells me I need a wheel speed of approx 400 rpms. Still interested in tooth brands and such but going to just go with one if I dotn get much response on this in a day or so.

Well thank u all much once again for replies.

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You've probably thought of this, but I always thought of the stump grinder as a giant horizontal miller. Or you could think of it as a lathe but you are spinning the tooling instaed of the work. The point is that spindle RPM is only a determiant of work feed rate... how many FPS pass your cutter(s)?

Now the best performing speed will depend on sharpness of cutters and hardness of work, in this case wood. Constant variation from job to job abs withing jobs.

So you will conttrol optimum performance with engine RPM.

So what you really need to match is the HP and wheel balance over the operating range of wheel RPM.

The story I alway remember is about the F4U Corsair, the gull-winged Grumman fighter plane. The reason for the gull wing ws that the engine was so powerful they needed a 13ft dia 3 blade prop to provide enough mass to take the engine and prop from tearing each other apart. To accomodate that diameter and provide ground clearance they had to drop the landing gear by dropping the wings down.

So wheel mass and HP are the real match to be made. You want that wheel to be vibration free at all RPMs. You want it to have enough mass to function as a flywheel and keep RPMs relatively constant through possible shock loads. And not be so massive that you waste HP just keeping it going.

If you were engineering for production, you'd build the machine over and over testing different configurations. You probably don't want to do that. So I think you want to design a system that is stable over the widest practical range of RPM so you can learn how to optimize performance.

As an example, If you were going to drive the wheel with belts like the old chippers and stump grinders you might make allowance for swapping out sheaves of differnt diametrs in your testing phase.

Take that all with a grain of salt of course. I;m a tinkerer, not an enginer.
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<SLJ Pat>
Well I will be able to adjust the wheel speed in many ways. The system will be a hydraulically driven. And the system between the hydraulic motor running the pump and the wheel will be chain based so I can change sprockets sizes to get an ideal speed with very minimal reworking. In addition to this I will be using flow regulators on all the Hyd cylinders, or combinations of cylinders, for each function. By doing this I can easily adjust side to side swing rate for example. Or any other aspect for that matter.

Wheel mass and vibration could potentially be a problem I had not looked at. Might be worth while to talking a bit to my father inlaw on this (he currently holds a degree in mechanical engineering, and is head of research and design at R&D company, essientially head engineer).

Granted the Speed is a factor, as well surface (surface of the cutting wheel) speed. I was tired the other night when I said 400 rpms. According to info I found the other night at a site that makes stump grinders I had calculated it to be 800 not 400. A VERY big difference. I had another number in my head at the time I had said 400.

Starting this project my goals were this...

- Make a machine self propelled
- Make it gate accessible (currently 34" seems to be the ending width but may vary a litle bit)
- Provide a wide wheel base which can be extended from a slim one (currently 5'8" seems to be the key) to a wide and stable one
- Minimize length unfortunatrly currently at 10 ft but think this might become as long 11.5 ft.
- Grinding depth to 24" Height to over 40" (might be as high as 50" have to verify a few parts and such before I am certain)
- Fast ground speed and adjustable as well 1/2-3.5 mph
- Wide cutting swath. At abut 90" at the moment
- Keep cost around $3000. Looks like all said and done will be more about $4-4500
- A goal I wont meet however is light weight. My best rough guess is going to be 2100 lbs. I had hoped to keep it under 1500. However, versatility and functon had out weighed (no pun intended) this goal in my eyes and so it was allowed to slip.

And Several other features I will not currently mention due to patent applying issues.

Your point Scott was a very note worthy one I will look into for certian. Another factor that is still key to to doing this is determining the cutting volume of wood *poportional to* power (hp and torque) *poportional to* rpms (surface cutting wheel speed).

I think I can play around with side to side speeds as well as depth at which I cut in on a pass. Alot of factors.

I had thought I had made allowences for how to adjust for all these different varibles but you are right. There are more than immediatly meets the eye.

I would like to thank you for your time you have spent to reply Scott. thank you much for the information and I shall go over it with a proffesional (thankfully that is as simple as talking with my fatherlaw whom I get along with like a father as is).

Thank you much, Patrick Dowling
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