Lets talk about fasteners

[Ol'fogasaurus]

This is part of a reply I had made. I have added some additional text to it since.

Your question go me thinking back to when I was involved in some fastener design notably self-locking fasteners; it was also roughly about the same time that Nylocs first came onto the market. I was trying to be clear on some things so I looked up the Nyloc fasteners and got this: https://en.wikipedia.org/wiki/Nyloc_nut. Self locking fasteners (including nuts, bolts as well as washers) have cycle limitations to them at several different levels but although the URL I gave you says different it itself isn't fully definitive either. I was also told a couple of years ago that the color of the locking material tells you where the fastener is made (country). I think the limit of cycles we used was something like 9 cycles (a cycle being on, torqued and off) while some of the commercial units were less than that; more like 5 to 7 cycles. I had designed a box for electronics to be housed, housed in a different area than normal and, as part of the design, we used the self locking Nyloc nuts. Several years later I got called into a meeting that dealt with the same area where the box was located and found out that the fasteners were replaced well over 9 times (I don't remember the number given but it was much higher than 9) before the airplane was delivered plus one more time at the time of delivery. That box had been removed and reinstalled that many times during the aircraft's assembly process.

https://www.bing.com/search?q=arp+faste ... 2cdc8f2607

Anyway, getting back to bolt design: fastener design and use is not really as simple as we Hot Rodders think it is. My recent foray (look up the origin of that word; 'tis interesting) into blind inserts (these were discussed at the same time the other fasteners were being defined to us) and the cycle limitations they also have were reintroduced to me and brought up some very old memories. Even split (locking) washers can "die" if allowed to be clamped fully for too long of a period of time (I am not sure they can be over tightened or not). I have heard people say they went to grad 8 fasteners but were clamping something that was "meaty" and had the potential of a lot of loading to one or two pieces of thin "tin".

Also, if you think about it when you torque a bolt you are stretching it. Torque and/or measuring its length determine the stretch of the bolt compared to it's strength. if you torque too much you exceed the limit of stretch, the bolt gets soft then breaks. Very basic but people often do not think in this direction. It is the same thing with the "grip" of the design; you have to account for stretch in the shank vs. the grip (the "grip" is the amount of materials you are clamping together which includes the washer(s). This is also for many different reasons.

I might as well continue a bit. Threads are either cut (lathe, tap and dye) or rolled. Part of the making of the bolts is keeping the grain of the material straight, heat treating (as I remember) does the same thing. When you "cut" threads you are also cutting into the grain which takes some of the strength of the bolt out in the threaded area. Rolling the threads compresses the material and somewhat reduces strength also... but not as nearly as much.

Bolt strength it part design (which includes the radius under the head and threads), part material, part heat treat and I think there are a couple of other things that I may have forgotten about. The end of the bolt, in the threaded area is tapered (one of the slang terms for that is "the easy on") so the threads are not full height. The nut (if you have noticed it) is done the same way but on both sides. This allows the bolt and nut to join easier (machine fasteners don't always do this for some reason) but the tapered section isn't as strong so the rule of thumb is "three threads showing" which usually gets you out of the taper OK. Racing rules often say 2 1/2 dia.'s showing which is for the case of the nut backing off and so you are less likely to loose the nut. This rule is often intended more for lug nuts.

Depending on what you are using for fasteners (amount of stretch) you can use a washer under the head or under the nut or both to draw back the shank of the bolt. There is a (an unwritten) rule that limits the amount of washers you can stack together to 3: and this is for good reason. I can draw this up when I get home if you want but when you look at the head of the bolt you will see a round flat spot that the radius flairs into, that is the load area of the head works with (he flutes on the head of the bolt are tapered up so they don't dig into what you are clamping and give you a false torque reading). As the washers tighten up they can move around due to their hole in their centers dia.. This is OK (usually) as long as the hole isn't too big. You add a second washer and it can off-set to a different location which reduced the load from the head quite a bit. Adding a third washer, if it off-sets in another direction reduces the heads ability to work even more. This is when you change to a "spacer" which you can make to suit the situation. I don't think a spacer under the head and under the nut is necessarily a good idea.

When you go to the box stores for fasteners they usually stock in 1/4" lengths. Even fastener stores do not stock everything available and in available lengths. SAE is usually in 1/6th or 1/32th lengths and that does not cover threaded areas (that probably means in the quadrillions). I don't know anything about Metric sizes but I am pretty sure that things are similar at least in this area. The size mating washers are a bit oversized in the hole and generally speaking you can go down one size and it will fit. You need to check the bolt's under head radius vs. the hole in the washer to see if they are free and clear of each other.

If I think of something or someone else has things to add... go for it.

Lee

[GS guy]

Lee,
Care to expand on this with regards to stainless vs. steel bolts, and the different grades and what grade/materials you should generally use for specific purposes?

For example, I was looking for some good bolts to bolt my turbo to the exhaust system. Lots of heat involved, needs to be fairly strong plus locking nuts were desirable. Spent a Bunch of time researching exhaust manifold bolts/grades/materials! Metric thread sizes too!

I think "hot rodders" in general tend to overbuild, I guess primarily because of availability of the fasteners they want to use or can find at the local hardware store, with a little "that looks about right" thrown in for good measure. As near as I can tell, Harley builders tend to "quadruple" overbuild with a "the more steel, the better" mentality. Asian motorcycle custom builds lean more towards "light is right".

Fiberglass buggy builders are all over the map on this!
Jeff

[Ol'fogasaurus]

Jeff, I'll be home late tomorrow then have Friday busy. After that I will do some research as I may be somewhat behind on fasteners material. The basics I pretty much remember but then I have been retired for 18 years, and "off the board" 9 years before that doing checking and procedure work. I seldom used CRES (aka SS) in design so some research is probably a good idea before I shoot my face off somemore.

I used the word "Hot Rodders" as it has become more generic; e.g., less involved with modified/stripped 20's, 30's then into the 40's and early 50's cars but now the word is tied to more for modifying almost anything. Hot Rodders are all over the board as far as most anything goes... they use what they have or what they can get.

Basically off-shore vehicles have gotten a lot better but I am not sure that parts and materials coming in from off-shore have. US businesses have given out a lot of information they shouldn't have and where they should have... I am not sure they always did or the specs were really used (for example, the porous materials now found in off-shore casting and forgings). One of the reasons some countries are trying to find stuff here that may or may not exist. Also, the same with the inspection/testing of certain things coming in may be somewhat lacking. Remember I am aircraft related and they have to be pretty particular because at 30,000 feet up you can't just go out and replace something.

Only once did I have to work on something that may have been around heat and it was a redesign of a company design that was made in-country... to the best of my knowledge. That was such a long time ago and the whole thing lasted just a couple of days; the info needed by me was given to me by the engineer not researched by me. You were very smart researching exhaust or high heat related fasteners on your own. Opinions on things are all over the board but so far ARP has been pretty trustworthy.

Yes, what you said about FG builders is pretty much correct. We often forget that we are dealing not exclusively with metal but something more of a brittle material tied to metal for example. Now you might understand at least one of the reasons why my black buggy build is taking so long.

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I'm still trying to figure out the stiffening up of the "wings" (front fenders) and the rear fenders when modified Model A taillights are being added. which cantilevers the tail lights out from the fenders. The pix is of the black buggy when is was to be street only. The engine was the Cologne V6 tied to an 091 and I was in the process of building an engine cover that looked like a travel trunk.

[Ol'fogasaurus]

Jeff, home now so some additional information.

https://www.marshfasteners.com/differen ... fasteners/

Some info on SS (CRES) fasteners

https://renovationwarehouse.co.nz/zinc- ... el-screws/

Zinc vs. SS fasteners.

https://www.boltdepot.com/fastener-info ... rials.aspx

This is a more general description but only alludes to the grade 10.9 fasteners. Read this paragraph: “It is a common misconception that stainless steel is stronger than regular steel.”

http://www.americanfastener.com/astm-sa ... fasteners/

Markings.

https://www.uboltit.com/bolts/hex-bolts ... bolts.html

Infor on grade 10.9. I always thought there was a Grade 12 but Fastenal says no (Hmmmm!) but off-shore suppliers say yes. Confused here so be careful.

I plan on doing some more info looking. I am being very careful as there is a bunch of questionalbe info out there now days.

Lee

[GS guy]

Here's some info from Totally Stainless - they're a good source specific bolt kits if that's what you're looking for:
http://www.totallystainless.com/faq.html

Nice to see they've finally gone "on-line" for ordering!
Jeff

[GS guy]

Another thing to note - many times you'll see what's called a black oxide coating on high strength steel bolts. It's a somewhat "oily" black finish that does a good job protecting the fasteners while in storage. However, when exposed to air (like inside a shed or garage) they "will" start to rust! Thought I was saving some $$ by getting black oxide ARP's, ended up having to re-buy in SS!
Jeff

[Ol'fogasaurus]

Another thing to note - many times you'll see what's called a black oxide coating on high strength steel bolts. It's a somewhat "oily" black finish that does a good job protecting the fasteners while in storage. However, when exposed to air (like inside a shed or garage) they "will" start to rust! Thought I was saving some $$ by getting black oxide ARP's, ended up having to re-buy in SS!
Jeff

Good point!

What they coat with can be for different reasons. It could be just for short protection say for shipping or in a controlled situation or it may have a lube of some kind in it. I have been lucky with my storage techniques but that is me and the situation I am in.

The materials they use for "the mix" of the fastener quite often is the deciding factor too.

Lee