Opus P. (continued)
Updated Friday 13th November
undaunted Stan Bray’s engine project continues
After having given the plans a good looking at I decided to proceed, amending the depth of the steam chest from 18mm down to 11mm (to be on the safe side increase to 12mm) which provides sufficient clearance for the valve movement.
One feature of particular concern was the process of making and attaching the two lugs either side of the cylinder, required to support the slide columns. To improve the accuracy of fitting I machined a pin on each lug and a corresponding location hole on each side of the cylinder. This modification eased the process of accurately silver soldering the lugs into position.
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- Opus Proximum steam chest block milled to a depth of 18mm (remember, I am working 50% up in size).
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- Lugs soldered to the sides of the cylinder are required to support the cross head slide columns.
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- After silver soldering into position the lugs were cleaned up on the milling machine and given a quick polish.
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- Having marked out the cavity on the steam chest a hole was drilled comfortably inside each of the corners.
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- Working in an anti-clockwise direction the holes are linked up with progressively deeper cuts. Don't try to cut right up to the line at this stage.
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- Having removed the bulk of the material light, full depth cuts are taken progressively up to the inside edge of the cavity.
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- The steam chest block has now been machined to final shape though widthwise it has been left slightly oversize.
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- The tailstock centre used to locate the steam chest in the 4 jaw independent chuck prior to drilling the valve rod hole.
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- Position of the valve rod hole is checked with a dial test indicator. 180 degree rotation should show the same reading.
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- With the aid of 'x' and 'y' digital positioning on the milling machine the stud clearance holes are drilled through the steam chest.
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- In the absence of a digital positioning facility the holes can be marked out and spotted in the conventional way before drilling.
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- The steam chest can be temporarily superglued in position on the cylinder port face and all holes spotted through.
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- Using a simple tapping block to ensure vertical alignment the holes on the cylinder face are threaded to take studs.
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- After machining 0.5mm overlength, drilling and tapping M3 each pillar was trimmed to final length on the mill.
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- The washers were turned to 15mm dia. and 2.25mm depth and mounted temporarily into position.
“to err is human……”
Having completed the cylinder, steam chest and valve the good news is that I am happy that they will perform their function. However, the downside is that visually the alignment between cylinder and steam chest is not good. Attempts to correct have not really been successful and to rectify would involve several days work.
The next stage was to sort out the motion plate by machining the top mounting lugs for the cross head slide bars. The hole centres on the cylinder lugs are 30mm apart so this dimension is repeated for the top slide bar positions.
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- The main components for the Opus P. main frame are assembled and checked to ensure everything is squared up.
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- The areas to be cut away are scribed in the normal way plus a bold indication of the areas to be removed are clearly marked.
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- A 2mm radius end mill provides nicely rounded internal corners which will match the rounded ends of the lugs.
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- A centre finder is used to locate the spotted postion of the lug hole. My finger nail test tells me when the centre finder is running true.
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- Using a drill bit as a fixed pivot point the lugs are neatly rounded off. Take fine conventional cuts and avoid any attempts at climb milling.
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- The main components are brought together for trial assembly checking for squareness and determining mounting position for cylinder.