Retractable top slide or cross slide?

[bernard towersParticipant @bernardtowers37738]

Be prepared to be gobsmacked when you see an ainjest in action it is quite inspiring

[Alan JacksonParticipant @alanjackson47790]

I described with drawings a retractable ML7 topslide which could retract for external/internal  screwcutting in the MEW mag. It used a  toothed belt which gave  a  smooth accurate retract of 0.125″ with zero backlash.

Alan

[JasonBModerator @jasonb]

Clive. I don’t see your point about keeping the dials in view. As I said I have the top slide parallel to the lathe axis so  it will be even further from the cross slide than if the cross slide were set at an angle.

You do not have to accept “chip crouding” a slight movement along the lathe axis of the top slide to each cut put on with the cross slide will see a cut on just one side of the Vee form tool. This is even an accepted method shown by the modern insert makes as well as alternating one side then the other to even out insert wear.

 

Ian, You will have to ask our Member Julie about how the ainjest works in more detail

[Ian Owen NZ]

On Ian Owen NZ Said:

…can the Ainjest do metric and imperial on an imperial lathe?

This discussion is going in 5 different directions at once (can we call it a multi-start thread?).

There was an attachment to the Ainjest called a Metradial, which allowed use of the Ainjest for metric threads on an imperial machine. The best account of its use is here:

https://www.practicalmachinist.com/forum/threads/chasing-metric-threads-with-metradial.214974/

If we go back to Cleeve’s book, still the best discussion on thread dial indicators I have seen, the problem with the Metradial is that you cannot escape the large minimum synchronisation distance involved, so while it works, it wastes a huge amount of time.

Perhaps the potentially better finish to the threads that a higher threading speed allowed by the Ainjest is what compensates for the wasted time.

[Clive FosterParticipant @clivefoster55965]

Jason

Apologies for being unclear, dial obscuration is with the cross slide and top slide in line not at 90° as in your case. On the 9″ SouthBend setting the top slide as you do was likely to argue with the tailstock unless the job was short or the tool overhang longer than ideal. I frequently found working with a tailstock centre something of a jugging act to make space. There is a reason for the American affection for lantern tool posts and Armstrong toolholders despite the inevitably large overhang between tool tip and locking bolt. Despite major similarities a Boxford is sufficiently different that this isn’t such an issue.

For me feeding the top slide back and forth a fraction to clear chip crowding was one more complication I could do without keeping track of. Essential when cutting an Acme to minimum backlash of course but for all the normal sizes folk like us deal with I never found crowding to be an issue even when using straight in feed before adopting the angular infeed and zero-2-zero strategy.

Like so many things best set-up can be machine specific.

The insert wear compensation makes sense given the normal use on CNC machines but it’s open to question whether any of us could put enough  miles on an insert for differential wear to be a thing. Given the warp factor spindle speeds involved with modern CNC calculating insert life in terms of miles of thread cut is probably pretty appropriate!

An Ainjest is indeed impressive but I always understood they were very machine specific.

Clive

[Graham MeekParticipant @grahammeek88282]

Hi Ian,

The sister magazine to HSM was Projects in Metal. This as you will see from the link below is now defunct so the plans don’t seem to be available. An example of Jim’s retracting device is shown below.

https://www.hobby-machinist.com/threads/a-cross-slide-retractor-for-my-th54.111385/

A do however recall someone else doing a similar thing, but for the life of me I cannot remember who it was. They id send me drawings of the attachment but I have searched my files and cannot find them.

Regards

Gray.

[Clive FosterParticipant @clivefoster55965]

Oh “and one more thing”.

If you have a belt drive lathe the quick, dirty and adequately effective method to getting a respectably repeatable stopping point is to graft an electromagnetic clutch into the drive line.  Control by a microswitch in a bed stop, best to include a relay to handle the current.

One fairly easy source would be the clutch off a car air-conditioning system. Well up to handling the power and inexpensive from car breakers. Odds are you will need to create a matching pulley to drive it tho’.

If you don’t already have one a clutch in the driveline is always useful. However the binary on / off function associated with an electro-magnetic one has disadvantages in general work compared to a mechanical one with a big sensitive hand lever. Maybe one of our electronic gurus knows how to do a soft start. But messrs Smart & Brown reckoned a clutch was an unnecessary complication on their “new cost is more than a house” 1024 VSL toolroom lathe and I’m usually (not always) willing to concede the point when I’m driving mine (cost less than a used motorcycle!).

With clutch disengaged and the lathe spindle stopped the phase relationship between spindle and the feedscrew is frozen. For native threads the half nut can be dropped and the thread dial used as a guide when winding the saddle back to start the next cut.

For non native threads a second bedstop on the tailstock side defining the half nut engagement position should work well enough after one dummy pass has been made. In non native mode the half nut must clearly engage at both the starting and stopping points. Inevitable minor variations in stopping distance should be considerably less than the feedscrew thread pitch.

However one caveat is that, for once, this suggestion is something I’ve not actually personally tried. Having done similar, but not in a lathe doing non-native pitches application, I’m sure it will work. Which inevitably is not as reliable as I’ve done exactly that.

Sorry.

A dummy pass is needed first to take out all backlash and clearance.

Given the inevitably limited resources of time and money that any individual can devote to home workshop / model engineering activities a degree of prioritisation is essential if you are ever to get anything done.

For me, having perhaps a little (not a lot!) more otherwise uncommitted financial resources than many but being somewhat time poor, buying a used Coventry Die Head and picking up potentially useful chasers economically in anticipation of need was a better way to get quick’n easy threading for smaller jobs than spending time making one of Grahams screw cutting clutches after adapting his design to whatever SouthBend, 9″ or Heavy 10, I was driving then. Jobs beyond the die head capability being relatively few I could live with standard methods.

But everyones situation and desires differ.

Clive

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