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PostPosted: March 30, 2013, 9:39 am 
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It occurred to me that if a high quality, self-tapping screw were available it might be a good alternative to pop rivets in a number of locations. The only self-tapping screws I've used are inexpensive ones from the hardware store. I doubt those would hold up in the long run if used on a Locost exposed to typical road conditions, moisture, etc.

However, if a good product could be found, might they not work well? I'm thinking primarily of the transmission tunnel, under-dash panels and other such places. All you'd have to do is put in a nice, healthy center punch mark and "drill" the fastener into place. Maybe the screw could be dipped in Loctite or similar just before installing it? You'd be able to remove the panels at some future time if you really needed to do so.

Wouldn't that save a lot of work and time since you don't have to drill holes or place the pop rivets in them? Has anyone tried them? What about the idea of using them in the undertray too? Are there any obvious corrosion risks using stainless steel (screws) through aluminum (undertray) into carbon steel (chassis tubes) where moisture might be present occasionally?

I'm just thinking out loud here, but it is an appealing idea to me.

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

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PostPosted: March 30, 2013, 9:52 am 
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You are right to be concerned about them backing out so you'd want to use them in non-critical areas, but I don't believe that loctite on a self tapping screw would work. I'd think you'd need to tap and then apply loctite.

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PostPosted: March 30, 2013, 10:00 am 
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I have an old supply of self drilling/thread forming 10-24 screws that I used during the early stages of my build. They drill the hole first, then form the threads. I didn't use them in structural areas and later, replaced them with real machine screws. You get < 2 threads in the 16ga steel tubes so I didn't trust them for structural use.

McMaster has them in many head varieties. Mine had some form of bugle head, and were not suitable for long term use. They looked like this without the "flags' on the shank.


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PostPosted: March 30, 2013, 3:30 pm 
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I don't like sheet metal screws, but auto manufacturers use them all the time. Presumably they know what applications they work best on. To me, the only advantage of screws over rivets is to make something removable, but lots of time the riveted panel isn't removable anyway, and sheet metal screws are heavier.

Any time I want high-quality hardware I usually go to Aircraft Spruce. They have sheet metal screws. They're probably stronger and more corrosion-resistant, but I doubt they stay in any better.


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PostPosted: March 30, 2013, 5:25 pm 
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They're used on Stalkers and my brother hasn't said anything about them falling out, but I think he used a dad of adhesive on each prior to installation.

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PostPosted: March 30, 2013, 5:31 pm 
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rx7locost wrote:
. . . You get < 2 threads in the 16ga steel tubes so I didn't trust them for structural use. . . .


Hmmmm, not much grip there. Sheet metal screws are pretty coarse. I wonder what length or number of threads are actively engaged in holding in that case. They're pretty strong. However, you have to pre-drill for sheet metal screws, so you back to the amount of work required for pop rivets, which probably grip even better.

Maybe a real-world test to failure using actual materials would be in order for self-taping screws?

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 30, 2013, 5:32 pm 
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KB58 wrote:
They're used on Stalkers and my brother hasn't said anything about them falling out, but I think he used a dad of adhesive on each prior to installation.


Do you know what adhesive they use or how it is applied?

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 31, 2013, 12:11 pm 
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when one backs out and instead of being lost for all eternity is immediatly found in the now flat rear tire, you will say to yourself, "i think i should have used pop rivets"

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PostPosted: March 31, 2013, 2:09 pm 
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Your observation about stainless and aluminum being problematic from a corrosion respctive is interesting. Stainless screws and rivets are the norm on aluminum sailboat hardware and if anti seize isn't used or there are insufficient fresh water wash downs after sailing in salt water you soon don't have to worry about screws coming out. The problem is, can you get them out when you want to do so.

But then again, we're talking about stainless rivets, aren't we?

Stainless and aluminaum are about as far apart as you can get in the galvanic scale and where the two meet there is generally an oxygen deficiency - so it's a breeding ground for crevice corrosion. As does Stalker, it's a good idea to apply a good dab of 'goop' to every screw, or ensure good surface protection if you don't.

I suspect that Airframe Fixer could provide some good advice in this area. Corrosion remediation is often a key element of major overhauls for aircraft.

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PostPosted: March 31, 2013, 2:50 pm 
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nick47 wrote:
I Any time I want high-quality hardware I usually go to Aircraft Spruce. They have sheet metal screws. They're probably stronger and more corrosion-resistant, but I doubt they stay in any better.


They sell duct tape too :wink: . No, they don't stay in any better. Non-structural interior use only.

Part of the problem is the guage of material plus the fastener head is on the bottom. Use well nuts. They are used on Japanese motorcycles, usually for hanging panels. A special tool is not required for installation and they seal. They cost a lot more than rivets, but may align with the cost of screws and goop.

Self tappers and sheet metal screws are fine for interior panels, where they just fall out on the floor rather than into your tire or mine. I don't know any oem that hangs panels underneath with vertical self tappers or sheetmetal screws.


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PostPosted: March 31, 2013, 4:36 pm 
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My Dodge Dakote sunvisors are held on by self tappers and the %^&^%* things are always loosening. I guess it's OK 'cause the screws won't fall on the road and cause punctures. Maybe I should drill a hole in the roof and let the corrosion tighten them up: wait a minute, the only evidence of non-contact corrosion on the Dakota's body is the upper corner of the windshield - it should leaking soon and my loose screw problem will be solved!

I shouldn't be so glib - the last time this happened to us was when my wife's Rabbit leaked at the windshield post and shorted out the fuse block. $$$$$$$ :(

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PostPosted: March 31, 2013, 8:44 pm 
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I wouldn't no way no how.
1. a car vibrates and flexes, and there will be screws popping out due to that.
2. mixing metals= corrosion steel+ al will be a problem
3.what everyone else said. not much holding power, half a thread you will notice older aircraft are put together with rivits, specific type rivits.
Pop' rivits will work, but only if set correctly, clean holers, no burrs, correct material etc. When I get to the part pf bonding my car together I will be using adhesives and rivits in concert. It helps to have an air powered rivit gun, I found a commercial aircraft gun at a pawn shop for 60$ ignore the HF guns, they are trash for the most part.


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PostPosted: April 26, 2014, 11:44 am 
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Like the stalker guys I used a lot of square head screws on mine and I have not had a single screw come loose, to my knowledge, in about 4000 miles.


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PostPosted: April 26, 2014, 12:43 pm 
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I thought you glued the floor on and riveted the rest.
Did you seal the screws to prevent water from entering the frame tubes?
Did you check each screw for tightness or just look at 4k?

Square head is not descriptive of the screw. Square head makes me think of deck screws.

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PostPosted: April 26, 2014, 2:01 pm 
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Another aspect of a self tapping screw fastener is that in shear there is a lot of slop.

When a rivet is installed it swells and fills the hole to a press fit.

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