86mm KILO 12G “lite” motor – liner fabrication

Boring post but to be used as personal reference

Liner dimensions:1629 x 300mm.

  • Width of liner: In general the liner is constructed with a 20% overlap. Hence: pi x ID of the casing x 1,2 = 301mm = approximate 300mm wide.
  • Length of liner: Depending on chamber length but chamber length usually is grain stack + 10mm. In this case 12 x 135 + 10 = 1630mm. Liner is kept 1mm shorter to prevent it from inadvertently compressing / collapsing ergo: 12 x 135 + 10 – 1 = 1629mm.
  • Liner is made from 1mm thick EDPM rubber bought at the local Intratuin. The EDPM is cut with x-acto utility knife along a 2m long sturdy angle bar. An appropriately sized piece of plywood is used for marking the 90 degree corner(s).

The typical roll and tuck method for rolling liners over a full length of casting tube works good up to a KILO 6G motor. Any larger and the liner fabrication became cumbersome to make with a high possibility of error and requiring multiple persons to keep it perpendicular. Hence a new method needed to be found. A more mathematical approach was selected. Goal was to check whether the average circumference between the inner diameter of the casing and the outer diameter of the casting tube would result in a workable liner.
Pi x 80 (ID motor casing) = 251mm
Pi x 76 (OD casting tube) = 239mm – average = 245mm.
A “ sanity check” was made by rolling a smaller test piece of EDPM liner over an actual casting tube which resulted in 242-243mm width of the EDPM liner.

  1. Before start marking I cleaned the EDPM liner from chalk etc at the appropriate place with some alcohol so the tape would stick to the EDPM.
  2. Using a steel ruler every 200mm (starting 20mm from the side of the liner) I measured 244mm with the ruler from the side and marked with a felt tip marker the head end of the ruler with a 10-15mm line. This line is about 1-1,5mm thick. So the middle of the marked line would be 245mm. Subsequently connected the lines to form a polyline out of 200mm lengths each along the length of the liner.
  3. Length wise I marked the liner every 100mm again starting 20mm from the end. Did this perpendicular thus intersecting the polyline and at the edge of the free overlap part of the liner so that when they were folded over they would match up for alignment.
  4. The liner was turned upside down and the flaps were folded over to align to the polyline and the perpendicular marks. Starting at the middle and working to one end of the liner, the flaps were taped in place at the 100mm marked points with some 7-10mm wide aluminium tapes.
  5. With all tapes in placed a single length of full width aluminium tape was taped over the overlap joint.
  6. The result was a liner which is easy to insert into the casing and the grains were easily loaded into the liner. During both operations plenty of chalk was used.

Photos will soon be inserted

  1. Liner dimensions
  2. Cleaned edges
  3. Liner ruler
  4. Folded over not taped
  5. Folded taped
  6. Fully taped

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