Friday, January 18, 2019

Bench Top Bungee Lathe Details

In my last post about the bungee lathe I promised to give some construction details, so here they are.
The bungee lathe
I started by squaring up a piece of 18" x 5 1/2" x 1 5/8" thick redwood for the headstock.  I wanted the pointed center of the headstock to be about 7 1/2" above the rails and I wanted a few inches of wood above that.  The rails take up 2 3/8" of the 18" height and what's left is held in the vise.  The 5 1/2" width is more than really needed, but I think having that width held in the vise helps keep the lathe from bending in use.
A 3/8" lag screw sharpened to a point provides the drive center
The rails are 22 1/4" x 2 3/8" x 3/4" thick red oak.  The tenons that fits into the 1/2" headstock  mortises are one-sided tenons.  That is, there is only a tenon cheek on one side, so they are basically a long rabbet at the ends of the rails.  I did it this way for ease of laying out the one inch spacing between them.
Spacing between the rails
Same spacing on back of headstock due to one-cheeked tenons
When I glued up the rails and headstock, I was very careful to keep the rails parallel.  When the lathe is held in the vise, the bottom edges of the rails sit directly on the vise chop.  The location is such that the bottom of the headstock almost (but not quite) touches the vise's stability rods.

The length of these rails allows a maximum turning length of about 15".  I didn't work this out ahead of time - it was just a couple lengths of oak that were available.  If and when I ever need to turn something longer, I'll just have to build something bigger.

At the other end of the rails is a 1" thick piece of poplar that is screwed in place and this keeps the rails spaced 1" apart along their whole length.
Spacer at the tail end of the rails
This spacer is also used for attachment of the leg that supports the tail end.  That leg is a 40 5/8" x 2 1/2" x 1 1/2" piece of redwood that I had used for something else years ago and for which I had cut out two notches.  Turns out one notch was just about in the right location for it to fit around the rails and spacer.
The leg with it's countersunk lag screw
Closer view of upper portion
Attached to the rail-spacer-rail
I cut the leg a little too short on purpose and I use shims to make the floor contact.  This was in case I move the bench around and the uneven floor causes problems.
Bottom of the leg shimmed
When the leg is shimmed and the lathe is held firmly in the vise, it's really solid.  The tail end barely moves when pushed.

The puppet, or tailstock, is a 17" x 2 13/16" x 2 1/2" thick glue-up of redwood.  Its 1" thick tenon that fits snugly between the rails is 6 1/2" long.
Tailstock, or puppet (or is that "poppet"?)
To find the location for the mortise that would hold the puppet in place with the aid of a wedge, I put the tailstock in place between the rails and marked a line at the lower edge of the rails.
The upper pencil line is the location of the bottom edge of the rails.
The lower line is angled for wedging and is 1/16" further from the upper line at front than it is at the back.
Notice that the mortise was cut about 1/8" above the upper line.  That places the upper 1/8" of the mortise within the rails.  Without an offset, the wedge would not be able to tighten the puppet properly.

This 1" wide mortise is cut into the 2 1/2" wide tenon, but it's not centered.  Rather it's placed more forward so that there is more tenon shoulder behind the mortise than there is forward of the mortise.  This will help to resist the backward force of holding the turning work between centers.

The center is another 3/8" lag screw and it's location was not measured, but determined by putting the puppet in place, sliding it up to the headstock and butting it up against the headstock's point to provide an exact location.
Finding the location to drill the tailstock (left) from the headstock's point
The wedge is a 5 3/4" long x 1" thick piece of poplar, planed to match the angle of the mortise.  It's 1" wide at the small end and 1 3/8" wide at the large end.  It was originally longer and was cut to length after final fitting to the mortise.  The final length allows about 1 1/2" to stick out at front and back when tightened.

The tool rest has a base and an upright.  The base is 7 3/4" x 2 1/2" x 3/4" red oak, slotted for the 1/4-20 bolt that would hold it to the rails.  The head of the bolt is housed in a wider slot that is sized so that the bolt head won't turn when tightening the nut.
The toolrest
The upright is cut from a 6 3/4" long x 7 1/2" wide x 13/16" thick piece of maple.  The grain is oriented vertically so that the surface that tools rest on is end grain.  I'm hoping this will be more durable.  The top end grain area is rounded and sanded smooth.  The tool rest is sized to have it's top at the same height as the drive centers.
Side view of upper portion of tool rest
The maple upper part is joined to the base in a shallow rabbet and held with screws.
Tool rest joint

The nut that tightens the toolrest to the rails is a 2 1/2" x 2 1/2" x 3/4" piece of red oak that is tapped for the 1/4-20 thread of the bolt.

The tool rest nut
The bottom surface of the tool rest base has strips of sandpaper glued to it and this keeps it from moving at all during use.
Sandpaper keeps the rest from moving in use
The treadle is a 31 1/2" x 1 3/8" x 3/4" piece of pine that is screwed to the short side of a 14 1/2" x 7" x 3/4" piece of plywood.  That piece of plywood is hinged to a larger, 23" x 19" x 3/4" piece of plywood that I stand on when turning.  My body weight keeps the treadle from inching forward as I turn.
The treadle viewed from the turner's side of the lathe
And a view from the other side showing the hinged parts 
The nice thing about this lathe is I can disassemble the leg and stow the lathe easily.
Upper part of lathe stored in a shelf
Leg and treadle assembly stored beside parts cabinet

With the exception of the hinges, this lathe was built from materials I had on hand.  So total cost was about $5.  Well, that's all I can think of.  If anyone has questions, please ask.  Next time I'll show some of my first turnings.