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Too_Many_Tools
04-17-2010, 02:04 PM
Has anyone built a hydraulic scale from Harbor Freight components similar to the Sherline offerings?

http://www.sherline.com/scales.htm

TMT

doctor demo
04-17-2010, 04:19 PM
Yes, a few years ago I used an Enerpac low profile 1/4'' stroke cylinder and some quick couplings with a gauge to use as a trailer tounge scale to locate a backhoe on a trailer for optimum tounge weight.
I took the cylinder apart and measured the bore and made a crude psi to lbs chart on note paper.

Steve

gary hart
04-17-2010, 04:58 PM
Built pull scale from stuff had on hand. Wasn't sure of gauge accuracy. Hung a barrel from the scale and kept adding measured amount of water. Averaged out the know weight with the gauge readings and came up with a factor to use for determining the reading in pounds.
http://img.photobucket.com/albums/0903/ghart3/Tools/Hydscale2.jpg

Black_Moons
04-17-2010, 05:13 PM
Hmmm.. Oh, so you just need a double acting cylinder and use the top of it?

Awsome. I was gonna buy one of the lift scales but then the distrubuter link showed $130 USPS shiping for a $230 6lb object.. so I said forget it.

Should be easy enough to build my own from stuff at princess auto. I had recently worryed about the force required to drag my mill/lathe outta the basement, now i'll be able to keep an eye on it..

metalmagpie
04-17-2010, 08:08 PM
Figure diameter needed to make a 1 square inch round cylinder
Turn a piece that diameter.
Bore a hole that diameter
Fit the end of the rod with an O-ring
Drill/tap the side of the piece for whatever size gauge you want
Use a gauge rated in thousands of pounds .. 1000 psi means 1000 pounds

Charlie C
04-17-2010, 09:44 PM
Hi Guys, I use to post and read the threads here but kind of got away from doing that for a while. At one time I had close to 1200 post plus/minus.
I found this thread and thought that I might add a couple of ways to make a load cell.
The last link is to my photo bucket site, where you might find some things of interest.

http://smg.photobucket.com/home/kcprecision/allalbums

http://img.photobucket.com/albums/0903/kcprecision/Load%20Cell%20Construction/LoadCellStorageBox2.jpg

http://img.photobucket.com/albums/0903/kcprecision/Load%20Cell%20Construction/2008_0316Image0001.jpg

CCWKen
04-18-2010, 12:46 AM
If you're using a hydraulic cylinder, you need to make sure you don't exceed the cylinder capacity on pull-back. You could pull the piston off the rod. :eek: If I were to use that, I'd attach a safety chain between the two hooks.

I like the Sherline style. It appears to be a one-piece piston and rod. If you use a bore diameter of 1.596 and a rod of 1.128, you'll come pretty close to a 1:1 ratio for the gauge.

camdigger
04-19-2010, 12:27 PM
The components are as varied as inventory piles.

All you really need for design info is f=P/A, A = Pi/4 *d*d, the knowledge that Orings are limited to 3000 PSI without back up rings, and the squish factor for groove depth.

From there, you can figure all kinds of diameters to make sense of the pressure readings a gage might give. My load cell gives 1 MPa per ton load 'cause I had metric gages laying around.

FWIW, these equations hold for hyd cylinders too, but you must use "net" or "effective" area for the rod side of the cylinder by subtracting the crossectional area of the rod.

Limiting the loads such that the original design pressure is not exceeded should prevent any issues with excessive pressures.