Sizing a Backhoe Thumb Cylinder

[Dougster]

Based on your description, Woods must have designed for similar net forces applied by the thumb and bkt, then added a relief valve to each circuit so they would retract under opposing pressure. Otherwise opposing pressure would have exceeded the pressure limits of the cylinders. I find it a bit surprising that the thumb can push the bkt back. I wonder what pressures they are seeing... They also may have INTENDED the user to be able to push either back by the other so he could position his load. The problem I see here is only if a relief in the bkt circuit is set lower than max press, which limits your digging capability. A tradeoff.

I found that to be an interesting operational feature as well... and I found myself wondering if it would be a more helpful or not-so-helpful feature on my own machine. The notion of being able to adjust your load while under a near constant pinching force is kind of interesting... but at what price in terms of reduced pinching power? And yet it sounds from his description like this "feature" can be defeated, when necessary or desired, simply by applying pressure to both sides at the same time. Sure wish I had more info on this... but I don't think I should let it affect my cylinder sizing criteria... still looking like 2.75" based on all the factors previously discussed.

Dougster

 

[MadDogDriver]

I really have enjoyed my hyd thumb. Like you've already mentioned Dougster, it's so convenient not having to jump down and reposition the thumb when needed. I haven't grabbed anything heavy enough yet where I've needed to apply hyd pressure with both the thumb and bucket simultaneously, although I do normally grab items that way at first and then step off the thumb circuit and bucket simultaneously and it holds the load. Like you've mentioned, it is nice to reposition as needed.

I'm happy with it. I'm sure you will too when it's all said and done Doug.

 

[Dougster]

I really have enjoyed my hyd thumb. Like you've already mentioned Dougster, it's so convenient not having to jump down and reposition the thumb when needed. I haven't grabbed anything heavy enough yet where I've needed to apply hyd pressure with both the thumb and bucket simultaneously, although I do normally grab items that way at first and then step off the thumb circuit and bucket simultaneously and it holds the load. Like you've mentioned, it is nice to reposition as needed. I'm happy with it. I'm sure you will too when it's all said and done Doug.

Hi MadDog - Can you explain how they do that without affecting (i.e., reducing) bucket digging force? I certainly don't mind putting a carefully chosen relief circuit on the thumb side... might do that anyway... but I don't want to give up one single ounce of bucket digging force.

Dougster

 

[MadDogDriver]

I'm not sure. If you look back at an earlier post of mine that had the thumb install pdf, you'll see everything that I have available to me (as far as documentation from Woods). When I first had the BH it came with the mech thumb while I was waiting for the hyd kit to arrive. To my knowledge, all the dealer did was install the hyd kit in accordance with that pdf previously posted. The hyd power for the thumb came off the left stabilizer (left as sitting on the seat looking at the bucket).

I have not noticed any difference in digging power before or after the hyd kit install.

EDIT: Just called Woods Tech support and asked that question....they said it's designed that way and does not limit digging power of the bucket.

 

[Dougster]

Just called Woods Tech support and asked that question... they said it's designed that way and does not limit digging power of the bucket.

But I'll bet they wouldn't tell you how they do it!

Same thing with Bradco. They want you to dig deep and buy THEIR system! Not build your own.

Dougster

 

[MadDogDriver]

Nope, just said "It's designed that way".

 

[dfkrug]

Hey, MadDog:

Thx for posting your experiences with your Woods hyd thumb. Real
world first hand experience is very valuable to those of us designing
our own systems. I have only been able to try hyd thumbs on
excavators and neither thumb nor bkt could push the other back
on those.

What Woods may have done is use relief valves in every work port of
their stack valve. The action by the thumb against the stationary
bucket may be making use of a relief valve already in the bkt circuit.
That standard relief valve is prob set just above the max recommended
working pressure of the system, so it would not reduce your digging
force. On my hoe, some of my shock reliefs are set at 175 bar and some
are at 180 bar (2650psi).

 

[MadDogDriver]

No problem.......You guys crack me up (the ENGINEER in you comes out loud and clear). It'll drive you nuts until you know exactly how and why things operate the way they do.

All the more power to you two (and others). I'm at that stage in life where as long as it works okay I leave it alone. However, the eng genes still come through when I need to fix something then I'm in your camp trying to get all the info necessary.

Good Luck.

 

[Dougster]

No problem.......You guys crack me up (the ENGINEER in you comes out loud and clear). It'll drive you nuts until you know exactly how and why things operate the way they do. All the more power to you two (and others). I'm at that stage in life where as long as it works okay I leave it alone. However, the eng genes still come through when I need to fix something then I'm in your camp trying to get all the info necessary.
Good Luck.

It is "the curse" MadDog. We are well aware of it... but we can't control ourselves. Forgive us... and maybe even feel sorry for us. Most of all, be very glad you aren't us!

Dougster

 

[dfkrug]

It's not just about HOW something works, and it's not just about
taking things apart AND putting them back together. And it not
just about fixing something either. It's really about making something
BETTER, or designing & building something NEW. The curse.

 

[MadDogDriver]

Yes, I know the "curse" well.

My Dad is 93 and going strong. He's a mech eng and still keeps himself occupied with "improving" everything he thinks needs improving. Makes me smile everytime I see him or talk with him. For Father's Day, I asked him to consider a plan on storing my pickup's canopy overhead when not installed. Thought that'd keep him occupied for awhile. First idea of his was a block & tackle system, an alternative was a modified coffin lowering system. What a great mind.

 

[bindian]

I have a fixed thumb on my Bradco 511 and like Dougster, will be converting it to hydraulic. I have talked to RakeSales.com and they suggested going with the Bradco kit ($1350) because of relief vavle issues. Now, as I see it, I could install the hyd kit and be unafraid of how hard I clamp onto something with the thumb, or I can just plumb the thumb actuator (cylinder) to a remote and deploy the thumb as needed and then let the bucket clamp down and grip the object I want to lift. The bucket will not overpressure because of the system relief valve. It all depends which technique you use in gripping. One question does come to mind........does a "factory" installation hyd thumb extend further than a fixed thumb? Do hyd. thumbs really work as a clamshell in gripping, or do you use hydraulics just to position the thumb and use bucket pressure to grip it? As I see it now...........you can plumb it two different ways. Since the Bradco's thumb and bucket pivot on the same pin, a clamshell would be the best, while deploying the thumb with a remote and using bucket control to grip and not squeeze would be the cheaper route.
Am I understanding this correctly?
Oh yeah.........I am waiting on a phone call from my Mahindra salesman to tell me how much just buying a Bradco actuator is.
hugs, Brandi

 

[Dougster]

I have a fixed thumb on my Bradco 511 and like Dougster, will be converting it to hydraulic. I have talked to RakeSales.com and they suggested going with the Bradco kit ($1350) because of relief vavle issues. Now, as I see it, I could install the hyd kit and be unafraid of how hard I clamp onto something with the thumb, or I can just plumb the thumb actuator (cylinder) to a remote and deploy the thumb as needed and then let the bucket clamp down and grip the object I want to lift. The bucket will not overpressure because of the system relief valve. It all depends which technique you use in gripping. One question does come to mind........does a "factory" installation hyd thumb extend further than a fixed thumb? Do hyd. thumbs really work as a clamshell in gripping, or do you use hydraulics just to position the thumb and use bucket pressure to grip it? As I see it now...........you can plumb it two different ways. Since the Bradco's thumb and bucket pivot on the same pin, a clamshell would be the best, while deploying the thumb with a remote and using bucket control to grip and not squeeze would be the cheaper route. Am I understanding this correctly? Oh yeah.........I am waiting on a phone call from my Mahindra salesman to tell me how much just buying a Bradco actuator is.
hugs, Brandi

First, just to bring others up to date on my own situation, I have found an alternative cylinder design for under $300 that is near perfect, but has an 8 to 10-week delivery time. I have also found a cheapy surplus cylinder with 5-day delivery time that costs under $150 but has the wrong ends which would have to be modified or replaced. Like Brandi, I am also awaiting more details about the $500 list ($450+tax locally) Bradco cylinder kit (half of the full kit... which is made up of cylinder kit plus valve kit) and exactly what it includes in the way of documentation, hoses, fittings, etc.

That being said, anyone following this thread knows that I am concerned about operating two different-size, different-rated cylinders against one another from different hydraulic sources with different leverage arms and different relief provisions. I am concerned about proper relief provisions and the very real possibility of physical/mechanical damage to the various thumb and BH components. I am also of the opinion that it shouldn't matter which cylinder and component is positioned first vs. second... or even both at the same time. The system should be designed to be inherently user friendly and safe regardless.

The easy solution is simply to dig deep and buy the entire "soup to nutz" Bradco system. But as you all know, I am dirt poor now... so every dollar must count. The full Bradco kit is simply out of the question for moi.

While I don't know enough yet about the Bradco kits and alternatives to address Brandi's questions, no matter what I buy, I will install reliefs to assure that the bucket-to-thumb force... no matter how applied... will never exceed the 80% level (compared to fixed) that Bradco has specified for its own design. This could be a mechanical strength limit (due to very different thumb geometry: fixed vs. hydraulic) or it could simply be due to thumb cylinder capability... but I don't want to find out. I'll stick with Bradco's limit and let it go at that.

Dougster

 

[dfkrug]

Do hyd. thumbs really work as a clamshell in gripping, or do you use hydraulics just to position the thumb and use bucket pressure to grip it? As I see it now...........you can plumb it two different ways. Since the Bradco's thumb and bucket pivot on the same pin, a clamshell would be the best, while deploying the thumb with a remote and using bucket control to grip and not squeeze would be the cheaper route.

I do not understand your question. If the thumb has an independent cyl
and valve, you will sometimes pinch the thumb against the stationary bkt,
sometimes pinch the bkt against the stationary thumb, and sometimes
operate both valves simultaneously.

A hyd thumb can
> use a cyl plumbed to its own independent valve
> use a cyl T-ed into the curl cyl circuit, controlled by the curl valve
> use a cyl T-ed into the curl cyl circuit, with a solenoid valve shutoff,
controlled by the curl cyl valve and an electric switch

My hoe now has the 2nd choice above, a thumb cyl in parallel to the
curl cyl. I also tried #3 with a 12V poppet valve, but that method did
not work too well with the valve I had (too restrictive). Another poppet
valve or a solenoid spool valve would work better. I plan to experiment
with other solenoid valvews in the future.

My thumb cyl is 2" ID, and my curl cyl is a little less than 2" ID. With my
setup, the thumb is a bit more forceful than the bkt curl, so it pushes the
bkt back slowly when pinched together. My thumb uses a plow steel tip,
which is harder than my cast bkt teeth, so pinching them together scrapes
steel off of the tooth.

 

[bindian]

My Mahindra dealer told me # 16955 hyd. cylinder for Bradco's thumb is $573.82
Now this is confusing..........# 16605 Mount............$116.32 I think this is the welded bracket on the dipper stick. My BH came with it.
I sent an email to ABC Groff - Skid Steer Attachments and asked.......Please give price and availability for these items listed below for Bradco's hydraulic thumb for their 509 & 511 Backhoes
Thanks, Brandi

# 15780 Hydraulic Installation Kit
# 16955 Cylinder Assembly
# 16702 Pin 1.25" x 5.13"
# 57693 Washer
# 1652 Snap Ring
# 16703 Pin 1.25" x 3.44"
I have parts call list and installation instructions for the Hyd. thumb, as it came with my fixed thumb.
Also......from the ABC Groff website...........
The hydraulic thumb provides a full 120 degree rotation. Unlike "knock off" thumbs, the Bradco uses the bucket hinge pin so the tines make constant contact with the edge during rotation. The load is not "rolled or bound" when the bucket is rotated.

 

[Dougster]

My Mahindra dealer told me #16955 hyd. cylinder for Bradco's thumb is $573.82

Ouch!!! I sincerely hope that is a mistake!!! Otherwise, looks like I am waiting the 8-10 weeks for the special order cylinder.

Dougster

 

[dfkrug]

Also......from the ABC Groff website...........
The hydraulic thumb provides a full 120 degree rotation. Unlike "knock off" thumbs, the Bradco uses the bucket hinge pin so the tines make constant contact with the edge during rotation. The load is not "rolled or bound" when the bucket is rotated.

Interesting quotation from Groff.
A full 180-deg rotation is a good thing. However the comment about
the load being rolled or bound is weak. Certainly thumbs that rotate
about their own independent pivot points can do this, but only if both
thumb and curl cylinders are operated at the same time a load is grasped.
How likely is that? And is it really a problem?

The thumb and bkt WILL meet at different points for an independent
thumb, depending on where they are in their respective arcs. That can
be a useful feature, rather than a problem.

 

[glmf]

The thumb and bkt WILL meet at different points for an independent
thumb, depending on where they are in their respective arcs. That can
be a useful feature, rather than a problem.[/QUOTE]

excellent point, never thought of that!

 

[bindian]

Interesting quotation from Groff.
A full 180-deg rotation is a good thing. However the comment about
the load being rolled or bound is weak. Certainly thumbs that rotate
about their own independent pivot points can do this, but only if both
thumb and curl cylinders are operated at the same time a load is grasped.
How likely is that? And is it really a problem?

The thumb and bkt WILL meet at different points for an independent
thumb, depending on where they are in their respective arcs. That can
be a useful feature, rather than a problem.

I agree with you. It also means Bradco's hyd thumb and bucket can function exactly like a clamshell bucket. That is all........not for or against it.
hugs, Brandi

 

[dfkrug]

Here is a neat machine I saw when I was in Stockholm last week.
It is operated by remote control and uses a clam shell to scrape up
the last little bit of sand on the bed of this truck. The clam shell
uses a mechanism that closes the jaw with the least back-pressure
first. Just like a clam shell on an excavator at the local scrap yard.
This kind of action can be mimic-ed with a hyd thumb....easily with
a thumb cyl connected in parallel to the curl cyl, and a little harder
with a separately-valved thumb by operating 2 valves at once.

My separately-pivoted thumb contacts the middle bkt tooth tip-to-tip
at mid bkt curl. It has a significant "overbite" at near-full bkt extension.
This latter condition allows the thumb to go a little INSIDE the bkt.
This has proven useful in breaking up rather thick branches. Otherwise,
it is no inconvenience.