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Where can I find engineering answers?

gundog

Hot Rolled
Joined
May 31, 2004
Location
Southwest Washington USA
Is there a place to get engineering information without hiring an engineer? Joint strength for example if I bolt 2 pieces of material using a fastener how strong will the joint be? I will be more specific but really I am wanting to learn how to find the info. I want to fasten some 6061 T6 extrusion together to make a right angle or possibly a "T" shape. I am working on a new part for my business and available extrusions are not working for my application.I would like to fasten the pieces together but I would like to know what kind of strength I will get so I can decide if this is a viable design. I am looking at Fastening .375" thick 6061 T6 flat bar together using #10-24 machine screws. I know the length of the pieces will come into play as the leverage will add more stress to the joint.

Thanks for any help.
Mike
 
Is there a place to get engineering information without hiring an engineer? Joint strength for example if I bolt 2 pieces of material using a fastener how strong will the joint be? I will be more specific but really I am wanting to learn how to find the info. I want to fasten some 6061 T6 extrusion together to make a right angle or possibly a "T" shape. I am working on a new part for my business and available extrusions are not working for my application.I would like to fasten the pieces together but I would like to know what kind of strength I will get so I can decide if this is a viable design. I am looking at Fastening .375" thick 6061 T6 flat bar together using #10-24 machine screws. I know the length of the pieces will come into play as the leverage will add more stress to the joint.

Thanks for any help.
Mike

The short answer is no. Consider the value of any answer to you from this forum. Should you trust it? The correct answer is to pay a competent engineer. Please note the word competent. This selected engineer should be tasked to explain his analysis to you. The other choice is to invest the time and energy to study the problem and learn yourself. Your call.
 
Any textbook on engineering statics and strength of materials will have examples and explanations that nearly fit your exact scenario. Determine the forces on each member, relate this analysis to the stress in the fasteners etc.

Many “engineers” will have you believe simple calcuations such as these are doable only by select individuals. And who can blame them? That’s how they’ve been indoctrinated from the first day of Intro to Engineering.

If it’s not a pressure vessel or a major structural component of a building greater than three stories, have at it. You’ll learn plenty.
 
Engineers Edge - Reference Data for Engineers | GD&T ASME Training | GD&T Training | DFM DFA Training | Engineering Supplies Store | Engineering Tools for productivity - Has the general formulas for the calculations you want to do.

Bolt Science Web Site - Is an entire website/consultation business dedicated to the type of question you're asking.

As an aside, it always strikes me as a little odd how this group reacts to the whole self-taught machinist movement (i.e. the YouTube machinists) when questions like this ("Where can I learn to do XYZ Professional Skill on my own so I don't have to pay anyone to do it?") from a machinist are treated completely differently. :stirthepot:
 
I build fishing related equipment worst case scenario is some guy loses his favorite rod to my design and to some that is life or death. My parts don't have huge margin in them fairly low volume so spending money on engineering is not on the table The other part of the equation is most of my products get knocked off by other manufacturers so the less I spend in development the better. Some things are not patent-able but they are new twists and if they are popular they get copied rather quickly. I have 2 US patents on other products and may look into a patent for this one but I am not sure it can be patented due to other products that do some of the same stuff. My patent attorney is very expensive but I will bite that bullet when I know the products perform as they should. I am a one man shop with over 80 different products so far. I was looking for some charts Etc to get me in the ball park before I invest in material build them and find out they break too easy.

Thanks Mike
 
Crazy idea here, I know I'm a little out on the edge--test it, try it, in a predictable environment. Engineer is presumably a person who does not need to do the tests. A person who can rattle off the predicted outcome, supposedly. Here is your grain of Salt.

R
 
Crazy idea here, I know I'm a little out on the edge--test it, try it, in a predictable environment. Engineer is presumably a person who does not need to do the tests. A person who can rattle off the predicted outcome, supposedly. Here is your grain of Salt.

R

A smart engineer will ALWAYS test his designs.

Tom
 
How can I get my appendix out without a surgeon? Where can I get my car fixed without an auto mechanic?

What a completely asinine comparison. The OP is using Al extrusions and 10-24 machines screws; he's clearly not designing a railway bridge. I firmly believe one of the characteristics of intelligence is the ability to discern when you're out of your element and to understand the consequences if you carry on.

The internet is full of automotive instruction, btw. Want to change your oil or a valve cover gasket on almost any type of engine? Go for it. No experience but want to tackle a wheel bearing or brake pad replacement? See tenet above- get professional assistance. Theoretical values are not a substitute for rigorous testing, hence why we build safety factors into critical components. If there's one thing I learned from MY Introduction to Engineering course, it's that there is no substitute for empirical evidence. Build a test rig such that the component can fail in a relatively controlled manner and you'll have solid evidence of its design strength and probable failure mode, be it shear/fracture/creep/yield etc. You'll be ahead of some of the "engineers" I know who think no red on the FEA = good to go.
 
I always test everything and try to break it I was just looking for info that may let me know it won't work before buying a bunch of material that doesn't work. Right now I have 2 pieces of aluminum extrusion worth a couple hundred bucks that doesn't work I was convinced in my mind when I bought the stuff it would be a piece of cake but no. I have designed a bunch of stuff and some of it never worked some of it did I am trying to learn how to design with a little engineering. I am 58 so I won't be going back to school any time soon not that I could not learn a bunch I am sure I can.

For the guy needing his appendix done I am game don't worry I will read a book first I have skinned deer, hogs and hundreds of miles of wire so you appendix should be no problem. I trained a lot of apprentices so your comments don't phase me.I can also fix your car since I worked as a mechanic in my younger days. I can even get your power back on in the middle of the night I did that too. So if we are done pissing on the post maybe I can get this figured out.

Mike
 
A smart engineer will ALWAYS test his designs.

Tom

Woah, thanks for pointing that out. Though the evidences provided by countless Engineers indicates something totally different. Maybe we need to define "smart" and determine what time line your "always" falls in, because it doesn't more often than not. Or maybe we need to determine what a "test" actually is. Seems that some ME's that I know, think that looking at a Mechanical Drawing, and signing the Title Block is a test.

Point is this person is asking about a situation where he doesn't have an ME on hand, so what should he do-----test it.

Engineers defend the College degree/Title, because no one else in the whole of Manufacturing will.

R
 
If you're making what I think you're making then the dilemma is that the stress points will change through at least a 120deg range. I fish and will go water skiing before I let go of a $600-$1000 set up. Do you have a mill available? Couldn't see your pics. Aluminum is forgiving to a point so it takes some of the stress away from the joint (I'm sure you know that).
 
Woah, thanks for pointing that out. Though the evidences provided by countless Engineers indicates something totally different. Maybe we need to define "smart" and determine what time line your "always" falls in, because it doesn't more often than not. Or maybe we need to determine what a "test" actually is. Seems that some ME's that I know, think that looking at a Mechanical Drawing, and signing the Title Block is a test.

Point is this person is asking about a situation where he doesn't have an ME on hand, so what should he do-----test it.

Engineers defend the College degree/Title, because no one else in the whole of Manufacturing will.

R

Where specifically have you run into engineers that don't test their designs?

Tom
 
Looking at your layouts, I assume the top drawing is for the two pieces to be joined to make a "T", using two screws/bolts. The second looks to be an "L" using 3 pieces of hardware. First question I have is, using the assemblies around water, the hardware to at worst stainless steel because aluminum is electrolytically attacked any metal other than magnesium. Water and salts in the water provide the electrolyte. Stainless is the only commercially metal to make hardware from that plays reasonably nice with aluminum. Next issue is the application, as in how and what stresses are applied to the assembly. Is it static or dynamic? Because of the "soft" nature of aluminum, I would use a course thread, more thread engagement. Probably want to assembly with thread locker like Loctite 270. Because this is a plastic, it also helps to seal the threads from water penetration. As far as thread/bolt strength is concerned, the aluminum thread is probably the weakest. Charts are available that list the pullout strength of threads in aluminum, but ita can be calculated by the stress area per thread times the number of threads engaged. The same stress area is for the screw, and since stainless steel is stronger than aluminum, the thread failure would be in the aluminum. A further calculation can be carried out on the shank of the stainless bolt. A final failure mechanism is bending of the joint causing plastic deformation of the aluminum and bending of the bolt. This can be attached by evaluating the bending moments on the joint.

Tom
 
Looking at your layouts, I assume the top drawing is for the two pieces to be joined to make a "T", using two screws/bolts. The second looks to be an "L" using 3 pieces of hardware. First question I have is, using the assemblies around water, the hardware to at worst stainless steel because aluminum is electrolytically attacked any metal other than magnesium. Water and salts in the water provide the electrolyte. Stainless is the only commercially metal to make hardware from that plays reasonably nice with aluminum. Next issue is the application, as in how and what stresses are applied to the assembly. Is it static or dynamic? Because of the "soft" nature of aluminum, I would use a course thread, more thread engagement. Probably want to assembly with thread locker like Loctite 270. Because this is a plastic, it also helps to seal the threads from water penetration. As far as thread/bolt strength is concerned, the aluminum thread is probably the weakest. Charts are available that list the pullout strength of threads in aluminum, but ita can be calculated by the stress area per thread times the number of threads engaged. The same stress area is for the screw, and since stainless steel is stronger than aluminum, the thread failure would be in the aluminum. A further calculation can be carried out on the shank of the stainless bolt. A final failure mechanism is bending of the joint causing plastic deformation of the aluminum and bending of the bolt. This can be attached by evaluating the bending moments on the joint.

Tom

The first 2 parts are a "T" (mortise and tenon type joint with a .125" deep dado slot and the middle tenon extending through to the back side of the base 2 screws holding from the back of the base)the second 2 parts form an "L" or right angle with one screw attaching from the top and 2 screws attaching from the back. There is more to the drawing as far as features go but I left them out as they have nothing to do with the joint. I am hoping to get a static strength of around 200# at 20" of leverage. I planned to use .375" x 2.25" 6061 T6 flat bar and #10-24 SS 18-8 machine screws with .375" of thread engagement.

I am fairly confident in the "T" shape but unsure of the "L" shape. I may use 6061 T6 angle but the center radius web create a problem I need the mating part to lie on the inside of the angle. I may end up doing them both as a "T" shape with the one having an offset base rather than centering it I could get away with it having a lip on the one side.
 
Firstly, this parts are going to have be machined. You would be money ahead to set up a piece of angle in the mill and cut out the inside radius as apposed to the way you are proposing and you would solve any strength and assembly issues. Depending on your dimensions, a piece "T" could also work. Thirdly, both of these cry out "EXTRUSION".

Tom
 








 
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