Author Topic: Model Woodsplitter  (Read 20008 times)

Offline Brian Rupnow

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Model Woodsplitter
« on: January 29, 2015, 04:29:26 PM »
As far as  I am able to determine, no one has built a model wood splitter. A google search on wood splitters show two main types, either hydraulic (which are not suitable for a model, in my opinion), and electric screw type which might hold some promise.  Then of course there is the cone shaped threaded splitter which bolts to a tractor wheel and screws itself into a block of wood, bursting it to split it, and the heavy revolving flywheel with an axe head mounted on it, which looks like a total suicide machine. I have seen one example of a steam driven wood splitter, which worked well, but I doubt that it would scale down very well.
Model engines simply don't have much torque. One of the primary things that a model woodsplitter would need would be a huge torque multiplier, and with torque multiplication, things slow down dramatically.
  I have a couple of ideas floating around in my head, one involving a rack which is pushed forward incrementally by a sprag driven from an eccentric, and one which had a heavy flywheel with an eccentric on both sides driving "pusher arms".I want to split wooden logs 1 1/2" long, and prefer to split them in one full movement of the splitter, not incremental units.

Offline Brian Rupnow

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Re: Model Woodsplitter
« Reply #1 on: January 29, 2015, 04:32:47 PM »
Of course, the wood splitting action would have to be controlled by a hand lever mechanism, so it would only split "on demand", and then only one cycle. Nobody wants a finger chopped off while removing the split piece of wood and putting a new piece on the splitter.

Offline Jasonb

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Re: Model Woodsplitter
« Reply #2 on: January 29, 2015, 05:06:12 PM »
Brian, although it won't do it in one blow have you thought of the type that work a bit like a slide hammer. Lift a weight up and let it drop onto the wedge, repeat until the log is split. Should be quite simple to lift the weight to the top of a guide and have the drive let go so it drops then picks it up again. You could change the wedge to a solid block and use it to drive mini fence posts too.

J

Online mklotz

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Re: Model Woodsplitter
« Reply #3 on: January 29, 2015, 05:39:15 PM »
Don't build this one...

<a href="http://www.youtube.com/watch?v=qMsObwqD788" target="_blank">http://www.youtube.com/watch?v=qMsObwqD788</a>
---
Regards, Marv


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Offline Brian Rupnow

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Re: Model Woodsplitter
« Reply #4 on: January 29, 2015, 05:57:55 PM »
Marv--That is the one I called a "Total suicide machine". The first one of those I seen in real life was a home made one in Juneau, Alaska, and I thought "Oh My God'--somebodies going to lose a hand!!" Jason, I am hoping to do it all in one blow.

Offline Brian Rupnow

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Re: Model Woodsplitter
« Reply #5 on: January 29, 2015, 06:02:01 PM »
 I have been setting designing in my head for two hours, and have decided that even though model engines don't have a lot of torque, they can spin a massive flywheel, and generate tremendous inertia. If one can then gear down the rpm of that big flywheel and use a dog clutch to engage/disengage an eccentric with pusher arms, that will work, and yes, I'm pretty sure that it can be set up to "go home" after each cycle and wait to be activated again. The dog clutch is something I haven't designed before, and as an added attraction, the mechanism is going to have to disengage the dog clutch automatically and return the handle to the disengaged position after each cycle.

Offline b.lindsey

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Re: Model Woodsplitter
« Reply #6 on: January 29, 2015, 07:23:42 PM »
Brian, so this would be sort of like a die stamping press in a way only horizontal rather than vertical ? I think you may be on to something with the dog clutch!

Bill

Offline Brian Rupnow

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Re: Model Woodsplitter
« Reply #7 on: January 29, 2015, 07:51:35 PM »
Bill--I'm setting here blasting away with my 2015 Solidworks, figuring it out as I go along. Dog clutches don't do well with high speeds, it tends to knock the dogs teeth out, but at a lower speed the dog clutch might be just the trick.---Brian

Offline Brian Rupnow

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Re: Model Woodsplitter
« Reply #8 on: January 29, 2015, 10:18:01 PM »
Okay--I've got the easy part sussed out. The flywheel and supports are going to be easy too. The Devil be in gearing down the flywheel to a reasonable output rpm and figuring out the dog clutch. And just for a sense of scale, the round part behind the splitter wedge is 3/4" diameter, mounted in a 1" wide plate.

Offline Brian Rupnow

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Re: Model Woodsplitter
« Reply #9 on: January 30, 2015, 12:30:44 AM »
Maybe we're going to rethink this a little. I have a 3" length of 24 DP rack left over from my sawmill. The "wood" I want to split is only 1 1/2" to 2" long. I found a video on the internet that is so simple I think I will try to copy it.


Offline Brian Rupnow

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Re: Model Woodsplitter
« Reply #10 on: January 30, 2015, 01:13:46 AM »
If you look at the diameter of the pinion in the video, it is much smaller in relationship to the rack than I am able to approach. The smallest gear I can cut is a 12 tooth, which has about a 1/2" pitch diameter. I will have to do some experimenting and see if this will drive the ram too fast or not. Although it would be less hassle if it doesn't, it's not a deal breaker because I can slip a gear reduction in between the flywheels and the pinion shaft. I have a set of 3 7/8" diameter x 1/2" thick steel flywheels that I have been saving for a project, and I think they would be just about perfect for this.

Offline Brian Rupnow

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Re: Model Woodsplitter
« Reply #11 on: January 30, 2015, 04:38:06 PM »
Here we have the new version in retracted and extended positions. I haven't designed the mechanism which holds down the rack in contact with the gear yet---I will do that this afternoon. those flywheels are 3 7/8" diameter. It will take a piece of wood 1.9" long.


Offline b.lindsey

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Re: Model Woodsplitter
« Reply #12 on: January 30, 2015, 04:56:51 PM »
Brian, I notice that the included angle (of the splitting wedge) on the one shown in the video is much smaller than you show in your drawing. I would think that could make a substantial difference in the energy required...perhaps not a factor in a model but was curious as to what you based your wedge angle on?

Bill

Offline Brian Rupnow

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Re: Model Woodsplitter
« Reply #13 on: January 30, 2015, 05:03:24 PM »
Bill--More than anything, it was a guess. This will be "trial by fire".--If the angle is too great, walk the part over to the mill or grinder and knock it down a bit. If it's okay, then leave it alone. You're right--it does look pretty abrupt.

Offline b.lindsey

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Re: Model Woodsplitter
« Reply #14 on: January 30, 2015, 05:14:03 PM »
True enough Brian...always easier to remove some metal that to add it back :)

Bill