2 nice plans for early crossbows (German)

I found these 2 plans for crossbows on German sites. Google translate does not like German though. If you look at the Templer Boehl plan, you will see that the prod is only 500mm (19.685in). That seems pretty short to me. It seems that the plan states a draw length of 330mm or about 13in. That seems like a long draw on such a short bow. What do some of you more experienced builders think?

http://www.templer-boehl.de/Armbrustbau.php

http://berwelf.de/artikel/anleitungen/armbrust.pdf

Ahh, these plans are rather old and in my opinion only useful for absolute beginners to get an basic overview about general mechanics.

Problem is, everyone who runs into that makes a tiller and then tries to get a fitting prod, which ist almost impossible.
I´ve seen them a lot of times before, and in the german forum where im active, every once in a while someone is asking for help because he credited the measurements too much.

The 500mm prod lenght depends on material thickness, but I am your opinion this is a bit short for most prods.
That is why everyone is running into problems.

If you have a look both plans base on the same creator while the lower one is a bit more evolved but still hase some points I bet.

Greetings Rizzar

500 mm is suggested length of string.
Prod obviously would be longer with high brace height.

On 33cm barrel 5-6" brace height means power stroke of ca. 20cm or less.



Btw -
Notice that the museum bow in the pdf is strung backwards . ( says so in the caption too )

I figured that those plans could be of help to some. I already drew out my own plan based on the longer slimmer one with the composite prod, but I will be using Power Tuff for the prod and stitching a thin leather cover over it to protect the prod from scratches. I will be making the prod first and then making everything else to fit. I did thonk the museum bow looked weird. The brace height looked way too high.

The long-slender museum bow has the prod installed backward.
The other plan specifies a prod that is much too short. Given the distance from belly of prod to lock, you'd be better off with a 28-30 inch prod.
The roller nut and socket are straight from Payne-Gallwey. If you cut a step right across the bottom of the nut for a sear, you'll be forced to mount the nut on an axle... no free running nut in socket. Otherwise, the notch in the bottom, coupled with the necessary notch in the top for the string will result in lots of oscillation as the nut rotates in its socket. This will lead to plenty of wear on socket edges, and possibility of having the nut hop right out the top on release. It's much better to mount the sear in a pocket/keyway very slightly behind bottom-center (a quarter-inch behind will do) That way, the trigger will prevent the nut from rising in the socket before release, and the round bottom of the nut will prevent the nut from oscillating quite as much. How do I know this? The first bow I built used the system shown, with step cut in the bottom of a brass roller-nut, and I had endless problems.
I will say the long, slender plan based on the Dresden bow is very handsome, should be a good starting place for a 14th century crossbow.
Geezer

Thanks, Geezer, I was hoping that you'd give some advice. I will do what you said for the nut and I will work out the cutout for the tickler using cardboard patterns. I am going to make a two piece stock so I can cut out everything and then bond it together. I'll hide the glue line with decoration.

Sure thing, Zardoz, you're quite welcome.
Though I've said it before, perhaps this is a good time to reiterate. The author of these German plans, clearly consulted Payne-Gallwey's work, which is, by and large, pretty good for its time (1907) The biggest error he committed in his Flemish arbalest pattern lies in the nut and socket. He fits the nut in a steel socket, made to order, and that will work okay, but unless you're really building a 1200 lb. siege-bow, you can use a bone-reinforced socket instead.
PG's roller nut is 1.5 inches in diameter, a reasonable size for a strong bow, but he only sinks that roller in the stock by 3/16 inch. (approx 3/5ths) You'll be much happier if you bury the nut by 2/3 rather than 3/5ths, unless you happen to have a carefully matched steel socket, like PG. If you make the nut as deep as 3/4 of its diameter, you'll have trouble taking it out of the top of the socket. At 2/3 below top-line, you'll have no troubles there.
Second point... if you put the sear-pin just behind bottom-center of the lock... a quarter-inch will suffice, rather than at dead-center, your trigger will take up some of the load the socket would otherwise handle, and most importantly, the trigger will prevent the nut from trying to rise out of the socket when under load from the string. This means you have less stress on the edges of the socket and it lasts lots longer without any adjustment or repair.
Last point, and this is one PG gets right, you DON"T want the sear cut all the way across the bottom of your roller-nut. Go to the extra trouble of cutting a pocket in the bottom of the roller, and fitting a steel pin or block for the trigger to work against. A notch all the way across the bottom will be a stress-point, which can lead to the nut's splitting vertically, from the backs of the lugs, right down through the sear-slot. That's why I drill and tap the roller from top to bottom and screw in a piece of allthread. Period bowyers didn't have allthread, so they had to use a chunk of iron or steel, but in fact, allthread makes it really easy to remove a worn or damaged sear and replace with another. Whatever you do for a sear, it really helps to leave the roller-nut round at the bottom. It will run much smoother with less oscillation on release.
So does that make sense? Geezer.

Yes, Geezer, it makes sense. I have been reading a lot of your old posts here and i was going to make the nut as you described and use the threaded rod too. But what is the weight limit for a delrin nut if I reinforce the sear and fingers with threaded rod?

Maximum weight for a Delrin lock, appropriately reinforced. Honestly I don't know. Generally I limit my bows to @ 200 lb. I have made a couple in the 220 range, and one about 350, but as I recall those were moose-horn locks. If I made a 300 lb. bow with a Delrin lock, I would be careful for the first few shots, but in fact, I think it would hold just fine. At some point, you might want to put 1/8-3/16 in dia. steel pins down thru the lugs and into the body of the nut... you see that done on bone locks for Really Strong steel bows (I'd estimate close to 1000 lb.) but I suspect Delrin is strong enough to take the load up to 500 lb. or so... certainly heavier than I intend to build.
And why don't I make stronger ones? Because I guarantee all my work, and stronger bows have more problems, the tolerances are closer, customers break bolts, and generally, I observe bows under 200 lb. are less fun to shoot, require cocking-aids. If you're hunting Large game, you may need more power to drive a bolt deep into the game, but remember, no bow you can carry around in the field has anywhere near the sort of power we expect from hunting rifles, or even strong pistols. But that's another discussion altogether. Geezer

Yes, I had said that I was going to reinforce the lugs. The really strong bow is for myself. I intend to use a belt hook or a whippe. It will not be for hunting. Just pretty much for blowing through things with 1/2 inch diameter bolts. A lighter one will be made later.

I have made one medieval with a 205 pound prod from Alchem using a Delrin nut that is 1" wide with a 1/4" gap for the bolt leaving a total of 3/4" of meat to hold back the string. I have shot this crossbow a fair amount and seems to work fine. Now if you made the nut 1 1/2" wide that would leave an 1 1/4" of meat or 66% more. So if a 1" nut works for 205 pounds then 1 1/2" nut should hold 340 pounds in theory.



Todd

Todd, 300-350lbs is about the draw weight I was aiming for. I will make the delrin nut and just to be safe, I'll let my wife test it.