Shurline scale accuracy?

[ROBERT CROSS]

Originally Posted by Cracker

That'll work! I'm still curious as to where the pivot point should be located to calculate the weight at the ball when measure at the jack - which, admitedly, is the easiest place to measure the weight??? If the trailer is dead level, and both axles are equal in capacity, I would use a point midway between the axles or, in the case of a 34', centered on the center axle. If "x" is the distance from the pivot point to the jack, "y" is the distance from the pivot point to the ball, "a" is the weight at the jack, and "b" is the weight at the ball, it follows that if "a" is known, b = (ax)/y. Conversely, if b is known a = (by)/x. One axle weaker than the other could throw the calculation off - but it would still be relatively close.

I don't think it matters, the axles are the pivot point while towing, the trailer is un-hitched & level, there is no pivoting involved. Just weigh at both points, and add. If your using an Arrow, and you leave it installed 365, just add about 75lbs. I'll be re-installing the Arrow in a few day's and will post the actual numbers for our Classic if that will help.




"I plan to get a Sherline and weigh the entire dead weight that's being placed on my tow vehicle receiver by leaving the spear in the Hensley and using the tongue jack to adjust the spear to the same height as the bottom of the receiver. I'll place the Sherline under the upper part of the spear at what would be the midway point when it's in the vehicle receiver; then raise the hitch jack to place the load on the scale. Does this seem reasonable?"

Phil,

Keep it simple, weigh the tongue at the jack post and add 75lbs. Trailer must be level.

Bob

[Cracker]

Without looking at my AS I was thinking that the distance from the jack to the hitch ball was like 2'-0"! My bad - it's only 9". That said, it's about 18'-0" from the centerline of my axles to the jack and 18.75" to the hitch ball. The last time I measured, ready for a trip, my tongue weight at the ball was 940#. So, using the formula a = (by)/x = (940*18.75)/18 = 979.17 lbs at the jack - a difference of only 29.17 lbs. Somewhat of an academic difference for my 30' Excella ("Classic") but perhaps more significant for other hitch arrangements where the ball is effectively a greater distance from the jack. As an aside, the weight on the scale would continue to increase, as it's theoretically moved towards the axle assembly, until at some point the axles are no longer carrying any load and the scale is carrying the combined weight of the axle load plus the hitch load. That point would, of course, be at the center of gravity of the trailer. That totally exhausts my limited knowlege of statics so I'll quietly crawl back into my box and shut up!

[ROBERT CROSS]

Cracker,

Just re-installed the Hensley during Spring get-ready.

Did some weighing....not loaded as it normally would be, no provisions, 2/3 lpg, empty fridge etc.

950lb at the ball, 1125, at the jack post, 15.5% difference.
Am I rong in assuming that that percentage will stay consistent when fully loaded?
How about other 25' trailers with the same distance between the jack, ball & axles?

So last year camping we had a weight at the jack post of 1250lbs, which at the ball would be 1056?

I've been a little off on my guesstimates'...

I need a Wallystein.

Bob

[Cracker]

Originally Posted by ROBERT CROSS

Cracker,

Just re-installed the Hensley during Spring get-ready.

Did some weighing....not loaded as it normally would be, no provisions, 2/3 lpg, empty fridge etc.

950lb at the ball, 1125, at the jack post, 15.5% difference.
Am I rong in assuming that that percentage will stay consistent when fully loaded?
How about other 25' trailers with the same distance between the jack, ball & axles?

So last year camping we had a weight at the jack post of 1250lbs, which at the ball would be 1056?

I've been a little off on my guesstimates'...

I need a Wallystein.

Bob

Interesting! Note the big difference, percentage-wise, between my theoretical calculations and your actual measurements. What is the distance between the jack post and the ball on your AS? If it's more than the 9" I used that could be the difference. Your numbers would suggest a distance of about 2'-10" (---for a distance to the jack from the wheels of 15'-5") which just doesn't sound right.

You're right Bob - maybe we both need a Wallystein!

[dznf0g]

I'm surprised too! Actually a bit relieved that my TW isn't as high as I thought after adding the bikes and rack. Yes, Bob, I think the percentage would carry through regardless of what you do with loading.

Thanks for the effort.

[ROBERT CROSS]

...I'll get those measurements and post.

I also want to get an accurate weight at the jack now that the Hensley is installed and test the % rule. Will be interesting to see how that beast effects the numbers.

I may be obsessing too much over this as I really only weigh the tongue if I suspect we are loaded + or - the norm, two, three times per Season at most.
Oh well...it IS raining.

Speaking of weight's......RIP Levon Helm. "take a load off Annie"

Bob

[dznf0g]

WHAT! When did Levon Helm die???? He's one of my favorites!

Hey, Bob, shouldn't your strut be located in the bottom hole of the frame bracket?

[ROBERT CROSS]

Originally Posted by dznf0g

WHAT! When did Levon Helm die???? He's one of my favorites!

Hey, Bob, shouldn't your strut be located in the bottom hole of the frame bracket?

Yes Levon passed..."Music from Big Pink" one of my all time favorites.

The head is not level in the pic, when hooked-up it is parallel with the A-frame.

Here is a newbie pic when I first installed the Arrow, 4" drop and top hole, then went with the 6" and moved to the center hole.

Bob

[mikapen]

Originally Posted by dznf0g

Question for you folks with a Sherline tongue scale. Do you find that it "zeros in" on a reading? Or if you push and pull vertically on the tongue does it settle on different numbers.

It seems , with mine, I can get as much as 100# difference when "rocking" the tongue up and down, like the shaft is sticking in the bore.

Any ideas?

I have also been frustrated by inconsistent readings on my Sherline. With my 1000 lb scale, it seems to be +/- 100 lbs or more. I think the scale is particularly sensitive to side loading.
I get the most consistent readings with the scale underneath the tongue jack, lifting the tongue free of the hitch and then lowering back down to towing height.
It's worse with a floor jack because the pivot point of the jack causes lateral movement as you raise the scale, causing a bind and slow response from the dial - i.e. it reads lower while raising and reads high while lowering.
That's a long description, but I am disappointed with my Sherline.
At least it shows +/- 100 lbs, which is more than I know without it!

[ROBERT CROSS]

Originally Posted by mikapen

I have also been frustrated by inconsistent readings on my Sherline. With my 1000 lb scale, it seems to be +/- 100 lbs or more. I think the scale is particularly sensitive to side loading.
I get the most consistent readings with the scale underneath the tongue jack, lifting the tongue free of the hitch and then lowering back down to towing height.
It's worse with a floor jack because the pivot point of the jack causes lateral movement as you raise the scale, causing a bind and slow response from the dial - i.e. it reads lower while raising and reads high while lowering.
That's a long description, but I am disappointed with my Sherline.
At least it shows +/- 100 lbs, which is more than I know without it!

Agree...the floor jack is not a not a viable support for the Shurline scale, vertical alignment is paramount.
I was advised at purchase to order the 2k unit, it is graduated in 50lb increments, plus the TW of the Classic is much more than stated in the factory numbers.

Bob

[ROBERT CROSS]

Originally Posted by Cracker

Interesting! Note the big difference, percentage-wise, between my theoretical calculations and your actual measurements. What is the distance between the jack post and the ball on your AS? If it's more than the 9" I used that could be the difference. Your numbers would suggest a distance of about 2'-10" (---for a distance to the jack from the wheels of 15'-5") which just doesn't sound right.

You're right Bob - maybe we both need a Wallystein!

Well it finally stopped raining...

Got the last weight I was curious about, the Arrow is installed and I'm more puzzled than ever!!!! 25lbs less at the post. I give up...no wait maybe not, I can't weigh at the ball 'cuz of the haha, that weight is concentrated in front of the post, am I making any sense? My head hertz. Fulcrum? Where's the assburn?

Cracker,
17'5" from the front of the tongue to the centerline between the two axles.

8" from the center of the ball to the center of the jack post.

FWIW...the Shurline, without the screw-in extension, fits perfectly on the post if you remove the foot pad.



Bob

[dznf0g]

Originally Posted by Cracker

Without looking at my AS I was thinking that the distance from the jack to the hitch ball was like 2'-0"! My bad - it's only 9". That said, it's about 18'-0" from the centerline of my axles to the jack and 18.75" to the hitch ball. The last time I measured, ready for a trip, my tongue weight at the ball was 940#. So, using the formula a = (by)/x = (940*18.75)/18 = 979.17 lbs at the jack - a difference of only 29.17 lbs. Somewhat of an academic difference for my 30' Excella ("Classic") but perhaps more significant for other hitch arrangements where the ball is effectively a greater distance from the jack. As an aside, the weight on the scale would continue to increase, as it's theoretically moved towards the axle assembly, until at some point the axles are no longer carrying any load and the scale is carrying the combined weight of the axle load plus the hitch load. That point would, of course, be at the center of gravity of the trailer. That totally exhausts my limited knowlege of statics so I'll quietly crawl back into my box and shut up!

Cracker has this right, I think....especially with Bob's erratic readings. (BTW, you have 39.17 difference, not 29.17) I have taken out some oil from the scale and it seems to be much better. After setting the AS down on the scale, I push it down and it settles in consistently. I try and lift and push down the tongue and get little movement of the needle, but it now settles consistently on the same number. I now have 5/16" between the bottom of the piston flange and the top of the scale housing.

So, for us HAHA users, I would use Cracker's formula in reverse.
A=(by)/x where
A = calculated weight at ball
b = observed weight at jack
y = center of axle(s) to jack in feet
X = center of axle(s) to center of ball coupler in feet.

After you get this number, we HAHA users need to subtract some weight for the weight that is actually supported by the TV and not loaded on the tongue like it is when disconnected.

According to Hensley, the entire HAHA weighs 166.5# (w/o stinger). The hitch box and head weigh 99 lbs. The remaining struts, brackets, jacks and spring bars weigh 67.5lbs.

All of the hitch box and head should be subtracted from your calculated tongue weight.
As a SWAG, 1/2 of the spring bars and struts are TW and 1/2 are supported by the TV through the hitch head.
All of the frame brackets and jacks are TW load.

I am just going to arbitrarily use 2/3 of that 67.5lbs as TW load and 1/3 as TV load. (Close enough)

So I will take my calculated TW - 99# - 23#.

I kinda need to be this accurate as I am close to maxing out my TW rating since adding bikes, scooter ramps, and bike rack to the tongue.

So for me A=(1100X18)/18.75
A= 1056

1056 - 99 - 23 = 934 actual tongue weight.

Does this make sense?

[slowmover]

It does . . but what shows on the scale wheel-postion by wheel-position is the result that matters in the end. Empty weights and laden weights; WDH applied and not.

The scale readings give us a vital check as to TW percentage (against TT wheel weights) under the differing conditions. IOW, when we're backing out of some less than acceptable numbers (or experimenting to improve numbers) the TW can then stand next to individual wheel numbers.

.

[dznf0g]

Originally Posted by REDNAX

It does . . but what shows on the scale wheel-postion by wheel-position is the result that matters in the end. Empty weights and laden weights; WDH applied and not.

The scale readings give us a vital check as to TW percentage (against TT wheel weights) under the differing conditions. IOW, when we're backing out of some less than acceptable numbers (or experimenting to improve numbers) the TW can then stand next to individual wheel numbers.

.

ABSOLUTELY! I use the TW to move things around where I THINK I will want them. Next is load up and head off to the scales. I do this once a year OR when something significantly changes. Like this year...added bike rack to tongue, along with two bikes and two scooter ramps. I also added the Hensley.
These big changes necessitate a complete do over on all my loading and scaling.

[ROBERT CROSS]

Didn't follow my own advise...

Went out this morning and re-did the whole routine.
Took the tile out from under the scale,(more stable), and made sure the trailer was dead LEVEL when scale the was fully loaded.
Variation minimal thru several weighings'.

Bob

[mikapen]

Originally Posted by dznf0g

<snip> I have taken out some oil from the scale and it seems to be much better. After setting the AS down on the scale, I push it down and it settles in consistently. I try and lift and push down the tongue and get little movement of the needle, but it now settles consistently on the same number. I now have 5/16" between the bottom of the piston flange and the top of the scale housing.

I have been trying to follow comments on the OP question about Sherline accuracy, so I ask:
What is the benefit of removing oil? How do / did you decide how much to remove? Didn't you introduce air into the scale when you opened it, and how did you deal with that?

[dznf0g]

Originally Posted by mikapen

I have been trying to follow comments on the OP question about Sherline accuracy, so I ask:
What is the benefit of removing oil? How do / did you decide how much to remove? Didn't you introduce air into the scale when you opened it, and how did you deal with that?

I had a feeling that the pedestal was riding so high in the bore of the red body that it might be cocking and hanging up in the bore.

To remove some oil (it only holds maybe 4 cc of oil), hold the body in you hand with the gauge pointed straight up. Use a wrench to remove the gauge on the brass flats. Set the gauge somewhere where the base is pointed up, so the oil will not run out of it.

Get a clean butter container, or sumptin' like that, hold the unit over the container and remove the pedestal. Pour the oil into the container.

Examine and lubricate the post and bore. Mine was very dry and the surfaces are not machined exactly smooth.

Reinstall the pedestal so there is only about 1/4 - 5/16" between the bottom of the pedestal pad and the top of the red body.

Again hold the unit with the gauge hole pointing up. Slowly dribble the oil into the hole. This hole is a high point and all the air will purge out the hole. slightly overfill so the machined area on the red body is also filled.

Set the body down with the gauge hole pointed up. Pick up the gauge, keeping the threaded end pointed up. Install new teflon tape on the threads. Put a drop of oil on threaded end to eliminate an air gap when mating the pieces.

Quickly "flip" the gauge into the body hole and reinstall. There should be about 1cc of oil left over.

It seems to work better now....but it may be just because of lubricating the shaft and bore. You might try to just oil the mating surfaces with jack oil before trying the disassembly.

It's not hard to keep air out of the unit.

[mikapen]

Originally Posted by dznf0g

I had a feeling that the pedestal was riding so high in the bore of the red body that it might be cocking and hanging up in the bore.
<snip>It seems to work better now....

Thank you for your observation and detailed instructions. It seems to make sense and be worth the effort.
My pedestal pad sits 1/2" above the body, so I will try the soon-to-be-famous "DZN MOD" to my Sherline.

[Airstreamer67]

I've compared the readings of the Sherline and a spring-type scale, and it's accurate when used correctly. But as noted above, if the load is not vertical but instead is canted, it does detract from the Sherline's accuracy because of side loading.