Sunday, May 8, 2011

Dividing Head for Taig (and others) - Part 1 - Body and introduction

The dividing head was inspired by the work done by Tony Jeffree, and then heavily modified to suit my own circumstances and situation. (Note - Tony has a second design which uses a Taig spindle - see this link)
All photos in this series of articles were taken after construction had concluded since I did not have a camera during the build. This build occurred in Q2-3 of 2005 and was documented on Nick Carter's page back then.

Figure 1 - Dividing head in use on Taig Lathe

You can buy dividing heads - example shown here from Amazon, and there are books which touch on building your own (another example from Amazon) - in short, you need to decide what resources you have,and determine the best course... in my case I did not have a great amount of money, and I did have some time, and a willingness to learn - this meant I made my own. If I had the money... the start of many dreams. I don't have either of these products, but show them as examples of alternatives to scrap metal, wrecked sewing machines, etc.


















Building the dividing head body and base.
I started by making up a spindle. Tony's one used a drill chuck, but after reading many text books which talked about not disturbing work in chucks, I decided it would be better to make my dividing head use the lathe chuck if possible. This meant I had to make a spindle with a nose of 3/4"-16 tpi, with a 30 degree included angle for collets, and a through spindle bore of at least 3/8".
I had previously bored the spindle of my Taig lathe to 7/16" not long after purchasing it so I could pass 3/8" stock through the head - I used the same drill size to bore out the spindle of the dividing head.

Using a larger lathe (Thanks Dad!) I turned a 3/4-16 thread on a piece of 3/4 shafting, and drilled/bored the 7/16" through hole. I then made a collar which was shrunk on to form the register face for the lather spindle nose. This register face ensures the alignment of the lathe chuck. Whilst facing the register face, I also bored the tapered seat for the taig collets.
At the same time as all this lathework, I also threaded the other end of the spindle (3/4-16) to use for thrust nuts, and securing worms , etc.

By the time I'd finished the spindle, I was back home, and unable to access Dad's lathe - this meant all subsequent work was done on the Taig Lathe.

The body of the dividing head was made from a short length of 50x50 (2' x 2") aluminium I picked up at the scrap dealers.
The base plate of the dividing head was made from some 1/2" plate which was a reject from some CNC mob (I picked it up at the same scrap dealer as the 2"x2" piece)
I found if I stacked the 2" x2" on the plate, on the carriage, the centreline was in line with the spindle. Perfect for my immediate plans, and in line with my longer term goal.
The theory was I'd build the head on the plate base, and then should I every need to use the head on another lathe, it was simply a case of making a new base plate.. all other parts will transfer across.

The base plate was cut to square the end (The off-cut piece became the handle of my 3/16" allen key) and appropriately drilled and counterbored for the Taig slot pattern.


Figure 2 - original base plate shape - allen key handle made from off-cut.






The square body was then bolted to the plate, and line drilled and line bored on the Taig. Somehwer in all the line boring I used a shaft as an arbor, and turned the square body on the shafting to form a spigot at one end of the body.

The line boring provided a clearance fit for the 3/4" diameter spindle, and a light press fit for the bushes used at each end.

Figure 3 - Body on base plate

A brake was made and fitted to the front of the body which engages the collar shrunk onto the spindle.


Figure 4 - Front of body showing brake on collar

The spigot which was turned on the rear of the body is used to support the plate carrier. I saw somewhere that some dividing heads are used horizontally and vertically, and that some models allow the position of the plate to be changed to make things easier on the user... seemed like a good idea to incorporate into my build.

The worm and gear for my dividing head was salvaged from an old Singer sewing machine I found on the side of the road on curb dump day. It's a 24:1 ratio set which is OK for this design. I bored out the spur gear to suit the spindle, and cross drilled and threaded some grub screws in place. A normal 3/4-16 nut was cut down and faced to become a thrust adjustment nut. The other half of the thinned nut is often spun on to the spindle after the spur gear as a lock-nut. The grub screws on the spur gear engage in filed flats in the spindle thread.

Figure 5 - spigot, thrust-nut and worm on spindle.

The plate carrier will be discussed in another article, but here is a photo of it in it's place on the spigot.

Figure 6 - Plate carrier in place on spigot

The body really isn't much more than support for the spindle, and a means to hold everything else on the dividing head. I tried to design the body to make the head transferable from one machine to another - the base plate is the designed mechanism to permit that.

The plate is designed with holes in a grid to allow the plate to be mounted on Taig T-slots either parallel, or perpendicular to the slots.

Next articles: Plate carrier, plate generation, and sector arms and worm driving.


In the meanwhile I got the carcass of the field desk made yesterday, and hope to have the woodwork completed over the next week or so, then make up the catches, hinges, and handle over the next week, then inletting, finishing and it's complete. Everything takes time since I only have one day per week to do work - I try to keep the Sabbath holy, and work does a good job taking the other 5+ days... My wife is a darling since she encourages me to spend at least half of every Saturday in the shed - for that I'm most grateful.

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