rds25

My Feedback: (8)

I just bought K&S 2-56 and 4-40 dies to use making control rods using Great Planes steel clevises. Upon running new threads on the rods, neither size clevis will fit, both are so loose they just pull off. Are my expectations on the use of these dies wrong or what is going on? Neither Tower nor K&S can give me an answer. Tower said to call K&S, and K&S said all they know is you have to use a .081 rod to make the 2-56 control rod with. I am using the cut off end of GP 2-56 and 4-40 control rods to make these out of. I can't even get them to chase the threads of either size control rod, they feel like they are trying to cut new threads when I start them on.

bkdavy

My Feedback: (1)

You're trying to cut threads. The typical threads on control rods are a rolled thread, which allows the maker to use a smaller diameter wire. The rolling process causes the threads to raise up to the proper diameter. Unless you're starting with the wire recommended by K&S, you'll not get a good result.

TFF

Rolled threads and die-cut threads come out different even though they are "the same." IF you make die cut threads on the rod, for it to match you would need to make and tap the clevis with a matching tap. At the small sizes, the errors in the difference really show up compared to a 1/2 in bolt.

ChuckW

Your wire is too small. Don't quote me on this dimension but I believe it is likely .074" diameter. As mentioned, the threads were originally rolled onto it which raises the material and creates a slightly larger diameter threaded area. Look closely at the threaded rod; you'll see that the threaded area is larger than the rest of the wire. Thread rolling is a common process for making fasteners.

If cutting threads manually with a die however, you must start with the correct size wire as K&S says.

rds25

My Feedback: (8)

Thank you all for the info. It is most appreciated. Would any of you happen to know the correct size to use for 4-40 rods?

Lnewqban

rds25,

According to the Unified Thread Standard, machine bolts under ¼” diameter are described by a number plus the number of threads per inch.

The proper diameter of the rod for a thread to be made with a cutting die can be found by using this formula for the diameter of the finished thread:

D = 0.06" + (number x 0.013") (Edited for correction)

Hence,

D=0.086” for 2-56 (Aprox. 5/64” diameter)

D=0.112” for 4-40 (Aprox. 7/64” diameter)

Selecting a slightly smaller rod diameter makes the job easier, since some metal is always pushed to the crest by the die.
For our uses, the metal does not need to be super hard.

I believe there is nothing wrong with the dies you have bought.
The rods that you are using are probably of diameters smaller to the required for those threads.
This is common for threads that are made at the end of a long rod by lamination, which is a press-roll process that makes the metal flow to the top and bottom of the crest of the thread, starting from a rod of smaller diameter.

Dsegal

In order to cut your own rods see http://www.rodchuck.com/

Villa

Hi lnewqban
It took me a while to figure out your formula. In my old Machinery's Handbook the formula is shown a little different (everything is divided by 1000), but works out the same if you change the minus sign in your formula to a plus sign. Do you agree? Let me know so I know I have not lost it. You and I may be one in a million people that know about this formula. Since the correct diameter rods for the 2-56 thread are not readily available to me, I always purchase a threaded brass adapter that I then solder to the rod end to get a threaded end. I am not happy with this because the 2-56 brass thread is weak for landing gear application.

Lnewqban

I stand corrected, Villa, thank you!
I have corrected the sign typo in the posted formula.

You may find suitable bars (pre-cut and flat) at this site:

Fully threaded plain steel
http://www.mcmaster.com/#98837a003/=43n3wr

In stainless steel
http://www.mcmaster.com/#catalog/115/3136/=43n2f5

Steel bars of precise diameters:
http://www.mcmaster.com/#steel-rods/=43n97i
http://www.mcmaster.com/#steel-rods/=43nc0g

(These are for tool making, but they have good machinability before hardening)