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Wow! This is going to be a great show. I am happy to see you undertake the undercarriage parts yourself. Just one track frame with sprockets and tracks would be a challenge for anyone. You will surely produce a great model.Tracks are an area of special interest to me since I spent a fair part of my life in the construction equipment industry, mostly involved with surface mining machines. The biggest Caterpillar and Komatsu dozers are used in strip mining and the details of track maintenance and repair constitute a a major share of the operating expense for these huge machines. Draglines and power shovels are also track mounted but they move material by swinging a long boom rather that pushing it around, track wear is less of an expense factor. Lombard's early track design was much more like today's dragline or shovel tracks than they are like modern buldozers. The track pads or plates of today's dozers do not incorporate a pivot pin. They are bolted to links which are pinned together to form the track chain. Lombard's later machines used this link structure but his original machines used pinned pads as you have shown.There are some details of these pads that do not show up in your plan but may be critical in keeping the track in alignment under the machine. These details can be seen in some of the photos and on other views of the manual. I am talking about the four bars on the inside surface of the pad which form guide channels for the track rollers. These are visible on view 81M of the pad. There is also a large lug in the center that is engaged by the deep groove on the sprockets (#77 and 76 Lags on the manual page). The shallow groove in the sprocket engages the roll #89 which is on the pivot pin but the deep groove engages the lug which is located on the narrow part of the pad in the center. For a lightly loaded model, you can probably ignore the lug but I think that the guide channels may be important. It will need a thicker plate to start with the channels milled back to your working dimension. I am pretty sure that the originals were cast. You will still want the deep grove in the sprocket to avoid contact with the shoe. I can't help using current terminology for these track parts. Today, we say pads or shoes instead of lags.Jerry
Chris - I don't know that length makes much difference. There are a lot of pin to pad holes that must be loose enough for the track to flex and it will flex right and left as well as around the sprockets. I see a real challenge in drilling those pivot holes in the padsThe lug doesn't do much for track alignment but the guide chanels may be critical. It is not unusual for a modern dozer to run out of a track if the track is not well maintained and adjusted. Wear of the pivot pins and bushings causes the track to get longer but wear of the sprocket causes it to get smaller and eventually, the difference in pitch will let the sprocket climb out of the track. This usually happens in a turn where there is a lot of side force.You will not likely get enough wear to make a difference but unless you have enough clearance in the pivot pin holes, the track may be too stiff. The Lombard does not have a very tight turning radius and unlike modern dozers, it has a differential to equalize some of the forces. If you run it on grass or snow there may not be much side force and you can run it with skis instead of wheels.
Chris - Big dozers don't have the ability to counter rotate. That is only on the smaller machines using hydrostatic drives. Big dozers with mechanical drive have a clutch and a brake for each track. For a short turn, one track is locked by releasing the clutch and applying the brake. The other track can run forward or reverse to swing the machine. There were two big dozers that could counter rotate but I don't think it was used often. The Euclid dozer had two separate engines and drive trains that could operate independently and the Komatsu 455 had one engine but two independent transmissions, one for each track. Of course things may have changed a bit in the past twenty years. John Deere has been using hydraulic transmissions in bigger machines but they don't compete in the biggest class of dozers.It never hurts to make a few test pieces to see where the sticky parts are.
That's a fine challenge you have set for yourself I will be following along One of this type of log hauler was featured in the German 'Maschinen in Modellbau' magazine a little while ago.
I am sure that you will be happy that you are including the guide channels. You didn't have to go that far to see them. They are clear enough in your first post on this thread in the photo with the rollers. That photo also shows the drive lug. That roller system is a very nice feature and though not used on later track designs looks like it would be very efficient. It brings to mind the recirculating bals in a linear bearing system.By the way, that same photo is also the only one that I have found that clearly shows that there are two roller chains on each track frame, four in all. I was almost sure that there had to be but it took me more than a few looks at that picture before I spotted the inside rollers and chain, peeking through the spokes of the sprocket.
Hi Chris, oh and more , plus or two to wash it down with all sorted!You don't let the grass grow under your feet! Once you get this finished any grass left growing at your place is going to be under threat!Question for you..... How come you are not building a full loco style boiler, ie multi tubes but only a fire tube? Cheers Kerrin