DoALL bandsaw questions

I have a DoAll wit dat vane pump, and, eat your heart out, mine works!!! lol I didn't initially, tho, and I remember pouring lots of oil in it, which may have served to not only clean shit out, but also to act as a "seal" for the blades. I've got a foot out the door, so I'll check the rpm thing later, but have no idea of clearances. It will be tough to get access to the back of the saw, as well, so I cain't guarantee an rpm reading, either, but I'll try. And the pulley diams, as well.

Well, I found the tach. It says the wheels are spinning at the correct RPM. So when the pointer on the saw indicates 300 SFPM it is correct. Which means that the 1725 RPM motor is at least the correct speed even if not original. So, should a vane type air pump with a rotor housing inside diameter of about 5 inches and graphite vanes be spinning at only 860 RPM? That equates to about 1125 SFPM. I'm thinking that it should spin much faster, like 3450 RPM. Eric

Do not know about general purpose air pumps, but the vane pumps in vacuum pumps run at a lot lower rpm than 860.

Dan

Greetings Dan, This pump relies on centrifugal force to keep the vanes in contact with the inside wall of the pump chamber. There no springs behind the vanes to hold them in contact. And the vanes, being graphite or a graphite composite, are very light. So I'm thinking that they need to run much faster than they are now. Eric

I peeked inside my DoAll ML, which is very similar to the band filers I've seen. The pulley ratio between the (original) motor and pump appears to be close to what you've got.

The DoAll instruction book I have describes the vanes as plastic, though I'm pretty sure those in my pump are graphite. My pump didn't work when I got the saw. My recollection is there was so much graphite dust in the pump that it was packing around the vanes and jamming them in their pockets.

I imagine the plastic the manual refers to was linen phenolic, which would be an easy material to make a new set from.

Linen phenolic is commonly used as vanes in air motors, IME. Air motor vanes in pneumatic tools withstand much greater pressures, and give excellent service life when kept lightly oiled.

If the pump is clean now, adding some oil into the pump should improve the pumping action. New vanes finished to close tolerances would likely make the 'ol pump good-as-new if the cylinder bore is undamaged. I dunno what kind of specs would apply to end gaps, but it doesn't take much end gap wear for an air tool to exhibit a substantial decrease in performance.. generally seen in old air tools with countless hours of use, or neglected tools run dry.. failure to routinely add a small amount of oil into the air inlet.

Wear is slow and basically goes unnoticed day to day, but in a year/couple years time, an air impact wrench, for example, will be lower powered than when new. The difference is definitely noticable when the motor is rebuilt with new vanes.

Maybe you could use an adapter on a VSR drill motor to spin the pump at other speeds for comparison, while checking the air inlet and outlet delivery.

Maintenance departments used to rebuild tool air motors by precision grinding the cylinder bore on a lathe if there were indications of wear.

Does your air pump work now? Mine was totally gummed up inside and now it is pristine. There is no visible wear inside the pump. Is the air outlet on yours closest to the inside wall of the saw? Thanks, Eric

Greetings Bill, The directions on the back of the saw to use graphite powder only as a lube and then only when deemed necessary. Eric

Thanks for mentioning that, Eric.. graphite is about the last product that occurs to me when I think about lubrication.

I have a small vane pump in a desoldering station, and graphite should be a lot better than oil for that application.

It's been working with no attention for many years now. Though it was a long time ago, I think all I did to fix it was dump out the loose graphite and scrape off the caked deposits that were jamming the vanes. The orientation is as you describe - the pump is on the right when facing the back of the saw, the outlet is on the top right of the pump housing, and the pulley rotates CCW.