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    mini-ulrich questions

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    stuckinthemud1
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    mini-ulrich questions

    Post by stuckinthemud1 on Thu Feb 13, 2014 2:57 pm

    First topic message reminder :

    I am new to all this, and have spent the last week reading through the medieval/early crossbows forum, and  Iolo's primer (thanks Geezer, really enjoyed it).  Anyway, I do like the curvy Ulrich-type of crossbow and think I am going to cut my teeth with a mini version (1:4 scale), using a pin-lock like in the loose-lam crossbow by kenh.

    I have a number of questions about the prod.

    I am going to make a wooden prod; at small scale, a laminate prod is probably un-necessary but am unsure as to how to proceed. I know the prod must describe a long shallow v when viewed from the front elevation but carving the prod so that the limbs reduce in thickness when viewed from above (like on a long-bow) will cut through the grain - is this a no-no? Any advice on making solid wood prods gratefully accepted as I want to do this as a technical exercise, preparing for a larger bow at a later stage.

      A fly in this ointment is UK crossbow law - I want to involve my kids in the project but to do so the 'bow will have to qualify as a 'toy' as I believe the current legislation is that no-one under the age of 17 can have anything to do with a crossbow - even if supervised by an adult over the age of 21???

    Thanks in advance
    Stuck

    kenh
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    Re: mini-ulrich questions

    Post by kenh on Fri Mar 07, 2014 5:12 am

    Original "open sight" is like an archer with his longbow -- apparent location of the arrow tip against the target or background, modified by knowledge of the bow, length of the arrow, and power of the bow..  Hold tiller in a given position, look at "sight picture", adjust up or down, left or right, and watch where the bolt flies.  Repeat until you hit what you want.

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    Re: mini-ulrich questions

    Post by stuckinthemud1 on Fri Mar 07, 2014 7:19 am

    Hi Hermit, looking at pictures of medieval bows there seems to be a sight which looks like a circle on a stick but it is very hard to tell what that is, what it does and how it does it, so I imagine that to be a peep-sight of some sort? Some other crossbows have a blade-type of rear- sight while the vast majority have no apparent sight at all.  Hence the question - what sort of sight is an option for a medieval style bow? At the moment I am favouring just sighting along the bolt but this build is to learn as many techniques as I can so when I go full-size I am a bit more clued-up.

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    Re: mini-ulrich questions

    Post by Hermit on Fri Mar 07, 2014 8:34 am

    My interest is primarily modern hunting crossbows,so I'm not really the person to ask,there are other members whose interest is more on the historical reproduction side,who may be of help to you.Many years ago,I read what is probably the first definitive and comprehensive book on the crossbow.The author is Sir Ralph Payne Gallway,in  fact,I owned a copy.This book will likely be available from your public library,if you don't want to buy it,tho' it is available from Amazon.You may find the info. you're looking for in Sir Ralph's book.
                                         Hermit.

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    Re: mini-ulrich questions

    Post by Geezer on Fri Mar 07, 2014 12:39 pm

    The circle on a stick sight is a rear sight for a sporting crossbow... I've never seen one that dated before @1500, but that doesn't necessarily mean much. Most of these sights fold forward when not in use, to facilitate use of a spanning device.  Some have peep-aperture plates, while others use a combination of peep-holes, with a V-notch at the top. Most are adjustable right-left and up-down via simple set screws.  In most cases, the fore-sight is simply the point on your bolt, though a few target bolts actually had a little blade or nub just behind the point to serve as a front-side. 
    And yes, Payne-Gallwey's "The Crossbow" or "The Book of the Crossbow" is still in print and an invaluable source on crossbows for English speakers. Nowadays there are other excellent books on ancient crossbows, but PG is still highly regarded. 
    Just be aware that when PG wasn't sure of something, he wasn't afraid to guess.  Sometimes he guessed wrong.  So its generally safe to use his book as a starting point, but be prepared to discover a few things are just flat wrong. My biggest gripe: In his pattern for the Flemish Arbalest, he makes the roller-nut lock too shallow. he buries the roller by 3/5 in the socket.  I recommend 2/3 for a safer lock-socket, particularly if you haven't built your socket of steel.  If you bury the roller by 3/4 you won't be able to remove it from the top of the socket.  Then it will have to go in the side.  
    Otherwise, find a copy of The Crossbow, read, and enjoy.  Geezer

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    Re: mini-ulrich questions

    Post by kenh on Fri Mar 07, 2014 12:44 pm

    The Book of the Crossbow by Sir Arthur Payne-Gallwey is available free online, here:

    http://www.crossbowbook.com/

    I have it permanently bookmarked....

    Hotspur
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    Re: mini-ulrich questions

    Post by Hotspur on Fri Mar 07, 2014 6:59 pm

    A version of that peep sight in on page 136 of Sir A. P-G's book.

    stuckinthemud1
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    Re: mini-ulrich questions

    Post by stuckinthemud1 on Thu Mar 13, 2014 8:20 am

    Thanks for the reference, really been enjoying Sir PGs book, filling in lots of questions.

    No. 1 son is very happy with his new 'bow (sister want a pink-one with sparkly bits!), it fires a 5" long pencil 17m but the release sounds noisy and the pencil seems too light a bolt - any ideas how to assess the best weight for a bolt - I had thought to add blue-tac to the pencil until the distance maxes out?

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    Re: mini-ulrich questions

    Post by kenh on Fri Mar 14, 2014 5:02 am

    IIRC the mass of a bolt should be 1/12th the mass of the prod.  Correct me if I'm wrong, guys.  It has to do with how much energy the bolt soaks up when the string is released....  too little mass (like a dry fire) and the prod can break; too much mass and the bolt is reallllllllly slow.

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    Re: mini-ulrich questions

    Post by hullutiedemies on Fri Mar 14, 2014 8:45 am

    1/12th is likely to be optimal for a low braced D-tiller bow. But this is just a safe starting point for testing.
    Brace the bow half way the bolt track and you can effectively go as low as 1/50th of prod mass.
    Optimal bolt mass depends on the geometry of the bow and really should be tested.


    OTOH 5 inch pencil is a bit short and fat to fly stable.
    You might want a heavy point or longer shaft. Probably both.

    Pin locks can have noisy release btw.

    stuckinthemud1
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    Re: mini-ulrich questions

    Post by stuckinthemud1 on Sun Mar 16, 2014 3:33 pm

    Cheers both, seems like 10% of prod mass might be a good starting point.  The reason for the bolt length is that that is just over the 4.5" draw of the bow.  Think I might whittle and fletch some yew bolts of varying sizes and see where I get to.

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    Re: mini-ulrich questions

    Post by Hotspur on Sun Mar 16, 2014 4:28 pm

    In some tests I found 1/12th delivered the maximum kinetic energy to the target.  The trade off being trajectory and speed.  You will probably find that something less than 1/12th shoots best.

    stuckinthemud1
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    Re: mini-ulrich questions

    Post by stuckinthemud1 on Mon Mar 17, 2014 6:28 am

    Thanks Hotspur.

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    Re: mini-ulrich questions

    Post by Hotspur on Mon Mar 17, 2014 7:17 am

    I settled on 1/19th or 5.21% of prod mass.  A 42 gram (650 gn) bolt on a 806 gram prod.

    Here is the test data.  Note the slightly declining returns of foot pounds of force and a linear drop in speed:


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    Re: mini-ulrich questions

    Post by kenh on Tue Mar 18, 2014 8:00 am

    I've been reading Stephen Selby's landmark book Chinese Archery, and in the crossbow section found a reference to bolt weight from Chen Yin's Han dynasty Archery Manual (2500 years ago).

    Chen Yin calls for the equivalent of 1 gram of bolt weight for every 1.92 kilograms of prod draw weight.

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    Re: mini-ulrich questions

    Post by Hotspur on Tue Mar 18, 2014 10:53 am

    kenh wrote:I've been reading Stephen Selby's landmark book Chinese Archery, and in the crossbow section found a reference to bolt weight from Chen Yin's Han dynasty Archery Manual (2500 years ago).

    Chen Yin calls for the equivalent of 1 gram of bolt weight for every 1.92 kilograms of prod draw weight.

    Interesting.  I think the deciding factor in fine-tuning any given bolt weight has to be the purpose of the bolt.  Armour piercing, target shooting, hunting will all have bias in one direction of force or speed and trajectory.

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    Re: mini-ulrich questions

    Post by Hermit on Thu Mar 20, 2014 9:36 am

    Given the huge number of variables involved in the design,operation and construction of crossbows and their accessories,for me,empirical data(test,or otherwise)is nothing more than a 'rule of thumb'.As I see it,there is only one immutable rule........................"Whatever works,Baby"!
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    stuckinthemud1
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    Re: mini-ulrich questions

    Post by stuckinthemud1 on Thu Mar 20, 2014 3:40 pm

    Hi All,

    for anyone interested I have posted a couple of entries of the build of the mini-bow on my blog   Not an Ulrich, but for a first effort I am not dissapointed - it is definitely medieval in style. Any comments on how to do it better are very welcome.  When I find out about string-making and when I make some bolts I'll post some updates there Very Happy 


     story of my medieval style mini-bow.

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    Re: mini-ulrich questions

    Post by stuckinthemud1 on Fri Mar 21, 2014 2:26 pm

    I have spent the afternoon messing about with some ash laths and odds and ends of timber, drilling sequences of holes and cutting more hooks into the laths than a shark has teeth in an effort to establish the geometry for a goats foot spanning device. I have arrived at a solution and now have the measurements I need but surely there must be a more scientific approach?

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    Re: mini-ulrich questions

    Post by Geezer on Sat Mar 22, 2014 7:45 am

    Payne-Gallwey's pattern is a good approximation for shapes and proportions. Of course I have a quibble. He shows the hooks that grab the string pivoting on a solid axle... while that will work just fine, swinging it on individual rivets with the space between open will allow the lever more swing room, since the string-hooks won't bottom out on the stock at the end of the stroke.  A properly made gafa is a wonderful machine.  Have fun!  Geezer.

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    Re: mini-ulrich questions

    Post by Hermit on Sat Mar 22, 2014 8:12 am

    I just googled"goats foot lever"............When I arrived at the site,one of the references there was to this forum,and to an extensive thread on goat's foot levers from 2011,one of the postings described how to make one from wood and materials available from the home depot.
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    Re: mini-ulrich questions

    Post by Hermit on Sat Mar 22, 2014 8:35 am

    At 7.00 a,m, this morning,it was -20C (-4F)here in Northern Alberta,could be a record low for this time of year....................World's going to hell in a handcart!!
                                                                          Hermit.

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    Re: mini-ulrich questions

    Post by stuckinthemud1 on Sat Mar 22, 2014 9:56 am

    Thanks Hermit, I'll check out the thread straight away.  -20?! that's just a little too invigorating Smile 


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    Re: mini-ulrich questions

    Post by stuckinthemud1 on Sat Mar 22, 2014 2:58 pm

    Read through the thread and through the entry in the book , seems like trial and error is the best way forward, but the details were for wippe not goats foot spanning; the concensus for GF was to only do this in metal. Presumably because of the shearing force on the string hooks. Fortunately I didn't know that before i started and my test contraption worked well so I'll have a go and see what happens.

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    Re: mini-ulrich questions

    Post by stuckinthemud1 on Sun Mar 30, 2014 9:43 am

    Hi All, I've been spending some time looking at the Met Museum images of the Ulrich crossbow.  I am admitting defeat: any one know how the polychroming was done.  It seems to me the patterns were etched/engraved into the stock and then 'coloured in' - there are lots of ways to do this, oil-paint, gesso, coloured-wax, and even guilding.  Any one more kowledgable than me know what the original colour scheme was as it is very likely not what has degraded to the current colours (though the original colours could be the colours as we see them??) and what the pigments were?

    Stuck

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    Re: mini-ulrich questions

    Post by Geezer on Mon Mar 31, 2014 6:37 am

    I think the pattern on the stock was probably done with iron stamps, similar to leather work.  You would probably want to wet the wood well to soften it a bit before going to work, then fill when dry with some sort of dark paste or gesso.  I can't tell the original color, but it looks very dark now... black or deep brown. One wonders if the carved bone bits were ever colored.  I've seen plenty of examples from later, 16th century bows with color, as well as a really lovely bow (formerly in Tower of London, maybe now in Leeds?) It's probably late 15th century... the one with serpentine dragons carved on the sides... it's prominently featured in one of the Tower Armouries pamphlets on crossbows.  Anyway, the 'Tower' bow in my catalog is based on this one, and it has plenty of color in the background.
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