Bogging flexible panels

[Ext User(Jason James)]

The LTD bonnet I'm working on has had other accident damage repaired before
and a hairline occured in that repair at some time. The area is beside the
grille which is very heavy. Its an old fashioned all-metal psuedo RRoyce
type Ford used back then prior 1982. Looks like the grille flexed the
surrounding metal and the bog just snapped.

My question is: because the area I will be repairing are on top of the
bonnet, flexing is less, but the sheet-metal still "drums" when you have
shut it.

Would it be best to keep the bog as thin as possible? Keep the angle of the
damaged area as it meets good panel shallow as possible? I'm repairing rust
holes left after rust-pimples formed when the crap paint-job cracked up.

tks for any comments

Jason

[Ext User(Noddy)]

"Jason James" <home@work.1.0> wrote in message
news:44b2d2be@news.comindico.com.au...

> Would it be best to keep the bog as thin as possible? Keep the angle of
> the
> damaged area as it meets good panel shallow as possible? I'm repairing
> rust
> holes left after rust-pimples formed when the crap paint-job cracked up.

Drumming (or "oil-canning" as the Yanks call it) in large flat panels can be
reduced to a large degree (depending on the panel) by shrinking the area
that has the problem. Shrinking will tighten the panel and remove some of
the "give", and there's a few ways you can go about this.

The first two involve heat.

One way involves the use of an acetylene torch, whereby you heat a small
section of the panel no bigger than a ten cent piece until it just glows
red, and then cool it rapidly by wiping it with a wet rag. It might be
necessary to do it on a couple of locations, but the rapid contraction of
the sheetmetal will pull it tight and eliminate a lot of the flex.

The second involves the use of a shrinking disc.

Shrinking discs aren't commonly available in Australia, but they're not hard
to make. Basically, all they are is a piece of stainless steel sheet cut
into a circle of around 8 inches in diameter, and centre drilled so they can
be used on a 7 inch grinder just like a regular grinding disc would be. To
use them, you simply spray a little bit of soapy water on the panel as a
lubricant, then run the disc over the affected area in much the same way as
if you were grinding it.

The friction of the stainless against the tin causes heat, which is then
rapidly cooled in the same manner as the shrinking method listed above.
Shrinking discs are an amazing tool, and can make repairing a piece of
damaged sheetmetal *easier* than using body filler.

The third method of shrinking involves mechanical means, and in particular a
hammer & dolly.

To shrink a flat panel with a hammer & dolly, you first need to whack a dent
in it (known as a "tuck") that pulls the surrounding metal into the dent.
You then set about squashing that dent down with a flat faced hammer and
solid dolly by starting at the outside edges of the dent and gradually
working your way into the centre in a circular fashion.

The idea is to pull the flex into the dent, and then compress (and shrink)
the dent when you're knocking that back out.

It's not as complicated as it sounds, and it works very well. However, you
need to be careful if performing this near any contoured panelling, as it
can pull contours out of shape relatively easily.

If after all of this you still need to use bog, then go for the fibreglass
reinforced stuff that's less likely to crack with movement.

Or, if you wish to do it *properly*, use lead :)

--
Regards,
Noddy.

[Ext User(John_H)]

Noddy wrote:
>
>The third method of shrinking involves mechanical means, and in particular a
>hammer & dolly.

A fourth method is to strike an arc across the loose portion of the
panel and quench it with a wet rag (for those who still own stick
welders).

Whatever the method to be used, it'll probably pay to practice on a
spare panel first. :)

--
John H

[Ext User(Jason James)]

"Noddy" <dg4163@dodo.com.au> wrote in message
news:44b2e000$2@news.comindico.com.au...
>
> "Jason James" <home@work.1.0> wrote in message
> news:44b2d2be@news.comindico.com.au...
>
> > Would it be best to keep the bog as thin as possible? Keep the angle of
> > the
> > damaged area as it meets good panel shallow as possible? I'm repairing
> > rust
> > holes left after rust-pimples formed when the crap paint-job cracked up.
>
> Drumming (or "oil-canning" as the Yanks call it) in large flat panels can
be
> reduced to a large degree (depending on the panel) by shrinking the area
> that has the problem. Shrinking will tighten the panel and remove some of
> the "give", and there's a few ways you can go about this.
>
> The first two involve heat.
>
> One way involves the use of an acetylene torch, whereby you heat a small
> section of the panel no bigger than a ten cent piece until it just glows
> red, and then cool it rapidly by wiping it with a wet rag. It might be
> necessary to do it on a couple of locations, but the rapid contraction of
> the sheetmetal will pull it tight and eliminate a lot of the flex.
>
> The second involves the use of a shrinking disc.
>
> Shrinking discs aren't commonly available in Australia, but they're not
hard
> to make. Basically, all they are is a piece of stainless steel sheet cut
> into a circle of around 8 inches in diameter, and centre drilled so they
can
> be used on a 7 inch grinder just like a regular grinding disc would be. To
> use them, you simply spray a little bit of soapy water on the panel as a
> lubricant, then run the disc over the affected area in much the same way
as
> if you were grinding it.
>
> The friction of the stainless against the tin causes heat, which is then
> rapidly cooled in the same manner as the shrinking method listed above.
> Shrinking discs are an amazing tool, and can make repairing a piece of
> damaged sheetmetal *easier* than using body filler.
>
> The third method of shrinking involves mechanical means, and in particular
a
> hammer & dolly.
>
> To shrink a flat panel with a hammer & dolly, you first need to whack a
dent
> in it (known as a "tuck") that pulls the surrounding metal into the dent.
> You then set about squashing that dent down with a flat faced hammer and
> solid dolly by starting at the outside edges of the dent and gradually
> working your way into the centre in a circular fashion.
>
> The idea is to pull the flex into the dent, and then compress (and shrink)
> the dent when you're knocking that back out.
>
> It's not as complicated as it sounds, and it works very well. However, you
> need to be careful if performing this near any contoured panelling, as it
> can pull contours out of shape relatively easily.
>
> If after all of this you still need to use bog, then go for the fibreglass
> reinforced stuff that's less likely to crack with movement.
>
> Or, if you wish to do it *properly*, use lead :)

Thanx for those. The lead repair sounds good, so does the fibreglass.
I remember a guy cutting thru an EK back-guard fin with oxy. He hit the lead
fill, spraying molten lead on his arm and front,..ouch.

I've done a lot of soldering at work and lead-wiping, great idea. I wouldn't
have thought of it otherwise.

Jason

[Ext User(Jason James)]

"John_H" <john4271@hotmail.com> wrote in message
news:asp5b29ns4pl9fa6ctjdh3uqbk1n4ea82o@4ax.com...
> Noddy wrote:
> >
> >The third method of shrinking involves mechanical means, and in
particular a
> >hammer & dolly.
>
> A fourth method is to strike an arc across the loose portion of the
> panel and quench it with a wet rag (for those who still own stick
> welders).
>
> Whatever the method to be used, it'll probably pay to practice on a
> spare panel first. :)

Thanx, for that idea J. The bonnet on the XDs is one expanse of slightly
convex sheet-metal. Its supported by ribbing underneath, but it still flexs.

Jason

[Ext User(Noddy)]

"John_H" <john4271@hotmail.com> wrote in message
news:asp5b29ns4pl9fa6ctjdh3uqbk1n4ea82o@4ax.com...

> A fourth method is to strike an arc across the loose portion of the
> panel and quench it with a wet rag (for those who still own stick
> welders).

Didn't think about that one.

> Whatever the method to be used, it'll probably pay to practice on a
> spare panel first. :)

And I forgot to add this :)

--
Regards,
Noddy.

[Ext User(Noddy)]

"Jason James" <home@work.1.0> wrote in message
news:44b2f804@news.comindico.com.au...

> Thanx for those. The lead repair sounds good, so does the fibreglass.
> I remember a guy cutting thru an EK back-guard fin with oxy. He hit the
> lead
> fill, spraying molten lead on his arm and front,..ouch.

Yeah, that can be nasty if you're not expecting it.

Always a good idea to run the torch over any factory joins without pressing
the "cut" lever for a few seconds to melt the lead away and wire brush it
out.

> I've done a lot of soldering at work and lead-wiping, great idea. I
> wouldn't
> have thought of it otherwise.

Not many bother with it these days, but it's still far and away the best
product to use for repairs in areas that have flex and you wish to avoid
cracking.

--
Regards,
Noddy.

[Ext User(atec77)]

John_H wrote:
> Noddy wrote:
>> The third method of shrinking involves mechanical means, and in particular a
>> hammer & dolly.
>
> A fourth method is to strike an arc across the loose portion of the
> panel and quench it with a wet rag (for those who still own stick
> welders).
>
> Whatever the method to be used, it'll probably pay to practice on a
> spare panel first. :)
>
Or run the tig or mig across the back of the panel and then add a damp rag .