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Attacking the 4x6 bandsaw

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vtsteam:
I bought a 4x6 band saw from Harbor Freight a couple years ago, and was immediately disappointed with it as blades jumped off, cuts were far from vertical, some hardware parts were missing, etc.

After reading a lot including the 4x6 Yahoo group messages, I finally got it under reasonable control by increasing the tension on the blade and shimming out both guides nearly 1/8".

Still, it's never been very satisfactory and the blade stops cutting vertically at random times.

I finally got a hold of the 4x6 bandsaw tune up sheet which has circulated, and yesterday had time to go through the entire procedure.

A real difficulty was finding a suitable narrow straightedge 28 inches long for checking the wheel alignment. It's a close fit inside the band saw housing I eventually cut and planed up a piece of wood to use. There was also a problem following the instructions re the blade guide rollers -- the instructions assume that the inner rollers can not be adjusted -- mine were adjustable -- but there was no indication where they should be located, since otherwise they serve as a reference for the other bearings. Anyway,

Steps:

1.) I first checked that the lower wheel had no axial play on the driveshaft. It didn't. Good!

2.) I then checked with the straightedge that the two wheels were in the same plane after adjusting the upper wheel to vertical.

They weren't. The top wheel was 1/4" inside the lower wheel. I therefore removed the top wheel and was able to fit it on the bench vice with the inner bearing face resting on the jaws. and the shaft free. A few taps with a hammer and brass drift moved the shaft in the required distance. The press fit wasn't super tight, and it really was just a few taps to shift it.

3.) Re-mounting the top wheel I then checked that the wheel was parallel in the horizontal plane with the lower wheel by checking at both edges of the rims with the straightedge. This was problematic because the upper rim has so much slop. The stamped metal slides are a very loose fit -- apparently intentionally. I therefore took the average by checking play to either side.

The top wheel was far from parallel in the horizontal plane with the lower wheel. So I added a 1/16 shim to the leftmost slide. This brought the wheel average of play to parallel the lower wheel.

4.) I removed the blade guides. I then added a little tilt via the blade tracking adjustment screw and mounted a new 10-14 TPI bi-metal blade and, with the motor belt disconnected, turned the pulley by hand for one full blade revolution. The blade stayed on, so I reconnected the motor, and turned it on. The new blade was adjusted to just contact the upper wheel rim without riding heavily on it.

5.) I turned the motor off and reconnected the blade guides and loosened all of the roller bearings for adjustment. Here was the first real problem. The instructions said that the inner guides are fixed and to adjust the outer guides to allow .005-.010" clearance. But the inner guides on my saw were adjustable. On a vertical wood cutting bandsaw, I would normally just bring the guide in to close contact with the blade.

But on these horizontal metal cutting band saws, the guides intentionally twist the blade out of the plane of the wheels. So they must be brought in to apply pressure.  And a single guide roller will not fully twist the blade. It requires the opposite roller to pinch the blade in and give it the full required twist. Therefore it is difficult to determine where this all should be located. The blade without guides is no longer a reference for guide location.

I finally decided to bring the inner guides in as far as they could go -- reasoning that they would act like a 3rd wheel on the band that way, pushing slightly outward, rather than the opposite. Then the inner roller was adjusted to give .007 clearance -- but where measured? The blade actually rides at an angle to both guide rollers because of the twist. I measured it at the front.

Another problem, seems to me, is that because the rollers aren't tight to the blade (to prevent swarf from jamming it) the actual blade twist is less than if it were tight, and proportional to the clearance provided. So how do we get the blade perpendicular to the saw clamp for a vertical cut? Any time the clearance changes, the saw will not cut vertically.

Another problem showed up -- after adding the guides, the blade no longer tracked well on the lower wheel. It rode out about 1/8", though seeming to ride well on the upper wheel. I therefore shimmed the lower guide support back. This helped reduce but did not eliminate the override. But was left as acceptable.

6.) The only way to adjust the saw to cut vertically considering the variable pinch angle of the rollers is to take some test cuts and shim up the blade guide supports to eliminate it. So, per the written instructions, I used a piece of wood 2x2 to do test cuts while adjusting shims under the guide supports, taped on with duct tape (ugh). When I had it looking good in wood, I switched to a metal bar to do the final cuts.

A few slight shim adjustments and I had a perfect vertical cut. Phew!

The new bi-metal blade does a nice clean job, and the vertical cut is a pleasure to work with. I hope it stays.

I'm attaching the adjustment instructions I found and used, in case this is of use to others.

spuddevans:

--- Quote from: vtsteam on April 05, 2013, 02:29:03 PM ---I'm attaching the adjustment instructions I found and used, in case this is of use to others.

--- End quote ---

Indeed it is very useful, I've saved a copy, thank you very much  :thumbup: :thumbup: :thumbup:


Tim

Fredbare:
Thanks for that, mine is fine at the moment, but thats a very comprehensive list to sort out any future problem.

John

velocette:
Well done vtsteam
Well thought out attack on a fairly common problems with horizontal bandsaws. Armed with this information the job of tuning a band saw to get the best performance is a much less onerous task.
 
Many thanks for the PDF File Download 

Eric

Brass_Machine:
Thanks for posting that guide. After I finish working on my lathe, I plan to tackle the 4x6. I want to add some kind of chip collection and coolant a well.

Eric

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