Randy Ferguson
01-08-2005, 09:43 PM
Hi Folks,
The '40 Willys I'm currently working on has about 90 percent of the roof covered with dents. Not small dents, like hail damage, etc., but big ol' nasty lookin' things. I'm going to use the text that Wray Schelin wrote a few years ago on the jaglovers list and add a few pictures to it. Wray covered the subject very well, so no reason to re-write it.
Tools for Removing Dents
By Wray E. Schelin
How smooth are your stripped body panels? That is the question you need to know before you advance to the primer stage. If they're not smooth you can fill them with bondo and heavy primer- but if you do so you run a high risk of a early paint failure and all your work will be in vain- or you can smooth them by accurately working the panel back to a smooth condition. If you rub your hand over the metal and feel low spots or high spots, you can be sure that they will show . Before you get your spray gun out you should be able to rub a panel in any direction and feel nothing but smoothness.
If you choose smoothing instead of filling, I'll share with you the technique that I use and some of the tools needed.
First the tools:
All body tools should have smooth working surfaces; hammers, slappers, and dollys are like printing presses, they will transfer the imperfections on their working faces to the metal over an over. Its best to take the time and smooth your tools first , because any imperfection transferred to the panel can make itself known later in the topcoats,as a paint shrinkage depression.
The higher quality body tools are made of heat treatable steel. You should have at least one hard hammer and one hard dolly- for hammering welds. The reason for this is the welds are harder than the surrounding metal and if you flatten them with a non hard hammer you will mark the hammer and then you will have to keep smoothing it. The working faces of hammers and slappers should have a very slight crown to them and the edges should be radiused. With the edges smooth and the center crowned slightly, you will not mark the panel if you inadvertently strike with the edge of the tool.
The slapper is the most important smoothing tool. You can make a slapper out of a old rear leaf spring. Car springs are harder than welds, so they will not mark up. My slapper has a working face of 2.250" by 5". The thickness is .250" and the unbent starting length is 14". You can also get a single spring leaf new from your local truck spring rebuilder. You can cut it to shape with a cutoff wheel or a torch, but cool it quick so you don't anneal it. I bent mine with an offset of 1.625" . The offset allows you to affix a wood handle and provides the clearance for your fingers. Heat with a torch to bend the offset and then narrow the handle end to a width of 1.375". The narrowed part is 5" long.
This slapper will smooth all body panels except for concave areas. For concave areas you will need to make a special slapper or use hammers. Once you start to use a slapper you will retire your hammer.
You will also need a few dollys. I found most of my dollies at flea markets for a few dollars each. Three or four dollies will be more than adequite to deal with all the different shapes and contours that you encounter . Each dolly usually has several different contours and crowns. As long as you have a straight edge , a low crown, medium crown, and a high crown you will be able to smooth any panel. Don't hesitate to alter the dolly to fit a need ,grind them with a body grinder, to rough shape then use a DA sander- with finer and finer sand papers- in rotary mode to achieve a fine polished finish.
Next you will need a body file and holder. The holders have a turn-buckle on them to allow you to flex the file to a concave, flat, or convex shape. The file that I use I was able to order from my local welding supplier. They are a dealer for a German company called Pferd. I got a Pferd catalog, an found that they offer a 12 tooth per inch body file , which is considered a fine cut body file. Most of the files that I had seen previously were 8 or 9 teeth per inch which are coarse body files. I like the fine file because I can use it on aluminum , steel, or body solder. When I use it on aluminum I load the teeth with a candle wax, this allows you to skate over the aluminum without digging in and making gouges. This type of file is 14 inches long and has cutting surfaces on each of its sides. On one side I grind the edges smooth in effect killing them so they do not dig in as you skate the file sideways. Pferd also sells the holders and a multitude of different style files and abrasives, all are of the highest quality available anywhere. Pferd has distribution centers all over the world. In the USA they can be reached at
Pferd Inc
30 Jytek Dr.
Leominster, MA 01453
Phone 508 840-6420
In Australia:
Pferd Australia (Pty) Ltd.
Moorabbin, Vic.
3189 8 Capella Cresent
(03) 5531946+5531933
You can also try your local welding supply house and they might have a catalog.
Another item I use is a large magic marker or felt marker. The ones that I use are called magnums and they mark a swath about 1/2" wide with a tenacious ink that dries very quickly. I like red ink the best.
A heavy duty 9" body grinder is the most expensive item needed. You can use a lighter duty 7" grinder but it won't work as well as the 9" in all cases.
Also a 9" 120 grit grinding disc. Grinding discs when they are new are very sharp when you run your finger over them , after grinding a heavy piece of steel for a few minutes you will dull the disc. This is how I prepare my discs, purposely dulling them to make them suitable for use.
Lastly you will need the Amazing Shrinking Disc. I mentioned this tool before in another post, it is a 9" disc of .050" stainless steel with some ruffles pressed into the outer working surface. This tool is most effective when used with the heavy duty 9" body grinder. I can't say enough about how good this simple tool works.
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_1-med.jpg
In my next post I will explain the process that I use in conjunction with the earlier mentioned tools. For many years I haphazardly removed dents with a method which always left the panel in a improved state, but not perfect. I frankly didn't believe you could restore the damaged metal to a state were no filler other than primer would be necessary. Like most things once you master them they are quite simple, all you need is the determination and the correct method.
Regards,
Wray E. Schelin
Removing Dents
by Wray Schelin
--------------------------------------------------------------------------------
In the last post I described the tools necessary to completely remove
dents, waves, and dings in your body panels. In this post I will share with
you how I use the tools to achieve a panel smoothness that will require
very little or no bondo filler. It is best to keep your bondo use down for
two reasons. One,bondo use is not craftsmanship, its just a cheap
substitute. If your trying to achieve a high standard restoration- in my
opinion it is best to have the craftsmanship on more than just what you
see. The value of these cars is more than just the dollar amount. The
second reason is, if you keep your substrates (bondo fillers and primers)
to a very minimum and apply just enough topcoats you will have an ideal
thickness of paint coatings. With an ideal thickness your paint system will
be able to expand and contract with the steel and aluminum surfaces of your
cars body as it heats and cools. This correct thickness insures you against
an early paint failure. Coatings can fail for many other reasons, but too
much paint and filler I believe is the most common culprit.
The most surprizing thing about high quality metal finishing, is that is
not that difficult to do; but it does take patience, good eyesight, a fine
sense of touch, and the tools that I previously mentioned.
First what's fixable and what's not. If you have, say, a 120 front fender
that was severely damaged in a accident many years ago on its leading
surfaces, an was quickly repaired by sewing up tears with brazing rod,
crudely hammered out, ground very thin, and then filled with bondo, forget
it; in that case you are probably better served by replacing that heavily
damaged section. Another impossibility is an area that has been incorrectly
torch shrunk; what had started out as an earnest limited attempt,
inadvertently expanded to large area, leaving heat damage with heavy
intractable waves.
Fixable dents and damage, listed in a descending order of severity:
Bodged past repairs that are still fixable, because the metal has not been
ground too thin,
Collision damage with stretching and tearing,
Sandblasting with excessive pressure causing a wave effect,
Smoothing out the seam of a butt welded patch panel,
Small dents with little or no stretching,
I 'll share with you how I remove a small dent . An easy example will work
best, so lets say, its the rear fender of a XK120. The dent is in the
middle of the rear section of the fender, and its is about the size of your
fist, sunken in about 3/4" in the center. All paint and undercoating should
be removed first. I would first select a dolly that has a crown that is
close to the fender; in this case that would be a medium crown. Using a
glove to protect my fingers I would palm the dolly and lightly tap it
against the bump on the inside of the fender; carefully watching the
progress of the rising depression. I would use this process until I got the
dent up to within 1/8" of the surface. This will happen within minutes-
this is called roughing out the dent. Next I would hold the dolly tightly
against the center of the damage , on the backside, while I use the slapper
on the front, tapping the circumference of the dent. This is a dolly off
action, the slapper and dolly are not clashing with each other, they are
beside one another. I would keep tapping away with the slapper, moving the
dolly tightly with some force, against the lowest area of the dent. Slowly
the dent will rise to very close to the surface level. The slapper does
this operation very effectively because it has such a large surface area,
compared to a hammer. With a hammer you're hitting a smaller area and you
might dent the area you're hammering against because it will yield easier
than the center of the dent.
Roughing and slapping the dent has reduced the dent by about 90% and
progress was swift. The next stage of metal finishing requires the bag of
tricks and the tools. The problem that you encounter at this final stage
is, you have trouble seeing what you're doing because your actions have to
be small. When you were roughing you could easily see the metal move closer
to the surface; but now you might only have to move the metal forty
thousands of an inch or less to reach the true surface. At this stage a
common practice is to use a pick hammer. In my opinion a pick hammer has
many drawbacks: one- you need room to be able to swing it; and generally
the hammer itself might be 6" or more across the head. Two- it is very easy
to over hit with a pick hammer and cause irrepairable damage. Three- more
likely than not you will not be able to strike the low spot, instead you
will hit the high spot worsening the problem. The safest bet is to retire
your pick hammer. This verdict also applies to the bulls-eye gimmick tools
which use a C shaped frame to guide you to the elusive low spot. If you go
down the bulls-eye road you will find your garage populated with many
expensive sizes and versions absolutely needed to remove all those pesky
dents and dings. You will always be one bulls-eye tool short.
What I do at this stage is coat the damaged area entirely with the 1/2"
wide red magic marker ( thats a US trade name for those who might not be
familiar with them- there is no magic, its just a felt ink marker) Next I
draw the fine body file over the area, just lightly skimming the surface,
this will quickly reveal the high and low spots. The object now is to raise
the low spots. You can do this by placing a dolly with a high crown surface
tightly against the low spot. You will only be guessing at this point
unless you have x-ray vision . You find out where you really are with the
dolly by lightly slapping the surface, with the the slapper a few times,
trying deliberately to strike the dollies crown. If you are successful -
and you probably will be, because of the slappers large working surface-
you will hear the ring of the contact of the metals. Slide the slapper to
the side, but leave the dolly where it is. You should be able to see a 1/8"
diameter ( a 1/8" inch affected area will raise quickly with little force ,
the size of the mark made when you slap it determines the speed of the
metal rise. 1/8" is fast 1/2" is slow) clear spot, or slightly less inked,
in a region of the small low spot that you were raising. If you goofed and
hit a high area instead you should be able to see a difference there too.
Whether you were in the right area or not is not important, what is most
important, is establishing where you are and being able to adjust . Watch
the trail marks left in the inked surface and you can steer the dolly, on
the backside, easily to where it is needed. Slap lightly, slowly raising
the low spot. After a few minutes, refile the area and your progress will
become apparent.
You might have to wash off the marker ink ; re-ink, and refile several
times. Each working of the area will reduce the size of the low spots.
Remember that the filing is meant just to scrape off the ink and not to
reduce the thickness of the metal. The force and stroke of the slapper will
be less as you progress. When you have reduced the low areas to less than
1/2" in diameter, and when you rub your hand over the area you still
slightly feel them, you are ready to use the shrinking disc.
The condition of the metal at this point is stressed and springy as a
result of all the trauma inflicted on it. The original damage has been
raised but in the process the metal has been stretched a little. If you
applied bondo at this stage some of the bondo would surround the damaged
area, feathering in the new surface height.
With the marker ink still on, and a wet rag handy, crank up the body
grinder with the shrinking disc and rub the area. You vary the pressure
according to how much you need to shrink. On the first pass I usually apply
light pressure. The metal will quickly begin to rise and expand from the
heat build-up. Remove the disc and wipe the area with a wet rag. With that
operation you have started to shrink, stress relieve and further fine tune
the outline of the low spots. You can now re-mark with ink, file and
further tap out the low spots with the slapper and dolly. Some dents might
require several cycles, but as you hone your technique you should be able
to remove most dents in fewer cycles . At this stage an obvious high spot
might have developed. You can easily remove it by rubbing the shrinking
disc over it; it will heat to a blue condition in seconds, and then cool
with the wet rag. After I'm satisfied that I can no longer effectively
raise any remaining tiny low spots (depressions only a few thousands of an
inch deep). I then install the very dull 120 grit 9" grinding disc and
proceed to work the area with it. The grinding disc will level the area
leaving a almost polished surface, it will heat the area quickly also, so
cool it with a rag after you done grinding. If you have done everything
correctly you should have a very smooth surface , that is stress free and
in no need of bondo.
If you practice these techniques on some old , damaged, and unimportant
sheetmetal parts you will quickly hone your skill.
On some areas of the XK Jaguars it is almost impossible to get a
conventional dolly into the area; in those cases you have to be resourceful
and fashion something that will snake into the damaged area, it will be
effective as long as it resists the blows of the slapper causing the metal
to rise.
Regards,
Wray E. Schelin
-----------------------------------------------------------------------------------
Here are a few shots of the progression from the severely dented roof, to one that will need no more than two medium coats of hi-build primer to fill any minor flaws.
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_2-med.jpg
In this next picture, it looks worse than it really is. In reality, the high spots need only slight shrinking to bring them down to the proper surface level. If I were to bring the entire area up to the point there were no low spots and all the marker were sanded off, it would take a considerable amount of shrinking to get the job done. As it is, the high spots are only a few thousandths of a inch high and lightly running the shrinking disc over the entire roof panel will quickly level it out.
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_4-med.jpg
This is the result after a couple passes over the roof with the shrinking disk. It's pretty good at this point, but there are 3 or 4 small areas that need a little work yet.
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_5-med.jpg
And here is the final product. If I had sanded it more, it would perhaps have shown better how straight and smooth this roof panel is, but I haven't got the time right now. The dark spots you see is where the shrinking disc run on the surface and discolored it a bit.
All total, I have just under 3 hours repairing the dents, which covered the majority of this roof. Having spent years smearing body filler, I know it can't be 'fixed' any faster going that route. In fact, I can guarantee I would have spent at least twice that long using filler and perhaps much longer!!!
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_6-med.jpg
The '40 Willys I'm currently working on has about 90 percent of the roof covered with dents. Not small dents, like hail damage, etc., but big ol' nasty lookin' things. I'm going to use the text that Wray Schelin wrote a few years ago on the jaglovers list and add a few pictures to it. Wray covered the subject very well, so no reason to re-write it.
Tools for Removing Dents
By Wray E. Schelin
How smooth are your stripped body panels? That is the question you need to know before you advance to the primer stage. If they're not smooth you can fill them with bondo and heavy primer- but if you do so you run a high risk of a early paint failure and all your work will be in vain- or you can smooth them by accurately working the panel back to a smooth condition. If you rub your hand over the metal and feel low spots or high spots, you can be sure that they will show . Before you get your spray gun out you should be able to rub a panel in any direction and feel nothing but smoothness.
If you choose smoothing instead of filling, I'll share with you the technique that I use and some of the tools needed.
First the tools:
All body tools should have smooth working surfaces; hammers, slappers, and dollys are like printing presses, they will transfer the imperfections on their working faces to the metal over an over. Its best to take the time and smooth your tools first , because any imperfection transferred to the panel can make itself known later in the topcoats,as a paint shrinkage depression.
The higher quality body tools are made of heat treatable steel. You should have at least one hard hammer and one hard dolly- for hammering welds. The reason for this is the welds are harder than the surrounding metal and if you flatten them with a non hard hammer you will mark the hammer and then you will have to keep smoothing it. The working faces of hammers and slappers should have a very slight crown to them and the edges should be radiused. With the edges smooth and the center crowned slightly, you will not mark the panel if you inadvertently strike with the edge of the tool.
The slapper is the most important smoothing tool. You can make a slapper out of a old rear leaf spring. Car springs are harder than welds, so they will not mark up. My slapper has a working face of 2.250" by 5". The thickness is .250" and the unbent starting length is 14". You can also get a single spring leaf new from your local truck spring rebuilder. You can cut it to shape with a cutoff wheel or a torch, but cool it quick so you don't anneal it. I bent mine with an offset of 1.625" . The offset allows you to affix a wood handle and provides the clearance for your fingers. Heat with a torch to bend the offset and then narrow the handle end to a width of 1.375". The narrowed part is 5" long.
This slapper will smooth all body panels except for concave areas. For concave areas you will need to make a special slapper or use hammers. Once you start to use a slapper you will retire your hammer.
You will also need a few dollys. I found most of my dollies at flea markets for a few dollars each. Three or four dollies will be more than adequite to deal with all the different shapes and contours that you encounter . Each dolly usually has several different contours and crowns. As long as you have a straight edge , a low crown, medium crown, and a high crown you will be able to smooth any panel. Don't hesitate to alter the dolly to fit a need ,grind them with a body grinder, to rough shape then use a DA sander- with finer and finer sand papers- in rotary mode to achieve a fine polished finish.
Next you will need a body file and holder. The holders have a turn-buckle on them to allow you to flex the file to a concave, flat, or convex shape. The file that I use I was able to order from my local welding supplier. They are a dealer for a German company called Pferd. I got a Pferd catalog, an found that they offer a 12 tooth per inch body file , which is considered a fine cut body file. Most of the files that I had seen previously were 8 or 9 teeth per inch which are coarse body files. I like the fine file because I can use it on aluminum , steel, or body solder. When I use it on aluminum I load the teeth with a candle wax, this allows you to skate over the aluminum without digging in and making gouges. This type of file is 14 inches long and has cutting surfaces on each of its sides. On one side I grind the edges smooth in effect killing them so they do not dig in as you skate the file sideways. Pferd also sells the holders and a multitude of different style files and abrasives, all are of the highest quality available anywhere. Pferd has distribution centers all over the world. In the USA they can be reached at
Pferd Inc
30 Jytek Dr.
Leominster, MA 01453
Phone 508 840-6420
In Australia:
Pferd Australia (Pty) Ltd.
Moorabbin, Vic.
3189 8 Capella Cresent
(03) 5531946+5531933
You can also try your local welding supply house and they might have a catalog.
Another item I use is a large magic marker or felt marker. The ones that I use are called magnums and they mark a swath about 1/2" wide with a tenacious ink that dries very quickly. I like red ink the best.
A heavy duty 9" body grinder is the most expensive item needed. You can use a lighter duty 7" grinder but it won't work as well as the 9" in all cases.
Also a 9" 120 grit grinding disc. Grinding discs when they are new are very sharp when you run your finger over them , after grinding a heavy piece of steel for a few minutes you will dull the disc. This is how I prepare my discs, purposely dulling them to make them suitable for use.
Lastly you will need the Amazing Shrinking Disc. I mentioned this tool before in another post, it is a 9" disc of .050" stainless steel with some ruffles pressed into the outer working surface. This tool is most effective when used with the heavy duty 9" body grinder. I can't say enough about how good this simple tool works.
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_1-med.jpg
In my next post I will explain the process that I use in conjunction with the earlier mentioned tools. For many years I haphazardly removed dents with a method which always left the panel in a improved state, but not perfect. I frankly didn't believe you could restore the damaged metal to a state were no filler other than primer would be necessary. Like most things once you master them they are quite simple, all you need is the determination and the correct method.
Regards,
Wray E. Schelin
Removing Dents
by Wray Schelin
--------------------------------------------------------------------------------
In the last post I described the tools necessary to completely remove
dents, waves, and dings in your body panels. In this post I will share with
you how I use the tools to achieve a panel smoothness that will require
very little or no bondo filler. It is best to keep your bondo use down for
two reasons. One,bondo use is not craftsmanship, its just a cheap
substitute. If your trying to achieve a high standard restoration- in my
opinion it is best to have the craftsmanship on more than just what you
see. The value of these cars is more than just the dollar amount. The
second reason is, if you keep your substrates (bondo fillers and primers)
to a very minimum and apply just enough topcoats you will have an ideal
thickness of paint coatings. With an ideal thickness your paint system will
be able to expand and contract with the steel and aluminum surfaces of your
cars body as it heats and cools. This correct thickness insures you against
an early paint failure. Coatings can fail for many other reasons, but too
much paint and filler I believe is the most common culprit.
The most surprizing thing about high quality metal finishing, is that is
not that difficult to do; but it does take patience, good eyesight, a fine
sense of touch, and the tools that I previously mentioned.
First what's fixable and what's not. If you have, say, a 120 front fender
that was severely damaged in a accident many years ago on its leading
surfaces, an was quickly repaired by sewing up tears with brazing rod,
crudely hammered out, ground very thin, and then filled with bondo, forget
it; in that case you are probably better served by replacing that heavily
damaged section. Another impossibility is an area that has been incorrectly
torch shrunk; what had started out as an earnest limited attempt,
inadvertently expanded to large area, leaving heat damage with heavy
intractable waves.
Fixable dents and damage, listed in a descending order of severity:
Bodged past repairs that are still fixable, because the metal has not been
ground too thin,
Collision damage with stretching and tearing,
Sandblasting with excessive pressure causing a wave effect,
Smoothing out the seam of a butt welded patch panel,
Small dents with little or no stretching,
I 'll share with you how I remove a small dent . An easy example will work
best, so lets say, its the rear fender of a XK120. The dent is in the
middle of the rear section of the fender, and its is about the size of your
fist, sunken in about 3/4" in the center. All paint and undercoating should
be removed first. I would first select a dolly that has a crown that is
close to the fender; in this case that would be a medium crown. Using a
glove to protect my fingers I would palm the dolly and lightly tap it
against the bump on the inside of the fender; carefully watching the
progress of the rising depression. I would use this process until I got the
dent up to within 1/8" of the surface. This will happen within minutes-
this is called roughing out the dent. Next I would hold the dolly tightly
against the center of the damage , on the backside, while I use the slapper
on the front, tapping the circumference of the dent. This is a dolly off
action, the slapper and dolly are not clashing with each other, they are
beside one another. I would keep tapping away with the slapper, moving the
dolly tightly with some force, against the lowest area of the dent. Slowly
the dent will rise to very close to the surface level. The slapper does
this operation very effectively because it has such a large surface area,
compared to a hammer. With a hammer you're hitting a smaller area and you
might dent the area you're hammering against because it will yield easier
than the center of the dent.
Roughing and slapping the dent has reduced the dent by about 90% and
progress was swift. The next stage of metal finishing requires the bag of
tricks and the tools. The problem that you encounter at this final stage
is, you have trouble seeing what you're doing because your actions have to
be small. When you were roughing you could easily see the metal move closer
to the surface; but now you might only have to move the metal forty
thousands of an inch or less to reach the true surface. At this stage a
common practice is to use a pick hammer. In my opinion a pick hammer has
many drawbacks: one- you need room to be able to swing it; and generally
the hammer itself might be 6" or more across the head. Two- it is very easy
to over hit with a pick hammer and cause irrepairable damage. Three- more
likely than not you will not be able to strike the low spot, instead you
will hit the high spot worsening the problem. The safest bet is to retire
your pick hammer. This verdict also applies to the bulls-eye gimmick tools
which use a C shaped frame to guide you to the elusive low spot. If you go
down the bulls-eye road you will find your garage populated with many
expensive sizes and versions absolutely needed to remove all those pesky
dents and dings. You will always be one bulls-eye tool short.
What I do at this stage is coat the damaged area entirely with the 1/2"
wide red magic marker ( thats a US trade name for those who might not be
familiar with them- there is no magic, its just a felt ink marker) Next I
draw the fine body file over the area, just lightly skimming the surface,
this will quickly reveal the high and low spots. The object now is to raise
the low spots. You can do this by placing a dolly with a high crown surface
tightly against the low spot. You will only be guessing at this point
unless you have x-ray vision . You find out where you really are with the
dolly by lightly slapping the surface, with the the slapper a few times,
trying deliberately to strike the dollies crown. If you are successful -
and you probably will be, because of the slappers large working surface-
you will hear the ring of the contact of the metals. Slide the slapper to
the side, but leave the dolly where it is. You should be able to see a 1/8"
diameter ( a 1/8" inch affected area will raise quickly with little force ,
the size of the mark made when you slap it determines the speed of the
metal rise. 1/8" is fast 1/2" is slow) clear spot, or slightly less inked,
in a region of the small low spot that you were raising. If you goofed and
hit a high area instead you should be able to see a difference there too.
Whether you were in the right area or not is not important, what is most
important, is establishing where you are and being able to adjust . Watch
the trail marks left in the inked surface and you can steer the dolly, on
the backside, easily to where it is needed. Slap lightly, slowly raising
the low spot. After a few minutes, refile the area and your progress will
become apparent.
You might have to wash off the marker ink ; re-ink, and refile several
times. Each working of the area will reduce the size of the low spots.
Remember that the filing is meant just to scrape off the ink and not to
reduce the thickness of the metal. The force and stroke of the slapper will
be less as you progress. When you have reduced the low areas to less than
1/2" in diameter, and when you rub your hand over the area you still
slightly feel them, you are ready to use the shrinking disc.
The condition of the metal at this point is stressed and springy as a
result of all the trauma inflicted on it. The original damage has been
raised but in the process the metal has been stretched a little. If you
applied bondo at this stage some of the bondo would surround the damaged
area, feathering in the new surface height.
With the marker ink still on, and a wet rag handy, crank up the body
grinder with the shrinking disc and rub the area. You vary the pressure
according to how much you need to shrink. On the first pass I usually apply
light pressure. The metal will quickly begin to rise and expand from the
heat build-up. Remove the disc and wipe the area with a wet rag. With that
operation you have started to shrink, stress relieve and further fine tune
the outline of the low spots. You can now re-mark with ink, file and
further tap out the low spots with the slapper and dolly. Some dents might
require several cycles, but as you hone your technique you should be able
to remove most dents in fewer cycles . At this stage an obvious high spot
might have developed. You can easily remove it by rubbing the shrinking
disc over it; it will heat to a blue condition in seconds, and then cool
with the wet rag. After I'm satisfied that I can no longer effectively
raise any remaining tiny low spots (depressions only a few thousands of an
inch deep). I then install the very dull 120 grit 9" grinding disc and
proceed to work the area with it. The grinding disc will level the area
leaving a almost polished surface, it will heat the area quickly also, so
cool it with a rag after you done grinding. If you have done everything
correctly you should have a very smooth surface , that is stress free and
in no need of bondo.
If you practice these techniques on some old , damaged, and unimportant
sheetmetal parts you will quickly hone your skill.
On some areas of the XK Jaguars it is almost impossible to get a
conventional dolly into the area; in those cases you have to be resourceful
and fashion something that will snake into the damaged area, it will be
effective as long as it resists the blows of the slapper causing the metal
to rise.
Regards,
Wray E. Schelin
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Here are a few shots of the progression from the severely dented roof, to one that will need no more than two medium coats of hi-build primer to fill any minor flaws.
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_2-med.jpg
In this next picture, it looks worse than it really is. In reality, the high spots need only slight shrinking to bring them down to the proper surface level. If I were to bring the entire area up to the point there were no low spots and all the marker were sanded off, it would take a considerable amount of shrinking to get the job done. As it is, the high spots are only a few thousandths of a inch high and lightly running the shrinking disc over the entire roof panel will quickly level it out.
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_4-med.jpg
This is the result after a couple passes over the roof with the shrinking disk. It's pretty good at this point, but there are 3 or 4 small areas that need a little work yet.
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_5-med.jpg
And here is the final product. If I had sanded it more, it would perhaps have shown better how straight and smooth this roof panel is, but I haven't got the time right now. The dark spots you see is where the shrinking disc run on the surface and discolored it a bit.
All total, I have just under 3 hours repairing the dents, which covered the majority of this roof. Having spent years smearing body filler, I know it can't be 'fixed' any faster going that route. In fact, I can guarantee I would have spent at least twice that long using filler and perhaps much longer!!!
http://www.metalmeet.com/photopost/data/3474/11roof_dent_repair_6-med.jpg