circle mill carriages

[nativewolf]

Question for our circle mill gurus.  What is the reason for running a 2 headblock vs a 3 or 4 headblock carriage?  

Saw a mill yesterday that had a 2 headblock carriage on the tracks and they had a nice newer 4 head block corley sitting on a pad inside the mill.  

[Bert]

I'm sure there are more reasons but support and log length are my concerns. A 2 HB carriage typically cant saw short logs because the supports are spaced to far. If they are moved in, you cant saw long logs because the ends of the log are not supported. I see alot of 2HB mills set up for tie logs where the log length is pretty standard.

This is from the Dept of Ag Lundstrom publication- A carriage should be equipped with
sufficient headblock-knee assemblies to adequately support and hold the logs to be
sawn. As a general rule, two head-blockknee assemblies are sufficient for softwood
logs up to 12 feet long. Three are adequate
for logs up to 16 feet long and for logs 16
inches and greater in diameter up to 20
feet long. For logs under 16 inches in
diameter and longer than 16 feet, four
headblocks should be used. Overhang on
logs under 16 inches in diameter should
not exceed 2 feet. For hardwoods, 4 headblocks should be
used to assure that logs 10 feet and longer
will be dogged in at least three places. Much of the inaccuracy in sawing
hardwoods results from the log being held in only two places and not restraining
growth stresses while sawing.

All that said, if i could run a two HB carriage I would just for the ease of maintenance.

[Ron Wenrich]

2 headblock carriages are good for cutting ties and maybe up to 10' logs.  The more dogs in the log, the better control over the log springing. 

The last mill I sawed on had 4 headblocks and they were spaced out 14' from front to back.  I could saw a 6-8' log with 2 headblock, 10-12' with 3 headblocks, and anything longer with 4.  I sawed 23' switch ties on that carriage.  With that much overhang, I did have some problems with log spring on the ends.  It depended on the log.  But, most times it turned out okay.  A friend of mine could cut 40' on his mill, but he had 2 carriages tied together - 8 headblocks.

We didn't saw much pine.  Maybe pine mills can get away with a longer span, but I doubt it. 

[nativewolf]

Thanks all!