Attacking the 4x6 bandsaw

Gallery, Projects and General > Project Logs

<< < (2/7) > >>

vtsteam:
All is not right yet, unfortunately. This morning I went to cut two pieces of 1/2" x 1" steel bar and the blade jumped off the wheels twice. :bang:

I readjusted the top wheel to give it more camber, and was able to saw my pieces. However, when the sawhead was horizontal and cutting, I could see that the top backing roller wasn't contacting the upper part of the blade. So I tried to readjust the upper and lower backing rollers and couldn't get them both to contact at the same time -- there wasn't enough adjustment available.

So I'm thinking I have to move the lower guide support arm back. Stay tuned for further developments......

vtsteam:
Okay, got it sorted out today after another hour on it. :borg:

Mine needed the lower blade guide arm moved back (in the direction of the back of the blade). To do this I shimmed the frame even more than it had been already. To move it back evenly, I shimmed the rails on both sides where the arm slides.

After additional shimming, I was finally able to make a square cut and that was repeatable. I now also had both backing rollers in contact and working. The blade rides where it should on the lower wheel now. And I have made many cuts since moving the guide back, and the blade has not jumped off again. To further test the saw, I cut out 7 blocks of steel to make some new tool posts (inspired by the 48 tool posts made by Daveo J).

So the tune up method works, but my saw requires a LOT of shimming even after truing the wheels. The reason was simply that the arms and roller guides are really not located properly in relation to the trued up wheels.

I'd like to do a better job of it than what I have now -- I don't like duct taped stacks of shims recommended in the tune up guide.

Options:

1.) If the lower wheel could be moved out, that would reduce the number of shims needed under the lower guide support arm. I don't know if this is possible, but will check at some point. I don't want to readjust everything again for awhile -- I want to use the saw for projects now.

2.) I was thinking that instead of shims, perhaps I could drill and tap 4 holes into the main casting where the support arms slide, and install long grub screws there. Two on each side. By backing these out of their holes they would act as adjustable shims. I could do this now without having to re-true the wheels. So probably will.

I've come to realize that the amount of shimming needed depends on the gap I set between the pinch rollers and the dimensions of the saw blade itself. Because the pinch rollers twist the blade, the closer they are set to each other, the greater the twist, and vice versa. And twist affects the squareness of cut.

The adjustment guide above suggests that the pinch rollers not be set too tight, to allow swarf to clear without jamming the blade . Because this gap is somewhat variable and blades aren't uniform, shimming the guide arm will probably always be needed to get a perfectly square cut. At least on my saw. Therefore easily adjustable shims per #2 above might be used to compensate for changes in twist angle that will likely happen after blade changes. Well that's my theory :smart:

Anyway, hope this info also helps others. :thumbup:

black85vette:
I did the shimming on mine back some time ago. Also worked on getting the blade to stay on. Didn't know there were actually instructions out there. :doh:

One of the best additions I made was to make a .25" plate table to use the saw in vertical mode. Made it as large as possible and still be able to drop down completely. Also used an old cheap vice mounted vertically and held by the built in vise on the saw. It allows me to cut off very short pieces that could not be held by the built in vise.

Thanks for posting your observations and the instructions. :thumbup:

Lew_Merrick_PE:
One of the things I have noted about the cheap Chinese 4X6 horizontal/vertical bandsaws is that none of the surfaces are either flat or true when it comes out of the box. About one-third of the units brought to me for salvation have serious problems with drive and idle wheel alignment. About one in ten has seriously eccentric bearings. And about two-thirds have the pivot for the saw-drop located out of true with the table.

I have reached the point where I dress the "table" in the base as without even bothering to check it out. I then index to the "table" and rebore the holes for the "pivot axle," install bushings, and line drill & ream them. The "pivot fence" (used in the horizontal orientation) gets replaced with one made from dressed L2X2X3/8 angle. The "pivot" itself gets swapped out to a ø.625 shoulder screw (stripper bolt) that allows me to drill & tap to a .3125-18UNC hole that will be known to be true & square to the table. A custom acetal (Delrin) washer gets made to assure that the fence pivot mates properly.

I then mount a block to the (driven wheel side) lower guide arm such that I can measure the sweep as the bandsaw head pivots from the vertical to horizontal positions. I rebore & bush the pivot axle holder to make that square to the table. Then I start looking at the alignment of the wheels and guide bearings.

Properly set, I have sawn 4X6 blocks of merchant steel and ended up with faces that were flat & true within .004 FIM. I have sliced pieces as thin as .035 from such blocks and had the thickness be consistent +/-.006 (though +/-.012 is more common).

The comments about good quality blades is essential! I have been a Starrett and Lenox blade snob for several decades. I have added the higher-end blades sold by Grizzly to my acceptable list. Poor quality blades = poor quality results. A .500 X .025 (inch) blade can typically be tensioned to 800 lbs of tension. That is a torque of 35 lb-in (3.95 N-m) on the blade tensioning screw.

Hopefully, this gives you some ideas...

Meldonmech:
Thanks for the details of your fixes, and for the attachment. I had this annoying blade jumping of the wheels, have done quite a lot of mods now to improve the machine, but have never seen this detailed check and remedy you have shown. I must go over my machine and make some checks.

Cheers David

Navigation

 Message Index

Go to full version