Thread: Variable speed Bandsaw Upgrade

The relatonship between “Speed and Feed” is vital to the proper function of a Band Saw and requires a saw operator’s full attention least the saw fail to perform as anticipated.
Blade Speed is defined as the distance in feet the blade travels in one minute. That is a measurement of S.F.P. M. or Surface Foot Per Minute.
In order to insure the proper blade speed, the SFPM must be optimum for the application. The drive belts must not be slipping under the load being machined and the tachometer must be checked often to assure the proper RPM’s are being maintained.
To insure that those RPM’s are being maintained properly and making the assumption that you may not have a tachometer, there is a simple and actually kind of fun method to assure that RPM’s are being maintained (this only works for RPM’s being set up to 600 SFPM)
• Use the weld as a reference point or make a dark line across the blade with a Magic Marker
• Start the saw and count the number of times that the mark comes around in one (1) minute
• Multiply that number by the length of the blade in feet and inches
(12’ 6” blade; the mark or weld comes around 14 times in one (1) minute;
12.5 x 14 = 175 SFPM
Easy right?
Now, what is the relatonship between feed and speed and tooth pitch?
* INCREASING THE WORK SIZE will decrease tooth penetration

* REDUCING THE TOOTH PITCH will increase tooth penetration
* INCREASING THE TOOTH PITCH will decrease tooth penetration
* INCREASING THE BLADE SPEED will decrease tooth penetration
* REDUCING THE BLADE SPEED will increase tooth penetration
For example if your work piece is a 1″ solid round and you set the machine to 100 pounds of feed pressure on your blade;
If you have a 2 T.P.I. blade, that would equal 50 pounds per tooth of penetration
If you have a 10 T.P.I. blade, that would equal 10 pounds per tooth penetration
Understanding and learning these rules will be a huge advantage as you develop into a professional and thoroughly competent band saw operator.

Hi Bosox,
thank you for the thorough reply.
So if I understand you correctly, the idea is to to reduce the tooth penetration for a given feed rate by increasing the sfpm.
This would therefore also change when using a different tpi blade.
Is there a scientific formula to determine the optimum sfpm for a given blade width and tpi?
I'd imagine that there is a diminishing rate of return when reducing tooth penetration to the point where the blade cut is ineffective.
Thanks for your help. Cheers Ian

My job is to cut metals and woodworking is just my hobby. But I am quite sure of the facts and ideas I gave you. The problem is, in metal cutting, speed and feed rate charts are already available so we don’t bother asking how the metal cutting industries have arrived to such results(we just follow them). To answer your question, No, I don’t know (if there is) the scientific formula to determine the optimum sfpm for a given blade width and tpi. But in cutting wood, it's recommended that you stay around 2000-3000 sfpm. If you go beyond or below the recommended rate, blade problems may arise. Let me explain to you how it works.

As I have said in my previous post, when you increase the blade speed, the tooth penetration decreases. And when blade speed is increased, sfpm also increases. Therefore, when sfpm increases, tooth penetration decreases. The harder the wood, the closer you stay on 2000 sfpm for better tooth penetration. Softer woods could allow you to stay at maximum 3000sfpm for they require less tooth penetration than harder ones. You must stay between 2000 – 3000sfpm to perform accurate,straight and good cuts.

With this rate, you wouldn't come to the point where you experience diminishing rate of return caused by reduction of tooth penetration that results to ineffective blade cut.

Cool, this makes a lot of sense then.
Your earlier method of determining sfpm works up to 600sfpm you say.
I suppose I could use a contactless Tach to determine the higher sfpm.
Once I've established the relationship between the Hz on the VSD and the sfpm,
I'll be able to set the bandsaw speed I need by simply dialling up the required Hz on the VSD.
It looks like I will only need to vary the sfpm between 2000 and 3000 depending on the timber and the blade.
Experience will soon tell me what works for a given combination.
Bosox, thank you very much for your help. Cheers Ian

Yes, that method works up to 600sfpm without the use of a Tachometer. Mostly compatible sfpm’s for specific metals. Don’t forget to start slow before achieving the required maximum band speed. Experience is always the best teacher. It’s my pleasure to help a fellow woodworker. Good luck to you, Ian!

That's the beauty of a VSD. I can program an acceleration curve to suit.
Cheers Ian

Good thing you have a VSD. Make sure you’re on the appropriate sfpm range for best results. Good Luck! I appreciate some updates from you!

Have finally finished the last room of the house.
This means that the next weekend I get to spend some time in the shop having fun.
Will be having the tidy up from hell and then I'll look at doing the bandsaw upgrade.
Will post photos when I can. Cheers Ian

Good for you! I don’t have much time for my shop for the moment, so I’ll be missing the fun for a week or two. I’ll catch up with all your photos if you post some. Good luck!

I put a 3kw 3ph motor on my 19" a while back, I wanted more speed over what was original so I changed the drive pulley so now I have 6000+fpm and that is the slow speed, the high speed is not much faster but it is, I use the Lennox woodmasterB or woodmasterCT, I cut green, dry, soft, hard, thick, thin, boards, veneers and the occassional curve, the only time I have drama is when the blade goes dull

To check your blade speed as it is now just put a chalk mark on the motor pulley (power off)and the blade wheel, rotate the wheel once while counting the motor pulley turns, my guess would be around the 3 to 5 turns, do this for both ratios, then it's simple calcs
Surface speed=motor rpm x pi x dia wheel / ratio
for mine it's 2850 x 3.14 x 0.48/2.2=1952m/min or 6246fpm
I'm guessing you know motor speed =120f/p so for a range of ~30 to 50 hz for my case I could go from 3946fpm to 6246fpm.

The electronic braking is a good option for stopping the BS, I have it as standard on my TS works well


Pete

Lennox blades are good blades but they dull fast. I got my blades from sawblade.com. Their blades last longer than most of the brands. Their blades are 30% less compared to other blades. I purchase on volume orders for greater discounts.

Hey Ian how did you end up going with this?

Cheers

Originally Posted by simonmags

Hey Ian how did you end up going with this?

Cheers

Chuckle, was looking at the motor and VSD gathering dust under the bench on Sunday. Will get around to it someday, just can't quite afford the downtime to spend on this particular project.

I have got to say though that the 3K spent on the Carbatec was money well spent, thing takes a hammering and has never let me down.
I promise to update this thread when I do the change over, with Pics.
Cheers Ian

Hi PJT, why did you end up going so fast in fpm with your blade, is 6000 not a bit on the high side, just going off some of the previous posts? Thanks for the ratios you guys have put up here too, will be very useful to ensure correct cutting when i get mine going.

I''m guessing you guys either run commercial operations or are more talking about bandsaw mills than your garden variety vertical bandsaw. I'm just trying to work out this VFD / VSD stuff my saw. https://www.woodworkforums.com/f27/ce...-450nl-166960/