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Excavator thumb

priemsy1

Member
Joined
May 27, 2023
Messages
17
Location
Australia
I have a CAT 305.5 D and a Hydraulic thumb. There weren't any instructions with the thumb so I will have to wing it.
 

Tinkerer

Senior Member
Joined
May 21, 2009
Messages
9,342
Location
The shore of the illinois river USA
The serial number of your 305 will be needed.
You bought a thumb for the machine and need help installing it ???
Who is the manufacturer of the thumb ?
Is it pin mounted on the bucket, or does it need to have brackets welded on the dipper ???
Is the backhoe plumbed for a thumb or, do you need help with that to ??

One picture is worth a thousand words.
 

priemsy1

Member
Joined
May 27, 2023
Messages
17
Location
Australia
The serial number of your 305 will be needed.
You bought a thumb for the machine and need help installing it ???
Who is the manufacturer of the thumb ?
Is it pin mounted on the bucket, or does it need to have brackets welded on the dipper ???
Is the backhoe plumbed for a thumb or, do you need help with that to ??

One picture is worth a thousand words.
The 305.5 is a mini excavator. The thumb is locally Aus manufactured ( Aus buckets) and a weld on. The machine is plumbed for attachments. I just need to work out the right spot to fix it on the stick.
 

Tags

Senior Member
Joined
Feb 19, 2012
Messages
1,610
Location
Connecticut
I believe that you want the lower edge of the main pin bushing of the thumb to be roughly 1” from the edge of the ears of the bucket/coupler when it is curled all the way in. Not 100% sure, it’s been a while since I installed one.
 

priemsy1

Member
Joined
May 27, 2023
Messages
17
Location
Australia
I believe that you want the lower edge of the main pin bushing of the thumb to be roughly 1” from the edge of the ears of the bucket/coupler when it is curled all the way in. Not 100% sure, it’s been a while since I installed one.
Thanks, Tags. That's what I needed to know.
 

joe--h

Senior Member
Joined
Jul 22, 2009
Messages
1,259
Location
Utah
Wouldn't asking the manufacturer make more sense than asking a bunch of people who have never seen one and aren't there to see it ?

Joe H
 

Welder Dave

Senior Member
Joined
Oct 11, 2014
Messages
12,257
Location
Canada
Clamping or temporarily tacking it in place could work. I think you'd want to fit the thumb so it aligns properly with the bucket when the bucket is straight out from the stick or slightly forward of that. You don't want the thumb going inside the bucket and you don't want the thumb 6in. past the bucket. There are probably mounting instructions on the internet if the manufacturer can't provide them.
 

JD955SC

Senior Member
Joined
Mar 13, 2011
Messages
1,349
Location
The South
Clamping or temporarily tacking it in place could work. I think you'd want to fit the thumb so it aligns properly with the bucket when the bucket is straight out from the stick or slightly forward of that. You don't want the thumb going inside the bucket and you don't want the thumb 6in. past the bucket. There are probably mounting instructions on the internet if the manufacturer can't provide them.

Yes you will want to tack (with substantial tacks!) and make sure of fitment, travel, interference with bucket teeth, etc before final weld up


You really need to get the instructions from the manufacturer for the installation. That should give you positioning instructions and weld procedure. For Cat typically you will not weld across the stick, they don’t like that.

Cat can also supply the valving/fittings to install a small valve block upstream of the final aux valve block allowing the thumb to be shut off when stowed and another tool being run

And MOST IMPORTANT! You will need to tee in a gauge and set the pressures on the aux circuit relief so that the thumb can be overcome and collapsed by the bucket and also so that when stalled out the thumb is not getting to much pressure. If you do not do this you can bend or snap the thumb cylinder rod. This valve on the smaller equipment is set manually with an Allen wrench and a regular wrench for the lock nut.
 

Welder Dave

Senior Member
Joined
Oct 11, 2014
Messages
12,257
Location
Canada
Yes, don't weld across the stick, only length wise and use 7018 or equivalent wire welded by someone with enough experience. You don't want it breaking or twisting.
 

Acoals

Senior Member
Joined
Dec 15, 2019
Messages
1,273
Location
Wisconsin
Occupation
Jack of all trades/Master of none
Yes, don't weld across the stick, only length wise and use 7018 or equivalent wire welded by someone with enough experience. You don't want it breaking or twisting.

Why ought it not be welded across the stick?
 

chidog

Senior Member
Joined
Jun 21, 2021
Messages
770
Location
kent, wa
Yes, don't weld across the stick, only length wise and use 7018 or equivalent wire welded by someone with enough experience. You don't want it breaking or twisting.
Have to keep the water out of there some how. I as well prefer it to be like a fish plate with 45 degree vee's, but then a bead that runs inline parallel to beam that strings off each corner is a good preventative measure after the non lengthwise bead. I always like full (for lack of a term) circle welds to keep water out, water will just start the rust process inside where the welds were made.
 

priemsy1

Member
Joined
May 27, 2023
Messages
17
Location
Australia
Yes you will want to tack (with substantial tacks!) and make sure of fitment, travel, interference with bucket teeth, etc before final weld up


You really need to get the instructions from the manufacturer for the installation. That should give you positioning instructions and weld procedure. For Cat typically you will not weld across the stick, they don’t like that.

Cat can also supply the valving/fittings to install a small valve block upstream of the final aux valve block allowing the thumb to be shut off when stowed and another tool being run

And MOST IMPORTANT! You will need to tee in a gauge and set the pressures on the aux circuit relief so that the thumb can be overcome and collapsed by the bucket and also so that when stalled out the thumb is not getting to much pressure. If you do not do this you can bend or snap the thumb cylinder rod. This valve on the smaller equipment is set manually with an Allen wrench and a regular wrench for the lock nut.
Unfortunately, the manufacturer didn't include instructions but provides any amount of information over the phone. I would have preferred something in writing.
 
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