18 replies to this topic

[mariner]

I have often wondered how the task of re - riveting a worn out alloy monocoque chassis is actually done? As I understand it you painstakingly drill out every solid rivet then drill the holes out over size and "set" the new , bigger rivet in.

 

Fine but drilling out the old one without damaging the holes means drilling the exact centre of every rivet. Somebody who should know told me you need a special tool which fits exactly over the old rivet dome and has a centred hole for a centre punch to start the drilling out.

 

Is that how restorers do it please?

 

 

[Barry Boor]

Most of the rivets in our chassis were fine but where we needed to remove any we simply centre punched them then drilled through with a drill bit slightly smaller than the rivet.

[Bikr7549]

The tool is easy to make on a lathe - a counter sunk or spherical cut on one end of a steel bar sized so that it is centered on the rivet head and large enough in dia so that it seats flat on the sheet. A hole thru the center for the right size drill allows you to drill the rivet head off. I have done this on things other than chassis and it was a quick job. I believe that over size rivets are available if the holes have damage. The rivets (as formed) are harder than you might think.

[Lee Nicolle]

Been watching videos from Fantasy of Flight on You Tube and watching them drill rivets out of aircraft wings. An exacting and monotonous job.  makes a racecar tub look simple!

For anyone with any sort of interest in Aircraft have a look. They are rebuilding all sorts of planes.  Mostly war planes WW1&2 but not all.

There is another site of rebuilding a Lancaster as well by a Neville Wheeldon as well. 

I am not really a plane buff but the mechanicalness of it all is my interest.

[Doug Nye]

I was involved years ago when filming with a monocoque single-seater car at the Chobham test track, just north of Woking in Surrey, here.  The jounce loads upon landing after a yump caused a rear radius rod Rose joint to snap off at the neck. Upon inspection one could see the beach marks of a progressive fatigue failure extending through 2/3rds of the neck's diameter.  It was a disastrous incident just waiting to happen... 

 

When it broke, the rear wheel turned in and the car spun into a raised brick-edged manhole cover at trackside. The brickwork was about 4 feet square so one side of it fitted nicely between the front and rear wheels as the car struck it broadside, at speed.  

 

As you can imagine, this inflicted considerable damage upon the tub skinning - and how on earth the driver escaped serious injury I will never, ever, know.  Some force was smiling upon him that morning...  Both front and rear suspensions, and wheels, also took a pasting. 

 

Anyway, from everyone present admiring this absolutely lovely little jewel of a car at around 11am, by 12.30pm we were in a nearby workshop drilling out the rivets to remove the crushed tub side's mutilated skin. Centre-punch, slightly undersized drill, buzz down to skin surface level, and then prise off each rivet head - then punch out the headless shaft of the rivet.  Did that about 100 times, and the crumpled skin could be removed.  Then it was a question of straightening or replacing the internal bulkheads, shaping a new skin, and riveting the whole thing up again. On a tight time scale to make the next event - including sourcing and collecting replacement wheels, suspension and body parts in addition to tub repair and rebuilding occupied - I think - about 48 hours.

 

Not at the time - but in retrospect - it was a truly riveting experience. 

 

DCN

[SJ Lambert]

Dad (the skilled one) & I drilled out all 2000 odd rivets in this Elfin Mono tub, freshened the skins and put them back on with original sized 3/16" rivets and sealed the skins against fuel in one process.

 

In drilling them out we were super careful to be precise with 3/16" drill bits.

 

Dad was part of the original build team, one of the other guys reckoned that a chisel could be employed to remove heads before drilling, but we just drilled them from the head in.

 

We had one weep, built a powered rotisserie and slosh sealed it.  It's fuel tight now and has remained so for 5 years.

 

Edited by SJ Lambert, 14 May 2019 - 05:03.

[10kDA]

Interesting question - the task may have varying degrees of difficulty depending on what rivets were used, that now need to be removed. Doug's description is of the best way to approach it. First, lock up all chisels. An easy way to do it is to use a countersink stop on the drill - a spring-loaded cage gadget that sits flat on the skin and restricts the depth of the drill's travel. Set it to keep the drill depth just higher than the skin. Stick a punch the same diameter as the drill you've just used to make the "socket" in the drilled rivet head and pop off the head. The idea is to avoid disturbing the holes in the sheet. Use the same punch to gently knock out the rest of the rivet. Sometimes you may need to drill a size bigger when replacing the rivets.

If the rivets were 2117 aluminum to begin with (and they are for-real aircraft rivets), they will have a dimple in the center of the head, making centering easy. However, 2117 rivets are not as strong as rivets made from 2017 or 2024 (which have a raised lump in the center and two raised lumps at the edges, respectively - there goes the easy drill point placement) so, knowing that most race car designers go for max material properties in minimum packaging, I'm wondering how many cars were designed with 2117 rivets to begin with? When replacing 2017 and 2024 rivets with 2117 the best practice is to go up a size by 1/32". Next time at the vintage races I'll have to eyeball rivet heads to see who has done what These numbers for material designations are what are used in the US, I don't know what you guys in the UK, Oz, or elsewhere have to work with.

Though I've been accused of OCD and never of ADD, this kind of boring tedium associated with sheet metal work is exactly why I can't stand working on aluminum airplanes. I don't know how someone can build one - alone - without going completely crazy.

[sabrejet]

Never had a problem: a lot of solid rivets (esp. uni head US-spec and most/all countersunks) have a centre-punch as supplied and make drilling-off that much easier. UK-spec dome-head hiduminium etc require you to file a flat on each head and then manually centre punch.

 

Standard procedure for (for instance) 1/8-inch rivets is to drill the heads using a 3.2mm drill, then knock the heads off with a chisel. That's 1980 Halton RAF apprentice training advice and 25-odd years of aircraft work. Never had an issue with drilling-off and replacing rivets by the hundred unless they were those awful dural things. Luckily most are not.

 

In most cases you don't need to oversize....

[mariner]

Thank you all fro so much info. The process sounds the same as I had described to me by a restorer - and VERY tedious.  I didn't realise some rivets have the convenient dimple built in!

 

My understanding  is that the rivet holes in alloy monocoques slowly elongate with use in the direction of stress  so I had assumed that drilling the holes out larger and using over size rivets was often necessary on full chassis rebuild.

 

Thank you for the Elfin chassis pic, it is superb.

[Peter Morley]

With rivetted and glued monocoques, how do you "unstick" the glue after removing the rivets?

[SJ Lambert]

Chisel

[sabrejet]

non-metallic wedge (chisel)

[SJ Lambert]

And acetone, once we’d chiseled the skins off.

[Doug Nye]

...followed, as I well remember, by the inevitable Elastoplast...  

 

DCN

[Lee Nicolle]

With rivetted and glued monocoques, how do you "unstick" the glue after removing the rivets?

Very carefully!

And yes rivets do viabrate out. Heard the story from someone who was there about John McCormacks flat plane Leyland engined 5000. The viabrations were shaking rivet loose every meeting. 

[Peter Morley]

Chisel

 

Good to know that there's a high tech, sophisticated solution!!

And that the option I would have considered is the correct one.

[Ray Bell]

It's said that many rivets were missing from the M10 tub Niel Allen ran at Bathurst...

It was an early flat-plane crank in the engine and apart from the tub Niel reckoned his body took a hammering from the vibrations, he was having double vision IIRC.

There are, though, lots of different types of rivets. Matich's later tubs, and no doubt many others, had the rivet locations in the alloy countersunk and the rivets matched that.

[Lee Nicolle]

Actually it makes you wonder with aircraft as well. A lot of the piston engined ones viabrated fairly bad. Yet do not seem to shake rivets loose. And those skins are not for the most part bonded either. 

Watching an article on DC3s and some have been flying forever and I suspects that many of those rivets have been there since WW2 or before. And having once having been a passenger in one they viabrate very well.

Watching these aircraft vids makes you realise how many styles of rivets are around.

[10kDA]

Lee - something seen on aircraft which have been in service for a long time is the so-called "smoking rivet", where a rivet usually near the leading edge of a wing or tail surface seems to be the source of a dark streak on the skin trailing back opposite the direction of travel. That rivet is loose enough to be fretting itself against the holes in the skin, causing the trail of powder. Many times you can't detect any movement of the rivet if you poke at it. Smoking rivets probably are easier to spot on aircraft than cars since so many metal airplanes are painted white, generally the cheapest pigment/surface area.