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Cross Bunk width

Started by JimFX, May 02, 2013, 08:45:12 AM

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JimFX

I am wondering about cross bunk thickness .... some machines have robust versions others are thinner.
The thinner ones say they collect less sawdust. While I can see this may be advantageous, strength is also a factor. So, could I get some feed back on whether sawdust is an issue or not ...
Thanks!

Chuck White

I don't have any trouble with sawdust collecting on the bunks, but once in a while when turning a log, when it finally turns and lands on the bunk it won't sound right so I lift the log with the toeboards and I'll find a piece of bark between the bunk and the log!
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dboyt

I have milled logs up to the Norwood's maximum 34" cutting diameter without a hint of deflection on the 1/4" plate steel cross bunks.  Here's a link to a sweetgum log I recently milled: 2,457 pounds, according the the FF log weight calculator.  https://forestryforum.com/board/index.php/topic,66351.0.html .  As long as the manufacturer uses good quality steel, you won't have a problem.  When I ran a TimberHarvester with 2" tubing for cross bunks, loose bark between the log and bunk was a frequent issue and would cause a tapered board if I didn't pay attention.  Fortunately, it had hydraulic to rollers, so it was easy to lift the log and clear off the bunk (if I caught the problem).  I have yet to have a piece of loose bark get caught under a log on the Norwood mill.
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Macgyver

Hey JimFX, just curious, but why do you ask?  The reason I ask is because if there's a possibility that you're building something on your own, why not get the best of both worlds?  I have an MX34 with the really thin cross bunks.  Like dboyt mentioned, you can put anything on them and they wont bend with a vertical load.  Horizontal is a little different, and when using a machine to move a log in the longitudinal direction it gets a little scary and I'm afraid I'll bend them with the slightest miscalculation in force.  I was designing my own mill at one point, and had the idea to use rectangular tube for the cross bunks with a piece of angle iron or even just flat bar stock welded on edge....best of both worlds in my opinion. 
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Brian_Rhoad

Thin bunks will wear more from turning logs on them. My Breezewood mill had 3/8" x4" steel for the bunk. They had wear from turning logs so I replaced them with 2"x4" steel tube. I capped them with the stainless caps from Woodmizer. You do have to watch for bark and sawdust on them when you turn the cants but they do work much better.

dboyt

Quote from: Brian_Rhoad on May 02, 2013, 01:16:37 PM
Thin bunks will wear more from turning logs on them. My Breezewood mill had 3/8" x4" steel for the bunk. They had wear from turning logs so I replaced them with 2"x4" steel tube.

That's another reason the quality of the steel is important.  There is no excuse for 3/8" thick steel wearing from turning logs.  Never even thought about it on my mill.  The stainless steel caps are are mainly from keeping the wood from picking up blue stain from contact with steel, but could be replaced if they ever do show signs of wear.
Norwood MX34 Pro portable sawmill, 8N Ford, Lewis Winch

JimFX

Macgyver you post is exactly why i was asking, the horizontal force. I like the Norwood mill and didn't see a problem with downward force however try any push a big log on the horizontal plane and you could have problems. Of course trade offs are made between better engineering and cost all the time, the point is can I live with the trade that has been made.  The Norwood states the narrower bunk collects less debris, probably quite true, lighter product, less $ to ship, easier to mount and therefore they can provide more features for the same cost ...

and no I am not building my own mill just trying to vet the mills that are out there to see what might work best for me when I throw down some cash.  Going to see the mills is a perfect idea but doing research in advance will help me focus on key items for me instead of getting lost in the excitement of the mill running.

I know dboyt is quite happy with his mill, how about you?

Thanks to everyone for taking the time to post ...........

5quarter

Both ways work fine. But the bunks take a great deal of punishment. Thick walled box steel is stronger in both dimensions than vertical steel plate. also, the wider surface area means better weight distribution, which means easier turning, especially if you wax the bunks. also, they can be capped with stainless or aluminum to protect the cant. No one ever griped about their mill being built too heavy.  ;)
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Nomad

     I used to use an older Norwood mill, and liked it a lot.  I recently got a chance to look at an MX34 for the first time.  About the only thing I really did not like about it is those vertical plate bunks.  I can see a couple of advantages to them, yes.  But as stated above I think that moving a big log longitudinally on the mill would be problematic at best.  Not only would you risk bending the bunk, but it would tend to dig into the log from the weight.
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