|Nigel Graham 2||06/04/2021 22:25:11|
|1241 forum posts|
The badge says 'Alpine' but it's one of those cloned, one-for-all, horizontal and (for the brave or foolhardy) vertical, Taiwanese band-saws.
New-to-me about 3 or 4 years ago but from a model-engineer I know would use tools properly, it gave good service until very recently. I had made a proper trolley on castors to replace its near-useless wheels and handle, and replaced its motor about 2 years ago when the original suddenly failed.
The blades have started running obviously out-of true, with a distinct twist, and in a shallow arc across wide work.
The block holding the tensioning pulley was very sloppy in its guides. I improved that a bit but it is not designed for adjustment. Also, a grub-screw that adjusts the wheel's tilt had been contacting the bearing-slide out of the dimple provided for it.
I cleaned and re-set the guide-rollers (sealed bearing races) as they appeared right, but when running the blade was still twisting and eventually snapped, even though not heavily worn.
The broken blade had become rolled to a shallow channel profile so I assumed I had set the guide-rollers too tightly.
I fitted a new blade - that was always difficult and hazardous. This time it was possible only by removing both guide-assemblies, fitting the blade to the pulleys, closing the door and only then tightening it; before re-fitting the guides. I set the guide-rollers fairly open, as seemed necessary for the blade to be tangential to the pulleys.
On both pairs, only one roller is adjustable, by rotating its eccentric axle. It does not look as if the other can be moved.
It all seemed OK, but sawing even a piece of 25 X 10 mm hot-rolled steel, the blade was clearly twisted, cut at a vertical angle and came to rest about 5 or 6mm off the cut end. Luckily the work-piece is a blank for further operations , and its ends are not critical.
Where have I gone wrong, please?
It seems not to matter how I adjust it, but I may have missed something. (I do not have the manual for it.).
Might it respond to re-building the tensioning assembly to keep the pulleys aligned? Not sure how...
Is it likely that the machine has in fact worn beyond practical repair?
|Martin Connelly||07/04/2021 07:59:35|
1687 forum posts
I have fallen foul of the overtightened guide rollers and ended up with a distorted and prematurely snapped blade so don't feel too bad about it, you are not the first and probably will not be the last.
Tension is sufficiently important that industrial machines often come with means of setting it correctly and it is usually a lot higher than you would expect. I have seen them with hydraulic piston tensioning operated by a screw driving a piston in a pressurising pump and a gauge with a narrow pressure band marked on it. I have also seen screw operated ones with parallel stacked Belleville springs where the operating screw has coloured bands on a collar and there is a pointer on the frame to line the bands up against. As the tension is increased the springs compress and the screw and collar moves to the point where the pointer indicates correct tension. Where they were not fitted with an inbuilt system like this you bought a band tension gauge to check the blade. A gauge like this is probably not cost effective for occasional home use but a saw in regular use that is having blade changes weekly benefits from getting the tension right. If the blade does not twang when plucked it is probably too slack.
Edited By Martin Connelly on 07/04/2021 08:03:36
|Clive Foster||07/04/2021 08:31:57|
|2622 forum posts|
Sounds like you have run into the same sort of issues that my Alpine bandsaw suffered many years ago. I got mine maybe a year or so after they hit the market and, after a deal of tweaking got it to work OK.
Maybe 7 years or so later it decided that it wouldn't play ball. No amount of fiddling, cursing and adjusting would make it behave for more than a cut or two. After snapping a couple of blades in short order I took a careful look at the geometry and decided that neither the blade guides or tension adjuster were working in the correct planes or lines.
I made a new set of 4 eccentric carriers for the blade guides with the maximum amount of shift that could be accommodated. Found some proper bolts to hold them on instead of the standard soft screw things. With all four adjustable I was able to get a much cleaner run between the pulleys so the blade wasn't so forcefully twisted as it came off and on the pulleys.
The casting surface under the tension adjuster was neither smooth, flat or in line with the screw. I filed it back flat and square to the screw. I imagine the top wheel is supposed to just sort of hang down on the tensioning screw and be pulled into alignment by the blade tension. With the original skewed surface under the knob this clearly wasn't happening.
Its still not the most wonderful performer in the world but its back to working OK and blade life is reasonable.
As as been frequently said good quality blades are essential.
|Andrew Tinsley||07/04/2021 10:14:50|
|1335 forum posts|
Clive is dead on the money, my Alpine responded to the treatment that Clive suggests. When I first got it, the performance was rubbish and it stayed in a corner for maybe 25 years. I needed the space so it was either make it work or dump it time. It is now surprisingly good and I am very pleased with it.
|1980 forum posts|
Here's a link to 1 of many you tube videos that may be helpful.
|Brian Wood||07/04/2021 10:53:04|
|2380 forum posts|
I cured my Axminster 6 x 4 bandsaw of equally bad habits by going back to basics and aligning the blade guides against a tensioned wire. The wire was snugged fully into the right angle of the flange on both top and bottom wheels. However, before I was able to set things up that way, the blade guide blocks were clamped up crudely on as cast surfaces so these had to be milled flat and at right angles.
On my machine the blade runs between sealed ball bearings on either side of the blade and one running on the back of the blade. The work which had the greatest influence on blade life and truth in a cut was getting the geometry right against the tensioned wire.
It now cuts correctly on demand and with a bi-metal blade in place [10 tpi for most work, 14 for pipe] the blade life is excellent. Prior to this work blade life might have degenerated to one blade for each job..
|Martin Connelly||07/04/2021 13:47:07|
1687 forum posts
|Howard Lewis||07/04/2021 15:30:55|
|4662 forum posts|
My 4 1/2 bandsaw used to break blades and cut in arc, until the tin spacer between the bearings went throughb the bottom bearing and seal.
having breplaced bearings and seal and made up a substantial spacer I then wemt through the machine.
Both pulleys were skimmed to reduce the run out, the blade guiderollers were adjusted in both vertical and horizontal planes., and the tracking adjusted.
Cannot recall at this distance whether or not I bushed the Idler wheel.
I also made a tension meter, as designed by Jacques Maurel, and the subject of an article in Engineering in Miniature in June 2016. Having set the tension using this, unless I force the cut, it is straight, and blades wear out instead of breaking.
At the time, as a test, I cut a disc about 1/16" wide. The thickness differed by an incredible, and very probably unrepeatable, 0.001" So the time spent in fine tuning was not wasted.
It is not a perfect machine, after all it is relatively cheap, but it now functions well enough for my purposes.
|269 forum posts|
An excellent guide to setting up a bandsaw
|Nigel Graham 2||08/04/2021 12:45:13|
|1241 forum posts|
Thank you All.
It does look for your various comments that the machine is recoverable.
The tensioning arrangement is rather crude, and its simple tracking-adjuster works in only one plane.
I think now the real fault on my saw is the tensioning-pulley's stub-axle carrier tilting sideways, pulling the blade too far out of line for the guides to cope with it. Consequently, the guides cannot not work correctly and may even be making the effects worse. It would explain why I had to take the guides right off to be able to fit a new blade, and possibly why it was so difficult to make the blade stay on the pulleys even then.
The carrier is a very loose fit in the slot in the casting, so it can twist. Its keep-plates take out some of the twist, but are not enough on their own and might be intended not to align the carrier but just hold it with minimum shake. I may need make and fit either thin horn-plates, machined from steel-angle, and adjustable, or a new carrier-block.
I think my first move is to measure where everything both should be and is relative to each other, then dismantle the tension-pulley bit by bit, assessing what parts are worn in what way.
|Clive Foster||08/04/2021 14:22:38|
|2622 forum posts|
As I recall things design of the top wheel mount is such that it just hangs on the tension screw with a certain amount of play so the blade tension can pull the wheels into alignment.
The keep plate at the back has a tilt adjustment so the wheel axles can be made to point in the same direction.
The blade tension applies inside the saw some distance away from the keep plate so when all is copacetic the blade tension pulls the wheel assembly into the saw until the keep plate sits hard against the casting. Although there are no properly positive fixings things ought to be pretty stable.
Effectively the blade tension does all the work. Simple, cheap and no accurate machining needed but the blade tension line needs to be correct. Darned if I can recall whether there is any mechanism to vary the top wheel position relative to the back of the main casting. Have a feeling I ended up doing "something" in that area.
|Nigel Graham 2||08/04/2021 16:58:38|
|1241 forum posts|
Thank you Clive.
Yes, I've found the tilt adjustment. It's just a grub-screw, and it fairly obviously should engage a hollow in the block holding the axle. Only a scar on the steel showed it had clearly been missing the hollow and the block was twisting across the plane of the tilt.
When the tension is unwound, the wheel and axle assembly can wobble all over the place, making me think that as a result of wear the belt pulls itself out of alignment. Take the guides right off and the blade is an appreciable distance from its intended path. It also twists incorrectly, so something is preventing the guide-rollers from threading the blade properly.
|vic francis||08/04/2021 19:39:36|
|63 forum posts|
Hi Nigel, I had the similar bandsaw; I found that a thin layer of cork glued onto the drive wheel gave friction and cushioning drive... not only did the blades last longer and needed far less tension... but always cut material dry...
|Nigel Graham 2||08/04/2021 22:04:18|
|1241 forum posts|
Thank you for that link, Oldvelo. I have saved it, will print it to form the workshop instruction s.
Interesting suggestion, Vic.
I used at work a long time ago now, a large, vertical-only Starrett bandsaw, and that had an equivalent, rubber tyres on the wheels. It was used for cutting anything from small pieces of aluminium-alloy plate to two-foot squares of quarter-inch gauge-plate, so I had to change blades back and forth fairly often.
(A hacksawing machine dealt with all the bar stock down to sizes too small for the machine's ill-conceived vice, which was three pairs of geared, vertical rollers. I used a circular-saw - toothed, not abrasive disc - for the smaller sections.)
Edited By Nigel Graham 2 on 08/04/2021 22:07:27
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