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

Al Slitter

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Hello All;

I have an issue with my 4” x 6” metal cutting band saw that I hope someone can help me with?
The issue is the blade keeps jumping off the lower wheel when cutting at an angle or when cutting tubing. It is as thought the blade gets pinched or the cutting is interrupted.
I have been unable to remove the lower wheel even though I removed the retaining clip and grub screw.
The saw is very difficult to set up to track properly but when done it cuts at a nice 90 degree angle.
I have spent many hours trying to get this machine to operate better but have had limited results. I have changed blades, adjusted the upper wheel, adjusted the guide bearing as well as the dovetail holders on the blade arms.

I hope someone might assist me with this very frustrating situation?
 
Hi, Al,

I am no expert, but I believe that cutting tubing is a special problem because the blade is actually engaging very little material. I *think* you can mitigate this by manually lowering the saw more slowly during cutting. Some users who cut tubing often install a hydraulic cylinder whose purpose is to slow the rate of downward movement to perform the same function. There is an excellent Yahoo Group called the 4x6 Bandsaw group that could give you more expert information. Hopefully I am not violating any forum rules by mentioning it...

Good luck!

Charlie
 
The bottom wheel is not adjustable. All the adjustment is the other wheel and the guides. If you are cutting thin materials, you need to have a fine tooth blade. A general rule of thumb is that you should have 3 teeth in contact with the material. That doesn't really work with real thin materials but it is a start. If you have a large tooth, the material will just go down in the gullet of the tooth and jam the blade. Not a good thing, as you have found. If you get down to really thin stuff, you might have to go to a different kind of saw such as a diamond blade or just move over to hand saws because they don't have that small of tooth available on a bandsaw. About the smallest I have seen is 32 tpi. These guys have a nice reference as to matching the tooth to the material: http://www.allbandsawblades.com/nubmer_teeth.htm
 
My feeling on the 4 x 6 band saws is that when problems with bad cutting arise, no matter if it is jumping off wheel or no longer making straight cuts, your first move is to tighten the blade as tight as you can with your bare hands. If problem still persists put a new blade on and adjust till it tracks well on the wheels without cutting and then see if it cuts worth a darn. Grizzly use to have pretty good instruction manual on line which showed how to adjust, might be worth looking for. The blades are so cheap starting with a fresh one for dialing it in might be a good call. While blade is off clean the wheels and guides. Every once in a while I have troubles with my Jet branded one, a little cleaning, futzing around and or a new blade gets it back
 
Thank you all for the replies so far!
Let me reply by addressing the first reply about cutting tubing, the saw cuts well through the top of the tubing it seems to pinch when it switches the cutting action to the side walls and the blade comes off of the lower wheel (Power driven wheel).

The reason for wanting to remove the lower wheel is to move the wheel in or out to get a perfect alignment of both wheels. In addition by having the wheel of it can be checked for concentricity .

I understand about using the hydraulic arm to lower the blade, I do not have this on my saw but I always lower the blade very slowly until it is well on its way to cutting.

I am a member of the 4" x 6" Yahoo forum and have asked for assistance and received many replies however none of the suggestions have worked for me.

The saw currently will cut when set up 90% of what I need cut, I use only high quality bi-metal wavy tooth blades and they cut very well, however getting the saw running well for angle or tubing cuts is an issue.
Plus there is an issue with getting the blade to track well, in a blade change I have to spend up to 4 Hours in adjusting the saw to finally get the saw to track properly. Tightening and or over tightening the blade causes
the blade to jump of the lower wheel. Tightening up the side support rollers will do the same. In my mind the lower drive wheel is not flat but tapered outward and this might be the issue.

Regards

Al
 
Another member was having a similar problem, and he found bad bearings in the lower end was causing the problem. Maybe the same applies here.
 
If you have the common Rong Fu style bandsaw which most 4x6s are, you need to adjust the angle of the top wheel if you have problems with the blade falling off the bottom wheel. As stated, the bottom wheel is fixed. The top wheel angle can be adjusted by using the set screw shown in the diagram below.

Loosen 56 as needed, adjust wheel angle with 110, the retighten 56 to lock the setting. Once adjusted properly, you shouldn't need to mess with that in a very long time.

images?q=tbn:ANd9GcQKgtx58oj66BuTxXzkppSzoTQiPe5wZExhD29U4cYHXyjXFy3t0Q.jpg
 
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.
 
Thank you all for your comments, I will follow up on some of the suggestions.

Best Regards

Al
 
When you cut thin tubing your blade's teeth get jammed in the thin wall tubing. The lower wheel continues to revolve,causing the blade to slip off.

I'm not sure what to suggest other than clamping a piece of thicker stock beside the tubing that the blade must also saw through. That will keep it from jamming in the thin wall tubing. This is a quick fix,and getting a hydraulic cylinder that really slows down the descent of the blade is a better solution,if you can find one. My Roll In saw has such a cylinder,with a little thumb wheel adjustment to adjust how fast the blade can advance into the work. But,that little cylinder costs a LOT from Roll In. I don't know if this is a commonly available cylinder that Roll In is using. It could well be. I am sure it is not as expensive as they are asking for it.
 
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