Roller Nut Material

I was wondering about what materials work for roller nuts. I'll take a stab at recording what I have learned. Please comment with more details or point out were I am wrong.

Delrin: Relatively easy to get and work with, light weight, low friction, stable, looks like bone, works well for lighter (hand pull bows) crossbow.

Horn: light weight, period correct, looks good, strong, but more difficult to get (can't order horn from McMaster Carr )

Wood: Light, really easy to get, easy to work with, needs to be be treated to keep it from swelling from absorbed moisture, not strong enough for heavier crossbows, mostly replaced by Delrin.

Aluminum: Common, easy to work with, light weight, may have galling issues with the trigger especially in higher draw weight bows.

Brass: Shiny, period correct, heavy can cause misfire issues due to slow rotation, may be an decent choice for heavy draw weight bows.

Steel: Similar issues to brass, heavy but strong, could a good choice for really heavy crossbows.

So am I missing anything?

-Out of syntherics there is also Epoxy putty's and casting resins that can be reinforced with Fiberglass.

-Out of metal there is also Bronze...in fact there are also such things as Aluminum-Bronze Alloys

I would like to keep this going. I want to build a hunting weight crossbow (150-250 pound draw) and having read above that derlin is best suited to lighter bows and horn not readily available, does anyone know of a synthetic material that is strong enough. how about phenolic materials?

Todd

Maybe fiberglass-reinforced plastic or some other composite?
Fiberglass has an abrasive edges, so roller nut will require some other material on its surface..

Phenolic is a sort of composite right? Sort of like the fiberglass composite only reinforced with paper/organic fiber? If so, then it would land in a similar category as resin impregnated wood, right? Sounds interesting.

As for fiberglass nut, I really like that idea...given that on medieval war crossbows a horn nut was used and seems to have had sufficient strength for such applications, even thou it did need reinforcing of certain areas. This reinforcing, seems to have required drilling/tapping/gluing/pinning which is all avoided in our case with fiberglass/resin technology.

I've recently went through preparing everything for casting a nut in metal (Al) and it is a little more work than I have anticipated, requiring some special tooling to be fabricated first. With fiberglass thou I could have already finished it three times from start to finish , when in casting I would have only been up to fabricating the wax model(that would still need to be invested, burnt out, cast, finished, ... ) V

As a form for the composite nut I propose using a section of PVC pipe (plastic water pipe) of appropriate diameter. This is a similar method I used for making the wax nut model.

...drilling/tapping/gluing/pinning...

I guess it is possible to incorporate all the reinforcements and simply pour/pack the fiberglass/resin mass and allow to harder. And the coolest part is>>> If we do everything properly and all is centered then the nut will not need additional adjustments and that form made from plastic pipe can be used to make the roller nut seat that can be adjusted and made into a block reinforcement as was described in this topic >>>Link

The issue with abrasiveness of the nut that had to be adjusted would be further eliminated if the form was sprayed with an insulation medium and then a coat of durable paint applied prior to filling the form with the F/R Mass. Theoretically, the paint should bond to the composite nut...Sounds like fun.

Hmm 150 lbs may not be too heavy for a Delrin Roller nut. Need to break out the material properties books to figure out the shearing load of Delrin.

There is at least one example of steel reinforced horn nut. I wonder if that would work for Delrin.

If it worked with 400lb for horn, it should work for delrin.

As for metal pin reinforcements, I believe practically ALL horn/bone nuts were reinforced with metal pins...I think delrin wont suffer from a little extra inner support in the areas of teeth and sear.

Thank you, Pavise, for such an entertaining and yet extremely informative post...

A man who knows HOW to do something - Will always have a job.

A man who knows WHY things happen - Will always be the Boss.

A man who can explain difficult things in a way that even a kid would understand - Is a Magician

Found this searching on-line:

http://www.usplastic.com/catalog/item.aspx?itemid=36423&catid=679

I believe it is sold in 48" lengths. Should yeild about 32 nuts and be cost effective.
Let me know what you think.

Todd

Thanks for the kind comments Ivo.

Meanwhile, here you go guys. Phenolic rod is not much different than linen micarta, but of course there are several variants that might do the job we have in mind. It is possible to make your own by press-molding even Denim fabric together with epoxies but why, when there are ready-made materials available that took millions of dollars to develop?

http://plastics.dupont.com/plastics/pdflit/americas/delrin/230323c.pdf

And again like dear Robin always says, "Try it and see if it works mate."

Pavise

The thought of epoxy impregnated denim sounds fun.

And I do agree, the action will most certainly reflect the materials good qualities as well as bad, so having a little extra reassurance is always a good idea...be it reinforcements or simply the structural properties of the material itself.

Now the question that kinda bugs me is the inner structure of horn, I've never seen what horn looks like when it breaks, is it fibrous like the fiberglass reinforced plastic?...just an interesting though came to me when attempting to compare the two in my mind as I'm awaiting my shipments of various castable plastics. Does any one have a good information resource to the physical/structural properties of horn?

Hi Ivo,

A late friend if mine once used to make walking sticks for a living and he used horn of various kinds for some traditional models. Horn varies a lot between the type of host animal and some "horn" is not really horn at all. Keratin is the protein basis of horn and this is the same as for hair and fingernails which are similar fibreous materials. It is these fibres that give it strength the same as do glass fibres incorporated in glass reinforced plastics. However stability under a variety of conditions is important in a crossbow nut. It may be plus 100 degrees in one area and perhaps minus 40 in another, not to mention high or low humidity.

Meanwhile you might like to take a look at the following website for more information about this natural medium.

http://speyside-horn.co.uk/

Pavise

Just want to say that horn and antler are not the same thing. Horns grow continously while antlers are shed every year. I think horns are hollow while antlers are solid. An exception is the pronghorn antelope which has horns that it sheds every year. I believe horn can be boiled and bent to shape like plastic don't think you can do that with antler. Antler is (I'm guessing) probally like bone.

And then ivory is something else again.

Todd

Ahhh Thank you fellows,

I feel like I overdid it with my imagination.

It's starting to clear up now, Antler and Ivory is most likely to be the materials we would use here.

Just to once again clarify this for my self
Horn - A fibrous structure comparable to fingernails and hair, hollow (usually has no bony core). Availability>>>Plenty, but who cares, it's no good for making roll nuts anyway.

Antler - A solid and in some areas porous bone like structure that is covered with a thin velvety skin that supplies the growing bone with oxygen and nutrients...when skin is shed the antler dies and is also shed. Availability>>>plenty...good stuff.

Ivory - A dense solid tooth like structure...Availability>>>illegal to sell on E-Bay since 2009, but yeh...good stuff.

...Wicked info I found out about horn...thou doesn't fit as a nut material, some farm animals animals can have up to four horns.

Creepy stuff

Also a cool site I dug up and hope to find more like it. >>Distinguishing between Bone, Ivory, Plastic

Geezer here: just back from the big SCA meet. I use Delrin nuts up to 175 lb. without fear of failure, based on substantial experience. No doubt the stuff does have its limits.
Horn nuts in very powerful medieval bows sometimes have steel or iron pins to reinforce the lugs. These go well down into the body of the roller, if not quite out the other side. I have installed steel lugs (about 3/16 inch dia) in horn-nuts on request. They look sharp, make the lugs stronger, and only add marginally to the weight. Glued with silicone-glue or epoxy, they don't come out. Geezer.

What do people think about (I know it's not medieval) aluminum for nuts? I am thinking about a flapping catch out of cast aluminum for my next push bow. I have some standard 1.5" stock I have been playing with.

Aluminum for nuts? Tried it, didn't like it.
pros: It's fast and strong. Put in a harder metal sear, like brass or steel and it will last a long time.
Cons: Aluminum is 'sticky' and surprisingly hard to machine. It work hardens, builds up heat fast. The surface of your aluminum nut will oxidize very quickly. The oxide on the nut tends to stick to the oxide that builds up inside the socket. Result: Your nut will be 'sticky' for the first few shots if you haven't played with it in a week or so. Second, all that grey/black oxide will distribute itself all over your string-serving and thence to the table and into bolt groove. It looks really-really nasty.
So I made some aluminum nuts, won't do so again. If you want something super-strong machine the nut outa steel... some late period bows did that. If you want it quite strong and spiffy, get some moose-horn or Axis-stag horn and lathe-turn a nut. Aluminum is a non-starter... and of course I don't expect any of you to believe me till you try it... that's how life goes. Geezer

The surface of your aluminum nut will oxidize very quickly. The oxide
on the nut tends to stick to the oxide that builds up inside the socket.
Result: Your nut will be 'sticky' for the first few shots if you
haven't played with it in a week or so. Second, all that grey/black
oxide will distribute itself all over your string-serving and thence to
the table and into bolt groove. It looks really-really nasty.

Yeh, that's why they anodize the aluminum...to prevent it from oxidizing...well I'm not sure if it's actual oxidizing - perhaps some aluminum salts forming as the material is exposed to the atmosphere. If it's not anodized and you just paint it...the nasty will still some out eventually, paint just buys you some time. You have to anodize or use a similar chemically sealing/isolating process to keep the yacky out of sight.
After that there are a million finishes out there that can be sprayed and baked on the nut - one of which that would be really sweet is Teflon.

Aluminum is 'sticky' and surprisingly hard to machine. It work hardens, builds up heat fast.

I cast an aluminum nut a while back...hmmm never reported on that did I?...why? Never finished it.

I mounted the nut in a jig connected to a power drill in an attempt to smooth the surface with a file - result: a nice dull and clogged metal file. I got a belt sander now, but the pure aluminum is really sticky stuff as Geezer said and basically just smears when you put some power to it - result: I decided to keep the belt. Nasty stuff, perhaps a higher grade alloy will work better, but no such stuff on hand right now.

Ivo

Thanks Geezer. Good to know. I have access and ability to tool either so I will opt for some hot rolled steel.

Got a second, so a quickie post for you all to think about.



So, considering pool balls were made of the stuff and there is talk about using them to make a nut...also we talked about a resin/fiber nuts...put two and two together? ...how about it guys? Got Milk?

Perhaps reinforce it with some fiber? (...synew/natural/synthetic/glass)

Ivo out.

Hi All,

I am in the process of making a hunting bow and ended up here!

Alchem sold me a few parts and the nut was ABS plastic. For the first nut I ever made its okay and the ABS is nice to work with but I will need to remake it as it was a bit of a learning exercise and is less than perfect. The ABS is holding up after a few test shots but I am having a hard time sourcing more so was considering Delrin. The prod is 175' and I gather from reading this thread that the current wisdom has 175 as the max weight for delrin? One might rather be 'well within' the maximum as one sits in the tree blind ideally. Any thoughts on that maximum for Delrin?

Hotspur,

AboMickey rescently made a roller-nut from a pool ball looked very nice, don't know if he actually has used it in a build yet. However, one from a in all white cue ball should look very much like bone. You might check out his post with photos.

Chaz

Hotspur,

Welcome. Is ABS what Alchem uses? I noted that it was a bit different consistency than the delrin I aquired on my own. I'm using 1.5" diameter delrin roller nuts in a couple of bows that are over 200 pounds with no problems. As long as you're thoughtful about your design and how you place your sear reinforcement, you should be fine, there's lots of good examples to find here on the forum.

Gnome

Thanks for the input!

Looks like Delrin is the way to go. I found it locally at an industrial plastics supplier. For what it is worth, the representative stated that Delrin is superior to ABS in "almost every way" when I asked about mechanical strength.