Hi all. The hollowing would have been done originally using a " French Spindle " ....This uses a pretty standard spindle moulder , which must have a slotted shaft . Into the shaft fits a double edged cutter ( for ballance ) .The cutter is usually of 4mm High Speed Steel , shaped to the exact * shape required , thus it can easily be ground , with adaquate cutting angle ,** by hand to the drawing . The corresponding other side may be a little smaller , so that it doesn't actually do any cutting , but acts as a ballance . This being necessary as the speed is likely for this job to be about 10,000 rpm .
*..When using a cutter block and inserted cutters , such as a Whitehill or similar ,( As oposed to the French cutter as described above )..it should be noted that as the cutters are set at a forward angle to the diameter ,then their profile is NOT the same as that of the finished shape required ; the cutter shape being " generated " to achieve this in the grinding shop .**
The action of the French cutter is more of a "scraping action" than the cutting with a cutter block , as the blade is naturaly , being on the diameter , set at perpendicular to the cut .This method is used for quick /low volume /low expence manufacture and is very suitable to working curved edges using a curved guide fence or ball bearing guides , and the run out radius at the ends , will be far less than with the larger dia. circular cutter block .
For large items such as wing spars , where stop hollowing out of a larger section , requires the timber to be " Dropped " on.( a mis-nomer as it has to be fed onto the revolving cutter VERY carefully to avoid Grabbing of timber and consequental Accident ! )..then the circular cutter block should be used . ( In WWI era . they would have used a square cutter block , but this being responsible for many a lost hand , was soon replaced by the Whitehill type circular block , this in turn , being replaced some 20 years ago by the safty block and included the leading , back sloping anti-kick back cutters , but these are very expensive )..
" Ramps" are NOT used on spindle moulders to feed the work on and off the cutter ....This is a tool for use on a Router application .
Wood work machinery can be very dangerous . If you dont know what you are doing , and , MOST essencially , PLAN AHEAD the cutting opperation FULLY , an accident will be inevitable .
I have been doing precisely just this sort of WWI aircraft woodwork for some 30 years ,using the above machinery , and I still have a healthy respect for spindle and planners etc...There's no substitute for hands-on experience.
Generally , Routers are less inherently dangerous IF used with care , and if as above ,you run through the opperation first with the power OFF. For the Nieuport Strut hollows , you would not want to have special cutter shapes made to the profiles , as there are for a start , 4 different (Expensive ) cutter profiles required for these items alone , and secondly ; The rear section hollows are around 45mm deep which would be along the C/L axis of the cutter , and a cutter with such a long side cut , with dia around say 30mm widest is only safe in a fixed head machine .
The way you could do it with a router , Safely ,and relatively cheaply , would be to use a bull-nose cutter ( sperical ended parallel cutter ) of say " standard " ? 20mm dia and 25mm deep , and cut a series of varying depth trenches ,overlaping /close together ,and finish by hand if necessary ...A ramp may be used at either end to start and finish the cut smoothly and according to the drawing .
If the hollow has a " flat bottomed " wedge shape ( As appx. the trailing portion ), then you could incorporate a suitable depth runner- spacer strip tacked along the trailing edge , to raise the router base plate up to the incline of the floor of the hollow section ...If a curved bottom /floor to the hollow is needed,. then this spacer strip could be replaced at appropriate place with different thickness strips to achieve what's required .
One final point is that in order to get a good clean cut , especially in soft woods such as spruce / pine , you should always try to use High Speed Steel cutters ....These can also be readily re-profiled to special shapes " at home ".
If you use Tungsten carbide or similar , the finish of cut is nowhere near as clean as HSS, (for the edge can never be as keenly sharp ) and in general they will have to be made for you at a tool firm ( you don't want an insert flying off at 20/30,000 Rpm.with only you in the way of it ! (TCT tools are mainly for repetition work or on abrasive or glued/laminated timber ) .
Best regards ,John .
And may you have as many fingers at the end of the job , as when you started !
PS, Bryan ...I can't get that last link to " Photos/-/ Flugsport " to work ?