Richard Braithwaite
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Everything posted by Richard Braithwaite
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First pic shows seat back machined on Unimat and second pic shows the outer and inner radius shaped by hand... The piece is deep enough for me to cut the rake of the seat back. I think I will cut the mortice and tenon first to give the join some strength and then work out how to mount it on my milling table to cut the rake...
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I think you may be right. With my 100mm saw blade I can do a deeper cut. So I don't think you will be exceeding the spec if you can make the cut. It wont cope with a 5 foot long 1 inch thick holly plank though, so at some point I shall have to get/borrow a larger saw to cut some usable pieces for model building.
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Marking out and machining the chair back timber. I've purchased a set of 0.5mm engraving end milling tools which I'm using here to cut the base of the back and accurately cut the sides so that the width of the chair will be correct. As you can see the tool is very slender and delicate, I broke one by being overambitions about the depth of cut (0.2mm cut and a slow steady feed is tops for a hard wood like holly...). The cutting part of the tool is only 5mm long so I had to finish the cuts with a saw (maximum cut shown in the picture), but still a great improvement over me trying to do it freehand... m also hoping to use the tool for cutting mortices for the various joints as its is the right size
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I am using holly for constructing the Trierarch's chair. Its a remarkably fine grained hard wood that can be machined rather like a soft metal such as aluminium and I hope to be able to mill scale joints in accordance with the drawing. I have a large amount of holly from an 8 inch diameter tree that I cut down about 30 years ago (!!). I cut the (5 foot) log into 1 inch planks, painted the ends and stacked them to dry out in our garage. As you can see from the picture below they warped a bit while seasoning, which makes it a bit awkward to cut pieces from it, particularly as my circular saw (https://www.byrnesmodelmachines.com/) can only cut a maximum depth of 15mm...so I've been cutting chunks out of it with a handsaw... Here are some timbers machined to size from this log ready for final shaping and jointing to make up the various components for the chair.
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Pat Thanks for the comment. Yes I was thinking that split pigskin lining shaved down might work. It needs to be about 0.25mm thick to fit in the recess in the arms of the chair...
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Unfortunately the shape of the hull changes so that these timbers have to be shaped individually. I used the jig shown in the photo below to ensure that the outer canopy supports would line up with vertically above the outrigger at the correct height...I cant find a photo of the arrangement I used for the outrigger supports, but the issues are very similar...
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I like the idea of controlling oar position with software as it allows experimentation with different oar paths and velocities...I've also been developing some rowing machinery for my trireme model. My prototype does not use software to control the position of the oars, but drives the oars (port and starboard independently) in a simple, sinusoidal, elliptical orbit which enables the oar handle path to fit within the close constraints of the trireme structure. Video of prototype in action below:
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Starting to plan the first of these projects... Extract of plan 26 - looks quite involved... The timber frame is covered with leather on the sides and back and has leather strips for the seat "upholstry" Would be nice to make from real leather, but not sure if I can shave it down thin enough for 1/24 sale...
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Working on the penultimate deck canopy section. these will complete the main structure of the trireme. Its then outfit items like the Trierarch's chair, ladders etc and then 170 oars and seats...
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Completed stern fairing shown alongside the relief carved beside the steps leading to the Acropolis in Athens, John Coate's interpretation (extract from his drawing No 12 © Estate of John F. Coates, reproduced with permission) and a picture of the full size reconstruction. John Coates drew his reconstruction from a number of sources (there is surprisingly little, given the impact of the trireme on Athenian civilization, and how well they documented other aspects of their life...) and managed to come up with something that actually worked and also looked (I think) very elegant. Not a trivial task given that the Athenians invested a huge effort in developing these ships over a number of generations... The geometry of the stern is quite complex, involving a number of curves in 3 dimensions coming together. Precise offsets for these curves are not provided in the design definition that Coates provided (in fact the form of the stern is shown slightly differently in each of his drawings) and so some hands on setting out and fairing is involved. So my model, inevitably, will differ from Coate's drawings (and from the full size reconstruction). The photo of my model is also difficult to compare directly with the drawing due to perspective effects.
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I started with a piece of wire to get an approximate shape that looked about right and then made up an (again approximate) pattern in balsawood. The vertical timber is loose, held in place with the steel square (set on a piece of balsa sheet resting on the aft platform) to confirm the fit to the first stanchion. I'm not sure how the original was made up, but I'm planning to make it rather like a grown frame pair, with overlapping "futtocks" so that the grain follows the curve and gives the fairing piece some strength. I machined a plank 0.8mm by 12mm (max depth for my fine circular saw blade) and set out the sections as shown below (I've drawn around the sections so I can duplicate the arrangement for the starboard fairing):
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Still planking canopy sections...10 out of 12 done so far. Embarked on another project to fill time while glue on planking is drying. The fairing piece between the quarterdeck and the stern is shown in John Coates drawing no 23 In plan view the faring runs in line with the gunwale as it curves into the stern and also needs to be vertical so that it mates with the vertical stanchions supporting it along its span. This makes it quite a complex shape to lay out.
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Had a go at go at focus stacking to get full depth of field down the gangway. There are some artifacts and out of focus areas. Could probably do better selecting and stacking the images in Photoshop rather than letting the camera do it automatically...
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Continuing with planking the canopy.... The cutting tools from my Unimat Lathe make convenient weights for holding down the planks while the epoxy dries on the current section. The gap between planks across the sliding joints is kept consistent with the spacing jig as shown. The fastenings on the last section have still to be trimmed and sanded down (which is why they look a little conspicuous).
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Continuing to add canopy sections. On the full size ship the sections were kept separate so as to minimise stress in the lightly built canopy as the ship flexed in a seaway. On the model I have left the outer rail continous so that alighment is maintained.
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First section of canopy with the planking completed, showing brass pins at base of inner stanchions which engage in brass ferrules in the deck beams and brass bolts which hold secure the outer edge. and here it is mounted on the model:
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Starting to plank the canopy today. Olympias's canopy was constructed from a number of sections so that the delicate structure would not be damaged by the hull girder stresses as the long thin ship flexed at sea. The sliding joint between each section is shown in John Coates Plan No 23 (Quarter Deck) The start of this joint is indicated by the arrow on the following picture of my model:
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Since this is intended as a model of "Olympias" rather than an updated attempt to model an Athenian Trireme, I shall stick to the Olympias Ram. As a parallel project, I am also working on a software simulation of the maneuvering of oared warships, which I am validating against the sea trials of Olympias. One of the original ideas was to use this model for testing to find some of the coefficients for the software simulation. Must admit that I got a bit carried away with the model. Rather more detail than would be strictly required for a tank test model... I (sort of) justified it to myself on the basis that If I built it to the full size drawings, from wood of the same density, then the weight distribution would be about right.... But there are easier ways of doing that. Probably also easier to use Computational Fluid Dynamics Software to derive the coefficients. Anyway, I thought it would be fun to see if I could build an accurate enough model of Olympias at this scale and fit a rowing machine in it. Haven't yet decided how I will make the ram... John Coates "Plan No 20 Trieres Ram" drawing shows details of the wooden structure (which I have used for my model as you can see from the whole ship picture at the beginning of the blog) but does not detail the construction of the "Ram Sheath" other than to say that is based on the Athlit Ram as described in the Mariners Mirror , August 1983. The views in the drawing suggest that it is fabricated from plate. Ill need to do some more research...
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Yes, remains to be seen whether I can achieve the required level of accuracy. Placement of the thole pins in relation to the oar ports is critical to achieving the required length of stroke. The following photos show the approach I used: 1. A jig used for drilling the thole pin mounting blocks to ensure that the hole is in the right place and angle: 2. Some pins installed on their blocks together with a jig for installing at the correct angle in the boat: 3. Installing the pin in position using the jig: 4. The pin in position: 5. Finally, a check on the clearances to give the required stroke angle:
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I've used lime pretty much throughout, mainly because the density is close to that of the pine used for the full scale reconstruction. Its quite a soft wood (compared to fruitwoods such as holly or pear), but that doesn't seem to have been too much of a problem and it has a very fine grain, which is nice..
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Before I embarked on this project I built a section model to see if I could fit machinery below the central walkway to operate the oars. This remains an option for this model which is why the canopy and internal hull structure is removable (see bolts in the above pics). The machinery is quite crude (I would aim to improve on that with the full model) but did demonstrate that independent control of port and starboard oars would be possible with machinery that would give an elliptical oar path with the right stroke length.
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There are 170 oars on Olympias. One of the purposes of the reconstruction was to demonstrate that that many oars could be operated effectively from a 37m long vessel...
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