Mandrel Handle - Graduated Lathe Dials

Mandrel Handle

The indexable mandrel handle. - Cost = $0.50

Not only do I use this to do indexing on the lathe, but also to rewind the leadscrew when cutting a metric thread (my leadscrew is imperial, so the thread chaser can't be used).

	Platter from a record turntable (found on side of road during rubbish collection).
	Drivers' steering handle normally attached to a car's steering wheel (found in junk box of old car parts).
	Short length of cold drawn round steel (scrap dealer, 50-cents), machined on the lathe to just fit into the lathe mandrel. It is also drilled through for the inner shaft to fit into. The end has an internal taper & is slotted so it can expand outwards.
	Internal shaft made from old inkjet printer shaft (junk, side of road).
	Short length of round steel, machined to an external taper, this expands the outer sleeve when drawn up - taper tip is brazed onto the end of the inner shaft (junk box)
	Tensioning nut - screws onto end of inner shaft at record platter end - tightening it pulls on the inner shaft, which pulls the external tapered section into the internal tapered section of the outer shaft, hence making the outer shaft expand & lock into the mandrel. It is made from the the playback head drum in an old VCR (Junk from the side of the road)

You can see that this was made for a material cost of less than $1.

Manufacture:

Components showing the pin & slot mentioned.

Measure the bore of the lathe mandrel & estimate how long you want the shaft be. Make this as long as possible without interfering with a Morse taper being used in the headstock.

	Machine the shaft to this outer diameter.
	Drill a hole through the shaft to accommodate the inner shaft.
	Using a cheap tapered reamer (from somewhere like Tandy) to ream the taper in one end.
	Cut slots along the shaft for about 25 to 50mm to allow for expanding.
	Cut a thread on the outside of the other end - any size suitable for the outer shaft to attach to the turntable platter - I used 1/2" BSW.

Inner Shaft. Make about 25 to 30mm longer than the outer shaft.

	Thread one end - I used 1/4" BSW on 1/4" shaft, but it's not critical.
	Turn down the other end a little, just to form a shoulder, in my case to 3/16" Dia. This will be brazed into the taper piece.

Make the expanding taper piece next.

	Drill a hole through a short length (probably about 20mm length of round steel), to match the inner shaft (3/16").
	Make the piece tapered to match the taper in the outer shaft. Cut off at the point where the maximum diameter of the taper is just a touch smaller then the diameter of the outer shaft.
	In the middle of the tapered side, drill a small hole to accommodate a pin which stops the end turning when tightened. I used a 1/16" hole, holding a piece of broken 1/16" drill, Loctite it in then grind down when set, so it will not protrude beyond the outer shaft & mark the mandrel bore.

Turntable Platter & Crank handle.

	Drill & Tap the record platter to take the threaded end of the outer shaft.
	Near the outer edge of the platter, attach the steering wheel handle. (A counterbalance weight equal in mass to the handle may be added later on the opposite edge, if required).
	After applying 'Loctite' to the thread, screw the outer shaft into the platter. & leave to cure.

Tensioning nut - anything suitable, I used an old VCR part but a large wing nut would be just as good.

Drill & tap to fit the end of the inner shaft.

After assembly, a good idea is to put graduations around the platter circumference. I chose to put 1-degree markings on the circumference. This makes it usable for indexing purposes & is used whenever I am graduating a new dial etc..

	Find circumference of the platter.
	In a CAD program, make a line equal to 1/4 of this circumference & let the drawing package divide this line into the 90 required divisions. A good free CAD program is ProgeCAD LT 2005.
	Make 4 printouts of this line with its graduations. Cut into narrow strips along the lines & glue the 4 strips around the platter with water soluble woodwork glue distributing any errors equally.
	Mark all 360 divisions with file, saw or small Dremel cutting disk.
	Soak the paper & platter to dissolve the glue & remove the paper & residue.
	Using number punches or an engraver mark out the 10's of degrees.

The outer end of the thread is protected by using a dome cap nut. Washers were added under the adjusting nut to reduce friction.

There you have a mandrel handle for working the lathe by hand (without the motor) - as I sometimes do for cutting small threads. This can be useful at times when screwcutting where you can't disengage the leadscrew half-nuts, but want to move the carriage back along the bed between cuts (having moved the cross-slide outward first of course).

By clamping the handle in position, it is also fully functional for simple indexing.

The photo shows it attached through the mandrel, and using a piece of angle aluminium clamped to the tray as an index pointer. The self locking wrench is my temporary method of stopping the mandrel from turning while marking on the work held in the chuck or on the faceplate. Play safe though, always unplug the lathe before clamping the mandrel - it makes sure you can't accidentally turn it on.

Hand dial for leadscrew. - Cost = $0

Made from the flywheel off an old 1960's Singer sewing machine bored to fit the end of the leadscrew, a grubscrew holds it in place, a bolt with its head cut off, 2 Nylock nuts & a small piece of stainless steel tubing as the handle. Graduated with my 'turntable platter' Mandrel handle. My leadscrew is 8-tpi, so each revolution is 125-thou, hence 125 divisions on its perimeter.

I just set up a spreadsheet to calculate the degree position of each of the 125 markings, then marked each one based on that. Marking out was done by holding the item in a 4-jaw chuck, align the mandrel handle for each division in turn, clamp the mandrel handle to stop it rotating, use the saddle controls, scrape a pointed lathe tool past the item a couple of times. Marked lengths were set to be different for 10's, 5's & 1's.

Let a spreadsheet calculate each of the 125 marking position for you in degrees - don't do it by just adding 2.88-degrees to each new mark, as by the time you have made 359 measurements, the cumulative error will be a problem & likely to be quite large.

Simply fasten with a grub screw & mount it on the gear end of the leadscrew.

Graduated dial for leadscrew. - Cost = $0

Made from the base of a set of VCR heads (Identical original part shown resting on bed, final on leadscrew end). Graduated with my 'turntable platter' Mandrel handle. Graduated the same as the above hand dial, but for the opposite end of the leadscrew.

Fastened only by friction fit onto the tailstock end of the leadscrew. Instead of using a pointer to the markings on the dial, I just line it up by sight on the edge of the bed when I am using it.