1956 Maserati 250F Sept 4, 2016 9:31:40 GMT -5
Post by EM on Sept 4, 2016 9:31:40 GMT -5
In the course of one of the Wolverhampton meetings some years back I had the good fortune to strike up a friendship with Dave Jones, modeler and body shell builder extraordinaire. At the end of the meet, Dave made me the very generous gift of 2 of his Maserati 250 F shells, versions 1954 in 1956.
I decided that the best way I could show my appreciation was to build up the models in good fashion. To that end I obtained a copy of McKinney's book, Maserati 250F. As is often the case, events intrude and the book has remained on the shelf and the shells in a drawer for some time. The addition of a 50s GP class to the VRAA offer the opportunity and incentive to proceed.
(This was all decided while I was in the course of a major relocation and had no idea where my parts and tools relocated!)
The first decision that I made was, in view of the uncertainties of my workshop facilities, to buy one of Richard Mack's 250 F chassis. It arrived promptly at my new address. It is an elegant piece of work comprising a laser cut steel chassis and a very substantial (1/16 inch) brass "rattle pan" attached to the chassis by socket head screws threaded into captive nuts. Mine came assembled which was a good thing. Cutting apart a laser cut plate is not an issue but there is no way, despite the fact that I'm a fair hand with an iron, I could match the jewelry quality soldering on the assembled chassis as received.
In due course, I managed to find and unpack some of my slot gear and immediately offered up the 1956 Maserati shell to the chassis. 2 things were immediately apparent: I needed to narrow the rattle pan a bit and the guidepost mount on the chassis was very far forward, covered by the narrowest of margins by the lower edge of the nose opening.
Work began on the body and chassis simultaneously. The first thing I did with the body was to use Milliput to reshape the nose opening extending the lower margin to create a more vertical opening. (This should be in no way taken as a criticism of Dave's modeling. Looking at the McKinney book, it is clear that any discussion of a 250 F body must not only specify the year but the race and, in many cases the driver) while that was hardening in preparation for priming. An important step: Cutting out the rear suspension openings and the cockpit leaves the front and rear body sections connected by only two slender bridges. These were reinforced by short pieces of 1/16 steel wire set in epoxy. I turned my attention to the chassis filing the rattle pan and laying out wheels, tires, gears and considering the guide issue.
I pondered a bit on the front axle mount. The holes in the uprights measured about 0.09 inches, not a ready fit for any axle in my collection nor did it seem likely to me that the narrow steel part was a suitable bearing. I opened out the holes to 1/8 of an inch with a diamond burr in my flex shaft tool. (Don't bother to try and drill spring steel with an ordinary bit). 1/8 inch brass tubing was cut to length and soldered in. Bronze bushings were soldered into the rear axle mount and reamed for a precise fit. Time to do the trial fit with axles, wheels and tires. – First problem!
The rules for this class specify a 3/32 inch ground clearance. This is greater than usual but not unreasonable for the class. With the selected wheels and tires fitted and the rattle pan about 0.01 inches loose, it doesn't make it. Tightening of the rattle pan will just barely provide clearance but it is clear that this clearance will disappear when the tires are trued. All right, let this issue incubate for a bit and set up the gears to start bedding them in while the paintwork on the body is drying. Another problem:
My preference in these builds is to use 64 DP crown gears mated, surprisingly, to 72 DP pinions. The issue arose because all the crown gears that I had readily at hand use what I call an "external" hub – I.e. the hub is fitted to the side opposite the gear teeth. This means that the spacing of the rear axle supports must be great enough to accommodate the hub, the gear, and one half the diameter of the pinion. On this chassis, that space is not available. Given a whole series of constraints including time I had no choice but to fit a set of Slot – It gears. This may seem like heresy but these gears are not my first choice. Their versatility and ease of fitment carries with it compromises in tooth shape that results in a gear set that is, in my experience, a bit "notchy". Y MMV. I fitted the motor and set up the chassis on the bench for a 12 hour run at 5 V.
The body was now painted, decaled and clear coated. Time for details: the exhaust system was fabricated from 1/16 inch plastic rod (the stuff I have is very convenient – it is tubing with soft iron wire down the center so you can bend it and it holds shape without heating). My airbrush had appeared and the exhaust was sprayed with ALCLAD jet exhaust. The windscreen was masked and painted then cut and sanded to shape. I use fast setting (5 minute) clear epoxy for screen attachment. The driver is from Immense Miniatures – Stirling Moss head and short sleeved body.
Time to turn my attention back to the chassis again. I did something I probably should've done much earlier in the process. I put the chassis on a scale. 78 g! (Without body) this was disconcerting. While things were still in the planning stage, I recognized that the opportunity for track testing the build would be limited so I look at the extensive data from last year's event and collected and graphed a number of parameters.
There was a weak inverse correlation between weight and finishing position but, in fact, the first and second-place cars were the lightest. This makes sense in view of the limited power of the motors specified. My aim had been to come as close to the minimum weight (65 g) as possible. Clearly I was going to be way way off. An obvious solution would be to remove the rattle – it weighed 20 g – this would, in one fell swoop, cure most of the weight problem and address the ground clearance issue.
I retired to the patio with a whiskey (Macallan 12) to ponder. While the above was an appealing avenue I was also swayed by the fact that I have had very good luck with rattle pan chassis in models of this type. They tend to be easy to drive and very forgiving – good qualities in a proxy race.
I settled on a compromise. I pulled the rattle pan and cut an irregular pentagonal shape from the center reducing its weight by about 6 g.
And last but not least....the guide. Reshaping of the nose notwithstanding, things were still very tight. The height of the ferrule/braid holders and vertical exit of the lead wires on a conventional guide was a problem. The solution was a TSRF guide modified per a suggestion from Al Penrose (Mr. BWA). Cut off the mounting post of a TSRF guide (thread it first). There is a hole down the center of the post through which on can insert a piece of 1/16" hard wire, extending a bit from the bottom. Drill a hole at the very front of the guide and assemble with a high strength epoxy - sounds dicey but it has worked for me in the past.
Tires large enough to afford the required clearance were fitted and trued, body and chassis united (a hefty 90g) packed and sent off.
"The night has been long, ditto, ditto my song and thank goodness they're both of them over" (Iolanthe)