Evolution of a 4 Tool Turret

Those members who have followed my work over the years know I favour the 4 Tool Turret. While I know this is not everyone's cup of tea it does have its place in machine tool history.

A recent problem with my adaptation of George Thomas's Turret design was the tendency for the turret to stick firmly on the cone. Rather than just flick the turret round with the index finger of my left hand. I had to grasp the turret with my hand to free it.

Cutting oil was migrating along the bottom face of the turret and then up the cone taper. That plus a "close fitting" cone which has got better over the years required a solution.

George said in his article originally that he would have liked to make the turret self indexing, similar to the "Herbert Combination Turret lathes at the works". As my thought began to work out what to do as regards the sticking of my turret my mind went back to the above statement.

Two spring loaded urges pressing on the ratchet face would take care of the sticking problem. If these urges were so placed they could be used to re-index the turret as it moved around the central post. The angular faces sliding down the ratchet faces so urging the turret towards the indexing pin with a constant force.

The only problem now was to move the turret as the locking lever was operated. This came in the form of a one-way clutch, which came direct from the pages of MEW.

A clutch is preferable to a ratchet system, especially when the turret is being swung through an odd angle. Such as it would be when screw cutting for instance. Always assuming the reader uses this method of screwcutting, not everybody does. It allows for the turret to be set at any position and not dependent on any ratchet position.

Below is my original design adaptation for comparison.

The only external difference is the additional flanged plate held on by two M4 capscrews. This also stops small particles of swarf migrating into the needle roller race that I use in my adaptation.

I have been using this set-up now for a few months and it has come up to my expectations. All the parts are mild steel, with exception of the curved spring loaded cams and the rollers in the clutch which are silver steel. If wear does become a problem then I shall think again about my material choice, but for the time being I am prepared to run with this.

I have schemed out an adaptation that could be fitted to George's original design. If there is enough interest shown, I am prepared to write this design up and incorporate the modification to GHT's original.

Regards

Gray,

Interesting to me as I am a long-term, happy user of a GHT turret.

I admit that, having read this post and turned up GHT's description, I am not sure about the difference between "self-indexing" and the GHT "simple ratchet" design. Is it simply that with self-indexing moving the locking lever moves the turret as well?

I would certainly welcome a write-up of the adaptation.

When the turret locking lever is undone the one-way clutch instantly comes into play and moves the turret as the lever, or in GHT's case the ball handle continues to be undone. Going slightly past 90 degrees of movement allows the index pin to drop. As the lever rotation is reversed the clutch dis-engages and the spring loaded urges bias the index pin towards the ratchet face. Further movement of the lever merely locks the turret.

The biasing of the index pin towards the ratchet face has totally removed any very slight variation I was getting in repeatability prior to this modification, (George talks about "tenths of a thou" with his own turret). As there is now a constant force being applied to the indexing pin and no chance of the pin moving away from this face even slightly.

Regards

Gray,

Hi

I have not come across the word "urge" used in this context.

Can anyone explain please.

Fascinating modification, I feel sure George would approve.

Thanks

Rod

Graham Meek:

Many thanks for the explanation - no doubt I was a little dense to begin with!

Is "manual control" still available for intermediate settings? My turret is normally loaded with four indexable holders and intermediate positions are not normally needed unless the topslide is set round.

Rod Renshaw:

I understand that "urge" is part of the standard vocabulary of technical writers.

Many of the tools I have built in my career as a Toolmaker have been fitted with "spring loaded urges" to bias the component being machined or assembled in a specific direction. WDS tooling aids call them "Spring Loaded Stops", but it is not what I have known them as and in this instance it is not what they are.

Urge might not be the exact word to use in this context, grammar was never my strong point, but it is what is happening to the index pin of the turret. The vertical spring loaded pins, due to the large radius on the end faces are forced down the angular face of the ratchet. This induces an anticlockwise moment on the turret which "urges" or "forces" the indexing pin towards the ratchet face.

Under normal circumstances with GHT's original design the torque applied by the locking lever, combined with friction contact between the various components provides the anticlockwise moment. Depending on the enthusiasm used to tighten the lever, (the human element), then there will undoubtedly be a variation, due to the varying moments of inertia involved with each tightening sequence.

Regards

Gray,

Graham

Many thanks for the explanation.

Rod

.

It's easiest to consider the verb first ... one definition of 'to urge' is 'to strongly persuade'

It's use as a noun, for these components, then seems reasonable.

MichaelG.

The use of a one way clutch was to permit both the Turret, or the topslide, to be set at any angle.

If a ratchet based self indexing system had been used then this would have compromised being able to set the topslide at any angle. Only those angles that were within the ratchet geometry would have been possible. This was a situation which I considered intolerable as it seriously reduces the flexibility of the original design.

Regards

Gray,

With the original Tool Turrets which George had in mind on the Herbert Combination Turret lathes. There was no topslide on these lathes to worry about. Thus these tool posts only ever had to index every 90 degrees. The inner workings of these turrets that I have seen, is truly a work of mechanical art.

The sequence of events for those interested goes something like this.

As the locking lever is being undone one paw engages a ratchet, with a cam that retracts the indexing pin mechanism down into the base. This base supports the turret on a central pillar, and attaches it to the cross-slide. Shortly after another paw engages another ratchet which moves the turret to the next indexing position as the lever is unlocked further. When the turret is over its next location the indexing mechanism is now free to engage and the turret snaps into position. The locking handle is returned for the process to be repeated, or to be tightened. The number of parts and the complexity is mind boggling, no one would ever consider this from the outside. Yet these turrets worked faultlessly for many thousands of operations, maybe millions?

Regards

Gray,

I must say I am now a fully paid up fan of this use of urge, quality work as usual Gray.

Mike

No wonder GHT called them "splendid"!

Another great job graham ,just love them tool holders,well done.

john

Hi John,

Thanks for the kind words, the toolholders eliminate the need for packing due to the sloping tool slot. The close fit in the toolpost means swarf is not a problem each time the toolholder is changed. Plus they are cheap and dead easy to make.

Regards

Gray,

NIce use of a roller clutch, Gray!

Neil

Hi Neil,

Thanks for the kind words, MEW came to the rescue there and saved me a lot of time having to re-invent the wheel.

I have been pondering today whether to add the self indexing mechanism to my Compact 5 version of the turret, it will fit in a reduced size and it would be nice to have continuity.

Regards

Gray,