Long ago I watched Art use his own jig to speed build FAI contest models. It was pretty impressive, but that *is* the design target for the way this unit is built, and there are not many folks for whom the ability to rapidly build many identical, small LPR contest models with consistent fin alignment is worth a fair amount of money. A couple of years ago I had some extended conversations with Geoffrey Kerbel about the jigs (Geoffrey was an experienced machinist who had been working on production of new jigs in direct collaboration with Art while Art was still around). Many of you probably know that Geoffrey himself passed away during NARAM last year.
One thing I'd say up front for people who are concerned about the cost is that given the amount of machining needed, the pricing for a metal unit seems fair. And I don't think that making a mostly 3d-printed version is going to be too easy. The Rose jig design depends on holding a fair amount of rigidity despite cantilevering both the rocket body spindle and the fin support plate.
I'm just throwing the following information out here so that it won't be lost.
One of the design issues that Geoffrey and I talked about was the fin thickness adjustment mechanism. It's kinda handy but it becomes the upper bound on rigidity and perpendicularity of the fin support plate due to the small bearing surface sliding in the little track. An idea we discussed was to eliminate the screw adjustment and instead make a small number (maybe 3) of thickness-milled plates with a consistent thickness at the mounting end (~0.25") that could be bolted to a beefier and higher precision support angle with substantially more bearing surface. The bolt pattern could be done to provide a considerable range of positioning for the fin support plates, and help enable swept fins, avoidance of tail cones, etc. that the original design is not well suited for. I'm probably going to build my own unit this way, but that might make costs too high for a production run given the extra fly cut / face mill operations needed.
The other design issue, especially for scaling up to a larger version, is runout on the spindle. In the original LPR unit you have a fairly thin steel shaft passing through holes drilled in a pair of aluminum plates that are less than 1" apart, secured by collars on each side. This is the simplest possible implementation but is also the least accurate and most prone to wear. It's adequate for light LPR models. I haven't seen the larger model in person so I don't know what Art and Geoff did differently there. Improvements: 1) install some press-in bronze bushings. Doesn't help runout directly, but costs little and limits wear. 2) Increase spacing of bearing plates - reduces runout linearly. 3) increase diameter of spindle shaft - reduces runout both due to flexure and ratio of shaft size to hole/bushing fit tolerance 4) Use actual shaft bearings - best result but highest cost.