DIY Converting Rob Allen shafts for use with American guns

I've been reading a few times now how people are saying that the RA shafts are more bend resistant than all others. Also they are made in 7.5mm diameter, this I've been wanting to try for a long time as I find the 9/32 shaft flimsy and the 5/16 heavy. The problem is that I really like my American mech hip loading wood speargun and don't want to change to a pipe gun.

I asked around a little and no one makes a 7.5mm shaft for an American mech. Since the RA shaft has the diameter that I'm looking for plus it is said to be a stronger shaft all around, it makes sense to me to try and modify it.

I think it is within my capabilities to work the rear of the shaft to the same specs as an American shaft. I could probably treat it in some way afterwards to avoid corrosion in that area.

The difficult part is welding the sharkfin tab on. I could get away with one tab also using it as the line anchoring point. It would be great if RA would manufacture them but it appears that they don't. Would it be possible to weld on these tabs?

A description of the RA shafts.

Quote

Railgun shafts are engineered from ultra tough oil-quenched carbon spring steel. Highly durable tri-cut tips ensure efficient penetration. Once ground and polished, the shafts are zinc plated to combat corrosion.

Tin Man did the welding work on the tab and it turned out very clean. I then did the notch. It took me about an hour to do as it was all done with files. None of the power tools I have gave me the precision I needed and I almost f*cked it up, but I caught it in time and continued with the hand tools. It was somewhat tedious as I had to make adjustments over and over again on the top part for it to finally click in the mech smoothly. But it is doable and was a good learning experience. Then I did a quick bluing job. The tab did not accept the bluing and remained shiny.

I used the spear on an outing and it performed fine. I only fired twice during the whole day. Once I stoned an AJ and on another shot I had one tear off, I don't know why. At the moment of lining up and shooting I didn't think about the different shaft at all which is a good thing. I love the fact that it only has one tab, very convenient. The bluing however didn't work very well. There was oxidation all around the back of the shaft.

I cleaned the oxidation off and applied bluing again this time doing it more carefully. The pic is what it looks like before exposure to saltwater. Overall I like the shaft but that depends if it will rust after every dive. I can handle some surface rust on top but rust in the notch makes me nervous. If RA would make these shafts I would buy them. Of course I need to use it more and get some good size fish to see if the shaft is more bend resistant and if the tab will continue holding.

I will not be able to continue using this shaft. The corrosion at the notch happens very fast and aside from making me worry that it will eventually deteriorate the notch to the point of not being safe it is making the trigger mechanism corrode as well. Although it appears to be only surface corrosion on the mech the Riffe trigger mech has never corroded before and I had three of them which I never even bother rinsing after use.

I have not been able to check the shaft against a big fish. I was told by an experienced spearfisher and gun builder that it will bend like any other shaft provided the forces are strong enough.

I believe the tab will reliably support two short 5/8 bands.

The flopper on the shaft is very nice and comes perfectly tuned. If the RA shaft is left in original condition and the original notch does not corrode it is probably a good shaft, especially considering the price.

I do not believe that there is a coating that I could apply to make the machined areas of the shaft corrosion resistant.

The only other idea I have of adapting an RA shaft is by threading the rear end and creating a stainless steel adapter which will screw onto it and contains a notch and a tab. With the forces acting on the shaft at that point though and considering the small diameter I do not think it is likely to work.

I have some good experience straightening shafts which essentially entails bending them over my knee. I am familiar with the amount of force I need to exert to bend a 9/32 (7mm) and a 5/16 (8mm) shaft. Since I have no further use for the RA shaft I'm considering trying to bend it over my knee. It will be a pretty good indication to me of its strength and ability to go back to straight afterwards. If I do it I will let you know.

Welcome to this episode of myth busters. I just finished playing with the RA shaft.

Results:

The 7.5mm RA shaft was as easy (and that's being conservative) to bend over my knee as the 9/32 Riffe shaft.

As far as getting it back to straight, considering it was one simple bend in one direction it was more difficult to get it straight than the 9/32 Riffe shaft. The Riffe shaft assumes straight easier.

The only advantage to the RA shaft as I see it is the price and the well tuned flopper. Considering however that if it were to be manufactured with a couple of full size tabs and a square notch the price would probably go up significantly, that advantage is therefore offset.

When you have no personal experience with something trying to make a decision based on what others say is always iffy. So if you like, discount my experience and keep on believing what you want. I will say conclusively that I'm no longer interested in RA shaft as long as I have the option of buying Riffe or similar. This experiment cost me $80 so take from it what you will. At least I learned that I can make a notch if I need to, that I prefer a shaft with one tab and that Tin Man can do an awesome job of welding on a sharkfin tab.

One last observation. This shaft almost did have the last word sucking a final $3 out of my pocket. I attempted to cut through it with a hack saw to see if I could use it for a sling. In under 5 minutes I went through two hack saw blades, dulling them to uselessness with nothing but a scratch on the shaft. I guess this supports Tin Man's finding that on a hardness scale the steel of the RA shaft is harder than the Riffe. I conclude that hardness isn't really a major factor in how bend resistant the shaft is. I did end up cutting it fairly easily with the grinder.

Welding does weaken the area. But I think there's never too much stress on that area of the shaft so it should be ok. If the fin is for loading only adding a pin is easier.

Interesting how things change with time. SA shafts with sherkfin tabs for US mechs are now available.

You can file down a little bit to create a flat surface on an angle. This way you can maybe drill the hole on an angle rather than bend the pin afterwards. Make the tolerance really small, to the point you can't insert the pin, then heat the shaft and bang the pin in. It will never come out by itself, no welding necessary for one or two 16mm bands.