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    In-Progress German Crossbow

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    stoneagebowyer
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    In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 11:57 am

    Hi, everyone. I have never posted photos on this forum, and still am not sure about if I am doing the posting correctly, but here goes.
    I've mentioned already in the newcomer greetings that a primary goal of mine is to build a Roman arcuballista for a 4th century Late Roman living history unit I am a member of, Exculcatores Iuniores Britanniciani. I am grateful, as probably many of us are for Kurt's build-along on his Knight's Armory site. I am pretty much following his instructions religiously, and thus far, it has been a joy to build.
    I am not going to post individual descripitions for each photo (if I can figure out how to post photos, of course), but just include photos for each major stage of the building process. Maybe that will give others ideas or reassure them that they too are doing something correctly (or, err, incorrectly in my own case).
    And so, I will post this intro and then subsequent responses with each additional section of all this. Everyone, feel free to jump in, give me hints, tell me I am an idiot, or whatever. It seems very civil for a forum to design and build pretty killing machines, and I love that kind of thing.
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 12:12 pm

    Okay, to start off, I ended up purchasing a nice live edge cherry plank, 6' long, 11" wide, and 1.75" thick. I would have preferred to find one fat piece of wood for the tiller, but loved this piece of cherry, and it was also on sale for about 21 bucks, so I have enough material for two or even three tillers.


    After cross cutting a 30" piece and then ripping it in half for a 3.5" by 3" by 33" tiller block, I used a cheap-o thickness planer to smooth the sides down, then laminated it with Tightbond III glue and some clamps. In it went into my planer to square it all up and make it happy. The glue line is perfect on one side, so that is the side that will be the bottom of the tiller. The other glue line will be hidden by the table facing material.

    I subsequently used traditional hand tools to carve the tiller to basic shape. Mainly, I used a draw knife, wood rasps, a replica Viking bearded hatchet and adz, and my beloved farrier's rasp, then cabinet scrapers to get the basic shape of the tiller. It is a bit on the fat side, but it pleases my eye and feels good as I hold it and imagine the King's deer in my sights.
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 12:14 pm

    Okay, got all cocky, but didn't read the FAQ on posting photos yet, and tried to do that from my computer. I'll have to put some photos into Photobucket and then continue all this.
    Sorry about any delays, folks.
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 12:28 pm

    Okay, this is a testing posting.

    Nice. It seems to have worked. I have to go back to real life, but will be back later. The photo you see is my first-ever moose antler nut.
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    Re: In-Progress German Crossbow

    Post by Todd the archer on Fri Jan 14, 2011 2:51 pm

    Sounds good so far. But you could have inletted for the trigger assembly before glueing together. I didn't do that with mine, but my stock/tiller was made from one piece of wood. Any way keep going and lets see more pics.

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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 3:24 pm

    I agree, Todd, and also the rolling nut socket could have been done first. But this is a first crossbow, so I am facing a steep learning curve. Planning ahead is always wise.
    Here are some photos taken in my little shop area. My shop is, as much as when I am in the kitchen, a sanctuary from the world, and time disapears. I find woodworking very meditative.
    Anyway, here are the shots of the board being worked down to the lamnnation stage, and then the final block ready for carving.
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 3:27 pm

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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 3:34 pm

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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 3:42 pm





    The last set of images is in backward sequence.
    So, the next set of shots shows the process of carving the tiller. As I said, I used traditional hand tools, and just took my time, got into a groove, and had fun. As well, there is one shot of the socket hole being drilled. I used a benchtop drill press and a 1.25"Forestner bit. I wish now I had drilled the entire length I needed, as hand drilling as Kurt had suggested in his building instructions was not easy, and I could have easily deviated and screwed this up.
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 3:50 pm





    The next five pics show the tiller when it was as the basically-carved stage. I could have made the tiller less wide, and a bit finer, but I am happy, and it feels good to handle, so should fit my hands well when I eventually shoot it. I did rough sanding as well, and in the last set of pics where tiller is posing on a blacktail deer pelt, I have sloped the nose as per the instructions I am following.
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 3:56 pm




    Now, for the making of the nut. I purchased a shed moose antler shed from my favorite dead animal stuff vendor. I spend 55.00 on it, and so was on tenter hooks about making this part, as I had never used a lathe before. I had purchased one of those little 7'X10" benchtop lathes from Harbor Freight a number of months back, mainly for catapult part making, but thought it could be pressed into service here.
    You can see the roughly cut antler on the lathe, some of the turning sequence, and then the drilling process for the binding hole. I think it came out well, and I had enough for a second nut, which is 1.25" in diameter and 1" wide.
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 4:05 pm






    The photos are still backwards in sequence, and if anyone has suggestions as to how to avoid that, I'd love to know.
    Here are a couple of shots of test fitting the nut into the socket hole. It rotates beautifully. You can see my pug Davenport in the background.
    Next, the sequence of refining the nut. I used a belt sander to square up the ends, and made sure using a caliper, as I did for the basic turning, that the nut was exactly the dimensions I needed it to be. I used a band saw (a dinky little 9" benchtop machine), as well as chisels and mallet and round files to make the notch and the ears. It was a lot of fun, and far less stressful then the initial turning and drilling had been. The secret as with making bows is not to rush, and take your time on a given task. Patience is definately our friend.
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 4:09 pm

    Finally for tonight, a shot of the nut in the socket. I deepened the rolling nut socket, and will later make a plug out of cherry as per Kurt's instructions. The nut rolls very smoothly in the socket, and I am happy overall how it turned out.

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    Re: In-Progress German Crossbow

    Post by Todd the archer on Fri Jan 14, 2011 5:03 pm

    Good work, what are you going to use on the deck?
    The nut I made was made from walnut. It is 1 1/2" wide and 1 1/2" diameter with a steel insert epoxied in.

    Now the real work begins: inletting for the trigger!!
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 6:35 pm

    Thanks, Todd. I like the way you created your sear. Nice, simple, and workable.

    I am actually not at all worried about inletting for the tickler / trigger. I love using chisels and mallet. An English buddy of mine called me a chippie, which I consider a high compliment. I got a ton of experience with chisels while making Roman catapults, where you have many, many mortise and tenon joints.

    Once I get the material for the tickler, I will begin that step. I am buying the prod (175 lb.) from Alchem along with the tickler and stirrup, but the prod is in the current production run, so I dont know when I will receive it.

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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Fri Jan 14, 2011 6:39 pm

    Todd, to answer your question about material for the deck, I had planned to use cow bone. But, I changed my mind and am going to use holly wood. I was very lucky and found a piece that is a very lovely white, almost an ivory color, with absolutely wonderful grain. I will resaw the piece, as it cost me 40 collars for a 36 inch piece, then plane it down to about 1/8 inch in thickness, glue it to the tiller, and continue sanding it down until it reaches the thickness I am aiming for.

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    Re: In-Progress German Crossbow

    Post by Tinker on Sat Jan 15, 2011 11:41 am

    stoneageboyer: Caught the picture of the PUG. PUGs always keep good people around! Smile
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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Sun Jan 16, 2011 7:11 am

    Tinker, thanks. Davenport is the love of ours lives, and I only wish I could have her out in my shop.
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    Re: In-Progress German Crossbow

    Post by Ivo on Mon Jan 17, 2011 12:56 am

    stoneagebowyer

    Good to see a buildalong coming along so well, I know it takes some time to get that prod, but don't let that drive you nuts...make sure to cut the slot for the prod only after you actually get it...check out Tinker's build for more info.

    http://thearbalistguild.forumotion.com/t180-my-medieval-arbalist-project

    Regarding picture order issue....the thing is they show up in the same
    order as the image links are posted in...editing posts is allowed, so just play around with it a bit.

    Good luck,

    Ivo




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    Re: In-Progress German Crossbow

    Post by stoneagebowyer on Mon Jan 17, 2011 3:47 am

    Hi, Ivo. I was just reading through Tinker's build-along, and it I think will prove very valuable to me, so thanks for the link.
    Bow making teaches one patience, so I can wait until the prod arrives. I finished planing and rough cutting the holly for the tiller table yesterday and making a bone quarrel rest, and there are a lot of other steps to undertake in any case.
    I'm sure I will get used to the idosyncracies of this site soon enough.
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    Re: In-Progress German Crossbow

    Post by Ivo on Mon Jan 24, 2011 11:55 am

    I think
    it's also worth mentioning at this point the design requirements for even
    heavier prods. It is becoming widely accepted that the nut socket can be
    bored through the side with a forstener bit and it's a great solution, but there
    is a limit to what weight prods can be used with that design. As seen in
    museum pieces, there is no evidence of the nut inserted from the side,
    but rather a "roll nut block" inletted from the top of the tiller just
    as Tinker did in his build.




    Perhaps
    it is a myth, but I often hear and always considered the side bored
    hole to weaken the tiller and would only take this path with a 175-200#
    and may be stretch it out to 250# max...I'm wondering how heavy of a
    limit would Geezer and other experienced builders recommend..

    Ivo




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    Re: In-Progress German Crossbow

    Post by DARIVS ARCHITECTVS on Mon Jan 24, 2011 5:16 pm

    It s a myth. I have a 350# based on a custom Geezer-built stock that has worked for well over a decade. The forces exerted on the tiller are primarily in compression between the socket and the prod, and the tension force applied to the front end of the tickler, as transfered to the tiller, are minimal, so the removal of wood at the side of the socket has negligible effect on the tensile strength of the tiller in the volume of material near the socket. Mortising a complete socket into the tiller offer the ability to assemble multi-piece lock mechanisms withe greater ease, and I believe this is the main reason why complicated sporting bows used mortised locks as opposed to side drilled sockets. Since most of us make low power crossbows (relative to originals), side drilling the socket introduces no design strength problems.

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    Re: In-Progress German Crossbow

    Post by Ivo on Wed Jan 26, 2011 8:02 pm

    Thanks Darius, definitely clears it up. Smile

    Reason for my worries is the great number of such myths...prods snapping if not tempered right, prods being unbalanced and snapping the stock, an improperly built cranequin anchor tearing out ans sending the thing flying, etc...that kinda stuff tickles my nerves a bit.

    Not saying this to discourage you in any way stoneagebowyer, just I ordered a really heavy prod and it got me all worked up and jittery both with bit of fear Embarassed and lots of excitement , so it shows.

    Carry on. Laughing




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    Re: In-Progress German Crossbow

    Post by DARIVS ARCHITECTVS on Wed Jan 26, 2011 8:06 pm

    One only has to imagine the forces of compression, tension, and shear in the 3-D volume of the tiller to understand what the effects of the geometry changes would be. This comes with study of stress mechanics.

    A super heavy prod is really hard on the bindings, which in turn tug forward on the volume of wood between the binding hole and the rear face of the prod when the crossbow is fired. If you imagine a huge sudden pull on the binding hole in the forward direction, you can see why there would be two shear flat horizontal planes between that section and the wood immediately above and immediately below. Since this in along the grain, cracks form over time. Imagine you grabbing the front end of the tiller at the binding hole and tearing that volume of wood right out. As a result, the upper and lower volumes of wood in the nose of the tiller were tied to the central volume with a steel rod. The rod transfers the force on the central section to the upper and lower sections, so no shear cracks form.

    Now this rod is required, but ANYTIME you drill a hole in wood, that GEOMETRICAL IMPERFECTION from a SOLID piece of material introduces a STRESS RISER in the material.

    In this case, the drilling of a hole, installation of a rod, and the introduction of the resulting stress riser is a necessary TRADEOFF to eliminate the problem of the shear stress of that "tugging" on the binding hole which will crack the wood. Sometimes you have to add a negative design feature in order to get rid of a GREATER negative design feature. The trick is known WHEN to do this!



    As with siege engines (which I LOVE to build), a crossbowmaker MUST have a good understanding of the strength of his materials, especially ones like wood which are stronger in some directions and not in others, and a good understanding of:

    1) The directions and magnitudes of the forces in 3-D space within the materials,
    2) How sharp changes in geometry, like holes, inside corners and outside corners, can concentrate stress.
    3) How these more concentrate stress areas will reach the breaking point first, before other areas of the material do, as you apply more and more force on the object.

    So if you want to really design good crossbows, study basic stress mechanics. Then you can choose the best materials, best shapes, and best dimensions to withstand the forces without overbuilding the shit out of everything like a novice.
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    Re: In-Progress German Crossbow

    Post by Todd the archer on Thu Jan 27, 2011 4:51 am

    Darivs is right those heavy steel prods put a lot of forward jerk strain on the bindings. Here is what happened to me on the first shot when I tried to use leather latigo lacing to bind on a 205# prod from Alchem:

    I then used waxed juted string which has stretched some and needs to be cinched tighter but otherwise is holding up well.

    Funny thing is that I used leather lacing on another crossbow that has a laminated prod from Elk Ridge Archery and that one is holding up fine.
    Todd

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