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Discussion Starter · #1 ·
I am attempting to build a thru truss bridge and want to use real nuts and threaded rod. My question is what size die to use on 3/32 brass rod? I don't want to buy a whole die set just for one project.

Kevin
 

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Hi Kevin: 3/32" is kind of a tough call. I've 2 x 56 over it, but it's a tight go. 3 x 48 may be a better fit.

What kind of brass are you using? Hobby shop brass or brazing rod is fairly hard stuff. There is a real risk of breaking off a threaded portion in the die.

I think I will use 3 x 48 next time.

Bob
 

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Discussion Starter · #7 ·
I thought about using K&S brass. I always thought brass was soft enough to cut threads without breaking the die. The size of the brass is not critical, I would just like it close to the proper scale size. That's why I chose 3/32 rod. It scales out close to 2" in 20.3 scale.

Kevin
 

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I thought round stock used to make bolts screws and or threaded rod is a different diamater than regular round stock off the shelf.

There for one could not just pick up a 1/2 in round bar stock and tread it with a 1/2 in bolt die.

Am I wrong in this thinking?
 

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Kevin - Search the threads for a topic called scale nuts/bolts..There was some good info on what you are looking for...

If you want to use some nice hardware try Microfasteners here in NJ they have all kinds of stuff. For the dies they also carry then but I think MSC is the cheapest on tooling for what I looked at..Of course for some off the wall model pipe threads they do not carry them and ya need to shop the UK for those..
 

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Posted By John J on 08/05/2008 8:55 PM
I thought round stock used to make bolts screws and or threaded rod is a different diamater than regular round stock off the shelf.
There for one could not just pick up a 1/2 in round bar stock and tread it with a 1/2 in bolt die.
Am I wrong in this thinking?




I think you are right for most everything below 1/2 inch, except for 3/8, 1/4, 3/16 and 1/8 which are standard rod sizes. I think that none of the other 1/32 step sizes of rod match standard bolt diameters.
 

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3/32 diameter rod can be threaded with a 3-48 die without issue. A 3-48 thread has a basic diameter of .099” which is only .005” larger than the 3/32 diameter rod (.094”). Since commercial screw threads are typically .001” -.005” smaller than basic diameter the 3/32 diameter rod is almost perfect for a 3-48 die. I have not found any scale size nuts larger than 2-56 but if the nut size doesn’t matter a 3-48 die on 3/32 rod will work fine (you can also make your own scale nuts). Additionally a 2.5mm die (.45mm lead) is essentially the same size thread. As long as you use some type of lubricant on the brass and a thread, unthread, thread again motion you should never break a hardened steel die on brass rod.

As far as standard rod sizes, a 5/32 rod can be threaded with a 4mm die (.7mm lead).

To determine the basic diameter of a numbered screw multiply the numbered screw size times .013”, and then add .060”. For example a #3 screw will be ((3 * .013”) + .060”) or .099”.
 

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I used 3/32 diameter BRONZE welding rod threaded with a 3-48 die I bought from MicroFasteners. Yes, the welding rod was hard to thread but I really like the natural RUST weathering it takes on after only a few months outdoors. The price difference between the welding rod and brass rod is also significant.
I threaded the rod by chucking it up in a hand drill and feeding the rod into the die that was held in place in a vise. I kept the rod from kinking by using a rigid tube around the rod. It is slow going, you have to go in a little and then carefully back the rod out. I found I had more success using the drill to go in but unthreading the rod by hand. That was you could feel if the threads were binding and avoid stripping the threads. I have 70 rods, threaded both ends, in this Howe Truss Bridge.





Russ Miller
 

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Posted By Kevin Miller on 08/05/2008 10:11 AM

I am attempting to build a thru truss bridge and want to use real nuts and threaded rod. My question is what size die to use on 3/32 brass rod? I don't want to buy a whole die set just for one project.
Kevin

Depending on if you've already purchased the brass rod and/or that you specifically desire to use brass. Also depending on how long the rods need to be.

You might consider using old bicycle spokes, you can usually find old abandoned rims with spokes, laying around most places. Depending on just how long the bridge is and how many rods you'll wind up needing it could save you a fair amount of $$$ considering the current price of brass.

Just a FYI, average single rider rims have 28~36 spokes & tandem rider rims have 40~48 spokes.
 

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Discussion Starter · #14 ·
Russ,

I'm impressed by your bridge. I'm building a straining beam pony truss bridge using plans by Whit Towers found in Model Railroad Bridges & Trestles. There are only 27 truss rods in it. I like the look of the smaller truss rods although 1/8 inch would probably be just fine. I like to keep things somewhat close to scale but exact is not necessary.

Kevin Miller
 

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How can you soften the brass rod from the hobby shop to make it easier to thread?? Don't need all the strength, as the rods are just detailing.
 

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Don't know if you really want to do that, as you may find it more difficult to do the threading because the chips will tend to clog the die/tap threads and not fall free.

As far as I know you can only anneal copper alloys to Dead Soft, and the only way to harden it again is by working the metal. To anneal brass heat it to cherry-red and then either let it cool slowly or quench it in water, unlike ferrous alloys it makes no difference.

This is totally unlike what you are used to with ferrous metal alloys. Where temperature heated to, the rate of cooling and the atmosphere in which its cooled has an effect on the end result.
 

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I'm completeing an arche bridge. used 3/32 brazing rod threaded 4-40 to make bolts using nuts on each end.
The brazing rod threaded easily,i Want to use 3/32 rod for the deck hangers but have not been able to locate
the right size turnbuckels. Checked with Ozark, Trackside details and three catalogs at local hobby shop.
Fab'd one using 4-40 nuts and flattened 3/32 rod , but it to bulky. I need 14 of them. Working with Dave at Ozark
for a solution. I may have to down size, but I think smaller would not look good on a 48" bridge. Especialy
when they are single rods.
 

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Discussion Starter · #19 ·
I finished my bridge today. I used the bronze rod that Russell suggested. Using a drill really saved a lot of time. I even threaded some extra so I'd have some all-thread latter. The brass fittings will darken with age. The dark finish I put on the wood will weather out to a light brown. It is roof patch thinned with paint thinner.
I used plans from the book "Model Railroad Bridges & Buildings".
Kevin


 

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Posted By Kevin Miller on 08/05/2008 10:11 AM
I am attempting to build a thru truss bridge and want to use real nuts and threaded rod. My question is what size die to use on 3/32 brass rod? I don't want to buy a whole die set just for one project.
Kevin





I ran thru the posts about threading. I COULD have missed it, but nowhere did I find mention of the use of thread-cutting fluid. It's not quite crucial, but it's a very very good thing to do. They sell a commercial fluid called 'Tap Magic' but I use Kroil. If you have nothing else, use WD-40 or at least light household oil. Your taps & dies will last longer and you'll have fewer breakages.

Les W. (Ret machinist)
 
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