Dividing Head for Taig (and others) - Part3 - division plate generation

The division plates used on this dividing head are made from old Hard Disk platters - the part of the harddrive which actually stores your data.
Each 3.5" hard disk will contain one or more of these disks which is 5.25" in diameter, with a 1" hole in the middle. The nominal thickness of the disks is around 1mm (less than 1/16") - I say nominal because I've found the more modern disks typically are thinner (less rotational inertia), whereas the older drives are thicker (up to 1/16")
The only thing you can rely on is that all disks in the same platter (collection of disks) will be the same thickness.


Figure 1 - Collection of platters destined to become division plates


I've been collecting hard disks for salvage for quite a while. The magnets are useful (see shed tip #1 ), and I also salvage bearings from them. The disks get shuffled into the pile for making division plates, and the casings go into the scrap aluminium bin (for foundry supplies) - only the boards, screws and little plastic doo-hickies get tossed. I learn a fair bit about mechanical design from looking inside the harddrive as well - there's some really clever braking mechanisms used to return the head, lock it, and so forth simply driven by ground effects from the spinning disk platter.

To make up a division plate:
I insert this mandrel into the back of the spindle of the dividing head. (see figure 2)

 Figure 2 - Direct indexing mandrel

The mandrel is made to expand and grip the inside of the spindle once the 1/4" nut is tightened up. A gear is placed between the 2 large washers which is an exact match (or multiple of) the desired index count. When I generated the 40 hole plate, I used a 40 tooth gear, but I could have used a 80 tooth gear if I had one.

 Figure 3 - Mandrel in place

The mandrel is sized to match the collection of C218 changewheels I purchased a few years ago. Those changewheels are the basis for the leadscrew of the Taig lathe and are the same metric mod 1, 20 degree PA changewheels used in the myriad of 7x12 lathes available in the US and other locations.

I place a chuck on the dividing head, and use a holder to grip the blank division plate in the chuck.
A centre drill is gripped in the lathe chuck using an arbor supporting a normal drill chuck.

Figure 4 - Dividing head spindle nose

A detent plunger mechanism is attached to the dividing head body which engages the gap between the teeth of the gear wheel. Turning and locking the spindle turns the blank plate, and all I need to do is feed the head into the drill to make the holes in the plate. The bracket supporting the detent plunger system is made from an offcut of an aluminium angle extrusion. The bracket is bolted to the body with two socket-head screws, and has holes to pass over the heads of the body bolts. Figure 5 (below) illustrates how it is fitted, with one securing bolt removed for demonstration purposes.

Figure 5 - Detent plunger system fitted

The detent plunger has a wedge shape when viewed from the side, but an inverted V shape when viewed from the front - this is to allow the indexing of the tooth tip instead of the gap between the teeth. This means I can index in the gaps of a 20 tooth gear, then rotate the plunger 90 degrees, and then index off the tooth tip and obtain another 20 positions - allowing me to generate a 40 hole plate from a 20 tooth gear.
The mount block for the detent plunger is bolted to the vertical arm of the bracket in one of 3 positions, allowing for a wide range of gear diameters. The large hole drilled through the body (from it's previous scrap origin) is used to secure the plunger with an elastic band if the internal spring is needing a little help.
The last article will cover (albeit briefly) the sector arms, plunger arm, and retaining mechanism.


Next project for documentation will be the field desk if I get it completed on schedule.

Hose suspenders - Part 2

I tried using a similar method of bending the tighter curves for the "square hook", but it was too tight a turn, and the forces tore the slipper apart. I was back to either forging, or some other method. (Trust me, I want to forge, but I also want to reduce the number of outstanding projects first.. once I reduce my workload, then I'll fill it back up again)
In the absence of forging, I decided to cut the rod and using the cuts as weaknesses, bend and then reweld (sort of like scoring cardboard to bend it)


The above photo shows a piece of rod with the cuts made, and another piece already being bent using the cuts as a weakness.



This photo shows how the pieces come together to make the finished hook. They are welded together as part of the construction, and the cut rod will have the exposed areas built up by welding.

Nine hooks welded up, all cut areas built up, both hooks joined at the top, bottom, and back, and the ring added.

A note about the rings. They started life as an offcut of scrap I fished from the scrap bin. I cut them into 1" (25mm) long pieces on the cutoff machine (aka drop saw) and then took them home. I chucked them in my lathe, and deburred them inside and out. I then turned a deep 30 degree chamfer on the inside at each end of the pipe section.

Once everything was welded, I hit then all over with a flapwheel in the grinder (these things are amazing!!! never used one until Bender - Now I'm buying them online whenever possible)


The results of flapwheeling the hooks was pretty good, I found a few welds to redo, then got the hooks ready for painting - the primed hooks shown below.



After two coats of primer, I painted two coats of epoxy paint over the hooks. It's "handrail yellow" supplied from the fitters at work. I reason the paint stands up to a lot of knocks and scrapes pretty well, and the bright colour will help the equipment stand out, and not be missed on the fireground. From memory the paint brand is "Galmet" - I can't be sure since I returned the tin once I was finished with it. The primer was the same primer I used for Bender - local "White Knight" steel primer.



Part 3 will cover the other part of the hose suspender.