Back on 16 April ’09, I sought advice from PD’s re materials for fabricating paddle wheels given the current high cost of brass. Stuart Badger responded with “In fact, from personal experience I would suggest investigating the possibility of using plasticard for the wheel rims, floats and supports and only using brass for the actuating arms etc.”
My previous use of plasticard (styrene) had been largely confined to use of sheet to fabricate superstructures, battery holders, etc. So I thought that the challenge of fabricating and machining ‘bits and bobs’ for wheels would be interesting, with the material relatively inexpensive compared to brass. So if all went pearshaped I could write it off to experience and would not be too much out of pocket. The investment in time comes free when you no longer work for a living!
Longbow requires wheels with feathering floats. The wheels have an outside diameter of 176 mm and are (loosely) based upon the Edgar T Westbury (ETW) design for an eight float feathering wheel for a diagonal paddle engine (Sheet 2 of myhobbystore.com drawing M9), scaled by approximately 1.2 : 1. I decided at the outset to replace all the rivets in the ETW design with 8 and 10BA set screws.
To check that the scaled feathering mechanism would work as intended, I captured the design full size in a drafting tool and worked the space diagrams over the full range of mechanism. A few tweaks to rod lengths, pivot radii and eccentric offset and I had a working design. This exercise also provided the working ‘stick-on drawings’ for the four side frames, sixteen floats, thirty-two float arms, etc. [As an aside, just as I completed this drafting exercise, I saw the link in one of Eddy’s posts to a paper by Ivor Bittle re feathering mechanisms, space diagrams, etc. It was interesting to compare Ivor’s thoughts and conclusions to the results of my drafting exercise and the parameters of the ETW design; we disagree on the range of viable solutions but that is another story.]
The attached photographs show the results to date.
Photo 1 shows one of the side-frames fitted with a set of eight ‘stepped washers’ that act as the bearings for the float shafts. The frames are cut from 1.5 mm sheet with the outer rim machined in the lathe so that it runs true on the hub. Also shown is one of ‘cotton reel’ hubs machined from 38 mm diameter aluminium bar.
Photo 2 shows one of the assembled wheels, before the floats were fitted to their shafts, being trial fitted to the hull. The shafts are machined from aluminium bar because I could not source in small quantities styrene round rod in sizes greater than 6 mm diameter. The outer tie rods prevent the outer rims ‘flapping’ .
Photo 3 shows a wheel fitted with the floats. The float arms are cut from 1.5 mm sheet; the floats are 2 mm sheet preformed using heat and a mandrel to get the required radius of curvature. Parts were ‘plastic welded’ together in a jig to ensure consistency from float to float. The floats have been positioned to show the complete range of float articulation.
The eagle-eyed will note use of steel set screws; the brass ones are still awaited. Three weeks and counting.
Next job is to machine and fabricate the eccentric and actuating rods. Current plan is make the rods from 2 mm diameter brass, and use 10BA set screws for the pivots.
Brian.
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