Blade Tracking on a 4 x 7 bandsaw

M

miro

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Recently ( finally) got a 4x7 bandsaw.
I read with great interest the posts on
www.hobby-machinist.com

4 x 6 horizontal vertical band saw.

To move to Florida to assist parents, I sold out in Virginia including my entire shop. That included a Harbor Freight band saw (see title). I loved this saw even though it was from Harbor Freight. The saw was accurate and reliable. Parenthetically, if you know what you are buying, you can do...
www.hobby-machinist.com www.hobby-machinist.com

The challenge I have is the blade won't track. It's OK for a while and then slips off the drive wheel.
I noted that my saw does not have an adjustment bolt on the upper driven wheel assembly. I tried some shims under the 2 bars that hold the upper wheel assembly - better but still slips off.
I plan to replace the 2 bars because there's quite a bit of slop with the grooves for the wheel assembly ( bars are 0.225, the grooves are 0.248). he blade tensioning screw gets quite hard to turn once the tension starts to build up.
Aside from adding the adjustment bolt, are there any other hints / tips to make the blade track better?
Thanks
MF
 
What do you mean no adjustment bolt on top? Some picture may help. Also, new blade helps also.
Maje sure all bearings are smooth and the two wheels don't have any friction on them when the blade is off
 
Sorry for the bad pic, was the only one I had on hand of my old RF-128. There's a set screw (circled in red) that tilts the upper wheel. Tilting that wheel is what prevents the blade from falling off the wheels.

20191205_130411.jpg
 
There are probably other areas that causes this. I would adjust it back to somewhere in the middle, then look at other bearings to makes sure they are smooth and not stuck. Also check the wheel to maje sure it's not out of balance with respect to the center (bent wheel for example)
 
Thanks for that link - I pretty well went through all of hat procedure except that I do not have a new blade.

However, I DID find the the TILT adjustment - it was a hex set screw buried in the threaded hole. That seemed to help a lot. But the blade would still come off after about 2 minutes or so of cutting.

I then increased he load on the saw by slackening the big tension spring quite a bit.
That seemed to do the trick. I was able to cut a 1 inch bar all the way through.

Lingering concern is the alignment of the blade guides . If I have the saw in the UP position, you can clearly see that the upper blade guide holds ( forces ?) the blade way over from a straight line between the wheels.
( pictures are coming up).

And yes, I will be getting a new blade.
 
Here are some pictures that show the (maybe ?) mis-alignment. The blade guides are a fixed position side-to-side
so maybe that how it should be - dunno.
Anyone have suggestions?
Bandsaw 1.jpg

bandsaw 2.jpg

bandsaw 3.jpg
 
Looks like someone replaced the bearing guides? For each pair of bearings, one bearing should be mounted on a fixed shaft, the other bearing should be mounted on an eccentric shaft. The eccentric allows for blade gap adjustment for the bearings. In the first pic, looks like that feature is non existent for the top set of bearings. Which looks like they have been replaced with roller bearings, that don't look stock. Looks like the other set of bearings have been modified also.
 
Like darkzero said, 4 bolts holding the bearings can be eccentric, or some of them.
Make sure to turn it in a way to keep the gap correctly.
After running 2 minutes and it jumps, if all aligned, could be broken bearings somewhere.
But get your alignment fixed first. I would remove all 4 bolts and have a good look at them and understand how they work.
 
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As darkzero indicated---the bearings dont look right. In yor first picture you can see that the bearings used for the guides are different sizes top to bottom. In the five saws that I have refurbished - all bearings were the same. Also the bolts passing through the bearings were all identical and all were cammed.
 
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