[TheForge] layout help {long procedure, best to hit delete now}

[Andy Vida]

Dan Scheid wrote:
> 
>  ok I'm going to start my first gate and I need some help with layout. the
> gate that have a arch on the top.
> 1) what is that called?

	An arch?  Just guessing. :)

> 2) there has got to be a simple way to figure the arcs and lay it out  help
> please

	Well, i used to get all flustered about this myself because I
	am a super anal type and I used to have the very bad habit of
	taking my machining skills to the forge.  That is to say, I
	got all nuts because I could not figure out how to bend an
	arc of 40' radius to a precision of 0.0001".  The time I spent
	doing this for a living rapidly drove home the fact that most
	of this work is not high tolerance by any means.  Curves and
	arcs are, generally speaking, just fine if they approximate 
	what you see on a design sheet.  What is far more important is
	whether two sides of a gate are bilaterally symmetrical, which
	is to say, very close mirror images of one another if that is
	what the design calls for.  The human eye is very precise in
	this regard and can pick out even the smallest variances in
	symmetry.

	OK, that said, I'm not sure what you mean by "figure the arcs".
	If you mean in terms of design, which probably you do not, then
	they are whatever you want them to be if you are doing the design.
	If you mean in terms of figuring their dimensions from a third
	party designer, which you may well mean, then it is up to the
	designer to specify these things if they have a specific tolerance
	in mind.  Otherwise, it is up to you to interpret.  One can get
	dinemsions from full size patterns.  These are often not available,
	so the best thing to do is to become skillful in the use of the
	porportional divider.  If you do not have a pair, get some.  They
	are absolutely indispensible to the blacksmith for layout work.
	
	Try this source:  http://tinyurl.com/254g2

	At $40, these are dirt cheap, very well made, and precise.  Don't
	ever put the tips onto hot metal.  Major no-no. 

	Anyhow, I am amazed that I've yet to see another smith make use of
	these instruments.  They are so basic to this sort of work, they
	should be in every blacksmith's shop.  There are many many ways in
	which even an small pair can be used to scale dimensions up that
	are even beyond the physical limitations of the dividers themselves.

	Anyhow, back to your question... what is important is that you
	lay out with great precision the linear dimensions of the gate
	such as the height and width, which is easily accomplished with
	straight edge and silver pencil/soapstone.

	Look here for visual reference:

	http://netlabs.net/~osan/Photos/gate.jpg

	Here we see a simple counter curved arch atop a very simple
	gate design.  Regardless of the specific design, the methods
	are basically the same.  In this case you would drop verticals
	(in this case just use the pickets) from the curve to some
	convenient distance below the bottom-most point of the arch
	as a reference point.  Draw a similar line on your pattern
	material (paper, perhaps?) to its full length and divide it
	into the same number of divisions that you did on the design
	print.  The number of divisions doesn't matter, but the more
	you use, the more precise your translation to the pattern 
	stands to be.

	Next, measure each vertical dimension, convert it to actual
	size and transfer to the corresponding position on the full
	size pattern.  When finished, you can use what I believe is
	called a French wheel (I may have that wrong, it's been a LONG
	time) and a pounce bag.  The wheel is carefully run along the
	lines of the pattern, perforating it at regular intervals.
	You then place the laid out curve onto a metal plate of the
	appropriate size, tape it down perhaps, and run the pounce
	all over the perforations.  The fine dust will mark the pattern
	onto the metal.  Carefully remove the pattern and you will
	see a precise layout on the steel.  You can then trace this
	with a silver pencil to obtain a sturdier mark with which to
	work.

	Making the jigs.

	Making good jigs to bend curves requires a lot of eyeballing
	and experience will make you better at it.  One method I have
	used to great success is to reproduce the innermost dimension
	of the curve in steel.  Take an appropriate length of stock
	that you deem heavy enough so you may bend the work against.
	Obviously if you're bending cold this will have to be much
	heavier than if you're bending hot.  In this case you would
	need to build two bending forms because the counter curves
	are not the same.

	See http://netlabs.net/~osan/Photos/jig.jpg

	The stock for the form is bent as needed, again by eyeballing
	and adjusting curvature to fit the pattern.  One thing that is
	critical it that the steel for the form be perpendicular to
	the plate to which it is welded.  If it is obtuse on the working
	side you may find yourself having fits trying to keep the work
	from slipping off the form, presenting a serious safety hazard.
	If it is acute, the problem isn't as great, but good and square
	is really the best way to go.

	Tack the form in place from BEHIND the working face, never on
	the working face itself.  Then weld a bunch of supports from
	behind.  The can be triangular buttresses at regular intervals
	that brace the form and keep you from tearing from the base
	plate or bending it.  I learned this the hard way... don't ask :)

	You have to have the buttresses at an interval such that you 
	don't bend the form between two buttresses.  Don't over engineer
	the form, especially if you are only making a couple of curves,
	never to lay hands on it again.  This is time consuming work
	and greatly contributes to the cost of the job.  Gravity issue.
	But with experience you will come to know how heavy the stock
	must be to bend a curve of a certain size on stock of a certain
	size either cold or hot.  Notch the buttresses at the right angle
	corner so they fit over the weld beads where the form and base
	plate are joined.  Be sure to weld the seam all the way.  If you
	just tack at intervals you may break the form, which when it 
	happens after bending 36 of 44 pieces, you will be so pissed
	you son't know what to do with yourself because once a form is
	altered, it is very difficult to get it back where it was, and
	always remember what I said about the precision with which the
	eye perceives forms... especially simple geometric ones.  You don't
	really need the backer bar if your buttresses are heavy enough.
	Just tossed it in for good measure.

	You have to make a stop and clamping devise ("vise") wherein you
	insert your work to make the bend.  This is often just a passage
	with a stop plate at the end.  It is just wide enough to accept
	the stock and should have a tab running over the top of the
	stock to prevent it from popping out vertically, which is a most
	unpleasant thing to have happen when you're wailing on a piece
	of cold steel so hard that your newts are about to spiral onto
	the floor and roll off into a dark corner, never to be seen
	again.  Also, make the vise VERY strong for precisely the same
	reasons.  Large stock and welded like crazy.  I even like to
	add a plug weld or two if possible.  I've had all these nasty 
	things happen to me, usually with Terry standing there laughing
	at me fly across the shop floor looking like a complete idiot.

	Then you put in the work and bend away.  You may have to cut
	the stockoversize for leverage, or you can use a pipe as a cheater
	bar, but be careful if you're bending tubing as you are likely
	to crush or dimple it if you don't exercise proper care when
	applying force.  

	Bending curves like this isn't fancy, but the setup is rather
	time consuming.  You may be arbitrarily precise about it, but
	diminishing return sets in rapidly when one goes beyond a
	certain point.  But if one needs high adherence to a design,
	one can always CAD up a jig and have the form water jetted.
	More costly in terms of materials, but that MAY be offset by
	time savings.  We had monster forms jetted for Mongo the
	world's largest bender.  They were cut from 5" thick tool
	steel plate.  Bending 1"x2" into scrolls the hard way and 
	cold is not only touchy, but scary. The stored enegry in
	the stock is tremendous.

	OK I guess that's about it.  Did this answer your question at
	all or did I miss the mark? 

	-andy