A Quick-release Spindle Crank for the Mini Lathe

This is my version of a spindle crank for the mini lathe which is useful for manually turning the work in the chuck eg to carefully cut short threads, threading holes and rods with taps and dies, etc.

There are many versions of this attachment that have been made by lathe owners and I have based my version on Steve Jordan's. I like his idea of being able to remove the handle easily so that the mandrel can be left in the spindle for other uses eg indexing, etc. I haven't indexed my disc yet but will do that later.

Measurements of the spindle length etc are not critical but you need to work out the overhang of the handle so that it doesn't contact the gear cover - see images.

Basically the mandrel expands and clamps in the spindle so that you can turn the spindle, chuck and workpiece, by hand, either forwards or reverse. The gears must be disengaged when this is in.

NB: It is important to switch the electrical forward reverse switch to OFF just in case you switch on the lathe while the handle is still in the mandrel. In this project the handle can be easily taken off with the mandrel left safely to turn in the spindle.

This is just a view of all the parts laid out in the assembly order

The mandrel is turned from a length of mild steel which is about 110mm long. The bar is chosen to be slightly larger than the spindle hole size - in the mini lathe is just under 20mm. I used 25mm round bar and cut the mandrel insert length to 55mm.

A 6mm hole is bored right through the mandrel to take a threaded 6mm bar which is to be used to pull a cone shaped brass expander into the inserted end. Just a small tension on this cone will expand the mandrel to tighten into the spindle so it can be turned with the crank.

The insert end of the mandrel is bored out with an approximately 10 degrees taper leaving about 1mm of rim at the end.

The end is now marked for cutting through and again at right angles - ie 4 cuts - see image. I just used a 1mm disc in the angle grinder to do this. Then remove all the burrs with some emery paper or a file.

The outside end of the mandrel is turned down to a diameter of 12mm. The length of this cut will depend on the thickness of the disc plus the thickness of the crank handle.

The STEEL DISC is just from a scrap of steel 70-80mm in diameter with a 12mm hole drilled through the centre. Another small hole will be drilled through the disc towards its edge to engage with the crank when it's put on. The hole will be drilled later at the same time as it's done on the crank so that the holes (and the pin that's fitted) are in perfect alignment. My disc is a tight fit and is currently "glued" in place on the mandrel using locktite, but I have plans to brass braze it on at a later date.

I chose to use a short length of brass round bar (slightly larger than the final bore of the taper). This is also turned down using the same 10 degree angle set to cut the taper into the end of the mandrel.

I made this part before I changed the compound slide angle on the lathe.

Bore a 5mm hole through this brass "expander" and tap it for a 6mm thread. Cut a length of 6mm steel rod, enough to fit tightly into the brass "expander" and to extend slightly from the other end of the mandrel when the expander is loosely pulled into the taper. Thread both end of this bar. The outer end will take the nut and washer to tighten the mandrel into the lathe spindle.

NOTE: you could use a 6mm threaded bar (M6) and just cut this to length.

You will know the final length of this 6mm rod when the handle is made up.

The handle can be made from any length of metal. Mine is 160mm long by 20mm wide and 5mm thick. I felt that using a 10mm thick bar would be overkill and so I just brazed a short length of the same bar over the area when the 12mm spindle hole would be bored. Using just the 5mm thickness might be ok but, as the bar is a "loose" fit, I didn't want the bar to wobble on the spindle. So, I made it up to 10mm thickness.

The spindle end of the bar has a locking pin inserted to engage with a hole in the disc to drive the mandrel.

The placement of the spindle hole and pin will depend on the diameter of the disc used.

Lay the bar a cross the disc and mark the appropriate points to drill for the 12mm centre and the pin. As I was fitting a 5mm pin I drilled the pin hole out to 4mm (to tap with a 5mm thread later). Then drill the centre with a 12mm drill. Place the bar onto the 12mm end of the mandrel and clamp it in place - then drill the 4mm pinhole right through the handle and the disc. This will give a perfect alignment for the driving pin.

Now remove the handle and drill out the disc to 5mm, and then tap the 4mm hole in the handle for 5mm.

Make a short 5mm pin and thread one end with a 5mm die. The length of the thread and the length of the pin is determined by the disc thickness and the handle thickness.

Some people make a brass handle section but I decided to make a wooden one with it's own spindle allowing it to turn when cranking the mandrel.

This component is pretty straight forward. I used a M8 (8mm) bolt 150mm long. A couple of washers and nuts. For the wooden handle I selected a small table leg from the local hardware store and turned it down on the lathe to the shape you see. I then drilled a hole through it for a loose fit of the bolt.

The hole where this handle goes into the steel crank was drilled for 7mm and taped to M8 (8mm).

I finished the wooden surface of with fine sandpaper and a few coatings of super glue as one would do if making pens. The superglue is good for handling.

Put the components together with the nut on the outside of the handle lever and screw the bolt on. When the wooden handle is tight loosen the bolt a fraction until it turns easily and then tighten the nut against the handle lever. Cut off the overhanging thread and clean up any burrs with a file.

ENJOY!