Author Topic: "The LM was made of aluminum foil and tape!" - counterargument  (Read 2256 times)

Offline bknight

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #30 on: September 11, 2019, 11:30:42 AM »
I'm not familiar with gaffer's tape, but you work with all these kinds of tapes and if you recommend it, somebody lurking in the wings should pay attention.  8)

I guarantee you've seen it.  It's the black cloth tape that electricians and other technicians in film and theater ("gaffers") use to tape cables down.  It actually comes in different colors, but black is by far the most common.  The substrate is a cloth duck, so it's very durable.  It can be torn with the fingers.  It's electrically insulating and able to endure quite high heat.  The adhesive releases easily from any surface, but it sticks quite well in the meantime.  The disadvantage is cost.  A large roll of high quality gaffer tape will set you back about $12.  Our theater buys it by the case, so I get a deal.

But as with duct tape and the home handyman, gaffer tape is the go-to way to temporarily repair almost anything in the film and theater world.  Gray gaffer's tape, manufactured by Shurtape, was what was carried on the Apollo missions.  Apollo 13's LiOH canister adapter was rigged using gaffer tape.

And here I thought it was duct tape, but as per normal I learn something again that I didn't know.  :)
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Offline JayUtah

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #31 on: September 11, 2019, 11:36:43 AM »
And here I thought it was duct tape, but as per normal I learn something again that I didn't know.  :)

Back in the day, duct tape was closer to gaffer tape than it is now.  The tape I've removed from old ducts (with full PPE, because asbestos) is close enough to gaffer tape to be essentially the same product sold under different names.
"Facts are stubborn things." --John Adams

Offline ka9q

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #32 on: September 12, 2019, 11:52:00 AM »
Speaking of the tape used to hold the thermal blankets on the LM, it was almost certainly Kapton. That's the DuPont trademark for a polyimide plastic. It has an orange color, the darkness depending on the thickness. Kapton's forte is its ability to withstand a very wide temperature range.

You can readily buy it today. I have a roll of it somewhere that I've used on our high altitude student balloon experiments. It gets very cold up there.

Offline JayUtah

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #33 on: September 12, 2019, 01:15:32 PM »
Speaking of the tape used to hold the thermal blankets on the LM, it was almost certainly Kapton.

Not almost certainly, definitely certainly.  That was one of the boons of rehabilitating poor LM-2.  Some of its constituent components were still being made and sold -- namely, Kapton tape.  And yes, one can get it in varying degrees of stickiness.  I admit I probably went down the rabbit hole of pressure-sensitive adhesives and their varying availability.  There's no engineering requirement I'm aware of that specified a tape for the LM that was stickier than an over-the-counter version.  You can literally buy this stuff at Home Depot.  That doesn't make it unsuitable for aerospace.
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Offline Count Zero

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #34 on: September 15, 2019, 08:47:09 AM »
I've always thought that looking at the outside skin of the Lunar Module, and deciding that it's construction is too flimsy was just plain weird.  This makes no sense.  Do they think their shirt is holding them upright in their chair?  No?  What about their skin - is that holding them up?

What is important is what's under the skin, so let's have a look at what's under the LM's skin:


Here it is one on the factory floor at Grumman Aviation in Long Island.
To the left is the Descent Stage.  Note that it is not actually octagonal, but rather is five box structures welded together, with vertical reinforcements rather like a wine box.  This provided fantastic vertical strength for the mass of material used; allowing it to support the weight of the Ascent Stage during Saturn V liftoff, and also for it to serve as a launch pad for the AS when it takes off.

To the right is the Ascent Stage.  You can see that the inner skin of the pressurized crew cabin is supported by closely-spaced ribs for maximum strength at minimum weight.  One of the ascent fuel tanks is visible to the right.


Here is the Ascent Stage of the LM,viewed from the right-rear.  To the right (partially obscured) is the drum-like crew compartment.  To the left is the aft electronics bay.  You can see the thin stringers from which the outer skin will hang, but don't get them confused with the much sturdier structural framework underneath that you can see supporting the AEB and oxidizer tank.


Here's another view of the Descent Stage, showing its rugged construction.  The descent fuel & oxidizer tanks are inside the boxes.  The triangular sections between the outer boxes were storage areas for auxiliary tanks and equipment the astronauts would need on the Moon, including tools, science packages and, on the later missions, the folded-up lunar rover.

Grumman, whose proud engineers built the Lunar Module, also built the best and most durable naval aircraft ever - they didn't do flimsy.


When I first saw pictures like this, I thought that they had formed the skin to the right shape, and then added the ribs, or that they built the rib framework and the attached the inner skin to it, like you would build a ship.

The reality is far more interesting and clever (and stronger):  The skin & ribs are a single block of aluminum!  They milled-down the sections between the ribs to the desired skin thickness.  They did this for each section of hull, then welded the sections together at strong edges.

Here are pictures of the pieces coming together (click on the little blue arrow on the right to page through each pic).

Grumman went onto use the same technique to build the F-14 Tomcat.

Hope this helps

 8)
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Offline JayUtah

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #35 on: September 15, 2019, 01:20:17 PM »
What is important is what's under the skin, so let's have a look at what's under the LM's skin:

This is why any LM fan needs to make a pilgrimage to Hutchinson, Kansas.  They have a LM ascent stage pressure hull you can inspect relatively up close.

Sadly none of these photos reveal the real structural design of the ascent stage.  This page is instructive.  http://heroicrelics.org/info/lm/lm-structural.html  Scroll to the Ascent Stage Midsection drawings, SK 17-31-18 (3 sheets).  These describe the central structural core of the ascent stage.  It's built very much like the wing box of a large airliner's airframe -- the thing that takes the brunt of aerodynamic loads in several directions.  The fore and aft frames of this box are machined frames.  You start with a slab of aluminum and machine away everything that's not a structural load path, leaving behind only a thin webbing between the bosses.  This is why aerospace is so expensive.  You start with a chunk of rather expensive metal and throw away 80 percent of it.  But the result is as light and strong as a frame can be.  The fore and aft frames are connected with a ventral beam assembly

See figure R-123 in the ANR:  https://www.hq.nasa.gov/alsj/LM19_LM_Manufacturing_ppB10-17.pdf

What's in this part of the LM?  Mostly the ascent engine and the environment equipment and controls.  The crew cabin is cantilevered out front of this structure, so that the crew and flight instruments balance the AEB to provide inherent pitch stability.

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To the left is the Descent Stage.  Note that it is not actually octagonal, but rather is five box structures welded together, with vertical reinforcements rather like a wine box.

We still build spacecraft chassis like this, where possible.  That is, we design them presuming they'll be made of a honeycomb sheet or other such material.  This is the aerospace equivalent of corrugated cardboard.  We can cut it into shapes, then we weld, glue, or bolt the shapes together, oriented in different cardinal directions, to build up the desired shape.  Not the outer boundary of the shape, but an internal wine-box  arrangement.  The electronics, propulsion, tankage, and what-not to support the spacecraft's mission are attached to these pieces.  Then the outer skin goes over that, which may or may not contribute to the overall structural design.

Grumman was well ahead of its time.

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To the right is the Ascent Stage.  You can see that the inner skin of the pressurized crew cabin is supported by closely-spaced ribs for maximum strength at minimum weight.

The skin-and-stringer method of building lightweight structures is no secret.  Everyone uses it.  The corrugated parts of the Saturn V show the interstage portions, where the skin is not being stiffened by pressurized propellant.  The stringers there were on the outside.  In the airplane designs of the time (and earlier), the stringers were on the inside.  Normally you assemble these out of sheet metal.  You cut strips of metal, bend them in a press brake, and then weld, rivet, or glue them to the skin (often made from the same material as the stringers).  It behaves like corrugated cardboard with one of the facing sheets removed.  it will bend very easily at right angles to the stringers, but remains exceptionally strong in the other direction.

For airplanes, the stringers are attached to the formers first, and then the skin is riveted or screwed on, usually from the outside.  In advanced expressions of this standard method, the skin takes a lot of the structural load.  So temporary fasteners called clecos are inserted in the rivet holes until the permanent rivets are installed.  Building an airliner is surprisingly like building a ship.  You lay a ship's keel.  You also lay an airliner's keelspar.  To the ship's keel you attach frames at intervals along the keel's length  These frames describe the shape of the ship as if it had been sliced at intervals moving fore and aft.  The shapers in an airliner's structure perform the same function.  Then between the frames/shapers you attach the stringers at intervals, and onto this, the skin.  The lunar module's longerons and stringers go every which way because there is very little other structure besides the skin and stringers at that point.  Internal structure of the cabin was more concerned with those blasted windows.

When you see the complicated shapes that the ascent stage had to achieve, you see that the typical skin-and-stringer assembly methods wouldn't really work anyway.  The stringers would have to attach at odd angles  There would be tight corners where rivet guns couldn't reach.  You could weld the skin together, but aluminum sheets that are thick enough to weld would be too heavy.  Enter chem-milling.  That's a process whereby you mask off certain parts of a sheet of material, then dip it in acid that eats away the unmasked portions to a carefully controlled depth.  So you cut a sheet of aluminum into the right shape, like a dress pattern.  Then you form if (if necessary) by rolling.  Then you chem-mill away the parts that don't need to be thick enough to weld, or to attach stringers to.  What you have is a thin plate of aluminum that is thick enough to weld or rivet, but only in exactly the places where it needs to be that thick.  Elsewhere it's only as thick as it needs to be to hold cabin pressure.

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You can see the thin stringers from which the outer skin will hang...

Minor nitpick:  I will argue those are struts, not stringers.  Yes, the thermal skin attaches to it, but its structural role here has it acting in longitudinal compression.  The thermal skin is about as thick as the sheet metal used in the U.S. to make HVAC ducts.

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The triangular sections between the outer boxes were storage areas for auxiliary tanks and equipment the astronauts would need on the Moon, including tools, science packages and, on the later missions, the folded-up lunar rover.

The end caps on the cruciform structure were for structural strength, not necessarily to protect (as with a skin) what was contained therein.  Because the struts for the landing gear attach there, the end caps resist the torsion load that would occur if the LM landed at a more acute angle than strictly planned.

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Grumman, whose proud engineers built the Lunar Module, also built the best and most durable naval aircraft ever...

I had the pleasure of helping to restore an F-14 Tomcat when I was a volunteer at a small air museum in Oakland, California back in the 1990s.  Tom Kelly's team built that too.

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When I first saw pictures like this, I thought that they had formed the skin to the right shape, and then added the ribs...

The reality is far more interesting and clever (and stronger):  The skin & ribs are a single block of aluminum!  They milled-down the sections between the ribs to the desired skin thickness.  They did this for each section of hull, then welded the sections together at strong edges.

I've been saying that for years, so you're to be forgiven for repeating it.  But I've lately found out (after having a good close look at the construction) that the integrated skin-and-stringer method was used only for very small elements.  (I also asked some people, to confirm it.)  The larger ones, which comprise what you can see in the photos, were made in a semi-traditional way.  Which is to say, the skin and stringers were separate pieces.

As I said above, the only milling done on the skin was done chemically, and it was done to selectively reduce the thickness of the skin where not required.  The skin was 0.055 to 0.065 inch thick under the stringers, and somewhat thicker (I don't have an exact figure) at the edges where welding might occur.  The spaces between the stringers were only 0.015 to 0.025 inch thick.  (For comparison, a carbonated beverage can in the U.S. is 0.015 inch thick.)  The variable thickness was achieved by chem-milling.  The stringers were either formed or milled, depending on whether they were for flat or curved sections, and attached by various means.

The confusion is natural, even among engineers, because that's exactly how we make some of the formers.  As I said above, you start off with a slab and then mill it down to have just a very thin web between the thicker remaining parts that bear most of the load.  If you wanted to go extremely thin, past the point where mechanical milling is no longer feasible, you could conceivably use chemical processes to erode the material further, leaving essentially a large integrated skin and stringer component.  I don't know of anyone who does that, though.  Such a thing would be strong, though, that one in which the stringers are attached later.  This is because the loads passed between skin and stringer wouldn't be concentrated at attachments or weldments that would need to be thicker than the surrounding material to bear them.

I said semi-traditional methods.  The skin panels were typically welded together first, then the stringers were attached.  This is the reverse of the typical process.  In aircraft the stringers are longerons too, and are attached first to the formers.  In the Saturn V, the skin and stringers were assembled first as a large sheet, then formed into the shape of the rocket.

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Grumman went onto use the same technique to build the F-14 Tomcat.

It definitely shows.  Crawling around in the guts of one of those, you definitely see echoes of the LM.
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Offline bknight

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #36 on: September 16, 2019, 10:59:42 AM »
The start with a block of metal and mill away everything but the thin shell is astounding to me.  I continue to learn fact from this web site.
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Offline Northern Lurker

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #37 on: September 16, 2019, 12:01:28 PM »
I know metallic swarf from mechanic machining can be recycled. Can chem milled metal be reclaimed and recycled?

Offline JayUtah

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #38 on: September 16, 2019, 12:23:36 PM »
The start with a block of metal and mill away everything but the thin shell is astounding to me.  I continue to learn fact from this web site.

A lot of mechanical parts are made this way.  You start with a billet that's slightly thicker than the thickest part, face it (to create exactly parallel top and bottom surfaces), and then mill away large amounts of it.

Imagine the end cap to some casing for a mechanical assembly such as a gear train.  You could just have a plate cut to the right outline, with a hole for the shaft and smaller holes for the bolts.  And that's the cheap, simple way.  But let's say you wanted a bearing for the shaft.  You could allow the casing to be 50 mm thick there, but maybe only for a 15 mm radius beyond the shaft.  Then you want a similar buildup of material around the bolt holes.  The face material may not have to bear pressure.  It may only need to keep in the lubricant and keep out particle contaminants.  It may need to be only 3 or 4 mm thick.  But that's not strong enough to handle the loads between the shaft bearing and the bolt holes.  But because we know how stress acts in a material, we can allow thick ribs -- say 20 mm thick and 20 mm wide -- between the shaft bearing and the bolt holes.  This accomplishes the structural goals without all the weight.

Another related case for the same part would be if the part needed (or wanted) to be domed in some fashion.  Instead of a metal forming process, which may leave microfractures and weird stress effects, you would machine it out of a thickness of stock that can accommodate the dome.  It's like turning a wooden bowl on a lathe, only with possibly more complex geometry.
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Offline JayUtah

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #39 on: September 16, 2019, 12:33:55 PM »
I know metallic swarf from mechanic machining can be recycled. Can chem milled metal be reclaimed and recycled?

Yes, for certain values of "can."  Since the chemicals are difficult to handle and almost always toxic, any process that involves them is expensive and dangerous.  And the amount of metal you get out of the process is small; the goal is almost always to recycle the chemical for reuse.  The metals are generally present as ions in the solution and must be extracted chemically, usually also involving a fair amount of energy input.  This is different than simply sweeping up shop waste or emptying filters and washing off the lubricant materials for mechanical recycling.  Recycling the chemical baths is not always cost-effective.  But increasing attention to environmental concerns are changing that equation.  Recycling chemical consumables from engineering processes is kind of a hot button for research in academic engineering these days.  I'd like to think that Grumman did the responsible thing and properly recycled all its chemicals from the LM construction.  But it was the 1960s, so maybe.
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Offline bknight

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #40 on: September 16, 2019, 01:57:12 PM »
The start with a block of metal and mill away everything but the thin shell is astounding to me.  I continue to learn fact from this web site.

A lot of mechanical parts are made this way.  You start with a billet that's slightly thicker than the thickest part, face it (to create exactly parallel top and bottom surfaces), and then mill away large amounts of it.

Imagine the end cap to some casing for a mechanical assembly such as a gear train.  You could just have a plate cut to the right outline, with a hole for the shaft and smaller holes for the bolts.  And that's the cheap, simple way.  But let's say you wanted a bearing for the shaft.  You could allow the casing to be 50 mm thick there, but maybe only for a 15 mm radius beyond the shaft.  Then you want a similar buildup of material around the bolt holes.  The face material may not have to bear pressure.  It may only need to keep in the lubricant and keep out particle contaminants.  It may need to be only 3 or 4 mm thick.  But that's not strong enough to handle the loads between the shaft bearing and the bolt holes.  But because we know how stress acts in a material, we can allow thick ribs -- say 20 mm thick and 20 mm wide -- between the shaft bearing and the bolt holes.  This accomplishes the structural goals without all the weight.

Another related case for the same part would be if the part needed (or wanted) to be domed in some fashion.  Instead of a metal forming process, which may leave microfractures and weird stress effects, you would machine it out of a thickness of stock that can accommodate the dome.  It's like turning a wooden bowl on a lathe, only with possibly more complex geometry.

As a youngster, I did witness the finishing of a crankshaft from an piece that hand been poured, I guess, into a mold, left to harden.  After cooling then the machinist milled holes and then finished the bearing surfaces.  It was cool and much better IMO than taking one out of a junk yard and then replacing in the engine.
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Offline jfb

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #41 on: September 16, 2019, 02:52:52 PM »
The start with a block of metal and mill away everything but the thin shell is astounding to me.  I continue to learn fact from this web site.

A lot of mechanical parts are made this way.  You start with a billet that's slightly thicker than the thickest part, face it (to create exactly parallel top and bottom surfaces), and then mill away large amounts of it.

Imagine the end cap to some casing for a mechanical assembly such as a gear train.  You could just have a plate cut to the right outline, with a hole for the shaft and smaller holes for the bolts.  And that's the cheap, simple way.  But let's say you wanted a bearing for the shaft.  You could allow the casing to be 50 mm thick there, but maybe only for a 15 mm radius beyond the shaft.  Then you want a similar buildup of material around the bolt holes.  The face material may not have to bear pressure.  It may only need to keep in the lubricant and keep out particle contaminants.  It may need to be only 3 or 4 mm thick.  But that's not strong enough to handle the loads between the shaft bearing and the bolt holes.  But because we know how stress acts in a material, we can allow thick ribs -- say 20 mm thick and 20 mm wide -- between the shaft bearing and the bolt holes.  This accomplishes the structural goals without all the weight.

Another related case for the same part would be if the part needed (or wanted) to be domed in some fashion.  Instead of a metal forming process, which may leave microfractures and weird stress effects, you would machine it out of a thickness of stock that can accommodate the dome.  It's like turning a wooden bowl on a lathe, only with possibly more complex geometry.

Every now and again a random video will show up in my YouTube feed demonstrating CNC and milling machines cutting out gears and parts from solid blocks of aluminum, and I'm always amazed by the following:

  • The amount of material that gets milled away (which I'm assuming is fairly easily recycled);
  • The fact that the cutting bits last for more than a minute - aluminum's not that soft;
  • The speed with which they cut - I can't cut wood that fast;

I'm one of those people who's less impressed by the building than by the crane used to build it.  When you look at the tools behind something, they're almost always far more interesting pieces of technology than what they build. 

Offline JayUtah

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #42 on: September 16, 2019, 03:19:00 PM »
The "cast-then-machine" fabrication steps have been de rigueur since probably the early 1800s.  I think the Periscope Films channel on YouTube is the one that has a lot of films on vintage industrial processes.

The cutting tools on the newer CNC machines are fantastically expensive.  The machines are amazing not only for their cutting power, but for the ability to zip through the manufacturing space with sub-mil accuracy.  The ability to stop milling, fly over to the tool crib, change tools, and fly back to the same place to a precision of 0.0001 inch blows my mind.
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Offline Everett

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #43 on: October 18, 2019, 07:18:30 PM »
Speaking of production methods, there are times when "cast then machine" has its downsides, though...

Looking at WWII weapons where "produceability" was a very important factor, "cast then machine" is a very time/machine/material intensive way to make a part - when the goal was to make as many as possible as fast and cheap as possible. Almost the inverse of spacecraft. The 40mm Bofers (Swedish design) and 20mm Oerlikon (Swiss design) were great weapons, but the original designs were not quite suited for mass production:

"It should be noted that the USN considered the original Bofors Model 1936 design to be completely unsuitable for the mass production techniques required for the vast number of guns needed to equip the ships of the US Navy. First, the Swedish guns were designed using metric measurement units, a system all but unknown in the USA at that time. Worse still, the dimensioning on the Swedish drawings often did not match the actual measurements taken of the weapons. Secondly, the Swedish guns required a great deal of hand work in order to make the finished weapon. For example, Swedish blueprints had many notes on them such as "file to fit at assembly" and "drill to fit at assembly," ::) all of which took much production time in order to implement - there is a story that one USA production engineer remarked that the Bofors gun had been designed so as to eliminate the unemployment problems of the Great Depression."

(I presume a design for "file/drill to fit on assembly" is a quick way to end the design's engineer's current employment? :)) )
The Oerlikon was just as bad if not worse:

"It should be mentioned here how unsuitable the original Oerlikon design of the Mark 1 was for mass production. Each weapon needed to be tailor made with a great deal of hand fitting during each stage of assembly. Likewise, the manufacture of individual parts was a long and labor-intensive process. BuOrd and private USA manufacturers completely redesigned almost every part of this weapon in order to speed up production. To give just one example, the barrel spring casing as designed by Oerlikon started as a 56 lbs. (25 kg) solid alloy steel forging. This casting required a great deal of machining in order to produce the finished part which weighed only 6 lbs. (2.7 kg) :o. BuOrd experts redesigned this piece to consist of a hollow forged base to which a tubular steel extension was welded, thus reducing the starting weight to only 14 lbs. (6.5 kg) with a correspondingly large savings in man-hours, machine tools and costs in making the finished piece. As a result of such redesigns, production time in the USA dropped from 428.4 man-hours per gun in 1941 to only 76.2 man-hours in September 1944."

Yah. Good designs, they made in Sweden and Switzerland, unless you want a lot of them...
(Both quotes courtesy of NavWeaps.)

In Germany, meanwhile, the MP40 and MG42 used a large number of stamped components, which strikes me as the fastest way to make a part. Ease of manufacture was as much as anything why MG34 production stopped in favor of the MG42.
« Last Edit: October 18, 2019, 07:37:55 PM by Everett »

Offline Everett

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Re: "The LM was made of aluminum foil and tape!" - counterargument
« Reply #44 on: October 18, 2019, 07:30:48 PM »
So apparently CNC machines have made chem-milling obsolete, then? And its seems Grumman had a Kelly too, just like Lockheed. (Not related.)