Installing thumb on an excavator

[JimP]

I'm not sure if this belongs in welding or construction equipment so mods feel free to move.

I have a Volvo ECR88, its about 8 tons so in between a compact and full excavator. It has a Geith coupler and I'm installing a Geith pin on hydraulic thumb. The bottom of the thumb is held to the bottom of the stick by a longer pin. At the top of the stick a hydraulic cylinder mount will be welded. There are no other attachment points between the thumb and stick.

I am getting different opinions on whether to use doubler plates on the stick. The stick is about 6 inches wide and 3/8 thick on the mount face. If I do plate I'm thinking 3/8 low carbon or HSLA steel. Plate the stick end? Under cylinder mount? The whole stick? None of the above? TIA. Jim

 

[Shield Arc]

Always use doubler plates in high stress areas! Make sure you do not use any 90-degrees corners on the doubler plate.

 

[SSdoxie]

Use a doubler plate. And as Shield Arc mentioned "round the corners" and weld around the corners. Do not stop or start at a corner.
I have seen many of these grappler/thumbs installed over the years, some with a doubler and some without. I have not come across one with a plate that showed any sign of dipper stick distortion, material bending, or tearing on those with a plate but have seen a few that did not have a doubler plate.

 

[Arc weld]

I think just mild steel plate would work. The thumb may have recommendations for welding the cylinder mount. If not, there should be lots of pics of thumbs on the internet.

 

[JimP]

Thanks guys. I should clarify that the cylinder mount ears are on a 5/8 thick mount plate (5 x 9 1/2 diamond shape). Good enough to weld to the stick? I can put a doubler between the stick and mount plate, but it would add length only as there is barely enough width to step the plates. Jim

 

[SSdoxie]

Thanks guys. I should clarify that the cylinder mount ears are on a 5/8 thick mount plate (5 x 9 1/2 diamond shape). Good enough to weld to the stick? I can put a doubler between the stick and mount plate, but it would add length only as there is barely enough width to step the plates. Jim

With that mount plate no need for a doubler. Direct pull will be at the 5" sides and directly in line with the perpendicular side plates and the 9 1/2" diamond shaped length will spread any center stress out far enough.

 

[Arc weld]

Yea, you're good to go. Use 7018 to weld it on.

 

[CJONE]

With all this good info on welding, just to add, be sure to use a cross over relief on the thumb cyl. Even better is a work port relief that dumps to tank on the extend side [base] of the cyl. Most who do not do this end up with a bent cyl. CJ

 

[firemanmike69]

With all this good info on welding, just to add, be sure to use a cross over relief on the thumb cyl. Even better is a work port relief that dumps to tank on the extend side [base] of the cyl. Most who do not do this end up with a bent cyl. CJ

I've always just set the circuit relief and never had any troubles