Forums: Skydiving: Gear and Rigging:
Pull force scales?

 


Premier PhreeZone  (D License)
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Sep 22, 2012, 7:17 AM
Post #1 of 9 (1215 views)
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Pull force scales? Can't Post

I am looking to upgrade to something better than the existing fish weighing scale I have now. I am looking for something a little more accurate. I have heard of some sort of scale that records max force and things like that but I don't know what I should be looking for.

Any suggestions on a replacement?


councilman24  (D 8631)

Sep 22, 2012, 7:48 AM
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Re: [PhreeZone] Pull force scales? [In reply to] Can't Post

Dave Singer at Sunpath told me they use these.
http://www.mark-10.com/...uments/force/mg.html

I was able to get a MG100 off ebay, new old stock, for less than half price. Came with NIST traceable calibration.

Just looked on ebay and didn't see any. Cheapest on google search was about $517.


mark  (D 6108)

Sep 22, 2012, 9:22 AM
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Re: [PhreeZone] Pull force scales? [In reply to] Can't Post

If all you need is a go/no-go gauge for your rigging work, consider calibrated weights. I have a 22# shot bag for ripcord pull tests (downside: rig has to be oriented so the desired direction of pull is straight down), and an 8# shot bag which adds to the 22# to make 30# for the PD fabric pull test. I went to the post office on a couple of slow days, and the lady behind the counter thought it was kind of fun to be involved in a parachute project. She was quite helpful as we counted out the very small quantities of shot to get the weight to within 0.1 ounce. For the 8# weight, that included the weight of one fabric clamp.

Mark


Premier PhreeZone  (D License)
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Sep 22, 2012, 9:54 AM
Post #4 of 9 (1140 views)
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Re: [mark] Pull force scales? [In reply to] Can't Post

I'm looking for something to use for the PD test, I am also looking for something to record the weights on so I can put it in my logbook for my own documentation and to show a few other riggers that their packjobs are well over the legal limits since they don't seem to trust fish scales and instead use a "It feels fine" test. Unsure


erdnarob  (D 364)

Sep 22, 2012, 11:03 AM
Post #5 of 9 (1109 views)
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Re: [PhreeZone] Pull force scales? [In reply to] Can't Post

You can buy recording max scales at Walmart or other hardware stores. Tight accuracy is not what we need in rigging therefore those scales are perfectly suitable for testing pin motion force for instance. If by any chance you don't trust your scale, you can establish a calibration chart by testing it with different certified weights. This is done for aviation compasses and mechanical altimeters too. But I suggest you to buy the little metal adaptor sold by ParaGear for pin motion force in conjunction with that scale (PARAGEAR M5995 PULL FORCE TOOL). Choose a scale going up to 50 pounds. You then can use it for fabric tenslle test as well where you need 30 lbs.
For higher forces like testing ripcords at 300 pounds for 3 seconds, I have designed a device based on levers.


fcajump  (D 15598)

Sep 23, 2012, 3:54 AM
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Re: [PhreeZone] Pull force scales? [In reply to] Can't Post

While I'd like to have a high end system, its just not in the budget... But found a 50-lb fish scale that has a second needle that indicates max force. (shoved into place by the primary needle)

I check it with known weights once a year.

I use it to check all rigs that come in where the owner has not chosen to test deploy (in the loft of course).

Have found 30+ pulls on pack jobs from other riggers and 3 that were last packed at the factory (2 were 50+ lb)

JW


dpreguy  (D 835)

Sep 23, 2012, 10:07 AM
Post #7 of 9 (995 views)
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Re: [fcajump] Pull force scales? [In reply to] Can't Post

Agree with fcajump .

My opinion: Fish scale with sliding max indicator is adequate for loft use. I stuck an adhesive pointer at 22 lbs. to make it visual. Using the hand held scale allows me to always align the pull with the housing. I put my fist in the shoulder part of the harness to wimulate the wearer's shoulder. Works the same way for pilot emergency rigs. Pull aligns with housing.

Just test scale with known weight regularly (annually)

I also have the 40 lb marked with an adhesive colored pointer for fabric .

Having said that, there is an "electronic" digital scale, with batteries for those who find comfort in lighted dislays. Improvement? Probaly not. They still rely on an internal spring; so the lighted digital display is only a comfort to those who are dazzled by such and those who believe that a lighted display gives any instrument enhanced credibility.


mark  (D 6108)

Sep 23, 2012, 10:27 AM
Post #8 of 9 (987 views)
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Re: [dpreguy] Pull force scales? [In reply to] Can't Post

In reply to:
Using the hand held scale allows me to always align the pull with the housing.

The 22# pull is measured "in the direction giving the highest pull force under normal design operations." (AS 8015B 4.3.2.4, AS 8015A 4.3.2.2; NAS 804 doesn't give a direction of pull.)

I think you'd get higher pull forces by pulling at a right angle to the main lift web, that is, when the user is punching straight out.

Aligning the pull with the housing should produce the lowest pull force, which is useful for checking for the minimum of 5 pounds.

Mark


dpreguy  (D 835)

Sep 23, 2012, 6:53 PM
Post #9 of 9 (932 views)
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Re: [mark] Pull force scales? [In reply to] Can't Post

Yes of course friction, however slight, will change (increase) the pull force a bit.

I align the pull because it is the only consitent way to measure. I don't don the rigs I get and try to pull and guess what 90 degrees, (or even more degrees or fewer degrees) may be. If the harness is loose on the user, it isn't 90 etc..
I am aware 804 doesn't specify. If an aligned pull results in more than 22, then there is a problem.



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