Screw Type Log Splitter
- Thread starter BillyBoy
- Start date
- Views: 61232
Eagleview
Veteran Member
Willl , That's probably one of the most dangerous thing's i have ever seen . With no way to shut the PTO down from where you are working , anything could happen 
.
.
Slackdaddy
Gold Member
Brad_Blazer
Veteran Member
You just had to ask! I just wasted 10 minutes figuring it out!
Let's say the screw diameter increases 1/4" per turn and splitting force is 10 tons.
20,000lb x 1/4" divided by 12 inches/foot = 417 ft-lb of work per turn.
Imagine a 1ft lever turning the shaft. It will travel 6.28ft in one turn.
417/6.28 = 66.31lf of force on the lever which means 66.31 ft-lb of torque. Pretty nice!
What about friction? Let's say the screw diameter is one inch and the friction factor is 0.5. The drag force of 20,000lb x 0.5 moves a distance pi inches or 0.26 feet. The friction work comes out to 2,618 ft-lb. Divide by 6.28 like above and the torque to overcome friction is 417ft-lb. (not so nice!)
Luckily the biggest force when splitting happens when the diameter is small!
Feel free anyone to check my math/logic. The numbers sound about right. If it wasn't for friction you could just about hold the log to keep it from turning (not that you would want to!)
A friend of mine bought a used 3-pt Unicorn splitter some years ago and I helped him split some wood with it with his Kubota at idle. A few logs snubbed it and a couple spun. Exciting stuff!
J_J
Super Star Member
- Joined
- Sep 6, 2003
- Messages
- 18,952
- Location
- JACKSONVILLE, FL
- Tractor
- Power-Trac 1445, KUBOTA B-9200HST
Although your math is probably correct, I don't think you answered my question. What I was expecting was something like this. Based on the number of threads, and a cone base of 8 in diameter, and an rpm of 540, gives a force of so many tons.
You started out with 10 tons, where did that come from.
The friction would decrease as soon the log starts to separate.
I would think the most friction and the most torque would be in the first several inches of the screw type splitter.
I don't want to argue about this, I just want to know. how they compare to a hydraulic log splitter.
Otherwise, how does the splitting force compare to say a 20 ton splitter?
You started out with 10 tons, where did that come from.
The friction would decrease as soon the log starts to separate.
I would think the most friction and the most torque would be in the first several inches of the screw type splitter.
I don't want to argue about this, I just want to know. how they compare to a hydraulic log splitter.
Otherwise, how does the splitting force compare to say a 20 ton splitter?
Brad_Blazer
Veteran Member
Hi J.J.,
All of the "givens" in my calculation were assumed. Force really relates to torque and not RPM but RPM does let us convert HP to Torque. In my example above the total torque was about 480ft-lb which requires about 50hp at 540RPM. My 1/4" per turn assumption would require 32 turns to reach a diameter of 8". Check out this closeup:
http://www.hycrack.co.uk/images/hycrack_home2B.jpg
They use a smaller pitch at the tip where the splitting force would be highest.
My 10 ton value was an assumed spreading force to split a log. Hydraulic splitters have a nice shallow blade angle but with friction the spreading force is probably similar to the rated pushing force.
There are lots of big assumptions here but it looks like it takes the spiral splitter about 5 PTO HP per ton of splitting force. Assuming a diesel tractor has a flat torque curve, a tractor with enough rated horsepower should be able to run the splitter at any speed.
Now I don't know how many tons it really takes to split a log but my guess is typically less than 10. My 3ph hydraulic splitter rates about 15 tons and it doesn't seem to slow down when it cuts into an oak burl across the grain. One big advantage of a hydraulic splitter is the knife action which cuts through the strings, etc. Just like when using a Go-Devil, squirrely, stringy wood grain might be something of a pain on a spiral splitter.
Brad
All of the "givens" in my calculation were assumed. Force really relates to torque and not RPM but RPM does let us convert HP to Torque. In my example above the total torque was about 480ft-lb which requires about 50hp at 540RPM. My 1/4" per turn assumption would require 32 turns to reach a diameter of 8". Check out this closeup:
http://www.hycrack.co.uk/images/hycrack_home2B.jpg
They use a smaller pitch at the tip where the splitting force would be highest.
My 10 ton value was an assumed spreading force to split a log. Hydraulic splitters have a nice shallow blade angle but with friction the spreading force is probably similar to the rated pushing force.
There are lots of big assumptions here but it looks like it takes the spiral splitter about 5 PTO HP per ton of splitting force. Assuming a diesel tractor has a flat torque curve, a tractor with enough rated horsepower should be able to run the splitter at any speed.
Now I don't know how many tons it really takes to split a log but my guess is typically less than 10. My 3ph hydraulic splitter rates about 15 tons and it doesn't seem to slow down when it cuts into an oak burl across the grain. One big advantage of a hydraulic splitter is the knife action which cuts through the strings, etc. Just like when using a Go-Devil, squirrely, stringy wood grain might be something of a pain on a spiral splitter.
Brad
HI Randy. My Name is Garry Doney and I would love to have that Stickler log splitter. If you could send me the cost to ship it to 2907 Skeena St Terrace BC V8G3K3 Canada. I will send you the money. I realize the danger involved. Thanks again. Garry Doney