External Threads on 5/8" DOM Tube Using a Die

[EddyCurr]

A local friend is trying to use a die to cut 5/8"-18 UNF threads on
0.625" x 0.125" DOM tubing.

He called me to say that the die is not doing the job. In efforts to
proceed, he has turned down the OD of the material below 0.600"
but is finding that while the die will start to thread, in short order
it ceases to pull itself forward and then damages the threads already
cut.

The die is a P&N, mfd in Australia.

When I checked for Major Diameter for a 5/8-18, I found tolerances
as follows:

Major Diameter

Max Min
1A - 0.6236 0.6105
2A - 0.6236 0.6149
3A - 0.6250 0.6163

I have suggested turning a fresh section down to about 0.6105 (1A Min)
to see whether the die needs more engagement to thread successfully.

I imagine that the DOM tube is both gummy and hard for trying to thread
with a die. Any suggestions (annealing?) that might help this are welcome.

I am traveling out to his site this afternoon. I am not sure whether there
are tools or bits there for threading with his lathe. My usual holders are
too big for his toolpost, but I am going to check whether I can cobble
something together.

.

[JoeLee]

This might sound like a stupid question...... but is he using the starting end of the die???

JL.......................

[mark61]

The welded seem of the pipe may be hard enough to make a problem for the die cutting? How long does he need?

mark61

[squirrel]

What alloy is it? You might have crappy die since it is not USA made. If you are trying to thread 300 series stainless with a hand die you will not have much success, it should be cut on a lathe.

[Toolguy]

Threading

I would single point most of the thread, then use the die to make it a uniform, repeatable finished size. That way the pipe could stay around .620 major diam..

[Mcgyver]

You might have crappy die since it is not USA made. .

I'd guess you were being sarcastic?

[Evan]

Drawn Over Mandrel tubing (DOM) is seamless. Take some chlorinated brake cleaner to use as lube. It will reduce the cutting effort to a third of other lubes. Don't breathe the fumes and do NOT inhale any products of combustion.

[EddyCurr]

Take some chlorinated brake cleaner to use as lube. It will reduce the
cutting effort to a third of other lubes. Don't breathe the fumes and
do NOT inhale any products of combustion.

Caution !

Before anyone tries this with chlorinated brake cleaner, they should
familiarize themselves with the dire/fatal consequences that can arise
from exposure to hydrogen chloride gas and phosgene gas.

... is he using the starting end of the die???

Reasonable question and not easy for me to answer at a glance. My
dies all have the starting taper on the side etched with identification.
Though I didn't actually measure it, I would have bet a small sum that
his P&N die was shaped to start on the side opposite the etching.

mark61 & squirrel, the required thread length appeared to be about 3".

This material is some grade of carbon steel, not stainless. The receipt
did not have a grade and I did not see markings on the short lengths
on the bench. However, Google brings up links that suggests that DOM
to ASTM A 513 is commonly 1010, 1020 and 1026; but can be 1008,
1015, 1035 and a number of other grades.

Something that surprised me is that DOM does (or did) have a seam.

Tiancheng Group

Drawn Over Mandrel (DOM) refers to high-strength, electrically-
welded tubing that has been further processed by cold drawing through
dies and over mandrels to improve its uniformity, mechanical properties
and surface finish.

The manufacturing process for DOM tubing begins with coils of steel,
which are slit to the proper width for the desired tube size. The strip
is cold formed and passed through an electric resistance welder which
joins the edges together, under pressure, to complete the tubular shape.
After testing the weld's integrity, the tubing is cut to length for further
processing.

The cold-drawing process creates a uniform, precision product with
substantially improved tolerances, surface finish and tensile strength,
increased hardness and good machinability. In this process, the tube is
cleaned and annealed, and one end of each length is squeezed to a point
so it can be gripped by the drawing mechanism. The tube is then drawn
through one or more dies and over mandrels (see drawing).

This reduces the diameter of the tube and thins its walls to the required
dimensions in a controlled fashion to provide the qualities desired in the
finished product. Metallurgically, drawing improves the tube's concentricity,
tensile strength, hardness and machinability. Close dimensional accuracy is
achieved through tight control of both outside and inside diameters.

Closer to home

ArcelorMittal

Tubular Products manufactures DOM tubing to ASTM Specification A513,
types 5 and 6, using the Electric Resistance Welding (ERW) process.
This process produces the highest weld strength possible. Because it is
colddrawn after forming, DOM also offers a number of other advantages

Certainly the seam is not noticeable in DOM the way that it is in other pipe.

Drawn Over Mandrel tubing (DOM) is seamless.

Not always.

exerpts from pg 4 of ArcelorMittal

Tubular Products’ seamless mechanical tubing is produced from solid
round billets by rotary piercing and then is rolled in an Assel mill ... Tubes
are then processed through a multiple-pass sizing reducing mill and a rotary
sizer.

Tubes to be cold-drawn are normalized or annealed, depending upon
application requirements, and are then pickled, washed, rinsed and coated
with a drawing compound.

They are then cold-drawn through a die and over a mandrel. Next they may
receive a final or stress relief anneal and are straightened to established
tolerances on a specially-designed, seven-roll straightener.

Timken refers to their seamless tube process as rotary forging, but on
examination, it instead appears to consist of a rolling & piercing operation.

I would single point most of the thread, then use the die to make it a
uniform, repeatable finished size. That way the pipe could stay around
.620 major diam..

I was out at his place for a couple of hours and saw first-hand that
the DOM was not the nicest material to cut.

He has a QCTP holder for internal/external threading and had already had
a go with it on the DOM without much success when I arrived. In the
end, he used the method Toolguy proposed above and was able to get
results that will let him move on with the project.

Thanks to everyone for the contributions.

.

[mike4]

What alloy is it? You might have crappy die since it is not USA made. If you are trying to thread 300 series stainless with a hand die you will not have much success, it should be cut on a lathe.

P&N dies are not crappy ,at least not the ones I have used over the last few years , some stainless is very difficult to thread without galling.

Is he using the correct lubricant for the alloy he is trying to thread?

[EddyCurr]

The previous post is lengthy - somewhere in there I mention that the
material appears to be a low grade of carbon steel.

What appeared to be cutting oil was being manually applied from a
squirt applicator.

The die looks fine, it hasn't suffered from the mauling dished out to
the DOM material. I believe I have some metric P&N taps I bought to
flesh out my selection - I have no complaints about their appearance
or performance.

.

[Evan]

News to me about the seams. The DOM I buy here is definitely seamless as it also goes by the name of "hydraulic tubing" and is used to make cylinders.

Chlorinated brake cleaner is indeed dangerous if heated by welding or similar means. It shouldn't pose a problem in a threading application and it evaporates quickly. I use it for tapping steels and it is remarkable how well it works. As is the case with many products used in machining the appropriate level of care must be taken. The same toxins are produced if PTFE is burned.

[DR]

Several potential problems here.......

What alloy is the tube? There could be a hard weld seam area from the manufacturing process in making the tube unless it's seamless tube. DOM tube is also likely work hardened from the sizing process unless it's been fully annealed.

Die nuts (as opposed to chaser type threading heads, Geometric, Landis, J&L, etc) do a poor job of cutting new threads. They're better suited to repairing damaged threads. Is the die nut HSS (most are worthless carbon steel)?


The best suggestion we've had so far is to single point the threads, then use the die to size them if needed.

[EddyCurr]

Is the die nut HSS?

Possibly. I was staring at it whilst trying to determine which side had
the starting taper and I have a floating retinal image of 'HSS' on the
etched side. However, I can only find a catalog that mentions Chrome
as P&N's die material.

DOM tube is also likely work hardened from the sizing process unless
it's been fully annealed.

No word on the grade of the tube, yet.

In the OP, I alluded to an attempt at annealing. As you say, the drawing
process would work harden the tube and if it was left in this condition,
threading would be more difficult.

If I can get a piece of the tube, I'd like to see if annealing makes a difference.

I believe that the annealing temperature lies within a range of 950؛F-1200؛F
/500؛C - 650؛C (Black Red - to - Blood Red in colour). Any thoughts on what
length of time pieces of 0.625 x 0.125" x 8" should be held at temperature
and what an ideal cooling rate should be ?

.

[EddyCurr]

News to me about the seams.

I'd always equated DOM with seamless, too.

.

[Walter]

Well, from my past experience; DOM and seamless are two different monsters all together. While seamless is rather nice to work with I always found DOM to be a bit tuffer to machine / work with. Sort of like the difference between working with 1144 and D2. Both are great products, but DOM was always what we turned to for on size applications. Seamless (IIRC) is usually oversize ID/OD and meant to be turned to size.