A Way to Guesstimate Material Loss to Scale

[4575wcf]

Hey All

Newbie here with newbie question.  Is there a way to size a metal block to start with in order to arrive at a known forged dimension, taking loss through scale into account?  Probably a million variables, I know, but sort of a standard.  Say an allowable percentage overage on volume to get close?  Running the numbers and doing the math, trying to get a cost analysis.

[Frazer]

There are too many variables to give you a meaningful answer. The amount of scale is going to depend on the forge, the number of heats, the surface area of the stock, etc.

I suppose you could weigh a piece of steel, forge it into something, weigh it again. The difference is your answer. You can scale (ha) that number based on the number of units, an estimate of how many additional heats it will take to go bigger, or whatever you're trying do... Speaking of which, what are you trying to do?

I've heard damascus can be upwards of 50-60% depending on how many times you stack and weld. I don't do large nor complex billets so I probably lose less than that; I don't have numbers for you.

[George N. M.]

I agree with Frazer.  The percentage of loss will vary depending on how much oxygen the work is exposed to and how often.  If you heat the metal in a reducing fire you will have less loss than in an oxygen rich fire.  You will also have less if you do the work in 5 heats than if it takes you 10.  Experience will give you a general sense of how much will be lost but only a general sense.

"By hammer and hand all arts do stand."

[ThomasPowers]

A lot of the stock loss on pattern welding is often do to the patterning; you waste a lot of the billet grinding away material to get the pattern you want to show.    Some of the industrial forging books give a percentage per heat estimate;  but that won't be anything like a hobby smith with a hobby set up sees.

[4575wcf]

I am only researching at this point.  Heating and beating is still a ways off.  I did the math to calculate the volume of metal needed to fill the "axe head" end of a chopper lump forging.  Then I worked backwards to find a larger diameter rod with enough volume to fill it    Obviously some metal should go away in compression and scale though.  I won't be doing any Damascus, I Iove the patterns but that seems a whole nother lifetime skill set.

[Frazer]

Compression, no. Scale, yes. Assume conservation of volume, add a "scale factor" (say, several ounces) and grind out the excess in the end.

Just my 2c.

[ThomasPowers]

You can refine grainsize by forging; but you don't compress the atoms; leastways not without a lot of NASTY radiation being released.

(I've met folks who claimed that their pattern welding had layers thinner than the radius of the iron atom; funny they didn't show signs of radiation poisoning. What they had done was made very expensive mild steel from high carbon steel.)

[anvil]

If you are doing general blacksmithing, then the answer is yes, you can figure your starting material. You did it pretty well on your axe. Its called "equivalent weight", or equivalent volume.

Theres a lot of folks that believe you can only gestimate your material. Not so, you can be close enough for any material bid, if not right on the money. Proper fire control and hammer control are important, but even so, if you practice this setup and use it as your guide for forging, your material bid will be correct. Works for railings and gates to trivets and "S"hooks.

You need to know one term, besides equivalent weight, and that is "transition". Thats where one thing changes to another. Say you have a 1/2" square bar with a 2" taper at the end. Where the square ends and the taper begins is a transition. Take your drawing and locate each of the transitions. Now calculate the weight(pounds per foot, oz per inch, whatever) for each and add them together. You now have the total weight of the parent stock, the material needed for each piece, and can center punch your parent stock where each transition is. all ya need now is a little math.  Heres a simple example. I have a drawing on my table. it is 12" long and has a 2" single sided taper on one end. What length parent stock do I need and where do I mark the transition on my parent stock? The taper is a triangle 1/2" high and 2" long. Now I go to my steel weights tables and find out what 2" of 1/2" square weighs and divide by 2. Since these charts are to 3 or 4 decimal points, I'm pretty right on the money on what my start length is to get my taper. 1". So my parent stock length is 11" and the center punch for my transition is 1" from the end. Mark 2" on the heel of your anvil and forge from the center punch until its 2" long. If you got your length, and were right on your centerpunch, you should be pretty close to right on the money.

There is no compression and scale is not a factor that will change this setup unless it takes you 8 or 10 heats to forge out the above example instead of one or two.

If you keep good notes on this,should say a hinge need to be replaced, your notes and layout drawing should enable to match the original. 

Heres a pic of a complex hinge. the parent stock layout,shop drawing and the nearly finished test piece.

[4575wcf]

My forging is pretty much going to be limited to producing one part, made in left and rights, and figuring the best and most efficient way to get that part out.  I shouldn't be doing any forge welding, or much freehand work.  I can already tell it is going to be a challenge at any rate.  I hope I don't get hooked.  I am already a parts fitter, a stockmaker, and a machinist.  I will be signing up for welding classes upon retirement, that is another prerequisite that I am not overly good at.

[4575wcf]

On 1/9/2022 at 1:12 PM, anvil said:

If you are doing general blacksmithing, then the answer is yes, you can figure your starting material. You did it pretty well on your axe. Its called "equivalent weight", or equivalent volume.

 

This is very useful information.  I ran the volume mathematics and I ran the weight mathematics both using calculating aps online.  There seems no real difference, both results end at 16 inches of 1 1/2 diameter bar weighing almost exactly 8 lbs. What is the advantage to calculating by weight?

Edited January 11, 2022 by Mod30
Trim quote.

[ThomasPowers]

Weight is easy to determine for odd shaped items. Volume not so much.

[4575wcf]

Never thought of that.  Makes sense.  Thanks.

[anvil]

There is no difference. I used weight because its, perhaps, less intimidating than volume. When you look at the "weight" tables for common steel sizes, they actually give you pounds per cubic foot. This is easy to convert to ounces per cubic inch. For those who dont know, this math used to be taught in middle school. I have no idea about now.  ;). So if you know the oz per cubic inch of 1/2" square, you can easily figure the weight of any length. Knowing this weight, and if you know the oz per inch of any other dimension steel, say 3/4" square, you will know how much 3/4" square you need to forge it to your desired 1/2" square length. 

Im a bit removed from this definition, but I believe pounds per cubic foot is actually the weight of a given volume. 

The unique thing about forging is we change its shape by hammer in hand. The volume/weight, for all practical purposes, remains the same. So, for any given design we can see in our minds eye, and can draw on a table, we can, via transitions, simple math and a bit of geometry, break that design into easily forgable parts in order to achieve the design we chose. we can take any immovable hunk of steel and move it to whatever shape we want and have absolutely no waste. 

What Thomas said is true, but thats where geometry comes in handy. In my example of a 2" taper, using geometry I can draw a 2" square(on paper, and get its weight easily. Then divide that by 2 and I know the weight of the "wedge".

[Frazer]

Immerse in water and calculate the displacement.. Supposing you have an appropriate beaker/graduated vessel, volume is easy enough.

Weight is still easier, generally speaking. I usually start with one and switch back and forth depending on what I need to know or can easily measure.

37 minutes ago, 4575wcf said:

16 inches of 1 1/2 diameter bar weighing almost exactly 8 lbs

Working heavy stock like this will take more heats. Enough where scale will be a factor? If you're making an axe -- especially for your first few -- I would say it probably will. At the very least it will be more of a factor than on the hinge shown above.

[anvil]

Why would you want to use displacement of water in a blacksmith shop? Simple math is all you need. And no, in your example, scale is not a factor at all. Basically if you have to take enough heats where scale is a factor, you need to address your forging techniques. Again, with simple basic hammer control and simple fire management, no matter the weight of material, scale is not an issue.

[Frazer]

I know you wouldn't do that in the shop, more of a how to get the volume of irregular shapes in general.

wcf is just starting out...

"I am only researching at this point.  Heating and beating is still a ways off."

Of course he needs to address his forging techniques... I'm saying that the level of experience moving metal with a hammer needs to be taken into account before you say that loss to scale isn't (or won't be) a factor.

Also, you're telling me that when you make a 3# hammer you start with 3#s of material? Of course you don't. You add extra to account for (at the very least) grinding at the end... I bet even you would add an ounce for scale too...

[anvil]

Basically, every post I've made here apply to his original post. I appreciate your opinions. 

[4575wcf]

I really like this water displacement idea.  With a rectangular graduated tank of know dimensions about any weird shape could be calculated for volume/ weight very quickly, very easily and very accurately.  45wcf is just getting started alright!  This is the smithy.  Chock full of years of collected building material scraps, unprocessed firewood all around and farming junk.  Needs work on the foundation, framing, walls, and roof.  Other than that she is "sound" 

: ).

[ThomasPowers]

Besides the graduated tank there is always: fill any container to the brim, place item in, catch the overflow and weigh it; convert to volume.

[Irondragon Forge ClayWorks]

1 hour ago, 4575wcf said:

Chock full

No telling what  treasures are behind those doors.

[Goods]

Rather that weighing the displaced water, just weight the part. A lot less math that way…

[ThomasPowers]

If you know it's made from a single known alloy---remember Eureka!

[anvil]

Looks like you have a good start on a shop. I started with a small temporary shop,,, and 30 years later as a working smith, I left that temporary shop, and am now building in a new location, a new shop and Im bound and determined to get it done with some nice forged fasteners and the works. No more temp. Coming from a small space 16'x20', Tools needed a immediate and long term usage, so no Archimedes tub for me. But hey, whatever overflows your bowl, or floats your boat, as the case might be. 

On a more serious note, I meant no confusion. Everything I've said had to do with conceiving an idea, draw it full size on a table, making a layout stick and heating and beating it.  When done, you would then have something to go in yer displacement tank. 

Frazer, I just saw your comment on a 3 pound hammer. If I slit and drift the eye, I do it as I have stated. If I punch the eye, I take into account the plug. 3 or 4 heats for the eye, either way, and maybe 20 minutes for forging, and no grinder time. A little hot rasping at best. I finish the face by handwork. Most of my hot work handled tools are remade from other handled type tools, so,, simple quick forgings.