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Compound Curve Crown Molding

4/21/17       
David R Sochar Member

The following pics show a bit about how we make compound curve Crown molding. Their are more in the Project Gallery. "Compound curve" relates to the fact that the molding is curved in two dimensions, usually of different radii.

The blanks are glued up and sawn out of solid material. We use radii sticks to draw lines. Scraps from the sawing will make the complimentary radii fences. The blanks do not need any clean-up at this point if the are sawn accurately. The fences are sanded a bit and waxed.

The shaper uses a corrugated knife head, with knives hanging out the bottom of the head about 1/2" to get as much knife body in the head as possible. The fences are fastened together and then clamped to the shaper. They are designed to have the head 'run in' from above to excavate the wood around the head and leave a profiled supporting edge at the indeed side of the cut. This will support the molding at the cutter exit and help prevent tearout.

The mold is run in several passes - 4 in this case, with the last being about 0.030" for final cleanup. The first pass is a hogging event with large chunks flying everywhere. Dust collection should be attempted, but is marginal at best.

A bit of hand sanding to get out any washboard, and some edge clean up is needed. Bent laminated blanks can be used for one of the curve dimensions with the other curve being sawn. Plan the laminations carefully so there is little or no springback.


View higher quality, full size image (1800 X 1350)


View higher quality, full size image (1800 X 1350)


View higher quality, full size image (1800 X 1350)

4/24/17       #2: Compound Curve Crown Molding ...
Pat Gilbert

Thanks for posting that Dave.

Do you have any shots of the molding in it's intended position?

4/24/17       #3: Compound Curve Crown Molding ...
Pat Gilbert

Whoops I see the shots now.

What size shaper is that?

4/24/17       #4: Compound Curve Crown Molding ...
TimG

Great posting, thanks! Would love to see a short video of the actual cutting.

4/24/17       #5: Compound Curve Crown Molding ...
Paul Miller

Website: http://MCCWOODWORKING.COM

That is very good. However, if you had a CNC router, it would be much easier.

I have done moldings similar to what you are showing, except I us AutoCAD for my drawings, a CNC router to cut my shapes and a Mikron Arch molder to run my crown molding.

Every shop needs a CNC, trust me. The most valuable tool in my shop.

4/24/17       #6: Compound Curve Crown Molding ...
David R Sochar Member

Paul - I understand your point about the CNC. If you like to do it that way, it is fine.

However, I have made curved moldings this way for 45 years, with excellent results. It is a challenging and very interesting way to spend one's day. My co-worker and I had a great time, and we made some serious money. We can also make 16' or even 20' long straight moldings if we need to. I don't see any CNC machines doing that.

This old school method should be taught to all serious woodworkers so they know and understand the basics of a more complex and interesting but useful part of their craft. I make it available for anyone that is interested in more than one way to skin the ol' cat.

We are not all machine operators, nor do we need to be. Study your craft, as one notable woodworker likes to say.

A quick scan of the two digital type forums here on WoodWeb indicates there are quite a few people out there using CNC that have no idea about reading grain, joining wood, hygroscopic movement, or any of the thousand other things a competent woodworker should know.

TimG - No views of the cut being made. The rudimentary dust hood is only there for show, as we hoped to be able to catch some of the shavings. The helicopter type knives throw shavings everywhere, so there could be no usable video. Maybe 10% of a lot of wispy, curly shavings went up the pipe, 85% everywhere else, and the rest ended up in our hair, pockets, ears, back of shirt, and worse.

As I told my coworker as we first started up the shaper, most people would head for the hills to see and hear and witness what we were about to do. But we enjoyed it, fools that we are.

4/24/17       #7: Compound Curve Crown Molding ...
Paul Miller

Website: http://MCCWOODWORKING.COM

Dave,

Please don't take any offense at my comment. I am 67 years old and I have had a cabinet shop since 1986. I am not really a great craftsman. There are so many other things I have to do to keep my small shop going, I cannot afford to work all day in the shop.

I mentioned the CNC because it is a tool. There are no doubt many readers here that are younger than myself and I only want to share with them my experience in wood working.

With a CNC, you can do a 20' arch molding. It's called a step move. Dave, with you knowledge, you would fall in love with the CNC. It's like magic and it is so much fun.

If at the age of 50, with no computer experience, I can learn AotuCAD and then apply those years of experience building cabinets to working with my CNC, just about anyone can.

No offense intended.

4/24/17       #8: Compound Curve Crown Molding ...
B.H. Davis Member

Thanks David.........nice lesson for everyone.

We of course do similar work. Here is a link to a moulding we made several years ago. I posted this one as an example because the web page shows a number of the steps used to accomplish the final moulding. Wood was pine for a reproduction cabinet head piece.

BH Davis

Compound curved cabinet moulding

4/24/17       #9: Compound Curve Crown Molding ...
Pat Gilbert

Nice work.


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4/24/17       #10: Compound Curve Crown Molding ...
David R Sochar Member

Paul - Absolutely no offense taken. I really do appreciate the things a CNC can add to the craftsman's toolkit, even if I do not use one.
Being digitally defiecfive, I spent a few years trying to draw with a computer and just cannot get comfortable with it as I do not find it intuitive at all. Making two radii fences, on the other hand, is intuitive to me and a joy to discover as the solution to a problem.
Fortunately, it is a big world, and plenty of room for us all to find our way.

4/25/17       #11: Compound Curve Crown Molding ...
Jim Baldwin

I'm sorry, I don't see why the compound curve? I do see a flat, plan-curve, but I don't see how the crown also needs to curve to meet the curved ceiling? Wouldn't that just be a beveled edge to meet the slope?

Looks great!

4/26/17       #12: Compound Curve Crown Molding ...
Kevin Jenness

David, thanks for the post. Very interesting, and well illustrates the direct approach you bring to challenging millwork tasks.

B.H. Davs, would you mind elaborating on how you milled the profile on that complex serpentine piece? It appears that you used a cnc router to cut the initial shape in elevation. Did you then go to a bandsaw to cut the curve in plan, and what machinery did you use for the profile?

4/26/17       #13: Compound Curve Crown Molding ...
jl

Great work David.

I always appreciate the old school new school argument. The harsh reality is they don't build cars the same way they built the model t, why would you expect wood working to be the same way. I find myself some where in the middle, just old enough to have had to do it the old fashion way, young enough to know I would never go back!

I do take some exception to the notion if you use cnc or any other new technology you are any less of a craftsman. The cnc doesn't repair bad glue joints, hide flaws in the wood or grain, or cover up any other flaws in what you present it. The only difference between how you executed your product or how we would have on the cnc is probably the countless hours of labor. Same thought process, same understanding of how to layout a compound curve, same careful selection of material, it's just drawn in the computer .
The guys that did think cnc would make them an instant premier woodworker are selling address plaques on Craig's list.

4/26/17       #14: Compound Curve Crown Molding ...
Adam

I wouldn't look at this as David is an old world craftsman and some guy using a cnc is a high tech operator.

As in any business you should own the proper equipment and skills to use them for 95% of the products you produce in a year.

There is no point in having a $100k cnc that allows you to do one complicated moulding once a year, if you can use your experience and basic machinery to produce the same result with no more investment. Obviously, most of the cnc work is 2D on panels and they are sometimes used for 3D work.

BH's business is a very good example of how you can fully embrace new technologies as another tool in addition to your old standard tools. He is still using a modified WH moulder daily along with a couple of cnc routers to produce complicated mouldings. Most of the templating is done on the cnc. Depending on a speed/quality ratio he determines how much of the project will be milled on the Super Hussy or the cnc. Very smart business and craft.

4/27/17       #15: Compound Curve Crown Molding ...
David R Sochar Member

Jim- My thoughts exactly as the room progressed - the crown would follow the perimeter radius and run from beam to beam as a nice single radius.

However, once we put the 1/4" cherry ply ceiling on the 'top of the pie slice', the ply was defining a rise in the center of what is a 4' length along the edge where the perimeter crown was to go. We could have added a filler of some kind, and tried that, but it looked like a get-over. The plywood was bent where it would go, and basically it bent onion plane and was forced to bend to the outer perimeter.

So we either had to figure a way way around the problem, or make 12 concave, 3D formed, ceiling panels. Somehow. We decided to try to make the crown work, within the parameter of "no compromise".

We canted a single radius piece up in the center and it looked better. We calculated the radius needed to 'tilt' the piece up and made up a quick blank. That radius was 170", so rather flat in comparison the the 92" radius of the room at that point.

My concern, and your first thought I bet, is that the crowns were not 'laying' flat and would look like a scalloping as it went around the room. And in fact they 'scallop', but it iscompletely undetectable in the finished room. Whew!


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View higher quality, full size image (800 X 533)


View higher quality, full size image (800 X 533)

4/27/17       #16: Compound Curve Crown Molding ...
David R Sochar Member

The factor that came into play is that the beam crowns intersected the perimeter crowns at an angle - like trying to run crown on a cathedral ceiling. That would require what is called a 'developed' molding of two different widths, profiles stretched or compressed, etc. We needed to have the two crowns miter at a vertical (like a flat ceiling).

Since we could not have a flat ceiling, and we needed that miter to meet at a 'flat', we had to tilt a single radius perimeter crown down in the center. That would look very bad, so we forced it to a second radius to lay flat. And appear flat.

4/27/17       #17: Compound Curve Crown Molding ...
Chip Geffre

David -Beautiful work-Thanks for sharing some of your knowledge. I have nothing but respect and admiration for your skill.

4/27/17       #18: Compound Curve Crown Molding ...
B.H. Davis Member

Kevin,

First, my apologies for not responding sooner. Many months ago I changed my email address and didn't notice that the Firefox autofill feature had put the old one in as the notification address. As such I didn't receive emails notification of the responses. I didn't see your question until I came back to the thread today.

Yes, you are correct on the cut out procedure. We did the shallow elevation view (face) cut on the CNC to define that shape. Then since the blank was too tall to fit on the CNC for the plan view location cut we made the template shown in the photo on the web page. That template showed us how much wood had to be added to the top/center of the blank to achieve full horizontal projection depth.

After tracing the template we then did all the rest of the cutting on the band saw.

Profiling was done on our custom tilting Williams and Hussey (Tilt-O-Hussey) using a fence system similar to David's.

Since it was serpentine in plan view though the only curve to the table (bottom) fence could be the plan curve radius at the center of the cabinet. That gave us bottom support along the back of the curve for the center of the moulding. However for the reverse curve and straight ends the moulding had to ride on the single apex point of that curved table side fence. There is no automatic guide for this........it took the 15 to 20 years each of skilled Williams and Hussey experience of my two shop guys to pull it off.

BH Davis

4/27/17       #19: Compound Curve Crown Molding ...
Mark B Member

Awesome bunch of information in here. Phenomenal work David (and also B.H.). Crazy stuff.

4/28/17       #20: Compound Curve Crown Molding ...
Tyler

Thank you for posting david. B.H. What drove you to make a tilting head williams and hussey? How does the tilting head williams and hussey differ from a micron machine?

4/28/17       #21: Compound Curve Crown Molding ...
Jim Baldwin

Hey thanks Dave,

I think I finally see what you’re doing. The crown moldings are really functioning as large, panel molds, running along the ceiling beams and the top of the horizontal cornice detail? The problem, as I see it, occurs at the joints. This is understandable since any connecting joints, coupled with a turn, between a raked ceiling and a level one, is theoretically impossible, at least between two identical moldings (as you're aware).

You’ve addressed this by turning the horizontal crown molding, flatter along the wall (thereby, increasing it’s profile length) and forming a better mate to the raked, beam-crown? Since this action moves the curved, cornice molding, out of a horizontal plane, you’ve made it “double-curvature” and brought it back down? Is this correct? Very clever and perhaps the best way to approach this!

It is however, still theoretically impossible. Congratulations to you and the installer, for ferreting this one out. I do wonder though, if it might be possible to accomplish the same thing, without asking trim-carpenters and ourselves to jump through hoops, awhile pulling rabbits from hats? Doing “the impossible” always ends-up being expensive and time consuming.

Here are a few ideas of my own, which may (or may not) prove useful.

I’d leave the raked crown molding which runs along the curved ceiling-beams, unchanged, with the possible exception of milling it all flat (like any straight crown). These moldings are curved but only in the vertical plane and should be able to be cut from ¾” boards, especially since you have a W&H machine? A tilting shaper-head would also allow for an all flat, profile cut, that, or an Arch-Molder. (This is significantly safer and uses less material, than any horizontal milling-plan, with big propeller shaper knives etc.)
The profile of the horizontal, crown is altered to mate with the vertical crown and miter-joint. This is a “developed detail” (as Dave has already suggested.) Instructions for doing this, are in books or in the knowledge-base. This will require some custom tooling.

I might try a flat-cut, “spring molding” first, before surrendering to big glue-ups and horizontal milling. This is a process of making flat arcs, lay around a horizontal cone. All you need is a little trigonometry to determine the required radius and a bending-test to ensure success. The test is simple. Take a straight piece of crown, lay it flat, against the curved surface in question and bend. If it bends without breaking, “your in business” otherwise steam or kerf-cuts may make installation easier. Either way, the curved molding is bent and secured between the beams and actually “wants” to lay right.

These curved pieces of spring-molding, are milled exactly the same way as the ceiling crown. while paying attention to the profiles up-down orientation. They’re also the first to be installed and bent or “sprung” into position. The ends are left square. Next, useing a compound-miter saw, the raked moldings, are mitered and then coped to the mated horizontal detail.

Anyway, this is my attempt at “doing the impossible.” I can be more specific but I’m already writing a book here, sorry. This is an interesting problem, with excellent results already demonstrated by Dave. I just don’t like asking employees (or myself) to do impossible stuff. I'm interested in opinions and don't mind folks telling me that "I'm so full of it that my blues eyes are turning brown.

4/28/17       #22: Compound Curve Crown Molding ...
Russ

To: Dave, and all the other awesome craftsmen.
This is one of the best post I have read in a long time. To have so many of the best in the business chime in on Dave's post is remarkable. All of you do amazing work, thanks for sharing the pics and the information.
Jim I hear thru the grapevine you retired, good for you! enjoy
Have a great weekend
Russ @ MR

4/28/17       #23: Compound Curve Crown Molding ...
B.H. Davis Member

Jim,

If I understand your description correctly there are two problems to your solution.

First you can't really bend a standard straight run crown to a curve. I know you have tons of experience with curves so will defer to a more detailed explanation of why this should work if you can provide one. However my experience is that the top edge and bottom edge of the crown are bending at different radii and subsequently the crown stick will lay itself flat up against the ceiling rather than stay out at 45° or 52° angle as it bends along the curve of the ceiling.

Second is that if you bend a straight stick to a curve it will curve the center section in a non-true radius arc while the very ends will remain straight. Theoretically you could force the center to a uniform radius, and start the stick overlong to have it bend far enough out to do the job. However in this situation I doubt either could be done successfully.

Thanks for the long and detailed explanation of your theory. I too find it scary to run overly large knives on the shaper. Years ago I heard of a fellow designing a cone shaped shaper head. He made two of them as prototypes and I bought one. It made things a lot more sane for deep cuts on the shaper. Once we built the Tilt-O-Hussey though the cone head went on the shelf has has rarely been brought back out over the years. While it was safer than a cylindrical shaper head the geometry involved in making knives was complex. CT Saw & Tool got it down and made a lot of knives for that head. However it's been so long now that they would be scratching their heads again to come up with the forumlas they used back then.

BH Davis

4/28/17       #24: Compound Curve Crown Molding ...
Pat Gilbert

I don't have any experience with it, but it seems like a C axis would have to be considered for this.

4/28/17       #25: Compound Curve Crown Molding ...
B.H. Davis Member

Tyler,

I never bought the Micron because I felt it took the one downside of running curves on the WH and incorporated it as the primary drive method in their machine.

Running curves on the WH means the rollers are pushing the moulding straight while the centering fixtures guide bearings are trying to force it to a curve. The two systems are always fighting against one another. For true radius mouldings this is not a major issue so long as you make a curved fence. In daily production though curved fences take too much time to make plus most of our mouldings are non-true radius or have tangent straight legs. Only eyebrow shape mouldings continue to curve on the full length.

For curved crowns though when the head is tilted we don't use the centering fixture. Instead we use a single point full blank height block and or rubber roller. This holds the moulding at the correct distance from the post side for consistent cut position. It does however take a good deal of experience to get the feel for keeping the curved blank on the correct path into and out of the machine.

This is where machines like US Concepts and Stegherr have an advantage. They have outrigger roller pinch systems on either side of the entry and exit point to the cutter head. These outriggers float and can change their position as the shape of the moulding they are pushing through changes. Very nice feature.

The downside to these large machines, including the Micron, is the the 4" diameter cutter heads. The WH has the 1 1/2" x 1 1/2" square head that makes for a very small knife cutting circle by comparison. We've cut curves all the way down to a 5" radius without blow out on the WH. I doubt you could get anywhere near that small a radius with a 4" cutter head. The obvious advantage to those heads though is that they take standard corrugated knives so one set of 1/4" or 5/16" thick steel knives can be used for both the curves and straights.

BH Davis

4/28/17       #26: Compound Curve Crown Molding ...
B.H. Davis Member

Pat,

For shaper head profiling on the CNC I believe you would need both a C axis and an aggregate head. This is something I too have never undertaken.

We do profile crowns on the CNC on a regular basis. The Tilt-O-Hussey will cut down to a 12" inside radius. Below that we use 3D carving programming with Enroute to extrude the profile on screen and then create the code. This works for everything except where under cuts are involved. Then we'll typically split the moulding and do some of it on the shaper.

BH Davis

4/28/17       #27: Compound Curve Crown Molding ...
B.H. Davis Member

Tyler,

I should also mention that I'm pretty sure the Micron WH feed roller system is always parallel to the table. So when you tilt the Micron head the rollers don't tilt with it. As such on a crown moulding you only have the upper thin edge of the crown in contact with the feed rollers.

On our tilting WH the rollers of course tilt with the machine head. This mean that on a curved crown, depending upon knife design, the knives are either parallel to the face of the moulding or at least close to parallel. This gives better feed roller contact to the moulding.

I will confess that the Tilt-O-Hussey is not my own original idea. I have a friend in the same business in the mid-west who built one before I built mine........and he had seen one someone else had built.

BH Davis

4/28/17       #28: Compound Curve Crown Molding ...
Tyler

Thank you for the explaination B.H.
We have a belsaw machine that we use for matching historic mouldings in our shop and do make curved fences as you describe, however the first cut can be fairly heavy sometimes depending on knife projection/ depth of cut. On straight runs we usually waste out the excess with the shaper but this can be tricky with curved profiles. Floating infeed rollers would be nice. We also make alot of glass bead on our machine using angled sleds to avoid damaging the roller/ mouldingwith the sharp point left when run flat to the table. I can see how the tilting head could be an advantage. Thanks again


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4/29/17       #29: Compound Curve Crown Molding ...
TimG

B.H. Davis, I've heard about the tilting hussey but have never seen one, would you be kind enough to share a picture or two ?And thanks all of you for sharing what is sure to become a classic post in the knowledge center.

4/29/17       #30: Compound Curve Crown Molding ...
Adam

Tim,

There is a super crude setup on Youtube. I had to build a fixed table one like it for a big job of one shape and size curved crown(2.5" x 2.5"). Once you get your head around it there are many ways to do it. All depends on how adjustable you want it.

5/1/17       #31: Compound Curve Crown Molding ...
jl

I have collected all the different machines and they all have there special place. I own a couple Belsaws but the haven't seen the light of day in 15yrs. The WH is strictly tight radius stuff and sees infrequent use. Most of our radius stuff is done on the Mikron with the cnc as support and some 3D profiling.

Also, you don't always have to tilt the head to run radius crown!


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5/1/17       #32: Compound Curve Crown Molding ...
Jim Baldwin

B H Davis,

The hypotenuse of a right triangle, whose short or vertical side of the triangle, equals the radius of the curved wall, as calculated from the pitch-angle of the spring-molded- crown molding, and the short,vertical leg, will yield the radius for flat arcs or circular segments.

These flat but curved segments (after molding) are bent around, or into the curved-wall and voila, the curved crown molding is revealed.

This is early,19th century stuff but still very good. Believe me.

5/2/17       #33: Compound Curve Crown Molding ...
Pat Gilbert

This is a very interesting thread, but the last post by Jim is a head scratchier.

I found this thread where Jim AKA contributor J goes into this in more detail.

Conceptual understanding of the Cone.

5/2/17       #34: Compound Curve Crown Molding ...
B.H. Davis Member

JL,

That adjustable fixture is ingenious. I had to study it for a while to catch onto what it was doing.

With the adjustability of the individual leafs you can match the back of an eyebrow crown being profiled on the flat by having the fixture guide the blank both up/down from the table (elevation curve) and around or curving away from the closed side of the machine (plan curve) all at the same time. While this is sort of compound in nature you are actually profiling a single plane curved crown.

And the setup appears to be as simple as one could possibly get by just setting the blank on top of the fixture and sliding the leaves in and out to meet the back of the blank.

The central pair of fingers are under the low point cut of the knives and as you go outward from there in both directions the pairs of fingers pinch tighter for a smaller and higher V-bed for the increased height of the blank from the table, and move in or out from the closed side of the machine depending upon whether it is an inside or outside curve.

Honestly........this is a brilliant idea.

The only catch I see is that with standard crown knives it will only work on a 45° crown. For a 38/52 crown it seems you would have to have the knives ground longer on the top or bottom edge of the profile. However the fixture combined with a tilting head moulder eliminates this minor complication.

BH Davis

5/2/17       #35: Compound Curve Crown Molding ...
David R Sochar Member

I agree - JL's solution is a good one. Takes the notion of simplicity further down the road and offers that, plus the ease of using the v-shaped back as a reliable guide.

This is similar to the way I learned to profile twisted handrail on a shaper with with a simple twisted table. But that is another story.

This is indeed a great thread due to the fact that it got a lot of people thinking and some great solutions brought out. It is this ingenuity in craft, in manufacturing that I try to celebrate every day. This is where my interest lies - where need, knowledge, experience and experiment all come together to find solution.

5/2/17       #36: Compound Curve Crown Molding ...
Jim Baldwin

I think this is correct.

Where 6 is the plan radius and 14.29 would be the required flat, arc radius.

I've seen this in print in a 1921 woodworker's magazine but failed to bookmark it. I believe it was common knowledge before that.

My own milling methods for this type of crown molding, never exceeded Tyler's Belsaw set-up.

Click the link below to download the file included with this post.

curved_crown.pdf

5/2/17       #37: Compound Curve Crown Molding ...
jl

Dang, cats out of the bag. Works really well with the caveat being too tight an arc hits the feed wheel mount on the Mikron. Beauty is your're introducing the cutter to the material just as if it was in the moulder.

BH, sounds as if you have doubts but the Mikron really is an exceptional machine in it's simplicity and yet versatility. I looked at all the other radius molders and they might be better in one area but all around the Mikron is the deal. First and foremost over the WH is the ability to control the feed wheels independently of the spindle. Like many shops we've done some crazy stuff with it that it probably wasn't designed to do.

5/2/17       #38: Compound Curve Crown Molding ...
B.H. Davis Member

JL,

The Husseys too have variable speed feed wheels. It's an option add-on but the DC drive feed motor is a must in my opinion. We run all our mouldings at about 5 fpm on a final pass to reduce the amount of hand sanding required.

BH

5/2/17       #39: Compound Curve Crown Molding ...
Adam

The newer Hussey's post 2005 all have multiple pass springs. Like BH mentioned they have vario DC motor drive. There are a few different options for elliptical curved jigs.

Many people I know grind the casting away so you can run bigger knives. In order to instantly align the knives, you can use flat head allen cap screws.

You can do some serious work on the WH with a little farm tech. The trick to the thing is its small size. The small cutter head and close rollers allow for accurate milling.

Once you realize its not going to blow up or lift off the WH is a worthwhile investment. Not the best thing for straight runs, but its hard to beat for curves under $3k.

5/3/17       #40: Compound Curve Crown Molding ...
jl

BH, not variable speed which the Mikron has, but the feed wheels move up and down completely separate of the spindle. Really helps for difficult profiles where you need to take a light pass first or you just want to make sure your lined up. The WH you have to engage enough material for the feed wheels to grab often meaning you get one shot at it. In addition the reverse is awesome, spin the head around and go the other way if needed.

5/3/17       #41: Compound Curve Crown Molding ...
B.H. Davis Member

JL,

Yes.....absolutely correct. Sorry I misunderstood your comment.

It would be nice to not have to deal with light feed roller pressure on initial passes. The longer, softer springs on the feed rollers help but don't do what you can with the independent roller lift on the Micron.

BH

5/6/17       #42: Compound Curve Crown Molding ...
Joe Calhoon

Good and interesting thread! I have always managed to get through our curve mouldings with the shaper but picked up a used W&H a while back and anxious to try it out.
Joe

5/6/17       #43: Compound Curve Crown Molding ...
B.H. Davis Member

David,

I've come back to this a few times and it finally dawned on me that the simplest way to explain what you did in those short rake sections of crown at the bottom of each "pie slice" might be to say you put a twist in the crown as it approached the ends/miter points.

Is this an accurate description of what was done? If so where did the twist begin......just either side of center of the length of the crown, or within a few inches of the end?

If I'm correct about it being a "twist" then isn't this more of a spiral than a compound curve where a curved wall and curved ceiling are involved? That is does it fall more into the category of spiral hand rail but with a crown profile?

Thanks,
BH Davis

5/6/17       #44: Compound Curve Crown Molding ...
David R Sochar Member

B H - Let me try to restate what I was not too clear on in the beginning of this thread.

If you tried to run crown mold on a cathedral ceiling, you quickly realize it cannot miter as it hits the run at the level ceiling line. One can make a 'developed' molding for this problem, where the widths of the two moldings will differ. This is not the solution we needed here since we wanted all the crown to be the same width.

Picture a true triangular pie slice that is flat, with only a curve at the rim, all in one plane. The outer rim will be curved - a nice flat curve, the same radius as the room or rim, and will fit nicely up against the wall/pie pan. All the miters will work nicely.

Then lift the center of the pie slice a few feet. The curved rim/room radius will dip in the center of its curved length and no longer fit to the radius of the room. We can force it flat, and it will then fit the wall and be level as it runs around the room, as it should. But the widths of the two crowns have 'developed' and are no longer the same.

Now alter the pie slice so it is curved from the rim to the center, about a 100" radius. The rake curved crowns coming down the beams now are at an even greater angle as they arrive at the outer radius. Forcing the outer radius ever more out of level to preserve the widths of the two moldings. Cheating could not resolve it.

So, we measured up the amount of drop at the center of the outer wall radius and the length and calculated what that radius was, and then made the compound curves. One radius being the room radius at that outer wall, and the other being the 'developed' radius to overcome the drop or dip that the miters required.

This means that the compound molding was a continuous radii, one portion of length is the same as any other length. The beam radius mold was also a continuous curve. There was no alteration at the last moment, although a quick little curve at the end of the beam mold would do it, or even a flat miter in the beam mold at the very end would probably also work. Both had their reasons for being discarded. Logic said it could be done with a constant curve in both parts, but it was not apparent.

The photos may help with my explanation. The last photo shows some parts after they came back from the job site with the comment that "the crown won't fit". We set it all up and realized that the single radius crown we made could not be made to work. We then went thru a couple of alternates roughed up in Poplar- as the photo shows - trying to understand how to make it work before we realized what in retrospect now seems clear.


View higher quality, full size image (1350 X 1800)


View higher quality, full size image (1350 X 1800)


View higher quality, full size image (1350 X 1800)

5/6/17       #45: Compound Curve Crown Molding ...
Kevin Jenness

David,

Thank you for the further explanation. I believe I understand now that the cylindrical surface on which the compound curved crown is bedded is not vertical, but tilted so that it meets the radial crown elements squarely, allowing for a simple miter at the corners. Because of the tilt, the crown has to be curved in the second aspect so that its base is level when installed. Do I have that right?

5/6/17       #46: Compound Curve Crown Molding ...
David R Sochar

Kevin - Yes, you have it correct. The ceiling does not hit the outer vertical radius as a 'flat', so the crown must tilt to meet the ceiling as well as the outer panel as seen in the skeletal photos. But it needed the secondary radius to lie flat in a horizontal plane.

Serendipity that it actually was relatively simple once we saw the problem after the mock-up.

5/7/17       #47: Compound Curve Crown Molding ...
Kevin Jenness

I am glad that this thread has unspooled far enough that I finally grasp the problem whose solution was clearly shown in the first post. Along the way I was exposed to some new ways of skinning cats. Many of my continuing education credits are hard earned at the bench, and I am grateful when I can glean one or two from others' experience here.

Jim Baldwin said "Anyway, this is my attempt at “doing the impossible. I can be more specific but I’m already writing a book here, sorry." I think he was referring to his extended post, but if he and David are able to in fact take the time to write their books they will have a well-earned place in the canon. In the meantime we will have to make do with archiving Woodweb threads like this one.

I thank all the accomplished woodworkers who contribute to this resource.

5/7/17       #48: Compound Curve Crown Molding ...
Jim Baldwin

Thanks Kevin. Yes I was referring to my long post. You may be interested to know that I've already written a bit of a book but thus far have found no one to publish it. I don't blame anyone for this, since the idea is to make money, not throw it away publishing stuff, no one wants to read. Perhaps David could help?

Anyway, it's much like this post. I say something which I know is important, yet no one seems to notice or even comment other than one honest but negative response.

Truth is, David figured this out on his own and it's his business. I'm retired and therefore have nothing to do but butt into other peoples business.

Stuff like this still makes it fun.


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