Andy Pullen":21wczv5g said:
I recall the manual said a 20mm blade was the max but it will physically take a 1" comfortably with sufficient tension.
Just because it will
accommodate at 25mm blade it doesn't mean to say it will
tension that blade adequately. Experience tells me that to tension a 25mm blade you need the sort of frame rigidity that only comes with a 500 or 600mm wheel fabricated steel saw (or a cast-iron frame machine) - something the 613 clearly isn't. Therefore the machine is simply incapable of tensioning that blade adequately. Period. I'd suggest that you go the other way and install a thinner 1/2in blade, preferably a hook tooth form blade from a good quality supplier such as Dure-Edge or Dragon and try again, this time with a point fence to overcome the drift which is more inevitable in narrower blades.
Andy Pullen":21wczv5g said:
I was advised that the issue with the wider blades was the thickness of the steel folding around the smaller band wheels if anything.
Then I'd say you were wrongly advised. The issue is that a machine with smaller wheels runs a much shorter blade than one with bigger wheels and those blades are being "bent and unbent" around a much tighter radius wheel many more times in every hour's running, e.g. the weld on a 3 metre or less blade on a 14in saw will need to go round the wheels twice as often in every hour as the 6 metre blade on a 20in wheel bandsaw. Ergo weld failures happen earlier on smaller wheeled bandsaws because the number of bending actions and the severity of the bending are so much greater. My experience with bigger bandsaws is that you're more likely wear out a 3/8in or wider blade than to break it prematurely, whilst on 12 and 14in machines the converse is truer.
Andy Pullen":21wczv5g said:
The Kity has a substantial steel tube that supports the tension on the blades and isn't just metal pressings like some others.
The frame still isn't all that rigid, though. Most blade stock manufacturers recommend somewhere going for around 15,000 to 20,000 psi blade tension (a measurement of beam strength) for carbon steel (black) blades.
Beam strength is the blade's ability to resist deflection. It is achieved by combining several factors: correct blade pitch, blade width and blade guide settings. A key factor in achieving beam strength is applying the maximum blade tension that the blade manufacturer recommends. Because resawing hardwood places is so demanding of the blade if the blade tension is inadequate, the blade will bow (vertically) in cut and can even start to snake - the sort of behaviour you seem to be describing.
I have a Starrett tension gauge (necessary on large saws as they have the strength to pull blades apart if you get too gung ho) and I can tell you that my old Startrite 352 saw could manage about 12,000 psi on a thin 1/2in carbon steel blade, but only 9,500 psi on a similar thickness 3/4in Starrett carbon steel blade. Needless to say befoe I got the Aggy I used to resaw using 1/2in blades on the Startrite and live with the almost inevitable blade drift. By way of comparison I can pull more than 25,000 psi with a 3/4in carbon steel blade with my 700mm (28in) Agazanni like this:
and can top 20.000 psi with a thicker-bodied Lenox 1-1/4in TCT resawing blade - a figure which my smaller cast-iron frame machine can't quite match, mainly because the tension spring needs to be retempered. Assuming that your 25mm blade is thicker than a 1/2in blade, which it probably will be especially if it is a bimetallic blade, then you stand no chance at all of reaching adequate tension on the Kity. Either the tension spring will compress fully or the frame will flex long before you achieve the required tension.
A note here for anyone tensioning blades for resawing - at the end of a session I was always advised to drop the blade tension with fabricated (i.e. steel frame) bandsaws to avoid running the risk of warping the frame or simply compresiing the tension spring permanently.
Scrit
