Hind Axle and Shafting (September 2014 - August 2016)
Spacing With The Third Shaft
When the project was inspected it was found that the hind axle, which had been made to size, didn't quite fit through both of the bearing blocks, this was found to be due to the horn plates being slightly twisted and the bearing being mounted a few thou off where they needed to be. However, that said the horn plates did line up accurately with the boiler and the crank, second and third shaft ran nicely in their respective bearing blocks. Thus, the horn plates need to stay were they were and either shaft or hind axle bearings needed to be fettled to suit.
Before modifying anything the mesh of the compensating gear and the spur gear on the third shaft was also inspected and found to be too tight when in position. This cause of this was later identified to be the effective diameter of the compensating centre was about 0.4 mm larger than specification. Thus, I deducted that the as the hole centers between the bearing blocks on the horn plates were pretty much spot on, they must have been made before the hub of the compensating centre was machined, and thus the error was unknown.
Spacing With The Third Shaft
When the project was inspected it was found that the hind axle, which had been made to size, didn't quite fit through both of the bearing blocks, this was found to be due to the horn plates being slightly twisted and the bearing being mounted a few thou off where they needed to be. However, that said the horn plates did line up accurately with the boiler and the crank, second and third shaft ran nicely in their respective bearing blocks. Thus, the horn plates need to stay were they were and either shaft or hind axle bearings needed to be fettled to suit.
Before modifying anything the mesh of the compensating gear and the spur gear on the third shaft was also inspected and found to be too tight when in position. This cause of this was later identified to be the effective diameter of the compensating centre was about 0.4 mm larger than specification. Thus, I deducted that the as the hole centers between the bearing blocks on the horn plates were pretty much spot on, they must have been made before the hub of the compensating centre was machined, and thus the error was unknown.
At the begin of the project it was found that the rear axle didn’t fit in the bearing blocks when the horn plates were attached to the side of the boiler, whilst in this arrangement the crank, second shaft and the third shaft ran ‘relatively’ smoothly, however this was left as a concern and put to one side and left until now to investigate further. To date, the horn plates had been removed and the bearings reworked, to fit the water pump and tidy up some of the machining, plus oil reservoir caps made for the rear axle bearings and the third shaft. So now was the time to refit the horn plates and investigate further.
As discussed before my Grandad had come across a number of issues when soldering the boiler, one of which was that the fire box had not ended completely perpendicular to the barrel. This resulted in issues with aligning the horn plate fixing holes with the fire box stays. For example, the rear vertical row of 5BA bolts could not be fitted and were thus made as dummies, and a number of holes had to be made at complex angles to ensure the outer appearance retained the rivets in straight rows. All this ultimately resulted in the horn plates not sitting completely true to each other.
After inspection the horn plates were removed again and were assembled, minus the boiler and utilising the spectacle plates to see if the shafts would fit. They did! Thus, the error was identified as being a misalignment between the horn plates and the boiler as result of several fixing holes being out of alignment. This issue took a massive amount of time to fully identify due to the number of fasteners and possible degrees of freedom (plus it was the result of someone else’s work!).
The issue was corrected by easing out the offending holes with a small file and until the plates sat in the correct position. To align everything the engine sat vertically, with the rear (vertical) edges of the horn plates resting on a surface plate. Immediately it was noticed that the crank and second shaft rotated freely in the bearings, however the third shaft was still overly tight and the rear axle was not quite aligned to be fully inserted, but not far off.
The next step undertaken was to check how the shafts fit in the bearings and weather there was any angular misalignment when the shaft were inserted into each bearing (i.e. one bearing at a time). It was found that both shafts were an excellent, verging tight fit in the bearings, which was great but allowed for no misalignment. However when the angle to the surface plate was measured both shafts were off by a fraction of a degree.
The conclusion was therefore drawn: top marks for the shaft to bearing fit, but fail on the angular alignment of the hole in relation to the mating face (the assumption was the bearing mating face was hard to the horn plate!) So a number of actions could be taken, 1) Line bore the bearings and make larger shafts, 2) line bore and press in sleeves then line bore the sleeves to suit the shafts, or 3) ease out the existing holes to see if alignment could be found.
Option 3 was taken as even if it didn’t work then any modified surfaces in the bearings would have to be bored out to complete option 1&2 so there was nothing to lose. For the third shaft a 9/16” reamer was used to ‘ease’ the holes into alignment. It was possible to start with the reamer engaged in both bearings as the alignment was already pretty close and a few passes with the reamer through both holes opened the holes nicely and allowed the shaft to pass through with a resulting excellent fit.
The rear axle was still a problem because when inserted in the bearings there was approximately 0.5mm of misalignment, which prevented the problem from being directly corrected with a ¾” reamer engaging from both sides thus a slightly cruder method was used! A 4 flute end mill was chucked in a large drill chuck, inserted into the bearing and then the hole opened using hand pressure. As the bearing was cast iron it cut freely and with a minimal amount of fettling allowed for sufficient alignment to enable the reamer to be passed through both bearings. A few twists of the reamer and the shaft fitted smoothly.
I expect that if the bearing was subsequently sectioned then it would be found that the axle was only running on a small portion of the bearing surface, which is not completely ideal and will no doubt result in premature wear and early effects of backlash, however, in reality, this concession can be lived with. Should the engine actually be used sufficiently that wear becomes unmanageable then the bearings can be line bored and sleeved at a later date. Plus by this point the horn plates will also be final fitted and secured by the tender, which will allow for greater rigidity when machining. Result, rear shaft complete - no further action.
Gear Depthing
Rear axle – 3rd. This was the first opportunity for all the gears and shafts to be fitted to the engine to check for free running, engagement, backlash etc. Knowing that I had previously doubted the rear axle to 3rd shaft depthing, this is where I started. The compensation gear was fitted to the rear axle and the small spur gear temporarily pressed onto the 3rd shaft, to my delight the shafts both fitted and the engagement was tight but ran freely with very minimal backlash. This was a result as neither of the shafts have any adjustment!
3rd – 2nd. When the project was started it was already identified that there as a number of shims between the 2nd bearing and bearing cup, however these had become ‘shuffled’, thus it is was best to start again and find the required arrangement. The 2nd shaft did need an arrangement of shims under both bearings to allow correct meshing with the 3rd shaft, however an excellent fit was achieved.
2nd – Crank
No adjustment was required.
2nd Shaft Locking Ring
The second shaft includes a locking ring which acts on the inner face of the right hand bearing and holds the shaft in position. The location was identified using the output gear and gear selector splines as references and a piece of 0.1mm shim (cut in a U shape) used to maintain the running clearance. Once the correct location was decided the shaft, ring, bearing and gear assembly was moved to the mill and clamped down. The drawings states a 3/32pin should be used, however I used a taper pin which was about 2.2mm at the lower (smallest end). The hole location was set in the centre of the ring and drilled through to 2.2mm and then a 7/64 taper reamer (1:100) used to gently open the hole to a taper. The pin was tapped home and the ends finished flush with a file.
Keyways And Shaft Length
To finalise the shafts the lengths needed taking down to final length and the keys needed making.
Rear Axle
This shaft requires two keys to be made, one for the inner hub of the compensation centre and the other for the right hand driving hub. Both were made from 1/8” square section key steel, and both required the height of the key to be slightly machined down as when aligned the height of the slot was just under 1/8”. However, both keys fitted snugly and provided a backlash free drive.
3rd Shaft
The output end of the 3rd shaft was machined as an interference fit, flush with the outer hub of the spur gear. A square key was cut from the key steel and engaged in the slot and the gear pressed firmly in position. All being well this gear will never have to be removed again!
The input end engages with the break wheel and large spur gear assembly, the shaft had been left long and need to be turned to length (which in hindsight would have been easier without the output gear pressed on the other end!). The shaft was left just proud of the gear hub (1.5mm) and this distance would then be repeated for the 2nd and crank shafts.
A tapered gib key was machined for this position from a piece of steel gauge plate. A gib key was a new experience for me and I have to admit that I scrapped two before getting it right! Neither the book nor the drawings detail the dimensions or even refer to these features, so I had to go free lance on these parts. I took the overall scale of the design from various pictures that I could find online and then made the set to match.
I milled the upper surfaces and gib end of the key first, then flipped the key over in the milling vice and set it at a very slight angle. The height of the opening of the shaft/hub key slot was measured and the lower face of the key machined to 0.2mm wider. The key was then test fitted in the slot (the first two made fell into the slot and were therefore scrapped!) to see how far it engaged. It was then a session with emery paper on a surface plate to slowly reduce the height until the key slid into position leaving a gap of about 2mm between the gib and the face of the gear hub. A gap such as this should allow the key to be tapped into a flush tight fit on final assembly and still allow removal.
2nd Shaft and Crank
The crank key (for the flywheel) was identical to the 3rd shaft key except for the height which was reduced to suit. The 2nd shaft gib key is thinner than the others and was therefore scaled down, including the height of the gib end to suit. The crank was already taken to finished length however both ends of the 2nd shaft needed taking back to allow for a uniform 1.5mm extension.
So gearing was completed, the horn plates were attached to the boiler (all be it temporarily, however in the final alignment) and all shafts run freely and gears mesh sweetly! So a good result.
As discussed before my Grandad had come across a number of issues when soldering the boiler, one of which was that the fire box had not ended completely perpendicular to the barrel. This resulted in issues with aligning the horn plate fixing holes with the fire box stays. For example, the rear vertical row of 5BA bolts could not be fitted and were thus made as dummies, and a number of holes had to be made at complex angles to ensure the outer appearance retained the rivets in straight rows. All this ultimately resulted in the horn plates not sitting completely true to each other.
After inspection the horn plates were removed again and were assembled, minus the boiler and utilising the spectacle plates to see if the shafts would fit. They did! Thus, the error was identified as being a misalignment between the horn plates and the boiler as result of several fixing holes being out of alignment. This issue took a massive amount of time to fully identify due to the number of fasteners and possible degrees of freedom (plus it was the result of someone else’s work!).
The issue was corrected by easing out the offending holes with a small file and until the plates sat in the correct position. To align everything the engine sat vertically, with the rear (vertical) edges of the horn plates resting on a surface plate. Immediately it was noticed that the crank and second shaft rotated freely in the bearings, however the third shaft was still overly tight and the rear axle was not quite aligned to be fully inserted, but not far off.
The next step undertaken was to check how the shafts fit in the bearings and weather there was any angular misalignment when the shaft were inserted into each bearing (i.e. one bearing at a time). It was found that both shafts were an excellent, verging tight fit in the bearings, which was great but allowed for no misalignment. However when the angle to the surface plate was measured both shafts were off by a fraction of a degree.
The conclusion was therefore drawn: top marks for the shaft to bearing fit, but fail on the angular alignment of the hole in relation to the mating face (the assumption was the bearing mating face was hard to the horn plate!) So a number of actions could be taken, 1) Line bore the bearings and make larger shafts, 2) line bore and press in sleeves then line bore the sleeves to suit the shafts, or 3) ease out the existing holes to see if alignment could be found.
Option 3 was taken as even if it didn’t work then any modified surfaces in the bearings would have to be bored out to complete option 1&2 so there was nothing to lose. For the third shaft a 9/16” reamer was used to ‘ease’ the holes into alignment. It was possible to start with the reamer engaged in both bearings as the alignment was already pretty close and a few passes with the reamer through both holes opened the holes nicely and allowed the shaft to pass through with a resulting excellent fit.
The rear axle was still a problem because when inserted in the bearings there was approximately 0.5mm of misalignment, which prevented the problem from being directly corrected with a ¾” reamer engaging from both sides thus a slightly cruder method was used! A 4 flute end mill was chucked in a large drill chuck, inserted into the bearing and then the hole opened using hand pressure. As the bearing was cast iron it cut freely and with a minimal amount of fettling allowed for sufficient alignment to enable the reamer to be passed through both bearings. A few twists of the reamer and the shaft fitted smoothly.
I expect that if the bearing was subsequently sectioned then it would be found that the axle was only running on a small portion of the bearing surface, which is not completely ideal and will no doubt result in premature wear and early effects of backlash, however, in reality, this concession can be lived with. Should the engine actually be used sufficiently that wear becomes unmanageable then the bearings can be line bored and sleeved at a later date. Plus by this point the horn plates will also be final fitted and secured by the tender, which will allow for greater rigidity when machining. Result, rear shaft complete - no further action.
Gear Depthing
Rear axle – 3rd. This was the first opportunity for all the gears and shafts to be fitted to the engine to check for free running, engagement, backlash etc. Knowing that I had previously doubted the rear axle to 3rd shaft depthing, this is where I started. The compensation gear was fitted to the rear axle and the small spur gear temporarily pressed onto the 3rd shaft, to my delight the shafts both fitted and the engagement was tight but ran freely with very minimal backlash. This was a result as neither of the shafts have any adjustment!
3rd – 2nd. When the project was started it was already identified that there as a number of shims between the 2nd bearing and bearing cup, however these had become ‘shuffled’, thus it is was best to start again and find the required arrangement. The 2nd shaft did need an arrangement of shims under both bearings to allow correct meshing with the 3rd shaft, however an excellent fit was achieved.
2nd – Crank
No adjustment was required.
2nd Shaft Locking Ring
The second shaft includes a locking ring which acts on the inner face of the right hand bearing and holds the shaft in position. The location was identified using the output gear and gear selector splines as references and a piece of 0.1mm shim (cut in a U shape) used to maintain the running clearance. Once the correct location was decided the shaft, ring, bearing and gear assembly was moved to the mill and clamped down. The drawings states a 3/32pin should be used, however I used a taper pin which was about 2.2mm at the lower (smallest end). The hole location was set in the centre of the ring and drilled through to 2.2mm and then a 7/64 taper reamer (1:100) used to gently open the hole to a taper. The pin was tapped home and the ends finished flush with a file.
Keyways And Shaft Length
To finalise the shafts the lengths needed taking down to final length and the keys needed making.
Rear Axle
This shaft requires two keys to be made, one for the inner hub of the compensation centre and the other for the right hand driving hub. Both were made from 1/8” square section key steel, and both required the height of the key to be slightly machined down as when aligned the height of the slot was just under 1/8”. However, both keys fitted snugly and provided a backlash free drive.
3rd Shaft
The output end of the 3rd shaft was machined as an interference fit, flush with the outer hub of the spur gear. A square key was cut from the key steel and engaged in the slot and the gear pressed firmly in position. All being well this gear will never have to be removed again!
The input end engages with the break wheel and large spur gear assembly, the shaft had been left long and need to be turned to length (which in hindsight would have been easier without the output gear pressed on the other end!). The shaft was left just proud of the gear hub (1.5mm) and this distance would then be repeated for the 2nd and crank shafts.
A tapered gib key was machined for this position from a piece of steel gauge plate. A gib key was a new experience for me and I have to admit that I scrapped two before getting it right! Neither the book nor the drawings detail the dimensions or even refer to these features, so I had to go free lance on these parts. I took the overall scale of the design from various pictures that I could find online and then made the set to match.
I milled the upper surfaces and gib end of the key first, then flipped the key over in the milling vice and set it at a very slight angle. The height of the opening of the shaft/hub key slot was measured and the lower face of the key machined to 0.2mm wider. The key was then test fitted in the slot (the first two made fell into the slot and were therefore scrapped!) to see how far it engaged. It was then a session with emery paper on a surface plate to slowly reduce the height until the key slid into position leaving a gap of about 2mm between the gib and the face of the gear hub. A gap such as this should allow the key to be tapped into a flush tight fit on final assembly and still allow removal.
2nd Shaft and Crank
The crank key (for the flywheel) was identical to the 3rd shaft key except for the height which was reduced to suit. The 2nd shaft gib key is thinner than the others and was therefore scaled down, including the height of the gib end to suit. The crank was already taken to finished length however both ends of the 2nd shaft needed taking back to allow for a uniform 1.5mm extension.
So gearing was completed, the horn plates were attached to the boiler (all be it temporarily, however in the final alignment) and all shafts run freely and gears mesh sweetly! So a good result.
Spectacle plate modifications
Once the steam union was fitted the spectacle plate could be completed with the two recesses to clear the two outlets. Again there were no details of this on the drawings (at least that I could find!), so the actual dimensions needed to be taken from the job. This was a simple measuring and marking out task and the slots were milled into the plate.
Whilst the spectacle plate was off I took the opportunity to fit the pressure gauge bezel. Again the drawings were very vague on where this should sit so a best fit position was identified and the bezel clamped on with a small tool makers clamp and the tiny 12BA holes produced.
Gear selector attachment
The holes were already drilled in the spectacle plate for the gear selector bracket (@ #50), however again there was no detail on the drawings as the nature of the bolting arrangement to be used. I opted to tap the holes to 8BA and cut the bolts off flush so that they would not interfere with the pressure gauge mounting position on the drivers side of the spectacle plate. Now the 2nd shaft was complete the gear selector bracket could be held in place with a clamp and the operation checked. When I was content with the position the holes were spotted though on to the gear selector bracket.
Whilst checking the operation it was noticed that the selector did not have sufficient thrown to fully engage low and high gear, thus the bracket was shortened slightly to allow the lever to travel slightly further.