bleeding bandsaw downfeed cylinder

[umahunter]

Well I put together a bimba cylinder with parker flow control valve with check valve . Couple questions for those in the know . Is there a trick to getting it full of oil ??? After you fill it what's the best way to bleed the system?? I've got it coming down nice except one spot. which I figure is either lack of oil or air bubles

 

[Ulma Doctor]

Nice job mounting the cylinder,

bimba's are normally used as air cylinders,
i'm not saying that they can't handle hydraulic function, just be careful how much hydraulic pressure you put to a cylinder that is rated for pneumatic function.

you can barely crack the fittings one at a time under pressure until oil and/or air releases.
start with the highest elevated fitting first.

without a reservoir you'll have to be creative.
fill both ends of the cylinder with oil prior to installation to minimize air introduction.

 

[Mark_f]

bimba's are normally used as air cylinders,
i'm not saying that they cant handle hydraulic function, just be careful how much hydraulic pressure you put to a cylinder that is rated for pneumatic function.

The air cylinder is fine for this application because there is not much pressure. I have a hydraulic cylinder for my saw that I made, but I installed mine vertically. in doing so the tiny bit of air is always at the top and not a problem. The stroke on mine is also 10 inches so I only use about half of it and I don't bottom out the cylinder. this helps keep a small amount of air from being a problem. Because of the piston rod, there is a different amount of displacement from the top to the bottom. This is why a lot of guys put a small reservoir on the cylinder to allow for the difference and a small amount of air. When I bled mine , I held it vertically and moved it up and down slowly to get as much air out as possible out of the top connection. You should be fine once you bleed the air out. YOU CAN"T GET 100% of the air out, but you can get almost all out. An air pocket will make the cylinder "spongy" which you don't want.


Mark Frazier

EDIT: In looking at your photo, that "one spot" wouldn't by chance be when the saw is almost down is it?

 

[kd4gij]

When I built mine I used hose at the top side. Took the hose off the valve and used a short hose on the valve. Then put the ends of bouth hoses in a jar of oil. With the valvefully open raise and lower the head untile no bubles then hook the hose back up. Hope that makes scence.

 

[Ulma Doctor]

When I built mine I used hose at the top side. Took the hose off the valve and used a short hose on the valve. Then put the ends of bouth hoses in a jar of oil. With the valvefully open raise and lower the head untile no bubles then hook the hose back up. Hope that makes scence.

Yep,
i used to bleed forklift brakes and clutches kinda the same way!!!

 

[NightWing]

If I am looking at that correctly, it looks like you are cushioning on the outstroke. I have never seen a hydraulic damper used that way.

 

[Mark_f]

If I am looking at that correctly, it looks like you are cushioning on the outstroke. I have never seen a hydraulic damper used that way.

You are correct that it should ideally cushion the other way, but it will work either direction. The photo looks like when the saw is up, the cylinder is mid travel. If you adjust the mid travel point to be the mid travel of the saw also, you will have less problem because the cylinder won't be near either end of travel.

Mark Frazier

 

[JimDawson]

If I am looking at that correctly, it looks like you are cushioning on the outstroke. I have never seen a hydraulic damper used that way.

I have mine in tension also, it seems to work fine.

I thought about the difference in displacement of the two sides of the cylinder, but I didn't compensate for it. I'm using a 2 inch cylinder with a 3/4 inch rod, so there is about 15% difference in the piston area. Not sure where the extra oil goes, it must be magic or something.)

 

[umahunter]

Ok I'm back at this and decided to remount the cylinder vertically to put pressure on the down stroke. so what I'm trying to figure is since I have a maximum cut height of about 4 1/8 inch and my cylinder has a 7 inch stroke. should I mount it with a inch or so of cylinder out to keep any air out of the 4 inch cut zone what do you guys think ???

 

[Mark_f]

Ok I'm back at this and decided to remount the cylinder vertically to put pressure on the down stroke. so what I'm trying to figure is since I have a maximum cut height of about 4 1/8 inch and my cylinder has a 7 inch stroke. should I mount it with a inch or so of cylinder out to keep any air out of the 4 inch cut zone what do you guys think ???

Mount it to center the amount of saw travel in the cylinder travel. That way you will stay away from the ends of the cylinder.