Blade Jumping Off The Lower Wheel Of A 4" X 6" Bandsaw

Thank you very much I now have a better understanding of why this is happening.
 
Surely I don't know if this applies at all. I bought a used horizontal saw that had the same problem.....I found that the driving wheel was worn at a slant that encouraged the blade to fall off. I turned it square in the lathe and it helped tremendously. The saw is still pretty worn and has some issues but still does a lot of work for me.

Tim
 
We had a 4x6" bandsaw at work that was used a lot. We did have to re turn one wheel eventually due to wear. One time we had a 10' piece of 5" diameter Naval bronze to cut. It weighed a ton,needless to say.We took the legs off of the little bandsaw and laid it flat upon the floor. Then,we were able to lever up the bronze onto the bed of the saw and saw the bronze into more manageable sizes,rotating it to cut all the way through. It was very handy to have a saw only a couple of inches off the floor upon that occasion. I certainly could not have gotten that bar way up onto the Roll In bandsaw.

When you have a real heavy piece of metal to saw,remember this trick.
 
David Kirtley said:
What you describe does not sound like the alignment is off. If it runs and stays on the wheels when not cutting, your wheel alignment is fine. If the alignment is off, the blade will jump off whether you are cutting or not. If it tracks fine when you are not cutting and doesn't track when you are cutting, then most likely your guides are not adjusted properly or the tension is *way* off. If you are cutting too thin of material for the tooth size, the material will go deep into the gullet between the teeth and something has to give. Either the tooth will bend or break, or the blade will stretch from the impact and jump off the wheel. That is what it sounds like is happening.

When you are at the top and bottom of tubing, there is more material in contact and larger teeth do fine. When you get to the sides, the material is more perpendicular to the teeth and you will see the problem because you will not have enough teeth in contact with the material. The only way to avoid this without changing the blade to a smaller tooth is to have finer control of the feed of the blade into the material. The spring of the 4x6 doesn't have that fine of control. Hydraulic feed control is about the only way for that.

If the tracking and alignment is giving you fits, the best thing is to start from scratch. Remove the guides. Put the blade on just the wheels and see how it tracks. It should track without moving and close to the inner rim. You adjust it on the end where you tension it. Once it tracks properly, you can then put the guides back on and get them aligned. Don't tension the blade all the way. The rollers should be barely touching the blade. Move the rollers until the blade is perpendicular to the fixed jaw of the vise. Then slowly tighten down the rollers until it twists the blade to the right vertical cutting angle. Once it tracks properly and the guides are aligned, you are ready to adjust the tension. It only needs to be tight enough that it doesn't flex when you are cutting. Too tight and you are just making the bearings and blade wear prematurely. Too loose and the blade will deflect and make a curved cut.
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David:
Thank you so much for this. It is an issue that has been vexing me for sometime. I had thought about the Just start from the beginning but the instruction I could find from JET were akin to "Enjoy is product" So no help at all. This REALLY cleared things up.
b
 
Sounds as if the blade is hanging up when the material thickness diminishes on the walls. Use a fine tooth blade, run at a high speed and manually lower gently when the material is thin. I have a 7" x 12" and cut thin wall tube often, Saw has a hydraulic feed down but I still lower manually or I have the blade jump off.
 
Well what you recommended worked just fine. Thank you.
For your dampening issue. Hydraulics is most likely the best answer. But as you say, they can be proud of them. I would offer two possible solutions.
1) pneumatic. Put a small Clippard valve on the air line and you will have a fine snubber. These vales come as an open flow one direction and restricted in the other for a fast recovery. You would have to pull the cylinder back to it's stating position by hand or rig up some sort of pressure to drive it back. But cheep and easy? Just an air cylinder with a flow restrictor valve will work very well.

b
 
Bruce Billett said:
Well what you recommended worked just fine. Thank you.
For your dampening issue. Hydraulics is most likely the best answer. But as you say, they can be proud of them. I would offer two possible solutions.
1) pneumatic. Put a small Clippard valve on the air line and you will have a fine snubber. These vales come as an open flow one direction and restricted in the other for a fast recovery. You would have to pull the cylinder back to it's stating position by hand or rig up some sort of pressure to drive it back. But cheep and easy? Just an air cylinder with a flow restrictor valve will work very well.

b
Click to expand...
Sorry, got interrupted.
The other is hydraulics, pretty much the same as the pneumatic solution above but charge it with a fluid. kind of a DIY version.
I also just thought of using one of the snubbers as you find in the lid of a hatch back car. These come in many different flavors. The big issue is finding the right lift weight and angle to install it in.
I suspect it could even be fitted in place of the spring on the tool. Remember you can slow the movement of an air cylinder by both limiting how fast the air exits the cylinder and by how fast it flows in if you were to use a double acting cylinder. We have a place around here called "Surplus Gizmos" and they have all sorts of bits and pieces, like cylinders and air valves. I would guess you have something like that where you are? I am fortunate enough to live and have worked in the silicon forest so we are up to our eyeballs in this sort of thing.
Hope this helps and gives you something to think about.

Hopes this helps or gives you some ideas.

b
 
There's any number of articles about adding hydraulic downfeed to a 4x6 all over the interweb ... most of which cost as much as or more than the saw originally did. I came up with one based on a screen door closer, total cost about $25-50. It's written up in the November/December 2018 and January/February 2019 issues of Home Shop Machinist.
Back Issues « The Home Shop Machinist « Metalworking « Storefront « Village Press
 
can't see the article but I'm sure it's the same thing. I'm talking about.
What I'm talking about is a simple double acting Bimba cylinder. (get them surplus for next to nothing.) Need a stroke about 6" long depending on how you mount it. Dia. really doesn't matter. Add a bleeder valve with a built in bypass. (maybe hard to find as surplus but they are there) and outside of the first inch of so as the air compresses in the cylinder, you have outstanding control of the speed of the drop. If it weren't for the @$##^&* virus I would go down to Gizmos and collect the parts for you and send them to you.
If you have an air cylinder around prove it to yourself by putting your finger over the port, You'll notice you can only move the cylinder about 1/4" before it stops until you move your finger.
You could sort of make it yourself, but control would be a bother. Just put a plug in the air port and drill a VERY tiny hole in the plug. As the air slowly leaks in or out, depending on the port you have it on the cylinder will slowly move. Another method would be to just put a plug in the hole no teflon tape and as you loosen the plug and the air leaks out. Gives you control, but it is a pain pretty much like drilling the critical orifice above.

b
 
Bruce Billett said:
can't see the article but I'm sure it's the same thing. I'm talking about.
Click to expand...
The two back issues you want are about ⅔ of the way down the page -
Screen Shot 2020-09-19 at 10.38.34 PM.jpg
I'd love to scan and send you the pages, but am not allowed to until HSM runs out of copies.

My cylinder makes use of the unique O-ring seat in a screen door closer - fast opening (raising the saw) and dead stop on closing (lowering the saw). When closing a screen door, a separate air bleed valve controls closing speed. I block off the bleed valve and add a coaxial needle valve to the piston; use drugstore mineral oil as a working fluid.
 
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