Blade speed. I need a math whiz

[ozarkgem]

I have not been happy with the speed my mill cuts. I have had 3 different motors on it. I have a 20 HP 3 phase electric on it now and it doesn't seen to make any difference on the size or species of the log ,I can only go so fast (slow). I got the tach out and measured the blade speed. The wheel on the tach is 6" in cir. So the blade is running about 4800 FPM. I am not sure if this is fast enough. I have adjusted the flatness of the blade and tried every other thing I have read about but nothing changes.  the motor is  1750 RPM. the motor pulley is 4 3/4" and the drive pulley is 8". So if I need to speed it up what size motor pulley do I need? Or does anyone have any other suggestions?  Running 1 1/4 X 7/8 pitch Cooks blades. I can usually saw one good sized Oak and the the blade is dull. I don't have a debarker but if the log is dirty I use the log wizard to make a path for the blade.I have watched a WM saw and I can saw at about half the speed it does.

  

  

  

  

  

[ladylake]

 4800  fpm should be fine but if any thing I'd slow it down a little..  Are you running out of power or cutting crooked.  A 20hp electric should have plenty of power if it's putting out the full HP.  If using a phase converter I think some only put out 2/3 of the actual hp. Is your wiring heavy enough, too light the motor wont make full power. Steve

[ozarkgem]

I am running a 20KW generator so power is not a problem. Not cutting crooked just slow. How much should I slow it down?

[ladylake]

I'd try a 4-1/4 pulley on the motor and see if that helps.  Is there a chance you belt or clutch is slipping, that's a lot of power to put through a single belt.  Steve

[bandmiller2]

Ozark, Steve is right about the single belt for that power you should have at least two "B" series belts. Another possibility is your electric clutch is slipping. I have a 15 hp Baldor 1725 three phase on my mill and scads of power to run the mill and hydraulics. Have someone else make a cut with your mill you tach it before and during the cut the truth will surface. A 20 hp three should not slow down. Frank C.

[ozarkgem]

I'd try a 4-1/4 pulley on the motor and see if that helps.  Is there a chance you belt or clutch is slipping, that's a lot of power to put through a single belt.  Steve

it has 2 belts. I don't think the clutch or belt slips as I can hear the motor pull down a little.

[ladylake]

 Opps it looked like 1 belt but looking closer I can see 2.  I'd give the smaller drive pulley a try .   Steve

[venice]

4800 FPM sounds good to me on a manual mill. Did you try other blades yet? Could make a difference.

If you want to play around with different pulley sizes and see what the resulting speed is, i just send you a link to a calculation form. One thing to consider; if you are changing the pulley size, torque will be also affected to some degree.


Hope it helps. venice

[backwoods sawyer]

The wheel on the tach is 6" in cir. So the blade is running about 4800 FPM.


 

Seems the reading would be the actual reading unless the book for the tack says other wise :P 

been a while but it seems like 3,500-4,500 is the ideal blade speed, to fast has as many issues as to slow.

[ladylake]

 
http://www.cookssaw.com/Articles/bandsawturn.php 

Here is good reading from Cooks and they know sawmills.    Steve

[Joe Hillmann]

What type of wheels is your blade running on?

[ozarkgem]

What type of wheels is your blade running on?

18" v groove with a v belt in them

[ozarkgem]

The wheel on the tach is 6" in cir. So the blade is running about 4800 FPM.


 

Seems the reading would be the actual reading unless the book for the tack says other wise :P 

been a while but it seems like 3,500-4,500 is the ideal blade speed, to fast has as many issues as to slow.

that is the actual RPM but the cir of the wheel is 6" so each rev is 1/2 foot. So half of that would be the actual FPM. (I think)

[Joe Hillmann]

What type of wheels is your blade running on?

18" v groove with a v belt in them

Then I can't make any suggestions.  I thought maybe it was a homemade mill that uses trailer tires to run the blade on.   There were several issues that I could think of that could happen using trailer tires.  But none of those would be an issue with v-grooves and belts.

Are you sure there is nothing your blade may be hitting/rubbing that may be taking out the set.  Could the blade be running too far back on the wheels causing the set to be taken out or are the teeth riding on the blade guides?

Have you tried more than one brand of blade?  Do they all have the same issue? 

[dablack]

I have not been happy with the speed my mill cuts. the motor is  1750 RPM. the motor pulley is 4 3/4" and the drive pulley is 8". So if I need to speed it up what size motor pulley do I need?

I don't know what the optimum FPM a blade should be moving but if you want it to move faster, you need a BIGGER motor pulley, not a smaller one.  Going to a bigger motor pulley will move the drive belt faster for the same motor RPM.  You will lose some torque but pick up speed.  Just wanted that to be clear.

thanks
Austin

[Delawhere Jack]

I'd guess you've got some slippage as well. Your band speed is right in the proper range, and the power is adequate. I'm with Bandmiller, see if you can get a reading on the band while it's cutting.

Cutting too fast, and I think too slow also will dull bands prematurely.

[ozarkgem]

What type of wheels is your blade running on?

18" v groove with a v belt in them

Then I can't make any suggestions.  I thought maybe it was a homemade mill that uses trailer tires to run the blade on.   There were several issues that I could think of that could happen using trailer tires.  But none of those would be an issue with v-grooves and belts.

Are you sure there is nothing your blade may be hitting/rubbing that may be taking out the set.  Could the blade be running too far back on the wheels causing the set to be taken out or are the teeth riding on the blade guides?

Have you tried more than one brand of blade?  Do they all have the same issue?

The blade runs where it is supposed to. Not taking out the set. I have just got some Cooks and they do last better. I talked to a Amish and asked him how many blades he used in a day and he sharpens 3 of a morning for the day. I will use 7-8 a day in Oak. To be fair he has a debarker and I don't but I am very careful  about not sawing dirt.

[Delawhere Jack]

Not counting metal strike bands, I'll go through 4-6 bands sawing oak in 8 hours. No debarker, clean to slightly dirty bark. Really dirty logs, out come the wire brushes. All hands on deck tasked with brushing the mud off.

[BCsaw]

I have to agree with Austin. If you are correct with the pulley size, you have an under drive situation. A torque increase and a speed decrease from what was input. If your motor is 1750 rpm you would only be seeing 1039 rpm out of a 4.75 to 8 " pulley arrangement. If the 8" was on the motor then you would have a speed increase and torque decrease. Your output rpm would higher than what was input.(an overdrive situation) Near 3000 rpm.

My 2 cents.

[pineywoods]

Ozark, it sounds like something is slipping somewhere. I see the tach on the blade showing about 4800 fpm, and that's good, BUT that's with no load. Here's something you can try, cheap and quick. Get yourself a bicycle speedometer ($9.95 at walmart) and install it on the idle bandwheel. Just a small magnet glued to the bandwheel and a pickup coil mounted so the magnet passes close by. Watch the readout while you saw a log, any slippage will show up quickly.

[venice]

If the 8" was on the motor then you would have a speed increase and torque decrease. Your output rpm would higher than what was input.(an overdrive situation) Near 3000 rpm.

...and would give you the blade speed of an high speed industrial saw - aprox. 13.880 pfm. 

Must be like standing next to an helicopter.  :D

Have a good weekend everyone. venice

[ozarkgem]

Ozark, it sounds like something is slipping somewhere. I see the tach on the blade showing about 4800 fpm, and that's good, BUT that's with no load. Here's something you can try, cheap and quick. Get yourself a bicycle speedometer ($9.95 at walmart) and install it on the idle bandwheel. Just a small magnet glued to the bandwheel and a pickup coil mounted so the magnet passes close by. Watch the readout while you saw a log, any slippage will show up quickly.

good idea

[scor440]

Water drip to cool the blade?

[schmism]

pure math says blade speed is 4894 sfpm   
8/4.75 = 1.6842 *1750 = 1039rpm *pi*18/12 = 4894sfpm

use a clamp on ammeter to measure current draw in each leg of your 3 phase power to determine if your motor is putting out full power.  You should be able to compare that to nameplate amp listing.  (although freewheel amps,  under load amps and locked rotor amps will all vary)   Im to tired at the moment to look up what nameplate amps are listed at.  (i dont think they are locked rotor amps but they might be)

[WoodenHead]

pure math says blade speed is 4894 sfpm   
8/4.75 = 1.6842 *1750 = 1039rpm *pi*18/12 = 4894sfpm

use a clamp on ammeter to measure current draw in each leg of your 3 phase power to determine if your motor is putting out full power.  You should be able to compare that to nameplate amp listing.  (although freewheel amps,  under load amps and locked rotor amps will all vary)   Im to tired at the moment to look up what nameplate amps are listed at.  (i dont think they are locked rotor amps but they might be)

I would rewrite the equation a bit  ;), but I agree with your answer 4894 fpm by calculation.  I thought I had read somewhere that 5200-5500 fpm was ideal, but I couldn't say if that is your problem.  On paper you have plenty of power and torque for the application.  If you want to test your motor output, you should measure each phase current under load and compare to the motor name plate values (FLA - Full Load Amps).  If there are considerable differences between phases that could mean problems.  Locked rotor btw is a different number (usually not shown on the nameplate) that is about 3-6 x FLA.