5mm x .8 pitch

Thats almost 32TPI, if you have that cut most of the thread and then chase it with a M5 die

Jason

Hi Jason, thanks for the info, its an internal thread so is a littl

more compilcated but i will find a way, regards Dav

-- DCree

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5mm x 0.8 is a common metric tap.

Not sure if you can trust a tap to cut concentric enough to be worth it for a collet drawtube - but maybe you could make your tube oversize, tap it, and finish it after; maybe find some way to mount a collet backwards in the lathe chuck and screw the tube onto it for finishing.

I wonder - it could be important for it to be accurately central, but does it matter?

The thread only draws the collet into its hole (tm), so the force is longitudinal, especially if the thread is a bit loose. Doesn't the hole keep the collet straight?

Hmmm - collets with a land at the back to accurately fit the hole? Doesn't R8 do that?

Just wondering - and I'd guess it would be easy to finish the collets when screwed onto the drawbar anyway, if needed. Put the drawbar in a collet ... ouch ...

-- Peter Fairbrother

HAD we but world enough, and time, This coyness Lady were no crime. We would sit down and think which way To walk, and pass our long love's day. Thou by the Indian Ganges' side Shouldst rubies find; I by the tide Of Humber would complain. I would Love you ten years before the flood, And you should, if you please, refuse Till the conversion of the Jews. My vegetable love should grow Vaster than empires and more slow; An hundred years should go to praise Thine eyes, and on thy forehead gaze; Two hundred to adore each breast, But thirty thousand to the rest; An age at least to every part, And the last age should show your heart. For, lady, you deserve this state, Nor would I love at lower rate.

But at my back I always hear Time's winged chariot hurrying near; And yonder all before us lie Deserts of vast eternity. Thy beauty shall no more be found; Nor, in thy marble vault shall sound My echoing song; then worms shall try That long preserved virginity, And your quaint honor turn to dust, And into ashes all my lust: The grave's a fine and private place, But none, I think, do there embrace.

Now therefore while the youthful hue Sits on thy skin like morning dew, And while thy willing soul transpires At every pore with instant fires, Now let us sport us while we may, And now, like amorous birds of prey, Rather at once our time devour Than languish in his slow-chapped power. Let us roll all our strength and all Our sweetness up into one ball, And tear our pleasures with rough strife Thorough the iron gates of life: Thus, though we cannot make our sun Stand still, yet we will make him run.

Andrew Marvell To His Coy Mistress

If you can get a threading tool small enough to go down a 4.2mm hole you could again cut 32TPI and then chase with a M5 tap.

Jason

On Varmint Al's page:

There is a link to a program which will calculate changewheel setups for whatever pitch you want. It works very well and you should be able to cut a very close approximation to 0.8mm pitch on the imperial machine, without a 127 tooth gear.

Just checked and the closest would be 0.80211 I think with gears

20,50,45,57 (assuming they are part of the set. If you can get hold of a suitable 127 tooth gear, of course, then an exact pitch would be possible. No, sorry, I don't know where to get one.

Pete Harrison

I can't see what you gain by trying to screwcut it rather than tap it. If you can hold the piece in the lathe which clearly you can to be able to screwcut it then use a tapered 1st tap, put the tap in the tailstock chuck, leave the tailstock unclamped and by pushing on that with one hand and turning the headstock chuck with the other you start the tap dead central and concentric and gradually work it into the job.

Once it's in a good few turns you can finish with a tap wrench and then go through it one more time with a finishing tap if need be. You won't make a thread any more accurately any other way. Just remember to turn a bit, back off to break the chip and just go at it gradually like that.

No longer needed to back off with modern HSS taps. This first came about when we were using carbon taps with old cutting geometry. Since the advent of HSS and new geometry backing off actually reduces the cutting tool life and causes rough threads.

Plenty of research been done on this subject which has resulted in modern methods that don't need to back off.

Even seen a tapmatic tapping head that backs off in the cut to break the chip ? Ever seen a CNC machining centre that doesn't push the tap thru in one go ?

The answer is good taps, correct cutting fluid and keep a positive feed on, push the tap, don't let it try to pull through.

-- Regards,

John Stevenson Nottingham, England.

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