"John B." wrote in message
...
On Fri, 15 Apr 2016 17:02:48 -0400, Ed Huntress
wrote:
On Fri, 15 Apr 2016 16:14:43 -0400, "Jim Wilkins"
wrote:
"Ed Huntress" wrote in message
...
On Fri, 15 Apr 2016 12:35:08 -0700, Larry Jaques
wrote:
On Fri, 15 Apr 2016 06:01:39 -0500, Karl Townsend
wrote:
I've got a project where i need over a hundred feet of 1.38 ID
by
1.625 OD DOM tubing.
Turns out this is almost exactly the same size as 1 1/4 water
pipe,
MUCH less expenisve.
Need to do a lot of machining and some bending of a small tab.
Will
water pipe work as well?
I'd seen the term "DOM" mentioned a few times recently, and
finally
decided to find out what it was. Here are some of the sites I
visited
in my research which might be of interest to you, Karl.
http://tubular.arcelormittal.com/ima...l_DOMSpecs.pdf
https://www.rme4x4.com/showthread.ph...s-D-O-M-tubing
http://metalsupermarkets.com/blog/di...seamless-tube/
https://www.youtube.com/watch?v=buu3Ytubp1s
http://www.jalopyjournal.com/forum/t...tubing.286487/
http://products.anssteel.com/item/st...un-1-1-4-2272?
http://products.anssteel.com/item/steel-pipes/galvanized-standard-steel-pipe/g-1-1-4-2272?&bc=100|1002|1016|1047|1049
http://www.industrialgroupco.com/ass...ifications.pdf
Pipe seems to be made from a mutt steel; whatever they find. If
I
were making a simple bench or something for intermittent use or
of a
light-duty nature, I'd use pipe, the cheapest.
If I wanted a chassis for a vehicle of some sort, I'd definitely
want
to go with DOM. It has a much higher safety factor. 1020 seems
to
be
the standard the 4-wheelers use.
I'd also avoid 4130. Chromoly is nice, but is way too expensive
and
too finicky for proper welds.
Not really. It's easy to weld with O/A or TIG. You just have to
know
how it behaves, and if you won't learn that, I wouldn't want to
ride
in anything you welded, anyway.
1020 is (or was) used on NASCAR racers, for two reasons: The
weight
restrictions allow(ed) you to use tubing so heavy that you're at
the
limit of practical strength anyway, even with 1020; and if
(scratch
that -- "when") you crash it, you can cut out old tubes and
replace
them without worrying about it.
--
Ed Huntress
I didn't have any trouble welding 4130 aircraft tubing tees for
practice.
Wasn't there a problem with chrome-moly frames so strong and stiff
they overstressed and killed the driver instead of progressively
absorbing energy?
--jsw
No, it's just somebody's old tale. I've heard it before, too.
First, the stiffness of 4130 and 1020 are almost exactly the same
(as
is true of all steels, except for the slightly less-stiff
stainless).
Second, there isn't *that* much difference in strength. (yield is
around 65 ksi for normalized 4130; 54 ksi for DOM 1020). The
ductility, elongation and ultimate tensile strength are better for
4130 than for 1020 in the hard-drawn condition. 4130 tubing is
almost
always used in the normalized condition; 1020 in the hard-drawn
condition.
So you get some more strength and a lot more ductility with 4130.
Your
welds can be somewhat stronger because hard-drawn 1020 loses a lot
of
its strength from heating at the weld. 4130 is very
slow-quenching --
on the verge of air-hardening, and, in thin sections (like the
light-gauge tubing used on aircraft and smaller race cars), it *is*
air-hardening. Strength *at the weld* is pretty good.
It can get tricky with thicker sections. There is a lot of voodoo
surrounding 4130, but the major welding equipment suppliers can
clear
that up for you if you ask. They also have info about it on their
websites.
BTW, the Brits, including Lotus, Cooper, Vanwall, etc., used 1020 or
its equivalent for race cars through the '60s, and they performed as
well as 4130 cars. They bronze-brazed their chassis joints, for the
most part. Chassis stiffness is the issue, unless you care about the
safety of your drivers, which some didn't. g 1020 is just as
stiff.
If I remember correctly Norton built some of their racing frames
using
"bronze-welding" and claimed that the brazed joints were an
advantage
as they were less stiff then welded joints and didn't break as often
:-)
John B.
A flexible end connection is called "pinned", and if done right it
allows the connected members to behave as centrally loaded columns
with no imposed bending to weaken them in compression.
http://www.redbuilt.com/documents/Pin_vs_Plated.pdf
http://www.eng-tips.com/viewthread.cfm?qid=4945
The Tay Bridge collapse is a notorious example of a pinned-joint
structure whose failure was analyzed in detail. You don't hear about
the bridges that survived.
http://www.open.edu/openlearn/scienc...nt-section-4.5
Figure 29 shows an intact and a failed pinned joint between the
columns and the diagonal braces. Subsequently the recently introduced
affordable steel quickly replaced wrought and cast iron for bridges.
The design should have been strong enough, but the casting of the
columns was seriously deficient and the supervising engineer was a
mason more interested in the troublesome footings.
The I-35 bridge in Minneapolis failed at a rigid truss joint:
https://en.wikipedia.org/wiki/I-35W_...i_River_bridge
--jsw