A nut from washers, and the use of metal nuts in general

I was looking at this older post about gluing together washers to make a nut (I want to attempt this myself as well), apparently many thought this sort of construction was less than desirable structurally, but I don't see why it would be a problem as long as the trigger mechanism surface was pushed against the entire surface of all the washers so that the force was distributed in a way that doesn't shear the washers apart. A tight fitting axle through the washer holes would further prevent sliding of the washers.

The OP's prototype broke apart while he was cutting the trigger notch, I guess because he was using a power hacksaw or bandsaw to cut it? I myself would be cutting the notches out with a hand hacksaw and file, so I should be alright. And before you suggest it, no I don't want to use a solid round bar because I don't think I have anything that can cut through something like that, hence the washers solution. 

Also, in the post someone said something about metal nuts being too slow, I'm confuse because I see a lot of medieval crossbows using iron nuts, so can someone elaborate?

Are you planning on cutting the washers before glue up? It seems like that would eliminate your issue with it possibly breaking apart from the strains the saw would put on it. I wonder as well if it would help to drill a couple small offset holes and you could run some small round stock through the block of washers to help reinforce it?

And I still say making a nut by glue-ing together a bunch of steel washers is Doing It The Hard Way.  And when you're finished, you'l have an inferior product that's way too heavy.  Expect misfires and string-hop.  Geezer

As for medieval crossbows with iron nuts.  I've looked at a lot of medieval crossbows and find few that have metal nuts.  Most are bone/antler, with an iron or steel insert for the sear.  I have seen a few renaissance crossbows with iron or brass rollers. In most cases, they're very powerful crossbows, in which the inertia of an all metal nut may not matter as much.  If you Must make a metal nut, I recommend making it as narrow as practicable, and make sure the lugs are as far out on the periphery as possible (to improve leverage) Still, when you've made enough crossbows, you'll understand why most makers avoid metal rollers.  
    And yes, you can always cut your roller out of aluminum rather than brass or steel, but you'll eventually figure out why that's not such a good idea after.  Been there, done that, discontinued the practice.  Geezer.

Gotta agree with Geezer.  Washer roller nut would be 'way too much effort.  Plus glues are not really designed to work with serious shear energy, which a roller nut will have as it spins.

I must say that I haven't seen ANY medieval metal nuts att all, not even with 16th century crossbows. 
And if one would have that I guess that it's a later replacement, many crossbows were used for a very long time. Bone or antler is the stuff they were made of historicaly, nothing else. 
The biggest wall crossbows could have copper or copper alloy nuts, probably not because of their power but because it was hard to get antlers that big.
I have seen a big "ganze rüstung" crossbow in Skokloster Museum here in Sweden with a steel bow 20 mm and with an antler nut about 5 cm in diameter.

Thanks for replying guys, so I guess all those steel/iron nuts I see on mueseum pieces are inaccurate replacements? Blimey.

So is the main issue with metal nuts is fear of string jump from a slow turning nut? Would this stil be an issue in a non-historic top mount nut?

Also Geezer, can you elaborate on the problems of aluminum. I originally wanted to cast a nut from aluminum, i made a simple trigger for a miniature torsion ballistae this way with a clay mold, but I no longer have a backyard available for such venture (condo-dweller now). I find aluminum very easy to work with, its sturdier than wood but easy to shape with a hand file and cut with hacksaw. With the casting, getting rid and cutting through the outside scale was the main difficulty, which was rock hard and slipped my files a few times.

Geezer here, trying to answer cogently (suffering from the Mother of all Allergy Attacks-imagine this note punctuated with drool)
As for 'period' bows with steel/iron nuts, it depends on how you look at it.  I've seen a bow in the French Army Museum in Paris (as I recall) with a bronze nut... the caption claimed it was medieval... one of those heavy Flemish deals with the square console on bottom.... in fact it might have been 17th century.  The Metropolitan has a lovely little german-style self-spanning bow that's a combination stonebow/boltbow/wheel-lock.  That one has a shiny steel lock and steel bolt-track.  It might be as late as 17th century.  Certainly some of the really big wall-bows or heaviest field-bows might use metal rollers, but in fact inertia of a large metal nut does seem to be an important factor in misfires... the damned thing just wont accelerate fast enough and the string climbs over the lugs on release.
As for aluminum, I think I've mentioned this before, but here goes.  First: aluminum is quite unpleasant to work.... it's sort-of sticky- fouls up your tools and builds up lots of heat when you work it.  But if you persevere, you'll eventually get a beautiful, shiny lightweight roller.  You'll want to insert some sort of hard metal sear for the trigger to work on, and that may lead to weird bi-metallic interactions later, but let us forge on.  Eventually you make that beautiful aluminum roller, place it in the socket and get to work shooting.  You'll discover the roller oxidizes around the periphery pretty quickly. Over the next few months, you'll get a buildup of grey oxide on the inside of the socket.  If the bow is left unused for a few weeks, the roller will tend to stick to the oxide-deposit in the socket.  So your first few shots will tend to hang up, possibly causing misfire, or just longer lock time and be a pest when resetting for follow-up shots.  It's mostly just a nuisance, not a game-changer.  But then you discover a grey oxide buildup on your bowstring, which is being distributed along the track with every shot, and honestly, it just looks nasty.  Again, it isn't necessarily a project killer, but the beautiful piece with its shiny/silvery lock starts to look like something from a run-down tenement.  After making 3 or 4 aluminum rollers, I decided it was no more trouble to turn a piece of moose-horn stem and do it right the first time.  So I'd say, if you want to do medieval locks, there are three ways to go: First, build the roller in hardwood, with a solid steel plug sear.  This will work great on lightweight practice bows (100 lb. draw or less) Second choice, go for an industrial plastic like Delrin... they can be got in white or black, the stuff works great and doesn't look too tacky. Good for bows of a 200 lb. or so.  Third: invest in a chunk of real moose or axis-stag antler big enough to lathe-turn down to a cylinder and use that.  Most of the other alternatives I have seen will produce an inferior product even after hours of careful work and thought.  Those ancient bowyers knew their business.  If you're gonna make it the way they did, you probably oughta pay attention to their methods.  Geezer

Thanks for the lesson Geezer! Abandoning the washer nut for something else. Would a steel plate (18 gauge?) reinforce red oak piece for a nut be able to handle 150 pounds?

I think red oak dowel might well do the trick if handled correctly.  You'll want the grain to run top to bottom, and for a sear, I recommend drilling a 5/16 in hole (or slightly smaller and thread it) top to bottom, from between the lugs, to the bottom, just behind dead center.  Then screw in a piece of allthread rod for a sear.  I do not recomment you make a sear plate that runs all the way across the nut... that will encourage the whole thing to crack along the line of the sear-plate.  A threaded-rod sear, with a notch cut in the bottom to take a screwdriver will give you greater strength and resistance to wear without building in a shear-point for splitting the nut.  Does this make sense?  Geezer

This thread is beginning to get a little baffling to me.I can understand the need,if you are  into medieval crossbows for a faithfull reproduction.I can also understand the desire to use  materials that are readily available locally,or that you already have.What I find difficult to understand,is why anyone would wish to use materials that are totally unsuitable for their required usage.
                                                Wood has many uses,but is not known for it's frictionless properties,so why try to use it for a nut?Medieval crossbow makers I'm sure tried to make their bows as  useable and efficient as  possible with the most up to date and readily available materials of their time. After spending 100hrs or so planning and building your crossbow,why would you use a material that while it might work,it won't work well or for long for the nut?.I know some people like a challenge,and that the rule is "different strokes for different folks" but being the practical soul that I am,don't think I'll ever understand.
                                                Hermit.

Geezer here:  Hermit, in most respects I agree with you entirely.  But in fact, if you use a sufficiently hard wood, like Lignum Vitae, a wood roller should work very well even for substantially powerful bows.  And in fact, ordinary hardwoods like red oak and rock-maple will serve admirably for many thousands of shots for lightweight backyard practice bows.  In my early days, I built literally hundreds of lightweight bows for SCA (on the order of 500 inch/pounds-say 65 lb. draw) many of which are still giving excellent service.  Still I don't recommend making ordinary hardwood rollers over @ 100 lb... not when you can get Delrin which looks pretty much right and is very strong, or antler, which is absolutely right and lasts nearly forever.  Still there are always a few people out there who like tinkering with materials at hand.  Sighhhh.  Geezer.

Look at the roller nut on my kid's bow in classic crossbows. It is 5 layers. Aluminum, nylon, steel, nylon and aluminum. It has a heavy stainless tube for the axle bearing and two thread rods that thread through the materials. The whole thing is heated and pressed together and it makes a solid roller nut. This is my 4th nut of nylon and metals. It's tough and reasonably lightweight. I use a nylon/steel/nylon nut in a 200 lb bow with no problems. It was not easy getting the manufacturing steps right but I am glad I learned this composite nut construction.

I would like to propose a nomenclature.  I think it would be useful to draw a distinction between a "nut" and a "tumbler". 


I propose restricting the word "nut" to a string restraining component of a lock which uses its cylindrical outer surface as its bearing.  Any axle it may have, be it a shaft or just a few turns of thread, is only there to keep it from falling out and getting lost.

I further propose using the word "tumbler" for those string restraining lock components which use an axle, shaft, or pin as their bearing surface.  As such, a tumbler may have any external shape that is convenient to its function.  It may be cylindrical, but it need not be.

So, looked at another way.  If the pressure from the string tension is born by a bearing block, it's a nut.  If the pressure from the string tension is born by an axle, its a tumbler.

By this reckoning, a lot of "nuts" have suddenly become "tumblers", but I think it's an important distinction, and it will help us to think about and discuss them.

Mac

But it won't significantly change its construction will it? Just whether it has an axle or not.

It's a good point and a significant distinction but ultimately I think they have similar physical needs and can definitely be made with similar materials and techniques.

It changes how we think about the project. 

If we are building a tumbler, It does not matter if the periphery is concentric with the bearing hole.  As long as there is enough clearance in the tiller that it can rotate as far as it needs to, everything is OK.


By contrast, if we are building a nut, the periphery must be a true cylinder, and if it also has a hole for an axle or thread, that much be reasonably concentric.

I think that distinguishing between them will help us discuss them without conflating their essential qualities.  If we know that someone is trying to build a "nut" but he has not adequately addressed the question of how he will achieve sufficient concentrically of the outer cylinder, we can advise him.  If we know that someone is building a "tumbler" but he has speced an under sized axle, we can point that out.

Mac

Good points. Having never built a true rolling nut I haven't had to give it much thought.

For me, it seems like a very useful distinction.  When someone says they want to build a "nut" out of a stack of washers, my first thought is "how will they ensure that they end up with a true cylinder?"  But, if they are really building a "tumbler" out of a stack of washers, the first question is "how will they hold them together against the shear forces".   The whole problem of concentricity becomes a non issue. 

Mac

So in either case I guess I feel like I have a solution to the shear forces which doesn't depend on glue and using composites answers the weight question as well.

Wouldn't a stack of washers automatically be as cylindrical as you could need?

I see that you have dealt with the shear problem.  Between the bushing tube and those rivets, it ain't going nowhere.  I have used rivets myself to repair nuts made of Micarda, which came apart along the laminations.

I wonder how much or a problem the weight problem really is.  It's clear that a heavy nut must rob some of your energy, but I have had no first hand experience with the misfire thing.  The only metallic nut (a "tumbler" really) that I have used is in my ballistrino, and it shoots very reliably.   I need spend some time experimenting with metallic nuts until I understand the issues.

A stack of washers will be an adequate approximation of a cylinder only if they are secured together concentrically.   If any of them are out of center, or if the whole thing has a sort of lean, it won't really do.  To make a nut this way, you would have to make sure all you washers were accurately lined up while you riveted or soldered or otherwise joined them together.  

I suppose that if I had to make a nut out of washers I would proceed thus....
--find or turn a tube that exactly fit the holes in the washers
--cut the tube to a length just greater than the with of the washer stack
--cut the washers to shape for the fingers etc.
--clean the surfaces of the washers and the outside of the tube with HCl.
--flux the surfaces of the washers and the outside of the tube appropriately
--assemble the stack on the tube, making sure of the alignment
--using a tapered punch, spread the ends of the tube to rivet the assembly together
--spin the assembly on rod passing through the tube to check concentricity
--adjust as necessary and tighten the rivet
--repeat until true
--thread the assembly on a wire
--heat the assembly until it will accept solder 
--apply solder evenly to all joints
--When cool, check again for concentricity.
--remove excess solder carefully with a file of scraper, taking care not to disturb the truth of the cylinder
--remove as much of the protruding ends of the tube as possible by using a Dremmel  tool
--finish leveling the ends of the tube by careful filing

It's a lot of work to do it that way.  It's probably easier to buy a second hand lathe on Craig's List, or get a cheapy from Harbor Freight. 

Mac

I should make a video of my roller nut method. I start with just raw materials. I stack, fix and drill them on the press. I countersink the outside holes so the pins can be pounded into the hold to lock the thread rod in place.Then I tap the holes and while it's all still clamped together I thread the rod in. Then I cut the rod leaving a half cm of thread rod and pound the end into the countersink. Then I drill two large holes, one for the claw curve and one for the arrow rest semi circle. Then I shape it out around the holes with hacksaw and files. Having a nice drill press and some metal work knowledge is key.