7. Making the Film Gate

  1. Start by using the ‘ to mill a cube’ technique to make the fixed part of the film gate block to the 40 x 20 x 18.4 mm size as shown in the drawing.
  2. Mill the one large face of the floating part of the film gate flat but leave it oversize at this stage.
  3. Mark out the location of the centre line of the film gate aperture on all 4 faces of the fixed block, the dowel holes on the top face and tapping holes for fixing on the bottom face.
  4. Mount the fixed block on parallels in the milling vice and using the X Y table position it for the first dowel hole to be drilled. Next place the floating part of the film gate milled face down on top of the fixed block and clamp it in position. Now slot drill the dowel hole through the floating part and to the required depth in the fixed block part. Insert the hollow dowel so alignment is maintained. Change to a twist drill of 2.55 mm tapping size for 3 mm thread and peck drill through the remainder of the fixed block.
  5. Use the X Y table dials or DRO to position it for the second dowel hole to be drilled. Make sure the current clamping of the two pieces together does not impede drilling if it does I have used a self tap screw located in a non-critical area to clamp effectively the pieces together. Now slot drill the dowel hole through the floating part and to the required depth in the fixed block part. Insert the hollow dowel so alignment is maintained. Change to a twist drill of 2.55 mm tapping size for 3 mm thread and peck drill through the rest of the block.
  6. Rotate the film gate parts through 90° so the base of the fixed part is against the fixed jaw of the vice. Only the fixed part should be on the parallels. The front face edge of the floating part of the film gate can then be milled level with the fixed part. Keeping the base against the fixed jaw of the vice rotate the film gate parts end wise through 180° so the back face can then be milled level with the fixed part. Repeat the process for both ends always keeping the base against the fixed jaw of the vice.
  7. Keeping the base against the fixed jaw of the vice, mount the fixed part of the film gate only on parallels in the milling vice, and then mill the film channel to depth and width.
  8. Mount the fixed and floating parts together using the dowels and mount the unit on parallels in the milling vice. Place one of the parallels so it supports both the fixed and floating parts of the film gate. With the grooving tool fitted in a suitable chuck lower the milling head so the tool just touches the surface of the film channel, move tool so it just touches the side wall of the fixed part of the film gate, then withdraw the tool from the work piece and start tool rotation. Move the tool into the work and adjust the traverse to form the required depth of groove. It is possible to establish the groove depth indirectly by using a feeler gauge between the 5 mm diameter part of the tool and the sidewall but is dependent on the cutter being 6 mm diameter. The method I adopted is to use my eye to judge the gap between the 5 mm part of the tool and the sidewall, make the first cut along the full length of the fixed part of the film gate. Check if two layers of film leader just enter the groove, if they do, OK, a film splice will be handled smoothly, if not take a second cut to get a greater groove depth that meets this test. The film sprocket holes of a Super 8 mm film leader will be fully exposed and clear of the sidewall when the groove depth is correct. If the groove depth is too great the film sprocket holes will not be fully exposed and the sidewall must be cut back to compensate. Next cut the groove in the floating part of the gate and check if two layers of film leader will just enter the groove.
  9. With the film gate still held in the vice test if a piece of 8 mm film leader can be threaded through the gate in the grooves, it should be too tight to allow this. Remove the gate from the vice, now thread the 8 mm film leader into the film gate grooves and the floating part should slide on the dowels away from the fixed part of the film gate and allow easy passage. Compress the floating and fixed parts of the gate together and the film leader can be firmly held with only slight pressure.
  10. Remove the floating part of the film gate. Keeping the base against the fixed jaw of the vice, mount the fixed part of the film gate only on parallels in the milling vice, and then mill the film relief channel to depth and width.
  11. Rotate the fixed part of the film gate only so its front face is against the fixed jaw of the viceand its base is on parallels in the milling vice. Then mill the film gate aperture and illumination channel.
  12. Tap 3 mm thread in the spring retention and fixing holes in the fixed part of the film gate. Fit the floating and fixed parts of the film gate together on the dowels, then fit the set screws, springs and washers, and finally with the set screws adjust the spring compression to hold the Super 8 mm film leader firmly. With a fine tipped marker pen mark through the sprocket holes at the claw end part of the film gate. The resulting marks are used to set the height of the slitting saw to cut the claw relief slot and motor sledge cam rider running slots.
  13. Mount the film gate on parallels/ring in the milling vice, adjust the slitting saw height to cut at the centre height of the sprocket hole marks and then lock the milling head height.
  14. First cut the claw relief slot in the film gate to depth 0.2 mm. Then mount the sledge side 1 on then same parallels/ring and cut the cam rider running slot to depth 2.5 mm. Make sure you have marked the front end of the sledge sides as these form a handed pair. For side 1 its front end is at the left hand jaw of the vice. For side 2 its front end is at the right hand jaw of the vice. This  sequence of machine operations should ensure alignment of the cam rider claw centrally in the 0.91 mm width of the Super 8 mm film sprocket holes.
  15. Replace the film gate on the same parallels/ring. Check the slitting saw still aligns with the claw relief slot. Withdraw the saw blade from the slot, unlock the milling head, and then raise the height of the saw blade to widen the slot until it meets the film relief channel level at 0.2 mm below film level. The latter process may require more than one cut to increase the width sufficiently. The extra slot width allows the claw end to have a clearance below film level when it is aligned for Standard 8 mm film sprocket holes when the sledge is raised on the shim.

 

Download PDF

Download the full PDF document

Video

videos

Contact METS

mail 100x100