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Part 1 of N (probably 3) of building a wooden model Liebherr 9800 mining excavator for my son. This part will focus on building the tracks and running gear.

Finished product here: https://pic8.co/sh/68lZs0.jpg https://poal.co/s/Woodworking/720966

The track segments are made from two parts, a Y shaped link and an inverted U shaped plate. There are around 65 links per track, I made about 150 of each part so that I would have some spares. These parts are quite small, so work holding was always going to be a challenge.

To create the plates, strips of wood (some sort of hardwood, likely a Eucalypt of some sort) were cut to the required width and height. Tine tuning of this was done with a planing jig. https://pic8.co/sh/Do4ib3.jpg https://pic8.co/sh/b7dzYh.jpg

These were taped together to cut to length in small groups. https://pic8.co/sh/Zj3LaY.jpg

Now I had a pile of tiny bits of wood. To make further cuts I would need something to hold them, so I made some wooden jigs to hold a reasonable number of parts to be cut on the table saw. Using my dial indicator against the table saw fence, I was able to fine tune the width of the cut so that (in theory) all the pieces would be a snug fit over the links. https://pic8.co/sh/NyJ7gq.jpg https://pic8.co/sh/c0MvF4.jpg

An additional jig was made to hold the partially finished plates so that the side bevels could be created with a block plane. https://pic8.co/sh/FC7hts.jpg https://pic8.co/sh/gGVosC.jpg

The link pieces were cut in a similar manner, then the pin holes were drilled using my (new at that time) milling machine so that I could maintain precise spacing. In hindsight, it would have been easier/quicker to make a jig to hold them and just use the vertical drill press. I ended up having to drill through from each side, as the small (2mm) drill bit would often wander due to density differences in the grain of the wood. https://pic8.co/sh/GMPjwY.jpg

Yet another jig was made to hold a set of links so that the rabbet portion of the Y shape could be cut. This involved holding the links in a position relative to the hole, then cutting a known depth into them. My saw blade is pretty dull and dirty here, leaving scorch marks, but these will be cleaned up later anyway. https://pic8.co/sh/C74nNr.jpg https://pic8.co/sh/7X5EM3.jpg https://pic8.co/sh/cF9WKB.jpg

Cutting the tenons to form the rest of the Y shape required another jig. The base of the Y was cut until it was a size that would (in theory) fit snugly, but not too tightly, in the throat of the Y. https://pic8.co/sh/4ocKBn.jpg https://pic8.co/sh/WGpK5w.jpg

This left me with roughly Y shaped links, but they had square corners. The corners needed to be rounded, and the inner edges trimmed to ~45 degrees to give clearance when flexing around the wheels. I made a simple jig to hold them in position to round the ends on my sanding disk. However, the wood quickly scorched and gunked up the sanding disk and made an all round mess. As an alternative, I made chiseled a pocket in a scrap of wood to mount the links in and trim the corners with a sharp chisel, this sufferer some wear during the process. https://pic8.co/sh/k6Oxl6.jpg https://pic8.co/sh/A5uFwL.jpg

Things were finally starting to take shape. More fettling would be needed, trimming the shoulders of the Y to ensure enough clearance without sacrificing too much strength. Some links broke due to inherent weaknesses in the wood, which was why I made more than needed. https://pic8.co/sh/k2U8Mc.jpg

Fitting the links together (2mm bamboo skewers were used as pins) was probably the most time consuming part. This was fiddly, but it got done eventually. I managed to only injure myself badly once, when I was tired and held a link in the wrong orientation, the wood split and my quite sharp 1/4" chisel managed to slice through my thumb and middle finger and stab into my index finger quite deeply. There was quite a lot of blood, but they healed quickly, being very clean cuts. https://pic8.co/sh/ji9xyQ.jpg

With the links connected, it was time to attach the plates. Before they could be glued on, a small notch needed to be cut out to give clearance for the joints to flex (if everything was perfect to the micron, this would probably not be necessary, but it's wood and made by hand, so there are variables). https://pic8.co/sh/y9Q1Kg.jpg

Once the notches were cut, it was a matter of carefully gluing the plates over the links. This greatly strengthened the whole assembly. https://pic8.co/sh/UEbbT3.jpg https://pic8.co/sh/gyP2o0.jpg https://pic8.co/sh/zLBjgU.jpg

Now that I had tracks, I needed to make the running gear. Templates for the various parts were printed out based on my design (which was done in SketchUp). There were two thicker (9mm) parts that were the backing plates, these would be attached to the turntable base and act as mounting points for the track assemblies. There were also two inner frames and two outer frames, 6mm and 5mm thick respectively. The thicker inner frame was designed to give clearance to the tracks. Of key importance here was ensuring that the holes for the various parts were accurately aligned. This was achieved by pinning already drilled holes in place with dowels while drilling the remaining ones. https://pic8.co/sh/Q2f4RH.jpg

The inner corners of the frames were created with a forstner bit, giving a consistent radius, then the remainder cut, planed & chiseled out. https://pic8.co/sh/Y4WJYh.jpg

Between the two frames, a block that would house the track tensioning spring was made. This block has scallops cut in the top for clearance of the top idlers. They also have two longitudinal holes drilled about 70mm deep to guide the tensioning wheel. https://pic8.co/sh/yDSQPV.jpg https://pic8.co/sh/9KfxFF.jpg

The frames were now roughly complete. https://pic8.co/sh/uzAP8V.jpg

The next step was wheels. The two larger wheels on each end were created from three pieces each. Two thin plates that would ride on the inside of the track plates, and a smaller inner hub that would give clearance to the track links. The side plates were made by drilling a center hole in a roughly round piece, then turning it to size on the lathe using a mandrel and pressure plate to hold them in place. https://pic8.co/sh/l9I0ap.jpg https://pic8.co/sh/OFigc4.jpg

Once the pieces were finished they were glued together, then mounted back into the lathe where the final 10mm center hole was drilled. https://pic8.co/sh/iJ3jR0.jpg

The idler wheels, of which there were 11 per side, were made by pre-drilling the center holes then cutting strips of hardwood into rough squares slightly larger than the final desired diameter. These were roughly trimmed into octagonal shapes by cutting the corners off with a chisel, then mounted onto a mandrel 12 at a time (resulting in 4 spares) and turned/sanded to size. These wheels were then glued onto lengths of 6.5mm dowel, after which the inner edges were tapered slightly to reduce the chances of catching on slightly misaligned track links. https://pic8.co/sh/gCA4kt.jpg https://pic8.co/sh/d1g0Ct.jpg https://pic8.co/sh/py5OX0.jpg https://pic8.co/sh/8uxFHW.jpg

The suspension components were next, each track has double walking beam suspension for the lower idler wheels, allowing the tracks to run over uneven surfaces without creating high point loads that could result in breaking. The main walking beams were made from some random wood, it was quite dark and soft, no idea what it actually was. The required holes were drilled and the pieces shaped. The overall shape was required to allow the desired range of motion of the suspension parts, it also looked pretty cool. https://pic8.co/sh/r0dos6.jpg

The secondary beams were formed as small triangles where the top hole was a press fit on a 6.5mm dowel, while the lower holes were a running fit. Holes were drilled first, using one piece as a template for the others. Then sets of 4 were clamped into a jig to cut the sides on the table saw, the holes being used to align the parts. Corner radiuses were roughly cut on the table saw jig, and sanded to final finish. https://pic8.co/sh/DwnkmE.jpg https://pic8.co/sh/vWzk8U.jpg

Originally, I had planned to glue the track assemblies together. However, since this will be actively played with by a child, even a careful one, the likelihood of damage to the tracks is very high. They could also get clogged with pet hair, etc. requiring cleaning. So, I changed my mind and modified the design to allow for disassembly of the tracks. To accomplish this, I would need some sort of fastener to hold everything together. Wood screws might work, but could fail over time due to the repeated strain put on these parts. Instead, I settled on a custom bolt design that would use a long turnbuckle to tighten both sides simultaneously. This meant that one side would be right hand thread and the other left hand thread. The bolts would go through the holes that the suspension beams pivot on, doing double duty. To hold roughly even pressure on the sides of the tracks, I created a weird looking bolt head that had a stubby pin on one side. From the outside, the bolt head looks like a round plate with two rivets. The bolt heads were made by drilling two holes into a 25mm rod, then parting off 2mm lengths of this. This was a sphincter clenching experience, as the parting involved a significant interrupted cut. I managed, slowly, to part off all 4 pieces. In hindsight, it probably would have been easier to make a jig to hold a 2mm disk in the mill and drill the holes in each. https://pic8.co/sh/LtoSCQ.jpg https://pic8.co/sh/PliJpT.jpg https://pic8.co/sh/oOBG1b.jpg https://pic8.co/sh/MlCrTJ.jpg https://pic8.co/sh/BkISWu.jpg

Finishing

Now that all the parts were made (I didn't detail the tensioner wheel frame because apparently I didn't take any photos of that), the only thing left was to finish them and assemble. The tracks (the outer plates) were ebonized with iron acetate. Once darkened, all of the parts were oiled with Danish Oil before being finally assembled. https://pic8.co/sh/NB4jG5.jpg https://pic8.co/sh/qmCOGJ.jpg https://pic8.co/sh/ifA2Au.jpg

The assembled tracks can be bolted on to the sides of the base. Four 10mm dowels provide alignment and load transfer of the track assemblies to the frames. https://pic8.co/sh/yxIdZO.jpg

Dog wants to come inside: https://pic8.co/sh/xxgon2.jpg

Part 1 of N (probably 3) of building a wooden model Liebherr 9800 mining excavator for my son. This part will focus on building the tracks and running gear. Finished product here: https://pic8.co/sh/68lZs0.jpg https://poal.co/s/Woodworking/720966 The track segments are made from two parts, a Y shaped link and an inverted U shaped plate. There are around 65 links per track, I made about 150 of each part so that I would have some spares. These parts are quite small, so work holding was always going to be a challenge. To create the plates, strips of wood (some sort of hardwood, likely a Eucalypt of some sort) were cut to the required width and height. Tine tuning of this was done with a planing jig. https://pic8.co/sh/Do4ib3.jpg https://pic8.co/sh/b7dzYh.jpg These were taped together to cut to length in small groups. https://pic8.co/sh/Zj3LaY.jpg Now I had a pile of tiny bits of wood. To make further cuts I would need something to hold them, so I made some wooden jigs to hold a reasonable number of parts to be cut on the table saw. Using my dial indicator against the table saw fence, I was able to fine tune the width of the cut so that (in theory) all the pieces would be a snug fit over the links. https://pic8.co/sh/NyJ7gq.jpg https://pic8.co/sh/c0MvF4.jpg An additional jig was made to hold the partially finished plates so that the side bevels could be created with a block plane. https://pic8.co/sh/FC7hts.jpg https://pic8.co/sh/gGVosC.jpg The link pieces were cut in a similar manner, then the pin holes were drilled using my (new at that time) milling machine so that I could maintain precise spacing. In hindsight, it would have been easier/quicker to make a jig to hold them and just use the vertical drill press. I ended up having to drill through from each side, as the small (2mm) drill bit would often wander due to density differences in the grain of the wood. https://pic8.co/sh/GMPjwY.jpg Yet another jig was made to hold a set of links so that the rabbet portion of the Y shape could be cut. This involved holding the links in a position relative to the hole, then cutting a known depth into them. My saw blade is pretty dull and dirty here, leaving scorch marks, but these will be cleaned up later anyway. https://pic8.co/sh/C74nNr.jpg https://pic8.co/sh/7X5EM3.jpg https://pic8.co/sh/cF9WKB.jpg Cutting the tenons to form the rest of the Y shape required another jig. The base of the Y was cut until it was a size that would (in theory) fit snugly, but not too tightly, in the throat of the Y. https://pic8.co/sh/4ocKBn.jpg https://pic8.co/sh/WGpK5w.jpg This left me with roughly Y shaped links, but they had square corners. The corners needed to be rounded, and the inner edges trimmed to ~45 degrees to give clearance when flexing around the wheels. I made a simple jig to hold them in position to round the ends on my sanding disk. However, the wood quickly scorched and gunked up the sanding disk and made an all round mess. As an alternative, I made chiseled a pocket in a scrap of wood to mount the links in and trim the corners with a sharp chisel, this sufferer some wear during the process. https://pic8.co/sh/k6Oxl6.jpg https://pic8.co/sh/A5uFwL.jpg Things were finally starting to take shape. More fettling would be needed, trimming the shoulders of the Y to ensure enough clearance without sacrificing too much strength. Some links broke due to inherent weaknesses in the wood, which was why I made more than needed. https://pic8.co/sh/k2U8Mc.jpg Fitting the links together (2mm bamboo skewers were used as pins) was probably the most time consuming part. This was fiddly, but it got done eventually. I managed to only injure myself badly once, when I was tired and held a link in the wrong orientation, the wood split and my quite sharp 1/4" chisel managed to slice through my thumb and middle finger and stab into my index finger quite deeply. There was quite a lot of blood, but they healed quickly, being very clean cuts. https://pic8.co/sh/ji9xyQ.jpg With the links connected, it was time to attach the plates. Before they could be glued on, a small notch needed to be cut out to give clearance for the joints to flex (if everything was perfect to the micron, this would probably not be necessary, but it's wood and made by hand, so there are variables). https://pic8.co/sh/y9Q1Kg.jpg Once the notches were cut, it was a matter of carefully gluing the plates over the links. This greatly strengthened the whole assembly. https://pic8.co/sh/UEbbT3.jpg https://pic8.co/sh/gyP2o0.jpg https://pic8.co/sh/zLBjgU.jpg Now that I had tracks, I needed to make the running gear. Templates for the various parts were printed out based on my design (which was done in SketchUp). There were two thicker (9mm) parts that were the backing plates, these would be attached to the turntable base and act as mounting points for the track assemblies. There were also two inner frames and two outer frames, 6mm and 5mm thick respectively. The thicker inner frame was designed to give clearance to the tracks. Of key importance here was ensuring that the holes for the various parts were accurately aligned. This was achieved by pinning already drilled holes in place with dowels while drilling the remaining ones. https://pic8.co/sh/Q2f4RH.jpg The inner corners of the frames were created with a forstner bit, giving a consistent radius, then the remainder cut, planed & chiseled out. https://pic8.co/sh/Y4WJYh.jpg Between the two frames, a block that would house the track tensioning spring was made. This block has scallops cut in the top for clearance of the top idlers. They also have two longitudinal holes drilled about 70mm deep to guide the tensioning wheel. https://pic8.co/sh/yDSQPV.jpg https://pic8.co/sh/9KfxFF.jpg The frames were now roughly complete. https://pic8.co/sh/uzAP8V.jpg The next step was wheels. The two larger wheels on each end were created from three pieces each. Two thin plates that would ride on the inside of the track plates, and a smaller inner hub that would give clearance to the track links. The side plates were made by drilling a center hole in a roughly round piece, then turning it to size on the lathe using a mandrel and pressure plate to hold them in place. https://pic8.co/sh/l9I0ap.jpg https://pic8.co/sh/OFigc4.jpg Once the pieces were finished they were glued together, then mounted back into the lathe where the final 10mm center hole was drilled. https://pic8.co/sh/iJ3jR0.jpg The idler wheels, of which there were 11 per side, were made by pre-drilling the center holes then cutting strips of hardwood into rough squares slightly larger than the final desired diameter. These were roughly trimmed into octagonal shapes by cutting the corners off with a chisel, then mounted onto a mandrel 12 at a time (resulting in 4 spares) and turned/sanded to size. These wheels were then glued onto lengths of 6.5mm dowel, after which the inner edges were tapered slightly to reduce the chances of catching on slightly misaligned track links. https://pic8.co/sh/gCA4kt.jpg https://pic8.co/sh/d1g0Ct.jpg https://pic8.co/sh/py5OX0.jpg https://pic8.co/sh/8uxFHW.jpg The suspension components were next, each track has double walking beam suspension for the lower idler wheels, allowing the tracks to run over uneven surfaces without creating high point loads that could result in breaking. The main walking beams were made from some random wood, it was quite dark and soft, no idea what it actually was. The required holes were drilled and the pieces shaped. The overall shape was required to allow the desired range of motion of the suspension parts, it also looked pretty cool. https://pic8.co/sh/r0dos6.jpg The secondary beams were formed as small triangles where the top hole was a press fit on a 6.5mm dowel, while the lower holes were a running fit. Holes were drilled first, using one piece as a template for the others. Then sets of 4 were clamped into a jig to cut the sides on the table saw, the holes being used to align the parts. Corner radiuses were roughly cut on the table saw jig, and sanded to final finish. https://pic8.co/sh/DwnkmE.jpg https://pic8.co/sh/vWzk8U.jpg Originally, I had planned to glue the track assemblies together. However, since this will be actively played with by a child, even a careful one, the likelihood of damage to the tracks is very high. They could also get clogged with pet hair, etc. requiring cleaning. So, I changed my mind and modified the design to allow for disassembly of the tracks. To accomplish this, I would need some sort of fastener to hold everything together. Wood screws might work, but could fail over time due to the repeated strain put on these parts. Instead, I settled on a custom bolt design that would use a long turnbuckle to tighten both sides simultaneously. This meant that one side would be right hand thread and the other left hand thread. The bolts would go through the holes that the suspension beams pivot on, doing double duty. To hold roughly even pressure on the sides of the tracks, I created a weird looking bolt head that had a stubby pin on one side. From the outside, the bolt head looks like a round plate with two rivets. The bolt heads were made by drilling two holes into a 25mm rod, then parting off 2mm lengths of this. This was a sphincter clenching experience, as the parting involved a significant interrupted cut. I managed, slowly, to part off all 4 pieces. In hindsight, it probably would have been easier to make a jig to hold a 2mm disk in the mill and drill the holes in each. https://pic8.co/sh/LtoSCQ.jpg https://pic8.co/sh/PliJpT.jpg https://pic8.co/sh/oOBG1b.jpg https://pic8.co/sh/MlCrTJ.jpg https://pic8.co/sh/BkISWu.jpg Finishing Now that all the parts were made (I didn't detail the tensioner wheel frame because apparently I didn't take any photos of that), the only thing left was to finish them and assemble. The tracks (the outer plates) were ebonized with iron acetate. Once darkened, all of the parts were oiled with Danish Oil before being finally assembled. https://pic8.co/sh/NB4jG5.jpg https://pic8.co/sh/qmCOGJ.jpg https://pic8.co/sh/ifA2Au.jpg The assembled tracks can be bolted on to the sides of the base. Four 10mm dowels provide alignment and load transfer of the track assemblies to the frames. https://pic8.co/sh/yxIdZO.jpg ---- Dog wants to come inside: https://pic8.co/sh/xxgon2.jpg

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