Backhoes and breaking frames: Back Hoe  -- Tractor Attachments Implements 3ph Discussion Forum and Review Backhoes and breaking frames: Back Hoe -- Tractor Attachments Implements 3ph Discussion Forum

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 02-01-2002, 22:44 Post: 35196
BillMullens

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 Backhoes and breaking frames

I've been itching to start a thread on this topic for a few months, every since I became interested in 3ph hoes.

My dealer warned me to be careful (with my NH TC29) because he personally had seen two tractors of this size "broken in half" by backhoes. I'm not sure if it was 3ph or sub-frame hoes. Anyway, at least one was broken (or was first noticed) either when tramming or trailering the tractor, that is, not when the hoe was in use.

Does anybody have a good idea where these tractors are breaking specifically, and what really causes it? I have a fair grasp of the statics involved, and really can't see how a 3ph hoe breaks the frame, unless perhaps a FEL was heavily loaded and a strong shock or dynamic load is imposed by the hoe.

I'm trying to design and fabricate a frame reinforcement for my tractor, just to ease my mind. Unfortunately, a full sub-frame mount (which would require hydraulic stabilizers on my CadPlans backhoe) isn't in the cards right now.

Thanks for any ideas.

Bill






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 02-02-2002, 06:50 Post: 35202
TomG

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 Backhoes and breaking frames

I haven't seen a broken one, but I believe the breaks are usually at one of the split points because the case bolts fail. I heard about a break on a Ford/NH 1720 (I think) described as right under the seat.

My impression is that a tractor just isn't like a dedicated hoe platform, and it's very easy to abuse a tractor with any hoe, but it's easier to abuse a tractor with a 3ph mount than a sub-frame. I describe the problem as abuse, because my hoe manual has a picture of the hoe stretched out and large letters 'DON'T DIG IN THIS POSITION.' The trouble is that it's very tempting to do just that, because often with a small hoe it means not having to move the tractor. I guess I have lost sight of the idea of abuse and rationalized: 'Well it's real sandy here anyway.'

The problem is that there is tremendous leverage on the tractor frame/cases when a hoe's boom and stick are extended. Any digging through, boom down, stick in or bucket curl applies force that travels right up the top-link and tries to jackknife the cases. The problem is magnified by the loader blade, which is dug in and extends the wheelbase. The only difference between a 3ph and sub-frame mount is that the sub-frame distributes the forces across more structural members than a 3ph mount.

I think my small 3ph hoe and tractor will get along OK as long as I keep the idea of abuse in mind. Easier to say than do though.






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 02-02-2002, 08:56 Post: 35208
Peters

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 Backhoes and breaking frames

The forces from shock waves as you slam into something hard can be tremendous.
I grew up on the west coast where there is a lot of rock. Track hoes and backhoes where used to lift basted depree and dig new roads for logging etc.
A new hoe would spend months in the welding shop where the welder would apply pounds of reinforcement. Some of it was for increasing the strength and some was for increasing the wear resistance.
If you ever watch an operator dig through soil and then hit the bed rock or a large rock, there would be no question as to how the large forces can be applied to a hoe.






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 02-02-2002, 12:12 Post: 35211
John Mc



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 Backhoes and breaking frames

If I'm following what you guys are saying, the best precautions when using a 3pt hitch backhoe (or any backhoe?) with a compact tractorare:
1) don't use a unit too large for the tractor
2) go slow when digging, especially where there are large rocks
3) dig in closer, rather than with the hoe stretched way out. If you are doing lighter digging (i.e. in sandy soil) you can probably stretch out further.

additions or corrections?






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 02-02-2002, 13:11 Post: 35216
BillMullens

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 Backhoes and breaking frames

Peters, I'm starting to see that this has to be a shock or dynamic issue; perhaps repetitive fatigue. If (on a 3ph hoe) the force is being transmitted through the top link (as Tom G. states) then a 3/4" diameter pin (in the case of a Cat.1 top link) in double shear is taking the same amount of force that is responsible for breaking the frames. That really boggles me. Or, the top link plate bolts onto the differential housing with 4 bolts that are about (metric equivalent to) 3/8" diameter. Why doesn't that pull loose? (OK, it is in almost pure tension, where the bolts holding the frame would be in tension and shear; but there are a lot of bolts holding the frame together.)
Does anybody know what actually breaks? Is it perhaps some bolts loosening and then breaking the casting around the other bolts? My dealer indicated breakage on top where the tranny and engine bolt together and advised me to keep an eye on those bolts; kind of hard to get to with the bodywork in place on the TC29.
Some I've talked to about this believe the breakage issue is exaggerated; that a tractor in this class, if not abused, will easily handle a hoe like mine. Abuse meaning not lifting the wheels off of the ground and slamming them down, etc. Any thoughts?
Thanks,
Bill






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 02-02-2002, 14:19 Post: 35217
Paul Fox



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 Backhoes and breaking frames

Hmmmm. Well. I think I'd vote for the "Tempest in a Teapot" theory, based on my experience.

I have a 3 point hoe for my JD750. I've used it HARD, in rocky ground (coastal Maine) and at full extension. I don't intentionally abuse my equipment, but I need to get work done, so I don't baby it either.

In 8 years of this kind of work, I've cracked two castings ON THE HOE, and egged out the toplink pin holes in the bracket on the tractor. The toplink attachment point wear was obvious after the first year. I took the bracket off and had a machine shop bore it out and press in hardened bushings. Problem solved.

I have seen or experienced NO damage to the tractor itself.

Of course, now that I've said this, the dang thing will fold in half the next time I put the hoe on it...






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 02-02-2002, 17:35 Post: 35221
BillMullens

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 Backhoes and breaking frames

Thanks for the note, Paul. This info gives much support for Tom G.'s statement that force is transmitted mainly through the top link.
I'm still working on a reinforcement.

Bill






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 02-03-2002, 07:04 Post: 35229
JohnS
2002-02-03 00:00:00
Post: 35229
 Backhoes and breaking frames

Here is a link that might give you some ideas. Its not with your tractor or a 3pt hoe, but it might generate some thought.

JohnS






Link:   JM Hoe mods 

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 02-04-2002, 06:17 Post: 35273
TomG

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 Backhoes and breaking frames

It sure seems that I spend a lot of time trying to visualize geometry, and with varying degrees of success.

I think that digging creates forces that try to lift the boom. However, the hoe is free to rotate on its lower link pins, which compresses the top link. It seems like there also would be a vector that applies down force to the lift arms so the hitch (and drawbar in some mounts) will absorb some of the force. I don't have the background to even guess whether the forces are divided fairly equally or not.

Since I'm in the guessing buz today, I'll also guess that the division of forces would be affected by which top-link bracket pin position is used. I think the upper positions are intended for use with heavy draft implements. The idea is that the upper positions provide more leverage on the cases to keep weight on the front end when the top link is compressed. If the top-link absorbs most of the forces frpom digging, them perhaps lower pin positions would be better. However, lower positions likely place greater load on the lift arms. Which parts would be the most vulnerable; Who knows?

Lifting the bucket reverses the forces. The stabilizers act as pivots and the back of the hoe tries to lift, which decompresses the top-link. I suppose there also is a lesser lifting force on the lift arms. So, in operation there is repeated compression and decompression of the top-link. I check my mount adjustments frequently during operation to make sure there is no free-play in the top-link.

I recall the broken 1720 story better now. It was one of the few first-hand reports I've heard. I believe the cases broke under the seat. I seem to recall comments that the cross-section of the cases was not constant and the brake happened at a thin section.






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 02-04-2002, 08:58 Post: 35281
DRankin



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 Backhoes and breaking frames

After reading the posts on this thread I would speculate that the free standing, self powered Trencherman II that Northern Tool sells would be too wimpy to do much real work. I think I will stay with my original assesment... there is just too much cost, complication and stress in a back hoe for a small tractor in my life. For the few times I would need the tool it makes more sense to rent the real deal down the road at $300 a day. Thanks for the input guys.






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Discussion Boards > Active Subjects > Messages as Posted > Back Hoe Forum

Thread 35196 Filter by Poster:
Allan 1 | Art White 3 | BillMullens 4 | DRankin 2 | Ed 1 | Harry W 1 | Harry Webster 2 | HarryW 1 | John Mc 1 | Johnl 1 | JohnS 1 | Lee 1 | lsheaffer 1 | Marc 4 | Mr Ethics 1 | Paul Fox 1 | Peters 1 | regniflow 1 | Russ. C. 1 | SIMPLE SIMON 1 | spb1971 1 | Spring Valley 1 | Ted @ Abbeywoods, LLC 1 | Ted@Abbeywoods 1 | TomG 14 |




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