Band Saw Guides

You don't want the bearing touching the blade, it produces too much heat and ruins the blade....I would go with ceramic guide blocks(linked) for precision cutting....

http://www.rockler.com/product.cfm?page=6542

Carter was the company I contacted. They told me to leave a dollar bill's thickness between the guide and the blade.

That makes sense to me. Sounds like a CYA moment, because they probably have to deal with people that overtighten the guides against the blade.

A dollar bill's clearance on either side, and those bearings are still going to be making contact with the blade. If not, there would be no reason for bearings.

The guy gave you some sound advice; which was intended to eliminate your drift, while at the same time, maximizing the life of your blade and guide.

At $350 a pop, I wouldn't want to buy those very often.

I could see people thinking, that the tighter they cranked down on the bearing guide, the cleaner the cut they would get.

Woodworkers aren't necessarily engineers.

I used these guides for over 30 years. I bought an old 36" Moak from a used equipment dealer. It had been set up for woodworking. When I told him that I was going to use it in a non-ferrous foundry, they changed out the motor from a 1800 RPM down to a 900 RPM to get the Feet-Per-Minute blade speed down to the range recommended for aluminum and bronze cutting. The FPM recommended for wood in far higher.

Besides the explanation for accounting for the width of the weld the higher speed found in wood cutting plus the wood dust that accumulates on the guides it would make sense to not have the guides too tight on the blade.

One of the biggest things I had to point out to any new operator was to make sure that the side wheels stayed about 1/4" back from the front edge of the teeth. If pushing and wear allow the blade teeth to get back to the side guides it takes the "set" right out of the teeth and even a practically brand new blade won't cut properly without enough set.

Generally when cutting metal your not going to to see the FPM on the blade, that you might with other materials. With most set-ups on metal cutting band saws given that fact the guides are generally set to the blade. This controls the blade and allows for a smooth and square cut. But as always, I would contact the manufacture for specific recommendations on each of the different styles of saws.

I replaced the old standard block guides with a guide that has roller bearings. The bearings are set against the blade no gap. You want both bearings to turn. Which puts the frictional heat internal of the bearing not on the blade.

Even with the old block style guides I set them against the blade no measured gap. What I did do was turn the wheel and take notice of the drag caused if too tight. Either way with or with out a gap the blade is going to make contact with these blocks generating some heat. It's a guide making contact and forcing the blade is it's function.

It is my reasoning that blade guides are used to keep the blade in a straight ahead cutting path. With a gap, the blade has a tendency to skew causing what is called "blade drift", the inability of the blade to track straight.

Yes and there is other things that can cause the same problem. Like a dull blade or feeding it too fast.

I received the following message in reply to my inquiry about blade guides.

Good question on the bearings for the guides. The clearance, which is only a few thousands of an inch, is for any variations in the blade, bearing or guide such as a thick weld or a guide / bearing that is not perfectly parallel to the blade. If you squeeze the blade between the bearings two things typically happen. The weld contacts the bearings and makes a clunking noise from the weld being too thick. Typically the weld on a blade is slightly thicker than the blade itself to ensure the integrity of the blade. This extra thickness causes thumping or clunking noises and extra wear on the bearings. The second thing that happens is that the bearings wear quickly with constant contact and can introduce blade tracking issues. If the bearing is not aligned perfectly parallel to the blade by giving the bearings constant contact you could actually "squeeze" the blade out of the guide and cause tracking issues. The slight amount of gap between the blade and bearings is so minor that the blade can't twist or turn enough in the bearing to introduce any blade drift.

Thank you,

Jeff Folkert

Carter Products

888-622-7837

I believe you've found a damned good US company.

I'll file their name in memory.

Let us know if you order these guides, and how they work out. I'd give the guy a GA if I could.

They work very well. Put them on an old Rockwell 14 saw a few years back.

I just love it when a tech department takes the time to actually answer a question, in detail.

If more US companies put the focus back into quality products and taking care of the customer, I think they would be amazed at what would happen to their long term bottom line.

With the picture of the bearings pinching the blade I can see problems with blade thickness variations causing very high bearing loading. If the bearings where offset then it would be more tolerant.

I currently use friction blocks and I allow about 3 thou so the weld passes without dragging.

I have found a worn blade wanders. Under a microscope I see the tooth set has been upset, or the one side of the blade has different wear patterns.

(hitting a nail really screws it up.)

Most of my blades are under $20 and I just scrap them when they start to wander. I cut them off to stop the temptation of getting more mileage from them.

For re-saw along the grain I find a wider heavier blade with significant tooth set tracks better and doesn't follow the grain so much.

I set my bearings so that they touch, but before I do I back off all bearings and then I make sure the blade is tracking right. Then I bring up the back bearing to just miss the blade as I find the thin edge throws sparks if it touches. I then bring one side bearing to just touch and then the other. Repeat for the bottom ones. I've been doing this for the past 20 years still on the same bearings. A word of caution, keep the side bearings back from the teeth a mil or so as the blade will move back onto the back bearing when you have to push hard to cut. I use blades with 1 tooth per inch on a 25mm blade and they have a lot of set.

Jim

If the ball bearings were not meant to contact the blade, they would not be needed, hence, yes they must contact the blade. They are the first "alignment" prior to the metal guides which are the final alignment of the blade into the material. If the ball bearing "pre-guides" are not set properly you will get premature wear (friction) on the metal guides, which in turn will produce heat, causing the blade to heat up.

As for the metal guides, I am not sure for wood cutting saws, but all my metal cutting saws use carbide guides which are "loaded" with belleville washers to ensure proper blade alignment with the material cut.

Every school shop I have gone to has the guides set wrong, most folks don't understand how they work and spoil perfectly good blades. The guides should be backed off of the blade, and the blade should be tensioned and allowed to center itself on the wheels. The wheels are crowned and if the blade doesn't track on them they need to be adjusted and the tires replaced, trued, until the blade tracks. The rear thrust guide can then be brought into contact with the blade with just enough pressure to get it spinning (otherwise it will develop a wear groove) but not push the blade forward, I do this with the saw running and the guards on the wheels. The side guides are adjusted with the saw turned off, and the wheels are moved by hand. They should be brought into contact with the body of the blade, behind the tooth gullet. If you don't do that, and bury the blade teeth in the guides it will take the set out of the blade first time you move the blade, now you have a dull brand new blade! The blade should then be hand fed through the guides by turning the wheels manually. Often the weld is not completely ground and the blade is thicker at that point, you will have to back off of the guides so that it passes through easily. Give it one last spin, and you are off to cutting!

by my point of view there should be a clearance to accommodate the blade when it hot .

for the straight cut there are many other factors also ,the tension of the band and un smooth/fast feeding of the material also the main Reason for skew

The expansion of the blade in thickness, which would be the important factor as it passes between the guides, is almost unmeasurable. A typical blade only has a thickness of only .025 in -.040 inch, it would need to have a temperature rise of many hundreds of degrees before it mattered, and if your blade is getting that hot you are doing something wrong. The length could increase measurably with temperature, this would be taken up by the blade tensioner, however it would have little effect on the guides. I agree that feed rate and tension matter a lot, as does the stiffness of the saw itself, but this was a question about setting guides.

It's the weld, if done properly the blade will be smooth at the weld, and dead straight on the back edge. Often the weld is slightly fat and that limits how close you can set the guides. If you hear a "thunk thunk" as the blade goes round most likely the weld is not perfect.