How much does your straight edge weigh?

Since I've gotten the planer going I've been planing a lot of straight edges, some of my own and some work for others. Today I was getting a couple of edges ready for the planer.





The one on the left is an unknown brand 48" and the right one is a 36" King Way. While only 12 inches longer the unknown brand weighs at least three times what the King Way does. The King Way tipped the scales at 28 lbs and while I did not have a scale large enough for the 48" I conservatively estimate it at least three times heavier.

Just moving that 48" one is a PITA!

I started studying both edges looking for why there was such a huge difference in weight. On the 48" every feature was at least 2 or three times the size of the King way. Now if I did not know the history of the King Way ( They have been made and sold by the King's for a long, long time) I would have just passed the light edge off as a cheap way to make the item and probably a product of China...

Obviously the King Way has been in use for a long time and has a proven record or we would have been hearing about it. I have two 24" King Ways and they both have the same features of the 36", tall backbone, large lighting holes and long thin ribs.. One is a dovetail and has a thicker base to accommodate ( I think) the area needed for the dovetail side but even then it is light enough to use with ease..

One difference I noted was the design of the back. The 48" has a curve that tapers down evenly to the ends while the King Way has a "trestle" design that brings the supporting back closer to the ends of the edge. Am I right in thinking this design allows a lighter yet stable tool?

Weight is an important factor in smaller straight edges. While a hefty straight edge builds muscle etc the extra weight can work against accuracy if poorly distributed.

I thought about this and have come to a few conclusions:

While lightweight and rigidity seem to conflict the reference face and upper limb and the stiffening elements between have be in balanced proportion to maximize rigidity.

Assume you're starting to design your own straight edge from scratch. You have a blank sheet of paper and on it you will set down your requirement and numerous sketches from which evolves the pattern for you wish tohave cast in gray iron.

Determine the accuracy required of your straight edge like +/- 0.0001" per ft.

Decide length, width etc (you may desire a non--customary length ie between 24 and 36") and any extra features like a projecting edge to reach under dovetails, a high square edge, cast-in locations for insulators and handling equipment, bosses to mount level vials, etc.

Remember you cannot make your straight edge infinitely stiff and accurate nor can you make it un-realistically light.

You might think the classic triangulated camelback design embodies the necessary elements in terms of weight Vs stiffness but that is not necessarily the case. One need only look at the Elmer King design and one of several I beam designs for viable alternatives of comparable weight Vs stiffness and possibly greater utility.

Rough out a design and draw it to scale. Calculate the volume of each feature and element to deterrmine tha finished weight. If you have the computer capability, model it and determine deflections in different conditions. Or you can weigh your pattern and calculate the casting from there. deducting for the machining stock You will probably make more than one mock-up. Make your mistakes in wood. Cast iron mistakes can be very expensive.

Consult with local foundries (if they will talk to you) and make your pattern to suit their molding requirements.

Remember you cannot make your straight edge infinitely stiff nor can you make it unrealistically light. Your straight edge has to be robust enough for normal use and handling. My thought for a rigidity requirement: deflection shall be no more than 1/4 the flatness tolerance measured at the center when supported at the ends and loaded with its weight in sandbags. An easy test to perform on a granite flat with 1-2-3 blocks and a 0.0001" reading DTI on a surface gaqe.

Vette Bob called me and said he was lifting a weight the other day. The Busch 36" casting he bought from them last year. He had it machined and said he scraped it and he figured he lifted It 80 or so times when scraping it (must have forgot to do blind and step scraping). My dad decided long ago thin ribbed and parallel design was a lot better for the scraper hand who had to lift it all day long.

I still produce those designed Straight-Edges and have sold more in the last few months then I did in the last decade.

I will be soon selling cast iron surface plate castings to. I have a great little 12" x 12 / 3 point leg plate pattern now and will be selling bigger ones too.

Have a nice Day. Rich

Found a good use for that HEAVY 48" SOB !



Making a 8 foot diameter turntable for a stage at the local community theatre. Need to keep all 8 of the outriggers in the same plane and I though of using that straight edge to help out

I planed the edge last night so it's ready to be scraped and not finished yet ....

Metal Lathe Access 18" SE finish scraped and in use: 14 lbs
Denis's casting 36" dovetail SE not quite finished (but final scraping ain't gonna remove pounds): 24 lbs
The about to pick up 48" SE: heavier...

Lucky7

My 6ft dovetail straight edge is heavier then I can lift. Have to use a crane for it.

Update: Collector was nice enough to machine a bit more off the bevel of my Denis Foster "feather weight" 36" SE. It's now finish scraped and in use at 22 lbs. Collector is also machining one of Richard King's 48" with angle SE's for me. We both commented it's heavy, but I'd say it ain't Busch heavy! One man can handle it ok without lifting gear pre machining.

Realized I should be a little more scientific. Looked up Busch's 48" with bevel SE 6600 series on their site (before it disappears) and finished it's advertized at 85 lbs. I'm assuming this is the one Cash mentioned was bloody (my paraphrasing) heavy to lift. It's base and bevel dimensions as well as arch size are a little smaller than what we're shooting for on Richard's casting as well. Hopefully the HKA-48 has the beef where it's needed.

Regards,
Lucky7

I just went out to the shop (in the rain) and put my 6 foot I Bean straight edge on the scale.

50# even.

I try to only lift half of it at a time. ;-)

Starting final scraping this week on my Richard King HKA 48" at 61 lbs. IMHO, a managable weight for it's length. Thankfully NOT the 85 lbs of equal length Busch...

Lucky7

Just for clarification: my 36" Featherweight can finish at various weights. Left with as much sole thickness as possible it weighs about 24 pounds. However, I prefer machining them to about 20 pounds. The difference in weight is due to about 1/8" sole thickness left in place vs removed.

I have a 48" drawn and am beginning pattern work on it as I get time here and there in between other duties and projects. It should weigh in about 26 to 32 pounds depending on finishing preferences. It will look a lot like the 36, but will have a slightly gentler arc and a similarly broad sole capable of reaching under vee-ways.

(Also in the planning stage and now preliminary drawing stage is a lightweight cored prism that will be designed as a 48" but will allow cutting at 12" stations so it can become 2 24" prisms or a 12 and 36 or, of course, 4 12's.)

Denis

Dgfoster, interesting that you are going forward with a lightweight 48". Looking forward to pics of drawings to see how you keep the weight off. (and castings when they arrive!)

Regards,
Stan.

I have two 48" from the same manufacturer but different styles. The lattice-frame one is 30% heavier than the plain round-hole one, which I think I recall is 23kg/50lbs

30lb would be very light for a 48" straight edge IMO.

Well mine weighs about 2oz. Oh whoops sorry wrong straight edge, that's a plastic ruler.
The 10" one my brother has weighs like 5-10lbs. The 72" weighs probably around 100.

My 48" Crown Windley cast iron is about 50lb
My 48" granite one is 64lb.

I will admit that I've used the crane for the granite one on occasion. That's mainly because it was simple to lift it up by an inch then move it out of the way and be able to put it down gently when needed.