Posthole Digger Hydraulic post hole digger

gray · May 5, 2004

I have been looking for a hydraulic quick tach post hole digger for my loader. I have checked with Bobcat and some other dealer but do not feel the pricing is very good or maybe the brand offered is premium?

I would use it occationally for pole barn construction with an 18 inch auger. Need about 48" holes. I have thought of the 3 pt type but many have said they are tough to use in that size auger. They do not reverse and down force is an issue.

Any information would be a big help.

Thanks to all for any help in this matter.

uhmgawa · May 5, 2004

( I have been looking for a hydraulic quick tach post hole digger for my loader. I have checked with Bobcat and some other dealer but do not feel the pricing is very good or maybe the brand offered is premium?)

Worksaver makes two hydraulic models. Even with the GPM available from the
L48's main hydraulic loop you will still get a fraction of the HP available via
the PTO.

Another possibility is to get a PTO driven PHD and adapt it to be driven by
a hydraulic motor. The works could be mounted either to the FEL or backhoe.
Assuming you don't modify the PHD it would still be usable as originally
intended via the PTO.

RedRocker · May 5, 2004

I was quoted $1550 for one yesterday.

kevincook · May 5, 2004

For occasional use I think I would just rent a skid steer for the day with a post hole digger on the unit. It would be VERY heavy duty and able to drill holes much better than a 3pt hitch model. And it is someone else's problem to store and maintain.

gray · May 6, 2004

I have often thought of rental options, but we have none here. It is 60 miles to the nearest rental place with any offerings. I would find many uses if I had one. I would rather have a full function one and not have the struggle that many have told me of with a 3pt type?

An 18 inch auger in clay needs some down pressure and would be best to reverse it at times? I am not sure of how many HP the 12.7 gpm at 2500 psi is but I think it may be enough for an 18 inch bit.

Looks like I am getting good insights, thanks.

DocHeb · May 6, 2004

Using the formulae:

Torque = [(PSI) * (Displacement (in^3/rev))] / 6.282

HP = [Torque (inch*lbs)*RPM)] / 63025

Displacement of motor in^3 per revolution = [(231*GPM)] / RPM

12.5 gallons/min at 540 rpm will drive a 5.35 cubic inch hydraulic motor. At 2500 psi, this motor would generate 2129 inch*pounds of torque, yielding 18.2 Horsepower. This does not account for system efficiency losses.

gray · May 6, 2004

Chris,

YOu appear well versed in hydraulics. Is it also true that if the hydraulic motor ran at lets say 80 to 100 rpm, then the torque would be much higher?

Would 18 net HP or around that amount do a good job with an 18 inch auger?

uhmgawa · May 7, 2004

( Is it also true that if the hydraulic motor ran at lets say 80 to 100 rpm, then the torque would be much higher? )

Torque is proportional to the product of pump displacement and
differential pressure seen by the pump. In a typical application
running the pump at reduced flow will simply scale back the
torque in direct relation to the speed.

( Would 18 net HP or around that amount do a good job with an 18 inch auger? )

I wouldn't assess suitability of a motor in terms of summary HP. It is
an issue of both torque and speed. Commercial hydraulically driven
PHDs of the size discussed here develop 8000-12000 in/lb of torque max
with a spindle speed of ~100 RPM and are used to drive augers of 6-24"
diameters.

Working backwards from this you can use the gear ratio of the gearbox
to determine what torque and speed are required of the motor. Note
motors of this size may not be designed to operate with 2500-3000 PSI
pressures and may require a relief valve set to their upper pressure limit.

BigMike · May 7, 2004

With all the hydraulics aside, I would like to know why you need an 18" hole, 48" deep? What kind of pole construction are you doing?

gray · May 9, 2004

Here in the UP of Michigan, we have a 42inch minimum frost depth and it often is not deep enough. Most builders go down 48 inches.
Also, we have state codes that call for 16 inch base footings on pole barns with 6 foot pole centers. We have a high snow load of up to 70 pounds per sq. ft. in our area and as much as 100 PSF in areas north of us. This great roof load forces larger footing pads.
I would like the 18 inch just for safety.
I just don't want to go with the 3 pt ones I have been quoted. Not that they are bad but some of the soils I have to think about may give me trouble without a down force or reversing option. I am concerned about the power I have with the flow rate. If I can find a good unit at a fair price for a quick tach loader set up, that is what I expect I will get.