Meek bigbore dog clutch

[Bjorn_B]

we seem to have gone full circle, but it has taken 40 years nearly.

My best regards
Gray,

Haha, interesting, never thought I would circle so close to the source, fascinating!

Thanks for your explanatory post about your very cunning modifications of GHT's design. I will look this up carefully before committing, maybe after the summer months..

[Graham Meek]

Hi Bjorn,

You are entirely welcome, I will see if I have some sketches of the mods, they should be in my shop journal, but I cannot give any guarantees.

My best regards
Gray,

[Bjorn_B]

It is done now... a video of the screwcutting principle of a clutch of this nature, bit akward filming this as I operated the lathe one handed..

[youtube1]https://youtu.be/gdFv8U5ZjnI[/youtube1]

And a picture of the result..

20160527_191600 by Bjorn Bursell, on Flickr

[Steamer5]

Hi Bjorn,
 That has come out really nice! May I suggest that you look up the flip up threading tool thread that Bogs put up on here in the early days, that way you don't have to back out the tool bit between cuts.
Have followed several of these builds for different lathes so Grey do you have a list of lathes that have been fitted? I have an Emco 10 which would be nice to have one on.......if my skills are up to it!

Cheers Kerrin

[Bjorn_B]

Hi Bjorn,
 That has come out really nice! May I suggest that you look up the flip up threading tool thread that Bogs put up on here in the early days, that way you don't have to back out the tool bit between cuts.
Have followed several of these builds for different lathes so Grey do you have a list of lathes that have been fitted? I have an Emco 10 which would be nice to have one on.......if my skills are up to it!

Cheers Kerrin

Thanks, I have looked something like that up. but I'll go for a retract mechanism of the entire top slide (saves changing toolpost). See Graham Meek's post above

[Graham Meek]

I regret to say the flip up tool will not work with the screwcutting clutch. This device relies on the work or spindle revolving "clockwise" or "in reverse"to lift the tool. The spindle on the screwcutting clutch continues to revolve in the normal turning direction, "counter clockwise". 

If a flip up tool was used it would just cut a left-hand thread over the right-hand thread on the return pass.

My best regards
Gray,

[Steamer5]

Hi Gray,
 Of course you are right! I was getting"those looks" to hurry up & didn't think this all the way through before posting!

Cheers Kerrin

[Graham Meek]

Hi Kerrin,

Not to worry, I know all about those looks. You are not the first person that has advocated the use of the flip up tool with the screwcutting clutch and I doubt you will be the last. The best route is as Bjorn intends to do and go for the retracting topslide. As this carries the toolpost it has the advantage of being able to hold internal or external screwcutting tooling. Which in most shops is already in existence. The next best thing is a retracting tool holder, but these are usually restricted to external designs. Multifix do an internal version but I found this had it's limitations.

My best regards
Gray,

[Bjorn_B]

Just a quick addition, half-nuts stay engaged all the time during screwcutting, correct pickup of thread is guaranteed every time regardless of pitch or any other odd pitch chosen (gearbox ratios, metric quadrant or even more strange pitches for worms). No time lost in reversing the spindle, the thread dial indicator is now redundant.. Thinking hard about that retracting top slide now.... This i a gem, thanks Gray!

[Holt]

I finally found the video I was looking for, in the mean time you have made a very good video yourself, thank you for that, but I thought I would share this anyway.
Not a valid vimeo URL

Holt

[KWIL80]

Bjorn,

I am now well on the way to making a "GHT" style retracting top slide. As Gray is aware, I have abandoned the gears and have gone for a miniature belt drive, hence able to use a standard (well modified standard) Myford leadscrew. Making a new topslide to go with it so a complete swap over is intended. Will let you know when it all works . It also include needle thrust washers as do all my other slides and leadscrews.

[Bjorn_B]

Bjorn,

I am now well on the way to making a "GHT" style retracting top slide. As Gray is aware, I have abandoned the gears and have gone for a miniature belt drive, hence able to use a standard (well modified standard) Myford leadscrew. Making a new topslide to go with it so a complete swap over is intended. Will let you know when it all works . It also include needle thrust washers as do all my other slides and leadscrews.

Interesting, I have contemplated a belt drive substitute too... Not put much thought into how to actually make this work yet.. Details welcome!

On my metric myford, the top slide graduations make no sense at all.. 40 divisions on a 2mm pitch lead screw, how was that ever a good idea? As the top slide is almost always used for radial dimensions, not diametric.

I see a need for a new thread on this this topic