undercutter / bed lifter - how thick and which steel to use?

[DaveOmak]

When I grew garlic, the lifter below is what I used... The blade is from a highway snowplow... The wings on the side kept the leaves in the rows... The triangle teeth broke up the hard packed soil and kept the lifter from rising up out of the ground...
The barrel is what I marked where to plant the cloves when it was rolled over the ground...
The lifter is difficult to picture due to the shadows etc...
If you are near Omak Washington, it's for sale....

 

[CoyPatton]

For a prototype, I like the ideal of a dirt scoop, also called in my area a pond scoop. They are often available on FB market place. I have not priced new recently (probably pre Covid crap) but you could probably not buy steel for the cost of a used one in decent condition. You might wish to do some reinforcing when you cut the back out.

 

[Ferpen]

I'm not sure where the OP is located but one of our suppliers carries this:
1055 Steel Beveled Cutting Edge | Coremark Metals

 

[MossRoad]

From the movie, it looked like the sides were at least as thick as the man's thumb, if not more.

 

[Wyobuckaroo]

If I were to build a tool like this, I would make it like the one in the first video..

The difference I would make is to make the vertical legs about 3-4" longer than you think you need.. And make the blade out of, maybe 5/8 or 3/4 mild steel about 8" wide... If your ground is abrasive enough to ware a dish in the blade there will be material available to straiten the cutting edge some what during re sharp..

Also the opportunity to add gauge wheels may be a consideration..

This will easy welding to the vertical legs, a large area to do repeat re sharpening, and the extra leg length will enable the cutting edge to be sawed off and replaced.. Again extra material to work with..

If this cutting edge works well then there is time to consider a cutting edge like a grader blade...

 

[sandman2234]

You might find a cheap solution to be a used rear dirt scoop. Cut the back end out of the bucket, and you're done! Used dirt scoops are usually sold for reasonable prices too.

Also realize that there are at least 2 different sizes of dirt scoops. I have a 24 and a larger 30". I paid $50 each for them. The 30 was like new except it had been stored sitting on the ground and tilted bavk so it stayed wet all the time. I built another bucket for it and used it lot till I got a FEL.
David from jax

 

[davedj1]

You might be able to score a broken/worn piece of cutting edge from your local municipality road crew.....
Otherwise I agree with the regular steel for home use. It will last a good long while.

 

[Renze]

My next question is, is yield strength directly proportional to how much the steel would resist bending in transverse direction (as opposed to axial)? Because it is nuts to think that 1/4" AR400 would resist more to bending than 3/4" S355 structural steel. Am I reading this numbers correctly?

Yes you read that correctly. And yes, the yield strength is that much higher, so you can excert 3 times as much force before you fold it in half. However the Youngs modulus of elasticity is grossly the same, so flexing under load is the same: its just that at 355 mpa the S355 starts yielding, while the Hardox just springs in the same rate to 3 times as much force.

For fatigue, the fatigue limit is grossly the same for S355 and S1100 super high strength steel. Thats why high strength steel is suitable for low load cycle structures such as telescopic cranes that do a load cycle every 15 minutes (all day average) where a digger has a 15 second load cycle (every cylinder stroke is a load cycle on the steel)

Anyways your undercutter isnt loaded very dynamically so no need to consider fatigue.