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Old 07-08-2018, 02:05 PM
Mr fixit Mr fixit is offline
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Default planishing vs stretching

Hi Group,

A basic question of how do you know when your planishing a sheet of steel vs stretching the metal. I'm assuming that some of both is happening using hand held hammers.
I'm not seeing the smoothing of the metal that I'm after (planishing) and I'm hoping it isn't getting much larger. This is a patch panel piece for a front fender that has a low crown bend to it.
I've also read about planishing welds, is this to smooth them out after grinding, filing, sanding to a OK finish then final smoothing with the hammer and dolly to planish the weld.

So the real question, how best to explain planishing metal for a beginner?

TX
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Old 07-08-2018, 06:28 PM
Charlie Myres Charlie Myres is offline
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Thoughts from an inexpert.
Imagine looking at the edge of a piece of metal with a small dent (low spot) in it.

With a dolly close to the shape of the panel, under the low pushing upwards; one strikes across the low with a flipper, or slapper. The flipper hits each side of the low and pushes the metal down a little and the mass of the dolly lifts the low upwards a little. This is probably not stretching anything, but it is rearranging the metal.

After a few more slaps the low has been raised, until the original shape has been almost restored. At some point the hollow drum-beat from the slapper on semi-supported metal, changes to a "tink" noise as the metal is directly hit against the dolly. When it "tinks" the metal is being stretched.

If you repeatedly check the profile with the flat-of-your-hand, or any other suitable tool or profile, you will have a very good idea when the metal has been stretched enough. If one persists with this technique using lighter and fewer taps with very smooth tools and files lightly and sands perhaps and polishes, then the metal achieves the smoothness you seek. One can say it is planished.

This of course is very laborious and is what a jeweller will do. Using an English wheel is quicker and takes the hit-and-miss out of the slapping,

Cheers Charlie
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Last edited by Charlie Myres; 07-08-2018 at 06:34 PM.
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Old 07-08-2018, 08:42 PM
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Kerry Pinkerton Kerry Pinkerton is offline
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Charles is right but a wheeling machine is a continuous impact hammer, if the wheels have pressure on them, stretching is happening. It may not be much but it's there. With no pressure but close contact, you can rearrange metal much like pressing it on something from one side only.


Planishing is French I believe and basically means, 'hit lightly many times'. Many planishing hammers can hit a ton and will stretch the heck out of a panel in half a nanosecond. It takes a good bit of experience to work with a powerful planishing hammer...especially in aluminum.


Welds are planished in order to stretch out the shrink caused by the heat of welding. Metal left 'proud' when planishing will be flattened and pushed into the surrounding area (metal flows in the path of least resistance). Lumpy or inconsistent prouds will create a wavy panel if you're not careful.


I hope this helps Chris.
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Old 07-09-2018, 12:39 AM
Mr fixit Mr fixit is offline
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Great advice guys! It sounds like I should get the English wheel project going so that I can get the desired results on the future project fenders and the rest of the car. Another tool to make to get the job done!
For now it sounds like I take my time, go slow, light hits of the tools, to get the smoothness of a finished panel to be coated with finish products for the end result of a painted fender.

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Old 07-09-2018, 10:10 AM
John Buchtenkirch John Buchtenkirch is offline
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Planishing (particularly with a pneumatic hammer) is just blending highs & lows into a smooth panel. Initially there can be a slight amount of shrinking during the smoothing process because you are trapping the highs & lows between the dies but once the panel is smooth enough that both dies have full on contact both sides of the panel you are surely stretching. Thatís assuming that you have a planishing hammer that works in pretty much a constant state of panel pinch like a CP hammer & most of the others do, I canít speculate about home built hammers only because Iím unfamiliar with their operation. A combination of dies with small hit point and using a higher air pressure can do quite a bit of stretching / shaping with a pneumatic hammerÖÖÖ so thatís what you need to avoid if youíre concerned about stretching the panel youíre working. ~ John Buchtenkirch !!!!!!!!!!CP2.jpg

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Old 07-09-2018, 10:43 AM
timothale timothale is offline
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Default metalurgy 101

Almost 60 years ago my college metalurgy professor demonstrated how steel behaves when heated and cooled. He had a steel wire stretched across the clasroom between 2 insulators and wired in series with a light bulb, he fliped the switch and the wire started heating up and expanded and started to sag, then as it heated and got to a dull glow the wire started to contract and pull back up. The professor explaned at a certain temperature the steel, carbon, and, othe elements rearrange the molecular structure , get dense and were non magnetic. When the metal is rapidly cooled the molecular structure stays locked in. This is the process to harden tool steal then reheating to temper and change some of the structure to get the degree of hardness you want. I have never seen a study to show how much shrinkage in weld cooling is molecular crittical temperature rearrangement VS simple expansion and contraction below the critical rearrangement temperature. I don't know if slowly reheating a cooled weld and slowly cooling would work with out over headin the metal around the weld and making it "dead".,.
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Old 07-10-2018, 03:39 PM
sblack sblack is offline
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John Glover said something wise that I did not pick up on at first, but if you shape a panel to a perfect fit but it is a bag of walnuts, i.e. lumpy, by the time you planish it likely it won't fit. You need to converge on fit and smoothness at the same time, so the closer you get to a fit, the closer you need to be to the final finish. If not, the final stage of finishing will mess up the fit.

If you are planishing you are very slightly stretching or shrinking. Could be either one. It's not like planishing and shaping are different things. You will be changing the area of the panel very slightly. It is a question of degree.
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Old 07-10-2018, 04:18 PM
toreadorxlt toreadorxlt is offline
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assuming there are no details in the panel, I don't worry about over stretching.. if I overstretch the center, I just hit the edges until its happy again. edges need less pressure/time.
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Old 07-11-2018, 08:14 PM
crystallographic crystallographic is offline
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Default not stretching when planishing

Hi Chris,
Stretching seems to happen along with planishing.
I've seen the stretched panels from some "top shops" out there.
The wheeling machine does stretch when planishing, and I have seen that from some top shops, too.
The pneumatic planisher hammers also stretch while planishing, although with some knack there can also be some shrinking.
The pneumatic hammer I use is fine for planishing without any stretching, and is also fine for shrinking while planishing.
Lots of ways to skin that old cat fish.
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Old 07-12-2018, 12:19 AM
Mr fixit Mr fixit is offline
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OK guys'

Planishing with the power tools I get, but hand tools for now is it, is it the same as the descriptions that you provide in the previous posts?
I'm going out on a limb and say yes just to a different degree and I will assume (we all know what that does) doing it with a hammer and dolly the hit strength and dolly control are what needs to be worked on to get the smooth finish I'm striving for.
Again appreciate all the comments and advice..

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