Thursday , February 22 2018
Home > Lathe Projects > Details of the Simple G0602 Reverse Idler

Details of the Simple G0602 Reverse Idler

by “JimSchroed”

Material:  Steel
Units: (in)

Earlier I posted a brief article in the forum on an a simple reverse idler gear for G0602.  I have received several requests for additional information on this project. This article will provide specifics on how to make this modification.  A few points before I get into the details:  First, you must have access to a mill to do much of the work on the bracket.  While this is not a beginner project it is within the scope of the less experienced if they take their time.  I must assume that if you are ready to cut left-hand threads then your experience level is probably at the level required for this project.

Examine the above photo to see the method used to reverse the direction of the gear box input shaft.  The G0602 comes equipped with a variety of gears used for controlling the gear box input shaft speed.  One of these gears is the 104 tooth gear which is not used in any of the common threading configurations.  We will position this gear between the “a” gear and the 127 tooth driven gear.  Adding another gear into the train will reverse the direction of the gear box input shaft.  I should point out that the “a” gear is one of two gears used to set threading pitch rates as shown on the front panel threading data plate.

We start with a piece of 3/8” thick x 1 ½” wide by 7″ long (or longer) rectangular steel, I used 1018 but just about any available type will work as will aluminum of a similar size.   Drill a 0.375” hole in one end that is centered side-to-side and 0.750 from the end.  If you want to round the end in the mill now is the time to perform that task.  I have a simple fixture that I use for this since it seems that many of my projects end up with a piece that needs rounding.  In this case I have an index wheel mounted on my spindle shaft and the brackets that hold this are in the way so rounding mine was a necessity.  You can see the interference in the above photo.  Below is a photo of my fixture and how I set it up to round the end.  One note of caution: be sure you are milling against the rotation of the cutter or you will quickly lose control of the situation and it will not end well.  I take a little at a time and advance the table after each pass until the desired point is reached.

To mill the slot used to tighten the bracket in position I used a setup like the one shown in the following photo.

Several points on this process.  Notice the stops that are on the table, these control how far the arm can swing from side to side.  Use Dykem to layout the size of the slot so that you can position these stops properly.  The work piece is held above the table by a clamping bar under the two hold down nuts, another piece of material placed in the table slot and between the two pieces that limit the side to side arch, this keeps the piece level when drilling and slotting.  Use two nuts to hold the piece firmly in position while slotting, this will eliminate chatter.

Start by drilling 0.375” holes at the each end of the slot and then mill between the holes, this will make the slotting task easier.  Once you center the mill table on the cutter then you can move the table forward 2.375” and clamp the work piece to one side of the path and drill that hole, then move the work piece to the other side and drill the last hole.  Use a 3/8” slot drill to open up the space in between.  Since you are moving this piece by hand limit your depth of cut so that control is easy to maintain, I usually remove about 0.050 per pass when doing this.  If you were planning ahead and did not cut your stock to the final length then you probably have plenty of material to hang onto, if not you might attach a “C” clamp to increase you leverage and move your hands out of harms way.  Just as a reminder, a slot drill is a two or three fluted end mill, not a four or more fluted end mill.

While you have the bracket arm on the mill, drill and tap a 3/8 x 24 hole 5.000 inches below the top pivot hole.  This second hole will hold the axle that the 104 tooth gear rides on.  Then cut the piece to a length of 6.250 inches.  Your finished bracket should look like the following drawing.

The first piece to make on the lathe is the shoulder washer used in the pivot hole.  The length of the shoulder needs to be 0.004-5 longer than the thickness of the bracket.  This will allow the bracket to move freely when installed on the lathe.  The following drawing will show the dimensions and form.

The clamping bolt is made from a piece of ½” stock and threaded 5/16 x 18 on one end.  A washer is made from a piece of ¾” stock or a standard flat washer may be used.  The Tommy bar is made from 3/16” stock and the caps are from ¼” stock and press fitted on the ends.

The last pieces needed are the axle and retainer washer.  The axle dimensions are shown below.  Start with a piece of ¾” stock, turn and thread the outboard end as shown in the diagram.

Finish turning the other sections as shown above.  When that is completed mount the axle on the idler bracket and use a marker to identify the vertical plane.  Return the axle to the mill and mill the flats on the end that will be straddled by the quick release washer.  These flats need to be near vertical so the washer does not get dislodged.

The retainer shown is very similar to one that holds the large driving gear.  The challenge is how to hold the washer while you mill out the slots.  I took a short piece of ¾” material and stood it on end in the milling vise with a v-block.  Then I bored 5/16” hole to a depth of about ¼”.  Next I milled the two slots, and then I returned the material to the lathe and cut it off to the indicated length.

Now we move on and prepare the G0602 head stock to receive the idler bracket.  Unplug the power, then remove the top screws from the front plate so that it is clear of the head stock and the interior is readily visible.  Next, using a square mark the head stock at the position of the pivot screw which is 2 9/16” below the upper right hand corner as viewed from the end of the lathe.  The following photo will show the position of the hole.  Center punch your mark.  It is important that this hole be perpendicular to the surface so we need to make a fixture to help guide our drill bit.  I used a piece of ¾” steel from the scrap bin, drilled it on the drill press with a #7 bit and a ¼” bit, the latter to serve as a tap guide.  With the #7 bit and the drill guide, place the bit on the center hole and drill all the way through the housing wall and then tap it for ¼ x 20.  Mount the idler bracket using a ¼ x 20 socket head screw and the shoulder washer.

Loosen and lower the lower gear assembly on the lathe then replace the “a” gear on the lathe with the 27 tooth gear.  This is the smallest gear and we will use this to position our bracket to ensure we can reach it with the 104 tooth gear that we are using for the idler gear.  Mount the 104 tooth gear on the idler axle; swing the idler bracket into position so that 104 tooth gear and the 27 tooth gear mesh.  With the bracket in that position mark the housing with a pencil outlining the slot that the clamping screw goes through.

Place a mark mid way between upper and lower bounds of the slot and in from the right hand side, center punch this point.  As with the top hole use a drill and tapping guide to keep things perpendicular to the surface.

You are now ready to run the carriage from left to right, either for turning from a shoulder or threading left hand threads.  When not in use remove the 104 tooth gear and the end doors has plenty of room to close.  If you have any questions post them to the forum discussion linked to this post and I will be happy to answer them.

Jim About the Author



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About Jim Schroeder

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  1. Hi Jim,

    Thanks so much for these plans!  I decided to build this over the weekend and I have everything complete (but haven’t attached it to my lathe yet).  One thing I noticed, and I’m trying to figure out whether it’s a problem with the plans or my reading of them, the half inch slot in the axle retaining washer allows the half inch portion of the axel shaft to fit regardless of whether the flats are milled into it or not.  This seems to make the flats unnecessary, but also could (in theory) allow the retainer to slip off (mine is so snug that I don’t expect that to actually be an issue).


    In order for the flats to actually retain the washer I think the half-round at the top end of retainer needs to be less than 180-degrees of arc.  Or I think the width of the slot (diameter of the cutter) needs to be the width of the axle across the flats (instead of a half inch).


    Just thought I’d see if there’s something I’m misreading on the plans


    Thanks again for making this design available!



  2. Finished mine and got it installed this evening. It works like a champ. Once again, thank you Jim for posting the detailed design and instructions. Here’s mine installed:

    518662b46fd4933870d0ef55c998535c_zpsc265a0a9.jpgImage Enlarger

    I ended up remaking the axle retaining washer. The original is on the left, and my new one on the right:

    51aa4afab413ad06b2819105a9f5a02b_zps02cfa954.jpgImage Enlarger

    I may have read the plans incorrectly, but my first washer was free to “spin” on the axle:

    7789a0dd473b0bd1810e21c58e0df31c_zps11c47c3e.jpgImage Enlarger

    For washer #2 I reduced the wider slot from 1/2″ to 3/8″ (the smaller slot remained 5/16″). I also modified the axle by filing down the top of the 1/2″ diameter section to 3/8 so it would fit into the wider slot in the washer. You can almost make that out in this picture:

    901acae2bf62fa1fadcaa46fe5d98487_zps8a0460cc.jpgImage Enlarger

    The new washer only slides on/off from the top and can’t rotate:

    02d776da65b8e988385c0e09149efc82_zps927c2005.jpgImage Enlarger

    This project was surprisingly easy and adds a cool feature to this capable little lathe. I can’t wait to give Jim’s cross-slide retractor a try (I’ve got the metal for it, but haven’t started it yet).

    Thanks again!

  3. I was giving this project some more thought (even though I’ve completed it) and think it could be made easier by replacing the curved locking slot in the main plate with a straight slot.  The new slot would simply need to “cover” the existing curved slot, then the washer would just need to be large enough to span the slot.

    I don’t have a rotary table, so I machined the curved slot using the method Jim described above and it while it worked, it was definitely a dicey operation.  A straight slot would have been much easier to cut on the mill.

    Just wanted to throw this out as a possible simplification to Jim’s awesome design.


  4. Ok Jim question…..

    Adding the 104 tooth gear in the mix to get the lead screw to turn opposite direction…..doesn’t this change the rotation count[rpm lead screw]?

  5. @cookj320

    I had the same question. The ratio between the 127 gear and the 124 gear works out to 1:974. May be it’s not enough to change the finished thread pitch on a short piece. Hopefully someone will answer.



  6. Do a search on “idler gear”…   It’ only changes the direction of rotation, the actual number of teeth don’t matter…  Only the number of teeth on the first and last gears in the chain define the gear ratio…


    (I thought this forum was dead a few years ago???)

  7. Dear Kizmit

    (I thought this forum was dead a few years ago???) I just joined the forum, wasn’t a member a few years ago. 

    Every lathe I’ve owned (9 inch SBL, 13 inch Sheldon, and 16 inch SBL), has had this same basic type of rocker for changing feed direction.  I just never thought about final gear ratio until I read this article. I appreciate the information. Thanks for reading and thanks for commenting.



  8. DocB said
    I just joined the forum, wasn’t a member a few years ago. 

    Hi Doc,

    There are still a lot of good ideas and some really nice projects documented here.  Just not a lot of new traffic, which is unfortunate as this one of the first places I found when I first got my lathe and mill, and several very talented folks used to frequent the forum.  But everything sort of died off a few years ago…

  9. (Late comeback)

    Thanks for the info Kizmit! I’m just poking around some. Glad you’re still alive!