locating lows for metal bumping - The 1947 - Present Chevrolet & GMC Truck Message Board Network

MP&C · 03-31-2018, 08:37 PM

We were blocking out the wagon's roof today, and had a few low spots to bump upwards. To locate the lows on the inside, I thought to use one of our rare earth magnets in the center of the low, and use the body hammer on the bottom side of the roof to pinpoint the magnetic pull. These are 65 lb pull magnets that we use for our paper patterns. By a stroke of luck (blind squirrel finds acorn) we noticed in scuffing the inside of the roof that the magnet location readily appeared, for a more accurate locating method.

Video:

https://www.youtube.com/watch?v=Ubq89aPMJjY

.

**mongocanfly** · 03-31-2018, 09:48 PM

that's a neat trick...

MP&C · 04-01-2018, 09:51 PM

Had a couple questions on what the heck I'm showing in the video.. Haha... so let's clarify..

We were blocking out the primer on the roof and came across a few low spots. These were low enough to be seen in the paint if left alone, and yet mixing and sanding any filler "repair" would have taken longer than some simple bumping of the low area.

Since I don't have a Bullseye Pick, we thought to use some gentle hammering with a crowned body hammer beneath into a small shot bag on the top (outside) of the roof. We have some 65 lb pull rare earth magnets that we typically use for our paper patterns, and this showed to have enough strength to pull through the roof skin. So we placed the magnet in the center of the low area, and in order to locate on the underside, would skim across the roof from beneath with the hammer face to see where the pull was strongest. The location was then marked underneath with a sharpie, magnet removed and replaced with the shot bag, and the area was tapped into the shot bag until blocking showed the area where it should be.

On one of these "marking with a sharpie" efforts, there was a slight bit of dust on the bottom side of the roof, so I gave it a wipe with my hand to displace the dust and instantly saw the outer circle of the magnet. This was much more accurate than using the magnetic pull test, so we changed to this, and the metal bumping effort worked well. We surmise that this "dust" that clings to the magnetic field is likely sanding residue from the primer, or sanding residue from dressing welds inside the car, or both. In any case, it worked well to help transpose the low spot locations to the bottom side for more accurate hammering.

03-31-2018, 08:37 PM	#1
MP&C Registered User Join Date: Jan 2013 Location: Leonardtown, MD Posts: 1,633	locating lows for metal bumping We were blocking out the wagon's roof today, and had a few low spots to bump upwards. To locate the lows on the inside, I thought to use one of our rare earth magnets in the center of the low, and use the body hammer on the bottom side of the roof to pinpoint the magnetic pull. These are 65 lb pull magnets that we use for our paper patterns. By a stroke of luck (blind squirrel finds acorn) we noticed in scuffing the inside of the roof that the magnet location readily appeared, for a more accurate locating method. Video: https://www.youtube.com/watch?v=Ubq89aPMJjY . __________________ Robert

03-31-2018, 09:48 PM	#2
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,582	Re: locating lows for metal bumping that's a neat trick... __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

04-01-2018, 09:51 PM	#3
MP&C Registered User Join Date: Jan 2013 Location: Leonardtown, MD Posts: 1,633	Re: locating lows for metal bumping Had a couple questions on what the heck I'm showing in the video.. Haha... so let's clarify.. We were blocking out the primer on the roof and came across a few low spots. These were low enough to be seen in the paint if left alone, and yet mixing and sanding any filler "repair" would have taken longer than some simple bumping of the low area. Since I don't have a Bullseye Pick, we thought to use some gentle hammering with a crowned body hammer beneath into a small shot bag on the top (outside) of the roof. We have some 65 lb pull rare earth magnets that we typically use for our paper patterns, and this showed to have enough strength to pull through the roof skin. So we placed the magnet in the center of the low area, and in order to locate on the underside, would skim across the roof from beneath with the hammer face to see where the pull was strongest. The location was then marked underneath with a sharpie, magnet removed and replaced with the shot bag, and the area was tapped into the shot bag until blocking showed the area where it should be. On one of these "marking with a sharpie" efforts, there was a slight bit of dust on the bottom side of the roof, so I gave it a wipe with my hand to displace the dust and instantly saw the outer circle of the magnet. This was much more accurate than using the magnetic pull test, so we changed to this, and the metal bumping effort worked well. We surmise that this "dust" that clings to the magnetic field is likely sanding residue from the primer, or sanding residue from dressing welds inside the car, or both. In any case, it worked well to help transpose the low spot locations to the bottom side for more accurate hammering. __________________ Robert



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