Bandsaw blade tension spring rate

[gordon 131]

I am working on a couple bandsaws right now, and while I am waiting on parts for my W/T 16” , I thought I would address the blade tension spring on my 36” ASMCo bandsaw. The spring on this saw has been mush , since I rebuilt and refurbished this saw years ago.
I typically use a 1/2” blade 3tpi on bothe saws , but do have a 3/4” and even a 1” blade I believe.
I am looking into replacing the spring with a die spring.
Is there a certain spring rate that one looks for when changing the spring?? Is there any spring places people have had good luck with?

I am looking at Lee Spring and have found a few die springs that may work, they have these spring rates 235,374, lbs./. Are these spring rates in the ballpark of what a guy wants?
Thanks for any input.
Gordon

[GNP]

Wow, 36" bandsaw, that might take a car spring.

[bjmh4]

I am working on a couple bandsaws right now, and while I am waiting on parts for my W/T 16” , I thought I would address the blade tension spring on my 36” ASMCo bandsaw. The spring on this saw has been mush , since I rebuilt and refurbished this saw years ago.
I typically use a 1/2” blade 3tpi on bothe saws , but do have  a 3/4” and even a 1” blade I believe.
I am looking into replacing the spring with a die spring.
Is there a certain spring rate that one looks for when changing the spring?? Is there any spring places people have had good luck with?

I am looking at Lee Spring and have found a few  die springs that may work, they have these spring rates 235,374, lbs./.  Are these spring rates in the ballpark of what a guy wants?
Thanks for any input.
Gordon

I can tell you it takes between ~350-500 lbs. to properly tension a 1/2" blade. My die spring has a rate of 130 lb./0.1" and a load of 1170 lbs. at max deflection (which is 30% of its free length or 0.9 in.)

[jteneyck]

I can tell you it takes between ~350-500 lbs. to properly tension a 1/2" blade. My die spring has a rate of 130 lb./0.1" and a load of 1170 lbs. at max deflection (which is 30% of its free length or 0.9 in.)

That's in the right range.  A 1/2" x 0.025" blade has a cross section of about 0.0125 sq in.  The gullets will decrease that value, but it's a conservative value to use.  If you want to apply 25,000 psi to the blade, the force on each side of the blade is 313, so the spring will see 626 lbs.  If you want to go to a 3/4" x 0.035" blade then the force on the spring will be about 1300 lbs.  Again, the gullets will decrease the cross sectional area and, therefore, the force required of the spring, but having a higher capacity spring is never a bad thing.  

The spring has to fit into your saw and the spring rate has to be high enough not to exceed the travel range you have in the tensioning mechanism on your saw.  The lower the spring rate the better, since you can better fine tune the tension, as long as it does not exceed the travel range.

[Cabinet Monkey]

Louis Iturra in Jacksonville, FL can help out, I’m sure. 


904-642-2802

[gordon 131]

Thanks for the replies guys.
I was doing some research and found a die spring that I am pretty sure will fit my saw. It is 5” long and has a spring rate of 374 lbs/in and fully compressed is 2.9 inches with a spring rate of 766 lbs/in.
John do you feel this would be a good spring for this saw?
Thank you
Gordon

[jteneyck]

Thanks for the replies guys.
I was doing some research and found a die spring that I am pretty sure will fit my saw. It is 5” long and has a spring rate of 374 lbs/in and fully compressed is 2.9 inches with a spring rate of 766 lbs/in.
John do you feel this would be a good spring for this saw?
Thank you
Gordon

Spring rate is a constant.  I suspect that last number you listed, 766 lbs, is the force when the spring is compressed to 2.99", yes?  If so, it will work with 1/2" blades, but won't provide adequate tension on a 3/4" blade.  It would be limited to about 14,500 psi blade tension at max. load.  

I would look for a spring with a spring constant of at least 700 lbs and at least 2" of travel if you want to use 3/4" blades.  Of course, this all assumes the frame of the saw can support that load w/o significant deflection.  

John

If your saw can handle a 8" long spring, this one would do it:  Link

[gordon 131]

Thank you John for the information.
I do not believe my saw can handle the 8” spring.
I think about 5” is about max on length.
And yes the spring is rated at 766 lbs at 2.9 inches in length.
I may just have to go with that spring I was referring to.
Thank you
Gordon

[jteneyck]

Thank you John for the information.
I do not believe my saw can handle the 8” spring.
I think about 5” is about max on length.
And yes the spring is rated at 766 lbs at 2.9 inches in length.
I may just have to go with that spring I was referring to.
Thank you
Gordon

Here's a 5" long one with a maximum load of almost 1500 lbs at 1.25" compression.  

Link

John

[gordon 131]

John, this is the problem I am having locating this spring. The OD of the spring sits down inside the casting of the upper main C frame of this saw, and the adjustment rod is a long 1” acme thread bolt that goes up through the underside of the upper C frame through the spring then up through the
Upper wheel mounting fulcrum. So the O D of the spring that is in there is only 1.67. There is a little room in there , but not 2”. It is kinda hard to measure as well, as it is just rough casting and not machined out. So with this limited OD I am working with , a spring with a larger wire gauge is hard to get in there. The spring that is in the saw now and complete mush is 4.67 long, 1.105 inside , 1.67 outside with .250 wire.
The one I am looking at from Lee spring is 1.73 outside with .283 wire , which may be the best option I have tried so far.
I talked with Louis Iturra this morning and he told me , based on my current spring specs that he cannot help with this one.
It is looking like I may have to just try the one I found, at least it will be better than the mushy one that is in there. I am going to look at trying to get a slightly longer one in there if it has higher rate , or maybe 2 shorter ones together.
I really do appreciate your info John , as I did not know what spring rate values I was looking for.
Thank You
Gordon