any guru on bandsaw designs?

[Tai Fu]

You know my 18" bandsaw has no tension spring. It's weird because normally there should be one, but on mine it's just a rod where you raise/lower the wheel, that bears on a square nut that goes directly on the upper wheel assembly, without a spring of any kind (I checked the exploded parts diagram and there is no spring).

Question is, are there bandsaw designs out there that does not need a tension spring, and what exactly is a tension spring for and why must a bandsaw have it?

It looks like there's enough space for me to insert a large spring between the bracket and the square nut, but since it's never a part of its design I just wonder what's the deal here? The saw works fine for the most part except for some weak links I had to fix... (such as 3/8" machine threaded tension rod that belongs more on a Delta 14" clone than a 18" bandsaw)

[Dennis Ford]

I am not a guru but will answer anyway: My band-saw does not have a spring either. Most of the smaller saws have a tension spring and those springs have some use in setting tension.

[Tai Fu]

What bandsaw do you have?

Most bandsaws sold in Taiwan do not correspond to what you guys use (especially not anything like Minimax), some may correspond with Laguna or Grizzly since many of them are made for export. However I have seen cast iron 26" bandsaws (as in the bandsaw frame is cast iron, like old Olivers) out there (that I would have gotten if it weren't for space issue) that uses a weight on a lever for tension, I doubt it has springs either. Seen them in use at lumberyards and they produce really smooth resaws with carbon steel blade, smoother than my Woodmaster CT in fact!

[jack forsberg]

spring assessed tension does a few things. One it maintains even tension when the blade gets hot and expanses in length and 2 It is also a shock absorber to save the tires when the blade hits something hard like a knot or worse. In the end blades last longer and so do tires.

[Dennis Ford]

What bandsaw do you have?

Most bandsaws sold in Taiwan do not correspond to what you guys use (especially not anything like Minimax), some may correspond with Laguna or Grizzly since many of them are made for export. However I have seen cast iron 26" bandsaws (as in the bandsaw frame is cast iron, like old Olivers) out there (that I would have gotten if it weren't for space issue) that uses a weight on a lever for tension, I doubt it has springs either. Seen them in use at lumberyards and they produce really smooth resaws with carbon steel blade, smoother than my Woodmaster CT in fact!

Mine is a "Laidlaw" (I believe that they have been out of business for many years). It is one of the OLD cast iron machines (30" wheels).

[Phil Thien]

I've played with saws w/o tension springs, but only small ones. Each turn of the tension screw was 1/24th of an inch of movement. Once all the slack was out of the blade, there was only a fraction of a turn to apply the correct amount of tension. Not a very fine-grained adjustment!

Likewise, small movements in the screw (loosening) during use may release large amounts of tension from the blade, whereas on a saw with a tension spring a small amount of rotation of the screw would release an insignificant amount of tension.

I did play with a very large bandsaw without a spring IN the tensioner, but was later told there was a leaf spring somewhere that I hadn't seen. This was 30 years ago after I first got my table saw and visited a commercial shop in downtown Milwaukee where my father had taken me to get cutoffs.

So Tai, how do the spring-less tension mechanisms on these saws work? Are they simply threaded screws?

[Tai Fu]

Pretty much... but maybe there might be some shock absorbing thing somewhere else I don't see... I never had a problem with tensions being released due to band stretch. Maybe on larger bandsaws it just doesn't matter so much...

[Phil Thien]

Pretty much... but maybe there might be some shock absorbing thing somewhere else I don't see... I never had a problem with tensions being released due to band stretch. Maybe on larger bandsaws it just doesn't matter so much...

I imagine many frames have elasticity which is greater than a nearly fully compressed tension spring.

[Chris Friesen]

The main issue that I see is what Phil mentioned. Without a spring in there, moving the axle support translates directly into an increase in blade tension....basically you're using the flex in the frame as your spring. If you add a spring in there, you get finer control over blade tension because you increase the distance the tension adjuster has to move to get the same amount of tension on the blade.