Flattening sheet metal

[bcarwell]

Hi folks,
I just got an antique 10 foot Dempster windmill I am going to rebuild. There are 15 fan blades which are variously bent up and dented quite a bit.
Could someone suggest some techniques for getting the dents out and getting them flat and straight again.
First (and call me stubborn), I do not want to take them to a metal working shop to be rolled but want to do it myself. Second, the most obvious thing is to get a rubber mallet and start pounding away. And third, I am aware that you can purchase replacements for maybe $20 each but don't want to do that unless necessary
But are there some better home techniques ? For example, does heating them with a brush torch first help ? Or is there some clever jig I can fashion using a hyraulic shop press ? Or are there some tools I should get used by auto body repair men. Can I rent a mini-steam roller for 1/2 hour and roll over them in a parking lot (partly serious, partly in jest).
And and all suggestions or pointers to websites/forums are welcomed.

Thanks,

Bob

 

[AlanB]

Probably one of the best modern day metalwork guys out there, and he writes and explains it real well.

Fournier Metal Work Questions & Answers

That said, a Stump, or an anvil, a hammer, some wooden mallets and blocks, some wedges, a vice, some pins driven into the stump to twist against, a leather bag filled with lead shot or sand are tools that could help you get there.

Time is money, for all of us it is just a different ratio. $20 a blade seems pretty cheap.

Got a picture so we can see how bent, bent is?

 

[john_bud]

Eastwood sells a "shrinking hammer". The head twists and that pulls the metal. You do need to heat the metal.

Nearly all beating methods will expand the metal. Heating ones will shrink, but harden. You will probably want to anneal the metal later.

 

[zzvyb6]

Place them on some wet sand and drive over them with the tires of your car with some air let out. Make sure you align the fan blades with the curvature of the tire. Yeah, they may stretch out a bit, all you want for this job is for them to look good at 50 yards. My Flint and Walling looks brand new. (Came down twice: once when the former owner sawed the shaft to get the thing down and once when it blew off its mount while I had it mounted on a basketball backboard to fix it). An old washing machine wringer makes a good curve bender, too. but your blades are probably too long.... Lets see a picture ! Mine still looks as good as new (1932 Star, 8' on a 30' tower).

 

[ray66v]

Stretching and shrinking sheet metal requires considerable experience to be done properly. There is no simple technique, or instruction for this.

I have spent 30 years practicing this, and often have to draw on all of my experience to be successful.

Yes, its possible you will be lucky, and have some degree of success. You also could quickly make the repairable, unrepairable.

If you can, find an experienced metal man to help you, at least rough them out. Then you could possibly take it from there.

 

[RWolf]

Working metal is an "art" and a "science". I've been working metal as a hobby for awhile and still can't get that finished look very oftain. You will need a variety of body hammers, bag of lead shot or sand (as been said) and plenty of time. I'd start with some scrap metal of the same type and thickness and work on that first. Metals come in different "types" i.e. cabon content. The higher the content the more brittle it is and harder to work. Heating will go a long way to help but you need to be at the right temperature to work it or you could possibly make it much worse. If you can find someone to show you how to work the metal you will be much better off. Maybe someone you know has a forge setup. Maybe you can find an old blacksmith that would be willing to show you the techniques. In the long run you will be happier when your done because you will be investing a great deal of time on this project.

Good luck.

 

[Farmerford]

zzvyb6:

Glad to hear about the windmill.

I am about to dismantle a Flint & Walling on my grandparent's farm, where I grew up. The tower is very good, the tank almost completely rotted, and the blades and wheel are gone, apparently the shaft snapped when the oil finally gave out. How about a picture of yours to give me something to anticipate?

Have you found any source for parts? All the antique windmill sites I found have parts for Aermotor, etc, but nobody seems to carry F&W. They were very popular here in the southeast before electricity made it to the farms in the 1930's. I can't decide whether to try to replicate the F&W wheel (assuming I can find the dimensions) or just make another brand fit.

Thanks.

Farmerford

 

[mwb]

depending on what kind of damage you are trying to remove try a few searches on "English Wheel" and how they work. Might be just the machine for you and not very $ (I think HF sells them).

Mike

 

[ray66v]

depending on what kind of damage you are trying to remove try a few searches on "English Wheel" and how they work. Might be just the machine for you and not very $ (I think HF sells them).

Mike

An English wheel is for forming curves in light sheet metal. It is not going to help to straighten fan blades.

 

[CCWKen]

An English wheel is for forming curves in light sheet metal. It is not going to help to straighten fan blades.

Oh contraire, I've used my E-wheel to roll out dimples and wrinkles. Just go light on the pressure and work in steps. But, you're talking about equipment costs that will exceed the cost of new blades. And as already stated, removing dents takes patience and experience. If you have more time than money, get a slapping spoon* and a chunk of flat hardwood for a dolly and go at it.

*You can make a slapping spoon out of a piece of a an old car leaf spring.

 

[ray66v]

Oh contraire, I've used my E-wheel to roll out dimples and wrinkles. Just go light on the pressure and work in steps. But, you're talking about equipment costs that will exceed the cost of new blades. And as already stated, removing dents takes patience and experience. If you have more time than money, get a slapping spoon* and a chunk of flat hardwood for a dolly and go at it.

*You can make a slapping spoon out of a piece of a an old car leaf spring.

NO contraire, an English wheel will not straighten fan blades. It's not a majic wand.

It could help to smooth out the metal, after it has been roughed back into the proper shape, provided the blades are not too thick.

However; if one possesses the ability to repair them enough to finish them on a wheel, they also would be able to do it, without the wheel.

English wheels are not found in body shops because they are not all that useful in repair work.

 

[chickenman]

a sheet of rather hard rubber on a plate of steel and a hard rubber mallet

 

[bcarwell]

Thanks to all for replying with all your suggestions. I hope the pics of the windmill uploaded, if not I'll try again.
Many focused on the metal stretching if I pound and I don't quite understand why I'd care. The fan blades are not high precision with precise joints so who cares if the blades stretch out a bit ?
Interesting technique about shrinking with heat, causing me to look on YouTube and elsewhere and I found some interesting additional information. One idea, though slower, is let it cool naturally so as to not require hardening and annealing. One other suggestion was to cool with compressed air.
As to just buying new blades for $20 each, there are 30 in a 10 foot wheel so its out of the question.
BTW I found that Harbor Freight has a 3 hammer and dolly set for $40 so I'm going to try that. Not high quality but good enough for my purpose. I also found the technique interesting to drive over the blades in sand and will try it.
Farmerford, sorry I'm a rookie so I don't know about Flute and Walling parts (yet) but will let you know if I find something. I see you've discovered the wealth of info and sources on the internet, so keep trying. It seems Aermotor and Dempster are the two biggies and still in business though at one time I understand there were 1000 manufacturers.
And lastly, does anyone have a good technique for removing non hollow, e.g. steel rivets (beside drilling them out) holding the blades onto the frames ? I've got about 200 to do. Best suggestion I've seen so far is to try grinding one side of the rivet and punching them out. Or if you have to drill, using a countersink high speed bit, some oil, and maybe just try to drill off the head and punch it out.
Thanks for all suggestions and help. I'm taking a blade to a metal man tomorrow to see if he can do any good cost effectively...

Bob

 

[CurlyDave]

As a complete amateur in this kind of stuff, it looks like many of those blades will need replacement. If you can get all new ones, they will at least all look the same.

 

[ray66v]

It would be better to just make new blades, than to try to fix most of these.

If you have a HVAC contractor that fabricates in your area, you could possibly buy some sheet metal scraps for a good price.

You could possibly make it look decent as a stationary unit, though I doubt if it will ever look good unless you start over with new parts.

If this thing is actually going to spin at any kind of speed, that looks out of the question right now. If you don't have the disc in a good, balanced alignment, it is going to shake and vibrate until the bearings give out, and it comes apart.

 

[CCWKen]

English wheels are not found in body shops because they are not all that useful in repair work.

They're found in my body shop. I have two. You don't see them in hack shops because nobody knows how to use them. Besides that, few shops "repair" anything. Autobody Steel after about 1976 doesn't take kindly to straightening. They replace parts or slap filler over the dents. And they're not very good at that either. Time is money in a production body shop so the intent is to get the job out fast. Repair is not in the equation. But apparently, you already knew that.

Pull up to a local body shop in a 1908 Buick, 1912 Ford or even a '58 Hudson. They'll laugh in your face if you ask them to repair body damage. Most won't even paint the parts you bring in. Lord help ya if you tell them not to use filler or make a door skin for a '25 Model T. I can't imagine real repairs to autobodies without an E-wheel. So our opinions differ on that.

 

[bjcsc]

Regarding the rivets, the best way to remove them in thin sheet metal is to drill and punch. My idea is similar to ray66v's. I would take my best blade to a wood shop and have, essentially, 'dies' made on a bandsaw from an oak block. Then I would buy a new piece of sheet metal, cut out the shapes, and form each one on a press in between the two dies. Once I made all the ones I needed, I'd make it known that I had others for sale for $19 each...

 

[joes_427_vette]

The english wheel won't help unless your putting a curve in the blade. I have a 1929 Sears windmill that has to be put it. Haven't picked a spot yet but the motor/ gearbox is intact with new seals and ready to spin. Have the 6' fan and a 8' fan for it.

 

[flusher]

Thanks for all suggestions and help. I'm taking a blade to a metal man tomorrow to see if he can do any good cost effectively...

Bob

Those blade look too corroded to me to bother. Just get yourself some galvanized steel sheet stock, a handful of cutoff blades for a 4-1/2 angle grinder, lay out the blade pattern and cut new ones. A waste of time to salvage that rusty junk.