Super Simple Arrow Spine Meter

thingiverse

Hi there, after looking for a super simple way to test and meter arrow spines, with no success in finding something simple, I have created my own version based on some videos and ideas I found in Internet.Arrow Spine is being measured supporting the arrow between two supports 28 inches apart, and then pushing down the middle with a force of 1.96 pounds. The amount of deflection measured in that middle point, in thousands of an inch, indicated the Spine of the arrow. The higher the Spine, the more flexible the arrow will be (for bows with less poundage) while the lower the Spine (thus meaning less deflection) the less flexible (more stiff) the arrow will be (for bows with more poundage)Commercial arrows got a Spine rating on them, and based on my experiments, same Spine number doesn´t mean exact deflection on both brands.But in 99% of cases the numbers and flex are good enough to serve our needs (most of the people is not an Olimpic gold medallist)The intention of this contraption is just to have a way to measure deflection, so we can compare different brands, check if the number is correct (twice I bought chinese tubes in Aliexpress, that came with mixed Spines on them) and if we build our own arrow made of wood, bamboo or other material, check that all of them have the same amount of flex.There is some eyeball measurement involved, but I´be found fairly low tolerances on the rig, with measuring deviating only a 5-10%, that is more than enough for my purposes :-)Hope this will serve you well too, feel free to modify it, but be aware that the design is protected with a non-commercial license, so please, dont try to make any money from it ;-)Any question, I will be happy to help!note: be aware that AMO Spine charts for hunting arrows, measure Spine with the supports 26 inches apart, with a force down the middle of 2 pounds. Modifiying this rig for measuring using that standard, it´s so easy and straight forward that I am sure that no one will have any trouble.Below the list of parts and basic intructions. Refer to the youtube video for detailled instructions and how to use this!Print 2 units of the side support (alternatively you can build them from hardwood, plastic or metal, filing the shape with a round file)Print one unit of the caliper support (again, you can build one from wood, metal or exotic alien material not known by the human race, you decide :-)Using the holes on the side supports, screw them to a self, to the wall of any other suitable and fairly rigid (important) surface. Ensure that the middle points between those suppports are exactly 28 inches apart.Then screw (or clamp as I do) the caliper support,and the caliper to it, so when slidind down the probe, it is exactly 14" away from each support. Do it in a way so you have space between the probe and the arrow tube.If possible, use a digital caliper (if having a dial indicator analog one you will need to subtract values)Take a piece of string and tie it to the neck of an empty water bottle (1 liter). Place the empty bottle, the cap, and the string in a digital scale. Fill it will water till you have exactly 1.96 pounds of total weight for all elements.Close the bottle with the cap, and tie the string firmly to the neck leaving a loop so you can loosly introduce the arrow in the loop.Put the bottle piece aside for now, and place the arrow on the two supports. Switch on the caliper and slide down the probe until you barely touch the arrow. Ensure that the probe is touching the arrow right on the top of the tube circumference and that you are not pushing down into it, just barely touching it. If using a digital caliper, set it to zero. If using an analog one, take note of the measurement.Now take the arrow out of the supports and make it pass the string loop in the bottle, and put it again in the supports. Ensure that the bottle is hanging freely from the arrow, not being supported by anything else. Slide the bottle so it hungs just right the middle points that the caliper probe will touch.Slide down the caliper exactly to barely touch the arrow tube again. Take note of the measurement in inches.. and voila! you have your magic spine number in front of you.Just to be sure that you rig is correct, and that the loop is not tangled, or god knows what, and compare measurements... in my case, for 600 Spine commercial arrows, my measurements are between 590 and 605... pretty good for my purposes. If using an analog caliper, subtract the first measurement (without the bottle) froim the second one (with the bottle) and you will be good to go.And there you go, you can now measure your arrows Spine, in a way that is fairly accurate and repeatable.... on the pictures I am measuring a 400 Spine arrow.side note: I am not a native English speaker, sorry if that makes tough to understand me.