Bandsaw downfeed getting air in it

[whateg01]

I have a shop fix 7x12. The downfeed cylinder does a fine job of controlling the cut. When I raise the saw though, it gets air into the piston. I have to raise the saw well above the work to get it to clear the next piece of I'm just sliding the stock out for the next cut. My buddy's jet doesn't do this and others I've used don't do this. Mine sits closer to horizontal when the saw is down instead of being positioned vertically like many others. Anybody else ever encounter this and what fixed it for you?

ETA: buddy's might not be jet, but I am pretty sure it is. Anyway, mine is arranged like this:



With many others like this, I don't think it's a bad design, but I can't figure out why mine does this. I've had it apart and cleaned it. Everything appears to be in good condition and when apart, it all seems to move like it should.

 

[darkzero]

Is the cylinder leaking anywhere? If air is actually getting into it, then I would assume oil is leaking out of it somewhere.

I've had my MSC/Vectrax branded Rong Fu 7x12 for 10 yrs now. Like 4 yrs ago or so it started getting slightly sloppy & I did notice some oil residue building up on the cylinder. I forget exactly how & what I did but I tightened whatever I could, bled the air & topped off with oil. I do remember changing the o-ring for the valve which started leaking on mine. It's been working like it was new ever since.

 

[darkzero]

mine is arranged like this:

Mine is mounted in the same orientation.

 

[whateg01]

Is the cylinder leaking anywhere? If air is actually getting into it, then I would assume oil is leaking out of it somewhere.

I've had my MSC/Vectrax branded Rong Fu 7x12 for 10 yrs now. Like 4 yrs ago or so it started getting slightly sloppy & I did notice some oil residue building up on the cylinder. I forget exactly how & what I did but I tightened whatever I could, bled the air & topped off with oil. I do remember changing the o-ring for the valve which started leaking on mine. It's been working like it was new ever since.

Actually that's a good question. I've never found any instructions for repairing or rebuilding this cylinder. Tbf, I haven't looked in a few years since I initially tried to fix it so maybe a new search would do better. Anyway, when I got it, it was not completely full of oil. It was used so who knows what the po might have done with it. But I drained it to open it up and try to figure out why it was doing what it does. I put back the same amount of oil. Should it be full? Since the rod takes up space, I would think it would have to have some amount of air in it to keep from building up. No?

 

[darkzero]

Actually that's a good question. I've never found any instructions for repairing or rebuilding this cylinder.

When I noticed mine was starting to get sloppy, I downloaded manuals for as many different brand 7x12 saws that I could find. The manual that came with mine was just the generic basic Rong-Fu manual & didn't mention anything or much at all about the cylinder. And the instructions (if covered) for other brands varied quite a bit on how to service it.

I got mine new but I have no idea if it was full when new. I wouldn't be suprised if it wasn't even if it was supposed to be. I don't know much about hydraulics but I assume it shouldn't be completely full.

None of the instructions I found actually covered in detail how to add oil. I forget which way, up or down, took more oil but I kept adding oil through the valve until I couldn't add anymore. Don't know if that was the proper way to do it but it worked for me & fixed my issue.

 

[darkzero]

Ok, looking through my collection of manuals, I kept manuals for a Grizzly, Jet, HF, & Wilton. I don't think the Jet & Wilton are made by Rong Fu/based but they use similar looking hydraulic downfeed cylinders.

The Grizzly & Jet manuals don't mention anything about servicing the cylinder, I can't remember why I kept these manuals. The Wilton does have a page on rebuilding the cylinder. I for sure did not do what the Wilton manual says, I never even took my cylinder off the machine. Hope this might help you any or at least more than my bad memory has.

 

[whateg01]

Thanks! Definitely not exactly what I was doing, but based on that, I almost certainly did not put enough oil in.

 

[slodat]

I put new o rings in a Grizzly I had for many years. Filled until it was full, then bled by cycling it several times. Worked great after.