Should Juniper be Ripped then Dried or Dried then Ripped?

Should Juniper be Ripped then Dried or Dried then Ripped?

by Scott Leavengood, OSU Extension Service

Several manufacturers have commented on juniper's tendency to warp when ripped. Drying studies have revealed the primary causes of warp in juniper are growth stresses, grain deviations caused by large knots, and cross-grain. Attempts to "relieve" the growth stresses through high-temperatures or pre-steaming before kiln drying did not prove to be successful.

So what is the best way to handle juniper lumber: dry wide boards then rip or rip to the final dimensions then dry? In the early 1980's, the USDA's Forest Products Lab. in Madison, WI addressed the problem of excessive crook from lumber sawn from small eastern hardwoods. The method developed by the Forest Products Lab. is known as Saw-Dry-Rip (SDR).

SDR involves live sawing logs rather than conventional cant sawing. Live sawn lumber is sawn through and through on the same plane whereas cant sawn logs are flipped continuously to remove the higher quality boards around the outside of the log, leaving a center cant. In SDR, the live sawn flitches are lightly edged in order to better fit into the kiln. After drying, the flitches are then ripped to the desired final width.

The theory behind SDR is that wider boards provide more restraint against warp in the kiln. Narrow boards have only the restraint of the stickers to prevent warp during drying. Wider boards have the restraint of the stickers plus the restraint provided by being part of a larger board. Studies have been conducted for several species and have shown that the SDR process produces boards that warp less than boards produced by conventional methods.

Mike Milota, wood drying specialist at OSU feels that the SDR process will result in less warp in juniper lumber. There are a few things the manufacturer needs to consider however:

  1. Is live sawing the best method to use to get the highest quality lumber from juniper logs?
  2. If SDR is used, the material is likely to be ripped just before some other operation such as edge-gluing. If the material warps after ripping, this may cause splitting in the final product, or at the very least, downstream material handling problems. On the other hand, if the material is sawn, ripped, then dried and it warps during drying, the warp can be handled (cut out, scrapped, etc.) before the initial remanufacturing processes.

Is SDR the answer for eliminating warp in juniper lumber? No. Is SDR likely to result in less warp for juniper lumber? Yes. Only experimentation, experience and each manufacturer's own situation will tell if SDR is the best way to go for juniper.