Question about hydraulic post hole digger

Scott65 · Sep 22, 2014

I read an article or two a while back about a couple of DIYers building some front quick attach post hole diggers. I can't find the threads on them but I don't think it will matter because I seem to remember reading them several times and not finding or understanding the lingo well enough to answer my questions:

The hydraulic motor, I believe what is used is a wheel motor, like what drives one of these tractors when a drive axle can't be used. I think I can handle sizing one up to my tractor's specs on hydraulic flow and whatnot (unless a hydro expert just WANTS to pitch in some advice on a model number, haha). But my question is, can these motors handle the force of being tipped up on end and having the force pushed against it directly with an auger bit, or does some sort of hub/bearing assembly need to be made so that the motor is only applying the turning force and the hub assy. is holding the vertical load?

Second question, any suggestions on how to get from motor shaft to auger shaft? It appears that most of the wheel mount hydro motors on Surplus's site are tapered, keyed shafts. And I believe auger bits come in either round or hex configurations. I don't guess I care which one, unless someone can suggest if one is more common than the other. I don't really need one that is stronger over the other, I've only got a Kubota L3301 (30ish H.P.). I don't have any auger bits, so I'll be purchasing whatever I need to fit on any adapter I can come up with or fabricate.

Thanks for any suggestions!
Build thread coming soon

J_J · Sep 22, 2014

You might consider something like this.

21.05 cu in DYNAMIC BMER-1-350 HYD WHEEL MOTOR

Have a machine shop build you an adapter for the auger you want to use.

Scott65 · Sep 22, 2014

Yes sir, one of the very motors I was looking at. The only doubt that I had was that one is made to run a higher GPM. My Kubota is rated around 10, this one is 18. But on the flip side, I only need about half of the RPM (I think). I'm basing this off of commercially sold model's advertised specs. So I'm assuming this will sort of even out in the wash.

So by suggesting an adapter to directly attach the auger to the motor, do you think the motor will handle the downward force being applied directly to it? It won't push the shaft through the back of the motor or something?

oldnslo · Sep 22, 2014

You would have to look at manufacturers specs on the motor to see what bearing loads it will withstand. Most wheel motors have some axial load capability but are designed more for radial loading from the weight of the machine and corresponding drive forces.

Yes reduced flow rate (GPM's) also reduces the RPMs of the motor. 10 GPM will spin the 21 CIR motor at around 110 RPM @ 100% efficient. Again look at manufacturers data: It should have a chart or graph showing RPM Vs flow & Torque Vs pressure.

BukitCase · Sep 22, 2014

Here ya go -

http://www.dynamicfc.com/documents/BMER-1.pdf

At a quick glance, looks like you're good to go both axially and radially... Steve

Scott65 · Sep 22, 2014

Great info, thanks for the help guys! I've got a nearly complete parts list I think. Now I'm just trying to decide about my valves. I have a real bad habit of going overboard, but I can't afford to do that right now. I have future plans for all sorts of home made implements for front and rear. But I think I'm leaning towards putting a set of spool valves next to the seat, one with a detent. I'll have 2 sets of quick connect hoses. I'll be able to connect either front or rear implements, depending on the task at hand. I don't think I'll ever need to use all at once. If so, then I'll pony up and buy more valves...

The two valves should work for most of my future builds I think. Front mounted, hydraulically powered box shredder and tiller will probably be next. For those, the detent valve will control the motor for blades/tines. The other will control tilt if I decide to add that for added maneuverability beyond what the FEL hydros allow. But for the auger, what I want to achieve is a rigid mounted bit so that it doesn't sway. I want it to be a one man operation. The FEL will control pitch forward and back. Obviously tractor drive and steering will get me to the location of the hole. One valve will run the motor. The other will operate a single ram. I will have the motor attached to a pivot that will allow it to swing side to side, but controlled by the ram, not free floating. I'm thinking of having something sticking up above and directly related to the auger bit with some sort of level to indicate the bit's location when its buried in the ground. I should be able to dig some pretty sweet holes with it when its done. Sounds good in my head anyway. Any thoughts?

vwnotrunning · Sep 22, 2014

Be sure to take pics and post some details if you proceed with this project. I have been interested in building something similar.

Scott65 · Sep 23, 2014

For sure! I enjoy building stuff that I can be proud of. And enjoy just as much sharing how I did it. I only hope I get to proceed with this fairly soon. It sucks that this will be the slowest of all the projects I'm sure. Since its the first, it will be one of the most costly. This one requires me to have all of the hoses and valves before any of it works so I will need to take my time and order components a little at a time. Once I have the hydros in place, the other projects should be a little easier to manage. But I will keep everyone posted. I will start a new thread though so that the title will reflect a show and tell rather than questions. That way people searching for answers will know to look there instead.

BukitCase · Sep 23, 2014

This should get you started, if you haven't already found it

2 SPOOL SV VALVE OPEN CENTER W/POWER BEYOND

Your tractor appears to be open center hydraulics at less than 12 gpm, which those are rated for - depending on how you plumb for the extra hydraulics, you might need the Power Beyond - if not, you can replace that plug with the standard plug. Choosing the stacked valves instead of a one piece body will let you expand by buying more sections and longer tie bolts.

Once you start down this path, you will likely want more things under hydraulic control - in my case, one future project (a serious back blade) will need side-to-side, blade angle in two directions, top and tilt, etc... Steve

Scott65 · Sep 23, 2014

Thats kind of funny. I had just clicked the link myself for that valve. It was still loading when I switched over to read your post. Great minds think alike I've always heard... I am reading another thread right now too of someone who used a loader valve for top and tilt, which was part of what I wanted to implement into this design. I'm undecided if I want to dedicate circuits and leave that, or save money and use front hydros when needed, switch to rears when needed, tnt when needed, etc. I realize its a pain to be switching hoses and stuff all the time but I have A LOT of projects to be doing right now. I love working on the tractor, but my wife, not so much! So I have to spend carefully. I'll keep reading this other thread and price out the loader valve route. I may decide thats the way to go on TnT and do it separately. Then do the stacked valves that you linked to for my other accessories.

Densleigh · Sep 27, 2014

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 · Sep 27, 2014

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 · Sep 28, 2014

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 · Sep 28, 2014

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 · Sep 29, 2014

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 · Sep 29, 2014

Well rig motor

CNC Dan · Sep 30, 2014

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

Scott65 · Sep 30, 2014

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 · Sep 30, 2014

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.