One big log, a 96" bar and my observations

[Can8ianTimber]

I have another 3120 but I need to have it worked on. I bought it used and it has never really run right so I don't want to pair it up with the good 3120.

I think the problem with the magnet idea is that as Bob was saying the force it multiplies as it gets closer to the metal. I think you would either have no effect or way too much effect and reverse the sag. It would be like saying you were going to have a piece of metal hover below a magnet without touching it as you found the perfect spot where the magnets force and gravity were equal.

 

[mortenh]

I wander if it would be worthwhile to mount one of those super magnets mid-point on the mill.

Those things come in various sizes & strengths. I am just curious to know if a good strong magnet would provide enough pull to offset gravity. And just how strong of a magnet that it would take......

The magnet idea won't work at all. Even the strongest magnet you can buy would, at a distance of 4 inches from the bar provide a pulling force of far less than an ounce.

Try a simple experiment. Find the strongest magnet you can, and notice how you can't even pick up a paper clip from a distance of a few inches.

 

[BobL]

The magnet idea won't work at all. Even the strongest magnet you can buy would, at a distance of 4 inches from the bar provide a pulling force of far less than an ounce.

I agree that no practical electromagnet on a portable CS mill would have sufficient strength to lift a bar through 1" of wood. On a carriage type mill it might be possible but a dedicated generator that could output about many kW would be needed to generate enough current to create the force required. The other thing that would be needed is coil cooling or they will melt.

We have an electromagnet magnet at work that weighs 6 tons and draws around 60A (it uses a chiller to stabilise the temperature). It doesn't operate at high magnetic fields but if you get too close with it with keys in your pockets it can pin your trousers to the magnet and depending on where on the magnet you become attached it's not always possible to get to the switch.

A electromagnet magnet from an MRI will pull a wheelchair with a patient into itself from a couple of feet away. They weigh a couple of tons and cost a $million or so.
Check out what MRI magnets can do here. They will send tools flying across a room and can be very dangerous. They also require bout 30 kW of cooling.

We have some smaller electromagnets at work. I might fire them up and see what force they can generate from a distance of one inch. For cross reference the small REE magnet I use on my anti sag device can hold 17 lb (or was it kg - I can't remember).

 

[Can8ianTimber]

I think the best way is to see if the bar manufacturer can produce the bar with an intentional sag or tension in the bar. Then mount it in the mill with the bow facing up. The trick would be getting just the right amount of intention sag so that once it is mounted in the mill with a chain on it that it would sit flat. The down side is that you would not be able to mill from both sides of the bar and you would have to have it ground twice as often. You would also only be able to use it in a horizontal possition but we are never going to use a 96" double ender any other way.

 

[BobL]

I think the best way is to see if the bar manufacturer can produce the bar with an intentional sag or tension in the bar. Then mount it in the mill with the bow facing up. The trick would be getting just the right amount of intention sag so that once it is mounted in the mill with a chain on it that it would sit flat. The down side is that you would not be able to mill from both sides of the bar and you would have to have it ground twice as often. You would also only be able to use it in a horizontal possition but we are never going to use a 96" double ender any other way.

If it was a double ender shouldn't it be able to just be turned it around?

 

[Can8ianTimber]

Yes, of course. Feeling kind of stupid. That would work. I think that would be the best options for really long bars. I am not a metal worker but I am pretty sure it would not be that hard to roll it and get enough of a curve to counteract the sag once it is in the mill.

 

[sbhooper]

That is some serious work. My question is, "What are you going to do with those giant slabs now?"