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7 X 12 bandsaw hydraulic downfeed leak

John Conroy

John Conroy

member
Premium Member
My Magnum saw started leaking oil from the hydraulic downfeed cylinder. I found that the external oil line that goes through the control valve is a stupid design. Each of the fittings in the cylinder body are 90 degrees so the openings face each other and a straight line connects them. This means that the line has to telescope so the compression fittings can be pulled into the 90 degree elbows when tightening the fittings. Of course the line is leaking where it telescopes. I removed it and pulled it apart to see if there was some kind of seal inside the hollow part but there is not. I bought a couple of bass fittings and some 1/4" copper line at Home Depot for the repair. After removing the bottom fitting I found it is some kind of straight thread very close in size to 1/8" NPT. I put the 1/8' NPT tap into the hole and only had to turn it 2 turns in order to get then news 1/8" NPT fitting to thread in. With the new fitting sticking out at a right angle to the cylinder body I bent up a line with a partial loop in it to allow wiggle room to make the compression fitting connections. Getting the cylinder topped up with oil was a PIA but I got enough in so it functions properly. I was just going to order a new cylinder until I saw the price $145 USD plus shipping!







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I retrofitted the same cylinder to my 4x6 and I think it’s pretty much leaked itself dry by now. Your post is an inspiration to get after mine. When you topped up the cylinder did you just funnel oil through one of the fittings before you connected them? And maybe 30wt hydraulic oil or something close to that?
 
I used iso 68 hydraulic oil but it is a bit thicker than what came out so Tom is probably right suggesting 32. I found the best way to fill it was with the cylinder held horizontal in the vise. With the pipe disconnected from the lower fitting I attached a short length of rubber hose over both the disconnected pipe and the lower fitting and both hoses submerged in the oil. I slowly forced the shaft full travel in both directions a number of times until air bubbles stop coming out. It's not necessary to get every bit of air out because the cylinder is not stroked through it's full travel when installed on the saw. Something to be aware of is that the piston actually travels past the hole the lower fitting is in if you push it that far when it is disconnected. That can cut the seal on the piston so be careful not to push the piston all the way to the bottom of it's travel. A poor design for sure. When I installed the new NPT fitting I made sure it does not protrude in far enough to get in the way of the piston.
 
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I've seen people use a screen door cylinder as the basis for a hydraulic downfeed. I think I have plans for it somewhere in the cloud. I will look for it if anyone is interested.
 
Hello John. I am interested in those plans. I believe they had something similar in one of the home machinist magazines, but I got the middle issue of the three part series and that was before I had the subscription, so I missed the rest.
 
[mention]johnnielsen [/mention] there was an arcticle on exactly that idea in the home shop machinist magazine last year if you can find it in an archivr


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Thank you Hruul and Kevin. I could not remember where I saw it. I have those magazines. I will find them and pdf for you Hruul. I can't post it but will forward via email to you. Again, it will take a couple weeks.
 
You can use a air operated pneumatic cylinder to replace or even add to a saw without the hydraulic down feed. I picked one up from Princess Auto and tied both inlet and outlets together, added a gauge, needle valve and ball valve on it to be able to lift the saw up. I filled mine u with mineral oil. If anyone is interested I can take a pic of mine, its still a work in progress but works ok the way it is. On the plus side the cylinder was cheap to buy.
 
Rotaxxx said:
You can use a air operated pneumatic cylinder to replace or even add to a saw without the hydraulic down feed. I picked one up from Princess Auto and tied both inlet and outlets together, added a gauge, needle valve and ball valve on it to be able to lift the saw up. I filled mine u with mineral oil. If anyone is interested I can take a pic of mine, its still a work in progress but works ok the way it is. On the plus side the cylinder was cheap to buy.
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What is your part number from Princess Auto? Kindly post some pictures!
 
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Heres a few pics of how I did it. Like I said before its still needs some work, I put it all together to try it and it works good. Now I just have to get back to it and take the lines out of it and get some nipples and unions to replace them. (it sucks when your closest hardware store is over 90km away that actually has anything) The cylinder I used was PA Part# 8188187. I think it was $20 at the time. The cylinder is rated for 120psi, I forgot to open the needle valve a few times and had seen the gauge up to 500psi and the cylinder hasn't leaked. Now the cylinder I used worked good, but may be too short or long for your saw. You will have to measure your saw, when closed and open to get the proper length. In the pics you can see the ball valve with the red handle is opened to bypass the needle valve which regulates the movement of the saw down. I usually adjust the needle valve to have the gauge read about 170psi. (make sure you install the gauge and valves on the port that will have pressure on it when the saw is lowering) The cylinder had 1/8" NPTF ports so I bought an adapter to go to 1/4" and all the fittings are 1/4" and the black line is just some 1/4" air brake hose. I put it all together and left the gauge out, and put medium weight mineral oil in the gauge port and bled the crap out of it to get all the air out. Once I got all the air out, I put the gauge in and haven't touched it in the two years I have been using it. If I was to do it again I would use some light mineral oil instead, the medium is pretty thick and my shop isn't the warmest in the winter.

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Now that I am looking at these pics I hope they show how they attached to the saw. The ends are just bolted in place of the spring that once was there. The one end of the cylinder I bought a clevis rod end for it. I could of made something in my shop to attach it, but at the time I had more money then time. Its the other way around now..... I hope this helped.
 
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