by Crankpin

HAVING purchased an old but superbly built Quorn T&C grinder some years ago, I am still trying to learn how to utilize its many functions. My purchase included many accessories but the shortage of collets, especially in metric sizes, has always been a disincentive to making more use of the Quorn for sharpening my increasing collection of worn, blunt and chipped end mills and slot drills.

Being intrinsically lazy and as well as possessing limited in engineering skills I have been reluctant to attempt manufacture of purpose made Quorn collets and this, despite the desire to sharpen twist drills to 4 facet points. The Quorn came with a superb arbor and chuck but the overall length of this prevents using drills of more than about 1½” in length which is hardly of much use for anything more than short ‘jobbers’ stub and centre drills.

However, noting that it was possible to buy an adapter which was 1” external diameter with a 2MT internal taper, I realized there was an option to utilize the relatively cheap 2MT collets known variously as ‘finger’ or ‘direct’ collets which are readily available from many of our usual suppliers.

The bore of a well-made Quorn’s collet holder should be exactly 1” diameter in its split clamp before tightening and a check of the adapter showed it to be accurately ground to 1” OD.

The first problem is that the adapter has a closed end and therefore prevents the use of an essential draw bar to pull in the collets. These collets have a metric 10 internal thread for a draw bar and accordingly a 10mm hole would have to drilled through the hardened steel adapter. However, this proved to be rather easier than anticipated by using a 10 mm carbide end mill, once a smaller pilot hole had been drilled (milled?) first with a 3 mm carbide slot drill. I used a slow speed in the lathe with plenty of lubricant. Do not attempt to use a twist drill to drill the 10 mm hole because it will snag badly as it encounters the 2 holes which are used to drift out a 2 MT inserted cutter.

No great accuracy is required in milling the central hole and the draw bar does not have to exert the pull which would be needed in say a milling operation. For use in the Quorn, sufficient draw is needed to just grip the cutter or twist drill during the sharpening procedure. It is, therefore, both adequate and easier to use 10 mm studding as a draw bar.

Reflecting my laziness again, no elaborately machined tightening handle was contemplated; instead a commercially available 10 mm ball handle was fixed to the end of the draw bar and in use this has served perfectly well.

I considered making a more elaborate draw bar where it would also act as an ejector for the collet, but this is hardly worthwhile as once the nip is released it only takes a light tap with the hand on the plastic ball to release the collet from the adapter.

In Fig 3 a brass packing washer can be seen between the lock nut and adapter, this is the simpler alternative to machining the 10 mm nut so that it will turn within the recessed top of the adapter.

In use on the Quorn the adapter does not interfere with the graduated locking plate so normal indexing of the tool for sharpening is maintained. If the adapter is slid right back into the clamped holder long reach mills and twist drills can be sharpened and of course, as Quorn users will know, special long-length tools such as D-bits, reamers can be now made. Because of the comparative cheapness of ‘direct’ collets (about £7 each) a wide range of imperial and metric diameters can be accommodated at minimal cost.

If extra long lengths of round stock (less than 10mm diameter) need to be ground then I’ve found that the draw bar unit can be dispensed with. A gentle tap with a plastic faced hammer on the face of the collet will hold it. Obviously this requires care and very light cuts to prevent the collet turning but then the Quorn is only designed to remove a thou or so at each pass.

Fig. 5 Basic dimensions of draw bar and brass spacer attached to commercial 10 mm internally threaded plastic ball.

Fig. 4 Installed and preparing for 4-facet twist drill sharpening in the Quorn.

Fig 3. Collet, adapter and draw bar complete.

Fig 2. Milling out the 10 mm hole in the end of the adapter with a carbide end mill.

Fig 1. The 1” parallel to 2 MT internal adapter and a ‘direct’ collet.