Grinding off bandsaw blade teeth to make a coarser blade?

[Flynth]

Well, there's the first clue as to why nobody makes a blade to do this. Of course, when I'm backed into a corner, I don't typically take good advice like that either.

But the saw is fully capable of handling a 5in round, or let's say 4in by 4in square for which one is supposed to use those blades. It just happens that the other dimension of my material is very big, but that doesn't affect the cut that much (only in the beginning when the saw is lifted at an angle). This is why I have to come up with "unorthodox work holding".

If your work holding involves a gantry crane, it is definitely unorthodox in my book.

I've since added another C clamp to hold the movable jaw. The configuration pictured is just to test if the saw will clear the material.

I suspect there is some technological limitation to making let's say 3tpi bimetal blade in half inch width. I saw a youtube video how they make those blades and it was shown they get hss in a form of a wire. They flatten it and laser weld it to spring steel back. Perhaps this is why there is a limit on total height of every tooth? If they made tall teeth, they would need to use thicker wire, that same thick wire would he part wasted on high TPI blades. So instead of running two manufacturing lines for coarse blades and high TPI blades, they probably just choose high TPI.

To me those bandsaws are pretty much superseded by "cool" cut circular carbide saws for thin section and let's say up to 2in thick solid material. My DeWalt DW872 cuts steel square tubing, round tubing, and small solid rods in seconds with no coolant required. I bought it 6 years ago and I'm on my second blade. I cut lots of metal in that time(One of the things I made was 55 meter long steel fence that contained 400 vertical pieces) . But where I still would use a bandsaw is for tool steel (DeWalt saw can't be slowed down), and big material (i don't want to risk overheating that expensive carbide blade). I think as time goes on more and more people will realise the same, so making low TPI blades only for big saws by the manufacturers is them shooting themselves in the foot.

I admittedly am one of those who will wait for the wrong blade to get done.... But when being cheap/lazy/practical, and when cheating just isn't working... I'm also a fan of not fighting with it too much. If you're really stuck, and the and the tool just isn't working, and clearly is not going to... If your available band saw blades cover the same price range/quality range as what's a available here, I think risking one small band saw blade might be cheap science. And if all of the tooth grinding fails totally, you still have a "test blank" to cut apart and weld together, to see if you and your welder can get it joined and straight and annealed and flattened to a satisfactory degree to consider actually making your own. That would open up a whole world of possibilities.....

That's an idea! I'm not sure I want to go down that rabbit hole, but maybe?

You're cutting the 5 inch dimension, right? And to clarify, your 6/10 blade has the variable pitch happen frequently enough that there's always a full section of 10tpi fully engaged in the cut, right? If so, here's my thought.

I can find recommendations for harder steel that are anywhere from 6 teeth in the cut, all the way to 20 teeth in the cut. I'd take a "hope for the best, but plan for the worst" approach. I wouldn't do one in three or two in three teeth.
If you started out by going to only the 10TPI sections, and removing every other tooth, your 6/10 blade would become a 5/6 blade. You'd go from (estimating) 40 teeth in the cut, to 27 or so. Still technically too many teeth, but WAY closer... So if you dug out those teeth (and increased the gullet a bit. The 6TPI portion would have gullets really close to exactly what you need, and I'd bet with a non-power fed saw, you wouldn't need a whole lot of extra. So a very good visual reference.

So then, you could test the results with a 5/6 blade. This saw won't have the horsepower to make that cut "fast", but Is that enough to work acceptably? Maybe. Maybe you're done, and you've still got a blade that's useful (maybe even good) and could possibly go down to cutting material that is an inch/25mm or more. Or maybe it isn't enough.

If it needs "thinning" again, you could do the whole blade this time, at every other tooth, which would take the 6TPI section down to 3, and the "custom" 5TPI section would drop down to 2.5. That's going to get you down to 13ish teeth in the cut. That will get more pressure on the teeth, but that will make the blade all but unusable on stuff that's smaller than 2inch/50mm.

And, if that all completely and wholly fails, you could one more time cut out every other tooth. 1.25/1.5 TPI. That's gonna be rough on a small saw, but maybe... That would put you with 6.875 teeth in the cut. This is pretty close to the lowest side of recommendations. Which means the blade will be of no use for anything smaller than than what you're doing.

Yes, that's the shorter dimension. I think this is a good idea.

For a start I decided to see how that cut will look like without removing any teeth. I started with an old 6 TPI blade that has quite a few teeth missing. Unfortunately that blade is old an dull, I thought it would brake or jam, but it started going sideways... Thankfully I caught it before it went more than 20 though to the side.

Then I decided I'm going to give the new 6/10tpi blade a try as is first. I couldn't use the same cut because the new blade has slightly wider set so I moved it few mm and I started the cut. This was yesterday night. It is a new blade and I'm trying to break it in easily so I tried to start it gently. I stopped it to go to bed when it cut maybe 2in deep. At this stage it was still cutting fairly well. Who knows, perhaps I'll not need to remove those teeth? I had to stop yesterday, because it got quite late. Well see how it goes today. It took 20min to cut 2in deep. By all accounts that is slow, but as mentioned, I'm trying to break that blade in easily. Halfway through I intend to try pushing it much harder.

And two additional blade suppliers that claimed to have coarse blades claim to have posted them (one was 4/6 if I remember correctly, the other straight 6). When they arrive we'll see if they both turn out to be 6/10 too.
Edit: Both blades turned out to be 10tpi. I can't even...

 

[Flynth]

I've tried using the 6/10 blade first as a sort of control. It was a new blade so I didn't want to push it too hard. The cut took approximately 6 hours... It probably could do it in 4~5h, but the downfeed stops on the saw from time to time and I need to touch the valve every 15~20min (open and close again the tiniest bit - there is more about it in another bandsaw thread).

 

[Jake M]

Wow.... That's one heckuva setup you've got there. What could possibly go wrong? You know how many safety warnings from the manual you've disregarded? When I've got something like that to do..... Oh, wait. Never mind. Carry on...... As long as your fingers aren't in the middle of it, that is making stuff work for you to get the job done.

If I were doing that on my saw, which is "spring controlled", I'd have that spring backed right off about as far as it would go. I wonder, and I do NOT know, just thinking.... Once you have established the cut to a third or half of the work piece, what would happen if you just opened the hydraulic damper, so that it "acted like" a gravity saw? I am not suggesting that for smaller pieces, where you want to hold back the depth of cut on each individual tooth, but something like that, where you have plenty of teeth engaged at all times, so the saw really doesn't have enough weight/downward force, so it realistically can not take too big of a cut?

I'm not saying you "should" try this, it's just a thought. And since you know the saw better than I do, you'd be in a better position than me to determine if that idea sounds reasonable... But maybe?

 

[Flynth]

Wow.... That's one heckuva setup you've got there. What could possibly go wrong? You know how many safety warnings from the manual you've disregarded? When I've got something like that to do..... Oh, wait. Never mind. Carry on...... As long as your fingers aren't in the middle of it, that is making stuff work for you to get the job done.

If I were doing that on my saw, which is "spring controlled", I'd have that spring backed right off about as far as it would go. I wonder, and I do NOT know, just thinking.... Once you have established the cut to a third or half of the work piece, what would happen if you just opened the hydraulic damper, so that it "acted like" a gravity saw? I am not suggesting that for smaller pieces, where you want to hold back the depth of cut on each individual tooth, but something like that, where you have plenty of teeth engaged at all times, so the saw really doesn't have enough weight/downward force, so it realistically can not take too big of a cut?

I'm not saying you "should" try this, it's just a thought. And since you know the saw better than I do, you'd be in a better position than me to determine if that idea sounds reasonable... But maybe?

Indeed, it could be better safety wise, but let me say the "operator position" is not from where I took the photo, but on the other side (behind the saw). So should something catastrophic happen, like that 150kg (300lbs) piece of tool steel got loose, I would be far enough. Also that red C clamp was just helping in initial setup. I added a 10mm (a bit under half inch) spacer between the solid jaw of the vice and the body and this allowed the workpiece to be clamped by the saw's vice in a position that made the left saw guide just clear the top left corner of material.

So the only thing I'm a bit uncomfortable with regarding the cut is that it starts when the saw is very high. Just about half inch below 45 degrees. There seems to be very little downfeed force with the head that high, but the cut started well.

The idea to open the valve crossed my mind. It would be a logical thing to do considering the force per tooth may be too low. However, I've observed very nice and big chips even with very slow feed. Based on experience how the chips looked and how the cut sounded I could've pushed it harder, but not by a lot. So I'm afraid I have to say my theory about high TPI blade running out of down force on my saw in such a cut is likely wrong. It is likely to run out of gullet space or power (or both).

There is one more limiting factor I haven't considered before. The motor. It is a 550W single phase 240V motor and it's getting rather hot during such a long cut(allegedly it has thermal protection). When it got hot to the touch I switched it off to cool down (the time to cool down was not included in those 6h mentioned). Later I found online for an E class motor like this one acceptable external temperature is up to 75C (167F) so I left it on. It never exceeded 55C (130F) as measured by my contact less thermometer. However, I suspect it is driving the saw mechanism itself that's causing it more than the resistance of the cut. The motor is only a 1420rpm and it has a rather small fan blowing through a narrow space onto the outside surface. So I will have to be watching its temperature when increasing the down feed.

Also, regarding blade availability, I found some company that claims on their website to have 5/8tpi variable pitch blade. Considering the coarsest I got so far was 6/10 this one would be much better. We'll see if it materialises.

 

[mattthemuppet2]

To be honest, if i was able to get that cut and it was straight, I'd be happy. Wouldn't really care all that much how long it took because a) I'd be doing something else in the meantime and b) it sure beats cutting it with a hacksaw

 

[Flynth]

To be honest, if i was able to get that cut and it was straight, I'd be happy. Wouldn't really care all that much how long it took because a) I'd be doing something else in the meantime and b) it sure beats cutting it with a hacksaw

I would be happy too if I could just leave it alone, but the issue with the hydraulic cylinder I mentioned in the other thread is that on very low settings it just stops on its own. So during that 6h cut I had to be around all the time. Every time I would leave it for 5~10min I would return and the downfeed would stop, the blade was not making any chips until I opened and closed the needle valve a tiny bit.

This is not specific to big cuts, or any particular blade use so I talk more about it in another thread. I did lots to troubleshoot it(changing oil, cleaning repeatedly, making sure there is no air in there). Eventually I came to a conclusion it is some property of the liquid that is stopping it during very low flow(I tried various oil weights BTW) as the same was happening with a ball valve.

 

[hman]

In one way ... it's probably good that you've had to stay there with the saw during that very long cut. I recall a post from a year or three ago, in which a user of such a saw reported severe overheating (possibly even burn-out) of the motor during an extended cut.

 

[Flynth]

In one way ... it's probably good that you've had to stay there with the saw during that very long cut. I recall a post from a year or three ago, in which a user of such a saw reported severe overheating (possibly even burn-out) of the motor during an extended cut.

Yes, those motors do heat up. I do check on it very frequently. I wish now I got a three phase version instead (allegedly 3 phase motors in those saws don't get so hot).