band wheels - the great debate

[Dan_Shade]

i'm kicking around the idea of building a larger saw, i'm trying to figure out the pros and cons of the wheel design...

TRAILER / BOAT TIRES
pros

• lower cost
• no band lube needed
• supposedly reduced band breakage
• easy to get large diameter wheels to extend band life

cons

• more difficult to drive the drive wheel
• needs to be turned true
• needs to be balanced
• needs tow-in set in the tires to keep the bands walking straight

SHEAVES
pros

• cheap if obtained from surplus
• drive wheel can be turned relatively easily
• can use belt for tires

cons

• difficult to find sheaves with large enough diameter to ensure long band life
• needs to be balanced
• needs tow-in set in the tires to keep the bands walking straight

METAL WHEELS
pros

• easy to get large diameter wheels to extend band life
• can be machined perfectly round
• wheels can be mounted in the same plane, which makes for easier setup
• drive wheel can be turned relatively easily

cons

• needs to be balanced
• cost
• needs shock absorbing band tensioner

have I missed anything?  there has been some discussion on this in the past, but it's tough sorting through it all...

If I'd use a trailer tire, I'd like to be able to use a full floating axle setup, but the problem there is I don't know of a "small" setup with floating axles.  with the smaller tires, I am concerned of putting too much stress on the tire or axle.

[getoverit]

I cant speak for all, but my preferences would be in the reverse order of the way you posted them, with all steel and larger wheels being the top choice, then sheaves, then tires. I might note that both of my band mills have sheaves with belts for tires.

Placed in that order, they are probably the most expensive to the least expensive. This is why the thread that was posted recently on casting aluminum was of such an interest. If someone could cast an aluminum wheel, then place a steel wheel around the outside of that, you would have the best thing going and be able to have a pretty good size wheel too at an affordable price. It is possible that an all aluminum wheel would do just as good as a steel wheel, but possibly require crowning the wheel more often?

just my $.02 worth

[Dan_Shade]

this isn't in any particular order, just compiling pro's and cons.

[pigman]

"TRAILER / BOAT TIRES
pros
* no band lube needed"
I don't see why the type of band wheel will affect the need for blade lube. I believe the sap from woods like white ash will be a problem no matter what type of wheels that are used.

"needs tow-in set in the tires to keep the bands walking straight"
I don't understand that statement. I thought the wheels should be in the same plane. I didn't build my mill, so my understanding of mill construction is quite lacking. ;)
Bob

[wiam]

Why do you not need lube with a tire?  A tire can be balanced at almost any garage for about $6.  My tires will keep a band on it with no "toe".  I can run a band anywhere on the tire if I choose.  I am not saying tires are better.  They work for me at an affordable cost.  Would I like 26" steel wheels?  Yes, I think there would be benifits. My bands run much better with lube.  I have no problem driving mine.  

Will

[Dan_Shade]

how do you drive your tires, wiam?

I've seen some mention (deadheader, maybe?) that they didn't use any band lube with homey, the theory being that the rubber pulled the heat out of the band....

it's easy enough to add a blade lube system, I don't consider that a big deal.

[flip]

Here's my .02.  I had steel wheels on the B-20 when I first got it-hated them.  Too hard to keep the blade tracking right and seemed to have more blade failures.  TK updated the wheels to sheaves which I used on the mill I built.  Belts are cheap and available anywhere, they absorb more shock than steel and in my opinion easier to adjust, plus less rotating mass that robs engine power.  Tires=heavy=rob engine torque=bad.

I used 18" A sheaves with B56 belt, got the drive shafts 1 7/16 from Linn lumber for about $35 all ya need then is bearings and a way to tension and voila! you gots a cuttin' head.

Flip

[Bibbyman]

Why re-invent the wheel?  I just use what came on my Wood-Mizer and been too busy sawing to worry about it.

[hookhill]

Hey Bibbyman,
If it werent for us tinkerer's then nothing would get invented. The guys that started Woodmizer were probably tinkerer's.

Jim

[logwalker]

  Quote:  "Tires=heavy=rob engine torque=bad. " 

I think that the tires and wheels can only add rotating mass and help the blade maintain a constant speed and torque. And that I think is a major factor in cutting straight lumber. I don't see it as a negative. Having said that I saw with a 1994 LT40 Hydraulic WM. JMHO. LW

[jrokusek]

Dan - stop thinking.  Start gathering up parts and steel.  Building my mill was one of the most fulfilling (and occasionally frustrating) things I have done.  I like trailer tires.  I didn't balance mine or true them.  Someday I may take them off and balance them to see if it changes anything.  If I had to do it over again, here's what I would do.

For the drive side:  Go get some 1.25" shaft.   Buy this coupler from Surplus Center

Now take that coupler and cut another keyway on the outside.  Get your trailer hub of choice, knock out the bearings and races until you have a straight through shot.  Have a corresponding keyway cut into the inside of the trailer hub. The few trailer hubs I measured in the store were just a hair over 2" (inner diameter) so you'll probably need a machinist to match the coupler to the hub.

For the idler side, buy another trailer hub and matching spindle and mount that on your mill.  Be sure you can adjust the spindle in and out a bit and can angle it up and down if needed.

Then I would find an inexpensive sheave from Surplus Center and mount that to my 1.25" shaft.  Anyway, that's what I would do.   Or you can throw caution to the wind and get a GIANT SHEAVE from the same vendor.  The price is right but at 280 pounds each, shipping would be rather painful!!!

Whichever way you go, building a mill was awfully fun!

Jim

[flip]

Torque gets you goin' horsepower keeps you rolling, most small engines don't develop a huge amount of torque so they rely on high speed to make up for the lack there of.  It ain't bad as long as your speed stays up which usually means your load/logspeed feed has to be slower.  Same reason everything on a cars engine that rotates is smaller and lighter, saves on HP loss due to parasitic rotational drag.

[slowzuki]

The weight of the wheels has nothing to do with the amount of power to turn them in a cut.  They will however take longer to spin up and longer to spin down, and they will not change speed as fast in a cut such as when you hit a knot.

So the heavier the wheels the better you can cut theoretical but you also get more unintended blade rotations so marginally less blade life.

[flip]

 ??? ??? ???

[Tom]

Yes, it is called inertia.  A body at rest tends to remain at rest.  A body in motion tends to rmain in motion.   The weight (mass) of the wheel creates greater inertia.  The definition of inertia being:  the resistance an object has to a change in its state of motion.


A heavy bandwheel doesn't rely as much on the responsivness of the engine because it has "stored" power in its weight

[mike_van]

Thats me Tom, about 9:00 PM, all out of inertia - body at rest, tending to stay that way  :D - I knew there was a name for it -  :D

[flip]

Ok, I'll bite.  Why then do  none of the mill mfrgs. not use 100lb "flywheels" for band wheels?

Our engines run WOT because that is where peak torque and HP are at.  If band speed starts to drop we rely on torque to bring it back up, I say it is easier to speed up a light object easier than a heavy one.  All of this goes out of the window though when you get into a diesel or something like a Wisconsin engine where it's all about torque.  Once you put a load on a blade HP goes out the window.  I'm still sticking to my guns on this. ;D

[Modat22]

They don't use 100 pound flywheels because it allows them to use a smaller less torqy motor.

If they had used 100 pound flywheels they'd have to use a heavier duty engine to get them turning or add a fluid torque converter to get the flywheel up to speed. Ether case adds to the cost of the mill IMO.

[Tom]

I was told that my idle wheel weighs in at about 200 pounds and my drive wheel at about 300 pounds.

when you are sawing and overcoming knots, etc.  You still depend on Horsepower to keep the wheels turning at speed.  It's just that the heavier wheels don't lose as much speed as the lighter wheels. You aren't having to depend totally on the engine.

You can't get them spinning quickly, but they are harder to stop too.

Kind of like comparing a 250cc Dirt bike to a Semi tractor-trailer rig.  Have you noticed that big engines with heavy flywheels (like tractors) can be lugged a lot lower and longer than a spiffey little, high revvin', lawnmower engine?

[slowzuki]

Tom is right on the money on this one.  Even the rotating mass (inertia) of a large, low power high torque motor contributes in some way.  One way to look at it is this with some simplified math:

To cut at a certain feedrate though a certain width with a certain set with a sharp blade it takes X torque and Y hp to power the blade.  This is a set thing.  If your motor is too big it just sits on the goveror with the throttle not wide open.  Most people just cut as fast as they can until there motor is the limiting factor.

If you where sawing an imaginary log that was ALL knot, it would take say 3X torque and 3X hp to saw at the same rate.  So if you ignore inertia you would need 3x the motor to saw a knot extending the full face of a board or you'd have to saw a third as fast maybe.

Now in life we have inertia that keeps the band turning when the motor doesn't have enough gumption to cut it.  Try it out, run your saw at max load in clear wood then double your feedrate.  Takes a bit for the speed to drop.  More inertia means long time for the speed to drop so the cut remains acceptable longer.  How this helps in real life is instead of running your motor governor up and down fighting every little knot, the engine is just charging the bandwheel / flywheel so it acts like a battery to help in the tough spots and recharge speed in the easy spots.

Making bandwheels larger diameter increases the flywheel/inertia effect better than just increasing weight so take a look at big mills.  A 30" bandwheel likely has 3-4 times the inertia of a 20" (I'd have to calc it for sure, just a rough guess) so you don't have to make solid discs to get the effect.

[firecord]

I think that technically you're both right.

I'm not an engineer, but I have done a lot of research.  In my opinnion it's not the engine nor the wheels.  It's the gearing. 

For example I have an Artic Cat 400 four wheeler.  I have 27 inch mud grips on it, but I had 25 inch.  It would go through anything with the smaller tires in high gear.  Now with the larger heavier tires I have to use low gear.  The motor just will not turn the bigger tires in the mud.  Same horse power - Same torque   Larger surface area to over come.

As for the band wheel  the blade speed is bound by the amount of surface area it must over come - period.  Lighter wheels will take less power to turn at the start and larger wheels will carry momentum further.  Both will be boged down by the surface area being passed through.   

Pick the wheels you want and build it to support them.

Just my .02cents

PS
Calculating Bandsaw Blade Speed
S.F.P.M. = Surface Feet Per Minute
   Knowing the S.F.P.M. for your bandsaw can be very important to getting the most from a particular blade and when cutting various types of wood. The blade manufacturer often specifies an optimum S.F.P.M. for the blade but attaining that rate depends on your saw and the speeds (pulley diameters) available.
The formula to determine S.F.P.M. is:
Motor RPM multiplied by the Motor pulley diameter divided by the Driven pulley diameter times the Bandsaw wheel diameter times pi (3.1416) divided by 12 = S.F.P.M.
Motor RPM X Motor pulley diameter / Driven pulley diameter X Bandsaw wheel diameter x 3.1416 / 12 = S.F.P.M.

[flip]

For the application at hand, a mill that will be cutting 32" and smaller logs, you will benefit more by using a sheave and a 18-25 hp gas engine than you would if you try and do the same with tires.  Less rotating mass means more gross HP at the blade.  Once your blade is in the wood HP and blade speed decrease minutely.  The only place where more rotational force would help is if, like said before, you are sawing in knots for just a second or two until the engine can catch back up, other wise it is a waste to swing that ammount of  rubber and steel.  Too much run out to deal with in that large of an assembly.  You're talking about 2 sheaves, 2 shafts, 2 taper lock bushings and 4 pillow block bearings.  the other way is 2 tire and wheel assemblies, 2 hubs, 4 wheel bearings, 4 pillow block brgs. 2 shafts, and some machine work.  Just buy the head from Linn lumber and be done with it.

[Dan_Shade]

what's the optimal minimum wheel diamter?

what's a good source for large sheaves?

[slowzuki]

The only hp loss between running sheaves or tires is the wind resistance, bearing drag differences, and the power to deflect the tread or v-belt (rolling resistance).  A steel band has the lowest rolling resistance the others I don't know.

As for the 4 wheeler analogy, you are on the wrong track for a comparison, putting larger tires on made all your gearing higher so your wheeler can go faster but you need to use a lower gear to get the same speed as before.  A sawmill is geared to produce near 5000 feet per minute at the band no matter what size bandwheel is used.

Changing to huge diameter bandwheels on the same gearing would sure change the dynamics, the blade would go way faster resulting in higher drag forces on the side of hte blade body which would equal more heating of the blade, would also mean you need faster advance speeds to keep the gullet filled which means more hp required.

The hp a mill needs is all about how fast you want to remove sawdust from the log.

[jpgreen]

A sawmill is geared to produce near 5000 feet per minute at the band no matter what size bandwheel is used.

Don't follow you there... Explain. 

Was that Spock that used to say that?  Who said that?..  ;D

Green sand casting could be used to make your aluminum wheels.  That would be a cool project.