sawing dogs and limit switches

[Jeff]

D._Frederick asked me in another thread if we had metal detectors, and others made comments about not wanting to hit something large like that horse shoe. That got me thinking about the bandsawers here. Almost all of you have talked about sawing into your dogs at one time or another. On our mill, and every other automatic circle mill I have run, there are limit switches that stop forward movement of the headblock at a preset distance that keeps you from sawing into a dog by accident. With a Circle mill, its still possible to hit one though because a hot saw can lay over an inch or two and still reach a dog.

That leads me to my question. Dont the more automatic band sawmills have limit switches that stop the downward movement of the sawhead in relation to the position of the dogs?

Our limit switches are a pretty simple device. The circuit to the headblocks forward movement goes through the limit switch in its normally closed position. When the switch is activated by coming in contact with the limit adjustment, (a simple bolt) the switch switches the circuit to the normally open that kills the forward power and activates a warning light on the console. The warning could just as well be a buzzer. Seems that a limit switch tied to dog position on a bandsaw would all but eliminate the dog sawing accidents except in the instances of switch failure

[Wes]

Jeff,
My WM doesnt have such a device, I think it would be possible on some mills,not as simple as make or break though.it would have to automaticly adjust to the dog height as it varies during cutting.On a mill with computer setworks there may be a way to link the dogs to the transducer.
 Interesting idea ???

[Jeff]

I would think adapting it to varying dog heights should be easy to overcome. Ours works that way, as we have an in and out position on our dogs.

[Ron Wenrich]

When asked if we have metal detectors, I usually say that we have 3.  One has 46 teeth and the other 2 have 22 teeth.  We usually can find any metal in a log with those things.   :D

Our limit switches are on a rocker arm.  The current goes to the valve and stops either forward or backward movement.  There are supposed to be limit switches on each headblock, and work with the in and out dogs as well as the tapers.  

"Supposed to be" is the operative phrase, here.  Often mine get ripped off by pieces of debris, so most aren't working.  

One problem we have is when we put on new dogs.  Sometimes they are a little long.  I make a habit of sawing my dog boards with the dogs back, which limits the amount of times they are shaved.  I've never hit a dog or headblock more than a shave, and that is rare.  It still dulls the saw, but doesn't do any damage.

I would think a  rocker switch would be pretty easy to set up on a bandmill.   The problem would be placement.  I would think a limit switch could be put in that would stop forward movement if the dog was in the way.

[woodhaven]

Ron is my kind of guy. I use the exact same brand and model detector. I have never seen any other as accurate.

[Neil_B]

A magnetic switch would work well on mills as they sense metal within a 1/2" of the switch so you would need to set it up ahead of the sawhead a short distance so that when it runs along side of the dog it will shut feed down. Would need a little PLC experience though. It would also have to be set up to run along side of the dog rather than over top so it doesn't get knocked off if the dog is too high.

One place I want to put limit switches are on the forward and backward travel of the sawhead. That way if I get caught doing something else when the head is in motion, it will close the valve at each end of the mill so it doesn't bang on the stops. I've had the head come back to me and almost come off the frame because it hit the stops so hard. Bent the brackets that are used to keep it on the carraige.
Almost had to go change my shorts after that happened  

[Norm]

That's a good idea Neil, something like a reed switch might work. On our wm the return speed is pretty fast and if you don't stop before the end it hits the stop pretty hard. It's just a piece of hard rubber that I've had to replace already. Now I'm careful to feather it if I need to bring it all the way back.

[Neil_B]

Yep, have to do that with mine as well Norm, if I have a long one on there. I can easily tie the switch into my hydraulic/electric solenoid. It will shut it off gigging back but still allow it to go forward and vice versa. Something for down the road anyway.  8)

[D._Frederick]

On my mill that I mostly designed and built, I have limit switches on the end of the tracks that shuts off the carriage drive. After ruining too many blades by sawing into the squaring posts or the log clamp, I put a limit switch with a cat whisker on the carriage. I welded a short length of rod horizontal (parallel to the log rests) on the squaring posts. The cat whisker on the limit switch is set so that it will stop the carriage drive if the squaring post are less than an inch from the blade. The cat whisker makes contact with the rod on the squaring post. I have not figured how to put a limit switch on the log clamp yet.

[Fla._Deadheader]

Too much automatic stuff to malfunction. :  The other day when I sawed the uprights, my son was tryin to hold the sawhead back and I was pushin it ahead. Guess the old man still has a little power left : ;D :D :D :D

  BTW, that's the first time in a looonnng while that I hit anything on the mill. The chunk I was sawin would have moved if I let off the clamp even a little bit. Had Ed hold the chunk with a cant hook and shoved the head on through.  ;D ;D