Howdy all,
I just bought some old equipment that has in fact square heads. A 24" planer and a 12" jointer. What about square heads make them so unsafe? One interesting part is the jointer came with molding type knives. They were making crown molding and what not with this thing! Been in service since 1916, until we unhooked it a week ago. Sad to see it come apart. I'm probably going to sell on ebay to some collector type and buy a newer model, but just curious about the word on the street.
thanks
kelvin
Part of the reason they are so unsafe is that they are capable of taking such a big bite every revolution. Modern, round heads, just snip off a little. An old square head can take off half of your hand with the pass of every blade. That's not the only reason though. Because of the ability to take a big bite, they can get a block of wood below the blade and stuff begins to come apart. It is recommended that square heads be replaced with round heads.
Square headed planers are bad about sending the work flying too. That is because it can get such a good grip on the board.
What tom said. Also they can launch blades, retainers and bolts as well. The new safety heads built with corrugations are much safer. Even the gib (wedge) retained blades are less likely to go flying. Those 100 year old bolts holding the blades in may be beyond their designed fatigue limit also. Just as you can bend a piece of wire enough times, it will eventually snap, so can you as well a bolt.
Kelvin,
here is an older thread on the subject..
https://forestryforum.com/board/index.php?topic=1447.0
I have an old Cresent 26" planer that has a 2 knife square head. It has 4 massive rollers driven with the top infeed roller serated. I don't see how a board could get kicked back feeding one at a time. Feeding more than one board at a time is asking for trouble without a segmentated infeed roller.
Jason
I have seen the tails of boards with diagonal grain shear off. The upward pull of the cutter can easily launch the last 4-6 inches and shred or hurl this like shrapnel. The deep pockets in square heads launches stuff like a lacrosse ball. I guess the lumber was better when they made these older machines.
If two boards overlap head to tail, the cutter can break through after planing a trough in the trailing board. Then the cutter can grab the new feathered front edge and kick the board back or shatter the front into splinters. This usually happens when the boards are not cut 90 degrees head to butt. Also when a curved board is put in concave side up or on lumber with thin ends.
How about having a new head made for it? Maybe a shelix or some other multi knife head.
There are some newman whitney spiral planer heads 44" for sale over at IRSAUCTIONS site. Could be machined down to 24". Heck the carbide alone is worth a few thousand. Would make a heck of a nice planer. Also saw some straight knife gib heads also for cheap.