Stem Bending Question (not trying to monopolize the forum)

[dumbquestionsguy]

At the risk of annoying people by overposting (hey, I like this community, what can I say?) I have a quick question after breaking yet another stem. I've already posted about my last project where I used some other less desirable wood (just for experimenting), and actually it bent ok, but now I've switched to white ash and though I've bent one stem successfully, I've broken probably 3 others. I can't even remember what I did on the good one anymore! I soak for about a day and a half prior to boiling for about an hour. Am I overboiling? Taking them out too soon? Just have a tough batch of ash? I'm trying to bend with the grain and all. I apologize, people, I know this is covered in books (which I've read) but you know how you get caught up in the moment of failure and just want some help! Sigh... I'd love to build a good boat with the "right" materials, but can't seem to get the second stem going, and hence, the last couple of ribs have to wait also, and on and on. Thanks all for your patience, your help, and may you all find a bit of peace this holiday season...

 

[dumbquestionsguy]

Someday I'll actually contribute something useful to someone else, I promise. Again, thank you all...

 

[Dan Miller]

Bending success depends on a number of things, any one of which can scuttle your attempts.

Bending stock: For stembending, you are ideally bending green wood. If you have a local sawyer and can get some straight off the saw, that is best. Air-dried is second best. Kiln dried wood is much more problematic, though it is possible. I've bent a fair amount of KD ash, and I've always soaked it several days, even a week, before bending.

Steaming length: when steaming wood, there is a window of opportunity. Too little and it breaks, too long and it breaks. Rule of thumb is that you steam for one hour per inch of thickness. In reality, this time varies depending on stock, steam source, time of day, whether its raining in Hong Kong, etc... If boiling, you can leave it in much longer without ill effect.

Amount of heat: Put a thermometer in your steam box. You should be reaching temperatures over 200 degrees F. Mine is typically at 210 degrees. Absolute minimum is 180 degrees. If you don't have a thermometer, you won't know when your steam box is up to temperature (which is well after steam starts to billow out of it).

Technique: If you don't use a compression strap, get one and use it. Don't rush the bend, give the fibers time to slide as you bend.

 

[Canoez]

One other thing to remember is that moisture is key - you can steam the wood for a bit longer if you keep the wood wet as you steam. Dan's rules of thumb work pretty well. If the wood dries as you steam it, you can actually start to kiln dry it and it gets brittle again.

 

[dumbquestionsguy]

I've actually been using the boiling method pretty exclusively. It seems to soften the wood I use a bit better. Of course, excluding the ash stems... So drying out shouldn't be a problem, since it's literally soaking in water. Though would overboiling cause it to break as well? Like make the grains come apart like an overdone roast?
Thanks again for your patience and knowledge.

 

[Canoez]

We've boiled ash for bending stems with good luck, too.

One thing we discovered was that we didn't pre-soak the pieces and we broke the first two - they were wet on the outside, but still dry on the inside so I'd still pre-soak the pieces. We pre-soaked the second set for two days and then boiled them with good results.

The big thing with boiling them is that you can get a bit of discoloration and it can go pretty deep.

I suppose you could over-boil them, but haven't had that happen or appear to be a problem. You could always let them boil for as long as you think is necessary and test them. If they're not as flexible as you want, put them back in.

The bending strap that Dan is talking about is key. It helps keep splits from starting in the fibers on the outside of your bend. I've seen straps and metal used for this. Jerry Stelmok used a sheet metal band with some tabs welded to it -to keep the stock from twisting and as a compression strap. Put some tape on the metal if you do this - I think that was Rollin Thurlow's suggestion - to keep from making marks on the wood.

 

[Andy Hutyera]

You can buy metal strapping used for joist bracing at most hardware stores. It's cheap and works great for bending stems. It is pre drilled with holes down the center to attach a longish handle on one end and a stop block on the other.

 

[ken mueller]

I don't recall where I read this, maybe in Stelmocks' "bible", but it was shown to bend a wider piece of stock, then cut both stems out of that one piece. Only one bend to worry about!

 

[Canoez]

I don't recall where I read this, maybe in Stelmocks' "bible", but it was shown to bend a wider piece of stock, then cut both stems out of that one piece. Only one bend to worry about!

Yes, that's exactly how he prepared the stock that he brought up to WoodenBoat. The advantage is in both prep time and that the wider piece doesn't tend to twist. He then split the two pieces lengthwise using a table saw and we continued on as usual.

The one thing to keep in mind is that not all canoe stems are symmetrical fore and aft.

 

[greatlakes]

Bending stem stock

I've tried steam bending the stems as a single piece and ripping it in two afterwards. I have also bent them as two single stems on the jig side by side. I've found that the two single pieces bent side by side tend to have much less spring back -- and thus conform to the form perfectly -- and no twist.

Here's my jig. After several pairs of ash stems, I have yet to break one.

 

[dumbquestionsguy]

Just broke stem number 4. I soaked it for 4 days, boiled it for an hour and 45 minutes, bent super slowly, and still had some grains let go. Although the splits only went down about 1/8 inch - 1/4 inch, so I might just try to get rid of them when I bevel the edges. I realize you probably shouldn't compromise with the integrity of the stem, but this is the closest I've come and at this rate I may never actually build a boat, so... I might have to salvage it. I'm only going to use this boat (if I can ever get it completed) for recreational flat water (no trips etc.) so maybe a stem that's slightly thinner (3/4'-5/8') just in the one spot will be ok. I might not have any other option...

Just thought you all might want an update. Maybe make you feel a little better about yourselves.

Dumb Questions Guy
The Failure of a Canoe Builder

 

[Canoez]

If you have difficult grain in your ribs or stems, you can use a sheet metal strip on the top of the wood that you are bending to help keep these splits from occuring or to keep them from getting worse. A piece of mild steel as wide as and as long as the stock you are bending does a fine job for most. If you are concerned about staining the wood from the metal, just cover the surface of the metal strip with masking tape or duct tape.

You will still probably lose a few pieces as you bend, but this should help.

Alternately, you may wish to try two thinner pieces.

 

[dumbquestionsguy]

Yeah, I know, the compression strap - I actually tried it on the last two. I somehow couldn't get a good grip on both the wood and the metal (that whole hold on to a dripping wet boiling thing) and still had some grain cracking. I had already cut my stem stock to 7/8 square, so I don't have the material to bend them two wide.

I'm not necessarily asking for suggestions. I know what I'm supposed to be doing. I know the methods. I just apparently can't carry them out successfully. Just commiserating, I guess... Someday I'll build a boat...

 

[Steve Lapey]

Steam Bending Stems:

I had problems bending ash ribs the first time I tried it; the wood wanted to twist and split to the point I almost gave up on the project.

The solution for me was to make laminated stems. Since then I have made many of them and they always go quickly and easily. They are both straighter and stronger when laminated properly.

Rip out the ash to 7/8ths by 7/16ths inch, soak 2 pieces overnight in water, steam them for not more than a half hour and bend them both at the same time over the form. Let them remain on the form for at least a day. With a wide enough form there is no reason not to make up two stems at once.

Next mix up a good batch of epoxy glue. brush it generously on the mating surfaces and return the pieces to the form, which is now covered with plastic or duct tape, and clamp together securely for 24 hours.

When the excess glue is cleaned up and the stems are installed in the canoe you will never know that they are laminates.

Steve Lapey
Stevens Canoe Works

 

[Dave Wermuth]

I broke several too.

I once laminated the outside stem on a Thompson Take a Long. I kept the strips in the same position and you could not tell they had been sawn and glued.
If the grain is straight an hour per inch with backing strap should do it. You may have to saw the board along a growth ring first if your board has runout.

It's not just a bent stick, it's a learning curve. ;-]

For inch thick ash I soak for a full week. Bend it while it's still two inches wide. Or 1 3/4" or whatever it is wide. and 7/8 thick.

Sometimes some grain will lift but it gets ground off when shaping the bevel on the stem.

Roy Underhill did some nice steam bending yesterday on PBS.

Keep at it.

 

[Dave Wermuth]

Actually, Steve's got a great idea. If your stock is already 7/8" square then resaw it and bend and laminate the two. should work real well.
Why didn't I say that before?

 

[Gary Willoughby]

Are you using kiln or air dried wood. With air dried you only remove free water
with kiln dried you also remove bound water from the cell wall materials. Once the bound water is removed the wood starts to shrink and no amount of soaking in water will replace bound water. So air dried will bend better because of the moisture content.

 

[jchu]

I felt the same way.. I wasn't sure if I could do it, so I did build some 1/8 inch laminate stems. I contacted some lumber cutters out east and put the word out I needed fresh cut, green WO. I had no problem bending it. I had a lengthy post about it with several good suggestions. And the stems I glued up turned out good to. I used Tightbond 3 waterproof glue. Cut of the tip and soaked it for a month. It didn't de laminate at all. I suppose others have glue suggestions.

Just get fresh cut ash, and extra as well, build a good jig, give yourself extra each way and shape it after your done. My small blow outs cut out. Maybe watch or copy someone else's method. Get the job done and have fun with it.

Jeff

 

[Rollin Thurlow]

If your stem is splitting along the grain and the wood grain is supposely good, its most likely that your comprssion strap is not being clamped in place tight enough or its not wide enough. Either way it does not have to ruin your stem. Just let the stem dry on the form and then glue up the split grain, clamp it back on the form and let dry. What you end up with is a steambent-laminated stem that will be as good as any other stem. With the trimming up of the bevel on the stem the glued up laminated part is most often cut right out of the stem but it doesn't really matter, assuming the glue up job is correct.

 

[dumbquestionsguy]

Thanks for all the responses. I never even considered laminated stems - seems awful close to stripper land, and I was always trying to really get an authentic traditional canvas construction thing going. I suppose expoxy with varnish over the top of it probably doesn't present any structural or rot issues. May have to try it...

And for the record, the ash is from a local mill - still had the bark on the sides when I got it, so it's air dried if anything. I havne't been using a compression strap correctly, I'm sure. I'll have to do some more experimenting. I'll keep you posted, promise. If I ever succeed at this whole thing, it will be completely because of all of you guys. No joke...