A question for MP&C - and anyone else who feels compelled to weigh in

[SuperBuickGuy]

as much as I'm enjoying everyone weighing in on the dangers of sand...

a question for the expert...

when using a shrinking dolly or hammer - what is the physics of what is happening when you whack the metal? I get stretching by squishing (technical term) the metal between two solid surfaces. But my head is not wrapping around the idea of how the metal shrinks by hitting it - even more specifically, does it matter what side the serrated tool is used on? I've also seen people doing it with heat and without heat... is there a best practice?

and as many tend to comment - I'll give some context with my nutshell of what they're saying

heat to red, use hammer, cool

https://www.youtube.com/watch?v=WgRaPWYT9vM

heat to blue, NEVER use air or cool and serrated hammers are stupid
https://www.tinmantech.com/education...-and-donts.php

don't heat, serrated hammers don't work
https://www.hotrod.com/articles/prof...rking-tips-13/

heat to red, hammer off dent, cool with air

https://www.bodyshopbusiness.com/heat-shrinking-metal/

Even more specifically, squishing I understand, stacking I don't. I understand how heat works by relaxing the molecules to allow the metal to get back to a more 'natural' shape (even though steel is anything but a natural shape - for those who are following along, see how steel is made and what happens at the molecular level).

[SuperBuickGuy]

I even understand what's happening with hammer off dolly work... anyway.... expert(s)?

[MP&C]

Do you have a dent in particular you are working on or is this a hypothetical lesson type thing?

[SuperBuickGuy]

Do you have a dent in particular you are working on or is this a hypothetical lesson type thing?

well sure, I have lots of dents.... not the bit that has grind marks on it, just to the left there is a wave that I'd love to fix - it doesn't oil can but it also doesn't stay convex



maybe this shows it better

[SuperBuickGuy]

above the weld, to the left of the spot with grind marks (that's actually already fixed)... it's funny, I guess, when it's a big issue (where the grind marks are), I have less problem going primordial to fix the dent.... it's the ones that I'd 'like' to fix but it could live without actually fixing it that cause me the most concern (maybe because it's so easy to make a minor problem into a major problem)

[MP&C]

Responses in Blue

as much as I'm enjoying everyone weighing in on the dangers of sand...

a question for the expert... I prefer "makes less scrap than he used to"

when using a shrinking dolly or hammer - what is the physics of what is happening when you whack the metal? I get stretching by squishing (technical term) the metal between two solid surfaces. But my head is not wrapping around the idea of how the metal shrinks by hitting it - even more specifically, does it matter what side the serrated tool is used on? I've also seen people doing it with heat and without heat... is there a best practice?

Because most people don't know/practice the proper use of the serrated dolly/hammer (including the dude in your first video), and let's not forget the twisty shrinking hammer either, they are mainly considered gimmick tools that don't produce good or consistent results.

1. Let's start with the twisty hammer. In order for it to actually "twist" to effect the shrink, it will take a considerable swing. I personally have found that it is a fine line between you've got all the shrink out of it that you're going to and oops, now we're stretching again. If given the choice, I would prefer a regular body hammer and donut dolly. If you absolutely must have one of these and try for yourself, please shop for a used one. There is bound to be someone else out there that had the same thought and getting $10 out of their now used hammer that didn't work for them is better than nothing at all. And you'll pay 1/4 to 1/3 of retail for a hardly used hammer.

2. Now let's talk about the serrated (waffle face) hammer. I'll start by drawing a comparison to a framing hammer. If you've swung a framing hammer (before the advent of so many pneumatic, battery, and LP nailers came along) and had the chance to use a smooth faced one, any slight mis-alignment and the nail was rather quick to bend over. Now if you've also swung the waffle faced framing hammer, you know that they seldom had that problem. The way this works is that the waffle face is essentially multiple tiny hammer faces, so when one tends to slip, another nearby will grab the surface of the nail to keep the momentum going forward instead of sideways. So keep that thought.....

2a. So the comparison between the framing hammer and body hammer stops there. I would suggest there is no need whatsoever to swing a body hammer as hard as you do a framing hammer. Technique and location far outweigh heft and velocity in producing better, consistent results. For the serrated body hammer, it is intended for use in an area that has a distorted, perhaps uneven surface, that when you TAP inwards, it grabs the high spots and doesn't let go (slip). So in a similar fashion to tuck shrinking, we should always be addressing the high spot. When the tuck moves and now the high spot is somewhere else, you move to the new high spot. The serrated hammer does a good job of grabbing the high spot. I would add here, that TAPPING the dent with said hammer should not sound like you are swinging a framing hammer, and if you are hearing the PING PING PING against the dolly, you are stretching.. Did I mention you only TAP the hammer? Now go back and watch dude in the wife beater again. Listen to the PING coming out of that dolly. I would suggest that you are hearing the metal stretch, and also it is leaving the waffle pattern in the face of the metal. Perhaps dad didn't know how to use it either. Now that you've heard the PING of metal stretching, go back and keep an eye on the nearest end of the square/straight edge. The gap may have disappeared where it once was, but now the gap is located at the nearest end of the ruler. So yes, what was once stretched inward as a dent is now stretched outward as a bulge.

2b. The proper use of these type tools is to not leave a waffle imprint in your sheet metal. If you do, you are swinging too hard. For someone to heat that dent as much as was done, there is absolutely no need to hit the panel so hard. Light TAPS will flatten it right out, when it cools naturally it will shrink up a bit more. And props to Kent White, you don't need to heat it cherry red, this is only forming mill scale. Blue is plenty hot enough. You don't need to quench, natural cooling will do the same thing. As he told me once on the phone, "all hammers shrink". So with that in mind, it comes down to technique, choosing the right tools, and not inflicting more damage into the panel.


As stated above, most people don't know the proper use. They are attempting to add a waffle pattern into the metal by their actions thinking that is drawing the metal together, and it is not the proper method. I think that's why you hear so many try to steer novices away from such tools, for the damage they inflict. Eastwood and similar companies don't care if you'll never use the hammer again, it's a sale. So if Mr. White says all hammers shrink, please choose one that doesn't screw up the nice flat surface of the metal. I've had good luck with donut dollies, small shot bags, and FLAT body hammers, that still leave the metal nice and smooth.






and as many tend to comment - I'll give some context with my nutshell of what they're saying

heat to red, use hammer, cool

https://www.youtube.com/watch?v=WgRaPWYT9vM

heat to blue, NEVER use air or cool and serrated hammers are stupid
https://www.tinmantech.com/education...-and-donts.php

don't heat, serrated hammers don't work
https://www.hotrod.com/articles/prof...rking-tips-13/

heat to red, hammer off dent, cool with air

https://www.bodyshopbusiness.com/heat-shrinking-metal/

Even more specifically, squishing I understand, stacking I don't. I understand how heat works by relaxing the molecules to allow the metal to get back to a more 'natural' shape (even though steel is anything but a natural shape - for those who are following along, see how steel is made and what happens at the molecular level).

[MP&C]

above the weld, to the left of the spot with grind marks (that's actually already fixed)... it's funny, I guess, when it's a big issue (where the grind marks are), I have less problem going primordial to fix the dent.... it's the ones that I'd 'like' to fix but it could live without actually fixing it that cause me the most concern (maybe because it's so easy to make a minor problem into a major problem)

For that, you have a weld above and below that have shrunk, pulling the panel together horizontally from front to back. The "extra" metal has formed a pucker as it looks for somewhere to go. Stretch the weld and the bulge will relieve, flattening the panel. Shrinking caused the issue, more shrinking does not fix it. Stretch the weld.. Stretch the weld...

[SuperBuickGuy]

For that, you have a weld above and below that have shrunk, pulling the panel together horizontally from front to back. The "extra" metal has formed a pucker as it looks for somewhere to go. Stretch the weld and the bulge will relieve, flattening the panel. Shrinking caused the issue, more shrinking does not fix it. Stretch the weld.. Stretch the weld...

I love it, I can go primordial
I didn't hammer that weld because God created me with arms that are too short - but I fixed that today with the addition of a dolly on a stick. It makes perfect sense that dent came from the joint shrinking along the weld line.

thank you for the explanation, the tools make a lot more sense now

Does it matter from which side you strike the weld? - not asking about using a domed dolly or hammer because that would move due to pressure points....

[squirrel]

I can't read blue on gray, so I copied/pasted the long reply, so I could read it. Hope you don't mind.

btw I always thought shrinking with heat had a lot to do with heating, knocking the bulge flat, then let it contract as it cools. But I've never been any good at it...

-------------------------

Because most people don't know/practice the proper use of the serrated dolly/hammer (including the dude in your first video), and let's not forget the twisty shrinking hammer either, they are mainly considered gimmick tools that don't produce good or consistent results.

1. Let's start with the twisty hammer. In order for it to actually "twist" to effect the shrink, it will take a considerable swing. I personally have found that it is a fine line between you've got all the shrink out of it that you're going to and oops, now we're stretching again. If given the choice, I would prefer a regular body hammer and donut dolly. If you absolutely must have one of these and try for yourself, please shop for a used one. There is bound to be someone else out there that had the same thought and getting $10 out of their now used hammer that didn't work for them is better than nothing at all. And you'll pay 1/4 to 1/3 of retail for a hardly used hammer.

2. Now let's talk about the serrated (waffle face) hammer. I'll start by drawing a comparison to a framing hammer. If you've swung a framing hammer (before the advent of so many pneumatic, battery, and LP nailers came along) and had the chance to use a smooth faced one, any slight mis-alignment and the nail was rather quick to bend over. Now if you've also swung the waffle faced framing hammer, you know that they seldom had that problem. The way this works is that the waffle face is essentially multiple tiny hammer faces, so when one tends to slip, another nearby will grab the surface of the nail to keep the momentum going forward instead of sideways. So keep that thought.....

2a. So the comparison between the framing hammer and body hammer stops there. I would suggest there is no need whatsoever to swing a body hammer as hard as you do a framing hammer. Technique and location far outweigh heft and velocity in producing better, consistent results. For the serrated body hammer, it is intended for use in an area that has a distorted, perhaps uneven surface, that when you TAP inwards, it grabs the high spots and doesn't let go (slip). So in a similar fashion to tuck shrinking, we should always be addressing the high spot. When the tuck moves and now the high spot is somewhere else, you move to the new high spot. The serrated hammer does a good job of grabbing the high spot. I would add here, that TAPPING the dent with said hammer should not sound like you are swinging a framing hammer, and if you are hearing the PING PING PING against the dolly, you are stretching.. Did I mention you only TAP the hammer? Now go back and watch dude in the wife beater again. Listen to the PING coming out of that dolly. I would suggest that you are hearing the metal stretch, and also it is leaving the waffle pattern in the face of the metal. Perhaps dad didn't know how to use it either. Now that you've heard the PING of metal stretching, go back and keep an eye on the nearest end of the square/straight edge. The gap may have disappeared where it once was, but now the gap is located at the nearest end of the ruler. So yes, what was once stretched inward as a dent is now stretched outward as a bulge.

2b. The proper use of these type tools is to not leave a waffle imprint in your sheet metal. If you do, you are swinging too hard. For someone to heat that dent as much as was done, there is absolutely no need to hit the panel so hard. Light TAPS will flatten it right out, when it cools naturally it will shrink up a bit more. And props to Kent White, you don't need to heat it cherry red, this is only forming mill scale. Blue is plenty hot enough. You don't need to quench, natural cooling will do the same thing. As he told me once on the phone, "all hammers shrink". So with that in mind, it comes down to technique, choosing the right tools, and not inflicting more damage into the panel.


As stated above, most people don't know the proper use. They are attempting to add a waffle pattern into the metal by their actions thinking that is drawing the metal together, and it is not the proper method. I think that's why you hear so many try to steer novices away from such tools, for the damage they inflict. Eastwood and similar companies don't care if you'll never use the hammer again, it's a sale. So if Mr. White says all hammers shrink, please choose one that doesn't screw up the nice flat surface of the metal. I've had good luck with donut dollies, small shot bags, and FLAT body hammers, that still leave the metal nice and smooth.

[SuperBuickGuy]

btw I always thought shrinking with heat had a lot to do with heating, knocking the bulge flat, then let it contract as it cools. But I've never been any good at it...
h.

You hit on the genesis of my question..... I've tried heating/quenching so many times and failed - it's not even funny. I only use heat, now, to soften the metal so I can bend it.

[squirrel]

When I was building my Chevy II, a friend visited for a month and helped a lot with the bodywork. He did a lot of shrinking with heat...doors, quarters, mostly. I should have paid more attention.

I did use heat to soften metal for bending just a little while ago, modifying a wrench to get the flywheel bolts off the T. It still works.

[SuperBuickGuy]

hammering the weld got about 1/2 the dent
I know it's harder to see, but where the seam is (top and bottom) it is flat - now there are 2 dents (still not the forward dent) on the left which look like elipses () the dents are outlined by pencil marks

my next step is a crown dolly behind the dent then hammer-off-dolly the circumference. After that, I think it is now is the time for a touch of heat.... but not until I get the body bolted back on the frame....

[MP&C]

Hammer the welds some more. Focusing above and below the “dents”. It was flat when you started, right? So the only thing that has happened is shrinking from weld heat. Stretch the weld...

[SuperBuickGuy]

Hammer the welds some more. Focusing above and below the “dents”. It was flat when you started, right? So the only thing that has happened is shrinking from weld heat. Stretch the weld...

flatish... this fender was supposed to be 'close'.... I'm thinking 'close' doesn't mean the same thing in Canada as it does in the US.

[MP&C]

For "close", the difference in meaning changes from buyer to seller...

Buyer: He said it was "close", this should be an easy fix...

Seller: Glad he showed up I was "close" to throwing that away...