DoALL bandsaw questions

I have an old DoALL bandsaw that uses a vane type air pump. The pump was all gummed up so I cleaned it up and now the pump is totally free
of any contamination. The vanes slide freely in their slots. The pump appears to be able to rotate in either direction and still pump the same because the vane hub is centered in the housing. There are no arrows showing rotation direction either. The pump hardly puts out any air though. So I'm wondering about clearance of the vanes and RPM requirements. The vanes fit snugly in their slots but move freely, maybe .003" clearance. But the vane width, the distance between the vane and the housing cover may be about .005". Is this too much? As far as RPM goes, the motor pulley is 3 inches diameter and the pump pulley is 6 inches. So, with the 1725 RPM motor the pump is spinning about 860 RPM. I suspect this is too slow. The saw is old and the original motor is not in the saw. I don't know if it had a 1725 or 3450 motor originally. So far DoAll has been no help. Also, the saw was originally a band filer and the wheels have no tires on them. They are crowned though. The crowning appears to be enough to keep the blade teeth from losing their set on the side that touches the wheels but I'm not sure. The saw does seem to be cutting too slow. The blade speed seems much slower than what the pointer indicates and the pointer is working properly. When the max speed is indicated the vari-drive is the proper position for max speed. I will be checking the wheel speed to calculate the band speed when I find my optical tach. In the meantime does anyone here know about the vane air pump clearances and speed? Thanks, Eric
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
--
EA




Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 09 May 2013 16:51:48 -0700, snipped-for-privacy@whidbey.com wrote:

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
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On May 9, 8:10 pm, snipped-for-privacy@whidbey.com wrote:

Do not know about general purpose air pumps, but the vane pumps in vacuum pumps run at a lot lower rpm than 860.
Dan
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 9 May 2013 17:21:44 -0700 (PDT), " snipped-for-privacy@krl.org"

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
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 09 May 2013 18:07:49 -0700, snipped-for-privacy@whidbey.com wrote:

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.
--
Ned Simmons

Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
--
WB
.........
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

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
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 10 May 2013 10:03:02 -0700, snipped-for-privacy@whidbey.com wrote:

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.
--
Ned Simmons

Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
--
WB
.........
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 10 May 2013 06:56:33 -0400, "Wild_Bill"

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
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
--
WB
.........
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.