Horizontal Band Saw Blade Pressure Question

Janderso

Jeff Anderson
H-M Platinum Supporter
Joined
Mar 26, 2018
Messages
8,354
I am in the process of customizing a brass needle valve assembly for my hydraulic saw arm blade pressure adjustment.It's been a while but I remember the goal is to have the blade come down at the same speed as the descending cut. If I can fine tune the needle valve to go anywhere from full drop to stopping in mid stream I am providing a way to increase blade life, allow the saw blade to cut at it's own speed and maintain a straight even cutting path correct?
Now, any idea what I should be watching for with regard to blade pressure?
In other words, with a 3/4" blade, cutting a 2" hunk of mild steel square stock with a 10-12 TPI Blade, how much downward pressure?
I'll have to guess as close as I can but say 5 lbs? 1 lb?
Anything published on this?
Thanks
 
From memory I believe my manual says 8lbs. I just rebuilt my drop cylinder. Pretty easy and simple design. I can take pics later if interested.
 
My 4x6 rong fu cuts fine without one, it dose have a spring gizmo for pressure I don’t mess with it. I’ll change blades for thin stuff.
 
From memory I believe my manual says 8lbs. I just rebuilt my drop cylinder. Pretty easy and simple design. I can take pics later if interested.

Whoa, My cylinder leaks, how do you rebuild it? Is it a seal or packing on the ram?Awesome, 8 lbs! That's the stuff. Thanks guys!!
 
There are some physical parameters here that seem to affect the desired measure. The 8 lb. is a force at the handle of the swinging head, which means some higher force where the blade is cutting (ratio of two distances from the pivot for that machine).

But knowing that static weight doesn’t say much about the desired downfeed does it?

Is the idea to have a certain pressure in the cylinder, or to have a certain feed per tooth? If the latter then I guess you need to know pitch and speed to set feed rate. How does thickness of the workpiece factor in?
 
For the cylinder leaking it kind of depends how yours is set up. Mine is a 10” cylinder that their is a cap that screws off on the rod end. Some are none serviceable welded cap.
There is usually a wiper seal on rod which mine was felt so I replaced with a o ring. Then my rod seal was also leaking the cylinder would just drop. That seal was so dry rooted that it looked almost felt. The seal is called a piston cup seal. It’s a flat thick rubber with a lip formed in the perimeter facing one direction. So it will seal on the way down but allow oil to bypass if you pull up. Pretty easy just hard finding comparable replacements.
As for the valve the needle on mine had the tip broke off. It worked but for fine feed I think I needed that section to work properly. So I took a roller pin out of a bad needle bearing mounted in lathe and ground a long taper on one end. Then I took the broke needle chucked it up faced the broken end bored for the new addition then jb welded once I got the depth of needle right.
I had the saw for about ten years finally rebuilt everything last winter. New bushing bearings,brushes,strip and paint. I 1B99C8E3-6C7E-4D92-B3B2-AABCA6FE8368.jpeg6E8BD7EA-DCCF-4980-8745-DF979EA3BA3B.jpegand always relied on the spring for the down feed. My unit has a spring and the cylinder. Now I can cut while not babysitting it. Another one of those “why the hell didn’t I fix it earlier”. Like a saw through styrofoam I love it.
 
Is the idea to have a certain pressure in the cylinder, or to have a certain feed per tooth? If the latter then I guess you need to know pitch and speed to set feed rate. How does thickness of the workpiece factor in?[/QUOTE]

Yes you should have the correct blade pitch speeds ,etc. for it to cut properly. Thickness of material means a lot. My machine has a generic chart but I believe I have a 10-12 variable blade and if something thin I use less down force pressure something thick I put a little more feed rate. Speeds I keep in the middle don’t know exactly. I was told you want little 6’s as your chips not dust. To me slow is better no production here. Have had same blade in for years. Cuts less the .005 out of square and plum.
 
I don't know the equations involved but with a hydraulic downfeed it's more a matter of blade downward travel per unit time rather than static pressure
because if the blade was not being driven eventually the full weight of the saw would bear on the blade and probably break it, so you are essentially clearing a path for the teeth to drop into, bit by bit...I suppose the effective dynamic pressure could be measured somehow-? Maybe a pressure gage on the table with some sort of hinged workpiece? Hmmm perhaps even measuring the temperature rise with an infrared gun?
Mark
 
Back
Top