How to get good DFT measurement?

Bill22Bill22 Posts: 1,561 Crazy Baller
Is there a video on BOS or youtube of how to correctly measure a fin?

I am a rookie at setting a fin. I am able to get consistent length and depth measurements. But with the DFT measurement, I found that if the calipers are just a very small amount off level with the ski, the #’s can vary. BTW I am just setting my ski to stock. I know newbies are not supposed to adjust from stock #.

Maybe it would be a good idea to have a link in the FAQ to a good ski setup video.
In gear. Hit It. Thank You!


  • jwrjwr Posts: 337 Baller
    Chris Rossi has a good one on youtube
    Obrien Elite 30" 6.845, 2.510, .80 PB [email protected]
  • Chef23Chef23 Posts: 5,801 Mega Baller
    There is a thread on fin measuring on here somewhere. Mapple has a technique also. Dft is the hardest measurement to replicat.
    Mark Shaffer
  • LeonLLeonL Posts: 2,300 Crazy Baller
    edited August 2013
    Slot caliper is the easiest. Agreed,it's the toughest measurement to get right consistently. Just try to hold the caliper tight against the bottom of the ski. For me it's easier to stand the ski on its tip while taking the measurement.
    Leon Leonard Stillwater Lake KY - SR Driver SR Judge
  • mwetskiermwetskier Posts: 1,329 Mega Baller
    rossi video using slot caliper is here

    written article using regular caliper is here
  • Bill22Bill22 Posts: 1,561 Crazy Baller
    I just watched the Chris Rossi, ski setup part 2. It’s a good one. I guess it get easier the more you do it.

    In gear. Hit It. Thank You!
  • fu_manfu_man Posts: 405 Crazy Baller
    I have always wondered...the bottom back of the ski is beveled. Do you measure to the initial curvature of the bevel on the bottom of the ski or do you just slide the caliper until it hits the bevel wherever it happens to land on the back of the ski?
  • KcSwerverKcSwerver Posts: 389 Baller
    There's an awesome one of mapple. That's how I learned. Ill find it when school gets out.
  • MattPMattP Posts: 5,969 Mega Baller
    @kcswerver checking the forum from class? Awesome. But pay attention learn something.
  • MattPMattP Posts: 5,969 Mega Baller
  • Bill22Bill22 Posts: 1,561 Crazy Baller
    @mwetskier, I did not see that you posted the link. Then I posted it seconds after you.
    In gear. Hit It. Thank You!
  • Bill22Bill22 Posts: 1,561 Crazy Baller
    @fu_man that’s my question too. If you change the angle of the caliper just a tiny about, it changes where the caliper contacts the beveled edge on the back of the ski.
    In gear. Hit It. Thank You!
  • KcSwerverKcSwerver Posts: 389 Baller
    edited August 2013

  • WaternutWaternut Posts: 1,511 Crazy Baller
    I was too cheap to buy a real slot caliper so I made my own. Regardless of the design, there are some crucial steps to maintaining consistent measurements. This is my method... First, look at the angle of the calipers when you lay them flat on the ski and try to measure DFT. Hold it flat on the ski but don't bow the calipers down. Raise the calipers up the fin trying to keep that same angle and zero the calipers. Close the calipers and they should display a negative number. WRITE THAT NUMBER DOWN because that is your new set point for all measurements to come.

    Since I just cut a cheapo HF caliper, I use that as my dedicated DFT caliper so the set point never changes but if it does, I can put it right back and get the exact same DFT measurement I had before.
  • DWDW Posts: 1,942 Mega Baller
    To measure DFT from the true tail of the ski, the EZ Fin tool will provide a method to correctly measure DFT by providing a jig that allows the calipers to be correctly used to measure a distance. All the methods using the head of the caliper only provide a reference number as the head thickness is not calibrated and is not designed or machined to be used as a measurement surface.

    It is unfortunate proper measurement techniques have not been established to generate a set of accurate measurement methods rather than establishing an easy method to generate a number (which in many cases is not an accurate number for that measurement) which gets thrown about as an indication of the length or DFT. Depth is the only measurment that tends to be accurately recorded and reported.

    PS: jaws measurements also fall in to the same category.
  • DragoDrago Posts: 1,394 Mega Baller
    Jaws for length is a real measurement, depth is a real measurement ( it's called a "step measurement " with the calipers) . The closest you can get to a real DFT is a step measurement: the thickness of the caliper, the amount of concave, and the radius of the tail will create variances. Press your thumb in the same place and try to press with the same pressure on top of the caliper head. My brother used to test for secret items going into space, says when you get 2 the same, that's what you go with. He also has an awesome set of tools.
    SR SL Judge & Driver (“a driver who is super late on the wheel and is out of sync”)
  • h2oskih2oski Posts: 176 Baller
    Thanks DW, I designed the EZFintool for myself and everyone else that needed a easy way to get accurate, consistent DFT
    measurements. A bonus is measuring depth without removing the wing. @Bill22
    Check it out at might be something that could help you.
    Terry Bandel AWSA Regular Judge & Driver
  • WaternutWaternut Posts: 1,511 Crazy Baller
    One thing that I really appreciate is Rossi doing those videos. It was massively helpful! In my quest for achieving stock settings which has so far been the best for me, it really helps to know how your ski manufacturer measures their fins and what kind of calipers they use.
  • DWDW Posts: 1,942 Mega Baller
    @Drago: You can't be certain that all calipers can zero the jaws portion & nobody has a standard for the perpendicular distance (or step height) from the ski surface at the fin slot due to differences in concavity between skis. The EZ fin tool as an example takes out all the variables you mention and allow one to measure the distance from the true or very tail to the trailing edge of the fin.

    If you want to use numbers from measurement methods such as jaws or using the caliper head as a comparative measurement as you make changes or feel you can communicate that to someone else, that is fine, but it is not the true measurement of that distance unless you define it as such (jaws would be @ x.xx off ski surface similar to how camshaft duration is measured which has been standardized to degrees @.050" lift in the USA)
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