BS Wheel size/power question

[Mark Neidinger]

It seems like a dumb question, after a quick read, but I think it might be more complicated than that.

Does a 14" BS with cast iron wheels and 2hp have the same power to cut as an 18" BS with cast iron wheels and 2hp?

I am asking about sheer power, not resaw height or throat width. Certainly the 14" wheels would get up to speed faster than the 18", but the rotational mass of the 18" wheels may result in more "power".

[Myk Rian]

Depends on the drive pulleys. If they were the same, the 14" would transfer more power to the wheels.

[Rod Sheridan]

Depends on the drive pulleys. If they were the same, the 14" would transfer more power to the wheels.

Incorrect, assuming similar frictional losses both saws would be able to perform the same amount of work in the same time frame.

regards, Rod.

[Mark Neidinger]

So, using Grizzly for an example:

Would the G0457 14" resaw wood with the same speed as the G0513x2 18"?

[Van Huskey]

So, using Grizzly for an example:

Would the G0457 14" resaw wood with the same speed as the G0513x2 18"?


The problem here is they move the blade at different speeds...

[Pete Bradley]

This is a difficult question since there's no good definition for "power to cut". Practically speaking:


proper band selection is far more important to cutting effectiveness than horsepower. An excessively fine band can turn a remarkable amount of horsepower into smoke and aggravation.
2HP is more than enough for the 14", plenty for 18"
band speed helps cutting speed in thick stock. It won't do a lot for you in thin stock unless you can feed as fast as the saw can cut. Machines with bigger wheels generally have faster band speed.

Impractically speaking, but since you asked:


a 14" wheel will soak up somewhat more horsepower than an 18" wheel due to the fact that you're bending the band around a smaller diameter

Pete

[Mark Neidinger]

I kind of thought that once you got the heavier/larger wheels spinning that the rotational energy/inertia might keep them spinning better when going through wood. Isn't that why people prefer cast iron wheels to aluminum?

[Myk Rian]

Incorrect, assuming similar frictional losses both saws would be able to perform the same amount of work in the same time frame.

regards, Rod.
As I said, if the pulleys were the same size, more power to the 14", and hence the blade. It would take more power to cut with the 18" if the blade was the same type.

[Van Huskey]

I kind of thought that once you got the heavier/larger wheels spinning that the rotational energy/inertia might keep them spinning better when going through wood. Isn't that why people prefer cast iron wheels to aluminum?


The increased inertia will help the saw in the event of a very short term increase in load, say a small knot etc. Once the extra stored energy is dissapated then you are back to even, actually the 18" at that point would be at a slight disadvantage since the motor has to work harder to cut and wind up the increased mass of the 18" wheels over the 14s.

The reality is the difference between a 14" and 18" BS with the same HP, cutting the same wood with the same blade is going to be pretty similar. There are a lot of variables that are hard to quantify without serious measurments but if resawing is the issue and throat depth is not a 14" BS will do the job just like a 18" save a few small factors most of which favor the 18" in some small way.

[Van Huskey]

As I said, if the pulleys were the same size, more power to the 14", and hence the blade. It would take more power to cut with the 18" if the blade was the same type.


I think you need to be more complete and clear. I am not sure I follow your point and thin it is incorrect.

Your first post:

"Depends on the drive pulleys. If they were the same, the 14" would transfer more power to the wheels. "

This is incorrect, given the same drive pully the power transfered to the "wheel" would be exactly the same, any variation would be in the power transfered to the blade. There are some torque issues here given the difference in wheel size but we need to decide whether the OP wanted "real world" differences or any measurable difference. The former is about equal in my eyes, the latter is going to differ.

[Myk Rian]

This is incorrect, given the same drive pully the power transfered to the "wheel" would be exactly the same, any variation would be in the power transfered to the blade.
You are correct. My bad. I did mean "blade".
The 14" will transfer more power to the blade.

[Lance Norris]

This doesnt really answer the original question, but Ive owned the G0457 for 4 years now and it chews through anything I throw at it. I recently resawed 10" purpleheart and it never ever struggled...well... thats not entirely true, but it sure powered through it with authority. Purpleheart is a tough one to resaw.

[John McClanahan]

Cast iron wheels won't help with power, except as Van mentioned.

All else equal, the 18" will saw faster as the blade is traveling faster (fpm), but would bog down faster than the 14". While the 14" may have more torque, force feeding the blade will only fill the gullets with chips, limiting the cut rate.

Overall performance is a combination of HP and blade speed. Here is a chart showing wheel diameter and speed recommendations for Timber Wolf blades.

John

[Phillip Pardue]

The most important consideration in this type of system is the torque exerted between the rotational motion of the wheels and the linear motion of the band. Assuming that the 18" has a larger wheel radius, given the same resistance from the wood to the band, the band will exert a greater "resistive force" or drag on the 18" wheels than the 14". This is due to the larger lever arm of the larger wheel. This, of course, assumes everything else is held constant. As noted before, the mass moment of inertia of the wheels will be helpful in the case of momentary changes in band resistance but will not increase power. A larger flywheel on a car does not make for a more powerful car. In all, I would not expect to see a noticable difference between a 14" and an 18" with the same motor attached.

[Pete Bradley]

This is going from academic toward silly. What counts is the system, not any one or two factors.

Mark, is your real question 'Can I buy a bigger motor and a riser for my 14" instead of buying the 18" Griz'?

[Rod Sheridan]

It hasn't become silly, if you adjust drive ratios so the blades have the same linear speed, and you put the same HP motor on each, they'll cut wood at the same rate.

A larger wheel doesn't give you more power, just a different set of drive ratios to design around.

Likewise inertia of the wheels is an instantaneous factor, as the energy must be provided by the motor on an average basis. A wheel with more inertia will store more energy for a fraction of a second, as another person indicated, when sawing through a small knot.

It won't help you with continuous sawing.

The larger wheels give you the ability to use thicker and wider blades and an increased cut width ( blade to column distance).

Faster sawing requires the choice of the correct blade, a saw that can withstand the forces involved, and a motor powerful enough to do the work in the time required.

If you are cutting a thick piece of timber, each tooth must have a large enough gullet to hold a chip that's the full height of the wood, so the teeth are far apart with large gullets.

The cutting speed will be chip thickness multiplied by teeth per minute.

If you are cutting a piece of wood half the thickness, you would generate a chip that's half as long, so the gullet could be smaller, hence more teeth on the blade.

Cutting speed would once again be chip thickness multiplied by teeth per minute.

So with the thinner wood, and more teeth you could cut faster, yet the work remains the same.

(Volume of wood removed per minute by the blade is the same, however feed speed is changed by a factor of 2).

The chip thickness determines the finish quality of the cut, if you're going to plane the wood, a low tooth count blade with high chip thickness is the fastest. (High feed rate).

If you want a nice cut for a piece of veneer, more teeth, low chip thickness, low feed rate.

The above of course are based on a suitable band saw, with mechanical feed, and a desire to optimise the sawing.

At home we don't tend to have a wide enough selection of blades, or mechanical feed to utilise a saw to it's maximum performance.

We therefore usually choose a larger saw so we can use wider/thicker blades, have a higher depth of cut.

We also expect higher workloads with a larger saw, so a larger motor.

Notice that wheel diameter doesn't come into play for feed speeds, just number of teeth per minute, chip thickness and horsepower.

Regards, Rod.

[Chip Lindley]

I will stick my neck out...and my foot in the door here.


All else equal, the 18" will saw faster as the blade is traveling faster (fpm),

ALL ELSE is Not equal. We must assume both saws run at the same surface feet per minute. (around 3000 sfpm) IF SFPM is equal, the 18" saw wheels will actually turn slower than the 14". McClanahan's claim will only be true IF both saws have same diameter motor and wheel pulleys. But, this would not the case! Larger bandsaws have larger wheel pulleys to achieve the same FPM, because during each revolution of the larger BS whee, the blade travels further The wheel must turn slower to achieve 3000 sfpm. Do the Math!

A larger wheel pulley/smaller motor pulley, in effect gives a lower-geared ratio to a bigger saw. Looks like this would transmit more power to the blade. The enertia of a larger heavier wheel would have a small positive effect also. All those fine 36" Tannewitz resaws can't be wrong!

[Rod Sheridan]

I will stick my neck out...and my foot in the door here.



ALL ELSE is Not equal. We must assume both saws run at the same surface feet per minute. (around 3000 sfpm) IF SFPM is equal, the 18" saw wheels will actually turn slower than the 14". McClanahan's claim will only be true IF both saws have same diameter motor and wheel pulleys. But, this would not the case! Larger bandsaws have larger wheel pulleys to achieve the same FPM, because during each revolution of the larger BS whee, the blade travels further The wheel must turn slower to achieve 3000 sfpm. Do the Math!

A larger wheel pulley/smaller motor pulley, in effect gives a lower-geared ratio to a bigger saw. Looks like this would transmit more power to the blade. The enertia of a larger heavier wheel would have a small positive effect also. All those fine 36" Tannewitz resaws can't be wrong!

Chip you're correct about the blade speed, a larger wheel would turn slower to have the same linear blade speed.

You are however incorrect on the drive ratio aspect, the shaft torque would be higher on the large wheel, however the blade force (downward pressure on the tooth) would be the same as the smaller saw due to the differences in wheel diameter. (You have confused torque with power).

Since the force and speed are the same in both machines, the power is the same.

Both machines would cut wood at the same rate, except for frictional losses, which would be very similar in the two machines.

Regards, Rod.

[William Falberg]

+1 , Rod.
And I might add that Tannewitz can be just as wrong as anyone else around here. They make a nice saw if you're into old locomotives, too; but they're not "the ultimate embodiment" by any means. In terms of mechanical efficiency they're probably at the bottom of the list.

Another case of not broke, but sure could use some fixin'.

[John McClanahan]

I will try again with the chart.

[William Falberg]

You have to take Suffolk's wisdom with a grain of salt. This is the same guy who claims three-wheelers create "excessive" wear where there's no evidence of it. I frankly don't know where he got the rest of that about "minimum" velocities. The high end admonitions seem to apply to clock time as opposed to cutting time. Like, yeah, it will wear out sooner, but look at how much more wood you cut.

Furthermore; there's no law says you can't allow for centrifugal run-off and adjust the guides with a centrifugal "allowance". I always adjust my guides to operational center with centrifugal forces figured in.

[Mark Neidinger]

The real world question is whether or not it makes sense (both in economic sense and in taking up basement space) to get the 17" grizzly v. the 14" grizzly. These are the G0457 and the G0513x2, with 10" and 12" resaw heights, respectively. Resaw height is not incredibly important.

The factors that might be important to me are table size and overall performance. As you might have noticed from another thread, I would like to use the bandsaw to reduce my reliance on my table saw.

Is the larger table worth the price difference and is a 17" saw with the same motor as a 14" saw underpowered?


This is going from academic toward silly. What counts is the system, not any one or two factors.

Mark, is your real question 'Can I buy a bigger motor and a riser for my 14" instead of buying the 18" Griz'?

[Josiah Bartlett]

There are a few areas that a larger saw of the same horsepower can help with when resawing:

Bigger table means the work is more stable so the blade is less likely to pinch in the kerf
Beefier guides mean the blade tracks better when abused
Stronger frame means the wheels don't deflect under the dynamic tension of the blade, resulting in fewer power robbing harmonics/chatter and a smoother cut
Larger wheels mean more time the teeth spend out of the cut, giving them a chance to cool off and shed their dust, resulting in longer blade life

[Pete Bradley]

The real world question is whether or not it makes sense (both in economic sense and in taking up basement space) to get the 17" grizzly v. the 14" grizzly.

The factors that might be important to me are table size and overall performance. As you might have noticed from another thread, I would like to use the bandsaw to reduce my reliance on my table saw.

I thought that was the question. My view(as someone who uses a 20" BS for many traditional TS operations) is that there's no substitute for a bigger band saw. Horsepower is overrated, but a big solid table, more distance to the left of the band, and more weight are all indispensable. Got the saw set up and want a quick crosscut? Got a log you want to slice up? Want stability to push a long board through? Get the big 'un.