From Newsgroup: rec.crafts.metalworking

Hello there

A friend approached me seeking advice. First thought - you folk.

He is good at ali TIG welding.
He wants to make ali (aluminium/aluminum) tubular fittings for
vehicles - kit-out vans; spare-wheel holders; etc.

He knows of mandrels which are bellows-like stainless-steel.

He's expecting sizes 50mm and 42mm, wall-thk. 3mm to 4mm
That's 2inch and 1 21/32nd inch diameter, 1/8th inch to 5/32nd wall.

My own rough impression is that tube/pipe benders often pull a bend
radius about 3 tube diameters?

Recommendations and guidance?

Thanks in advance,
Richard Smith
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From Newsgroup: rec.crafts.metalworking

"Richard Smith" wrote in message news:m1wlz30y60.fsf@void.com...

He's expecting sizes 50mm and 42mm, wall-thk. 3mm to 4mm
That's 2inch and 1 21/32nd inch diameter, 1/8th inch to 5/32nd wall.

--------------------------------

Customary US practice is to dimension and measure wood to fractions and cut
or drill visually to marks, metal to decimals and work to DRO or leadscrew dial readings. Not knowing that, early import milling machines sometimes had
8 TPI leadscrews, 0.125" per turn. They are a real nuisance to use without a DRO unless you've memorized fractional equivalents.

Many things sold in the USA as inch sizes are actually metric, chain for instance. Tubing size is actual measurement, pipe is nominal size, based on thicker-walled wrought iron pipe for early steam power, and the size doesn't match any measurement.

An engineer friend converted John Browning's drawings for the .50 machine
gun from 128ths to decimals. Foreign designs we manufactured during WW2, the Merlin engine, Bofors and Hotchkiss AA guns, had to be completely redrawn to US standards including much tighter tolerances to eliminate hand fitting.

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From Newsgroup: rec.crafts.metalworking


Richard Smith <null@void.com> posted:

Hello there

A friend approached me seeking advice. First thought - you folk.

He is good at ali TIG welding.
He wants to make ali (aluminium/aluminum) tubular fittings for
vehicles - kit-out vans; spare-wheel holders; etc.

He knows of mandrels which are bellows-like stainless-steel.

He's expecting sizes 50mm and 42mm, wall-thk. 3mm to 4mm
That's 2inch and 1 21/32nd inch diameter, 1/8th inch to 5/32nd wall.

My own rough impression is that tube/pipe benders often pull a bend
radius about 3 tube diameters?

Recommendations and guidance?

Thanks in advance,
Richard Smith

There are tables for bending radius of various size tube. Many of the available bending dies are larger than the minimum bending radius for a particular size tube, but that also depends on wall thickness. Contrary to popular belief, a thicker wall tube is supposed to bend more consistently than a thinner wall tube without kinking.

Jim is right in that tube diameter and pipe diameter are very different. Tube diameter is very close to the stated diameter. For pipe diameter, if you don't have it on hand to measure, there are lookup tables.

Since you mentioned diameter specifically, I assume you are talking about round tube but, square tube is also bent. You have to put a crease on the inside side wall.

The die needs to be a tight fit to the tube, and lubrication is a big help. Of course, remember that some types of metal will work harden including aluminum.

Depending on the type of Bender and the tightness of the radius, you can often get good bends without one, but there is a way of bending using a mandrill on a rod inside the tube that helps reduce the distortion in shape.
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From Newsgroup: rec.crafts.metalworking

On 3/23/2026 10:06 AM, Bob La Londe wrote:

Richard Smith <null@void.com> posted:

Hello there

A friend approached me seeking advice. First thought - you folk.

He is good at ali TIG welding.
He wants to make ali (aluminium/aluminum) tubular fittings for
vehicles - kit-out vans; spare-wheel holders; etc.

He knows of mandrels which are bellows-like stainless-steel.

He's expecting sizes 50mm and 42mm, wall-thk. 3mm to 4mm
That's 2inch and 1 21/32nd inch diameter, 1/8th inch to 5/32nd wall.

My own rough impression is that tube/pipe benders often pull a bend
radius about 3 tube diameters?

Recommendations and guidance?

Thanks in advance,
Richard Smith

There are tables for bending radius of various size tube. Many of the available bending dies are larger than the minimum bending radius for a particular size tube, but that also depends on wall thickness. Contrary to popular belief, a thicker wall tube is supposed to bend more consistently than a thinner wall tube without kinking.

Jim is right in that tube diameter and pipe diameter are very different. Tube diameter is very close to the stated diameter. For pipe diameter, if you don't have it on hand to measure, there are lookup tables.

Since you mentioned diameter specifically, I assume you are talking about round tube but, square tube is also bent. You have to put a crease on the inside side wall.

The die needs to be a tight fit to the tube, and lubrication is a big help. Of course, remember that some types of metal will work harden including aluminum.

Depending on the type of Bender and the tightness of the radius, you can often get good bends without one, but there is a way of bending using a mandrill on a rod inside the tube that helps reduce the distortion in shape.

HEY! Posting from Newsgrouper worked! Woo! Hoo!
--
Bob La Londe
CNC Molds N Stuff
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From Newsgroup: rec.crafts.metalworking

"Jim Wilkins" <muratlanne@gmail.com> writes:

.... Foreign designs we manufactured
during WW2, the Merlin engine, Bofors and Hotchkiss AA guns, had to be completely redrawn to US standards including much tighter tolerances
to eliminate hand fitting.

I've heard of that.
The USA had this "production engineering" which shifted a massive amoutn
of things and moved the price to vastly open-up the market - "a virtuous circle" at those times.
Ford Motor Company in Britain were bemused by Rolls-Royce aero-engine
tolerance on drawings - their production cars were made to much tighter tolerances...
Thing is, we did have a very developed engine, and when hostilities
started that was the engine we mass-manufactured - or had manufactured
for us - "like shelling peas".

I took a friend of mine to Kelham Island Industrial Museum this Winter/Christmas, and there is the one-and-only drop forging die set for
Merlin engine crankshafts during the Battle of Britain... It's
"vastiferous" how much of history formed around that.
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From Newsgroup: rec.crafts.metalworking

"Richard Smith" wrote in message news:m1jyv15e1a.fsf@void.com...

"Jim Wilkins" <muratlanne@gmail.com> writes:

.... Foreign designs we manufactured
during WW2, the Merlin engine, Bofors and Hotchkiss AA guns, had to be completely redrawn to US standards including much tighter tolerances
to eliminate hand fitting.

I've heard of that.
The USA had this "production engineering" which shifted a massive amoutn
of things and moved the price to vastly open-up the market - "a virtuous circle" at those times.
Ford Motor Company in Britain were bemused by Rolls-Royce aero-engine
tolerance on drawings - their production cars were made to much tighter tolerances...
Thing is, we did have a very developed engine, and when hostilities
started that was the engine we mass-manufactured - or had manufactured
for us - "like shelling peas".

I took a friend of mine to Kelham Island Industrial Museum this Winter/Christmas, and there is the one-and-only drop forging die set for
Merlin engine crankshafts during the Battle of Britain... It's
"vastiferous" how much of history formed around that.

-------------------------------
You had the labor force to do the hand fitting. We never did, immigrants headed for land on the frontier. Our urban architecture is much plainer for lack of hungry artisans. Labor-saving automation was necessary here from the start, by Eli Whitney, Simeon North & co. Henry Ford had begun as a watch maker, an industry that excelled in precise mass production tolerance.

https://en.wikipedia.org/wiki/Simeon_North
"North is now generally credited with the invention of the milling machine, the first entirely new type of machine invented in America and one which, by replacing filing, made the production of interchangeable parts practicable."

The Merlin and Allison engines were mechanically comparable, the difference
is RR had in Hooker a fluid dynamics genius to improve the air flow and Allison didn't, mixture distribution was a continuing problem on the
Allison.

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From Newsgroup: rec.crafts.metalworking

"Jim Wilkins" wrote in message news:10pundq$1a98l$1@dont-email.me...

https://en.wikipedia.org/wiki/Simeon_North

Military contracts offered an advance to purchase production machinery that would make interchangeable parts to simplify field repair. Otherwise a gunsmith would have to custom fit and harden spares made under or oversized. Before bicycles, sewing machines and typewriters military firearms were the only high volume tight tolerance steel product with a guaranteed production run.

This was invented to machine twist drill flutes for firearms manufacture. https://americanprecision.org/learning-resources/machine-of-the-month-brown-sharpe-universal-mill/
"Universal" means the table swivels horizontally, to mill at angles. The indexer rotates the work in sync with table travel to cut a spiral.

When I visited it was stored upstairs. When the manager saw I was taking photos with a 1936 Leica he brought out his own, chatted, and then let me wander through the storage rooms. I identified the machines from pictures in this:
https://www.gutenberg.org/ebooks/72046

Another treasure from an arms maker up there was an automatic lathe,
invented by Christopher Spencer who produced the most used US Civil War assault rifle.
https://en.wikipedia.org/wiki/Christopher_Miner_Spencer https://en.wikipedia.org/wiki/Spencer_repeating_rifle https://americanprecision.org/learning-resources/automatic-lathe-1871/
It's a general purpose turret lathe operated by a slowly revolving drum underneath surfaced with bolt-on cam plates instead of an operator on a
lever.

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From Newsgroup: rec.crafts.metalworking

"Jim Wilkins" wrote in message news:10pundq$1a98l$1@dont-email.me...

The Merlin and Allison engines were mechanically comparable, the difference
is RR had in Hooker a fluid dynamics genius to improve the air flow and
Allison didn't, mixture distribution was a continuing problem on the
Allison.

----------------------------
Here is further discussion on the differences. https://www.quora.com/Why-was-the-Merlin-engine-better-than-the-Allison

Engine durability wasn't too important at home but very significant for distant jungle or island bases.

The Spitfire and Merlin were the best for the defense against escorted
German bombing raids that Britain required. The fighting over Europe reached very high altitudes where the Merlin's superior supercharger gave it the advantage.

The P-38 effectively used turbocharged Allisons in its two nacelles which didn't also have to contain a cockpit and fuel tanks. It was the only twin engine plane that could fight fairly equally with single engine fighters,
the Mosquito had to try to outrun them and failed when they could dive from higher altitude. The P-38 had initial difficulties that weren't solved fast enough to keep up with the progress in Europe so the P-51 replaced it. The final -L version proved excellent in the Pacific which accepted and made
good use of whatever Europe turned down.

European fighter planes maximized turning performance by decreasing the
weight of fuel carried and thus their range, and they were too compact to
add more tanks later. That didn't matter when defending but limited their abilities to attack over each other's territory. German fighters had fuel
for only 10 minutes at full throttle over London and couldn't escort at all much further in. Spitfires couldn't escort bombers a significant distance
into Germany. America didn't require local air defense and could trade a little turning performance for much greater range, enough to defeat the
enemy instead of holding them off. Different needs, different solutions.

The Zero had the best combination of long range and tight turning at the expense of armor protection, Japanese design emphasized attack over defense. In the few Pacific encounters they defeated Spitfires. Once we discovered their limitations of no armor and loss of maneuverability at high speed they became fairly easy for our heavier and faster planes to defeat by
hit-and-run. The run was a criminal offense in other forces but trying to out-turn a Zero was suicide. Their Navy never perfected catapults to replace the Zero with their Army's faster and heavier late war designs on aircraft carriers.

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From Newsgroup: rec.crafts.metalworking

On 3/26/2026 5:24 AM, Jim Wilkins wrote:

"Jim Wilkins"-a wrote in message news:10pundq$1a98l$1@dont-email.me...

The Merlin and Allison engines were mechanically comparable, the difference is RR had in Hooker a fluid dynamics genius to improve the air flow and Allison didn't, mixture distribution was a continuing problem on the
Allison.

----------------------------
Here is further discussion on the differences. https://www.quora.com/Why-was-the-Merlin-engine-better-than-the-Allison

Engine durability wasn't too important at home but very significant for distant jungle or island bases.

The Spitfire and Merlin were the best for the defense against escorted German bombing raids that Britain required. The fighting over Europe
reached very high altitudes where the Merlin's superior supercharger
gave it the advantage.

The P-38 effectively used turbocharged Allisons in its two nacelles
which didn't also have to contain a cockpit and fuel tanks. It was the
only twin engine plane that could fight fairly equally with single
engine fighters, the Mosquito had to try to outrun them and failed when
they could dive from higher altitude. The P-38 had initial difficulties
that weren't solved fast enough to keep up with the progress in Europe
so the P-51 replaced it. The final -L version proved excellent in the Pacific which accepted and made good use of whatever Europe turned down.

European fighter planes maximized turning performance by decreasing the weight of fuel carried and thus their range, and they were too compact
to add more tanks later. That didn't matter when defending but limited
their abilities to attack over each other's territory. German fighters
had fuel for only 10 minutes at full throttle over London and couldn't escort at all much further in. Spitfires couldn't escort bombers a significant distance into Germany. America didn't require local air
defense and could trade a little turning performance for much greater
range, enough to defeat the enemy instead of holding them off. Different needs, different solutions.

The Zero had the best combination of long range and tight turning at the expense of armor protection, Japanese design emphasized attack over
defense. In the few Pacific encounters they defeated Spitfires. Once we discovered their limitations of no armor and loss of maneuverability at
high speed they became fairly easy for our heavier and faster planes to defeat by hit-and-run. The run was a criminal offense in other forces
but trying to out-turn a Zero was suicide. Their Navy never perfected catapults to replace the Zero with their Army's faster and heavier late
war designs on aircraft carriers.

I had heard that the primary thing that defeated the Zero was evaluation
of a captured wreck where they discovered that the pilots likely didn't
have the strength to muscle the controls against torque in certain
maneuvers. It meant they ALWAYS turned the other way making it easy to predict and the Zero would travel right across the allied pilot's gun
sights.
--
Bob La Londe
CNC Molds N Stuff
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From Newsgroup: rec.crafts.metalworking

"Bob La Londe" wrote in message news:10q3t47$1a9n7$1@dont-email.me...

I had heard that the primary thing that defeated the Zero was evaluation
of a captured wreck where they discovered that the pilots likely didn't
have the strength to muscle the controls against torque in certain
maneuvers. It meant they ALWAYS turned the other way making it easy to
predict and the Zero would travel right across the allied pilot's gun
sights.
Bob La Londe
CNC Molds N Stuff
------------------------------------

https://en.wikipedia.org/wiki/Mitsubishi_A6M_Zero
The reports on the Zero from China were ignored.

It had several weaknesses that resulted from its light weight and strength margin of only 1.5X, less than the standard of the time. The idea was if it could turn tighter than any other fighter it didn't need the weight of protection from the rear. It's been called the ultimate WW1 fighter. Japan wasn't alone in assuming the next war would be an extension of WW1. There
was relatively little advancement during the 20's and 30's, Germany, Italy, Britain and Russia began the war with biplanes still in combat use. https://padresteve.com/2015/05/26/16999/

I have designer Horikoshi's book on creating the Zero, in which he details
the difficulty of making a new higher performing plane as nimble as an
older, lighter one. He was watching a high speed dive test when the plane loudly broke apart from stress and plunged into the sea along with the
pilot. That caused the diving speed limitation, some US planes were faster
in level flight. At high enough dive speed air pressure froze the controls
and prevented maneuvering, the reason why a kamikaze had to be destroyed
with 40mm or 5" cannon shells instead of just killing the pilot.

On rec.aviation.military I discussed the book with Erik Shilling who had
been the engineering officer of the Flying Tigers in China. He claimed they fought Zeros, or Army Zeros, there's evidence at least some may have been
the very similar and even lighter and more nimble Ki-43 Oscar, which lacked the Zero's carrier landing reinforcement and 20mm cannons.

Horikoshi was very proud of his work but not to the extent of making
excessive claims, he also described the problems that aero engineering in Japan faced; inflexible demands, limited materials, too few skilled technicians and high power engine development issues they didn't have a
stress and vibration genius like Stephen Timoshenko to solve. https://en.wikipedia.org/wiki/Stephen_Timoshenko

Germany had a similar problem of drafting too many scientists, engineers and technicians. I think some of the wilder proposals for wonder weapons were merely self-preservation attempts. We argued that on r.a.m. with two Nazi supporters who claimed they could have won if only the war had lasted a
little longer. The general who commanded the jet fighters had stated if he could have stopped the Allied bombing the Russians would have simply
conquered further west.
https://www.facebook.com/groups/luft46/
Never mind that the 1200+ jet fighters they did build had little effect, and couldn't even defend their own airfields. AA fire became the main danger to bombers.

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"Jim Wilkins" wrote in message news:10q4fbr$39hmf$1@dont-email.me...

...

This is a good description of the problems and solutions in powering a plane at high altitude:

http://cdn.olpl.org/documents/AirplanePower1943.pdf

The drawings are of an Allison engine in a P-40 which was designed for and excelled at low level infantry support, and had a sea level supercharger
that was effective up to 15,000 feet. Due to higher altitude power loss a
P-40 needed half an hour to reach 30,000 feet, making it useless over
Britain. The engine has to be throttled down at low altitudes to limit manifold pressure and avoid damaging preignition, "knock".

WW1 had ended all European wars. During the Depression there was no extra money to plan to fight overseas and insufficient risk of threat from high altitude enemy bombers. Enemy carrier planes such as torpedo and dive
bombers operate at low level, P-40s shot some down at Pearl Harbor.

The bulk of the P-47 was needed to contain its turbocharger ducting. The
P-38 was an out-of-the-box design that avoided Army fighter specification restrictions by creating a new class of "interceptor" instead.


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