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Curved Panels - adding another dimension to woodworking.

15K views 27 replies 16 participants last post by  eyeman 
#1 ·
Curved Panels #1 - Introduction and some uses for curved panels.

With all the gorgeous and clever projects presented on LJs, it is hard to find something to contribute that isn't redundant (or just plain embarrassing after seeing some of your projects). I haven't seen much in the way of curved panels so I am going to offer my experiences on the subject here. I must admit that so far Les Hastings is "King of the Curves" and you should check out his work, but he actually carves his curves out of solid wood. I will be discussing curved panels made from thin and/or flexible laminations.

For my first installment, I'll just skim over a few of the curved projects I've done and see if there is any interest in learning how to lay-up curved panels. If there isn't I guess there is no point in continuing, but I suspect a couple of you will find the challenge irresistible and want to learn more.

There is more than one way to skin a cat, a lot of different kinds of cats, and even more tools and materials to use to get the job done. I don't think I have done the job the same way twice yet and always consider how I would do it "better" the next time. In other words, I don't claim to know the best way or all the ways. You can take what I have to offer and build on it. I'll be interested in hearing your comments and ideas on how I could have done it better/different.

My first curved panels were made from 1/8" door skin because I didn't know any better. I used hide glue to bond them and bent them over a 25.5" diameter form I made by bending heavily-kerfed plywood over 12" radius ribs. I can't find a picture of it. Here is the result of the lamination:

And the finished product:

By the way, using the door skin instead of a material made to bend caused the panels to spring back once they were released from the form.

The next curved project I worked on was to design this:

And build the curved panels:

I also did all the veneer work and helped assemble the cabinet, but the shop I did this for did the finishing.

You can see this was quite different from the crude way I made the flower box panels above. I upgraded to a vacuum bag system, used panels made for bending, ureaformaldehyde wood glue, but still struggled with a number of problems. I will elaborate on this method in a continuation of this blog.

The most complicated curved project I did was this:

Working from a simple sketch, I designed and built this lectern and table using curved panels of the same radius. I believe I had all but one problem licked with this technique which I will share in yet another continuation of this blog. Here is one of the panels being glued-up:

I think this is the way to go and I will share complete details of the materials and procedures I used to make these.

Finally, I will share how I made two curved flat-panels doors. I am not particularly proud of them, but I did this in a relative's basement in another state, without any of my tools and equipment, and without a vacuum press.

I brought only some 1/8" bending board and cherry veneer with me. We made a really simple form (sorry - no picture) and using 8/4 and 4/4 cherry my cousin had, whipped these doors together and hung them in a couple days' worth of spare time. Cousin Chris gets credited with the procedure for making the curved door rails. It was much easier than what I had planned and you can see the result is great! See how he cut these out of the 8/4 cherry.

Not as nice as Les Hasting's curved doors, but they worked and you can build them without a lot of money or time invested in jigs. Thanks for looking and check back for the details later!
 
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#7 ·
I just posted Part 2, might it might be too late to start reading it. Yes I make my own bags from vinyl I buy at Wal-Mart. I use a special cement that you can get from Joe Woodworker - can't remeber the formula-like name of it. I use an assorment of plumbing parts to attach the vacuum hose, but I wish I would have bought some valves from Joe. Next purchase I will.

Thanks for the compliment and thanks for looking. Happy to answer any questions and open to suggestions.
 
#9 ·
Building "flat" curved cabinet doors - 101

Note that this is Part 2 of a series and you may want to look at Part 1 to make some sense of it.

I don't have any pictures of the form I built for the flower boxes or any construction pictures so I am skipping right to the 2nd project I introduced in Part 1. If I explain the flower box panels at the end of the series, it will be much easier to understand. Further, it was very similar to making the panels for the last project I'll cover - the curved vanity doors.

The entertainment center I'll discuss here was a commission a buddy of mine got. I typically made the working drawings for his projects and produce 3D renderings for him to present for approval. Since I had experience veneering and making curved panels, he asked me to help with those parts of the project also and I'm glad he did. It was challenging and I am proud of the results.


The design started as a picture the customer had cut out of a magazine. He put overall dimensions to it and we took it from there. I purposefully designed the cabinet so there was an abrupt transition from the curved sides to the flat front. I don't think it detracted from the design of the piece and it made it a lot less complicated than building part-curved/part-flat doors. It was going to be difficult enough to get the doors square, snug to the case, and the gaps right. The alternative to blend the curve into the front of the cabinet required a much tighter radius and it just didn't look right. Perhaps this is a good time for a picture showing the shape of the cabinet.


You can see that in addition to the curved doors, at either end there were smaller fixed close-out panels needed. The front edges of the close-out panels were to be cut parallel to the radius of the panels like the outside door edges; however, the rear edges had to be cut at a much different angle. Likewise, the inside edges of the doors had to be cut to match the 90 degree angles of the front doors. I learned the hard way on this project to plan ahead because it took me days to cut the doors and close-out panels out of the curved panels. Just think about how you would keep them plumb to the curvature of the door, square, and the correct size. More about that later.

Further, the toe kick also needed to be curved but at a smaller radius. Rather than make another form to make curved panels with a different radius, I essentially built two small forms using the same principles I used to make the large panel form. I combined them with the square base/toe-kick for the middle section of the cabinet and veneered it as one piece. Take a look at the top view of one end of the cabinet:

OK so the toe-kick isn't shown exactly how it turned out but you get the idea.

Finally the good stuff. This was my first encounter with these materials so I had to learn what was what. Visit this link to see the selection of products I had to choose from http://www.qualityplywoodspec.com/ and/or check out specialty plywood stores in your area. I choose not to use the products that achieve their bending capabilities from kerfs, but have nothing negative to say about them.

I did pick from their selection of bending plywoods. I still don't get the difference between what they call bending birch and bending Lauan, but I do get the barrel vs. column part - do you want it to bend along the 8' axis or the 4' axis? It is available in 3 thicknesses; 1/8", ¼", and 3/8". I'll warn you these are not the actual thicknesses. You will NOT get what you expect! I used one 3/8" sheet in the middle sandwiched by two 1/8" sheets on either side and ended up with a thickness of 0.78" instead 0.875". I saw this coming and used what I did to get as close as I could to the thickness of the plywood used in the flat doors. This picture is stolen from the lectern project and is out of context here, but you can see the laminations (look below the special router base addition);


Did I mention that the panel gains strength from each layer of lamination? I hope you don't need a citation and will just take my word for it. Believe me when I tell you that these panels are every bit as rigid as the flat plywood you buy. And just in case I forget to mention this later, they DO NOT flex when you take them off the form. They retain the shape of the form to the point that if you have defects in the form, you will see them in the panels. Trust me!

OK - I think Veneer Joe has touched the hearts of every woodworker who has considered vacuum bagging. If you don't know where to find him, you better start looking. If you are going to attempt this, you will need some of his equipment. The adhesive I am going to recommend using requires 6-8 hours in the press so you better get that check valve, presssure regulator switch, and build a reservoir tank or you will surely burn out your pump. Joe has all the info you need so visit his site and download the instructions there. A little hint: If you just can't hold a vacuum, be sure to check the check valve for debris. A minute piece of Teflon tape was stuck in the valve seat of mine and held me up for 2 days while I tried to seal perfectly good joints that were not causing the problem.

The glue I used is a DAP product that was recommended by a friend and readily available in a local hardware store. It was my first encounter with urea formaldehyde glue (I'm pretty sure they only have one). It worked great and the only thing I have to say about it is make sure you buy or make something to stir it with as it does not want to dissolve easily. Read the directions carefully and measure precisely. Use a scale if possible.

You will need a roller system to apply the adhesive because you won't have a lot of time. I recommend applying the glue to both sides so for me that meant spreading it out over eight surfaces, stacking the panels, getting them into the bag, sealing the bag, and pulling a vacuum before the open time ran out. It is very doable but don't get hung up trying to save a roller. And DON"T be cheap about the glue! Buy more than they recommend and mix plenty. You can't possibly mix more in time if you run out!

You will need a vacuum bag comfortably larger than your form. Have the form ready and waiting inside the bag so when you get the panels glued up and stacked, you can slide them onto the form and close up the bag. You don't have time to fart around! See Joe again. There you can buy a valve and the glue to make your own bag out of vinyl that you can buy in the fabric department at Wal-Mart. It is ridiculously cheap! Find the one you think is strong enough and spend a few extra pennies to buy the next thicker one. DON'T FORGET TO TEST THE BAG/VACUUM SYSTEM FOR LEAKS BEFORE YOU MIX ANY GLUE!

Now you can be sure that glue is going to run out of the seams and your panels can easily become a permanent part of your form if you don't take the time to protect it. I am fortunate enough to have a large roll of real cellophane and I cover the form with it. Nothing water-based sticks to that stuff and I find it indispensable. You will have to get creative. I suppose a plastic garbage bag would work?

You aren't going to get anywhere without a form. I am warning you the second time now that if you aren't careful making the form, your mistakes will be reflected in every panel you produce on it. If it is wavy or twisted, your panels will be exactly just as wavy or twisted. And they WILL stay that way! Build it on a "flat" surface and take NO SHORTCUTS! More about this in Part 3.

You will have to make some calculations based on the actual thicknesses of the bending material and the panel radius you want. Here you need to include the gap between the door and the carcass and consider whether you are looking for the inside or outside radius. I admit that I made my form for this project backwards and regret it now, but we will continue to work with what I have here.

From that calculated radius, you need to deduct for the thickness of the bender boards you are going to use to construct the curved surface of the form. I used whatever I had left over that added up to about ¾" thick and it has worked fine for me every time. Using that radius, I constructed a plywood pattern from which I cut 12 identical ribs which would support the bender ply sheets. Below you can see the plywood pattern resting between the 2nd and 3rd ribs of the form. I rough-cut the ribs on the band saw and used a trim bit on the router to finish the job.


Notice it has an index on the left side so each rib could be aligned to the next so long as they were all attached to the edge of the base correctly and the base was square. Below you can see all the ribs, spaced 3" on center, ready for the bender ply sheets to be added.


I learned later that this next step is one that should not be skipped at any cost! I used the urea formaldehyde glue and the vacuum bag just like I would on the real curved panels and bonded the bender ply panels to the ribs of the form. I only used about 8 lbs of vacuum so as not to warp the panels by sucking them in-between the ribs. I repeat - I would not make the form like this again so there is no need to point that out. It will become clear in the next part of this series.


After the form was set up, I block sanded it using a curved block I made on the form with Elmer's glue and some scrap bender ply. It didn't take much sanding and I was ready to lay-up some panels. I hope I covered that part well enough above so I will skip to a picture of a panel in the bag. For what it was worth, I tried to get one edge of the panel straight and aligned with an edge of the form. It didn't do much good as far as trimming the panel into a door later.


Well now you have had a crash course in curved panel building. I am purposely skipping the part about how I got the panels square and plumb because I wouldn't go through that again for all the money in … well I won't put you through how NOT to do it. You can see below that I eventually got the panels to fit perfectly with European-style gaps.


If you noticed that the 3D rendering above was covered in beautiful lacewood but the project ended up being curly maple, you're correct. The people rejected the lacewood when they discovered that all of the fleck would not be the same size. No comment! Thank goodness I didn't actually apply the lacewood veneer. And speaking of veneer, it was just another trip into the bag.

A final note here. I mentioned that panels made this way do not lose their shape (don't spring back) when removed from the form; however, I strongly suggest that when possible you build your curved panels BEFORE you complete the design and/or shape any of the other elements of your project. I swear I am not telling you beacuase I make this mistake. My panels turned out incredibly close to plan, but I was able to make the curvature of the cabinet match the doors perfectly because I waited until the doors were made. Too bad no one will ever be inside the cabinet to see just how good. Well at least the customer could see before the granite top was installed.

Thanks for looking and watch for Part 3 - The Correct Way To Build A Form so it is easy to trim your panels. If all this is too much for you, Part 4 will be about making less complicated curved parts without a vacuum system.
 
#13 ·
Building a better form for curved panels - 201

In Part 2, I introduced the materials and methods. I mentioned that my form had a serious drawback and here I hope to explain why and send you down a better road. Here is the project - at least part of it:


The edges of the panels come out of the bag looking pretty rough. I can't think of a way to coat 5 sheets of bender with adhesive, stack them perfectly, and keep them stacked perfectly into the bag and through the vacuum process so when they come out you have perfect edge. Even if you could, it is not like you can put a square on it and get a second side at 90 degrees to the first. My solution was to build the form in such a way that I could use it as a guide to put the edges on all the panels that came off of it. Here is how I did it.


Above you can see the beginning of the construction of the form. Using a method similar to that explained in Part 2, I produced a number of identical ribs. Working on the flattest surface I have (it is under the form and perhaps the subject of another blog), I added one rib at a time. Each rib is forced to be perpendicular to the base and parallel to the next by spacers that you can barely make out below the clamp. Ditto on the ends of the ribs which are spaced about 3" on center.


Once again, using left-over pieces of bender I built up the curved surface of the form to about ¾". This time I got cheap and lazy and decided to use old yellow glue and a pin-nailer to hold the bender in place. I thought I was being careful to get the sheets down tight and all the air out from between, but I ended up costing myself a tough week of sanding and re-shaping.


Now I would have blocked the surface out like this anyway, but it was really bad. So bad I actually had to add bondo to fill in the lows. Here you can see how my auto body-work experience really helped out.


Unfortunately, my block didn't apply as much pressure as the vacuum bag and the panels I took off the form were horribly wavy. I burned up a lot of time, sand paper, and bondo getting them straight. Like I mentioned in part 2, YOU MUST USE YOUR VACUUM SYSTEM TO APPLY THE BENDER TO YOUR FORM!


For what it is worth, here is one of the panels cooking in the vacuum bag. Notice the bucket of urea formaldehyde glue in the upper right corner and that it has an orange label if you decide to use that product. Also notice I don't have gapping holes in this form for the bag to get stretched over. I do have holes in every rib to allow air to easily escape.


OK now the good stuff. You're looking at the form upside down. Notice the marks indicating that those are the corners I really concentrated on getting square. When I put the ribs together, I was very careful to get them perpendicular to the base. At this point, I cleaned up the side and end bender surfaces of the form to match the surfaces of the outer ribs and base ends. So what I should have there is a 3D object that is both square and plumb on one end and 2 sides.


Above I have attached one of the panels to the form with screws so that one side and one end overhang the form. I used a piece of bender lay-up I made on top of a panel (because the radii are different top to bottom) to adapt the router base to the shape of the panel. (I could have made it a little thinner as you can see the bit is protruding dangerously from the router).


Using the side of the form as a guide, I was able to put a straight 90 degree edge on a panel in moments. With the panel's end hanging off the form, I was then able to trim the end at 90 degrees to the side.


BTW - the center bender board here is really 3/8" thick (not 1/4"). As I mentioned in Part 2, the thicknesses are not what the descriptions state and you must plan ahead for this. Total thickness of this layup is actually 0.78". Before doing this again, I would try to find a longer ½" shank bit but it worked. I had my fingers crossed the whole time and I was wondering what a hot bit in my gut would feel like. I did it in many passes; although, with the correct bit you probably could knock the whole edge off in one shot. Still attached to the form, you see the result below.


When assembled, the front of the lectern stood perfectly plumb and the top and bottom edges were level for attaching the feet and upper mouldings.


The "un" finished product:


You most likely will need different angles on the ends your panels as I did for the bottom edges of the table sides shown above. At least I had something to reference by sticking to what I showed above. I'm sure you will have no problem modifying the form, creating router base attachments, or coming up with an entirely different twist to this. I am looking forward to hearing your ideas and seeing some more curved projects out there.
 
#18 ·
Easy Does It - curved panels without a vacuum press

I couldn't find any pictures to make this easier to demonstrate so I whipped up this:



The object here is to demonstrate how a curved panel might be made without a vacuum press. A picture is supposed to be worth a 1,000 words so I'll cut it short. The lighter-colored material in the center of the picture is supposed to be the end result. You will have to imagine that it is 2 or more layers of bender board (see #1 & 2 in the series). With this technique you will not want to use the urea formaldehyde glue and since you will most likely eventually have to veneer the curved panel, I recommend you get some of Joe Woodworkers cold press veneer glue and use that to bond your curved panel bender sheets.

The golden-colored objects in the picture represent more bender boards that bridge the ribs (labelled BENDER in the diagram below) and support the panel between the upper and lower ribs. Also, I might add that I don't think you need to actually bond these bender sheets to the ribs. Further, I can't prove it but it would seem that the more ribs you have, the better the form would be. I also think that may not be the case with the bender bridge sheets and I would use just one thickness of the thickest material you have. If you don't want to buy anything thicker than 1/8 bender, then maybe you ought to use 2 plys for both top and bottom bridge sheets.



You will have to make some calculations to determine the radii in the diagram above (NOTE - it is not to scale and not intended to suggest any proportions). Start with the finished panel and work your way out until you get the radii of the upper and lower ribs. Make all your ribs from a single pattern (one for upper and one for lower) and be sure to include some way to align them all.

This may be over kill, but you could also include the thickness of your veneer in the calculation. You should then place one thickness of the venneer above and below the finished curved panel when you lay it up. When you get your curved panel made, you can re-use the press to adhere the veneer to both sides of the panel at once by squeezing the veneer sheets and curved panel in the form again. I did not go to that extent and did not have any problems with the panels or the veneer. I would NOT try to do the panel and the veneer at the same time.

Maybe I'll come back with a little about the veneering later. It doesn't get any easier than in this application. Also I will share how my cousin machined the curved rails that hold the top and bottom of the panels in the doors shown below.



I see I forgot to mention that this will work simply by piling some weight on top of the form. The bender does not offer much resistance. You could use clamps and you could also find 13 other ways to accomplish this. Finally, be sure that your upper and lower ribs are aligned before you apply pressure or you may end up with a wavy mess!
 
#26 ·
Putting it all together - a simple curved door.

Now that the panel is made (in this case 2 layers of 1/8" bender), it needs to be covered with the appropriate wood. In this case it is cherry and I didn't have any veneer wide enough to span the panel, so I had to bookmatch two sheets. You need to have a special tape to hold the panels together through the glue-up process. You also need to have a special cold press glue to bond the veneer to the curved panels.

You can get both at Joe Woodworker. BTW - He has a new pressure-sensitive veneer tape that can be easily removed after the glue up. And it is cheap as regular masking tape! The alternative is the traditional water-activated glue tape that is next to impossible to remove. The new tape used in vacuum bag applications is not so easy to remove, but I'll take it over the other any day of the week. BE CAREFUL removing the tape from high figure woods as it will pull up some fibers! It is very sticky!

BTW - the bookmatch line should be almost invisible in the final product, but you need to be careful to get it centered and parallel to the sides of the panel because you can see it. Perhaps some notches in the veneer will help align them to the edges of the panel.

Folow the directions on the glue and apply to side one of curved panel. Apply the veneer being careful to center as described above. Squeegee out any air. Repeat on other side. Place in form. Apply some weight/pressure. Allow to dry. You should now have a curved panel that looks like this:



Now you will know the thickness of your panel (although you could have calculated it before) and the size your dadoes need to be in your rails and stiles. If I had it to do over again, I would have stuffed a layer of veneer between the bender panels because our thickness was about one thickness of veneer (about 0.042") short of 5/16". No problem on the stiles as those dadoes can be done to any size on the table saw. But as you will see, the dados get put into the rails while they are being machined. We were stuck using a 5/16" bit and had to stuff the back of the panel with veneer shims to make it tight to the outside of the rails.

The stiles are not curved in any way and I will not bother discussing them except to say that the 2" wide sections of the door at the stiles being flat did not significantly detract from the curved appearance of the doors. Also, we did not use raised panel bits to make these doors. A dado was added to the center of the stiles from top to bottom. The rails were made so that each of their ends included a tennon that fit into the dado. If you were to look at the top or bottom of a door you would see the difference, but again it was not too terrible. If we had raised panel bits to use, we could have as did Les Hastings (see link in earlier section), but this could no longer be the "easy way to make curved panel doors."

The rails were cut out of 8+/4 cherry using a router and the longest 5/16" bit we could find. We starting with the radius of the outside of the cabinet the doors were supposed to fit. Allowing for a small gap, we calculated 3 radii taking into consideration the diameter of the bit and which side of the bit was cutting the radius. One for the inside of the rails, one for the dado the panel was supposed to fit into to, and another for the outside diameter of the rail. It took a lot of beers and arguing and was a painful journey, but we figured it out.



This is how the 8/4 cherry looked after the sawdust settled. Since the bit was not long enough to cut all the way through, the pieces had to be separated on another saw. The rough edges were then finished on an OSS and voila!



If I remember correctly, we used the bottom of the form to support the rails on the tablesaw to cut them and the tenon shoulders on the outside. We used the top of the form to cut the inside tenons, but had to tilt the saw blade as there was no way it would reach high enough to cut with the blade at "0" degrees. Both parts of the form were slightly damaged but it was necessary to use them. If you don't see why, maybe I could whip up a diagram later. It is getting late and plently of things to do before monday.

Here is the door glue-up. Doesn't look like much care was taken, but it worked.



The doors are shown here from another angle after being hung . If you noticed that they don't sit perfectly, it is because they are not yet latched and have no stops. I haven't seen them since, but hear they lined up perfectly and hey are very happy with them.



That's it! Thanks for looking and I hope after you give it a try you will let us in on your adventure.
 
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