Gentlemen,
I have a 26-27" cross-section of the live oak trunk that I need to prepare for my daughters 5th grade science class. It is about 2" thick.
First need to sand it down, the put something on it to keep it from splitting. I am hoping by sanding it down I can make it smooth enough to make the tree-rings much for visible Her class is studying tree-rings in the next 1-2 weeks.
Any and all advice would be greatly appreciated.
Regards,
tstex
It is going to split. :( If they will be using it in the next couple weeks leave it outside away from the heat until you take it to school, it may be ok that long. Good luck!
Yup, it's going to split as it dries out.
Wont stop them looking at the growth rings of course, and it will also demonstrate how wood shrinks as it dries, so point out how it's splitting and let them watch it happen over a few weeks.
Counting some rings and putting some stickers on historic event years can make it more interesting too.
Only real way to preserve it is to soak it on PEG (Polyethelene glycol) for a few months. The PEG replaces the water in the wood, and stays in place. The wood never actually dries, no shrinkage, so the piece stays together.
Ian
Thx guys - the weather here in S/SE TX is 45-55 and pretty humid/moist - If I spray it down with water every morning, that should buy me some extra time, yes?
Ethelene gylcol is anti-freeze, correct? Is the "poly" a different version thereof? Not sure if the school folks would want me to bring something in that is basically embalmed that if the kids touched it, then their mouth - oops !!! Thank you for the suggestion though...
I could put stars on rings 14, 10 & 7...10, birth of my oldest daughter [that I did this for], ;) 7, birth of my second daughter, ;) and 14, an event that had to take place for the stars to be put on 10 & 7, but if there was an alternative, it would have been taken... :D :D :D :D :D :D :D :D :D x 10 = # of yrs I felt I have been married.... :o >:( :o >:(
Regards,
tstex
oops
If ya just want it for ring study let it split, as said.
Letting it split would be good for their education too. It is what wood does when it dries. Live oak will likely not lose moisture very fast, so while spraying it would help...prolly isn't necessary in that short time especially if outside in the shade.
Polyethylene glycol isn't anti freeze (ethylene glycol). PEG is used in many hand cremes at a very low molecular number (I think around 5) and is pretty inert as far as being toxic. No fears there.
For treating wood, it was found a molecular weight of 1000 was best for wood treatment. Any lower and it remained a liquid, and any higher it wouldn't penetrate the wood very well. At room temp, it was a solid (almost like wax). Heated it could be mixed with water and when kept warm, would penetrate wood if left to soak for a few months (yep, long time).
Oaks, and particularly white and live, were impossible to get any PEG into. Being hydroscopic, when the humidity changes, the PEG seems to bleed out of the wood which makes finishing a headache at best.
Yep, it is live oak...just cut today and we have had TONS of rain so I am sure she was H2O-logged to the max...
I will just tell her teacher to watch what happens over time and not to put near any heater !!!
BTW, what is the most common source of PEG?
Thanks again guys,
tstex
You can buy PEG at most wood working supply places.
http://www.rockler.com/product.cfm?page=686 (http://www.rockler.com/product.cfm?page=686)
It's used by woodturners etc to stabilise turning blocks and burls so they dont rip apart as they dry.
Probably chemical supply places you can buy it in bulk cheaper?
Ian
For what you are doing I would just sand it smooth and put on a coat of water-based varathane. Its dry to the touch in 24 hours and makes the wood grain/rings really stand out.
I agree with Sprucegum. PEG isn't cheap and, although it would soak into the cross section longitudinally faster than it would radially, you don't have time. Just avoid the splinters and explain that wood shrinks about two times more tangentially than radially. The teacher will give you an "A". :D
For small cross sections, 6-10" we always used 2 in 1 epoxy resin. They never split on us. It was done a few times to show the kids. Mostly spruce or fir cookies was used with rings that show up well.
If your going to tell'm how it shrinks dimensionally, at least show'm with your finger or arrow, the direction your talking about. Otherwise it won't mean a thing to'm. :D
GUys,
Thank you for the feeback.
The dimensions are exactly 26" x 2.5"...
It is still wet and when I tried sanding it with the orbital sander, it looks like it is "hiding the rings"? Is this correct or will they come back when it dries? Should I wait longer until it dries to sand it? I am basically trying to get the chain-saw groves out from having a 20" bar cut a 2' 2" trunk...
Finally, is there a preferred grit to either start with and finish or something else?
Thank you for the suggestions,
tstex
Sanding usually obscures the end grain. Try using a really sharp scraper or plane. Try a test piece.
Quote from: SwampDonkey on February 05, 2010, 05:24:55 PM
Sanding usually obscures the end grain. Try using a really sharp scraper or plane. Try a test piece.
Yep, found that out...I do not have a plane a scraper...is there some kind of translucent dye or something I could use to bring-out the tree ring grains better?
BTW, I was driving through Houston the other day when I saw a tree crew cutting down a huge oak...gave them a little ca$h to cut me the cross-section...
thank you,
tstex
Easiest way to surface the disk is to use a router with a "flat-bottom" bit. Then make a box frame, fasten the router to a bridge board that will allow you to move the router back and forth over the disk in a single plane (making sure the disk sits tight, and doesn't rock back and forth).
That, or just make a few passes across the disk to show the rings, but don't do the entire disk. If you want both sides parallel, then flip it over and do the other side too.
You will be a month of Sundays trying to sand it.
I used a power plane to remove the chain saw marks taking off only a small amount each pass. Then I sanded with a belt sander. Finished it with tung oil. My cookie was 34" dia x 3" and it split and has some rot but is still dramatic. Counted 207 rings. The acorn sprouted in 1795 and the ring spacing tells of an interesting history - around 1900 the ring spacing increases 10-fold presumably from clearing for agriculture. If interested I will try to upload a photo.
Bob
Quote from: kelLOGg on February 06, 2010, 05:27:58 AM
I used a power plane to remove the chain saw marks taking off only a small amount each pass. Then I sanded with a belt sander. Finished it with tung oil. My cookie was 34" dia x 3" and it split and has some rot but is still dramatic. Counted 207 rings. The acorn sprouted in 1795 and the ring spacing tells of an interesting history - around 1900 the ring spacing increases 10-fold presumably from clearing for agriculture. If interested I will try to upload a photo.
Bob
Bob - Pls do, thanks - tstex
I've tried to insert photo but with no success. It is in my gallery but is a disappointing one. The rings are not as clear as they once were. It has been in my unheated shop for yeats and I think some dark mold grew on it.
bob
I wonder if drilling some holes in the backside almost all the way through will help keep it from splitting???
I think the holes would happen to fall on the cracks. :D But cutting out a pie shaped piece would stop the worst of the uncontrolled cracks and might prove to be interesting to the kids.
Cut one kerf from edge to center and let it move. This will make sure it can move AND allowing one BIG crack will likely prevent multiples. I concur w/ all written about PEG, I have used it a good bit.
Ironwood