< Main Frames >
Material for the main frames is bright or black mild steel plate. The former is more accurate in thickness and easier to scribe while the latter has smaller stress in the metal. I chose bright one. To cancel the warp by the stress after cutting, first I cut radius and slots in smaller size, after that I scribed true cutting edge and true position for holes, and cut them to final size.
Metal cutting work is completely different from the wood cutting work. If you are familiar with the latter, it is worth while changing your style as follows.
1) Use a tough gun-grip hacksaw with H.S.S. blade and cutting oil.
2) Grab both end of the hacksaw and fix your right elbow to your side (if you are right-handed).
3) Swing your whole body, not your arms.
4) When you move forward, load your weight to the hacksaw until vapor of cutting oil rises from the blade.
5) Don't rush! Move as slowly as you can continue the movement.
Two plates are bolted together in each end. The longitudinal edge and the horn slots are sawn by the hacksaw while curved edge is broken out along a series of drilled holes. As I described, in this stage, the profile of the frame is a little larger than the final shape.
To stand against hard machine work, I also fixed the middle of the plates with copper rivets. The rivets are headless not to disturb the set up for machining.
Over 600mm longitudinal edge in the frame must be finished exactly straight. The guidebook said "If you don't have large miller enough to cut the length, scribe with a rule and finish with a file." It sounds terrible for me so I took another method as follows.
1) Stand the rough cut frame upon the lathe bed with two blocks under each end of it.
2) Scribe a horizontal line by a height gauge in the excess area of the plate. (See picture in the left)
3) Scribe vertical lines in every 100mm distance, punch and drill small holes - the distance 100mm is about 2/3 of the lathe's cross slide travel.
4) Push small pins into the holes.
5) Check the straightness of pins on the lathe bed. (See picture in the middle)
6) Fix a black steel angle (over 100mm) on the cross table of the lathe.
7) True up the front face of the angle with a large endmill in the headstock.
8) Lay the frame on the cross table with two blocks under it - the height of the frame bottom should be slightly higher than the angle.
9) Push a pair of pins against the angle plate and fix the frame using suitable clamps - now the scribed line on the frame becomes exactly parallel to the cross slider.
10) Cut the edge with endmill for 100mm length. (See picture in the right)
11) Loose clamps and slide the frame about 100mm to allow the angle catch the next pair of pins.
12) Cut the next 100mm edge with the endmill to the same depth.
13) Repeat this operation and cut whole edge.
14) Check the straightness on the lathe bed and saw off excess area together with pins.
15) Repeat the same procedure for opposite side, pushing the finished edge against the angle.
So as to scribe vertical lines on the frame, three steel cylinders are piled up to raise the height gauge. Each cylinder was turned to 200.0mm previously.
To cut large arcs and holes, a fly cutter or a boring tool is chucked in the headstock.
The hornblocks for William aren't castings but hot pressed brass closed to the final size. They can be finished with careful filing but I machined them to ensure accuracy.
A dead copy of the horn slot in the frame, as a jig to cut the hornblocks.
First the bolting face is milled to final depth and width to fit to the jig.
In the jig, the backward protrusion was cut by endmill and filed flush.
Cutting the top face to the final thickness. In this stage, inside of the slot is not finished yet.
Riveting the hornblocks to the frame. Too noisy work!
Cutting the horn slot to the final width with a large endmill.
Buffer beam is made from a black steel angle - cheap and low quality material. Choose truer part of the material and true up with an endmill.
Slots for frames are cut by a small endmill.
The frames are erected with flat and round stretchers made from bright mild steel. Lathe bed is suitable to arrange two frames parallel. We can determine true position of stretchers on it. After bolting all of the stretchers, the buffer beams are fixed to the frames with small angles as follows.
1) On the lathe bed, mount the buffer beams onto the frames. Ensure parallel arrangement, using a suitable packing between the buffer beam and the lathe bed.
2) Fix the small angles to the corner with suitable clamps, and drop the quick adhesive between the buffer beam and the angle. (See picture in the left)
3) Remove the buffer beams together with the angles from the frames.
4) Drill through the buffer beam and the angle, and counter from the front.
5) Insert iron rivets from back, hammer into the counter and file flush. (See picture in the middle)
6) Again, on the lathe bed, fix the buffer beams onto the frames with clamps.
7) Copy the holes in the frames to the angle and bolt them together. (See picture in the right)