Homemade "Skidder" Advice (metal frame thickness)

[Angry Beaver]

So, I am planning a long term project of, well, making my own skidder/tractor mostly from scratch.

I have in mind what i want build but just need to put it into a design program when i get the time and I'm figuring up costs at the moment which brings me to my question.

This is for the Frame of the articulated vehicle and made out of Hot-Rolled Steel.  Front section will most likely be 6-8ft long and 4ft wide and rear section will be about 6 ft long and 4ft wide, this is not counting axles/etc.  This is not meant to be a monster machine, just looking for something that can drag effectively 2-4 tons worth of logs and dont want the frame to bend but also dont want to spend a ton of money going overboard.

I'm planning on using [ (C-Channel) for the frames but I'm not sure on the thickness needed.  I am wondering if 4" with a 1" flange and 0.25" thick wall is enough or go to 0.3+" thick wall or upgrade to 6" with a 1" flange at 0.25" thick?

Note:  On top and bottom of frame there will be a 1" x 3" x 0.25" wall angle iron around the entire frame for drilling holds for bolt mounting things (I prefer bolts over permanent when possible as its so much easier to change things)

[mike_belben]

The sloped inner flange surface of angle iron makes it a pain to bolt things since the hole has a tapered depth and onlycthe uphill side of the nut or washer engages.  When its important i weld a bead up on the downhill side and grind it flat so the bolt can be tensioned equally. 


Other downside to angle iron is it is very happy twisting right up.  Very low torsional strength compared to round or square tube.     I think for these reasons you will be hard pressed to find a manufactured machine built with C channel frame.  Rectangular tube is a lot more common. 


If budget is an issue buy a pair of scrapyard cab/chassis frames.  Theyll have wider, full flanges and straight rails.  33" OC usually. 


Making a light machine pull a lot of dead weight takes a high cable and a long frame with good weight up front.  The log hitch, when raised high, will serve as rear tire ballast but you will need to keep the front down to steer.  
 

What have you got for parts so far?  Or what have you got in mind anyways?  Got a winch?  How big of tire and what type?  

[grabber green]

what engine ,transmission ,axles ,winch and tire size are you planning?That all will make a big difference on how strong your framework needs to be.   Unless your just building it for fun and have access to lots of scrap and junkyards that are cheap your way better off just buying a real skidder. My homemade skidder is my avatar.