Bandsawing a large board

[BuckeyeDennis]

Nice job on the setup, Forrest. The video was great -- it prompted some observations and questions that photos alone wouldn't have.

1) I was surprised that you needed to wedge the kerf while resawing, but I did seem to hear a slight change in motor loading each time you adjusted the wedge. Bandsaw blades are very "short" in the direction of feed, as compared to circular saw blades, so I would have expected the tooth set to provide adequate clearance for the rest of the blade in the kerf. Does that blade have an unusually small amount of tooth set? What happened before you started wedging the kerf?

2) Did you feel that the cutting speed was limited by the available power? The other limitation would be chip load in the blade gullets. If you think it was power-limited, I have an idea that might get you faster cutting speeds. That next board of yours would be a great test.

[masonsailor2]

Nice job Forrest ! Taking the SS band saw to its limits
I sent you a PM.
Paul

[dusty]

Very informative and very interesting. This thread and especially the video has relieved some of the concerns I had about resawing.

Thank you so very much for the effort spent and for the video.

[forrestb]

Nice job on the setup, Forrest. The video was great -- it prompted some observations and questions that photos alone wouldn't have.

1) I was surprised that you needed to wedge the kerf while resawing, but I did seem to hear a slight change in motor loading each time you adjusted the wedge. Bandsaw blades are very "short" in the direction of feed, as compared to circular saw blades, so I would have expected the tooth set to provide adequate clearance for the rest of the blade in the kerf. Does that blade have an unusually small amount of tooth set? What happened before you started wedging the kerf?

2) Did you feel that the cutting speed was limited by the available power? The other limitation would be chip load in the blade gullets. If you think it was power-limited, I have an idea that might get you faster cutting speeds. That next board of yours would be a great test.

1) I found in re-sawing the 5" board that the WoodSlicer blade was being pinched to the point the PP would shutdown. That never happened on the 6 ¼" board by stopping every foot or so and driving in the wedge. Remember that I had the cool blocks in the upper guide block actually touching the blade so that was requiring additional torque.

2) No, I don't think lack of power was an issue. I went slowly because I have had very limited experience re-sawing and none with a board this size.

The WoodSlicer is a 2-3 tpi blade so the gullets are pretty big. I have not measured the kerf.

And I don't know many woodworkers who would turn down an idea for "faster cutting speeds" as long as safety is not reduced.

Forrest

[BuckeyeDennis]

Nice job on the setup, Forrest. The video was great -- it prompted some observations and questions that photos alone wouldn't have.

1) I was surprised that you needed to wedge the kerf while resawing, but I did seem to hear a slight change in motor loading each time you adjusted the wedge. Bandsaw blades are very "short" in the direction of feed, as compared to circular saw blades, so I would have expected the tooth set to provide adequate clearance for the rest of the blade in the kerf. Does that blade have an unusually small amount of tooth set? What happened before you started wedging the kerf?

2) Did you feel that the cutting speed was limited by the available power? The other limitation would be chip load in the blade gullets. If you think it was power-limited, I have an idea that might get you faster cutting speeds. That next board of yours would be a great test.

1) I found in re-sawing the 5" board that the WoodSlicer blade was being pinched to the point the PP would shutdown. That never happened on the 6 ¼" board by stopping every foot or so and driving in the wedge. Remember that I had the cool blocks in the upper guide block actually touching the blade so that was requiring additional torque.

2) No, I don't think lack of power was an issue. I went slowly because I have had very limited experience re-sawing and none with a board this size.

The WoodSlicer is a 2-3 tpi blade so the gullets are pretty big. I have not measured the kerf.

And I don't know many woodworkers who would turn down an idea for "faster cutting speeds" as long as safety is not reduced.

Forrest

I'm happy to share the idea. But you'll have to bear with me while I while I explain the theory. Otherwise, folks may think I'm nuts.

It's widely believed that the PowerPro is more powerful than a conventional headstock throughout it's entire speed range. Take that with a huge grain of salt. What Shopsmith actually says is "More Power - 1-3/4HP at 120V, 2HP at 240V, Twice the torque at every speed." I do believe that statement, with the caveat that "twice the torque at every speed" is referring to the motor shaft torque, not the spindle torque. That is, it is believable that the PowerPro's DVR motor can generate, throughout it's entire speed range, peak shaft torques twice that of the standard induction motor.

But while electronic controls are great for controlling speed, there is a tradeoff. They can provide full motor torque throughout the speed range, but the motor power drops off at low motor RPM. Peak motor torque is ultimately limited by magnetic saturation inside the motor. And motor output power is equal to shaft torque x RPM. So as the RPM approaches zero, so does the available power. Trust me on this -- I'm an EE who specializes in motion control, and I have designed a number of electronic motor drives.

But when you use a mechanical transmission to vary the spindle speed, the available spindle torque increases proportionally when the spindle speed is reduced. Available spindle power is unchanged.

For example, if the Shopsmith Speed Reducer decreases the speed by 7:1, it also increases the torque by 7:1 (neglecting the modest mechanical transmission losses). It might just as well be called a "Torque Increaser". The same principal applies to the mechanical CVT (continuously variable transmission) inside the conventional headstock.

Now mind you, we don't know the "base speed" of the PowerPro's DVR motor. Above the base speed, the available torque decreases. Below the base speed, the available power decreases. An educated guess would put the base speed around the middle of the speed range, so perhaps 5000 RPM at the spindle. Thus at bandsaw drive speeds, the available power may be closer to 1/2 hp than 2 hp.

Now (finally ) here's my proposed experiment. If you have a speed reducer, use it to drive the bandsaw, and increase the spindle RPM by a factor of 7. The bandsaw blade will run at the same speed, but I believe that it will now have available the full 2hp, and a lot more torque. Probably enough to laugh at the drag from the cool blocks and the wood pinching.

I seem to recall another PP owner here on the forum saying that they do use their speed reducer with their bandsaw, but primarily to eliminate the PP "clunking" problem with the bandsaw.

Sorry for the dissertation, but I don't have a PowerPro to play with myself!

[forrestb]

Now (finally ) here's my proposed experiment. If you have a speed reducer, use it to drive the bandsaw, and increase the spindle RPM by a factor of 7. The bandsaw blade will run at the same speed, but I believe that it will now have available the full 2hp, and a lot more torque. Probably enough to laugh at the drag from the cool blocks and the wood pinching.

I seem to recall another PP owner here on the forum saying that they do use their speed reducer with their bandsaw, but primarily to eliminate the PP "clunking" problem with the bandsaw.

Sorry for the dissertation, but I don't have a PowerPro to play with myself!

Sounds like an excellent experiment. I think I'll put my speed increaser on CL in trade for a reducer. I have more plans for big boards.

Thanks, BuckeyeDennis

Forrest

[algale]

I don't pretend to understand your explanation, Buckeye, but if you are saying the PP headstock actually generates less torque at the spindle at slow speeds than the regular headstock, I think that (1) that's a big negative and (2) the advertising needs to be corrected.

I hope someone from Shopsmith is following this thread and will set the record straight if they think you are wrong. I for one will take Shopsmith's silence on this as confirmation that you are right.

[BuckeyeDennis]

I don't pretend to understand your explanation, Buckeye, but if you are saying the PP headstock actually generates less torque at the spindle at slow speeds than the regular headstock, I think that (1) that's a big negative and (2) the advertizing needs to be corrected.

I hope someone from Shopsmith is following this thread and will set the record straight if they think you are wrong. I for one will take Shopsmith's silence on this as confirmation that you are right.

Don't get me wrong, I'd like to have a PowerPro myself. Forrest's super-sized resaw project on a modified bandsaw is the first operation I've heard of that makes me suspect that any low-speed torque compromise even matters in a practical application. And besides, without access to the motor/drive system speed/torque curve, I don't know that the PP can't generate 2hp at a 250 RPM spindle.

What we need is an experiment. PowerPro, bandsaw, and a very heavy cut -- with and without a speed reducer.

[dusty]

If I had all of the equipment, I'd gladly become your "test station". But since I do not, I will patiently wait for the results. I am confident that there will be takers on this forum. That is what makes it so valuable to the Shopsmith community.

I am just disappointed that we do not see evidence that Shopsmith is listening (though I believe they are).

[JPG]

If I had all of the equipment, I'd gladly become your "test station". But since I do not, I will patiently wait for the results. I am confident that there will be takers on this forum. That is what makes it so valuable to the Shopsmith community.

I am just disappointed that we do not see evidence that Shopsmith is listening (though I believe they are).

We know of one that is listening.

I believe SS desires to be non intrusive to this forum. Other than direct forum related responses, only once(to my knowledge) has SS interjected a comment(i.e. SS engineer re power pro software tweaks) and that was for a very good reason.

I am not ignoring Nick's earlier responses. I did not consider them to be 'SS' responses. I do miss them!!