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Seeking advice concerning metal thickness for a tree digging spade

by AntonK
Tags: metal thickness
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AntonK
#1
Mar21-12, 09:47 PM
P: 2
Hello to all,

I have a question concerning what thickness of plate steel to use for a tree spade that I'm going to have made to help with transplanting some trees. The intent is to have a spade that cuts 1/4 of a cone that is 24" in diameter and 18" deep. After cutting the tree's root ball, separate cuts in the ground on one side of the root ball will be made to offer a bit of a slope to make easier the levering/dragging of the root ball out of it's original position so that it can be moved to a new location. I hope to attach a picture of what I'm proposing so that you can get an idea of the configuration. The blade portion of the spade is to be either 1/8" or 3/16" thick 1018 mild steel (I think hot rolled). It is to be a total of 21.625" tall and 19.75" wide at the top. It is also to have two bends that are about 25 degrees each segmenting the blade into three somewhat equal triangles. To the center triangle, there is to be welded a 1" square bar that will serve as the handle and as the means of transferring the force of a 17 lb, metal fence post driver to the blade. The soil in this area is about 110 lbs/cu. ft. and the volume of the root ball will be about 1.5 cu. ft.. Add to the weight of the soil a tree's weight of about 40 lbs and I estimate this spade will have to support about 205 lbs. But it's the levering and the driving (possibly into the occasional rock) that concerns me the most. The question is: is it better to use 1/8" plate or 3/16", or something altogether different?

Thank you for any input -- even if it isn't scientific.

AntonK
Attached Thumbnails
Tree spade drawings.png   3D view of tree spade.png  
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etudiant
#2
Mar22-12, 10:07 AM
PF Gold
P: 866
The spade would be stronger if the post can be extended to the tip, rather than attached half way.
This is especially so as the plan is to use the spade as a pry bar, to lever obstacles.
I would certainly go for the 3/16th thickness, as the actual stress in the field is almost always greater than the expected amount. People are hard on equipment.
OldEngr63
#3
Mar26-12, 09:21 PM
P: 343
I certainly agree with the comments above regarding extending the handle further down the blade and also with the use of heavier plate.

1) I would suggest a strap across the outside flanges of the blade at the top end of the blade, to help resist flattening.

2) Are you planning to make several of these, so that you can surround the tree, leaving each in place while you pry on another, with a helper inserting deeper those that become free in the process?

3) What you show here looks adequate only for manual operation. If you should decide to arrange hydraulic power for the shovels, much heavier material will be required.

AntonK
#4
Mar27-12, 07:47 AM
P: 2
Seeking advice concerning metal thickness for a tree digging spade

Thanks for all the input. Those are excellent suggestions. To OldEngr63, I'm only having one made and it will be a manual operation that involves surrounding the tree with four "cuts" to create a root ball. Then, on one side of the ball, cutting a wedge of ground away so as to create a bit of a ramp. Inserting the spade on that side of the ball, I hope to tilt the ball out of place so that I can pry/drag it out of the hole and to its new planting place. I know it sounds like a lot of effort, but readily available systems that don't require a bobcat start around $2K. If this were a business proposition, I'd make the investment, but it's a personal project so I'm trying to keep the cost down.

Thanks again for all the input,
AntonK


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