I don't own a welder that's worth using as it's a cheap stick welder. At some point I really want to get a decent TIG welder. Welding with shield gas and being able to control AC, DC, duty cycle and so on makes for really nice welds with out splatter and voids in the weld. After stick welding, I really hate it and refuse to settle for less than TIG.
So then, that leaves me with fasteners until I can get the welder I really want. AND I will still use fasteners no matter what. Grinding off welds is generally not a great idea when you need to take something apart, Undoing a few screws however is. Lots of things can't be welded, such as steel to aluminum so that again means fasteners (screws and bolts).
A few rules of thumb...
1. Threads in metal are almost always better than threads in wood.
2. Threads that grab only a few turns on the screw are very likely to fail.
3. If you can put threads into something do it.
4. If you can put threads into something and then have a nut behind it, that's even better.
5. Never use cheap bolts and nuts. They are made of soft steel, break easily and don't last.
6. Your safety is dependent on the fasteners you use and how well they do their job. Use good fasteners and use locktite.
On all of my EV's, there are places where screws, threaded holes, nuts and washers are perfect for the job. This is the bottom of the Curries battery bay. It is held onto the frame by 8 1/4-20 counter sunk stainless screws that thread into the frame. The battery box is wood and seals to the frame with weather stripping. 3" long 1/4" bolts were ideal for this purpose and the battery box is removable if needed.
You can't see them since they are covered up by the controller, but the screws that hold the controller in place are 6-32 and they thread into brass inserts. Threads directly in wood don't take much abuse before they are useless. The brass inserts thread in once and never get removed. The actual screws that hold down the controller can be removed 100's of times with no loss of mechanical holding power. If you know you need screws into wood that will possibly need to be removed periodically, then I really recommend using brass inserts. They are not very expensive and come in any size you can imagine.
https://www.ebay.com/itm/E-Z-Lok-Thread ... 362b1e2365
This is the access panel on the bottom of the battery bay. The 6 screw holes are 6-32 brass inserts. The cover that goes on here needs to come off periodically. Inserts were the only logical choice. Notice how close the inserts are to the edge of the wood. Threads into the wood would not hold up for long. The inserts provide much better support and can handle having the cover pulled off hundreds of times. The wood by itself would be getting pretty useless after just a few reuses.
There's a variety of metals that screws and bolts can come in. Depending on what your application is, you will need to make different choices. I like stainless steel, but it isn't very strong. As a result in applications where there is minimal bending forces on a screw, I'll use stainless. In applications where you need a length of bolt exposed to sheering or bending forces, stainless isn't a good choice. The ends of this shock require about 5/8" of bolt length to pass through it and into the bolt hole in the frame. If this bolt was stainless, it would shear off after a couple of months of use. In grade 8 or better, it will last many years. Stainless in this application is a poor choice.
In this application (holding an adapter plate to a freewheel), where there is no bending forces at all, just shearing forces, stainless can work reliably.
This bolt was originally grade 8 and 8mm, I replaced it with grade 12.2 and 10mm. It holds the handle bars to the forks. There's literally the 1 bolt that holds all of this together. It would be absolutely disastrous if it broke while riding along at 40-50 mph! I went for the strongest bolt I could find. The handle bars take lots of lateral loading when you accelerate and decelerate and 100% of those forces are on that one bolt. Nothing short of the best and strongest steel would do in this application. I think I paid $8 each for them, but now I have lots of confidence that this will never fail or snap off. Under the head of the bolt is a large, thick washer to distribute loading in the bolt hole.
This is another application where 12.2 bolts are used. These bolts hold the motor to the frame. They pass through 1/4" thick aluminum and into the motor. They have lots of torsional or bending stresses on them thanks to 4kw of motor power. Stainless would hold up for a while, but would eventually sheer off. 12.2 will probably never fail. These are M6 screws. I got screws that are long enough to use all the threads in the motor base. This picture doesn't show it becasue this is an early mock-up while I was still getting things fitted together, but later on, I used larger washers that are a bit thicker. The grip of the screw head is what keeps it from sliding in the slot. Also the 12.2 steel screw is holding against much softer 6061 aluminum. I needed to maximize grip and to keep the screw heads from wallowing out a hole in the aluminum. A wide thick washer distributes the screw heads pressure over more area so there's lots of grip and prevents the aluminum from deforming under the screw head.
In this application, there's 2 M6 stainless screws that go through the frame and into the 1/4" thick 6061 aluminum. There's lots of material to make threads in the aluminum so I tapped M6 threads into it. I was more concerned about the bolt heads compressing the thin walled steel frame tube so I added washers behind them to distribute the compression forces better. There's very little bending forces on the stainless screws holding the frame and motor plate together. I could have used a single M6 screw, but just in case, I put in 2.
This is a small bracket I made that adjusts the front brake caliper out from the axle about 1" so I could use 160mm rotors. It's cold rolled steel and it's 1/4" thick. I could have drilled out the holes and put a nut on the back side, but why bother when I have so much material to work with? I tapped it for M6 and then used a couple of grade 8 M6 screws to hold the brake assembly together. The bolt hole on the tab on the forks is elongated so I added a jam nut. That way I have the threads in the steel and a nut keeping things locked together in that elongated hole. The screw holding the top of the caliper does not move so there's no need for a jam nut.
If you don's have any, get blue locktite. I put it on every bolt and nut and thread. I buy the larger containers of it. You are paying for packaging, not contents so bigger is better. A tiny 10ml tube costs nearly as much as 50ml bottle and won't last very long. Blue locktite will keep your screws and nuts in place. Things come lose, why have to fix something on the side of the road when it rattles apart when a little locktite would have kept it from ever happening?
https://www.ebay.com/itm/Loctite-242-Bl ... Sw8gVX-1-8
How important are these 4 little screws? Not very when it comes to the stability of the EV, but when it comes to keeping someone from casually getting access to the enable connections, it matters quite a lot! They have blue locktite behind them and soon they will be security torx as well.
What's a jam nut? Well imagine if you put a bolt through a threaded hole and then want to make sure that bolt does not come lose. Locktite will often times do the trick, but maybe not as well as you like. I often times use threaded holes in things and then add a nut behind them on the bolt. This aluminum is 1/8: thick. It can take a few threads in it, but it won't hold on it's own very well so behind the aluminum is an added nut. It literally jams the threads in the aluminum and the threads under the nut together.
This is another example of threads in a hole and a jam nut. The threaded section passes through a threaded hole in the blue flange, through a nut, through the 2 pieces of steel, into another nut and finally into another threaded hole on the far side. The 2 pieces of steel have holes that fit the bolt. The nuts jam the threaded section to the threaded blue flanges. This keeps that threaded section locked in place so it can't ever move. Of course there is blue locktite in all the threads.
Sometimes you want to prevent tampering. I may leave my EV outside and chained to a bike rack for hours at a time. I want to make sure my expensive battery packs do not get stolen. As a result the covers on the battery bays are held down with security torx screws. Allen key sets are very common and getting security torx bits is not impossible, but they are probably not something that people happened to have on hand randomly. I have a small selection of security torx screws that get used for battery bays mostly.
https://www.ebay.com/itm/1-4-20-x-5-8-T ... Swa81aE3j3
Those 2 screws at the back of the battery bay have large washers on them and they thread into thick steel and the heads are security torx. The only thing I could do more is put a padlock on here to make it more secure.
Those 2 screws at the back of the lid are security torx. It's not perfect protection. For that, "i park the scooter some place lots more secure, but they do keep out the random dishonest person looking for a quick "smash and grab".
Lets talk about washers. This seems really obvious...flat disk of metal with a hole in it. Yes that's true, but washers are useful in many places you may not have thought of. I have washers that are exactly the same diameter as the bolt head and others that are 2-3X larger and everything in between. Oh and let's not forget thin ones and thick ones and non-steel ones. GEEZ! What on Earth for?
This is a wheel adapter and 219 wheel sprocket on the back of the Currie. It's not easy to see since all the parts are black, but there's a gap between the adapter and the sprocket. The gap is just right to make the chain line dead straight. With some generic washer in that gap, I could have gotten close, but with a couple of thicknesses of washers, I was able to dial it in exactly dead on. Washers make great spacers for small gaps!
On the XB-502, you can see the gap a bit better. There's a couple of different thicknesses of washers in there that make this gap exactly right so the chain line is dead straight.
Thick washers distribute clamping pressure much better than thin washers. For holding a bolt head to aluminum or to thin steel walls, a thick washer is really needed. The Currie has thick washers under all the screw heads that hold the motor to the aluminum. Thin washers have their place too. On just about all my EV's, to tune the brakes just right, there are thin washers under the caliper bolts to get the brake pads riding exactly right. I want no brake drag except for when I'm actually braking. Thin brass washers commonly work really well for this. If you need to tune a little better, brass files or sands much easier than steel to get things dead on and it doesn't rust like steel does. I have washers that are the same diameter as the bolt head. Sometimes there's plenty of support, but I don't want the bolt head galling the paint or anodizing under it. A washer of the same size protects the surface and allows the bolt head or nut to still turn and tighten up.
It's hard to see in the picture, but this axle tensioner is aluminum. The axle nut has a washer under it that is just barely larger than the nut. I can tighten and loosen the nut 100 times and never damage the anno on the tensioner.
This is the blue scooter and there is not a washer under the nut. Notice the circle galled into the anno on the tensioner from the nut.
Awe nuts! Yup...lets talk about nuts. Haha. There are basically 3 kinds that I get. Everybody is familiar with nuts that include a nylon bushing in them. IF you have something you need to put on once or twice and have the nut stay put, the these are a decent choice. After that the nylon is usually gone and you might as well NOT have the nylon at all. I have nylon nuts, but honestly, I'm going to add locktite becasue I don't trust the nylon to do it's job for very long. Thin nuts vs thick nuts. Sometimes the space is tight and you can't add a 1/2" thick nut, but a 1/4" thick nut will fit in the space. A thin nut is better than no nut. Thin nuts have like 3 or 4 threads in them. They can't take any amount of serious tightening like a much thicker nut can. Use a nut that has sufficient threads to hold reliably. This is commonly why I'll use a jam nut on the back side of something that also has been threaded. Nuts also make great spacers. I keep a few 1/2" nuts around for this purpose. Every body needs to get the side to side spacing of their wheels right between the forks. Sometimes you need just a washer. Sometimes you need 1/2 or so. A large nut drilled out to fit over your axle might be just the thing. I've used large nuts on many axles to get the wheel centered between the forks.
This isn't exactly what I'm talking about becasue I found an axle spacer that fit, but imagine that smaller spacer was just a bit shorter. A 1/2" nut could have fit in there instead. Look behind the brake rotor, I used nuts and 2 washers to space the rotor away from the wheel hub a little to get the caliper lined up.
1. Get a tap and dye set
2. Get bolts and screws that are strong enough for the job
3. Get a variety of washers and nuts that can be used for various things