Weight of a 21

[daveandsandyclink]

Thanks to AZJack, TAfraser, Brian B-P & all others. Keep the feedback coming in on your 21' ownership.

[Brian B-P]

Originally Posted by daveandsandyclink

Keep the feedback coming in on your 21' ownership.

... or at least virtual/desired ownership

[float5]

I am very sure that Sherline says not to keep weight on the scale. That is what you are doing when you do not take all of the weight off between weighings. Weight should not be kept on the scale for any extended time. You do a weighing and then you do another weighing when you are ready for the next one. That does not seem to be the case here and others have found that the scale will not work when used that way.

Originally Posted by TAfraser

Brian, I agree with you on not having to go back to zero in order to attain an accurate reading. Nowhere in the Sherline manual does it state that zeroing is a requirement. I also talked to their maintenance/testing department lead. I gave him a sequential list of my tests, their setups, etc. and they thought that the scale I had was sticking (seal resistance) because of the return inaccuracies. This new scale does basically the same thing though. I'll bet my setup, lack of control on tongue height along with my lack of understanding about dual axle and chocks, is part, or all of the problem.

Before I call them again, I plan on doing more testing. Maybe I'll take the scale into my old calibration lab and test it under a strictly controlled environment. We would know for sure how accurate the Sherline is along with any and all limitations. I'll let you know the outcome.

[gbaglo]

1. Do not pick up the scale by the black piston. Always handle and carry the scale by the red body or the gauge. The piston is held in place by friction with the O-ring in the cylinder only. Lifting by the piston can draw air into the system or, at worst the piston can come out entirely, spilling the hydraulic fluid. Air in the system will cause inconsistent and unreliable readings.
2. Do not drop a load onto or off of the scale suddenly. Shock loading can cause the gauge needle to spin and not return to the original zero range. In this case the gauge must be replaced, it cannot be reset to zero.
3. If the scale has not been used for a long time, rotate the piston back and forth in the cylinder to free up the O-ring so it does not stick to the cylinder wall. (Again, do not pull up on it.)
4. Do not leave a heavy weight sitting on the scale for long periods of time. Take your reading and then remove the load from the scale.

[Brian B-P]

Originally Posted by Floating Cloud

I am very sure that Sherline says not to keep weight on the scale. That is what you are doing when you do not take all of the weight off between weighings. Weight should not be kept on the scale for any extended time.

Originally Posted by gbaglo

4. Do not leave a heavy weight sitting on the scale for long periods of time. Take your reading and then remove the load from the scale.

They don't define "long periods of time", but I think they're talking about hours, not seconds or even minutes. The device has a simple single O-ring seal, and will leak under sustained force. If it can't handle a few minutes of use, I certainly wouldn't pay a hundred bucks for it! It would also be useless in a commercial setting.

[gbaglo]

It's the problem with manuals. What is a long time? Or, for my RAV4, what is hard towing for an extended period?
I'm planning on taking my Sherline gauge off again tomorrow, top up the oil and see if I can get the gauge to seat so that I can read it without craning my neck.
If anybody has a hint on how to start threading the gauge so that it ends facing up instead of facing down, I'd appreciate it.

[J Mac]

plumber's tape may help.

[gbaglo]

You mean Teflon tape? I used that. I was warned by Sherline not to apply it too close to the end of the threads or fragments can end up in the oil and plug the valve. I'm going to try to apply the minimum, maybe one wrap.

[Dave Walter]

Originally Posted by gbaglo

...If anybody has a hint on how to start threading the gauge so that it ends facing up instead of facing down, I'd appreciate it.

Is there room to add a lock nut on the threads of the gauge so that you can orient the gage and then tighten the lock nut?

[gbaglo]

Good thought. I will explore that. Have to ensure no oil can escape or air get in.

[Vermilye]

While i agree that keeping the Teflon tape away from the end of the threads is important, one wrap may not be enough to get a good seal. Most of the recommendations I've read recommend 3 wraps. You could use a few more to change the gauge face orientation.

I don't think the lock nut would work since it might allow the gauge to face the right way, but the threads not tightened enough to prevent leakage.

[Brian B-P]

"Clocking" fittings is certainly one of the annoyances of tapered pipe threads.

Originally Posted by gbaglo

You mean Teflon tape?

"Plumber's tape", "PTFE tape", or "thread seal tape"... there is no Teflon tape. But we know what you mean!

Originally Posted by gbaglo

I was warned by Sherline not to apply it too close to the end of the threads or fragments can end up in the oil and plug the valve.

Valve? In a Sherline scale? Do you mean the gauge? Bits could also mess with the O-ring seal. I didn't think there was a valve in these things.

Whatever might get messed up, I wouldn't worry about it too much: this is a static system, without significant flow of oil to carry bits.

Originally Posted by gbaglo

I'm going to try to apply the minimum, maybe one wrap.

Or go the other way and pile on an extra wrap (on top, not further along the thread) - whatever results in the thread getting tight at about the right position.


And I agree with everything Jon said.

[TAfraser]

Sherline Gauge Testing
Testing of the Sherline Hydraulic Tongue gauge was done in a calibration lab atmosphere under controlled conditions. Equipment used was a TiniusOlson system that was certified from 300 lbs to 20,000 lbs with a tolerance of +/-1% of reading. The system uses load cells for measurements and had a pre-load of 90 lbs. The load cells were exercised throughout the testing range prior to use per standard operating instructions. The Sherline was placed within the load frame, (capable of 20,000 lb testing) on a solid steel surface. The compression cylinder was part of the load frame, again, capable of testing 20,000 lbs. The whole setup is mounted to a thick concrete floor (we’re talking feet here) which is rated for some level of earthquakes. Using this system prevented any and all vibrations with no side loads being applied. The compression cylinder can be controlled using a motor or hand wheel. I used the hand wheel for its fine movement capability. I made 5 runs, both applying and relieving pressure. Each run took less than 3 minutes to perform, and the gauge was always returned to zero between runs. From those 5 runs I calculated the average and the deviation at 100 lb increments starting at 300 lbs (the certified lower limit of the test equipment.

Unless otherwise stated, when a manufacturer provides a tolerance, (2%) this tolerance is of full scale. In this case it’s 2% of 1,000 lbs, or +/-20 lbs. Sherlines’ statement that the gauge will provide a tighter tolerance in the middle of the scale is correct, but they don’t state what that tolerance is. In this case we have to go with industry standards. On an analog gauge, only the 10% to 90% range of the scale is expected to meet the stated tolerance. So this scale could be certified from 100-900 +/- 20 lbs.

Testing: Applying Pressure Relieving Pressure
Sherline TiniusOlson Difference Deviation TiniusOlson Difference Deviation
300 305 5 30 282 18 20
400 409 9 11 383 17 15
500 511 11 10 484 16 15
600 619 19 12 588 12 10
700 721 21 14 692 8 5
800 820 20 16 797 3 10
900 921 21 18 903 3 5
1000 1027 27 20

Summation: In my opinion, this scale is uncertifiable to the stated specifications. The uncertainty ratios would normally be calculated, and guard banding applied, but with deviations so great, this scale would be rejected.
I was hoping for more consistent results so that I could apply known errors to my own tongue weight measurements, but with the large deviations observed, an accurate measurement would be difficult. The production/quality lead for Sherline told me that this gauge was tested just before sending it to me, so it will be interesting what they say when I give them this information.

Sorry for the legibility issues, I tried Word, then Excel embedded in Word, and still can't get columns to line up. The first column is the Sherline reading, second the TiniusOlson reading, third the difference, fourth the deviation in the 5 tests, fifth the TiniusOlson readings relieving pressure, sixth the difference while relieving pressure, seventh is the deviation in the 5 tests while relieving pressure.
Tom

[gbaglo]

Or go the other way and pile on an extra wrap (on top, not further along the thread) - whatever results in the thread getting tight at about the right position.


And I agree with everything Jon said. [/QUOTE]

Thanks guys. The extra wraps of plumber's tape ( not Teflon ) appears to have done the trick. Learn something every day.

baglo

[Donna D.]

Originally Posted by TAfraser

Sorry for the legibility issues, I tried Word, then Excel embedded in Word, and still can't get columns to line up.
Tom

A mono-font would normally work, but the software strips out extra spaces.

[Brian B-P]

Originally Posted by TAfraser

Testing of the Sherline Hydraulic Tongue gauge was done in a calibration lab atmosphere under controlled conditions...

Excellent!

Originally Posted by TAfraser

Testing of the Sherline Hydraulic Tongue gauge was done in a calibration lab atmosphere under controlled conditions.Sorry for the legibility issues, I tried Word, then Excel embedded in Word, and still can't get columns to line up.

No apologies required, Tom! This is always a challenge in recent versions these forums. You can try padding a table out with spaces and forcing a monospaced font, but even that doesn't work well, especially if you include headings.

I pasted the information into a spreadsheet (in this case, a Google Doc in Google Drive: Sherline Tongue Weight Scale), then saved it as a PDF file and attached to this post. I hope I got the column arrangement as intended!

I see that it typically displays the offset which we might expect as a result of seal resistance, reading low while applying force and low while reducing force... by significant but manageable average amounts. It makes sense to take readings only while increasing load (lift some load off with tongue jack, change trailer configuration, set back down on scale), although there's no need to take the load off entirely.

The average difference (essentially, error) seems acceptable to me, but the deviation is disappointingly large.

It would be interesting to know how much of this is due to the hydraulic cylinder itself (such as the o-ring sticking), and how much is the pressure gauge. It would be completely unreasonable to expect anyone to do this, but it would be informative to see the two tested separately, testing force-to-pressure and pressure-to-reading independently.

[TAfraser]

Hi Brian, I would have tested the gauge separately, but the lab only had equipment that could take the gauge up to 100 psi. I would have had to interrupt a production line in order to access appropriate equipment. Didn't think they would appreciate that. I agree with you on the very disappointing deviation numbers. If the deviation was better I would just apply the offsets to my measurements and be done with it. Now, I think a talk with Sherline is appropriate. It was also a surprise that the center of the gauge wasn't more accurate then the rest. It indicated a linear progression. Could it be that their cylinder isn't held to tight enough tolerances for a one-to-one conversion from hydraulic pressure to psi?

Nice job on the spreadsheet attachment.

[gbaglo]

Just curious. What gauge do you have 0 - 1,000 or 0 - 2,000.
I replaced the 2,000 gauge so it would be easier to read and be closer to the middle of the gauge for accuracy.

[TAfraser]

I have the 1,000 gauge

[float5]

To state what apparently is not the obvious, incorrect use of the scale previously leaving weight on it instead of following the directions to remove all weight after each weighing, may have affected it. Plus anything else done wrong, not having followed the basic directions. Any testing afterward is, therefore, of no consequence.

We have the 1,000 and it works just fine.