Front Wheels (June - Sept 2014)
The front wheels were the first part of this project that was tackled, mainly because they are a stand alone item which could be completed with minimal knowledge of the rest of the engine. Plus, they are a 'mechanical' part of the project, which hopefully allow my skills to improve before any of the steam components are tackled!
Rims
The rims were bought was part of the original batch of casting and were a simple series of turning operations to reach the complete the finished size. One of the more complex elements was aligning the casting on the lathe chuck. It was found that there was only about 0.25 mm of green at a couple of points on the circumference thus the position had to be spot on. To achiebe was found that by loosely holding the casting in the chuck the position could be found by using the tool tip as a position marker and then gently moving the job about and rotating the chuck by hand until the final position was identified. It was a bit of shame the rim didn't have slightly more green as that would have made the job far easier.
The drawings/book say that the spoke fitting holes need to have first one of each group positioned using a dividing head then to use a jig to do the other two in each group. I managed to simplify this by doing all of them in one program on the CNC mill.
Jig
To support the wheel during assembly it was suggested to build a jig, which I did out of aluminium. In hindsight, I should have used MDF or some close grained wood, as it was found that the aluminium rim picked up unsightly scratches every time it was taken in and out.
The front wheels were the first part of this project that was tackled, mainly because they are a stand alone item which could be completed with minimal knowledge of the rest of the engine. Plus, they are a 'mechanical' part of the project, which hopefully allow my skills to improve before any of the steam components are tackled!
Rims
The rims were bought was part of the original batch of casting and were a simple series of turning operations to reach the complete the finished size. One of the more complex elements was aligning the casting on the lathe chuck. It was found that there was only about 0.25 mm of green at a couple of points on the circumference thus the position had to be spot on. To achiebe was found that by loosely holding the casting in the chuck the position could be found by using the tool tip as a position marker and then gently moving the job about and rotating the chuck by hand until the final position was identified. It was a bit of shame the rim didn't have slightly more green as that would have made the job far easier.
The drawings/book say that the spoke fitting holes need to have first one of each group positioned using a dividing head then to use a jig to do the other two in each group. I managed to simplify this by doing all of them in one program on the CNC mill.
Jig
To support the wheel during assembly it was suggested to build a jig, which I did out of aluminium. In hindsight, I should have used MDF or some close grained wood, as it was found that the aluminium rim picked up unsightly scratches every time it was taken in and out.
Tires
The tires were the next to be made from a newly bought length of steel gauge plate. The main challenge with getting these right it to get all the length right. I took the inside diameter of the tire from the outer diameter of the rim, then compensated for the increased diameter to the center of the tire thickness and the required end gaps and ended up with required length of each of the four pieces. The four pieces were then cut from the length and cut and draw filed to 45degs at each end. Gain I used the mill to drill and counter sink the fitting holes, however make the process repeatable I made jig to hole each piece in the milling vice.
Once drilled each of the piece were painstakingly hand bent to suit the rim, which would have the been far easier with a set of rollers! It was only after they were bent that my measurements could be validated, and as luck would have it they were slightly long resulting in one of the gaps being a shade to small. I corrected this by taking a shade off a couple of the ends to balance the error out.
To fit the tires the rim was loaded into the jig which allowed the rim to sit the required distance into the jig such that the tire could be rested on the jig in the knowledge that it was central. Each of the tires was in turn clamped using small tool makes clamps and then starting from the inside the holes were drilled through and 3/3"2 iron rivets fitted. Each rivet was inserted form inside to out and cut to sign length that when hammered it filled the countersink and left itself slightly proud. It must be said this was a lot more difficult that in sounds, as the tires tended to move on the clamps and the rivets are very difficult to get uniform.
The tires were the next to be made from a newly bought length of steel gauge plate. The main challenge with getting these right it to get all the length right. I took the inside diameter of the tire from the outer diameter of the rim, then compensated for the increased diameter to the center of the tire thickness and the required end gaps and ended up with required length of each of the four pieces. The four pieces were then cut from the length and cut and draw filed to 45degs at each end. Gain I used the mill to drill and counter sink the fitting holes, however make the process repeatable I made jig to hole each piece in the milling vice.
Once drilled each of the piece were painstakingly hand bent to suit the rim, which would have the been far easier with a set of rollers! It was only after they were bent that my measurements could be validated, and as luck would have it they were slightly long resulting in one of the gaps being a shade to small. I corrected this by taking a shade off a couple of the ends to balance the error out.
To fit the tires the rim was loaded into the jig which allowed the rim to sit the required distance into the jig such that the tire could be rested on the jig in the knowledge that it was central. Each of the tires was in turn clamped using small tool makes clamps and then starting from the inside the holes were drilled through and 3/3"2 iron rivets fitted. Each rivet was inserted form inside to out and cut to sign length that when hammered it filled the countersink and left itself slightly proud. It must be said this was a lot more difficult that in sounds, as the tires tended to move on the clamps and the rivets are very difficult to get uniform.
Spokes
The spokes were next to be made, from the stamped blanks that were originally bought. Luckily they had been well stored so were not rusty, however they did need a significant amount of draw filing all round to clean up the stamped edges. To drill the holes in the top again I made jig to hole them in the mill and in one program drilled all three holes in each spoke in turn.
The spokes were next to be made, from the stamped blanks that were originally bought. Luckily they had been well stored so were not rusty, however they did need a significant amount of draw filing all round to clean up the stamped edges. To drill the holes in the top again I made jig to hole them in the mill and in one program drilled all three holes in each spoke in turn.
Hubs
The first phase of the hubs was a fitting and turning job, consisting of centering each casting in the four yaw chuck and working through each feature in turn, whilst trying to be as efficient with the number of re-chucking! There are four pieces to each hub including the hub caps and as I found out it pays to keep each side clearly marked.
The second phase is the slot milling. This was the first time that I has milled 'gunmetal' and it was tougher than I had been used to having to date only really cut aluminium. I tried to do all five slots in each face on one CNC program, however found that the back lash in the mill resulted in some of the slots being slightly wider than the others. This wasn't ideal but could be worked around. To learn from this I will do the hind hubs on the dividing head in the mill and only along one axis.
The third phase of the hubs is the drilling an tapping. Each has no less then 19 threaded holes, matching plain holes and counter sinks. It was best to offer each spoke up and drill through top the hub using the tapping size then remove the spake to drill out to the through size and counter sink as a separate operation.
At this point I also made the oilers. This was to be first taste of the very small scale required on this project. For example the oil caps are less than 6mm^3 in outer dimensions and required flats being milled, threads being cut and transitions being filed!
The first phase of the hubs was a fitting and turning job, consisting of centering each casting in the four yaw chuck and working through each feature in turn, whilst trying to be as efficient with the number of re-chucking! There are four pieces to each hub including the hub caps and as I found out it pays to keep each side clearly marked.
The second phase is the slot milling. This was the first time that I has milled 'gunmetal' and it was tougher than I had been used to having to date only really cut aluminium. I tried to do all five slots in each face on one CNC program, however found that the back lash in the mill resulted in some of the slots being slightly wider than the others. This wasn't ideal but could be worked around. To learn from this I will do the hind hubs on the dividing head in the mill and only along one axis.
The third phase of the hubs is the drilling an tapping. Each has no less then 19 threaded holes, matching plain holes and counter sinks. It was best to offer each spoke up and drill through top the hub using the tapping size then remove the spake to drill out to the through size and counter sink as a separate operation.
At this point I also made the oilers. This was to be first taste of the very small scale required on this project. For example the oil caps are less than 6mm^3 in outer dimensions and required flats being milled, threads being cut and transitions being filed!
Final assembly
To assembly the wheels, the rims were initially set in the jig along with the hub centre and then each of the five spokes laid into place and the centre screws tighten down along with one 7BA bolt at each palm. The rim was then carefully inverted and same process taken. Once secured the rim was removed and span on a make shift axle to check the alignment and where necessary any adjustments made. At this point I should point out that I drilled the axle holes a shade under the finished size so the hole assembly could be reemed once tight.
When I was content the rim was true, the assembly was again returned to the jig and each spoke removed in turn and refitted with a covering of Araldite.
To assembly the wheels, the rims were initially set in the jig along with the hub centre and then each of the five spokes laid into place and the centre screws tighten down along with one 7BA bolt at each palm. The rim was then carefully inverted and same process taken. Once secured the rim was removed and span on a make shift axle to check the alignment and where necessary any adjustments made. At this point I should point out that I drilled the axle holes a shade under the finished size so the hole assembly could be reemed once tight.
When I was content the rim was true, the assembly was again returned to the jig and each spoke removed in turn and refitted with a covering of Araldite.
Riveting
To date I only tackled countersunk rivets and I it turns out that hemispherical snap rivets are much harder. The book says something like ‘three good hits with the snap and the head would be formed’ – ha! It took many many attempts on a piece of scrap to get anything like a good finish. In the end I made a jig to cut the rivet to the correct length. Through trial and error I concluded that 4.7 mm was the magic length of the 3/32" iron rivet, and the process I used was as follows. Cut the rivet, debur and file smooth, insert and then hold in the fixed snap. Set the rivet with a 3/32" tube, say one smart blow. Start the rivet with a tool with a 3/32" blind hole to a depth of 2mm, using say 2 sharp blows. Round the rivet with a 60deg con shaped tool, say one blow, then finish with the other snap, using the 3 sharp blows from the book. I found that work hardening was the enemy here and you had to be confident and firm to get a good finish. Of course the further you get through the process the more confident you get mirrored with the increased nervousness of buggering it up with a miss placed hammer.
To date I only tackled countersunk rivets and I it turns out that hemispherical snap rivets are much harder. The book says something like ‘three good hits with the snap and the head would be formed’ – ha! It took many many attempts on a piece of scrap to get anything like a good finish. In the end I made a jig to cut the rivet to the correct length. Through trial and error I concluded that 4.7 mm was the magic length of the 3/32" iron rivet, and the process I used was as follows. Cut the rivet, debur and file smooth, insert and then hold in the fixed snap. Set the rivet with a 3/32" tube, say one smart blow. Start the rivet with a tool with a 3/32" blind hole to a depth of 2mm, using say 2 sharp blows. Round the rivet with a 60deg con shaped tool, say one blow, then finish with the other snap, using the 3 sharp blows from the book. I found that work hardening was the enemy here and you had to be confident and firm to get a good finish. Of course the further you get through the process the more confident you get mirrored with the increased nervousness of buggering it up with a miss placed hammer.
Finishing
On completing the riveting the wheels were then chucked in the lathe about the rim and the centre holes reemed to suit the axle and there you have it finished!
On completing the riveting the wheels were then chucked in the lathe about the rim and the centre holes reemed to suit the axle and there you have it finished!