Fin adjustment and adjustment screws.

[Wish]

So I've been fiddling with my fin and wandered something. Can a turn of an adjustment screw be translated to a spacific distance the fin will move? Example; a quarter turn equals 0.10 on average.

[skibug]

Theoretically-yes; practically NO.

[ForrestGump]

Not really, especially with adjustment screws which have a beveled end. As the fin tips in the slot and rides on a different part of the bevel, the amount it's moved is different.

[kdameyer]

You can get close if you know what type of screws are used. For example if the are adjustment screws are 10-32's, the 32 denotes 32 threads per inch. So one turn on the screw would equal .03125 of an inch or a quarter of a turn would be .00781 of an inch. Like shaneH says if the end of the screw that is pushing against the fin is beveled then that would throw it off a bit. Always use a caliper to zero it in!

[alex38]

Sometimes I (amature fin adjuster) over turn set screws and have to spend 10 more minutes getting it back.

An estimate of how far a half or whole turn goes could be helpful, but would probably differ widely from ski to ski.

May be something I figure out for my own ski.

[Wish]

I do use calipers but often turn the screw to far and find myself turning and measuring, then re-turning and re-measuring to often to get what i want. Watched Andy set a screw and he turned it, measured it and didn't touch it again. Saw him do this multiple times as if he know how far to turn it and was just double checking with calipers. This was on different ski brands, not just his.

[skibug]

I have found I can increase depth by .001 by tightening down on the set screw (for depth) extra tight; then unclamping the two rear clamping screws and then just retightening. That pressure from the set screw acts as a type of preload and when you unclamp the clamping screws it will move .001 to releive the preload of the set screw.

[mwetskier]

works fine for depth and dft but wont translate in any linear fashion for tip / length.

[footloose42]

Well the way set screws work is by digging into the fin, so there's really no way to know if your turn of the screw is moving the fin x inches or digging into the fin x inches.

[A_B]

Maybe with depth. Length is too effected by depth, WAG. DFT is a kinda maybe, but round back of fin can cause issues.

 

Try some half turns and record your findings and let us know if length is the same change at 2.475 depth vs 2.510 depth.

[mwetskier]

footloose42 - 'Well the way set screws work is by digging into the fin, so there's really no way to know if your turn of the screw is moving the fin x inches or digging into the fin x inches. '

 

if your using a caliper to check the measurement thats a really good way to know. in fact if the caliper is in place and your increasing depth you can actually watch it change one thousand inch at a time.

[SkiJay]

It's not a good idea to force a tight fin to move using the set screws. Most stainless steel set screws have a sharp circular leading edge that cuts into the fin's soft aluminum quite easily. Once you've notched your fin like this, it can make it a lot harder to make small accurate changes. Most fin blocks can be set up so they don't grip the fin too firmly after the three clamping bolts have been loosened.

[skibug]

I use my own set screws that are a point or rounded nub and not the kind that has a circular edge to lock into whatever it is making contact with.

[plubius]

Adjustment screws are produced with what appears to be shaped like a volcano and the circular edge will, indeed, destroy the original flat upper edge of your fin. Such destruction leaves a roughness which prohibits easy tail adjustments. Avoid this by grinding down the volcanos using a nut to maintain a square end of the adjusting screw. If done properly a true square end of the adjusting screw will move the fin evenly and without ragging the fin edge.

[Wish]

@plubius I smell a sellable product.. I'd pay for a set.

[A_B]

Or just keep the set screws looser when making adjustments.

[PatRe]

Through the years, I've often asked ski setup advice from @plubius. I like the idea of having set screws that protect the fin from damage. That said, I've always loosened the clamp screws to allow the fin to flop around freely... move the ski and gravity will move the fin. In fact, I pull the fin away from the set screws before adjusting regardless of the move. IMO, it makes subsequent adjustments (especially fine moves) that much easier.

 

So, while I agree with @SkiJay @AB and others, @plubius always has great ideas!

[skibug]

@Wish, @plubius, as I mentioned above, you can also buy set screws with ball ends or flat; they come in many forms. McMaster Carr carries them.

 

[Skoot1123]

With the fin held in place by the clamping screws, you will not move the fin in a 1:1 ratio when you tighten/loosen the adjustment screws because of friction. For the adjustments to really work out to a 1:1 ratio - it would be really difficult due to all the variables of the fin and screws. That isn't even considering the thermal expansion coefficient differences of the materials used for the fin assembly (ie fin and clamping components). If we were only considering 0.010" increments, it would be a little easier, but when we talk 0.001" of an inch......that is very precise and tough to get when adjusting with two or three screws.

 

On the other hand - if someone could make a design that allowed you to do that - then you might have some buyers. However, be prepared to PAY for that system.

[Waternut]

For depth, I just hold the caliper in place and dial in the set screw until it reaches the right measurement. Really easy and always accurate.

 

Length is the hardest thing for me to measure just because the angle the calipers make to engage the tips can change by a few degrees which allows the caliper tips to measure further down the fin. It won't make more than a 0.005" difference but when you're only trying to adjust 0.002"-0.003", that can be a problem. Even DFT with slot calipers can be tricky because you have to zero the calipers at the same angle that they would lay flat on the ski or you'll get inconsistent readings.

[DW]

Try approaching it from a different perspective: make an ajustment (a couple of turns on a specific screw) and go feel the difference. Measure to see what how much it moved. Do again for the other screws and record the results. That way, you actually know what the effect of each adjustment does to your ski for you skiing. The number is simply a way to record what you did. That way, if in the boat w/o your calipers, you can make an adjustment and have confidence what the results will be. Have fun.