PHD Hydraulic Down Pressure � Lessons Learned

I just finished digging a couple dozen holes with my generic post hole digger (PHD) that I modified myself for hydraulic down pressure. Here are some things I learned and wanted to pass on.

Equipment
A generic post hole digger with a cheap 9 inch auger. The teeth on the auger consist of a center screw and two small 3/8x2 inch plates that really needed a good sharpening. All three pieces bolt on the end of the auger and is about as cheap as it gets. The PHD frame is 2 7/8 OD pipe that appears to be schedule 40. The gear box ratio is 2:1.

Hydraulic Down Pressure Modification
I completely redid the pivot bracket and added a 3x8� hydraulic cylinder. The main pivot pin is 1� in a 1.5�OD turned bushing complete with grease fittings. The rod end pins are 1�. The pivot bracket is made from two pieces of 1/2x5� plate. The stop block is also 1/2x5� plate and the tube bracing is 3/8x3� flat bar. All steel is hot rolled and nothing was hardened or heat treated. It�s a standard category one 3pt hitch.

Soil Conditions
The ground was a consistent, medium hard limestone rock. The dirt from the holes was chalky white as the auger ground it into a find powder. We dug about 24 holes 30 inches deep in about two hours. At about 20 inches deep, we had to stop on about half the holes and break through a small rock layer with a spud bar before continuing on. I�ve dug in this same area before with the exact same set up minus the down pressure. If I hadn�t made this addition, I�d still be there digging. I then moved to a different area that was medium hard black dirt with a high clay content and no rocks. I really didn�t need any down pressure to dig these holes.

Stability
If I put a lot of down pressure on the auger, the tractor would lift the rear tires completely off the ground (my tractor is small and weights maybe 2500 pounds). Of course, the brakes don�t work too well when the tires are off the ground and this can be a problem if you are on an incline. Also, most tractors have a pivoting front axle and with the rear held off the ground by just the auger, the tractor can rock from side to side. Kind of like it�s balanced on, you know, just two points of gravity. Placing the front end loader on the ground with a bit of a down force on it helps keep the tractor from rolling from side to side and creeping down the hill.

Reliability
The modifications held up well and it looks like there are no weak points that need to be reengineered. The stress points of the pivot plates, pivot pins, tubing and bracing all held up well and there are no preliminary signs of failure or fatigue.

Conclusion
All and all, it was a tremendous time saving feature for digging in this type of soil. A good set of teeth for the auger is the next and final addition required. Combined with the hydraulic down pressure, it should make for a powerful combination that I look to handle the really tough rocky conditions.

By The Way
My 9 inch auger is pretty cheaply made. The flighting is in pretty sorry shape and the teeth are pretty much non-existent. So, I�m just going to weld some 5/8 inch stock on the bottom, grind some hand made teeth into it and use it to the whole thing finally wears out. Who makes a high quality auger bit? I�m not too worried about the mount as I have a lathe, mill and basic machining ability. My current mount is a 2� round stud.

By The Way
My 9 inch auger is pretty cheaply made. The flighting is in pretty sorry shape and the teeth are pretty much non-existent. So, I�m just going to weld some 5/8 inch stock on the bottom, grind some hand made teeth into it and use it to the whole thing finally wears out. Who makes a high quality auger bit? I�m not too worried about the mount as I have a lathe, mill and basic machining ability. My current mount is a 2� round stud.

• Post Hole Digger Pictures - Zip FIle Size 439k

Could you do a sketch or something showing the various pivot points and how the stroke of the cylinder affects the gearhead on the auger?

Thanks.

Notice the angle of "U" shaped lower link piece compared to the boom in both photos. It changes by a few degrees. The two plates that attach to the rear of the cylinder are welded solid to the "U" shaped lower link piece and moves with it. The boom slides down between them. You can see the location of the pivot pin in the two photos. It's just below the boom pipe.

As the boom lowers, the two plates move forward about 6.5 inches. When the boom raises, the plates move backwards by the same distance. The cylinder I choose has an 8 inch travel, so it leaves just a bit of room on both ends.

I run the cylinder in a float mode and use the 3pt lift to raise and lower the boom in a normal manner. When I need some extra down pressure, I apply hydraulic pressure to extend the cylinder which forces the boom to lower. A similar principle is used in backhoes.

Hope this helps.

Looks like a great project for this winter.

I know what you mean on your auger too. Mine is rugged enough, but the cutting edge leaves a LOT to be desired.

I work at an equipment rental outfit, and we have a couple of different PHD's with much heavier duty augers. They're 1" square-drive, mine is similar to yours with a round drive stub. I'm also gonna make an adapter and try a couple of different styles of augers from work and see which works best in my ground before shelling out the bucks to buy one. One has a fishtail tip, and two cutting edges on the end of the fliting at different angles. LOOKS very agressive, but can't get an intelligent comparison from customers as they've never used anything else.