Cat 340D Excavator build

[crueby]

Originally Posted by skeeter

That's a nice looking scratch built bucket!

Thanks Skeeter! Just about to post some new pictures, now that the forum is back up...

[crueby]

Here is a shot of the boom/bucket assembly for the excavator all assembled and ready for the base bracket and lower cylinders.


And a shot of it painted. The yellow is actually from rattle cans of Cat paint, they sell it for touchup and repairs, covers amazingly well for a yellow paint. This is one coat. The black is Duplicolor ceramic engine enamel.

Underneath the boom you can see the little die-cast model that I am scaling up from. Next parts are the steel plates that form the framework that the base of the boom attach to, rough cut plates are in the lower left of the photo.

[crueby]

I am getting the base for the booms pieced together - from the weight of the boom assembly, I am wondering if I'll be able to use the same gear motor for it as I did for inside the booms, given how heavy the parts are. Even with the two cylinders, I may need to go to a larger/more powerful motor for this last one, but fortunately there is plenty of room inside the cab block. May wind up with a car seat motor or something like that. Possible that just another gear set will do - the two cylinders need to be kept in sync, so will be driving both from one motor with a line of three gears, motor on the center one. That gear set could be a 2 or 3:1 combination.

[crueby]

Okay, catching up on this side project build - been busy setting up a new computer, and all the time that always takes! Will be better suited for all the CAD work I am doing these days, so well worth the time. Anyway, I got the part in to switch the cylinder pair that holds up the entire boom assembly over to single-start Acme threads vs the original 4-start threads, which were just too aggressive on the movements. Here is the base assembly:

Each cylinder has its own drive shaft - in the picture the one on the right has a small drill chuck on it to make it easier to turn by hand. With the new leadscrews I can turn the shaft and lift/lower the booms with just one cylinder and a reasonable amount of force. Before, that was very difficult. The two shaftws will come back to a common drive gearmotor, have not decided if I'll do a gearbox to link them or use a small chain drive (leaning that way at the moment).
Here is a picture showing the entire assembly, bucket lifted off the table - stays there now, before it could spin the leadscrews and lower itself back, which meant that it would have been putting constant strain on the motors.

Lots of spare shafts and couplers in the foreground from figuring out the whole thing.
Here is a shot showing the part for holding and spinning the cab - there will be a lot of side force at times, so I wanted a strong way to connect things. Wound up with a spare set of tapered roller bearings from a trailer - figure it will be more than strong enough! The gear will be mounted to the track unit underneath, and a motor drive gear in the cab will engage it and turn the cab. There is a slip ring unit there to take the motor leads for the track drive motors down from the cab to the lower unit, but still allow the cab to turn as many full circles as it wants. The spindle will be home made, hollow unlike a normal car axle end to allow the wires through.

[crueby]

Got the sprocket assembly for the chain drive started - using some .250 pitch chain and sprockets from Servo City for these, nice fine chain for small spaces but plenty strong. They sell the master links and link pin removal tool too. I am going to use the same chain for the track drives too. So far have the sprockets on hubs, next will make up a support to hold the sprockets. The output of each shaft will go to one of the cylinders on the main boom via a shaft with universal joints. The input will be from a gear motor onto one of the shafts. So, one motor will frive both cylinders at a matched speed and direction.