# Grizzly G9729 Reverse Idler For Left Hand Threading



## Johnnybar (Dec 1, 2016)

There was some interest on another thread so I thought I'd post this here to make it easier to find for others. 

It's a pretty straight forward reversing modification.

Use a 5/16" cap screw about 1.75" to 2" long and a good quality flange nut.
Measure your gear plate's unused middle slot and mill or file two opposite flats off of the 5/16" flange nut to fit it but leave the flange portion fully intact....that flange has to hold the moderate clamping force when you position the idler gear.
Take the #39 or similar gear and needle file all internal edges of the keyway then polish it with some fine emery paper wrapped around a small rod. Clean bore and sides thoroughly. note: I picked #39 because I never use it for threading. Don't choose one too small as it won't fully reach the final drive gear to mesh properly.
Use some 1" round stock or larger to make the gear arbor by measuring your gears bore and reducing the size a couple .001's for the shaft portion so that you have a nice slip fit with the gear. The length of the shaft portion should be a few .001's longer than the width of your gear you are planning to use.
Measure the flange on the factory arbor for your large 120/127 secondary gear and duplicate that thickness on the reversing arbor you're turning. Turn the section left of the flange to approximately .700" diameter and .200" wide.
Center drill then drill a slightly oversized 5/16" hole through the arbor to a depth approximately the cap screw's length plus .250"... 2.250" for my project. Make sure your cap screw slips into it fully and easily.
Relieve all edges then part off at .200" left of flange.
Mill or file two opposite flats on the .700" dia x .200" wide section so that they will easily slip fit the slot in the gear plate.
Turn an outer washer on the remaining 5/16+" bored stock so that it is wide enough to just allow the cap screw to fully engage the nut but not protrude into the sheet metal housing. You can stack flat washers if you get this part too short.
Lube the gear and arbor with your preferred gear shaft lube and install the reverse idler first for proper tooth clearance.
Next, set the secondary 120/127 gears engagement to the idler gear and lock in place.
Lastly, pivot the gear plate to engage the spindle gear and lock into place.
Have fun cutting LH threads!
Remember to drop the gear plate away from the spindle gear when not threading to prevent unnecessary wear.


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