Coventry die head

[lug lordParticipant @luglord]

recently boight a myford ml7r and used to have a suoer 7. I am about to thread sone m8 bars using the coventry dir head fixed to a collet and mt2. I am worried about the die pulling out as my prrvious lathe had a clutch. The myford ml7r has no cluttch any ideas

[HuubParticipant @huub]

I have made a floating tailstock threading die holder that spins freely and has 2 handles. I set the lathe in its lowest speed and hold the holder by hands. When the die hits the shoulder, is lose my grip and that’s it.

You could thread M8 manually by rotating the chuck by hand, at least the last few rotations.

[bernard towersParticipant @bernardtowers37738]

If you are using a coventry die head the dies cannot pull out, if you stop the head moving towards the lathe chuck it will auto disengage.

[Andrew CrowParticipant @andrewcrow91475]

<p style=”text-align: left;”>If the taper in the tailstock quill is in good condition there shouldn’t be a problem, if there is problem I would suggest making a holder for your diehead that is located and locked to the external diameter of the  quill. In use let the whole tailstock/diehead slide along the bed, then either use the tailstock lock or a fixed stop so that the head automatically opens at the desired length of thread.</p>
It is not good practice to reverse a diehead off the just cut thread.</p>
Andy

[JohnFParticipant @johnf59703]

There should be no problem with the die head releasing from the Morse taper providing the taper is in good condition.

You can release the dies at the appropriate moment, some heads have a release lever intended for capstan use but you can use it manually.  If yours does not then just lock the tailstock a little before you reach the end of the thread and it will auto release.

Or depending on the model you will find you can release the dies manually by pulling the small lever that changes the cut from rougher to finisher cut.

John

[Clive FosterParticipant @clivefoster55965]

I’m not a lover of running Coventry die heads off the tailstock quill. Its hard to get a nice constant feed and, if the die doesn’t want start cleanly there is a risk of it twisting out of the taper.

I run mine from a tool post mount. Its easy to keep a nice constant feed using the longitudinal feed hand wheel whilst watching the die head bob back and forth on its positioning spring. A bed stop reliably sets the threading length. The pull forward distance to release the die once feeding has stopped is very repeatable.

My carrier was a simple weld up job. Fix a tube to bar to fit the QC post, weld bolting stubs on the side drilled to clamp bolt threading size, split the tube, tap the bottom parts of the stubs, drill the top plan generous clearance and clean up the bore in site with a between centres bar. Job done. I made an MT taper setting stub to fit the bore for rapid alignment using the stub in the tailstock.

If you don’t have a QC system a suitably bored block with similar clamping arrangements will work just fine.

Concerning clutches a simple spring loaded jockey pulley type works fine on smaller lathes such as the ML7. Simples way is to “obtain” a car auxiliary drive belt tensioner discarded after servicing “to the book” once the nominal service life mileage has been reached. Many makes use a complete assembly on a backplate so re-purposing is easy. Just a matter of arranging a suitable bracket and connecting a control lever. The spring will be too strong so a stop will be needed to regulate the pressure.

Clive.

[bernard towersParticipant @bernardtowers37738]

you can also fit an internal stop which takes away all the hassle of will it won’t it stop and if doing multiple items they are all exactly the same (handy for studs etc.).

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