Static Hydraulics Question

[Scotty370]

In this bandsaw mill I'm thinking of building, one of the critical factors is band blade tension. When the two wheels are frame mounted, the 'idler' wheel and pillow bearings, are mounted on a slide plate to adjust tension. This can be accomplished with a simple screw devise, but most builders prefer a small hydro-ram & gauge simular to a porta-power unit w/hand pump. No real mention is made of stroke/bore, so here's my question. 2400#, seems to be the number their shooting for so if you pressurize any ram, regardless of size, to 2400#, and stop, is the resulting pressure the same? If you mounted a ram to the ceiling over a floor scale, would the scale read 2400#s when the gauge did? Some simple things, I just don't comprehend, not to mention the complex ones! TIA ~Scotty

 

[tommu56]

most of the portapower gauges I'v seen are set for a set cylinder size and will read in pounds or ton's load on that cylinder length won't affect pressure.

tom

 

[Egon]

If you mounted a ram to the ceiling over a floor scale, would the scale read 2400#s when the gage did?

If the ram has exactly one square inch of pressurized surface the scale will read the same as the gage.

If the ram had exactly two square inches of pressurized surface the scale would read double what the pressure gage reads.

The gage will only read pounds per square inch. The scale will read pounds per square inch gage pressure times the surface area of the ram.

[Pounds/inch squared] times [inch squared] equals pounds.

 

[Willl]

so if you pressurize any ram, regardless of size, to 2400#, and stop, is the resulting pressure the same?

Only if that gauge is calibrated to that piston surface size. Regardless of length.

If you increase the piston surface by 2 fold, gauge difference should also be a 2 fold difference (or close to it).

 

[J_J]

I believe you would have to calibrate the gage for the ram used. So in essence, you want to be able to operate a ram the keep 2400 lbs of tension on the two band-saw reels, one secured and the other movable. Have you considered the fact that the tension will change as the blades heats up, and are you considering some kind of auto tension setter? There has to be some wear factor on the reels based on the materials that the band-saw blade rides on, and the tension. Be it rubber, or the metal of th reel itself.

 

[Egon]

For tensioning a band saw blade do you not measure deflection? If so You would only have to note the pressure at the proper deflection to get you into the right range.

 

[cameronjm]

Can I ask how big the saw blade is? 2400# is a lot for blade tension.

 

[Scotty370]

OK- Figured it out with you folks helping, and more surfin'. The pump and gauge measure pump output, which is magnified by the bore of the cylinder pressure area.
Thus, a 1-3/4" (bore) cylinder works out like this: Area=radius squared x 3.14, Thus .875=radius, squared = .7656 x Pi = 2.404 surface area inside the cylinder cup. Therfore, 1000#s pressure from the hand pump, would yield a stroke force of 2,404#'s. Right where I want to be! Using this math on a 4"bore cylinder would have a cylinder cup surface of 12.56sqin, meaning an inlet pressure of only 200#'s would yield a whopping 2512# of stroke force! Thanks guys! J_J- Duly noted that the Band Blade heats during use, expands, and you have to re-pressurize to maintain the 2400# target. Folks also say to de-tension the band after sawing, to allow for the contraction cycle. Cameron- I agree, that seems like a 'boatload' of pressure! 1-1/4" steel band, .042 thick! Thank god for guards/shields! Egon, Seems like that would be simpler! IE pull the blade with a spring scale! But no mention of this method in my research. Thanks again Guys! ~Scotty

 

[Willl]

Area=radius squared x 3.14, Thus .875=radius, squared = .7656 x Pi = 2.404

Ya, that's what I was thinking also.................................Not.

 

[Scotty370]

Come-on Willl, I know it was right on the tip of your tongue!