converting a PTO post hole digger to hydraulic drive

[ch47dpilot]

Have an older KingKutter post hole digger. Would like to convert to hydraulic drive. I've heard the ability to reverse comes in handy. Anybody attempted this and any opinion. My main concern is will my Kubota L3400 at 6.8 gal/min and about 2500PSI work. Also the best way to mount the motor. Plan on using a Surplus center Ag PTO 540 RPM motor(4.95Cu In). I know that the tractor will be under flow but my understanding is that will only affect RPM(SC calculated at 321RPM) and not torque(1970in-lbs). How much torque would I need to run a 12" auger? I have considered using a PTO driven Hydraulic pump to get higher flow but that seems like a lot of work and money.

 

[ddbackhoe]

I did one using a hydraulic pump to engine mount. I fabbed my own keyway coupler. The highest torque motor you can get. I cut part of the boom off and welded it to a skidsteer plate. Having it where you can see it plus reverse makes it soo much nicer.
This is the motor I used.

7.9 cu in White Drive Products 25513A1316BAAAA Hydraulic Motor | White | Brands | www.surpluscenter.com

Here's where the idea came from...
Model 614 and 624 Post Digger

Model 89-7 | Danuser

 

[ch47dpilot]

I was looking at the engine driven pumps 5.7 cu in Prince HC-PTO-2AC PTO Pump CI 54 RPM | PTO Pumps | Hydraulic Pumps | Hydraulics | www.surpluscenter.com. What size tank did you use and where did you mount it. Did some online calculating, my L3400 has rated 28.5HP at PTO which is 277 ft-lbs.(3300 in-lbs) of torque. To get that TQ number at 200PSI I'd need a 11 in/rev motor. But at 11.4 GPM I'd only get about 1/2 or 240RPM. So my question I is should I be more concerned with TQ or RPM with an auger. My gut says TQ since speed isn't required to dig but the TQ is. But I guess at some point slow can be too slow.

 

[countrybumpkin]

Torque is your big concern, you don’t need or want a high rpm on the auger. My hydraulic auger drives turns between 50-60 rpm and that’s plenty.

 

[countrybumpkin]

Also are you thinking a direct drive for the motor, if so you could always do a chain and sprocket drive to give you different numbers.

 

[Fallon]

I had a L3200 with a 3pt PHD, 25 PTO HP. Several upgrades on the PHD too. Now have a L4060 with as hydraulic SSQA PHD. I have maybe 10gpm of hydraulic flow, which at 2,500psi is 14hp, tops. It's very noticably my hydraulic PHD is missing over 10hp. The downpressure, reverse, ease of attachment & visibility make up for the lack of power, but it's still missing & noticeable.

If you are going from 25hp PTO or so to maybe 7hp hydraulic I dont think you are going to be happy at all. It's going to be spinning really slow & will have less torque. A PTO powered hydraulic power pack would get you the power & flow for good performance, but will cost at least as much as a new hydraulic PHD.

 

[polemidis]

I would go with a higher discplacement motor. I am not an expert, but I would go with a 20+cu.in displacement.
At 6.8gallons per minute a 24cu.in motor will rotate at 65rpm. I do not think you need more for an auger. And at 2500psi, you will have a 9150in-lbs
I am pretty sure that torque is more than enough for a 12" auger!

 

[texasranger556]

I would go with a higher discplacement motor. I am not an expert, but I would go with a 20+cu.in displacement.
At 6.8gallons per minute a 24cu.in motor will rotate at 65rpm. I do not think you need more for an auger. And at 2500psi, you will have a 9150in-lbs
I am pretty sure that torque is more than enough for a 12" auger!

65 RPM sounds too slow...12% of 540. I'd want it to spin fast enough to fling the dirt off the auger when you bring it out of the hole.

 

[Fallon]

65 RPM sounds too slow...12% of 540. I'd want it to spin fast enough to fling the dirt off the auger when you bring it out of the hole.

Actually, that sounds about right. Model G2/4 | G2 | PTO Auger | Danuser is running about a 3 to 1 gear reduction. That puts things at well under 200rpm (cuz I can't math). And personally I can tell you 3pt PHDs get dam scary if you are running them over half throttle. So that puts you easily in the under 100rpm territory.

Coincidentally the chart at Model EP6 | Danuser lists from 36 to 90 something RPM.

 

[majorwager]

CH47,

You will likely be disappointed. Torque is a product of gpm x pressure. Under producing gpm substantially reduces torque.

I have a direct drive system I built. My small ford output is similar to your tractor. Used a small white motor, don't remember cu in displacement, coupled to a used stihl drive head purchased from a rental store. No gearbox in the system.
Use 6 inch auger primarily for fence posts. Works Ok, reversing will sometimes loosen a large rock. I have a 8 inch auger as well. It struggles with that size. Anticipate little success w/ 12 inch. I did connect the unit to the large gpm output on my Lull once. Huge difference, using low engine rpm to not exceed max hyd flow. Built a simple fork receptor mount, using an PHD on FEL is the greatest.

If you really want production, you would buy a prince, PTO pump, and a hyd. Reservoir, and power it that way, but it would be a tower mount configuration to include the reservoir. A valve required, for reversing.

The biggest disadvantage to your proposal, NO Down pressure. That is the secret to production. That is why FEL mount is so functional. I added an additional 2 spool power beyond valve that sisters next to my loader valve. I usually stand next to tractor for unobstructed view, engage loader valve for down pressure, and motor valve for auger direction. With compacts, very accessible from ground for controls.

My system investment was about $500 in around the year 2000.