# Can I use a die on brass tubing (not solid)



## jimtyp (Jan 2, 2008)

I have some K&S tubing 5/8" diameter (not solid), .014" wall thickness. Can I use a die to make threads? I've seen solid brass used with a die but not the tubing.

If I can use a die, what size would be proper for threading 5/8"?


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## Semper Vaporo (Jan 2, 2008)

Posted By jimtyp on 06/10/2009 12:23 PM
I have some K&S tubing 5/8" diameter (not solid), .014" wall thickness. Can I use a die to make threads? I've seen solid brass used with a die but not the tubing.

If I can use a die, what size would be proper for threading 5/8"?




Hmmm... "Standard" threads for 5/8s is either 18 Threads per inch (National Fine) or 11 Threads per inch (National Coarse) (assumming U.S. standards), there are other standards but these will suffice to consider the following:

The distance between peaks for Fine threads is 1/18 inches (18 TPI) or 0.055555 inches.

The depth of the thread would be (assumming sharp peak and valley triangular threads) 1/2 of that or 0.027777 inches.

If your material is only 0.014 inches thick you no longer have a "tube" you have a "spring" which makes for a leaky tube!









To put threads on a tube of this sort you will have to go to a very shallow thread geometry which could be cut on a lathe, but would not be much of a thread strength wise. Maybe pick a larger diameter die, but there are no "standard" sizes defined that are just slightly bigger than 5/8 (the next step in my table is 3/4 and that is way too big), so it would have to be some specialty die if there is one available and still be a rather weak thread.

Questions:

Which diameter NEEDS to be the size of the .014 walled 5/8th tubing? The inner or outer? If the inner one can be reduced to beef up the tubing thickness then a short section of the next 2 smaller sized K&S tubes could be soldered to the inside and the result have threads cut in it. Silver (or 2 or 3% silver bearing) solder would provide some strength to the joint better than electrical or plumbing solder, but that may not be all that critical.

What is the purpose of this tubing? Why does it need to be threaded? Maybe there is some other way to accomplish the reason for the threads.

Also, I have seen a threaded tubing that is used in building electric lamps (table lamps or hanging lamps) that is thicker (I think it is 11 TPI) but it is usually a type of aluminium (or some sort of tin/pot metal of little mechanical strength) that might suffice for what you need. I think it is about 1/2in. or 5/8in. outer diameter but around 3/8iin. inner diameter.


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## jimtyp (Jan 2, 2008)

CT, I made a mistake, the tube OD is 5/32", not 5/8". I do have room to put a 1/8" inside the 5/32" tube to give it basically .028 thickness. 

For 5/32" tube, what die size would I need, tap and clearance drill?


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## Semper Vaporo (Jan 2, 2008)

Posted By jimtyp on 06/10/2009 11:25 PM
CT, I made a mistake, the tube OD is 5/32", not 5/8". I do have room to put a 1/8" inside the 5/32" tube to give it basically .028 thickness. 

For 5/32" tube, what die size would I need, tap and clearance drill?


That's okay, I was wrong about the lamp parts too. They are 3/8ths, not 5/8ths.

Anyway, I cannot find any "Standard" thread size specifically for 5/32nds.

5/32nds = 0.15625

The closest size rod would be a #8 (at a nominal diameter of 0.1640)... like making a number 8 sized bolt from the tube... it would be an undersized bolt, but pretty close. Standard threads are 36 (National fine) or 32 (National coarse) 8-32 is a very common size for bolts and nuts. If you threaded the 5/32 tubing as an 8-32 you could spin an 8-32 nut on and it would be slightly loose. 

But... uh what about thickness to remain intact after being threaded?

Hmmm, 32 threads per inch would be 0.03125 between threads and again assumming triangular threads with sharp peaks and valleys, the thread depth would be 1/2 of that at 0.015625, which means without thickening the tube wall you still have a "spring" for threads. Even if you were to use 36 for the thread pitch (0.0277777+ between peaks) you get a depth of 0.0138888+ and that leaves you with a pretty thin foil in the thread valleys (and given the tube is probably not really uniform in thickness a few holes in the "foil"!) so it would have no strength as a "bolt" to hold. Either way, I'd recommend thickening the tube wall somehow. K&S does make a thick wall tubing, but I don't remember the thickness now.

If you were to put a 1/8th inch tube inside and solder them together it would be better, but remember that the brass tubing is quite fragile and could easily bend and kink/collapse at the body of what it is threaded into.

Anyway... to tap a hole to fit this 5/32nds inch threaded tubing into you would use an 8-32 tap in a hole drilled with a #29 drill for either coarse or fine threads. A #29 drill is 0.1360 inches. I'd have to go down in the dungeon to look at my drill index to find which drill I'd use if I didn't have the numbered set of drill bits (which I don't!) I tend to use the next closest size I have when I do this (and I often do, so I really should buy the numbered drills!) and sometimes I like to use the next larger size to make it easier to use the tap, and sometimes I bite the bullet and use the next smaller size to leave more material to create threads in, which makes a stronger part... but it makes it much harder to run the tap in and greatly increases the risk of breaking the tap (and I do!) which often ruins the part.


You might also consider metric threads. 5/32nds is really close to 4-mm (=0.15748 inches, which only 0.00123 inches larger which is closer than the #8 American size). I think it requires a 3.3mm tap drill. I believe the standard thread size is .70 mm (metric thread size is specified as the distance between the threads) so the size would be designated as "4x0.70mm"; thus the depth is 0.35mm which is 0.013779+inches (about the same as the National Coarse 36 TPI) so you still need a thicker tube wall to end up with tubing and not "spring".

I would also recommend heating the tubing to glowing dull red to anneal it to make it softer and easier to cut the threads in... of course that weakens the material and makes a weaker joint (easier to strip the threads if you over tighten).

Remember (in my son's favourite little saying), "Tight, is tight; too tight, is broke!"


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## Semper Vaporo (Jan 2, 2008)

I forgot to add: 

If you don't have the #29 tap drill bit and have to pick the next larger size you have, make sure it is smaller than the tubing or the tap will just fall through the hole... rather obvious to say that, but I just had to point out the stupidity of my own actions once! 

Rather than go down in the dungeon, I looked at the charts I have been referencing for this and see that the nest smaller standard drill bit size is 1/8 (0.125in.) and that is way too small to attempt to tap as a #8 hole... you WILL break the tap. The next larger size standard drill bit is 9/64 (0.1406in.) which leaves very little material to be threads. probably better to use the #29 bit or go with the metric sizes. 

Also, Just a "so you know it" note; the numbered sizes of bolts is not the same as the numbered drill bits. A #8 bolt is 0.1640in. and that is between the sizes of the #19 and #20 drill bits (0.1660in. and 0.1610in. respectively)


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## SteveC (Jan 2, 2008)

Hey Jim, hold on there a bit,

Are you planning to put threads on the outside or inside of the 5/32" tube?
[*] If making an external thread on the outside of the tube, then you'll be needing a die.
[*] If making an internal thread on the inside of the tube, then you'll be needing a tap.
[/list] It might make more sense to me if you sort of explained what you are trying to accomplish.


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## jimtyp (Jan 2, 2008)

Steve, Yes, I'm trying to make threads on the outside of the 5/32" tube, which has a wall thickness of .014. I could put a 1/8" tube inside the 5/32" to give a wall thickness of .028, if needed. I'm then going to screw that into another brass piece, that is currently solid. I assume I can use a clearance drill and then tap it.

CT, so you think a 4x0.70mm would be better than a 8-32? From what I researched it seemed like the 10-24 would be a possibility. But I have no idea what I'm doing so that was my best guess.


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## SteveC (Jan 2, 2008)

Posted By jimtyp on 06/11/2009 9:36 AM
Steve, Yes, I'm trying to make threads on the outside of the 5/32" tube, which has a wall thickness of .014. I could put a 1/8" tube inside the 5/32" to give a wall thickness of .028, if needed. I'm then going to screw that into another brass piece, that is currently solid. I assume I can use a clearance drill and then tap it. _{snip...}_
Jim

Just a thought here, but have you considered simply soldering (i.e. either soft or silver) a length of screw thread (e.g. 8-32 x 1" with the head cut off) that fits snugly inside the 5/32" tube. Then drilling the correct size hole for tapping in the other piece for that size screw?


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## Dwight Ennis (Jan 2, 2008)

I'm then going to screw that into another brass piece, that is currently solid
Unless the tubing needs to be removed later, I'd drill the solid brass piece #21 (0.1590) to accept the tube, then insert the tube and silver solder (or if great strength was needed, silver braze).


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## jimtyp (Jan 2, 2008)

The reason I need the tube to be screwed into the solid piece is it does need to be removed, so soldering is out. 

The screw inside the tube won't work as I need to run wires through the tube, that's why it's not solid to begin with, unless the screw itself is hollow and will allow some wires to run through it.


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## Dwight Ennis (Jan 2, 2008)

How about drilling and tapping the solid piece perpendicular to the tubing for a 4-40 or 2-56 set screw? Or you could locktite it in place with Locktite #222. As was said, without knowing the specific application and the effect of various approaches on cosmetics, required strength, etc. it's difficult to suggest options.


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## Eric M. (Jan 3, 2008)

I gotta say that your wall thickness is just too thin. Sleeving one tube inside the other doesn't sound like a good solution either. The only way that idea might work is if you soldered the inner tube in, but getting the solder to flow between sounds almost impossible. The other thing that no one has mentioned is that getting a die started by hand and keeping it straight is pretty difficult. Even if you were able to solder one tube inside the other and get the threads cut you may end up with a very thin wall in the valleys of the threads and because keeping dies straight is tough, you may cut through on one side. At best it would be an extremely weak part. I really don't like nay-saying so I invite you to prove me wrong but since you are asking for opinions I thought I would toss mine in the ring.

I have a bit of experience with this sort of thing because I did all the pipe fitting on some 20.3 scale live steam donkey engines and many of the pipe connections were threaded. We used thick wall tube and MTP (model tapered pipe) dies that are specifically meant for tubing. We kept the tube aligned in the with the die by chucking everything up in a Sherline lathe and carfully rotating the chuck by hand to cut the threads. The MTP dies and taps are available from Coles Power models and they are $$$$$$$$$. They also have thick wall tubes in copper and brass.


Regards,


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## Semper Vaporo (Jan 2, 2008)

Posted By jimtyp on 06/11/2009 9:36 AM
Steve, Yes, I'm trying to make threads on the outside of the 5/32" tube, which has a wall thickness of .014. I could put a 1/8" tube inside the 5/32" to give a wall thickness of .028, if needed. I'm then going to screw that into another brass piece, that is currently solid. I assume I can use a clearance drill and then tap it.

CT, so you think a 4x0.70mm would be better than a 8-32? From what I researched it seemed like the 10-24 would be a possibility. But I have no idea what I'm doing so that was my best guess.


I think a 5/32 tube would just fall right through a 10-24 die. I have some time now to go down in the dungeon and I think I have some 5/32 K&S tubing... I'll go try a couple of these... ya gots me interested in seeing if my reading my charts is right.


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## SteveC (Jan 2, 2008)

Posted By jimtyp on 06/11/2009 11:26 AM
{snip..} The screw inside the tube won't work as I need to run wires through the tube, that's why it's not solid to begin with, unless the screw itself is hollow and will allow some wires to run through it.
OK, I was afraid you were going to say that.







Depending on the wire size you could drill the center of the screw.

Or you could go the other route maybe, use a screw that's large enough so you could drill a 5/32" hole in the center of it and make a threaded sleeve to solder to the outside of the tube. A lot of work I know, but I'm pretty sure that threading the tube itself with or with out the inner sleeve, will result in a very weak structure that will easily break at the first sideways pressure.


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## SteveC (Jan 2, 2008)

Jim

Even if you switched to *K&S 3/16" (i.e. 1/32" larger) tube with a .028"* wall thickness, that would give you an OD of .1875" and an ID of .1315"

A #10-32 machine screw has a major diameter of .1900" and a minor diameter of .1517" for the normal 75% thread.

That'll leave you with just .0101" wall thickness uncut, if everything works perfectly. Plus even if things hold together it'll be a wobbly fit at best because it's going to be way less than a 75% thread.


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## Eric M. (Jan 3, 2008)

BTW there is a size of die specifically meant for 5/32 OD tube in the MTP threads that I mentioned before. But it would be advisable to order a length of thick wall tube while you are at it-- and you would need the tap as well so you can make your part to screw the tube into. Give Coles Power models a call. They can advise you on the best way to pull off what you want to do.

Here is a picture of the 5/32 OD threaded tubing installed on the donkey before I painted it. 










You can see the threaded connections on the two side-outlets of the tee fittings. The connections on the vertical parts are silver soldered because I did not need to unscrew them. Just thought I would share that it IS possible to thread a 5/32 OD tube, but like I said, a special tap, die and tubing is required.

Coles Power Models:
(409) 547-3400

Regards,


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## jimtyp (Jan 2, 2008)

You guys are definitely resourceful  I appreciate all your input. Even if you say it won't work I need to hear it. 

Dwight, I'd prefer not to have to glue but will keep that as an option. How strong is #222? The part looks like a T. The long vertical is the 5/32" tube, the horizontal top is the part I can drill and tap. 

Steve, drilling a screw is something I hadn't thought of, but I need a bunch of these so if there is an easier way I'd prefer that. Regarding the thicker wall. I could put a 3/32 inside the 1/8 inside the 5/32. The 3/32 tube would still give me just enough room to run the wire. That would give a wall thickness of .014 * 3 => .042 It only takes me a few seconds to solder these together and they are super strong this way, I know as I've done it before. I've seen screws that were hollow but I don't know where to look, maybe McMaster-Carr? 

Eric, that is an awesome job! I assume that is an actual working Donkey not just a static model? I'll give Coles a call, thanks for the number. 

CT, that would be super if you could actually try it on a 5/32" K&S brass tube, as I stated I do have the luxury of putting some tubes inside each other for an OD of 5/8" and wall thickness of .042"


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## Dwight Ennis (Jan 2, 2008)

How strong is #222?
http://tds.loctite.com/tds5/docs/222-EN.PDF


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## Semper Vaporo (Jan 2, 2008)

Well... that was "fun"... I guess... at least it got me up outta my easychair for an hour or so...









I tried a 10-24 die. First without modifying the 5/32 tube. It did not slip over the tube like I thought it would. Instead, while using it to try to make threads it ripped completely through the thickness of the tube and reverse wound a spring of brass into one of the relief holes around the cutters in the die.

So I silver soldered a 3/4 inch length of 1/8 tube inside the 5/32 tube. I used 8% silver solder and had to use LOTS of flux in the 5/32 tube to get anything to stick. I assembled it and then re-heated the two tubes and pulled them apart to inspect the surfaces. The inner tube was well coated (probably because it got more solder on it while pulling it out of the other tube). The outer one got NOTHING in the inside surface until I added much more flux and then inspection showed good flow had occured. I then reassembled it (under lots of heat to get them to slide past each other again), let it cool a bit and then washed it completely, inside and out.

The 10-24 die then left a narrow spiral groove; I'd say that the groove was about 25% of the width of what was untouched between the segments of the groove... i.e.: lousy threads! This also shows that the tubing is quite weak if only that amount of engagement managed to rip the 5/32 tube apart when trying to thread it alone!

I then tried an 8-32 die over what the 10-24 did and then for another 1/4 inch or so. It ripped up both the 10-24 threads and the next 1/4 inch and separated the silver soldered joint to produce another reverse wound spring in one of the relief holes of the die. It did leave the 1/8 inch tube intact, but with a slight scaring of a groove in the silver solder coating on it. It could be the silver solder had not covered as well as I thought.

I also think my 8-32 die is bad (the three cutting sections are not equally spaced... it was cheap!) but I don't have another set so I cannot tell if a "good" die would do better.

I then grabbed a metric set and it has 4x.75 die. It destroyed both the 5/32 and 1/8 silver soldered tubes. Much too deep of threads.


Someone else, more adept than I, might get better results, but I don't think I would ever consider threading that thin walled tubing for any purpose.


All in all, I recommend you follow Eric's advice... Call Coles Power Models and get their MTP dies and thick walled tubing. BUT! Be prepared for sticker shock, as well as the necessity to practice a lot (and make lots of scrap) before you get a good usable part.


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## jimtyp (Jan 2, 2008)

CT, thanks for checking that. Sounds like it's not too feasible. 

I'll try Steve's suggestion next. I found a vented set screw:  Set Screw  

Looks like the drill size for an 8-32 tap would is a #29?


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## Mik (Jan 2, 2008)

How about ME (straight) threads instead of taper? They are definitely cheaper. See what PM Research in New York has... I KNOW they have pre threaded brass pipe nipples in 3/16 in stock as well, if it isn't too big.


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## SteveC (Jan 2, 2008)

Jim

The only concern I would have in your choice is it's length, at 3/16" length-over-all that will give you only 3/32" inside & outside the tube if you split the length evenly, which isn't much for either.

Did you happen to notice these *Hollow Lock Set Screws* that could be used as an external sleeve maybe? Note that the 5/16"-18 & 5/16"-24 both have a hex wrench size of 5/32". Since hex-wrenches are measured across-flats (AF) then your 5/32" tubing should fit. Additionally. 5/16" is a standard screw size.


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## SteveC (Jan 2, 2008)

Jim

Here's another possible solution, in looking at what McMaster-Carr has available in brass tubing, I found the following *Brass Round Tube;* OD 3/16", ID .0895", Wall .049".

If you can go up in OD by 1/32" (i.e. 5/32" to 3/16"), and you use a 10-32 die to thread the tube you'll wind up with an uncut wall thickness of .0311" which should be strong enough and still give you room to pass your wire through (i.e. depending on wire size).


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## jimtyp (Jan 2, 2008)

Mik, I'll check into PM Research, if end up going that roiute I'd rather have brass, thanks for the idea! 

Steve, I think I'll actually make that my next attempt, 'm going to give the thicker stuff a go  

I appreciate everyone's help!


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## SE18 (Feb 21, 2008)

would tining the end of the tube build up enough thickness?


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