Bevelling stems

[greenvilleguy]

Any reason why I can't bevel the stems before I bend them? It sure would be easier to do while the stem is straight.

My concern is whether or not it would increase the possibility of splitting while bending.

 

[martin ferwerda]

It might increase the chance of the stem twisting on the form.

 

[greenvilleguy]

Back to Basics

Yea, thanks. Maybe I better try the "recommended" way first. After all, Jerry makes it sound easy in "the book".

I'm not even sure I'll be able to bend them solid, but if not, I can follow the laminated method discussed in another thread.

For now, I'm still cocky enough to think "If Jerry and Rollin can do it, so can I." Pride goeth before the fall.

 

[Dave Wermuth]

I think that a pre-beveled stem would be much more likely to split. I think you can count on your first attempt at bending a stem to be a learning event and not end in a good stem. But with persistence you'll get there quickly, whether kiln or air dried. Here's a couple things I've learned.

1. Make the stem blank double width (2" or 1 7/8" or 1 3/4") and cut it after bending. that way it is roughly twice as wide as it is thick.
2. Soak it for several days before bending. Although not necessary I think this step gives me confidence. And I think it helps some. I've heard of soaking in kerosene and in fabric softener. I just use regulare water.
3. For every inch of thickness steam it for one hour. No shortcuts here. One hour of good high volume steam. If you're at sea level. If in the mountains water boils at lower temp and I don't know how to fix that.
4. Use a compression strap. Any flexible metal strap like the kind they use to strap things to pallets, as long as it is as wide as the stock you are bending. I have a double wide strap on one of my stem forms. This helps keep the outter fibers in place during the bending.
5. Fast/Slow. Do not waste a second once the stock comes out of the steam. But once you start to bend it, TAKE Your time. Put pressure on it and you will feel it give. If it stiftens up, slow down til it bends under steady pressure. You have to let the cells of the wood flex and this sometimes takes a few seconds with pressure on it. Once it gives, bend a little more. etc. You will find that there is a certain amount of pressure it will accept and that beyond that-- it will snap. Once it snaps you will have learned a great deal. Remember that moment. And dont' exceed it the next time. ( in my case it was several 'next times'). YOu can bend wood by boiling. If you have a long enough tank and good enough double burner it will work just as good. Mostly, stems are bent using steam, but either way works, depending on what you have available.

 

[greenvilleguy]

Thanks! Sounds like good advice. I'm headed to the shop now to:

Cut some blanks.
Make a PVC soaking tube.
Make my steam box. I'm making a 1 X 4 X 5.5 box and I've ordered a wallpaper steamer as the steam source. (After unsuccessfully looking for large kettles, pots, etc.)

Assuming I can get one to bend, how long should I leave it curing on the form?

 

[Mark Adams]

Hi All,

In response to Dave's remark about bending in the mountains, I have bent wood from 5800 feet to 7300 above sea level. The way I got around the decrease in the boiling point was to pressurize my steam keg. I have a 5 gallon stainless steel pony keg that is my "pot". I have a rubber plug with the compression bolt drilled out to 1/8". I then have radiator hose to my box. I regularly get 205 to 208 degrees in my steam box. (water boils at 198 degrees at 7200 feet).

I have noticed that I get a hotter boil on a clear day versus a cloudy one. This is the difference between a high barometric pressure day and a low pressure day.

I also presoak the hell out of my wood before I bend. I'd love to have access to air dried or green wood, but no luck in my neck of the woods. ( I am in NV now)

 

[Jerry Fruetel]

Suggest using a thermometer

A critical factor in successful bending is the internal temperature of the wood. 212 degrees F. is ideal. Although you may succeed at 180 degrees, your odds of success increase the closer you get to 212.

I suggest using a small meat thermometer, available at most grocery stores. It has a sharp 5-6" metal shaft about 1/8" in diameter, with a 1" round dial gauge on one end. Drill a small hole in your steam box and insert the metal shaft. Make sure the tip is not touching the steam box, wood piece, or anything else.

The thermometer will tell you whether your system is generating enough heat. If it's not heating the air in your box to 200 degrees or more, I would consider changing systems.

As for how long to leave the bent stem on the jig--- in my experience, anything less than 2 weeks may result in excessive springback.

Good luck, and let us know how it goes!

 

[Steve Ambrose]

4. Use a compression strap. Any flexible metal strap like the kind they use to strap things to pallets, as long as it is as wide as the stock you are bending. I have a double wide strap on one of my stem forms. This helps keep the outter fibers in place during the bending.

What Dave describes is a simple backing strap which will help keep fibers from peeling away but a true compression strap has blocks on either end that butt up against the ends of your blank. As you bend around the form the outer layers of your blank will stretch often resulting in a tension failure (crack or break). The blocks on the compression strap push against the ends to prevent this stretching from occuring. If the length between the blocks is too tight on your blank you can have a compression failure (kink or crushing) of the inside layers. This isn't likely as you'll probably break something else before the ash crushes! I've attached a picture of my stem form that shows a blank with just a backer behind it. I snapped several doing it that way (say 30% success rate) and then made a compression strap. It helps but I still have some fail (maybe 1 out of 3). Look for straight grain and orient the blank so you're bending toward what used to be the middle of the tree. Mark the blank before it goes in the steam box so you don't waste precious time trying to remember how it goes when you pull it out.

Once you reach success (inspect the blank closely without removing it the next day looking for cracks or splits that appeared overnight) leave the blank on the stem form until you're ready split it into the two stems, shape them, and attach them to your building form. The stems will attempt to relax if left laying around loose. You will snap some blanks so don't let that discourage you! Oh and make sure your form is anchored securely

 

[greenvilleguy]

Thanks! Lots of good advice.

I have a 5 gallon stainless steel pony keg that is my "pot".

"Honey, I have to buy a pony keg of Bud and drink it so I'll have a steam boiler." I don't think she's going to buy that one.

 

[Dan Miller]

Thanks! Lots of good advice.



"Honey, I have to buy a pony keg of Bud and drink it so I'll have a steam boiler." I don't think she's going to buy that one.

It is easier to beg for forgiveness than to ask for permission!

 

[fred capenos]

What Dave said, except I bevel the outside edges on the saw first then after I take it off of the form, I cut one inside bevel when I split the blank. Then cut the last bevel and Bobs your uncle.

 

[Steve Ambrose]

It is easier to beg for forgiveness than to ask for permission!

Especially if the keg is empty

 

[Fitz]

Got Milk?

"Honey, I have to buy a pony keg of Bud and drink it so I'll have a steam boiler." I don't think she's going to buy that one.

I recently inherited a stainless steel milk can used as a boiler/steam generator from a long time member.

 

[greenvilleguy]

Success!

Well, I finished my steam box last night and bent my first stem today.

Following the advice above, it worked like a charm.

The only advice above that I didn't followed was the bending a double wide blank. I already had the form built when I received that tip. Oh well, I'll let this one "cure" for a week or so and then try the other one. I used kiln dried ash soaked for a week, my box got well above 200 deg and I let it "cook" for about 1 hr 20 min.

I'm especially thankful for the tip - Go Fast, then slow. The wood seem to need to "rest" some in the middle of the bend.

The only issue was my steam box. I nailed it together and the stem bowed the wood and pulled it apart at the seams. I had duct taped the seams, but the duct tape didn't hold up to the heat. For safety, I drilled a hole and had a cone shaped bottle stopper loosely in the hole to act as a stem release value -- I didn't need it as steam was releasing from the seams. At the end of the time, the temperature was actually falling in the box.

No big deal, I'll just get some caulking to replace the duct tape and screw the seams back together.

All in all, I'd call it a tremendous success.

Thanks again for all the tips! What a great site!

 

[Dave Wermuth]

good

well done. But I broke my first couple tries, so you're ahead of the game.

 

[greenvilleguy]

Bevelling the stems

Well, now it was time to bevel the stems.

What seemed like a daunting task was actually quite easy and even fun. I used Jerry's bandsaw method in "The Book" (The Wood and Canvas Canoe to hog away most of the material; then I pulled out a very old and very cheap spokeshave. After sharping and tuning the spokeshave, it made quick work of the stems. A little touch up on the belt sander and that was it.

Lesson Learned: I found it difficult to clamp the stems while attacking them with the spokeshave. Then I figured out I could mount them back on the mold and use the mold to hold them steady while I used the spokeshave. (Of course, I had to take off the alignment scraps from the sides.)