After a long, hot summer during which we endured five consecutive heat-waves that kind of paralysed all work-shop activities and after several weeks of absence due to vacations, I finally mustered enough (mental) strength to return to the project.
Machining the mast – next round
Ruefully I returned to my first choice of material for such small masts – steel, after the failed attempt with acrylic rod. Steel is so much stiffer. Still, the use of steadies was needed to prevent flexing during the turning. Unfortunately, due to the arrangement of the cross-slide on watchmaker’s lathe, where the longitudinal slide sits on top of the transversal slide, normal travelling steadies cannot be used. An added inconvenience is that travel of the longitudinal slide is only 54 mm, while the whole length of the mast is 123 mm. This means that the cross-slide had to repositioned twice to cover the full length
The steel I am using is copper-coated welding rod, which has very good machining properties, but is not 100% round. This means that the turning operation has to be completed in one set-up, so that one does not loose concentricity. In consequence, step-wise turning while keeping as much material as possible in the collet, as one could do otherwise, is not really feasible.
The operation began by turning a point on the rod that was to be supported in a hollow fixed centre in the tailstock. Based on the (dimensioned) working drawing shown earlier, the various steps and rings were formed by reducing the 3 mm rod to the different enveloping diameters along the mast. According to the spar table in the original drawing, the mast had the usual slight taper above the deck. To turn this the top-slide had to be given a very shallow angle of 0.3°, which had to be eyeballed on the graduation. It is better to begin with a slightly steeper taper, working from the thin end. This prevents the thicker end from becoming accidentally under-dimensioned. Making the angle progressively shallower, one can approach the correct angle.
During this operation, the steel-rod was supported against flexing by my shop-made mini-steady, which easily moves along the lathe-bed and thus can be used as quasi-travelling steady.
The taper still had to be evened-out with fine files and sandpaper, checking the diameter along its length with a small micro-meter.
Set-up for turning the lower mast
The three ‘bands’ along the mast (two for the winch and one for the topmast-shrouds) were brought to the correct diameter as last operation on the lathe.
The various square sections of the mast were to be cut on the milling machine. For such operations I had adapted many years ago a watchmaker’s lathe bed as dividing attachment. The bed bolts to the table of the milling machine and can carry the same head- and tailstocks as the lathe, plus the various steadies to support slender work. The lathe-bed was trammed-in with a test indicator to ensure that it was parallel to the x-axis of the milling machine.
Set-up in the dividing attachment for milling the square onto the lower mast
Close-up of the milling set-up before the operation
The raw mast was set up in the dividing attachment, supported by the tailstock and a kind of steady that I had built some years ago for such purposes. A ring with eight stops was chosen in the dividing head: the main faces to be milled are square, but the edges of the doubling will need to be chamfered 45° to prevent damage to the shrouds and main-stay.
Chamfering the square doubling
Milling the tenon for the mast-cap
In the same set-up the holes for eyebolts to attach the topmast shrouds had to be drilled. To this end, the spindle of the dividing head had to be locked firmly and the indirect dividing gear had to be set-up. This became necessary, because I realised that somehow, when I built the dividing attachment, I only drilled a ring with 6 instead of 12 holes (I have to rectify this at some stage).
Set-up of the shop-made indirect dividing attachment
In the drawings I worked out that the eyebolts should be about 15° and -15° off the horizontal plane on either side. So, the necessary movements for indirect dividing were worked out. The holes were then spotted with a sharply pointed burr to prevent the drill from slipping on the round surface. Finally, the holes were drilled out with a 0.25 mm drill, which was a bit of a challenge on the big mill.
Drilling the holes for eyebolts in the spider-band
The mast was then returned to the lathe to cut off the excess material on both ends.
The lower mast provisionally stepped in the model
The next operations will be to make and solder on the cheeks and the eyebolts. Then the cross-trees have to be built.
To be continued …After a long, hot summer during which we endured five consecutive heat-waves that kind of paralysed all work-shop activities and after several weeks of absence due to vacations, I finally mustered enough (mental) strength to return to the project.
[b]Machining the mast – next round[/b]
Ruefully I returned to my first choice of material for such small masts – steel, after the failed attempt with acrylic rod. Steel is so much stiffer. Still, the use of steadies was needed to prevent flexing during the turning. Unfortunately, due to the arrangement of the cross-slide on watchmaker’s lathe, where the longitudinal slide sits on top of the transversal slide, normal travelling steadies cannot be used. An added inconvenience is that travel of the longitudinal slide is only 54 mm, while the whole length of the mast is 123 mm. This means that the cross-slide had to repositioned twice to cover the full length
The steel I am using is copper-coated welding rod, which has very good machining properties, but is not 100% round. This means that the turning operation has to be completed in one set-up, so that one does not loose concentricity. In consequence, step-wise turning while keeping as much material as possible in the collet, as one could do otherwise, is not really feasible.
The operation began by turning a point on the rod that was to be supported in a hollow fixed centre in the tailstock. Based on the (dimensioned) working drawing shown earlier, the various steps and rings were formed by reducing the 3 mm rod to the different enveloping diameters along the mast. According to the spar table in the original drawing, the mast had the usual slight taper above the deck. To turn this the top-slide had to be given a very shallow angle of 0.3°, which had to be eyeballed on the graduation. It is better to begin with a slightly steeper taper, working from the thin end. This prevents the thicker end from becoming accidentally under-dimensioned. Making the angle progressively shallower, one can approach the correct angle.
During this operation, the steel-rod was supported against flexing by my shop-made mini-steady, which easily moves along the lathe-bed and thus can be used as quasi-travelling steady.
The taper still had to be evened-out with fine files and sandpaper, checking the diameter along its length with a small micro-meter.
[img]https://www.maritima-et-mechanika.org/maritime/models/Rahschlup/model/Rahschlup-150.jpg[/img]
[b][i]Set-up for turning the lower mast[/i][/b]
The three ‘bands’ along the mast (two for the winch and one for the topmast-shrouds) were brought to the correct diameter as last operation on the lathe.
The various square sections of the mast were to be cut on the milling machine. For such operations I had adapted many years ago a watchmaker’s lathe bed as dividing attachment. The bed bolts to the table of the milling machine and can carry the same head- and tailstocks as the lathe, plus the various steadies to support slender work. The lathe-bed was trammed-in with a test indicator to ensure that it was parallel to the x-axis of the milling machine.
[img]https://www.maritima-et-mechanika.org/maritime/models/Rahschlup/model/Rahschlup-152.jpg[/img]
[b][i]Set-up in the dividing attachment for milling the square onto the lower mast[/i][/b]
[img]https://www.maritima-et-mechanika.org/maritime/models/Rahschlup/model/Rahschlup-153.jpg[/img]
[b][i]Close-up of the milling set-up before the operation[/i][/b]
The raw mast was set up in the dividing attachment, supported by the tailstock and a kind of steady that I had built some years ago for such purposes. A ring with eight stops was chosen in the dividing head: the main faces to be milled are square, but the edges of the doubling will need to be chamfered 45° to prevent damage to the shrouds and main-stay.
[img]https://www.maritima-et-mechanika.org/maritime/models/Rahschlup/model/Rahschlup-154.jpg[/img]
[b][i]Chamfering the square doubling[/i][/b]
[img]https://www.maritima-et-mechanika.org/maritime/models/Rahschlup/model/Rahschlup-155.jpg[/img]
[b][i]Milling the tenon for the mast-cap[/i][/b]
In the same set-up the holes for eyebolts to attach the topmast shrouds had to be drilled. To this end, the spindle of the dividing head had to be locked firmly and the indirect dividing gear had to be set-up. This became necessary, because I realised that somehow, when I built the dividing attachment, I only drilled a ring with 6 instead of 12 holes (I have to rectify this at some stage).
[img]https://www.maritima-et-mechanika.org/maritime/models/Rahschlup/model/Rahschlup-156.jpg[/img]
[b][i]Set-up of the shop-made indirect dividing attachment[/i][/b]
In the drawings I worked out that the eyebolts should be about 15° and -15° off the horizontal plane on either side. So, the necessary movements for indirect dividing were worked out. The holes were then spotted with a sharply pointed burr to prevent the drill from slipping on the round surface. Finally, the holes were drilled out with a 0.25 mm drill, which was a bit of a challenge on the big mill.
[img]https://www.maritima-et-mechanika.org/maritime/models/Rahschlup/model/Rahschlup-157.jpg[/img]
[b][i]Drilling the holes for eyebolts in the spider-band[/i][/b]
The mast was then returned to the lathe to cut off the excess material on both ends.
[img]https://www.maritima-et-mechanika.org/maritime/models/Rahschlup/model/Rahschlup-158.jpg[/img]
[b][i]The lower mast provisionally stepped in the model[/i][/b]
The next operations will be to make and solder on the cheeks and the eyebolts. Then the cross-trees have to be built.
[i]To be continued …[/i]