why no roller bearing behind the blade?

[steveh2112]

hi, i notice a big difference between 14" bandsaws for woodworking and big saws for lumber milling, is that the blade guide on the milling saws is always a single bearing with a flange at the back like this
How to adjust roller guides on a portable sawmill - YouTube

and on a woodworking bandsaw, they have 3 bearings like this https://www.youtube.com/watch?v=3MPR2kcMhJU

now i get that woodworkers are cutting at odd angles so the side bearings help keep the blade straight, but it seems the one behind the blade is useful to counter the forward pressure from straight cuts.

so why do bandsaw mills never use a bearing behind the blade?

thanks
 

[Dave Shepard]

The rollers are typically flanged. My Wood-Mizer ones are, and there is a specification for how close they are set to the back of the band.

[DanMc]

The guide bearings on the band mill also apply a preload to the blade, pushing it out, unlike a wood working saw that usually has a bearing on each side and the blade floats between them.  

I think the preload makes a bandmills blade stiffer and less able to follow soft spots in the wood.  

[KenMac]

Bandsaw mill blades are much sturdier and are tensioned much higher than woodworking bandsaws also. They don't depend on rollers to keep them tracking properly.

[JoshNZ]

I asked this question a while ago when I was redesigning my blade guides, the best answer I got was that it would cause the backbone of the blade to mushroom a little. Apparently it's been tried and you can feel a lip at the back of the band after some time.

[wiam]

On my home built mill I have a bearing behind the blade. Most of the time the blade is not touching it. I have not seen any damage to back of blade. 

[Magicman]

There has been much R&D into the blade guide design.  The flange on the back of the blade guide pulls the blade up and into the blade guide when it is contacted which helps to stabilize the blade.  A roller would do nothing but stop rearward movement.

[Larry]

I bought a Kasco 2 sawmill in 1994.  It had a bearing behind the blade.  Also had bearings above and below the band.  With the bands we were using at the time, the back of the band would mushroom.  After a few years the steel changed in the bands and that was no longer a problem.  The real problem was under hard cutting conditions, the band would push back hard enough that it could wear a groove in the bearing and eventually cut it apart.  I bought bearings for my old Kasco 10 at a time.

I think the flange rollers came about because of the use of a "V" belt on the band wheels.  A "V" belt is not a high precision item.  When used on band wheels it introduced vibration to the band especially with the loose "V" belts.  The flange roller can be adjusted to add down pressure on the band which takes the vibration out.

[steveh2112]

thanks for all the great replies, i'm building my own mill and planning to use this
Standard roller guide retrofit system by Cooks Saw
i assume that's the best system then?

i'll use 18.75" pulley wheels with V belts

[jpassardi]

Yes, I would go Cook's. That's was my plan for a build before I found my LT 15.
BTW: Woodmizer uses the same roller flange design.

[Joe Hillmann]

Keeping the blade guide compact could be part of it.  At one point my blade guides were made out of skate bearings because they are cheap and small.  They couldn't hold up to the speed and tended to fail quite quickly.  Using a larger bearing and putting a flange on it allows you to have a single bearing doing both jobs and, last a long time and fit it into as small a package as they can.

[RAYAR]

Here's a link to my blade support bearing set-up. It has a backer bearing. If you're blade is constantly or often contacting the backer bearing or backstop, your blade needs more tension. Mine has a spring tension set-up similar to a Cooks and I increased my tension a little more and never seem to force the blade back against the backstop anymore.

https://forestryforum.com/board/index.php?topic=111879.msg1753280#msg1753280