Fin Anomally

[Garn]

I'm measuring my fin's length. If I put the calipers on one side of the fin I get 6.922. But if i put the calipers on the other side, every time I get 6.929. What's going on? Why the difference?

[Horton]

Is depth the same on both sides?

[Chef23]

It is probably the way the calipers sit on the ski.

[Jordan]

...or the fin isn't 90 degrees to the base of the ski

[RazorRoss3]

Yeah, if the fin is bent left/right, or if it isn't running perfectly straight down the ski (nose of the fin is set right or left of tail) or if the calipers just rest funny on one side that would do it

[eleeski]

Disclaimer: ridiculous crap opinion. I personally can't feel miniscule changes. Choose a side, measure and ski.

 

It should be possible to get extreme accuracy. Caliper quality does matter. Chips or dirt on the caliper matters. Positioning matters. This is a tiny nearly invisible uncertainty you are trying to eliminate. Whenever I had to make a measurement of high accuracy, I had to use the machinist's tools in a rigidly controlled process. My personal calipers and techniques were only good enough to get me close enough to verify that it was worth doing a real measurement.

 

I've watched some guys measure fins. Always the same procedures, same caliper, same side, several measurements and lots of conscientious effort to achieve high accuracy. Remember, you are looking for movement of the fin more than an exact number. That is easier to obtain.

 

I'm happy to get my calipers to consistently read .000 when closed (not a given). TLAR (that looks about right) will get your buoy count "about right".

 

Eric

[skialex]

Every time I measure both sides I get slightly different numbers so I have chosen to always measure the same side, (left side). To me as a right handed it comes naturally to measure the left side and that is the side most people measure in videos.

[DW]

@Garn: as Chef23 indicates, the caliper is not sitting quite the same on either side of the ski due to many potential factors: fin tilt, ski surface difference side to side, caliper being reversed from other side measurement or actual angle of caliper relative to bottom of ski all which results in measuring as a slightly different spot on the fin itself.

[Garn]

So basically, I'll just chose a side and stick with it. Thanks everyone.

[SkiJay]

@Garn‌ So long as that side is with the caliper's slide pointing behind the ski (its head towards the front). That's pretty much the industry standard technique.

[skialex]

I have never thought that the reason we choose the left side is because we measure heads forward, it was just natural to me.

[BraceMaker]

@eleeski - depth and length I can usually get really repeatable measurements, DFT is much more of a trial and error, when I get ~4/5 out of 10 to be the same number I call it in.

 

I assume you are turning the caliper and not flipping it (as there is a bevel to measure between threads and such) most likely I would think that the error is coming from you being righty or lefty.

[Jordan]

DFT is complicated by the slant of the tail of the ski...often wondered if factories could put a small flat spot on the tail to make this measurement more consistent.

[BraceMaker]

I have a thin aluminum L square. I'll take the square and zero the caliper on the thickness of the square, slip it over the back of the ski along the fin, and measure the distance from the back of the square to the fin.

 

I can try to get a picture of this, but basically the L hooks over the back of the ski and you slide it forward while squeezing it against the fit - Then you take a needle distance from the back of the square to the fin. In this way I can get the DFT on the square to be = to what I want every time. But you have to then do a calibration/offset number, the square hits the back center of the ski - however that isn't where the caliper would hit it. SO if you go OCD and get the fin set where you want it, you then do the square method and compare numbers - write it down and you can modify your setting.

 

Again not perfect.