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  1. #1
    Silver Member
    Join Date
    Feb 2006
    Posts
    209
    Location
    Columbus, NJ
    Tractor
    Ferris/Simplicity/John Deere

    Default which 36" auger/post digger for 4720?

    I have the skid steer attach couplers on the front, also have front accessory flow lines on our 09 4720 deere... 2.4L turbo 4cylinder 66hp etc.

    I plan to run this auger/post digger on the front of BOTH our 4720 tractor 11.5~gpm max
    and our 2010 Deere 319D skid steer, same motor, setup but 60hp, about 18gpm flow.

    We already have a land pride PTO/3pt post digger already with 9 and 15" bits for smaller stuff

    Im looking ONLY to use this for potting trees and shrubs into the ground quickly with out tons of hand digging. I'm only interested in stuff thats 30-42" "tree augers" basically.

    We'll use it to dig mainly softer soil but may need nice "potted holes" in clay, harder soils but nothing rock laden. I could care less about the speed or RPMS since i know both machines will have plenty of power to put this sucker into the ground. Our 4720 will burry the 15" on the rear PTO/3pt in seconds through any soil without ANY engine bog or struggle whatso ever.

    Even our little "garden tractor" 27hp diesel simplicity will burry the 15" bit but doesnt have the rear massive lift capacity to remove the bit back out once its burried.

    Here are specs of two units, one probably is heavier/larger hydro motor and takes a little more flow to spin the same rpms as the smaller unit. If they say recommended flow 15-30gpm and you hook the 4720 up at 11-12gpm, will it move? Will it be slower than their slowest rated RPM or have NO power to turn?

    If its slow AND i can use it on the 4720, no problem, assuming the skid steer will just run it faster rpms.

    Id rather get the heavier duty one. The smaller model says 10-25gpm but ONLY 30" maximum bit... why? torque? Can it run the 36 or 42" sizes just might bog the machine, break the gearbox what?

    I know my little landpride on the back PTO flys... probably 60rpms at "normal" engine rpm speed, probably hits closer to 80-95rpms though when either tractor is FULL throttle/540rpm rear pto speed.

    Model HDA-20: Max Auger Diameter - 30"

    * Torque @ 3000 psi - 2419 ft. lbs.
    * Drive - Hex Type 2"
    * Weight 310 lbs.
    * Drive Type - Planetary
    * Gearbox Ratio - 4.08:1
    *
    Recommended Flow Rating of Skid Steer - 10 - 25 GPM @ 3000 PSI
    10gpm =38rpms
    18gpm=68rpms

    Model HDA-30: Max Auger Diameter - 36"

    * Torque @ 3000 psi - 3036 ft. lbs.
    * Drive - Hex Type 2"
    * Weight 325 lbs.
    * Drive Type - Planetary
    * Gearbox Ratio - 4.08:1
    *
    Recommended Flow Rating of Skid Steer - 15 - 30 GPM @ 3000 PSI

    15gpm =45rpms
    20gpm=61rpms

    Whats the worst that could happen with a larger flow unit? bogs the machine more? Im sure the 11gpm on the 4720 wouldnt even stall the engine if it stopped dead. The skid steer isnt high flow, which sucks but 18gpm should still operate one easily.
    2005-2008 Ferris & Simplicity Mowers
    06 Simplicity Legacy XL 27hp Diesel 4x4 Tractor
    09 66hp Deere 4720 http://entertainment.webshots.com/album/568957542RPhgRb
    09 Deere 244j lil loader jan2010
    2010, 2011, 2012 & 2013 Deere skid steers & track loaders

  2. #2
    Super Member
    Join Date
    Feb 2008
    Posts
    9,393
    Location
    somewhere usa
    Tractor
    Deere 110tlb, 4520, x749, L130

    Default Re: which 36" auger/post digger for 4720?

    I recently purchased a Frontier PA30 which is rated for a 36" bit. I installed it on my 110tlb which has a flow rating of 16gpm. Turns the bits about 45 to 50 rpm I would think that is plenty fast enough for a large diameter bit. You are correct that the engine will not stall while locking up the bit. You may wan't to compare specs on this unit as well.

  3. #3
    Elite Member
    Join Date
    Jul 2006
    Posts
    3,015
    Location
    midwest
    Tractor
    JD 4520, Toolcat 5610, Bobcat S300, Case-IH 125 Pro, Case-IH 245, IH 1086, IH 806

    Default Re: which 36" auger/post digger for 4720?

    Take a look at this bobcat brochure:

    www.bobcat.com/publicadmin/getFile.do?id=4576

    I have both the bobcat 15C and 30C. Have used them on my skidsteer (21gpm), Toolcat (18 gpm or 27 gpm if I use hi-flow) and CUT (previous JD 3720 and now JD 4520). I have 6", 9", 12", 24" and 36" bits. The TC and skidsteer are at 3000 psi. I increased the CUTs hydraulic pressure up to 2800 psi. I auger mostly in black dirt or clay. Torque is the power that drives the bit. The bigger bits need lots of torque. The higher the psi, the greater the torque. The slower the bit turns for a given hydraulic flow, the greater the torque. The 15C struggles with the 24" bit in moderate to hard digging. I can only go 12-18" with that bit in average conditions. The 15C does poorly with the 36" bit in all conditions. The 30C will run the 36" in nearly all conditions. The big bits due to their large diameter need to run slowly for best results and safety. (Just like using a large drill bit to drill a hole in steel). You will need the equivalent of a 30C for bigger bits. However, the lower flow rate of the 4720 will make the auger turn slow for the bits.

    Don't confuse the pto power of your 4720 digging a hole with rear pto auger. The power (hp) from hydraulic flow is not even close to your 4720 pto hp. If the hydraulics cant turn the bit, your relief valve will open and the bit simply won't turn. You will not hurt your CUT or SS with hydraulic auger. I have used an adapter and turned a 24" bit in my relatively cheap 3 pt pto auger. The 3 pt turns the 24" bit too fast for easy control. The 3 pt is difficult to control with bigger bit. I ran it at an idle, use a grade 8 shear bolt and prayed that the CUT (at that time a kubota 3710) would die before something broke if the auger hit something.

    I generally run the 15C on my 4520 at full throttle to get enough flow. The skid steer and TC and run at fast idle. The 30C is used at moderate to fast throttle on the skid steer and TC. I generally don't use the 30C on the CUT because the flow is too slow for any decent, rapid digging.

    Also, the torque mentioned on the Bobcat brochure is calculated at 100% efficiency. That is not even close to real life with hydraulics. 70% may be a realistic percentage.

  4. #4
    Elite Member
    Join Date
    Jul 2006
    Posts
    3,015
    Location
    midwest
    Tractor
    JD 4520, Toolcat 5610, Bobcat S300, Case-IH 125 Pro, Case-IH 245, IH 1086, IH 806

    Default Re: which 36" auger/post digger for 4720?

    Quote Originally Posted by Ramairfreak98ss View Post
    Here are specs of two units, one probably is heavier/larger hydro motor and takes a little more flow to spin the same rpms as the smaller unit. If they say recommended flow 15-30gpm and you hook the 4720 up at 11-12gpm, will it move? Will it be slower than their slowest rated RPM or have NO power to turn?

    If its slow AND i can use it on the 4720, no problem, assuming the skid steer will just run it faster rpms.

    .
    You 4720 will not drive the auger as well because its psi is only 2500 and the skid steer is 3000 psi. That's about 20% more torque to the auger with the skid steer. If you turn up the 4720 psi to 3000, both will have the same torque but the 4720 will just turn it much slower.

    Be a little careful if you read a flow range from 15-30 or 10-25 gpm for the auger. The auger will probably work more optimally in the mid portion of that flow range. Even at 10-12 gpm, the auger will turn but may not be practical.

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