Question about hydraulic post hole digger

[Densleigh]

Hi,


I built one of these using scrap parts mainly. The only 'new' item was the auger spiral and two hoses.

The motor came from a reel mower (ransomes) was then attached to a small car gear box (robin reliant 3 wheeler!), locked in reverse to slow the motor speed and up the torque.
The output of gear box has a prop shaft flange plate to which I made a simple gimble assembly and in turn bolted auger to that.
tractor hydro supplies around 30 litres/ min.

Whole assembly was then made to fit onto a set of fork lift truck tines with forklift mast mounted on 3pt of tractor. use forklift to raise and lower as required.

The auger will bore a 8" dia hole about 1metre deep with only a few clearances for soil removal. Fortunately soil here in my part of UK is relatively soft and light with no rock content (only rubble but enough on that) Works well, not the fastest but does the job ok.

Gimble allows for getting hole vertical when on sloping / uneven ground or indeed boring a hole at an angle if required.

Tractor has several hydraulic ports so easy to use these as opposed to dedicated valves.

Sorry no pics at moment as on other major work.

 

[bigdeano]

I would buy the wheel flange that bolts to the motor shaft when you buy the motor. Then all you need is a round plate with a coupling welded to it to take the auger shaft. Trying to machine the taper to match the motor shaft, and putting a keyway in it would be expensive for a one off item.

 

[JRP]

Bearings for wheel motors are set up for radial loads like a motor holding up a machine. Bearings for an auger are set up for high axial loads like a bit pushed into the ground, or the weight of the auger. You should install a bearing between the wheel motor and the auger to handle the stress.

PTO augers use round shafts so a shear bolt can be used to protect the tractor PTO. Shear bolts are a PITA. The hydraulic drive uses a superior 2" hex auger shaft because the tractor hydraulic relief valve will relieve if the auger gets stuck, making a shear bolt unnecessary.. If you build the auger drive yourself you should make the drive for a 2" hex so you have the option to buy auger bits.


There actually is a lot of engineering in a hydraulic auger drive. I considered the DIY route but instead chose the Beltec NC 150 model drive. It cost only $1000 and came with the hoses and hydraulic QD fittings ready to plug into the tractor. It was ready to go, with two year warranty. Also auger bits are $400 from the JD dealer.


So i could still build something I built the attachment plate to connect the auger to the Bobcat. I had a nice project that works, with warranty, and has very high resale value. Unless you have you own machine shop and lots of spare time you might consider buying the drive and auger as sometime store bought really is better, and not that much more expensive. Build the mount yourself.

You mentioned a valve. What for? Your tractor should have a valve for the hydraulic remote right next to the tractor seat, which is where you want to be. You dont want to be near the auger or drive. In this area a fried was killed helping a very respectable land owner and got wrapped around an auger when a very long bolt holding the auger to the drive snagged his clothes. The horror of seeing his friend literally ripped apart has been devastating to the land owner, who still has problems dealing with the memory. Be safe.

 

[JRP]

I looked at the motor you selected. 621 ft lbs of torque, which is 43% of the NC150 1450 ft lb of torque. Your motor should work OK for an 8" diameter bit.

 

[Scott65]

Thanks everyone for your input! This may be short, ill-worded, and full of typos, I'm on my phone.
I was thinking the same thing about the wheel flange since they are so cheap. That taper and keyway could be a trick. Getting the shank for the bit perfectly centered may not be easy, but not near as bad as the other.

JRP, first I'm very sorry to hear about your friend. I've grown up around this lifestyle and known people in similar situations. Always very tragic.
I know that buying a setup that is made for the job is ideal, but the budget doesn't always support it. And I'm one that's been known to spend even more sometimes just to say i built it myself. But this time it's money. Ha. It seems people have successfully used these wheel motors so I'll have to use caution. Or i may decide upon looking at the motor that i need to build a bearing. I'm a truck mechanic so that would be the easiest part to come up with for me.
As far as the machine shop question, it's funny you should ask. I have a fair amount of fabrication tools, and a good friend with a machine shop. I don't get it free, but at least cheaper. I still like to keep it as much in my own shop as i can

 

[JRP]

Scott,

I did use a wheel motor to make a water well drilling rig. It worked fine and can drill a 7" dia well bore with no problems. Just be easy on it with axial loads. I used this to save money, and it did. I used my CNC mill to machine an adapter to go from the wheel flange to the mud injection swivel. Ill look for a photo.

 

[JRP]

Well rig motor

 

[CNC Dan]

Could you use a car/truck differential? That would give some gear reduction and isolate the thrust loads from the hydraulic motor.

 

[Scott65]

I thought about a differential but it would make the unit much more cumbersome. I would like to make the unit compact. And I would also like to build it to pin onto a quick attach plate in such a way that I can pin it in either left, center, or right position. And then pin the "swing cylinder" in one of the opposing holes. That way I can have the assembly on which ever side of the tractor I need in case I am drilling next to a tree or existing structure or something.

I don't have a lot of rock in my area, thank goodness. So I'm thinking I may try my luck with just using the hydraulic motor at first. They must design it to hold at least a little bit of axial load, since that is the type of stress exerted when you would turn a corner and the vehicle would sway and "fishtail". I realize that a tractor doesn't really do this visually, but I would think that the forces are still there somewhat, so hopefully the engineering is in there somewhere.

Its hard for me to wrap my head around how much torque is needed to drill a post hole. But I know in comparison to any head bolts I've put in, 600 foot pounds is more than I care to grunt out. And 8" is as big, and maybe much bigger than I should ever have to drill. So hopefully this thing will work out. Its obviously not a good solution for everyone, but hopefully I can test it out and report back how much abuse it withstands under my conditions. Thanks for everyones input!

 

[JRP]

I also made mine pin onto the mount, and it can be moved left, center, or right. Good thinking. Most manufactured units attach in the center, making it necessary to extend the bit forward when you load the machine on a trailer. Makes travel akward. I have left mine attached on the right and such that it can fold to the left and when folded is about as wide as the mount. A chain holds it folded. I can travel easily with the bit at a low elevation. For storage a cart with casters about 2'w x 6' long rolls easily on casters. Most pics are on my phone. Ill look.