Breaking bandsaw blades

Do you think it worthwhile to set the top guide as close as possible to the work so as to minimise the twist (or maximise the length of blade over which the twist occurs)?

ega,

I know you asked Clive the question but I think whatever you can do to give the blade an easier track from the guide back onto the drive wheel must be kinder and therefore worth doing.

If you haven't tried the wire alignment set up yet, I can almost guarantee it will be very illuminating and worth the effort.

Regards Brian

Brian:

Thanks for your continued interest. I will try the wire test. I don't think you specified the kind of wire you use - I did think of using fishing line - but no doubt the workshop will yield something suitable.

I am reminded that the American TV series "The Wire" had the reputation of being largely incomprehensible and, at the same time, totally addictive!

Hello ega,

Fishing line, that sounds to be a fine alternative. I am not a fishing enthusiast so that would never have occurred to me. As for wire, I don't suppose the gauge matters a lot, I think I used earth wire from lighting cable. Being copper it will stretch nice and taut, that is really the essence of providing a good reference to set everything up to

Brian

More sound advice from Brian, as usual. This is something I must check, although I have not broken any blades recently.

Thanks again Brian for your input.

Here is the bandsaw blade tension device I made. It has been heavily "Meekised" from Jacques design to make use of a smaller dial gauge.

I have also added a photograph of the modification that automatically cuts off the power when the saw is through the metal. This has been described in EiM and Home Shop Machinist over the past few years.

Regards

Gray

ega

As Brian said anything you can do to give the blade an easier track will help. Adjusting the guides as close as possible to the work was always my normal practice. On my saw the guideways were a little out of parallel and out of plane adding yet more confusion to the mix.

Brians wire would probably have saved me a decade of on and off futzing around getting things a bit better every time I got fed up enough. At one point I seriously considered re-machining the wheels and the whole bow assembly.

The bigger version is much less trouble, although still not up to proper industrial saw reliability which Is probably indicative that our small ones push the design envelope a bit too far down.

I wonder if switching to 3/8" blades would help. My experience is that overstress breaks always begin with a notch from the back at close to 90°. The break then runs off at whatever angle was weakest. Which suggests serious stress concentrations at the back. A 3/8" blade will be outright more flexible and won't have the bit that really suffers.

Clive

Gray:

I assume that in use the device is clamped to the blade and a side load applied to the latter?

This is slightly reminiscent of the spoke tensiometers used by some cycle wheel builders; those with an ear pluck the spoke and note the pitch of the sound produced.

Clive:

Thank you.

I did try 3/8" blades for profiling in the vertical mode but my impression is that these small flanged-wheel H&V saws are really intended for 1/2" blades. Like the others, I have had good results from the Tuff Saws product and not yet had to take advantage of their re-welding guaranty.

Clive and ega,

I am fairly sure that industrial saws are set up by these or very similar means. Those blades are of course much bigger all round at one inch deep and perhaps 0.050 inches thick so are rather more forgiving than the hobby sizes but they will be subjected to the same sort of fatiguing forces if the tracking is badly misaligned.

When I was using one failures were always from wear on the teeth, never a broken blade.

I tension my blades to get a musical note on the long length down the back of the bow. A 'thud' is no good nor are notes in the high violin range. Too low blade tension leads to jamming in the cut and the natural reaction to lift the bow to ease that which is very likely to strip the blade off the wheels

Regards Brian

Graham's Blade tension meter is a much neater product than mine, but based on the one made and documented by Jacques.

The meter is clamped to the blade, before any tension is applied. Tension is increased until the DTI shows, FROM MEMORY, 0.05 to 0.07 mm extension.

Since using this technique, blades have lasted so much longer, and the cuts are more accurate.

I commend the device, and careful alignment to all readers.

Howard

There are numerous mobile apps which might help in finding the right pitch in between.

I have my own H&V saw set up so that one turn of the tensioning screw takes the blade from relaxed to correctly tensioned. This action is always coupled with turning the power (at the wall) on or off as appropriate which helps to avoid starting untensioned; as you rightly say, running untensioned will cause problems but I am not clear whether relaxing the blade actually helps to prolong its life.