HLV-H thread cutting single tooth clutch problem inconsistent disengagement

[alan.bain]

My HLV-H of the metric variety recently had a gearbox problem, where one of the bearing retaining collars on the shaft connecting the leadscrew to the gearbox output shaft came loose and pushed the tumber gear up against the gate peg (breaking it) and jamming the box solid. After dismantling (the manual isn't much help here as it describes the English gear box) and replacement of gate (milled from gauge plate) and a new tumbler gear & various bearings it is now back together and working.

I mounted the new leadscrew thrust bearings on an expanding mandrel and machined matrial off the central ring on one bearing so that when placed back to back with a bolt though centre and held in the outer races there is < 0.5 thou axial play in the central bearing.

However, the drop out at the end of a thread is not consistent. It occurs in one of two places, and measuring some workpieces shows that these are typically 3mm apart which is the pitch of the leadscrew (this may be a coincidence of course). Needless to say this can be a disaster if screw cutting up to a shoulder and the initial drop out is in the far from headstock position as sooner or later it keeps on going and drops out in the near headstock position and hits the shoulder chipping the tool and making a mess.

The gap in the two drop out positions is the same distance whether cutting a 0.5mm pitch thread or a 2.5mm pitch thread.

This all suggests that the single tooth clutch is disengaging at two positions. However, the clutch on dismantling was in perfect condition, was cleaned and reassembled with EP grease as lubricant and to the best of my knowledge there is no adjustment possible for the clutch mechanism.

Does anyone have any ideas?

Alan

 

[alan.bain]

Well it's months later and I'm replying to myself, but I finally tracked down the problem.

The shaft which caries the clutch shaft in the thread cutting gearbox is retstrained from lateral movement by an internal circlip in a groove which locks the bearing in place. The circlip had popped out the groove (probably not put in properly by me when reassembling the gearbox) and this meant when moving the threading lever to the left, if done vigorously it went past the location point and moved the bearing 2-3mm left.

As a result when the knock off rod came to disengage there was 2-3mm extra movement before the clutch dropped out. Obviously I sometimes push the lever vigorously and sometimes gently with the result that there was inconsistent drop out!

Having sorted the circlip it is now working fine and I just finished a couple fo 25.71tpi bolts (50 degree V form thread) for a machine restoration.

Posting this in case it helps anyone else in the future!

Alan

 

[Stradbash]

Thanks for the follow up! Hopefully no one will ever need this bit of information, but with the potential that you'll save someone grief, having the solution to your troubles here is great!