48" Camelback Straightedge Pattern is in Process

BTW, the pattern is Baltic Birch plywood. I point this out as an MDF pattern would not be nearly as durable as the Baltic Birch. I think MDF would be fine were I planning on only a very few pours. But the danger of disintegration of MDF if exposed to water (weird stuff happens) and the necessary rapping on the pattern incline me not to use MDF. Perhaps you were referring to the MDF template which is intended used once or at most twice to cut out the web of the pattern.

Denis

 

Adding chubby little cheeks to skinny ribs:

The wedge of yellow cedar used for cheeks. I’d rather have used 1/16 Baltic birch aircraft plywood. But my local supplier was out. The cheeks add thickness and strength to the rib as they span the joint between the base triangular wedge and the longer upper portion of the rib.

Outlining the profile as the rib sits in its slot


Tracing the rib onto the cheek.


Some of the stuff used to glue on the cheeks and fair the curve.


Checking both sides for draft—-about 3 deg.


All but the two end ribs are complete.

Denis.

 

Denis,
I won't argue further but you couldn't be more wrong about this. Any time you see only rectangles in a structure you can be absolutely certain it is flexible not stiff. Please don't take my word for it. Ask a structural engineer.

I build lots of structural stuff. At my last job another engineer designed this massive frame with no diagonals and when it was presented to a structural engineer for seismic analysis it failed miserably and he had to greatly reinforce it. I sent the same structural engineer a frame for a different job for analysis that the other engineer told me was way to flimsy, and it passed with no problem.

 

BTW, there is an exterior grade water proof MDF-like product called Extira, it's a little pricey certainly not any cheaper than Baltic birch but it's dimensionally stable and might be useful in applications where the wood grain of plywood or solid wood would cause problems.

 

What would be gained by increasing rigidity? I am not saying it is maximally rigid. But it is plenty rigid for the purpose. The essence of good engineering is not perfection or maximizing strength. It is getting a design suitable for the desired use expending a minimum of expense and time. The Golden Gate is not maximally rigid nor is a 787. But they seem to work well and look good. Those were my goals here.

Sorry I am so wrong!

Denis

 

I am not a structural engineer, but I had to take Statics in school, where we analyzed trusses and such (tension, compression, and all that rot).

And I do electrical designs that have to withstand a Seismic 4 Zone (the worst rating), so I am somewhat familiar with what you are talking about.

Generally buildings do fine with square steel tube columns as long as they are not subject to earthquakes.
For earthquake and wind resistance, you need diagonal members (often cross bracing) to prevent excessive motion.

But if the square tubes for building columns were sufficiently large in size, then no cross bracing would be required.
So that is what I see with the straight edge.
The width of the webs is such that the deflection is minimal.
There are no earthquakes with a straight edge, so no cross bracing required, and the problem defaults to a static deflection problem, which melter appears to have well under control.

My 2 cents anyway.

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LOL, with deflections as small at that, we need a lot more "wrong" stuff.

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Incidentally, the “Ultimate” rigid straight edge design is about 50 yrs old.

https://images.app.goo.gl/NQCdETM2JdUsbJiJA

I will leave to the eager beavers to make the patterns, cores and cast it. I know of not one in actual use.

Denis

 

The curved shape of the back of the straight edge somewhat mimics a graph of the stresses in the piece under load.

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Hey.. I've got that glue! What's the secret for it? I've pulled my hair out trying to glue pine crown molding with it. The guy in the video makes it look easy and its strong. I think he's just a whimp!

 

Not sure what video you are referring to. I think you are talking about the 2P-10 glue. Depends on the joint you are making in crown molding—-butt, scarf, miter... I usually use either yellow glue or epoxy for that stuff. 2P-10 can be quite strong but I use it when I need super fast assembly like these cheeks or repair of a split or splinter.

Denis

 

The guy for that 2p-10 on yt.. They show how strong this stuff is. I've tried 9ways from sunday to glue a simple miter for some pine crown. I've seen it work really well on mdf, I must be doing something wrong. I've put glue on both sides, one side, activated the glue, the wood, my hand. Nothing. It's been 30bucks down the drain for me.
The only thing that has worked for me so far is wood glue, clamps and 24hrs. I find it hard to believe glue can suck this bad for pine molding? Probably some low voc nonsense.

 

Brilliant! Try adding some VOC’s to see if works better.

Denis

 

I'd be happy to buy some VOC's to add to my rear view mirror glue! I've glued that sucker on 3times in the past month. FYI, most new aircraft use LOTS of glue to hold critical sections together.
Glue isn't what it used to be.

 

I agree it isn’t what it used to be. It works so much better. 2P-10 is the glue I use ten to twenty times for each time I use an epoxy or water-based yellow glue. Used the cyano 20 or 30 times today alone. West System (especially their G-Flex types) epoxies and System 3 epoxies are positively consistent batch to batch and are stronger than any wood I’ve used it on. Then there is the incredible line of adhesives manufactured by 3M and also Hinkle which are specified OEM by every large equipment manufacturer I know of. Indeed, being old enough to have grown up when glue meant hide glue, airplane glue, Elmer’s glue, and urea formaldehyde’s, I marvel at the palette of amazingly diverse and capable glues available. There are way more good choices than one person is likely to need in a lifetime.

Life is good!

Denis

Added: I forgot resorcinol glues in my recollections of early glues. things don't "stick" in my mind as well as I wish they did. ;-)

 

Here is an update of today's progress. I got the back ribs glued in place and faired the curves they make so that there is a smoth progression from one rib to the next. Even a 1/16th" deviation looks a bit like a sore thumb. I I end up squinting down the line of ribs from one end and then the other trying to see which one is a bit high which is a bit tricky since the curve of the bow varies the distance to the sole obviously and the top of each rib is different in height from its neighbors. then when you figure one is a bit high you have to use some sort of pointer to lay on the rib so that you can be sure which one you were looking at! then out come the half-round file, scrapers, sand paper and any other aids you cna think of. I find I have to be cautious not to overcorrect---it's sort of like cartoons of trimming the legs on a four-legged chair.

Anyway, I have got the ribs standing respectfully in a line with them more or less in register with each other.

And the other operation completed today was the nervous-making splitting of the pattern so it can, indeed, be molded as a typical split pattern rather than as a loose pattern with follow board the way I mold the 36 of similar design. I used a "meat saw" blade on my band saw as it cuts a very fine kerf. I think it took only 25 thousands kerf. I was worried that the blade, even though brand new and sharp, might want to wander off course. As it turns out it stayed on course +/- 15 thou except the last 8 iunches where gradually veered to one side 40 thou. I can easily shim that or ignore it. I would probably be bothered by trying to ignore it, however. A plane, some glue, and a thin shim of wood could bring the part line back to center.

Here are some pics:

Tomorrow I'll spend a fair bit of time filleting the numerous
inside corners (80) and straight junctions of sides with the web(80).
Fun times. Then I'll start spraying the pattern with white lacquer as that pain helps me see defects much better than clear lacquer. As it dries very quickly it allows sanding off high spots and also Bondo filling low spots.

Incidentally, I have yet to trim the ends where the bow and sole still "run wild."

Denis

 

Bravo!

 

Nice piece of pattern work.

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I agree with you and disagree with you. Yes a triangle is the strongest shape when directional forces can be calculated or applied. And they can assist in preventing racking. But the strongest shape in nature is a arch, bubble or sphere. The thing is triangles are easy for structural engineers and they get to overcompensate. The the great pyramids will last a long time (and I don't argue this), but the final shape they will take, is... a dome in time.

Some may argue the diamond has the strongest structure, but if you really work at a diamond, it will end a spear.

This is a 2 carat diamond that resisted for 15 years. Please note the shape. (10 times magnification). At one point in time and had a typical diamond shape.

 

I fully agree!! I'm now waiting the videos of sandcast and poor.