Amulet excavator thumb

[brain55]

I couldn't decide which forum to post this in. I finally decided it was more of a welding job than anything for me. Anyway, I ordered an Amulet thumb for a customer's Caterpillar 305 CR excavator Friday. They have to build it and ship it to me. I expect to see it the coming Friday and put it on Saturday. I will definitely post pictures before, after, and during. It should be a fun job. The hydraulics are already on the machine so all I really need to do is weld the brackets for the cylinder and thumb, mount them, and make the hoses to the cylinder.

I quoted my customer $3000 for the job.

Brian.

 

[firemanmike69]

Make sure to tack everything up and test fit it first, we just got the wrong size thumb from them twice. Looking forward to your pictures buddy

 

[brain55]

I definitely will tack and test first. Especially since it is my first time installing a thumb that wasn't a factory kit.

Brian

 

[Arc weld]

There should be instructions for welding the thumb brackets on. If it uses separate small brackets for the cylinder and thumb hinge pins, they can be welded all around. If it uses a large mounting plate with the cylinder and hinge mounts already attached, only weld on the sides lengthwise with the stick/boom. Don't weld across the top and bottom (across the width of the stick). That's an application where you could use Shield Arcs suggestion to put silicone seal across the boom to keep moisture from getting under the plate.

 

[TomSeller]

If it uses a large mounting plate with the cylinder and hinge mounts already attached, only weld on the sides lengthwise with the stick/boom. Don't weld across the top and bottom (across the width of the stick). That's an application where you could use Shield Arcs suggestion to put silicone seal across the boom to keep moisture from getting under the plate.

I have welded a little but in no way am I a welder. Why wouldn't you weld all the way around?

 

[brain55]

There should be instructions for welding the thumb brackets on. If it uses separate small brackets for the cylinder and thumb hinge pins, they can be welded all around. If it uses a large mounting plate with the cylinder and hinge mounts already attached, only weld on the sides lengthwise with the stick/boom. Don't weld across the top and bottom (across the width of the stick). That's an application where you could use Shield Arcs suggestion to put silicone seal across the boom to keep moisture from getting under the plate.

These are the welding instructions I have so far. We'll see if they send any more with the thumb.





Brian

 

[Arc weld]

I have welded a little but in no way am I a welder. Why wouldn't you weld all the way around?

It would add stress to the stick welding straight across it. The instructions show curved ends and also to leave a space un-welded in the middle. I'm sure Shield Arc could explain it better than I could.

 

[Coyote machine]

I hired a pro welder to attach the cylinder bracket plate to the dipper stick on my tractor's subframe mounted backhoe. The instructions for the weld process were quite detailed and clear. they said to fit the thumb onto the hoe and gave an area in which to locate the plate. They said to clean all paint from the weld area, to dry fit the plate and test the fitment before welding. We did this and then tacked the late to retest actual fit. Once verified, we welded ONLY along the sides of the plate and stick, NOT across as clearly stated in the directions.
We took the extra precaution to remove the battery ground during the process so no damage from the welding could carryover to the tractor's electrical system.
The work cost $150, and took a couple of hours to complete from start to finish. The results are good.

 

[Shield Arc]

I have welded a little but in no way am I a welder. Why wouldn't you weld all the way around?

Generally the reason is stress raiser. And the HAZ / Heat Affected Zone. That's why you see in really stressed area where fish plates are required, engineers will want a diamond or oval shape fish plate. With diamond shape fish plates its a good idea to tail out the weld like in brain55 weld detail he posted.

Stress concentration - Wikipedia, the free encyclopedia

 

[TomSeller]

Generally the reason is stress raiser. And the HAZ / Heat Affected Zone. That's why you see in really stressed area where fish plates are required, engineers will want a diamond or oval shape fish plate. With diamond shape fish plates its a good idea to tail out the weld like in brain55 weld detail he posted.

Stress concentration - Wikipedia, the free encyclopedia

Makes sense. Thanks

 

[brain55]

Picked up the thumb at the freight terminal this afternoon. Looking forward to putting it on tomorrow.





Brian

 

[Coyote machine]

Curious as to why/how the install of the thumb would cost $3K?! How much does the actual thumb cost?
Please take lots of pics of the install, thanks.

 

[brain55]

It may not be $3000, having never seen or installed one of their thumbs before I didn't know what to expect for installation time, so I quoted what I hoped would be a cushion. The thumb retails for $2395. The quote also includes the hoses, fittings, and flat-face quick couplers that aren't included with the thumb. You add in what will be over $200 in sales tax it won't be far from $3000.

I plan on taking plenty of pics for sure.

Brian

 

[brain55]

There are some pics.



Because the width of the mount and the arm were neatly the same I had to add a filler plate so the mount had a solid surface to mount to.







Here it is mocked up.







Here's the mount clamped down and then welded on.







Here's a few with it all attached and with the hoses made.











The last one is with the cowling off so I could adjust the overload relief.



Brian

 

[Shield Arc]

We may never know, but it would be interesting to see in the future if there is going to be an issue with you using 90-degree corners on that filler plate?
You see V-shapes, or radius cut fish plates used on excavators all the time. A good idea with V-shape fish plates is to tail out the welds like this guy did.

 

[brain55]

I wish there had been more room. The mount was the length of the arm if I had fishtailed the filler plate I wouldn't have been able to weld the ends of the mount. I guess I could have made smaller fishtails concentric with the ones on the mount.

Brian

 

[polarred21]

Good looking install. That is one heck of a thumb.

Does it have it's own dedicated hydraulic valve/circuit?

 

[Shield Arc]

I wish there had been more room. The mount was the length of the arm if I had fishtailed the filler plate I wouldn't have been able to weld the ends of the mount. I guess I could have made smaller fishtails concentric with the ones on the mount.

Brian

Well you gotta do, what you gotta do for the install!:thumbsup: It's just interesting to me, more for a learning experience than anything else.

 

[brain55]

Does it have it's own dedicated hydraulic valve/circuit?

Yes, it uses the auxiliary circuit on the excavator. All I had to do is make some short hoses from the existing quick couplers to the thumb cylinder. There was also a selector valve to switch the auxiliary from uni-directional to bi-directional. Even though the cowling came off to get to the valve bank, adjusting the overload relief was a bit of a challenge. It was tough to get to with all of the hoses in the way. The overload pressure was way off. It was at least 6000 psi and Amulet wanted it to be 2100 psi. The overload relief is what keeps the machine from bending or breaking the thumb or hydraulic cylinder when curling the bucket into the thumb.

Brian

 

[Coyote machine]

Cool! Looks good. Couple of questions from one who knows less than nothing about metals/welding/hydraulics...
The existing QD's on the dip stick were already there? For a thumb?
You welded the filler plate in between the sides of the dipper stick. When I installed my thumb, albeit much smaller scale, on my tractor, I was given a plate/cylinder bracket for the cylinder top mount which spanned the dipper and was welded at the side plate edges of the dipper and not across the dipper at the top and bottom of the plate. And I was told to bring the thumb to the bucket, and not to bring the bucket to the thumb, even though the cylinders have the same pressure ratings. My circuit(s) for the thumb/bucket don't have overload pressure reliefs built in, or adjustable to my knowledge, could this account for the bringing bucket to thumb method on the ex?
How long did it take to do the job, and what was the final cost, if you don't mind saying?
One last Q: your username is brain55, but your name is Brian? I'm confused, was that intentional?:confused3:

Thanks for any answers you care to share:thumbsup: