probably done to death... but going to ask anyway. blade popping off.
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Popping the blade off the bottom wheel (esp. when cutting in the vice or pushing hard on the blade in vertical mode) is very likely due to the bottom guide bracket (the casting with the two side guide rollers and the rear support roller) being too far forward on its guide bar.? If this is the case the bottom rear support roller will be turning all the time and it will be difficult to stop with your fingernail (correctly set it is easy to stop).?? What happens to pop the blade off is the weight of the sawframe in the cut pushes the blade backwards, between the top and bottom rear support rollers, and then the lower rear support roller (which is too far forward), acts as a fulcrum to lever the blade off the bottom wheel. There is a 5/16" bolt that controls the backwards and forwards movement as well as the twist of the guide bracket (more on this below).?? It should be set so that the rear support roller only just touches the blade in hit&miss fashion as the blade rotates, even a slight (~0.040") gap is O.K. (it's not like a wood bandsaw where the rear support roller setting is critical to good cuts - these horizontal vertical saws are very tolerant to rear support roller position - as long as it's not forward of the right position). One of the hardest things to set is the position of the guide brackets on their guide arms via that 5/16" bolt. since both backward/forwards and left/right twist is done at the same time.?? There is a very simple mod to separate the two adjustments.? Drilling/tapping for a small bolt (3/16"?x 1" (UNF is better than UNC, but there's?no weight on it so either will do) or M5 x25mm) though the picture shows an M6x25 bolt) in the back of the guide bracket as in the photo. This allows the rear support roller to be set independently of the twist of the blade. Just centre pop and drill with a handheld drill in the centre of the back of the bracket casting, then tap. Picture shows the upper bracket not the lower one because it is easier to see. Do both of them. While you're at it replace the metric headed UNC bolts with cap head screws and decently thick washers as in the photo. Use a nut to lock the bolt in position?once you've set the rear support roller-to-blade back clearance - jv On Wed, Feb 7, 2024 at 5:34?PM Wolf Gang via <wolfgang_90=[email protected]> wrote: I've got an older harbor freight 4x6 bandsaw that is probably 20 years old. It's green if that helps, and if I saw lightly, in ether horizontal or vertical mode, it seems to work. If I push on the work like my old saw, it pops the blade off the bottom wheel. I have not gone and replaced anything yet. I did change the oil (first time I think) and took the top wheel apart and put it back together with tighter tolerances. I've replaced the blade twice.? |
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On Wed, Feb 7, 2024 at 12:08 AM, John Vreede wrote:
There is a very simple mod to separate the two adjustments.? Drilling/tapping for a small bolt (3/16"?x 1" (UNF is better than UNC, but there's?no weight on it so either will do) or M5 x25mm) though the picture shows an M6x25 bolt) in the back of the guide bracket as in the photo. This allows the rear support roller to be set independently of the twist of the blade.I'm not sure i understand this modification. Does the small bolt on the side push against the key to stop movement. Most horizontal saws I've seen have terrible blade guides but these are the worst. I've always thought about redesigning them so that you could et them without twisting the blade and then rotate them into vertical position with the center of the blade as the axis. This is not easy to do but it is doable. Setting the height and horizontal is hard to do accurately. Maybe take another picture of you mod and post it. I actually had to mill the key slot wider (or the key, cant remember) to get the horizontal position correct and then when I got the height correct there was no way to make the saw cut through the stock completely. I sell what I call an elevating plate correct this problem. If anyone is interested, here's a link. If you buy one be sure and print the template to make sure your saw is that same, some are not. John, your last post on type of blades and the welds was interesting. I have been using the Imachinist blade without issue until I tried the variable pitch blade. I've used 2 and both were replaced for missing teeth. I think it was a result of several missing teeth at the weld when installed (or not smoothing ground). In about a week or two I had over an inch of teeth missing.? |
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Sorry it was not clear Mark.? Hopefully pictures 2 & 3 below will set that right. The adjustment screw/bolt through the back of the guide bracket casting bears on the 5/16" bolt clamping the guide bracket to the guide arm, so that the bracket can only be moved so far forward and?no more. Then the guide bracket pivots around the clamping bolt to get the twist of the blade?correct. I had to narrow the 'key' too, to get the bracket to twist enough.? Though 3rd picture shows that I did this in the milling machine, it can be done perfectly well with a file - jv P.S. Pity that Imachinist blades failed you too. Lose one tooth and you'll surely lose more.? For me they cut just as fast as any other, but their dressing of the weld was crap. Since I bought them from Imachinist in China, I went back to them explaining what was wrong but got no answer; I won't use them again. Just reinforces what I said about finding a blade that is?welded properly and you won't have any cutting problems with any brand of varipitch?blade which are always HSS.? Different story with carbon steel blades though, I always opt for a 'name?brand' for carbon steel blades and only use them for cutting soft materials like aluminium, brass, thermoplastic or wood. On Thu, Feb 8, 2024 at 4:08?AM Mark <mark21056@...> wrote: On Wed, Feb 7, 2024 at 12:08 AM, John Vreede wrote: |
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On Wed, Feb 19, 2025 at 04:34 AM, David Weir wrote:
That pivot bracket is priceless, I have my 6X4 cutting a slither like a penny, after doing all sorts of modifications, and copying your baseplate idea. I assume you mean the plate to go under the vise. Thanks, it makes a huge difference if you saw has the same defect as mine.? |
John Vreede
Mark
David Weir