Steaming

[ScottWidmier]

My modification project on my c12 is coming along well though it looks like I won't be finishing the decks bright (long story). One of my next steps is to put the mahogony cockpit coaming on. I bought some beautiful mahogony and had a friend mill it down to 3/8" boards. I shouldn't have any problems with the coamings on the sides but the forward coaming has to go around a fairly tight curve so I must steam.

My question is, can I build a steamer out of polytarp with pvc pipe as a frame to hold it in shape? I only have to steam one board and I don't have space to store a steamer. I figure I can dissassemble the pvc and polytarp and store it in the attic for future projects.

[Barry Pyeatt]

You might want to check this out. It works for small projects and is easy to do.

http://gaboats.com/tutorials/steambox_nonav.html

Over time I've bent some pretty large pieces of wood in steam boxes. The issue is really one of working fast once you get the wood limber enough to bend. You only have a min or two to get it wrapped to the curve and clamped or fastened inplace. But once it cools it is set.

Gloves cuz it is going to be hot enough to scald your skin. Extra helping hands to hold it while you fasten it, or to fasten it while you hold it. Or a jig to form it to with clamps and then place it after it has cooled down.

[Charlie Jones]

Scott- you can build a steam box out of most anything that will hold the steam inside and last long enough. Laura has built steam boxes from cardboard held together with duct tape, for just one small piece. Used a camp stove a boiler and a PVC pipe to carry the steam up. You can also use a chunk of PVC pipe (sched 40 or 80)

Strips of ply, anything that will hold up long enough. Incline the box slightly so the condensate can run out, fix one end closed and close the other with rags.

Use gloves and work quickly.

[ScottWidmier]

Thanks, excellent advice from the post and website. I really appreciate the heads up in regards to working time being one minute. That probably saved me a lot of headaches right there.

[ScottWidmier]

Here is a picture of the boat showing the curve at the front of the cockpit I am concerned with. I don't have the measurements on me but figure that this is a 12' boat and you get an idea of the dimensions of the curve. Would just soaking it with boiling water work in this instance or is it better to take the time to steam it? Also, what impact does the wetness of the board have on the epoxy that would be gluing it in? Or, do I first bend and clamp it to get the shape and then let it dry out before epoxying it into place? Thanks for all of the advice btw.

[Barry Pyeatt]

being 3/8" mahogany, I would first soften the edges by sanding or routing them to a finished roundover profile. This will prevent splitting out along the edges when you bend it.

I would use a steam box to bend it since mahogany is brittle and prone to splitting in a tight curve. I would also make up a slightly smaller radius jig out of MDF and clamp the board to it to take the curve. The board will spring back to some extent when it dries. Allow a couple days at least at room temp to allow it to dry completely and then place it where you want it to be on the boat. It is far easier to have it bent to a slightly smaller radius than needed than to try to force a larger radius piece inplace. The board will have a tendency to relax if you are spreading it, rather than wanting to split if you try to bend it more when it is dry.

The boiling water towel practice works fine on smaller, narrower ribs or pieces, on wider stock the towels tend to cool quite rapidly and as a result the wider boards of that thickness or thicker really don't get as much of a relaxing of the grain to allow the bend.

It is amazing how flexible the boards can become, but pay attention to your working time regardless, it is short and you have to work fast to get it clamped into place. I've bent coamings this way, using MDF jigs around a slightly smaller radius than finished calls for. Only had one problem with any of them in splitting and that was because I was trying to use a wild grain piece of wood and it just let go along a curved grain line.

In making up an MDF jig, I cut the curve into a single layer, then use that as a pattern to make duplicates of it building the layers up to the finished thickness. Then screw the layers together so there are male and female sections to clamp the coaming between. Sand them both smooth and then just clamp the board between the two layers. Goes quickly and no impressions are made to the coaming. I use pipe clamps but bar clamps would work just as well.

A friend of mine uses the same technique but has the female portion of the molds placed against the wall and secured then pulls the male portion to it and blocks it inplace with screws thru the blocks into a base board.

Lots of ways to clamp it but this works well since the entire surface of both sides of the coaming is held inplace securely.

[Hirilonde]

I would also make up a slightly smaller radius jig out of MDF and clamp the board to it to take the curve. The board will spring back to some extent when it dries.

Very good advice. You might be able to muscle the loss in curve back during clamping/gluing, but prebending to a tighter radius is definitely easier.

since mahogany is brittle and prone to splitting in a tight curve.

Honduras mahogany sure is, but African is quite stringy. That is why African is so often chosen for planking. Regardless of what species you have all precautions are good ones.

I will stay out of the hot towel vs steam debate But keep in mind that if you fail to get the curve on the first try the second one will be much more prone to splits or even breaking. Having everything set up, all your stuff ready and at hand, a helper already present, etc are key. The actual project is not overly difficult, but because you haven't done it before and you know you have such a small time constraint can sure be intimidating.

Best of luck.

[PAR]

Green mahogany will bend pretty well, but nothing like oak or other species. Kiln dried lumber will not bend near as well and should be soaked over night first or expensive and loud "crrraaaaks" may be heard, usually followed with louder cursing and often times crying for hours in the moaning chair.

Over bend the radius (to account for spring back) by 10% on green lumber, 15% on naturally seasoned (fully seasoned) and 20% (sometimes more) on kiln dried stock (and pray). Estimate the radius with a string or tape measure. Decrease the radius by the necessary amount (this is the over bend part) and build a bending form, which needs to be tolerant of the stresses involved in the bending process (make it stout enough).

Your deck crown doesn't look difficult to spring it down to or it can be cut to match, just focused on the bend. If you want the coming to splay outward a little (nice for back support and fending off boarding water), build this into your form.

3/8" green stock will need about a half hour in the steamer, maybe a little less, fully seasoned stock maybe 45 minutes and soaked kiln dried stuff probably the better part of an hour to get limber (did I mention the power of prayer). As everyone has said, work quick, use gloves, have all the tools, clamps, beer on ice next to the moaning chair, etc., as you will not have time to find a clamp when she's ready to go on the form. You have just a few minutes at that thickness, so do some dry runs to get everting where you'll want it. A helper or two is a great asset.

I've made steamers from foil faced foam from the Lowes/Depot store, secured with foil tape. It'll leak after a while, but it's cheap and easy. PVC tubing works, but my newest one is a piece of sheet galvanized chimney pipe (12") with wood plugs at each end. I have a 5 gallon, metal gas can sitting on a camp fire cook stove, powered with propane. The filler neck goes in the end (which is mounted lower then the loading end) and it works very well. The loading end plug can just be a rag stuffed in the end of the steamer. You want the steam to escape (at a controlled rate), not build up and blow up your steamer. Load the lumber, plug the end and wait for a good head of steam to come out, before you start the timer.

My experience with kiln dried lumber is 50% breakage on non-soaked pieces, 35% breakage on soaked boards, on fully seasoned stock about 15% breakage and green stock less then 10% will go snap when you put a good bend on them (turn of the bilge kind of bend). This isn't counting, "hoping the grain run out will make the radius" pieces, but good looking, straight grained stock with no run out. A couple of years ago, I bent nearly a hundred white oak ribs for a restoration, but was forced to use customer supplied kiln dried lumber. Even soaking, I had a pretty high breakage rate, on a species that doesn't mind being bent.

You'll be all right. That radius doesn't look too bad at all. She's coming along fine with some fine effort on your part Scott.

[ScottWidmier]

Thanks everyone for the wonderful advice. I have always wanted to steam bend something because it is one more step on the way to traditional boatbuilding but I do admit a bit of trepidation. I don't like having to work fast and I hate being on edge listening for the dreaded CRACK as you bend the wood just a little bit further.

Based on the advice posted here I think I will try steaming just to be on the safe, non cracking, side. Besides, I should learn how to do it sometime and, as was pointed out, this curve isn't extreem. I believe the wood is seasoned African Mahogony but I will double check so I have an idea of what I am working with. I also like the idea of the smaller radius form because I would hate to go through the steaming process just to struggle with it and hear it crack during the mounting. Can I use scrap ply to make the form or does it have to be MDF?

Thanks again.

[Charlie Jones]

If you have a table top you can screw into, you don't even HAVE to have ply. You can lay out your line and screw blocks down on the inside of it for the piece to bend against. Use some clamps to clamp at each block till it dries. I'd put the blocks fairly close together at the biggest part of the curve, further apart where it's more gentle.

The whole idea is simply to have a solid form to bend against and clamp to. WHAT it is is not really relevant.

Use a small chunk of your stock against each block and get the clamps pre set. Then you can bend and drop a clamp, bend and drop a clamp. then go back and tighten. Should go very quickly.

Tell ya what- put a cup of water into the micro wave, punch up 90 seconds and see how much you can do in that time. You'd be amazed

[PAR]

Ditto Charlie's method, that's how I usually do it. Chunks of wood, screwed down to a table to the radius I want, anticipated springback included. Have the clamps at each block or use double blocks and wedges (requires forethought and planning). I often use "L" shaped stands made of plywood and scrap lumber, for things that have to bend in two directions at once, like your coming (outboard tilt and curve in plan view). You could always kerf the crap out of a piece of plywood, bend it on, smear in goo, then laminate thin veneers of mahogany on, making most wonder how you did that on a continuous piece of mahogany . . .

[Wild Dingo]

Ive used both Charlie's and Barry's methods for forming curves... both work equally good...

One thing I will add is... Have everything ready BEFORE you start to steaming or bending!! There really is nothing worse than not having the clamps to hand when the wood comes out :evil: :oops: And I do mean to hand not on the bench or clamp rack on the other side of the shed or even a few feet away but right next to whatever form your going to use... in preference I would suggest you have them laying right next to whatever form its going to clamp to

Another person is handy and helpfull... but explain to them the method and what they will do and if a kid then do a dry run practice before you start so they know exactly what you are going to do and whats expected if them.. be clear... you avoid tangles trips yelling swearing and general roaring if this is done BEFORE HAND... dont ask :roll:

Good luck 8)

Shane

[Barnacle Jim]

Ahoy Scott,

Have you considered laminating? True, you may have exposed glue lines, but the lines and the wood can still be finished bright, and with respectable results.

You would still have to use a form, but without the possibility of the wood cracking or breaking. Indeed, the finished product would be stronger than the wood itself. Consider, for instance, heavy laminated beams in buildings.

Scott, here are some early photos of one such project for my own boat.

The suggestion to build a smooth curved form would give you better results. I just went with the crude blocks because it was a bit faster.

As I recall, we merely placed our block along the radius we wanted, and used some small handclamps to hold our stock to the blocks. Scott, I think I remember working in stages, glueing 3 or 4 strips at a time one day, and the remaining strips the next day.

Admittedly, with laminated stock, you will need to clean things up a bit, sometimes with a sander, and sometimes with a handplane, but nothing quite beats the joy of using a handplane on stock.

Here is a photo of the stock now ready for finishing. The lines are true, the curve remained just as we had wanted.

Here is a close-up of the stock. Yes, you can see that the stock is laminated, but if the lines are not objectionable to you, your stock will look good and finish bright. The glue is RAKA epoxy, straight from the bottle. (We may have used some thicker epoxy from Glenn-L; I don't exactly recall.)

Should you try laminating stock, don't forget the wax paper. Otherwise, you could end up having glued your stock to the form itself. That would not be a good day. In fact, doing something like that could really make you steamed!

[ScottWidmier]

Ahoy, life has gotten interesting and my boat project has languished. I plan on rolling her back over since the last stage I finished was filling, sanding, and painting the bottom. Once she is rolled over I will mount the seats and other interior bits before turning to the coaming...less to lean over when doing the inside.

Jim, I still plan on steaming just because I want to . I do like the effect of laminating but I am working with a 3/8" x 3" piece of wood and really don't have the equipment to cut that in half thickness wise.

[Guest Oyster]

If you have a table saw, then you have the ability to cut it in half. You run the board along the fence the three inch way, cutting as far as your blade will allow you to do, and then flip it over running the same side against the fence to cut once again, meeting or overlapping the first cut. Then you sand smoothe and reglue it back with thickened epoxy. Works everytime its tried, since most blades on even an eight inch table saw normally cuts a fat 1 1/2 with the blade extended full height, or has been my experience.

[Craig]

Scott no one has mentioned this so I will toss it out. When I build Tom's cover for his 55 footer we used a solid mold with the spring back accounted. We achieved very good results on a 12" radius 90 degree bend. The only problem was some of the edges splitting a bit following the growth rings. By banding the out side of the curve with aluminum straps between the wood and the clamps it bent perfectly and none of the stock split. The wood was 3/4" fir presoaked and steamed in a poly sewer pipe steam box. Larger radii pieces of about 8' length were also bent. The larger pieces did not require banding. Large pieces are better handled using two workers, one to bend the stock onto the form and the other to set the clamps. The steamng was the fun part of the project. You can do a lot with it.

[ScottWidmier]

Well, unfortunately my old tablesaw went with a previous house so no table saw. Besides, I really do want to try steaming because so many people, like Craig, have said it is cool and interesting to do.

On a positive note, we are buying a new house that has a basement that is stubbed but not finished. I have gotten permission from SWMBO to put in big double doors and take as much of the basement as I need for a good woodshop/boatshed! Guess she is tired of layers of dust on everything in the garage :oops: . I plan on doing everything I can when fitting out the space to make it dust sealed and am also wanting to set up a dust catching system.

[ScottWidmier]

Craccckkk! :oops: :oops: Steaming went well on the poplar but not on the mahogony. I kinda figured something was wrong when I pulled the mahogony out of the completely steam filled box and parts of it were dry. I am going to fit in some sort of rack system in my box instead of blocks on the bottom and leaning the piece against the side and try again.

[Craig]

I forgot to mention drilling through the pipe every foot or so to run coat hanger wire through to keep the wood sorta centered in the steam flow. A bit of angle down toward the steamer will recycle a lot of the water too. Sorry Scott. :oops:

[ScottWidmier]

Don't worry about it, several had mentioned the need for a rack but I was trying to cut corners. I was warned against using metal though because it might leave black marks on the wood.

I did end up building the rack by drilling some holes down the side and tapping in dowel sticks. I then tried it all again crossing my fingers. I was really worried my setup wasn't generating enough steam due to only 700 watts on the cheap hotplate I bought. I pulled the second piece out of the box and it was more evenly steamed throughout though there still was one little dry spot. Amazing given I soaked the wood both times for 24 hours! I decided to try again on my form this time working from one end to the other clamping in station in progression. Took a lot of effort but it did take the curve without a dreaded crack!

The wood dried very quickly and a day or so later I decided to mount it on the boat. I was concerned about first taking it out of the form because some judicious testing showed it was ready to at least partially spring back to straight. So, I ended up droppint the coaming and form into the boat where my wife held it up with her knees in position while I released the clamps. The coaming sprang from the form into position on the boat and some simple adjusting and clamping to hold it in place while the glue dried. I have since used thickened epoxy to give it a nice rounded transition from the deck and yesterday I sanded and sanded. I now have two coats of spar varnish on the coaming and it looks incredible! I picked out this particular piece of Mahogony because it had some beautiful cross hatches that add a lot of depth to the wood and the varnish has really brought this out. I will post pictures as soon as I get the varnishing done and paint the deck white. I am afraid the beauty of the wood won't come accross in pictures but she should look great none-the-less.

Overall, steaming wasn't that bad and I am very please with the nice sweep of the coaming. While I don't want to take up steaming for a hobby it does lead to wonderful results.

Thanks to everyone for your suggestions!