Thread: Band Saw Driving Me Crazy

I'm taking the table off again today so I'll get some photos and post in case anyone can see something.

Where did your blades come from, off the shelf somewhere or from a saw doctor/blade company that can make to order?

Quite often off the shelf blades with the retailers branding are fairly poor quality, often the cheapest they can source in Asia and while sharp may have uneven set on the teeth and other issues. On the other hand, saw specialists carry a wide range of quality blade stock in various width, TPI and material combinations and can assemble a decent blade fairly quickly and reasonably economically. If you can provide them with the nominal blade length, the material that you are mostly working with, the type of cut you are looking for (straight, gentle curves, tight curves etc) and the wheel size of the saw, they can recommend a particular stock to use.

If the blades have uneven set, the forces acting on the teeth are uneven and the blade will be twisted in the cut despite guide setup etc and will cut a curve toward the side with the deepest set and the blade twists in the kerf to try and balance the forces on the teeth. Even set on the teeth is as important co-planer wheels when setting up the saw.

Originally Posted by doragus

Thanks Neil and Skew. I'll check the coplaner issue but I'm starting to wonder if this whole band saw business isn't some kind of dark art. One expert tells you coplaner isn't an issue and not to mess with it. Snodgrass even says some manufacturers build in non-coplaner alignment because that's how their saws work. Another says wheels must be coplaner. I'll give it a go but I'm not sure about the issue.

Dislaimer: I have limited experience, having just setup and worked with only half a dozen bandsaws, so in comparison to someone like Alex Snodgrass, I'm a rank novice. Therefore, take the following comments as such.

I've looked closely at the Alex Snodgrass demo. When he talks about 'çoplanar' he is only referring to one dimension of coplanar alignment; ie. whether the top and bottom wheel are vertically aligned. He is right, that dimension is not relevant because the tilt adjustment to get the correct tracking of the blade invariable takes the wheels out of vertical anyway. The crown on the wheels compensates for any slight vertical (forward or back) misalignment. The only time that alignment can be an issue is if you cannot get the correct tracking position on the top wheel. I did have that problem when I tried to fit a 1-1/4" blade for the first time to one of my bandsaws and in that case I did need to shim the top wheel to get it tracking in the right position.

However, lateral or horizontal alignment is more of an issue in my experience. See post #5 in the following linked thread that raises horizontal misalignment as the cause of the twist problem.

Band saw wheel alignment -

Canadian Woodworking and Home Improvement Forum

One quick way of checking for this problem (without removing the table) is to back off both the top and bottom rear blade guides and manually turn the top wheel forward for a number of revolutions when it is adjusted to run in the correct alignment on the top wheel. Then turn the top wheel manually in the reverse direction for a couple of revolutions. If the blade stays align on the top wheel when rotated backwards then horizontal alignment is unlikely to be the issue. If the blade moves from the correct position on the top wheel when turned backwards twist may be a problem and it is time to remove the table (if necessary) to check for horizontal alignment.

This horizontal realignment solved the blade wander problem on several bandsaws hat I have set up/tuned up. Fortunately many newer and larger bandsaws now come with adjustment mechanisms for horizontally realigning the top wheel with the bottom. Without that mechanism built into a bandsaw realignment can be a challenge. If it is an old cast iron framed bandsaw, which is unlikely to have any adjustment mechanism built in, start with where the upper and lower castings are bolted together (taking care not to let any casting fall to the floor!).

Having got that solved, you still have to do all of the other setup routine covered by Alex Snodgrass.

Originally Posted by doragus

No can do Chris. The bolts come up through the trunion and the holes in the underside of the table are threaded for them.

AH! PM me your phone number and let's have a chat. I am home all day today.

I am far from being an expert and all that I know I learned on this forum plus some learning from making mistakes. Most times a blade will cut in line with my fence but not always so i tend to opt for what works.
Before we all went with Snodgrass fences were aligned to suit the blade drift or the single point fence was used. I made a version of this fence
Universal Bandsaw Fence - YouTube
I think some would see it as a cheat but it works.
Regards
John

Yes, drift was always allowed for in that way but in more recent times aligning the mitre slot and fence by moving the table has been found to give a better result. I sometimes wonder how much money Laguna made selling fences that are adjustable for drift.

Thanks everyone. I'm learning a lot from your advice.

OK so I did a complete tear down/rebuild this afternoon. Blade, guides and table set up a la Alex Snodgrass. I also tried with the blade centred on the wheel as recommended in the saw’s User Manual. I’m going to assume set up isn’t the problem.

The way the saw housing works it is not really possible to do the type of coplanar check recommended by Neil and Skew but, as you can see from the pictures, the blade seems to be located in the same position on both top and bottom wheels so I’m going to assume that any coplanar variation is only slight and it isn’t causing this problem which is quite exaggerated.

On closer examination I found there is some room for horizontal alignment of the table as Chris suggested. The holes in the trunnion are larger than the bolts allowing some movement. I aligned the table using the method Chris provided.

I’m a bit concerned that the whole table assembly is only secured by one relatively slight bolt that fits through the top and bottom sections of the trunnion and provides for the table to be tilted for angled cuts. It seems a bit flimsy but the table feels relatively stable when it is set up and tightened. I’m going to assume this is not causing this problem.

Anyway, all this and the blade still turns right as you can see from the first cut in the picture. The second cut with the blade is relatively straight cut freehand. I even tried Chris’ suggestion of a single point fence and, while this gives me a better result, the blade still wanders. In other words, I haven’t made any progress.

I’m down to a few possibilities now:

• The blades I have are crap as suggested by Malb. I did buy them off the shelf but assumed they would be OK as they are Starrett branded (with the exception of one branded Toolstorm which is probably a Chinese import). I tried a couple of different blades after setting up today and, while both turned right, one was a bit better than the other (the cut in the picture was the Toolstorm which I only bought last week). I have two other blades to try later. What sort of price would a “good” blade be and where should I be looking?
• The tyres on the saw look and feel to be in reasonable condition but there isn’t a very pronounced doming on the centre line of either tyre. Since this is my first band saw I’m not sure how much of a dome there should be. Can anybody point me in the right direction on this one.
• I haven’t got the blade tension right despite doing as Snodgrass suggests. The saw only has a thumbwheel tensioning bolt so it basically needs to be set by feel alone. Can anyone tell me how critical slight variations in blade tension can be.
• I need to dig a deep hole and bury this *&^%$# band saw before it buries me.

Tell me if you think I’ve missed something.
Thanks
Chris

Top Wheel Blade Position.jpgBottom Wheel Blade Position.jpgTable Mounting Bolt Through Trunion.jpgTrunion Base Mounted to Body.jpgTrunion Base.jpgTrunion to Body Mount.jpgCut Angle.jpgTrunion Top Mounted.jpg

With a blade of that size tension it as much as you can, the saw will most probably start to bend before the blade breaks. Me, I tension a blade by feel but there are ways of checking the tension.

This is one of many, I have seen a vernier caliper clamped to a blade and the stretch measured which would seem to be less trouble.

I think the best way to imagine how the blade relates to the fence and mitre slot is this, the blade changes angle across a crowned wheel as the tracking is changed and if all blades are set on the wheel using the bottom of the gullet at the centre line of the wheel then when blades are changed the new blade will be close enough to any other blade and will track in the same manner. To assist in this initially it might be a good idea to mark the centre line with a sharpie because then you have a reference if the tracking is changed.



I found this second video featuring Alex Snodgrass where he goes into a better explanation

Just put on more tension. If it still does it, put on more tension.

Originally Posted by doragus

• I haven’t got the blade tension right despite doing as Snodgrass suggests. The saw only has a thumbwheel tensioning bolt so it basically needs to be set by feel alone. Can anyone tell me how critical slight variations in blade tension can be.

On a blade of that size I wind up the tension until I can get a musical note out of it by plucking it mid-point on the free side of the wheels. I aim for a lower G... anything less is too slack.

Hear Piano Note - Low G - YouTube

That's a lot of tension on the machine with a blade of that size, so I don't leave that on the machine after I have finished with it for the day. Most models now have the advantage of a quick release lever to ease the tension between uses.

Originally Posted by doragus

The way the saw housing works it is not really possible to do the type of coplanar check recommended by Neil and Skew but, as you can see from the pictures, the blade seems to be located in the same position on both top and bottom wheels so I’m going to assume that any coplanar variation is only slight and it isn’t causing this problem which is quite exaggerated.

You can do an initial check for blade twist caused by horizontal wheel mis-alignment without having to get direct access to both wheels with a straight edge. As previously described...

Originally Posted by NeilS

One quick way of checking for this problem (without removing the table) is to back off both the top and bottom rear blade guides and manually turn the top wheel forward for a number of revolutions when it is adjusted to run in the correct alignment on the top wheel. Then turn the top wheel manually in the reverse direction for a couple of revolutions. If the blade stays aligned on the top wheel when rotated backwards then horizontal alignment is unlikely to be the issue.

Originally Posted by orificiam

I have the same Bandsaw as yours and have no problem with cutting straight as long as the blades are sharp,

Noting you have the same saw, I have some questions if you don't mind. Can you tell me if you have noticeable crowns on the tyres or do you know if the actual wheels are crowned? Do you centre your blade on the tire or do you centre the blade gullet? What size and type of blade do you run? How much blade tension do you use - as much as possible or allow say 5mm movement with gentle sideways pressure a la Snodgrass?
Thanks
Chris

Quote Originally Posted by NeilS

"One quick way of checking for this problem (without removing the table) is to back off both the top and bottom rear blade guides and manually turn the top wheel forward for a number of revolutions when it is adjusted to run in the correct alignment on the top wheel. Then turn the top wheel manually in the reverse direction for a couple of revolutions. If the blade stays aligned on the top wheel when rotated backwards then horizontal alignment is unlikely to be the issue."

Sorry Neil I missed this first time rouund...and I see what you mean The blade moves to the rear significantly - about 5-6mm - when reversed. Now if I could just figure out how to adjust it. I can't see any mechanism for adjusting the horizontal plane of the wheel so maybe I need to shim out the bolts which hold the wheel mount to the saw body. I assume the backward movement would indicate the left side of the wheel is too far "forward" and needs to be adjusted back.

Thanks
Chris

Originally Posted by doragus

Sorry Neil I missed this first time rouund...and I see what you mean The blade moves to the rear significantly - about 5-6mm - when reversed. Now if I could just figure out how to adjust it. I can't see any mechanism for adjusting the horizontal plane of the wheel so maybe I need to shim out the bolts which hold the wheel mount to the saw body. I assume the backward movement would indicate the left side of the wheel is too far "forward" and needs to be adjusted back.

5-6mm is not too bad compared to some I've seen. In one case there was so much twist that the blade ran right off the wheels when turned backwards. In that case I think they had just missed doing that adjustment before it left the factory.

Next question, does the same thing happen with any of the other blades you have for this bandsaw? Do they move back to the same extent when reversed? That would be a quick thing to do to make sure it's a wheel alignment problem and not a particular blade problem before tackling any realignment of the upper wheel.

Anyhow, if the same happens with your other blades and there is no horizontal adjustment mechanism built into the bandsaw then shimming on one side of the wheel mount is the only option.

I'd would still try to do some type of measurements to see how much the wheels are out of horizontal alignment before resorting to shimming. You might have to get a bit creative with that.

It's a while since I've done one of these horizontal realignments, so I can't remember which side to shim to adjust for a blade that is tracking back when reversed. Logic tells me it is what you have figured out, but logic doesn't always prevail. Go with what you think and see what happens.

If you are removing the upper wheel to do that the safest place for it while off the bandsaw is flat on the floor out of the way. Those cast metal wheels don't take kindly to any drops.