|Forum topic by William Shelley||posted 05-20-2014 05:23 AM||1329 views||0 times favorited||17 replies|
05-20-2014 05:23 AM
I’m looking to get some feedback on bandsaws tensioned with an air cylinder and a regulator vs. the traditional spring and screw mechanism on 99% of the bandsaws out there. I’m in the construction phase of a shop-made 20” bandsaw project, inspired by Matthias Wandel but the design is entirely my own. When I got to the point where I needed to come up with a design for the tensioning mechanism, I initially assumed that a screw and spring was the best option, but then I got stuck because I would have to buy a really heavy duty spring that could survive a lot of tension on a 3/4” or 1” blade, but which would be too stiff if I was using a 1/4” or 3/8” blade.
I realized that an air cylinder could apply a LOT of force (a 3-1/2” bore cylinder @ 100psi is about 962lbs), but had the added bonus of providing a cushioning action at the same time to absorb vibration. This would make the mechanism simpler overall, and air cylinders are incredibly cheap on ebay. In fact, even including fittings, valves, the regulator, and other items, I’m fairly certain it would be a price-competitive alternative to the spring and screw tensioning design. I’m trying to stay on a pretty tight budget but at the same time I’d like to be creative and innovative if possible.
I also like the idea of being able to de-tension the blade with the press of a button or the flick of a switch.
If I end up going with an air cylinder, I will probably use a pressure-actuated switch as a safety interlock to prevent the motor from starting if the blade is not tensioned, as well as to shut the motor off if the air supply dips below a certain threshold. I’m using a Square D variable frequency driver to run a 1hp 3-phase motor, which I can DC-injection brake to stop all motion in a matter of seconds, in an emergency like an air line bursting.
However, I’ve read a few articles or forum threads on other sites where a bunch of users are poo-pooing the idea of using an air cylinder to apply tension, saying things like “its a solution looking for a problem”, “whats wrong with just cranking a handle?”, and “not a single person i know has ever de-tensioned their blade when done working”. These kinds of attitudes are making me doubt my idea.
-- Woodworking from an engineer's perspective