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Milling Timbers for a Church Cross

Started by Ga_Boy, September 25, 2006, 03:34:33 AM

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Ga_Boy

I have  a request for White Oak Timbers for a Church Cross.

The beam that will be in the ground is a 6"X8" that is 12' to 13' above grade.

The cross beam will be a 6" X 8".

How far down should the cross beam be placed and how long should it be?




Mark
10 Acers in the Blue Ridge Mountains

DanG

I don't know of a documented correct proportion, Mark.  I also don't know that there isn't one. ??? :D  I'd just find one that looks "right" and measure it.  Better yet, let the Church draw the specs.
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

Radar67

Use the rule of thirds. Place the cross piece one third of the length on the main beam from the top. ie 12 feet above grade, cross beam is 4 feet down from the top.

Stew
"A man's time is the most valuable gift he can give another." TOM

If he can cling to his Blackberry, I can cling to my guns... Me

This will kill you, that will kill you, heck...life will kill you, but you got to live it!

"The man who can comprehend the why, can create the how." SFC J

Frank_Pender

A few years ago, I had an orther for one to be placed in a vaulted ceiling of a home.  To get the correct proportions, I used my wife for the dimensions. 8)
Frank Pender

BW_Williams

Frank, can you clarify the above statement? (without ending up in the doghouse) :D
Support your local Volunteer Fire Dept.  (not by accident)
Support your local Ski Patrol (by snowboarding:)
Mayor of Millerdale, Washington, USA (by God)!

raycon

Here's a link to  a  timberframer that built a cross for a local church. Remarkable story behind this fella worth a look through his site.
http://www.geocities.com/melsen2003/crossraising.html?1114390452394

Lot of stuff..

Ga_Boy

Thanks to all for the responses.

Dan, the problem for me is the Church folks are asking me for specs.... :-\ ??? :P

Maybe that chapter got left out of the re-write when the orginal ten commandments got busted...... ;)
10 Acers in the Blue Ridge Mountains

Lud

What about desired surface?  Cut a bit oversize and do some adze work for character.  ( They didn't use bandsaws in those BC days, y'know) ;D

And seal the ends good so they won't split!
Simplicity mill, Ford 1957 Golden Jubilee 841 Powermaster, 40x60 bankbarn, left-handed

Kevin

We plant shorter utility poles at 5-6ft.

Tom

I found, a long time ago, well back before the turn of the century  ;D , that customers seem to think that a sawyer is an expert at anything that has to do with wood.  I've been asked questions like "how many trees does it take to build a house?", to "what glue should I use?", "how many nails should I buy?", "can I make lumber out of that tree?".  You can't get away from it.   :D :D

Ga_Boy

Quote from: Lud on September 25, 2006, 11:13:13 AM
What about desired surface?  Cut a bit oversize and do some adze work for character.  ( They didn't use bandsaws in those BC days, y'know) ;D

And seal the ends good so they won't split!

That is OK Lud,

I use a swinger.  My neighbor came by one day when I was filling an order for grade stakes.  He asked me why I ran the blanks through a planner.  At first he did not believe me that that was rough sawn....till he looked at the stack next to the mill.... ;D
10 Acers in the Blue Ridge Mountains

getoverit

Quote from: Tom on September 25, 2006, 01:00:23 PM
I found, a long time ago, well back before the turn of the century ;D , that customers seem to think that a sawyer is an expert at anything that has to do with wood. I've been asked questions like "how many trees does it take to build a house?", to "what glue should I use?", "how many nails should I buy?", "can I make lumber out of that tree?". You can't get away from it. :D :D

Tom,

I'm experiencing some of that same delimma right now... a relative is asking me if there are enough trees on some property to build a 2500 sqft log cabin ??? ::)

how the heck am I supposed to know that one :D ???


Ga_Boy,

You can attach the cross member 1/2 the distance of the cross member from the top of the center pole. DanG-It, that doesnt make sense... lets try this:

If the cross is 12' above grade to the top of the center pole, I would make the cross member 8' long and attach it 4' from the top of the center pole. This would leave roughly 8' below the cross member to the ground. If it were me, I would also figure on at least 6' in the ground.  (elaborating on Radar67's rule of thirds)
I'm a lumberjack and I'm ok, I work all night and sleep all day

Chris Burchfield

Michael Angelo used the Golden Mean for proportion. This is evident in nature and is based on fifths. I have used this in projects I have made and it does meet the appearance I'm after. Michael Angelo used this and several years painting the Sistene (?) Chapel. I wake up every day and see what God has done over night to for what I see when I wake up. I think you will see that fifths work out very well for what you see above ground.. Hope this helps.
Woodmizer LT40SH W/Command Control; 51HP Cat, Memphis TN.

Stephen1

I used to installs poles, 1 foot down for 4 feet up. dang it was hard.
IDRY Vacum Kiln, LT40HDWide, BMS250 sharpener/setter 742b Bobcat, TCM forklift, Sthil 026,038, 461. 1952 TEA Fergusan Tractor

limbrat

What Mr Burchfield said rings true. 5 fifths high 3 fifths wide and put your cross member 2 fifths from the top looks just right. for whats above ground.
ben

Beweller

A rule of thumb is to bury wood posts 10 times their diameter, with the objective being equal probability that the post will break or up-root.  Obviously this result depends on the strength of the wood and the soil.

This is probably overkill for a cosmetic cross that will never (?) be subject to strong overturning forces.
Beweller

thurlow

Quote from: Beweller on September 26, 2006, 10:08:25 PM
A rule of thumb is to bury wood posts 10 times their diameter,

SHAZAM!!!!!! Whose rule?  Never heard that one...........When I think of the thousands of black locust, erc, used utility posts (many of 'em 12 --16 inches in diameter) I've put into the ground..........don't think a single one of 'em was in the ground that deep.  Let's see.......a 12 inch post sticking out of the ground  8 ft would be 10 ft in the ground.  I'd still be digging 8).
Here's to us and those like us; DanG few of us left!

Dan_Shade

I've heard 25% of the height, but never 10% of the diameter!

Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

BBTom

According to Wikipedia :

Perhaps the best-known form of the Christian cross is that depicted here, called the Latin cross, an equal-armed cross with a longer foot.

Somewhere I read that the crosspiece is 1/2 the length of the upright, but I cant find that reference today.
2001 LT40HDD42RA with lubemizer, debarker, laser, accuset. Retired, but building a new shop and home in Missouri.

Frank_Pender

Frank Pender

Beweller

With reference to Thurlow's posting, a 12 inch wood post with an ultimate strength of 10,000 psi can withstand a moment of about 1.7 million inch pounds.  If the soil strength is 30 psi, the soil will resist a moment of 60*d^2, d being the depth of burial in inches.  To develop a resistance of 1.7 million inch pounds, the burial depth must be 168 inches, or 14 diameters.

If you don't like these numbers, what numbers do you like?  Or do you have an alternate analysis?  I don't recall where I encountered the rule of thumb, but it seems reasonable--remembering it is the burial depth required to make it equally probable that the post will break or upheave.
Beweller

thurlow

Beweller; I don't doubt the accuracy of your calculations nor did I mean to put you "down".  Based on personal experience (AND NOTHING ELSE), I was never concerned with posts breaking or upheaving.  These posts were used in fencing, corral building and simple farm structures.......bridge piling, pier piling, pole barns, etc.  Two major TVA transmission lines run near my house (and across land I either own or have had leased).  As the creosote poles fail, they are being replaced with metal ones.  Even the largest of these posts being removed.......and some of them run 24 inches or better.........are in the ground a maximum of 8 feet.  I suppose what I was.....and am.........saying is based on practical use and not theory.

Regards, 
thurlow
JKoonce
Here's to us and those like us; DanG few of us left!

Tom

I base my holes on practicality too.  They end up being about 3 feet deep...  sometimes I can get them 4 feet deep.  The post hole diggers handles won't open up enough when you get that deep to get the dirt out. ;D

beenthere

Would be interesting to find the source of that rule (diam. X 10  =  depth of hole).  Buried lots of 4-10" diam posts, and never put 'em down to 40 - 100" depths. Just doesn't have common sense figured in, I guess. Like Tom, the post hole digger tool handles slow you down at about 30 - 36".  Now it might fit the 1" mater stakes, down about 10".  :)

Now, I once read some military specifications written for sterilizing bedding for animals, which read something like " heat to 3000° F " for a certain length of time. Most bedding we could think of would be long gone before reaching that temp.  Learned of it when a supplier was trying to find out what species of wood chips could be used to withstand that heat while sterilizing.  :D
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Beweller

First, the calculation was MY attempt to justify the rule of thumb. I have been unable to locate the source, but I have a note in a notebook saying "5 to 10 diameters".

My asumption of an ultimate strength (modulus of rupture) of 10,000 psi for the post was optimistic.  A value more in the range of 4000-5000 psi seems likely for the materials used for posts.

Power poles buried to a depth of about 5 feet are by my observation mostly in the process of failing by up-rooting.  But they do this slowly.

My calculation of the moment developed by the soil resistance seems way too low.  For example, for a 4 inch post buried 3 feet, the moment would be developed by a force of only 40 pounds 4 feet above the ground.  To break the post would require a force of about 600 pounds.

If I calculate a soil resistance equal to the breaking moment by assuming double shear of a 90 degree arc with radius equal to the burial depth, I find the post must be buried to only 20 inches.

I conclude that my knowledge of soil mechanics is insufficient to make a conclusion, but somewhere in the "5 to 10 diameters" range seems reasonable.

I note that breaking or up-rooting of posts are always of concern.  Otherwise we would simply stand the posts upright on the surface.  It is just that criteria other than failure by breaking or uprooting may control the post size and burial depth.
Beweller

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