# Making Things : Welding Vs Castings Vs Bolt Together Vs Glue



## BillWood (Jul 16, 2015)

Hello,

I've been puzzled for a long time regarding how people decide whether or not to weld pieces of steel together or bolt them together or to carve up a piece of cast iron to the desired shape for the current project.

For example - see attached Milling jig from an old magazine

I've got the impression some folk today might use a milling machine to carve the relevant bits out of a casting whilst other might weld or bolt or even glue pieces of steel together.

Does it simply depend upon what tools and experience one has got or are there sound technical reasons for using a piece of cast iron instead of bolting some steel plates together ?

Any books or web site that could educate me ?


Bill


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## T Bredehoft (Jul 16, 2015)

Bill, I'm afraid  that instead of a quick and dirty answer,  you need experience. 
Pieces made from weldments have problems with stability and hard/soft areas. Yes they can be machined to be exact, but may change due to stresses. 
Cast Iron is great for stabililty but has less than half of the tensile strength of solid steel. 
Bolts are good for assembling, but not for machine tooling, they aren't absolutely solid. 
Glue is good for poster board, or wood, not so much for metal.


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## Wreck™Wreck (Jul 16, 2015)

BillWood said:


> Hello,
> Does it simply depend upon what tools and experience one has got or are there sound technical reasons for using a piece of cast iron instead of bolting some steel plates together ?
> Bill



COST above all, weldments and fastened assemblies are far less expensive to produce then machining a complete part from a casting or multiple castings or a solid bar, making a pattern, having the part cast and then machining Etc.
That said, cast iron has physical properties that lend themselves to certain applications such as machine tool components, measuring instruments, lathe, mill and grinder bases and tables for instance. Cast iron is very stable and doesn't move around over time and has excellent vibration damping qualities, it is easily cast into intricate hollow shapes and can also be made quite hard.

The method used to produce a product is dependent on its end use and the profitability of the industry that will use it (including any Federal-State-Local agency regulations mandating production methods and materials for reasons of Consumer Product Safety), for instance one could build a very accurate push lawnmower that would last 50 years at the cost of a new small car. Very few people would buy such a device, who needs an overly accurate push mower that costs $10,000 and will be around 50 years from now and still use it?

If one is building lawnmowers cut, stamp, punch and weld away, if on the other hand you are building the components that direct lasers onto peoples eyeballs to correct vision the old slap and weld method will probably be less than satisfactory (-:


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## brino (Jul 16, 2015)

Hi Bill,

What a great question, I can't wait for all the responses.

The little I have to offer is:

I do remember in one of the Gingery books(okay, I found it; book #1 "The Charcoal Foundry")  a description of what led him to doing his own castings. He had tried  welding parts of machines together, but what started out as straight pieces warped during/after welding so he could never get precision fits.

-brino


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## coolidge (Jul 16, 2015)

Machining can also relieve stresses and warp metal. Put a straight edge across a few wood cutting band saw tables after they cut the slot in them for the blade, boing! If you were building a high performance V8 engine would you want cast iron connecting rods or forged steel? Just food for thought.


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## Wreck™Wreck (Jul 16, 2015)

brino said:


> Hi Bill,
> 
> 
> 
> ...


I turn parts weekly where the customer requires (on the drawings) Machine After Welding.
Some parts require finish turning after milling operations, large tubes that have had slots or large holes milled in them will go out of round from the relieving of stresses in the tube itself, we generally rough turn the part, do the mill opps and then finish turn any close bores or outside diameters which is always made more difficult by the now interrupted cut.

As a sidenote I make a family of parts on a lathe, 8" Diameter X .268" thick, after the counterbores in each side they finish at .102" thick from 7.5" to center some are 304 SS and some 6061 aluminum, these things have been a challenge every time as they chatter like mad yet require a very fine surface finish as they are used in high vacuum equipment for depositing something onto semiconductor wafers. I convinced my employer to buy a set of 12" Pie Jaws for the 3 jaw chuck that I use. I machined an .080 pocket in the jaws and did the entire job faster (higher feeds and speeds) without any chatter, it was magical. It took close to 2 hours to set up and machine the soft jaws but I saved 6 hours overall on the 4 parts. As Sherman Potter might say, I paraphrase here, the 360º soft jaws are the Goats Ovaries
They look like this on an 8" chuck.


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## RJSakowski (Jul 16, 2015)

BillWood said:


> I've been puzzled for a long time regarding how people decide whether or not to weld pieces of steel together or bolt them together or to carve up a piece of cast iron to the desired shape for the current project.


Casting are used because it a cost effective way to create large masses and complex structures.  It also lends itself to multiple pieces.  A sand casting, which the the type used for machine frames starts as a pattern usually made of wood which is used to make a cavity in a sand mold.  The pattern is removed and metal is poured or cast in its place.  Intricate internal structures can be made  using cores.  Another type of casting is known as lost wax where a wax models are made and  plaster is cast around the wax.  The wax is melted out (lost wax) and the cavity filled with the casting metal.  This process is often used to make jewelry.  Statues are another use.  A variant is lost foam where styrofoam is modeled and the plaster cast around it.  The metal can be poured directly because the foam, being mostly air, melts into almost nothing and subsequently burns out of the mold.  The most expensive process for up-front cost is die casting where a die is machined, hence the high up-front cost.  Because the die is reusable, the per piece cost is lower.  

Steel is often forged into a semifinal shape with some possible secondary machining.  Forging strengthens the metal which is why it used for engine crankshafts, axe heads, and the like.  Because the process consists of hammering the steel to fit into dies, parts are limited in their complexity. 

Fabrication through weldments is another way to create complex parts.  Think of a car frame. Casting a frame is unthinkable, as is machining one from a solid block of steel.  It could be bolted or riveted together but bolted or riveted joins are more expensive.  Welding can also simplify joinery.  Two bars can be welded end to end to make a single bar with uniform cross section.  As mentioned in above posts, welding can create thermal stresses, leading to warpage although these can be controlled somewhat with proper technique.  If precision fits are required , secondary machining may be necessary.

For precise control of mating surfaces, bolts are often used.  When used in conjunction with dowel pins or other locating features, very precise mates can be achieved.  Think of your lathe chuck and back plate.  Rivets can be a cost effective way to permanently join two pieces.Fastening with bolts or rivets is limited by the strength of same.  Bolts are great if you want to take something apart again, however. 

Gluing two parts together is limited by the strength of the glue.  Generally, the shear strength of the glue bond is considerably lower than that of most metals which is why glue is not normally done.  It can work well on nonmetallic materials however.  Products like plywood are good examples.  And gluing labels on is probably the best way.  Glue used in conjunction with mechanical fasteners can be a very effective way to create a stable structure.  

As also mentioned above, the material physical properties contribute greatly to the selection of manufacturing process.  Cast iron has some great compressive strength but is notoriously poor in tension.  Steel is great for tensile strength as well as compressive strength.  Welded steel can come very close to the strength of single piece construction.   

The internet is a great source of infomation.  If you  can access Wikipedia, you should be able to find answers there.  A number of universities offer on line course auditing for free although I don't know if that extends outside the US.  This site is also a great place to learn.

Note: due to my slow typing,  some messages  came through as I toiled.  Please excuse any redundancy.

Bob


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## coolidge (Jul 16, 2015)

Gunrunner you need to order a set of these for the Z axis hand crank. Bill did you just spit coffee on your monitor? :rofl:

View attachment 253356


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## BillWood (Jul 17, 2015)

Gunrunner you need to order a set of these for the Z axis hand crank. Bill did you just spit coffee on your monitor? :rofl:

View attachment 253356


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## JimDawson (Jul 17, 2015)

For what you are proposing, I think that simply bolting and perhaps dowel or taper pins would be more than adequate, assuming you used appropriate bolts and that the underlying material is strong enough to hold the bolts.  A couple dowel pins would take care of the shear load as long as the bolts can handle the tension load.  Properly sized dowel pins will take an incredible amount of shear load.  Flat head cap screws are my favorite for this type of application, they both center and hold the tension.

Your sketch did not attach, so I'm kind of guessing here.

EDIT:  I found your sketch and copied it to your post.


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## francist (Jul 17, 2015)

Bill- I don't think I'd have a problem building that the way you're proposing either. I made a tool block in exactly the same manner and for exactly the same reasons (no mill, marginal welding capabilities) and it's held up well. I would likely make two changes though: I don't think I'd use glue. For one, I always like to be able to take things apart later if I can, and for another, the glue (unless it is extremely hard) will likely be softer than the mating steel which can in some cases contribute to "wiggling" rather than prevent it. I would also try to run a pair of screws side by side if room allows rather than just a single row. I realize your sketch is more concept than build sheet, so perhaps you've already thought of that.

I do like the dowels as Jim suggested, because they fit so snugly they can stop a lot of shifting from getting started. 

-frank


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## Vladymere (Jul 19, 2015)

I like Jim Dawsons idea of dowels also.  Dowels will provide, as Mr. Dawson said, will provide shear load or minimize the side to side movement of the parts, assuming the dowels are fitted properly, and the screws, or better yet I think, through bolts will provide compression.

Vlad


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## Bill C. (Jul 19, 2015)

Gunrunner you need to order a set of these for the Z axis hand crank. Bill did you just spit coffee on your monitor? :rofl:

View attachment 253356


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## BillWood (Jul 19, 2015)

Thanks for the responses.

Will have a go and see what happens

The advice given above has made me ponder upon another issue and I think other newbs might benefit as well so I will start another thread for Screws vs Dowels vs Taper Pins.


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## brino (Jul 19, 2015)

BillWood said:


> I will start another thread for Screws vs Dowels vs Taper Pins.



Good idea! It is related, but will be more searchable under a new title.
Looking forward to the discussion!

-brino


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## Riaan (Oct 13, 2015)

Modern adhesives are amazing, mind you. 3M has a body panel glue that is super effective, it makes a super strong join for lap joins and the like where welding sheet sections are too risky.


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## benmychree (Dec 21, 2015)

What I have not seen in this discussion is the answer to welding stresses in a welded fabrication; it is stress relieving, generally done by heating the weldment in an high temperature oven, to about 900 deg. F. for a period of time and allowing it to cool in the oven.  Also it is done by a high frequency vibration process.  The company that I apprenticed with back in the 1960s had one oven that was about 20 ft high and wide and 40 ft. long. Things such as oil refinery distillation towers were stress relieved in it. Most all weldments that were fabricated there were stress relieved, except things like bridge towers that did not require it.   My personal favorite method for building machine parts and accessories is making the pattern, having a casting made and finishing it in an appropriate fashion, including a scraped finish when called for.  Steel is a poor material for any machine part that slides, as it tends to gall up.  Steel against cast iron is OK for such parts as gibs that do not need to move a lot, such as on a lathe compound rest, but generally, cast iron is better, especially if the gib is long and has to be scraped to fit and bearing.


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## planeflyer21 (Dec 22, 2015)

Riaan said:


> Modern adhesives are amazing, mind you. 3M has a body panel glue that is super effective, it makes a super strong join for lap joins and the like where welding sheet sections are too risky.



An entire family of general aviation airplanes starting with the Yankee have used metal adhesives with a honeycomb structure between panels, starting in the 1960s:  https://en.wikipedia.org/wiki/Grumman_American_AA-1

Most of the new aircraft rely heavily on bonding composite panels together for the large body structures...wings, fuselage, empennage, etc.  Still lots of other production techniques used for smaller systems, like the hydraulics and electronics.

To what the OP originally asked, price out the steel needed for making that lathe attachment from pieces versus milling it out of one giant piece of billet.  The cost of larger/longer tooling alone would cost as much or more than using your current tooling and buying multiple small pieces to fasten together.

What a great thread!


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## 4GSR (Dec 22, 2015)

Out of spectrum here, in the down hole oilfield stuff I deal with everyday.  Most everything is connected together with threads.  All kinds of threads are used, Vee, Acme, Stub Acme, and all kinds of special threads.  Some things get welded together.  Some of the parts we use are castings of some sort.  All kinds of heat treats and hardening methods are used, too.  
Things I build in my home shop are primarily bolted together.  Socket heat cap screws are my preference.   I use very little welding in the things I do.  But that is fixing to change with a couple of new toys (welding equipment) in my collection.


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