Thread: 55 Wagon Progress

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How do I double - like this? (The book idea)

You've got pictures. You've got dialogue.

It would be a minimal effort to add missing details, it might fetch a pretty penny.

BTW... hard copy, coffee table edition (over sized)

Progress pics from last night... Yep, we've been block sanding..





Using Evercoat 416 to address the few low spots..












Honing up on my painting skills with brush on seam sealer










Today's lesson is on media blasting and stretch damage that occurs. Here’s what a sand blaster will do to a roof skin when blasting the braces underneath.











Our blaster was doing the brace from underneath/inside and the inadvertent stray media hitting the adjacent roof skin stretched it, pulling it inward toward the media stream . On the outside the “unstretched” area shows as a high spot, the stretched part that needs shrinking is seen as a low. So if you must media blast any braces or internal structure, block off the skin next to it so no media touches it. Save yourself the extra body work.


We fixed the lows by locating the exact spots on the inside that needed shrinking and tapping outward into a small shot bag. To locate, a rare earth magnet is placed outside on the roof skin in each low spot, and some grinding dust finds the magnet on the inside where we can mark the perimeter both inside and out, and work with one person on either side to remove the lows. (See video, magnet marks highs or lows, it doesn’t care) For multiple lows, mark both sides of all spots and number them, so you can move from one spot to the next, calling out the number desired to your shrinking assistant. If your car is too clean to have grinding dust, look under your bench grinder.


Magnet use video:


https://www.youtube.com/watch?v=HHHTKiWZ2Xo


Note on the inside roof skin picture the multiple numbered circles where we found low spots to address.


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More excellent work! Have you seen the attachments for pressure washers that inject sand to sand blast? I'm thinking that would be pretty nice on sheet metal. No heat so hopefully no warpage and no dust too.

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Any heat noticed in normal blasting is a side effect of the peening action. Stretching has already occurred long before the heat shows up, so don't buy into the pressure washer hype too deep. They can cause just as much damage. Think of all that media as little hammer heads beating the sheet metal. In the case of our roof, it was being blasted from the bottom side to clean off the roof brace. The media that struck the roof skin to the sides of the brace was peening the sheet metal, in essence causing it to stretch the skin on the surface that the media is striking. This stretch on the one side of the sheet metal then causes the panel to balloon inward, TOWARD the media source, which on the outside appears as a low. Larger media = bigger hammers. Too much air pressure = a harder swing on those hammers. Whether the media is propelled by air, water, or anything else you can find, too much swing of too big a hammer will indeed stretch, despite the "water keeping the panel cool". Have seen it on hoods, trunk lids, you name it. Someone attempts to clean off an inner structure and hits the sheet metal from the bottom, and you have an instant low right where that brace/structure ends.


Here is a sandblast test I did on a trunk lid to learn up on the subject...


Repairing Sandblast Damage - The 1947 - Present Chevrolet & GMC Truck Message Board Network


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As usual - a great and interesting read. I learned a lot and won't ever look at a simple dent in the same way!!!

Thank You Robert, for sharing your knowledge... with us mere mortals!

i use cardboard inside doors and such when blasting. lot of damage is done by blasting inside .
that blast attachment for pressure washer is nothing new. one came with a washer i bought years ago. good way to destroy a car and make it a rusty mess .

Thanks again Mike. The quality of the build on the 55 makes me want to put Rita in the crusher LOL. I did a fair amount of siphon media blasting on Rita on the edges and corners and stuff. I stayed away from flat parts of anything, that being said I still ended up with some distortion on the roof or someone used it for a step ladder, I'm not sure what happened first. Very possible over the course of 70 years it got used as a step ladder.

Originally Posted by 53 Chevy5

Thanks again Mike. The quality of the build on the 55 makes me want to put Rita in the crusher LOL. I did a fair amount of siphon media blasting on Rita on the edges and corners and stuff. I stayed away from flat parts of anything, that being said I still ended up with some distortion on the roof or someone used it for a step ladder, I'm not sure what happened first. Very possible over the course of 70 years it got used as a step ladder.

More than likely that someone or someones used it to set on so they could see something they couldn't see clearly from the ground. Used to see a lot of that at drag races years ago.

I've been known to toss a bale (or two) of hay on the roof to finish off a field.
OK, OK... maybe it was 3 or 4.. LOL

Ok on the pressure washer blaster. Is there any safe media to use to keep war-page down to a minimum? Baking soda, walnut shells? I ask because I fell into another project and I am trying to figure out the best way to get the surface rust off without screwing it up.

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Originally Posted by 40FordDeluxe

I fell into another project and I am trying to figure out the best way to get the surface rust off without screwing it up.

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Noooooooo! I want to see the 40 live!

Originally Posted by 40FordDeluxe

Ok on the pressure washer blaster. Is there any safe media to use to keep war-page down to a minimum? Baking soda, walnut shells? I ask because I fell into another project and I am trying to figure out the best way to get the surface rust off without screwing it up.

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I use a garnet abrasive that is made for water jet machines. 80HPA made by Barton. Works well, or another is coal slag type like Black Beauty. In general, recalling earlier comments above, you want med to fine media (smaller hammers) and lower air pressure (lighter hits of the hammers) while holding the nozzle at an angle (less impact). When blasting inner doors, inner structures for hoods, trunk lids, etc, block off openings that you don't hit open areas and get the issues I showed above.


I wouldn't recommend soda, it will change PH of the metal where Epoxy doesn't have it's bite anymore, and may pull off in sheets, or sand as most also contain caustic salts, not something you want impaled into your sheet metal.

Originally Posted by 53 Chevy5

Noooooooo! I want to see the 40 live!

Yeah, What he said!!

I used black diamond media one time on tractor rims. Maybe you know of a different type, but it was soo aggressive that I ended up going back over with silica sand to smooth them out.