Like some here, I have been using the ProBox system for awhile and really like them. I have never been happy however, with the how firm the fins feel when installed in the ProBoxes or the FCS for that matter. I can never seem to get the set-screw tight enough without stripping on either system.
One thing I’ve been doing that seems to help a lot is to grind a little groove in the fin tab where the set screw hits it. Grind the groove at the approximate angle the screw is hitting the fin so it makes a more flush or perpendicular connection to the fin. I find the fins feel much more solid, the set screws firm up much better and are less likely to strip when tightening.
Howzit vern, Actually FCS says not to over tighten the screw because if you hit the bottom or reef you want to fin to come with out pulling the plug with it. After you screw down the fin unscrew it and you can see that the screw makes an indentation in the tab, plus the tabs have a small indented circle already in them. I have never encountered a problem with just cinching down the screw and the fins are securely firm in the plugs. Aloha,Kokua
It is much better to have a press screw rather than a set screw…
Have a countersunk bolt in one side of the plug go into
a through hole in that side of the plug and another through hole (aligned) in the fin.
Threads on the far side of the plug.
Clamp it in there. It reduces the necessary fin tab size to achieve adequate stiffness…it achieves a press fit, like a taper installation (a la Morey/Lokbox/Red-X) without needing a taper.
Aha I did wonder if I was the only one! I did talk to Robin about this after I first installed mine and used them with the Island Fin Design and Hanalei glass fins I ordered from Probox. I really feel that these could have benefited from grooves as you described and ground them into all my fins with a 4" grinder and thin stone cutting disk. The benefit is that the fin is pulled down into the angles insert which in turn is pulled down into the box making everything less wobbly.I found that it was important to have the fin tab manufactured to the correct thickness to be a snug fit into the inserts. If due to manufacturing error they were slightly too thin then no amount of tightening of the grub screws would stop the fin wobbling. I did use some resin to thicken some tabs. This was some time ago and was under the impression that the fins would in future have a better groove. I did find that the plastic FCS fins that I had were a better, tighter fit and because of the dimple would pull into the insert/box better. I agree that there should be no need to overtighten.
I have Probox on several boards and benefited in the ability to alter the fin cant. I had some issues with the box flexing out at the sides but I seemed to be an isolated case. I am going back to install some myself as I previously had the shaper do them and now have my doubts as to the quality of his install.I think that it is now recommended that some roving is wrapped around the box when installing. I am not sure why this is now recommended but it would perhaps have solved the problem I experienced.
Its to be expected that by introducing inserts that any slight manufacturing variation will result in the fins wobbling a bit which I found maddening. After I have redone the old installs and if I have the same problems I am consider gluing the angle insert into the box once finding an optimum cant.
Or you could just get a system that was designed to give a secure fit in the first place.
A press fit will always achieve a superior strength to weight ratio to a close tolerance fit. In a press fit, the force between the fin and box needs to be greater than the forces the fin will see in practice, and you’ve effectively bonded the fin to the box. This avoids stress concentrations, and lets you distribute the load more evenly and thus use a more lightweight material in the fin tab and/or box.
It can be achieved with a taper by pulling the taper into the cavity, or by clamping the fin between the two sides as I suggest above. There is nothing insecure in the first place about a press fit.
The upside of a clamping press fit is that the finbox will not split in strain each time you install the fin. This can have an impact on the glass around the box if it flexes, even a tiny amount, each time the fin is installed or removed. If you start with a close tolerance fit and enhance it with a press, bob’s yer uncle.
If you look at all of our more recent fins in both plastic and fiberglass you will see that they now all have something we call a V-notch. I will be putting a detailed description of this up on our new website within the week.
Simply put this notch forms a platform onto which the grub screw tightens, this has the effect of pushing the fin and insert down into the box causing everything to lock down. The best part of this notch is that it does not require the screw to be overtightened. Before this notch was present the screws had the endency to want to push down alongside the fin instead of pushing the fin and insert down. This was less a problem with plastic fins because the screws would dig into the plastic locking it down.
We have been doing this on all our fins for the last 6 months or more, our plastic fins have this notch molded into them and have from day one. It really tightend up the whole system.
Anyway if anyone would like to see a drawing showing how this all works let me know and I can post one of the 3D drawings that I have done for the website that details all of this.
As far as the inserts moving this was caused in some isolated cases by shrinkage of the insert, this problem has been addressed by making the inserts slightly over sized so that once the screw pushes down on the V-notch everything is forced into a compression fit into the box making for a much tighter fit.
Any flexing of the box, based on our experience has always been due to inadequate reinforcement around the box. A single layer of 4 oz. glass is not going to be enough to distribute the side loads on the box, so we always recommend that an extra football of 6 oz. be placed where the boxes are going to be installed. This makes a world of difference.
Please feel free to send them back to me and I will put the notches in them for you! Although if you have something like a Dremel tool it is really easy to do it yourself. But if you don’t want to do it I’ll be happy to add the notches for you.
We use a 90 degree 1/2" V-groove router bit to put the notch on the fiberglass fins!
i think i can handle it myself…i’ll give it a whirl and see how things turn out.
i’ve got the “thumb” fins – 6.5" center, 3.5" sidebites. i noticed awhile back that they are no longer listed on your website…any reason?..are you still making them??
i’d also like to try out the “elliptical” sidebites. maybe i’ll pick up a set with my next order. gonna need some more boxes next month!