Made a "Forklift Scale" for the working poor

Ever since I decided to get more into scrap metal, I always wanted to
add a weight scale to my 15k forklift, so that I would instantly know
how much am I lifting.
That way I could learn estimating a lot quicker, and also avoid those
overweight truck fines. We almost got his with one, with cops weighing
the rear axles at 33,100 lbs, so close to the 34,000 lbs limit.
The problem was that the scales are expensive, starting from $730 and
up. And all they do is measure the cylinder pressure and convert that
into lbs, according to a linear formula.
So, instead, I took advantage of an opportunity, since the main
cylinder hose on my forklift was leaking a bit and needed to be
replaced. I took a "precision temperature compensated 3,000 PSI
pressure gague", that I had laying around. When replacing the main
hose, I added a tee and hooked up the scale into that.
So, now I always know the main cylinder pressure. I am going to weigh
a few things of known weight (I do have a 10k floor scale, so it not
hard to come up with known weights). Then I would write up a table of
weight/pressure values and run a linear regression, then I would print
out a table with these values. That way we'll know for sure what
weighs how much.
I did hook all of that up yesterday, but did not yet play with this
due to lack of time, but I plan on doing so shortly.
i
Reply to
Ignoramus32392
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Print up a new scale for the pressure gauge so the weight can be seen at a quick glance rather than referring to a chart. Also make sure you put a pressure snubber orifice in the feed to the gauge to help protect it from pressure spikes.
Reply to
Pete C.
A shutoff valve for the gauge is also a good idea so you can shut it off if you're doing rough work that will generate a lot of pressure spikes, and also if the gauge fails you can easily shut off the line and replace the gauge.
Reply to
Pete C.
Ignoramus32392 fired this volley in news:uMSdnTLRGoDs4PzMnZ2dnUVZ snipped-for-privacy@giganews.com:
Ig, since the math is simple (and you, especially, know that), I'd suggest that instead of making up a table for your work-a-day weighing, you do it only once to determine if there are any non-linearities (in the gauge... the cylinder will be linear), then make a replacement SCALE for the gauge itself.
If you don't want to disassemble the gauge, you can just make it from transparent label stock, and stick it on the glass.
LLoyd
Reply to
Lloyd E. Sponenburgh
"Lloyd E. Sponenburgh" fired this volley in news:XnsA19B796348D48lloydspmindspringcom@216.168.3.70:
Hmmm... servers must've delayed messages. I see that Pete C suggested the same thing.
He's right about the snubber and cut-off, too.
Lloyd
Reply to
Lloyd E. Sponenburgh
OK, the "new scale" is a good idea. The pressure snubber is something that I never heard about. I would think that the forklift hydraulics is somehow protected from pressure spikes, anyway?
Reply to
Ignoramus32392
I've done something similar. My gauge was oil filled and on the end of about 8' of flex hose, no snubber. Gauge did bounce a little but was fine for years.
Reply to
whoyakidding's ghost
I would be interested is knowing how linear the weight / pressure is. Where I worked they have a sling test tower where they proofed and certified weight handling gear. I am pretty sure they ignored any possible non linear effects and just multiplied the pressure by the area of the piston. And I have always wondered how accurate that approach was. Have also been involved with making small weight scales to go under each wheel of a race car to set up the suspension. There of course one does not need absolute weight.
Dan
Reply to
dcaster
We low-buck racers used a bathroom scale and a 2 x 8 with a fulcrum. A mess to set up, but it worked.
And I made my own tire-temperature gauge with a 1N914 diode for a sensor and an op-amp and analog gauge. Accurate to within a degree or so, and dirt cheap.
1N914s, unlike thermistors, are linear as hell and they respond in about one second to tire temperatures. Leads must be short, however.
Reply to
Ed Huntress
It is not a lot of money to make a cylinder out of aluminum, make a piston using an O ring for the seal ,and connect it to a pressure gage. I think we made a set of four and spent less than $10 per wheel, not counting engineering and manufacturing time. It was worth while for circle track racing where you were adjusting the suspension often. Might not be worthwhile for sports cars.
Dan
Reply to
dcaster
whoyakidding's ghost fired this volley in news: snipped-for-privacy@4ax.com:
Hoses expand and contract more than one might assume, based on their pressure ratings. The hose (that long) WAS the 'snubber'. Essentially, the same as adding a small air accumulator near the gauge, but using the flexibility of the hose instead of the compressiblity of air to do the absorbing of the spikes.
Lloyd
Reply to
Lloyd E. Sponenburgh
Too_Many_Tools fired this volley in news: snipped-for-privacy@q6g2000yqa.googlegroups.com:
I did essentially the same thing in reverse when we needed a 0.01g balance at work ASAP, and the one we ordered was a week away.
I built a small lever/fulcrum arrangement from K&S brass stock and sewing needles that multiplied the force by 10X.
Of course, we were working with a total load of only 2g .
LLoyd
Reply to
Lloyd E. Sponenburgh
" snipped-for-privacy@krl.org" fired this volley in news:a5aaeefa- snipped-for-privacy@a14g2000vbm.googlegroups.com:
It's cheaper in mistakes and time to buy PortaPower shorty cylinders, and convert them to purpose. They're rated at 10Kpsi.
LLoyd
Reply to
Lloyd E. Sponenburgh
But not as much satisfaction in having made something. The 10kpsi would have been wasted. The car weight was about 2000 lbs and only about 500 psi per wheel.
Dan
Reply to
dcaster
"Ignoramus32392" wrote in message news:_KWdnQqkur_rBvzMnZ2dnUVZ snipped-for-privacy@giganews.com...
You might check if the indicated weight varies going up or down, or close in vs out at the tips, from friction. jsw
Reply to
Jim Wilkins
I will try to play with it and see.
I have a 5k forkilft that weighs about 8k lbs. I want to see if the position on forks matters, etc, and how to get the most reproducible pressure (creeping up vs stopped vs creeping down).
Extreme accuracy does not matter, +/-3% would be fine. i
Reply to
Ignoramus32392
I agree with Pete on the shut off. Use a needle valve. Also, if the gauge is oil-filled, the shocks won't damage it. there was an oil filled gauge on the main cylinder of a hydraulic plastic injection molding machine I used to have. Believe me, there was lots of shock there!
Paul
Reply to
Paul Drahn
My forklift is a double section unit. I know there is a name for that, but don't remember it. Once the fork carriage gets to the top of it's track, a second section begins to go up. If you machine is like that, your weight will only be correct when using the lower section.
Paul
Reply to
Paul Drahn
When printing a new scale for the gauge it should be easy enough to include different color scales for each mast stage and the weights corrected for that stage. Little different than gauges with PSI and KPa scales, in fact I believe the gauges Enerpack uses on their presses have scales for PSI, and several scales indicating tonnage for different cylinders they make.
Reply to
Pete C.

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