Sassafras Stave. Now what?

[Jim Davis]

Sassafras is weak in tension, but great in compression. If you believe the wood database, it is similar in compression quality to eastern red cedar, but still weaker in tension....

"Great." I don't think that word means what you think it means. (Tip of the hat to Mandy Petinkin.) First, red cedar is among the weakest of woods commonly used to make bows. According to the Forest Products Laboratories (whence the "Wood Database harvested its warmed over numbers), eastern red cedar has a compression strength parallel to the grain of 6,020 lbs. per square inch. According to the same primary source, sassafras has a compression strength of only 4,760.

Yes, a bow can be made of it. Tim Baker made one of white  pine. But neither wood is really good for making bows.

Since I have Sassafras growing on my property, I will probably make a bow of it, if I live long enough to get a round tuit. But I have no illusions about its fitness for the task.

[Chief RID]

Just building a bow. Slow going as you can see from the time period of this thread. I am not too worried about how it turns out. I'm learning as I go and I get stuck pretty often. Instructive words and ideas help me keep plodding along. Don't worry about the virtues of the stave. She is wide and long and might be a dog or a tomato stake but she will be my dog or stake. 8^)

[joachimM]

"Great." I don't think that word means what you think it means. (Tip of the hat to Mandy Petinkin.) First, red cedar is among the weakest of woods commonly used to make bows. According to the Forest Products Laboratories (whence the "Wood Database harvested its warmed over numbers), eastern red cedar has a compression strength parallel to the grain of 6,020 lbs. per square inch. According to the same primary source, sassafras has a compression strength of only 4,760.

You're right to say that in absolute terms, ERC and Sassafras are weak woods. Much weaker than osage. That's because they have low density compared to osage. In absolute terms, osage is much weaker than spring steel. So what's the point of making bows out of osage, this weak material when you have steel  ? But for the same mass, all three woods and spring steel are in the same ball park. When density is taken into account, ERC and sassafras are strong in compression. The two graphs should clarify this, with the position of ERC and sassafras highlighted. (Data from the wood database/Forest products laboratories). The perpendicular distance from the expected value (straight regression line in the graph) shows how much better or worse any wood is compared to "the average" wood.
The first graph shows that both woods can take much higher than average compression strain than the average wood.
The second graph shows that ERC is just below average in tension, and sassafras way below average in tension (at 12% MC; at lower MC compression strength increases and tension strength decreases). That's why a crowned sassafras stave will rather break than take visible set. 

Spring steel has about the same relative stiffness as ipe, european ash and guada bamboo (not on the graph). This relative stiffness tells you that for the same bow mass and bow design (thickness profile etc), a same draw length would yield exactly the same draw weight. Width of the bow is adjusted for mass (see TBB4 mass principle, first picture: bulletwood pyramid bow is much narrower than poplar pyramid bow). 

[Pappy]

I have a good friend from IN. [Ron Prusinski ] that makes a lot of Sassafras bows, he makes elb style, usually about 70 inches and most of the time he rawhide backs them , he makes them in the low 50's and 28 inch draw, they take a little set but he shoots the crap out of them and don't seem to have much trouble with them not holding up. Good luck and keep us updated.
 Pappy

[Chief RID]

Will do, Pappy. Like you said , it is suppose to be really nice here this weekend. I need to get out on the porch.

[turtle]

Several years ago the plant I work at had a temporary plant manager that came from a different plant in Alabama. He told me that his grandfather was full blood native american and spent the winters with his family in Alabama building bows. In the spring he would head north selling his bows. He would only use two wood species for his bows. Osage and Sassafras. He told me he still had two bows his grandfather made and would bring them for me to see after his next trip home. Never saw him again.

[Jim Davis]

joachimM, I recall seeing these charts before. Are they yours?

The placement of Osage on the charts has no real value, because there are no test results anywhere for dry Osage. The Forest Products Laboratories either did not do the dry tests or did not record the information. I have complained  to them many times about that, but they will not do the tests.

Your second chart deals with tension values. THERE ARE NO TENSION FIGURES AVAILABLE for the huge majority of woods. There are some for some of the oaks. So I am curious how this chart was compiled.

All my objections to the charts are irrelevant to the value of making a bow of sassafras. The only reason not to is that, as has been noted in other posts, the bow must be quite wide and/or long to survive.

It's always worth a try with most any wood, just to verify the principles. It would be possible to make a bow of balsa.

[PlanB]

Joachim, thanks for showing those again. Question, could you label the ordinates, and give the formulas you used for setting the values so it would be possible to add other woods to the charts? Thanks!

[joachimM]

Asharrow, I took all information I could find from various sources (mostly the wood database) and compiled an excel "database" with raw and derived data. These I used to make these graphs.
I just shared it on my google drive for people to play along with it and add their own pet woods as they please. The graphs don't work well in google docs, so best to use MS excel or open office. 

See https://drive.google.com/file/d/0B3YYA3Sr_3gqMm9oWkExTjdiOTg/view?usp=sharing
There's a tab explaining some basics, which also answer some of your questions here.
Note that if you want to add more species, and want to see them in the graphs, you will need to activate the macro and add the data in the indicated tabs (see the excel sheet).
As you point out, tensile strength is not the same as the modulus of rupture (which is provided in the wood database), but the latter will give you an idea about the former. See it as a relative measure of tensile strength when comparing wood species.
Some wood species have fairly odd positions on this graph, such as eastern hophornbeam and some elm species. I don't know why this is, so take these graphs (and the underlying data) with a pinch of salt.

PlanB: the X-axis shows relative stiffness (MOE/SG), the Y-axis the max strain in elastic compression or tension (daringly assuming modulus of rupture ~= tensile strength and crushing strength ~=compression strength before set).
Formulas for settings: see the raw data tab in the sheet and the comments tab for all the requested info.

Hope this helps.
Chief RID: sorry to hijack your thread

[PlanB]

Joachim, thanks very much for that!

(I have Libre Office, and am having to set the chart data labels and do some cell formatting, but the spreadsheet seems to work fine.)