# frame self-build: bolting vs welding?



## runcyclexcski (Mar 21, 2016)

Has anyone successfully built frames out of square aluminum tubes bolted together, rather than welded? I could use precision steel pins to align parts and to prevent them from wobbling (this is how I do it in my microscopes). My welding skills are non-existent, and I do not want to be paranoid about my joints failing. Plus, bolting is reversible and modifiable.


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## piotrsko (Dec 9, 2007)

At the risk of being flamed......

The reason why nobody really does it this way is because of the complexiity of making the joints and the annoying maintenance required to keep the joints tight under all that vibration.

Mig or tig welding aluminium with proper fluxes and gasses isn't that hard, and DIY home welders are pretty cheap with the benefit of a decent joint rather fast.

Aircraft are a collection of aluminum shapes held together by rivets and assorted fasteners.

My $.02 YMMV


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## Moltenmetal (Mar 20, 2014)

Be aware that most aluminum structural shapes are available in tempered grades- these materials are strong and stiff, but they lose that tempered strength in the heat affected zone after welding. Up to half the strength can be lost as a result of welding. The strength loss can be mitigated by proper joint design, but it isn't a simple matter of welding tubes to one another.

Is bolted, or better still riveted construction an option for a car frame? Probably not. It's impractical. Not impossible, but impractical.


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## scotmac (Feb 23, 2016)

Aircraft actually use riveting and bonding. In Fact, some of the automotive glues out there have impressive strength. Take a look at some of the two part automotive glue from Lord Corp.


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## bigmouse (Sep 28, 2008)

scotmac said:


> Aircraft actually use riveting and bonding. In Fact, some of the automotive glues out there have impressive strength. Take a look at some of the two part automotive glue from Lord Corp.


I agree, many modern cars are held together with adhesive. Rivets are used only for clamping and to hold the parts together during movement in the factory before curing.

Adhesive joints, like any other, need to be carefully designed in order to work properly. In particular, surface area and gap bond-line thickness are important concerns.


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## electron bom (Dec 4, 2014)

Attend a welding night class at your local tech/community college. Supplement with youtube instructional videos. There are a few channels with competent instructors. 

Buy a MIG welder from an online store. This one is inexpensive, but has at 30% duty cycle, so take lots of breaks: http://www.northerntool.com/shop/tools/product_200631881_200631881

Then practice on something small and work up to your project goal. I think it would be a satisfying process, if you're apt to enjoy that sort of thing. If you want it done quickly, look for a traveling welder in your area.


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## Yabert (Feb 7, 2010)

I'm in accord with comments from other member. Learn to weld can be relatively easy with current welding equipment.
I have to add than build a well designed steel frame for a small vehicle will only add few lbs on the overall and will be WAY easier to build and WAY more reliable.

If no, there is this guy who build his motorcycle bike frame from laser cut aluminum plate.
http://evalbum.com/3848


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## runcyclexcski (Mar 21, 2016)

From what I understand 7071 is the tempered Alu and 6061 is the 'general purpose' one. 6061 is also easier to machine, so I would probably just stick with 6061.

Something that might trigger more discussion: Titanium? It's expensive, but a small frame might not need much. I've been buying Ti grade 5 off ebay, and have been quite pleased.


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## Duncan (Dec 8, 2008)

Hi Runcycle

Titanium is great - for jets
I would suggest you start with mild steel

Steel is good not because it's strong but because it's malleable - it fails by giving a little bit

If you know what you are doing you can use high strength steel
If you know even more you can use aluminium
If you know much much more you can use titanium


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## scotmac (Feb 23, 2016)

runcyclexcski said:


> From what I understand 7071 is the tempered Alu and 6061 is the 'general purpose' one. 6061 is also easier to machine, so I would probably just stick with 6061.


6061 comes in tempered (6061-T6) and annealed (6061-O non-tempered). T6 is almost double the strength. However, if you weld it, it loses 80% of its strength, and will need to be re-heat treated to restore the strength.


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## Karter2 (Nov 17, 2011)

It may help if you explain what this "frame" is for.
Battery support ?
Bike frame ?
Vehicle frame ? ( chassis)
If so... Expected vehicle weight, size, configuration (2 wheel, 3 wheel, 4 wheel, etc )
I might be happy to propose adhesive bonded titanium for a wheelchair frame,.....
..... but not for a heavy road going, legal , EV.


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## Moltenmetal (Mar 20, 2014)

6061T6 is about 45 ksi tensile. Annealed aluminum is less than 18 ksi. You lose just over half the tensile strength when welding it- but what it does to the yield strength is even worse- it drops from 35-40 ksi to about 8 ksi- that's the 80% loss just mentioned. If your part is yielding, you're on your way to failure.

Again you can mitigate this with proper joint design. Or, you can use mild steel and sacrifice a little weight for dead easy fabrication by welding.

Don't even try welding Ti gr 5...it embrittles from exposure to either oxygen OR nitrogen, so purging it is essential on all sides until it's cool. It's definitely specialist work.


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## BWA (Mar 14, 2015)

Adhesive bonding is not meant for structural shape (square and round tube) conventional chassis building, though, it can have some uses in properly designed joints.

It is more commonly used in sheet (either metal, or fiberglass/carbon fibre) monocoque type constructions. Where you would join panels with a 1" overlap, using adhesives, in conjunction with rivets. 

This type of construction raises the instantaneous sheer strength massively over just rivets alone, while retaining the original strength if using aluminum, by not having to weld.....

Most modern airplanes are all glued together now for the most part....


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## runcyclexcski (Mar 21, 2016)

OK, sounds like I should not touch Ti, thank you ... I understand now why most folks use steel.

I did not like Al b.c. most bike companies do not offer a lifetime warranty on 7071 frames -- only 5 years. Steel and Ti are another story.

This would be a frame for a chasis for a 3-wheeler, two in the front, one in the back. Total load about 250 kilos. Will build a layout out of wood first and fiddle with it to find optimal dimensions.

There are companies like Dragonplate that sell carbon tubes and joints in all shapes. I might look into them as well, at least for some components


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## runcyclexcski (Mar 21, 2016)

As another update, I downloaded this book on Solar Car design:

http://www.springer.com/us/book/9783319174938

I understand that university-organized EV builds are expensive and over-engineered, but the book formalizes mathematically many of the issues that we touched upon in this thread, as well as an earlier thread on streamlined design. I will try to learn from their experience and only borrow design points that I need/can afford. After all, the EV I have in mind is basically a solar car, sans solar panels. Since I won't be using solar panels, I can reduce the size/weight and invest the recovered weight into safety/comfort.


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## Duncan (Dec 8, 2008)

Great start
But that book is EXPENSIVE $109 for an ebook!!


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## runcyclexcski (Mar 21, 2016)

I am at a University, so I got it at the library and scanned it into a PDF... It's a great read/data source, just want I need as a scientist .

As a way to test aerodynamic shapes I am thinking to build a scaled-down 'wind tunnel' out of a 12" wide acrylic pipe and a good-quality blower (already have both), and place 3D printed models into it (I already have a Makerbot works great). I would then measure the forces at different 'wind' speeds (scaled down accordingly) with a neuton-meter. Will start by printing 'standard shapes' for which Cds are known (cylinders, blocks, etc), and see if I get meaningful results.


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## brian_ (Feb 7, 2017)

runcyclexcski said:


> From what I understand 7071 is the tempered Alu and 6061 is the 'general purpose' one.


No, it doesn't work that way. The numbers describe the alloy (combination of elements), and the temper (heat treatment) is separately specified. Different alloys respond differently to heat treatment, so the two specifications are not independent.

This is a good illustration of how temper matters:


scotmac said:


> 6061 comes in tempered (6061-T6) and annealed (6061-O non-tempered). T6 is almost double the strength. However, if you weld it, it loses 80% of its strength, and will need to be re-heat treated to restore the strength.


This page from Metal Supermarkets describes the difference between 6061 and a 7xxx series alloy that they also carry (and is probably what was intended by "7071", since that alloy doesn't exist):








What are the Differences Between 6061 and 7075 Aluminum? | Metal Supermarkets


Two of the most popular aluminum alloy grades for structural applications are 6061 and 7075. While similar in some ways, there are also large differences.




www.metalsupermarkets.com




As it explains, both are routinely used in tempered form (-T6).


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## brian_ (Feb 7, 2017)

Melaniam said:


> Man, this thread is already 4 years old, what the actual hell are you looking for in here? Seriously, you think that anyone would actually answer in here? I guess even the author does not care at all about this thread anymore, he does not even remember it.


That's what you chose as your first post, Melaniam? Do you think that's a constructive way to start?


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## MattsAwesomeStuff (Aug 10, 2017)

Melaniam's location says New Orleans... followed by some Russian.

Sounds like a foreign instigator. One of the ways some governments in the world are being subversive, is just showing up in online communities and picking fights, driving wedges between people, instigating, and then stepping back and watching as people are trained to be increasingly less civil.

I'd pay him no mind.


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## remy_martian (Feb 4, 2019)

^ 'bot


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## brian_ (Feb 7, 2017)

Sure... although it is an unusual one, responding to post dates rather than post content.


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## remy_martian (Feb 4, 2019)

Date subtraction gone wild


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