Sizing a Backhoe Thumb Cylinder

[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.