DIY Friction Drilling

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bgkast
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DIY Friction Drilling

Post by bgkast » 01 Aug 2014, 16:07

http://www.locostusa.com/forums/viewtop ... 15#p186597

VERY cool, I plan to try this out. If it works well I may bolt on panels, rather than rivet.

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freakynami
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Re: DIY Friction Drilling

Post by freakynami » 01 Aug 2014, 20:01

Wow, haven't seen that before, I've worked with stir welding and spin riveting, but this is new. My thought would be how happy the tap is to run through metal that's been through a plastic heat cycle, but that seems to be the normal thing to do. Let us know how you get on :)

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Re: DIY Friction Drilling

Post by freakynami » 01 Aug 2014, 20:09

One more thought, if the panel is handy to be removable, and this process replaces rivnuts, cool.

If the panel won't ever come off and it's intended to be structural, then a rivet will still provide the shear strength that a screw won't.

Not that a screw doesn't have the strength, but for a screw hole you need some clearance where a rivet actually swells out and fills the hole tight as you dump it up, so there is no play or slop so all the rivets will be spreading the shear load through a panel, rather than just the first couple of screws to take up the contact load.

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Re: DIY Friction Drilling

Post by bgkast » 03 Aug 2014, 09:02

Good point about using this technique for structural panels. In Midlana's case I don't believe that any of the panels are structural. To me the idea of being able to remove any panel for crash repair or maintenance is appealing, even if realistically they will never come off the car.

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Re: DIY Friction Drilling

Post by Midlana1 » 03 Aug 2014, 09:17

I'm facing the possibility of that now, needing to remove and replace the panel under the engine. It and the rivets have become damaged by bottoming out on dips. The combination of low (18 psi) tire pressure, low ride height, soft springs, and soft shocks allowed that to happen. The point is that with aluminum rivets I can easily drill them out - with friction-drilled fasteners it would be a very different story. Also keep in mind that if and when the car drags its bottom across something, the first thing that'll get removed are the heads of fasteners, making them difficult or impossible to remove.

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Re: DIY Friction Drilling

Post by jgrewe » 04 Aug 2014, 21:21

Kurt, could you show the all spots you have had hit the ground in your build thread? Or describe the locations using tube # intersections? What I'm thinking of is building some sturdy mounts into the chassis for jabrock skid plates.

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Re: DIY Friction Drilling

Post by Midlana1 » 05 Aug 2014, 06:13

Very back right corner. Keep in mind that if you add skid plates, the very fact that they're there lessens ground clearence even more. Also, how are they attached? If they're screwed on and the material is thin, the fastener heads will get removed along with the skid plate material, making removal difficult. If they're thick enough that the plates can have recessed mounting holes, on the order of 1/4-1/2" think, that's a huge amount that'll cause it to drag over most anything.

The thing is though, where the chassis hits and why is entirely up to you. If you like stiff suspension it'll never happen. If you like 30 psi in your tires it'll never happen. If you like firm spring, 4.5"+ of ground clearence, or have smooth roads in your area, it'll never happen.

I'm not saying don't do it; I'm just saying to think through how to mount the material such that it doesn't end up creating the problem it was installed to prevent.

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Re: DIY Friction Drilling

Post by dpkilty » 05 Aug 2014, 07:25

Midlana1 wrote:Very back right corner. Keep in mind that if you add skid plates, the very fact that they're there lessens ground clearence even more. Also, how are they attached? If they're screwed on and the material is thin, the fastener heads will get removed along with the skid plate material, making removal difficult. If they're thick enough that the plates can have recessed mounting holes, on the order of 1/4-1/2" think, that's a huge amount that'll cause it to drag over most anything.

The thing is though, where the chassis hits and why is entirely up to you. If you like stiff suspension it'll never happen. If you like 30 psi in your tires it'll never happen. If you like firm spring, 4.5"+ of ground clearence, or have smooth roads in your area, it'll never happen.

I'm not saying don't do it; I'm just saying to think through how to mount the material such that it doesn't end up creating the problem it was installed to prevent.
Good points Kurt.

Correct me if I am wrong but I think since all this is still new and your car is the only one we have to base anything off of anytime we see a "problem" or issue with the car be it this or anything else we all start thinking of ways to "improve the design" or prevent it from happening. Its just in most of our nature. Heck I wouldn't go through the process of building a car from scratch if I didn't think I could improve on something over just going out and buying one. Its what we do here... There could be a much easier "fix" to the problem (if its even a problem). Like you said, run a bit more tire pressure, of firm up the suspension. We also tend to overthink things a bit (being a lot of engineering types its in our nature).

I am just making observations here so I hope non of it was out of line. I'm not trying to imply there are design flaws by any means, but there is always room for improvement. But what I might consider an improvement might be a hindrance or bring up new problems for someone else.

Back on topic...

Wouldn't friction drilling work harden the material to the point of making it very hard to tap? Or would you need to use a roll form tap? Just trying to get my head around such wizardry...

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Re: DIY Friction Drilling

Post by Midlana1 » 05 Aug 2014, 09:14

I haven't read up on friction welded fasteners... can they be removed after installation, or does the fastener effectively become "one" with the material? If you try to back them out with a drill-driver, do the heads just break off? If so, how do you replace a panel?

Regarding soft suspension, mine is very soft. I can go over speed bumps on our street and hardly feel them, while doing the same thing in our "real" car's is much more dramatic. My point is that my car probably isn't a great data point for "normal." Once I swap in the 30% stiffer springs and set shock compression/rebound to match, I doubt I'll have any more issues with bottoming. Like I said, suspension settings which affect the ride are very subjective. My car is probably a "worst case" setup in that respect, but it is comfortable on the street! Once it's stiffened up it'll no doubt be faster on-track, but less comfortable on the street - it's just how it goes.

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Re: DIY Friction Drilling

Post by jgrewe » 05 Aug 2014, 16:22

Jabrock usually comes in 4 or 6mm thickness sheets and we bond it onto the chassis with epoxy. If you look at the underside of just about any small formula car they are usually jabrock from nose to tail.

It sounds like dragging won't be a big problem for my purposes though. My builds will be 98% track oriented so I'll be at the opposite end of the stiffness range.

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