PDA

View Full Version : Quick question...Bandsaw RPM



Bruce Taylor
06-29-2003, 06:37 PM
Resawing some planks this afternoon, I fried the motor on my Delta 14". It was bound to happen, sooner or later...the machine was badly underpowered.

Anyway, I needed a quick fix, so I replaced it with a 2 HP compressor-motor that I had in the shop. It runs at 3450 RPM, instead of 1725. With the pulleys available to me, I partially corrected for the change...but I didn't have a large enough pulley to soak up all the extra RPM.

With the original setup, the saw wheels turned at 766 RPM. Now, according to my best guess, they're turning at 1054 RPM.

How stupid would it be to use the saw at this speed for a few days? I have some more resawing to do, and would rather not drive to town.

[ 06-29-2003, 07:42 PM: Message edited by: Bruce Taylor ]

ishmael
06-29-2003, 06:46 PM
Just an intuition, but I think the machine will handle it for a few days--maybe forever? Not that you'd probably want to leave it. If I'm not mistaken these saws have, in the past, been used with a variety of blade speeds, and this jump isn't huge.

In other words, I really have no idea. Someone will.

Dave Fleming
06-29-2003, 07:08 PM
Think blade tension, think weld strength, think tooth size and configuration. Proper pulley size can be figured out from some web sites or use your copy of Machinerys Handbook and look up the forumla for your self.
Whilst you are at it replace both the crappy pressed zinc pulleys or whatever that stuff is with two nice solid steel balanced pulleys, Browning is a name that comes to mind.

Ken Hutchins
06-29-2003, 07:16 PM
To add another factor, it will depend on what kind of wood you usually saw, the higher speed might be OK for softwood but a problem with hardwoods. :( You might try using bi-metal variable pitch metal cutting blades - Starrett or Lenox. These are usually twice the cost but the life is about 10 times the normal wood cutting blades. :D

mmd
06-29-2003, 07:18 PM
I'm on side with Dave. A 25% increase in blade speed will increase the dynamic blade tension significantly, and that extra stress will accumulate on the blade weld. IMHO, you have the choice of driving into town tomorrow morning for new pulleys or tomorrow afternoon for a new blade.

On the other hand, tomorrow might be your lucky day and you'll squander it on a bandsaw blade not breaking instead of buying a lottery ticket... :D

Bruce Taylor
06-29-2003, 08:25 PM
Good old forum. Thanks, all.

Michael, if it's my unlucky day tomorrow, I'd better stay off the highway. smile.gif

I guess I'll use it and see what goes sproing. I have a bunch of old blades that still have some life in them...don't mind wasting a few in the name of science.

Cheers.

Bruce Taylor
06-29-2003, 08:41 PM
Oh, and Dave...I'll look for some decent pulleys next time I'm in town. Might get some of those fancy link belts at the same time!

http://www.leevalley.com/images/icon/woodworking/03j8501c.jpg

Ed Harrow
06-29-2003, 08:45 PM
Iturra design recommends running the blade at a higher speed, tho the actual number I don't recollect. I will look it up and report back anon.

Dave Fleming
06-29-2003, 09:04 PM
--------------------------------------------------------------------------------
Iturra design recommends running the blade at a higher speed, tho the actual number I don't recollect. I will look it up and report back anon.
I would much rather take the word of a blade maker based on the particulars of the actual machine than some aftermarket accessory supplier.
NOT knocking Iturra but check out the Suffolk Machinery site and Highland Hardware site for what they that make the blades have to say about speed.
It all comes down to really taking the time to tune your machinery, don't matter if it is a drill press or a bandsaor, they ALL benefit from some time taken to 'sweeten 'em up'.
Ya folla?

Joel Herzel
06-29-2003, 09:07 PM
Pulley diameter tells the story. Twice the rpm motor speed? Use one half the motor pulley diameter. You have exactly the same blade speed. Or, it that size is too small to be practical, halve the saw pulley size. Same effect.

Ed Harrow
06-29-2003, 09:24 PM
LOL Dave, well at least in your collective opinionated opinions you both agree on Browning pulleys. ;)

Louis Ittura recommends 4000 fps blade speed. I'm not going to transcibe the whole details but...

Louis claims the old, lower speeds, were dictated by materials. High speeds with a carbon blade over-heated the blade and ruined the temper. A second limitation was the tires. He notes that simply substituting a higher horsepower 3450 rpm motor might well work but, given the 14" wheel on the delta, would probably lead to the blades breaking before they were dull, perhaps long before, in the case of carbide blades. So, therefore, he recommends 4000 fpm as a reasonable ocmpromise between the stock 3000 and the total to the max 6000. He also notes that, since they are borderline on power to begin with, a heftier motor is a requirement, esp if doing max resaw work.

They tested this setup by cutting a piece of 12 1/4" 5/4 mahogany into 8 pieces. They had a variation of .006 in thickness, with an "excellent surface finish."

Iturra Design
4636 fulton Road
Jacksonville, FL 32225-1332

888.722.7078
KALL@aol.com

His catalog is worth the price of admission; it has more information than some well-known bandsaw books. I say go for it, but mind the tires.

D Gobby
06-29-2003, 10:32 PM
Bruce
If my math is correct a 14" wheel turning at 766rpm would give you 2808fpm for the blade.
The same wheels turning at 1054rpm gives you 3863fpm for the blade.
If that helps any.
Check the recommended speed of the blade your using.

Darrel

Bruce Taylor
06-30-2003, 07:00 AM
Interesting stuff, Ed. If Darrel's math is correct (thanks, D Gobby) I've blundered into the right ballpark.

Oddly, the machine does seem to be running smoother with the cannibalized compressor motor than it did with Delta's unit...although the 2 HP motor makes a strange loud "click" when it is switched on, and again when powered down. I'll use it for a whle, but if it starts to affect the weather or create instability in the Middle East, I promise I'll stop smile.gif

Mike DeHart
06-30-2003, 07:50 AM
The *CLICK* you hear is most likely a centrifugal switch that cuts in and cuts out a starting winding in the motor. Nothing to worry about. It's a sign of a more powerful motor.

D Gobby
06-30-2003, 08:14 AM
Bruce

If you let me know the diameter of the drive pulley and the diameter of the driven pulley in inches then you would not have to guess the new rpm of your new setup. Let me know and I will run the numbers for you.

Darrel

Paul Scheuer
06-30-2003, 08:33 AM
Mike's right about the start winding switch being the source of the click.

I surprised that the original motor got toasted. Most have a thermal protector that disconnects power in an overheat situation. They usually require manual resetting. On the motor on my 14 there is red button the the end of the motor that pops out when tripped. (like a turkey thermometer). After the motor cools, you push it in to reset.

Bruce Taylor
06-30-2003, 09:00 AM
Thanks, Mike. I figured it was something like that.

Paul, I've overheated the motor before (resawing 6" maple is slow work at 1/2 HP) but this time, the little red button didn't bring it back to life. If I can rehabilitate the old motor, I'll find some use for it.

Thanks for the offer, Darrel. I did that little calculation (driven pulley diam. * driven pulley RPM / driving pulley RPM = driving pulley diam.) I found the pulley diameters simply by laying a measuring tape over them...but don't know how accurate that is.

It's amazing how much I don't know. Just the other day I realized that I had no idea where sesame seeds come from.

Dave Fleming
06-30-2003, 09:54 AM
It's amazing how much I don't know. Just the other day I realized that I had no idea where sesame seeds come from. Why I thought everyone knows they grow on Sesame Street!

<insert big silly grin here as I run and duck>

[ 06-30-2003, 11:31 AM: Message edited by: Dave Fleming ]