Saturday, November 26, 2011

Forging the BIG Time (again!)

...more on the Peterson House Project.

 In the last post, I described the creation process leading to the final design.
Now, that looks great on paper, or even as a sample piece, there are some practical realities that need to be considered.
'Expand the diameter to six inches for visual weight' :

Calculating pipe sizes against desired bundle width. Locating the tendril wrap locations.

This is a 'size as' drawing I used to visualize / convert my available stock sizes into the layout. I'm working with standard schedule 40 mild steel pipe (most typically used for water lines). One ongoing problem for me is that the material is defined by its *interior* diameter, but as an artist, I'm more interested in its *exterior* measurement. Of course all the specifications are in thousandths of an inch, which messes me up even more. (Additionally, something I just found out - and should have known - is that as the diameters increase, so does the individual wall thickness increases!)
So what I ended up with is using 2 inch (2 3/8 OD) for the central support. To evenly distribute a bundle of tubes around this circle, I have a total of four at 1/2 inch ( 3/4 OD) and four at 3/4 inch (1 inch OD).

Physical strength was NOT going to be a problem here! Physical WEIGHT on the other hand...

I've got a handy little booklet (from Canada Steel) which lists the weight per foot of many standard industrial steel stocks.
On my scratch notes, you can see the unit weight for the various pipe sizes.
Now, bare in mind that I will be working with pieces roughly 10 feet long. The central support pieces (that 2 inch) may not seem like much, at roughly 58 lbs total, but when you make that 10 feet long...
Try forging one end while your are holding (balancing) the other *with one hand*. And consider moving that length, part of it orange hot, around the shop.

My new 3 burner gas forge (rebuilt largely for this project) with the two main support tubes heating.
A larger view, giving some idea of how long those tubes really are!
Anvil? Using my heavy layout table (3/8 plate steel top) as a forging surface. Working with a 5 lb hammer.
Detail of the finished profiling. The surfaces more deformed than aggressively shaped.
Just to put the work into perspective (for those that don't know me).
Those 58 lb tubes represent over 1/3 of my own body weight!

The surfaces are deformed with slightly flattened and spiral shaped grooves. Because it is important to retain the load baring strength of the main tubes, the circular cross sections are not 'pinched' too much.

The next step was to work up the smaller sized pipe. Because this material was not really adding (much) to the structural strength, it could be much more aggressively flattened and folded. The smaller cross section also means that even as a flattened oval cross section, it was possible to twist sections.

Showing one end of the 3/4 ID pipe as forging was completed.
One last note:
On the calculation of weights is also seen the costing for the materials. For *small* objects, normally the cost of the steel is minimal next to the contribution for labour. Not so for architectural work, especially for pieces as massive as these structural uprights. Each finished support, roughly 8 1/2 feet long, will consume almost 200 feet of the various pipe diameters. The cost of this material is approximately $400. (An indication of the relative price for the finished project.)

Oh - one last thing. With the tendril wraps, and some vine work at top and bottom, each completed support unit is estimated to weigh roughly 150 lbs. (And yes, there is a 'large object tax'!)


David Robertson said...

Hi Darrell
Looks it will be a complimentary design to the house.

Are you going to dip paint the pillars?

David Robertson

the Wareham Forge said...

David (and other interested readers)
How to actually PAINT these things is a worry. When assembled, each of the supports will be in the range of 160 lbs each (my own body weight). More importantly, they will be over 8 1/2 feet long!

I think what I am going to do is paint each of the individual pipe pieces *before* I weld and wrap them to assemble. This will me re-painting over the areas that get heated for that work. Likely some combination of brush and pour over in those tendril wrap sections.

Although using a nine foot trough, roughly eight inches wide and deep may *seem* like a way to evenly coat the inner surfaces, consider the raw volume of paint required!

And its a dark brown custom colour to top it off. (Matches the earlier fence work.)


February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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