It is particularly useful when cutting threads on a lathe using a tap or die held in a holder placed in the tailstock. It is used whenever a very slow, controlled, rotation is needed. It should never be used under power.
Alternative names are: Mandrel handle, Threading handle.
There is not much new in my design - there are many other examples available online. However, I was quite pleased with the use of a large coach bolt as the axle for the wooden handle - the domed-end looks very neat and the threaded fixing method is very rigid. Also, the large aluminium knob works very well (mainly by luck) because when using the device, it does not need any tools (like a spanner or allen key). Also, when releasing the device, the knob is big enough to hit with the heel of your hand to release the wedge - again, no tool is needed.
This Instructable shows the basic design idea which was governed by the materials I had to hand! The main elements are in mild steel. The Instructable steps are in the same order as I made it:
The main mandrel
The axle for the handle
The wooden handle
It was pretty simple to make. I'm still a real novice on the lathe and there was little precision in the manufacture, but the end result is very useful.
Step 1: Main Mandrel
- Cut the bar to rough length.
- Turn the main outer diameter and check to see that it slides snugly into the lathe spindle
- Drill out the central hole (6mm) from one end as deep as possible.
- Enlarge the central hole by drilling out to 10mm diameter - for about 40mm depth
- Flip the bar in the chuck and drill a 6mm hole to meet up with the one from the other end (hopefully).
- Form a shoulder on the unworked end of the bar (this shoulder must fit through the hole in the changewheel guard).
- Turn down the top end of the bar, ready to accept an M12 thread.
- Cut the M12 thread (I used a die).
- Cut four slots to permit the mandrel to expand (I simply used a hacksaw, having no other method).
Step 2: The Wedge
- Centre-drill, drill and tap M6.
- Turn down 10mm of length to a diameter of 10mm (this will just fit inside the mandrel).
- Adjust the angle of the top-slide to 1 or 2 degrees (I lined it up by eye to give a very gentle slope). The angle did not seem critical to me because the mandrel is a close sliding fit inside the spindle without any expansion from the wedge; hence, the smallest increase in diameter due to the engagement of the wedge, is bound to clamp the mandrel very tightly against the spindle. I only needed to expand the diameter by a fraction of a millimetre to achieve a tight fit.
- To finish, I did a partial parting-off, then chamfered the sharp corner caused by the parting-off, then finished separating the job from the stock bar.
Step 3: The Knob
I wanted to knurl it, but I don't yet have a knurler so I cut a short length of bicycle inner-tube which fitted nicely around the circumference. This makes it easier to grip, especially with oily fingers.
Step 4: The Crank
- It was a devil to bend in a vice (I used G-clamps to fit a 1m length of 50mm square wood onto the bar - this gave me enough leverage).
- I had a rough drawing of what shape I wanted (so it would not hit any bits of the lathe, or its stand). I cut this out as a paper template, to help me make the correct bends and final shape. The drawing also let me know how long the original piece of bar had to be (23cm).
- Once the bending had been done, I used my bench-drill to make two holes (one 12mm diameter for the mandrel, the other 7mm - ready to be tapped out to M8).
- The final step was the tapping of the hole ready for the wooden handle axle.
Step 5: The Axle for the Wooden Handle
- The end was turned down to the diameter to suit an M8 thread, and then parted off.
- The thread was cut with an M8 die. Fortunately, my lathe chuck enabled the bolt-head to be inside the chuck without affecting the grip of the jaws. This let me thread the end on the lathe (rather than having to hold the bolt in a vice for threading).
- The square section under the head of the bolt was removed to leave a smooth axle.
Step 6: The Wooden Handle
- The diameter (on the right hand side in the photos) was made to match the diameter of the coach-bolt which was to form the handle axle.
- A clearance hole was drilled through the middle, so the axle could rotate freely.
Step 7: Final Assembly
- I spray-painted the crank, matt black.
- I couldn't find a suitable lock-washer to under the main M12 bolt, so I used some thread-locking liquid.
- The wooden handle axle was screwed into the crank and a locking nut was screwed on the back.
- The thread-locking liquid was also used to stop the M6 threaded-rod from unscrewing out of the wedge.
The spindle-handle works well.