Perhaps it would help to post a picture of the incomplete radius attachment and a link to a picture of a complete one so a potential informant has at least some idea of what you need measurements of.

There is an element of deja-vue to this thread. Did you post it before or on another forum?

I have a Mk11 radius attachment and I’ll happily get the dimensions you require if you give me a day or two.

There is a New Zealand fellow I follow on Instagram called Chris Cruickshank  (#cruiskshank_eng) who has built his own replica of the Clarkson drill and tap lead attachment. Worth having a look as he has some good pictures.

The spiral generating attachment is pretty rare and a complex bit of kit. I have seen one and had a play with it. I think it would be a major project to reproduce.

Sorry Ian, I made a typo.  search    #cruickshank_eng

https://www.instagram.com/p/C0qIiYLpWZF/?img_index=1

Ian sent you a PM

Looking at the Instagram video of the excellent drill grinding attachment made by Chris I see he uses a multi position cam on the rear end to align the flutes for grinding. I’m unconvinced as to the security, accuracy and reliability of this approach compared to the Clarkson design.

The Clarkson original carries a slotted indexing plate to select the necessary rotation to line up the flutes of the drill or tap being ground. As this, along with the rest of the back end of the spindle parts, was missing when I got mine I just copied the two slots at 180° one for doing drills. Interestingly the Clarkson latching tongue is tapered so making the slot to a matching taper and sufficiently deep for the tongue not to bottom out creates a very accurate and secure positioning device with inherent zero play and easy release. Figuring out the offsets for creating the matching taper side walls was “interesting” but it’s actually quite easy to do. Mr Clarkson was cunning with the angles.

The advantage of having only two slots is that there is no way to get things wrong. Disadvantage is that I will need another if I ever decide to get into tap sharpening.

One important, easily overlooked, detail on the Clarkson is the spring loaded plunger behind the chuck giving around 1/8 – 3/16 inch of movement to prevent excess pressure being applied to the wheel if the feed between cuts is too enthusiastic. I’m unsure how that would tie in with the spring loaded cam used by Chris. Tempting not to fit the prong plugger safety device on the grounds that you will always be careful and never overfeed.

However one thing I’ve learned in my (almost) 71 years of life is that betting on your personal ability to always be careful and never do anything silly is, ahem, “unwise”.

Clive

Having both the Clarkson attachment and a Brierley drill grinder, and if I wanted to make a drill sharpening device The speed and ease with which the Brierley works I would consider trying to copy the Brierley, the ZB 32. The capacity of 1.25″ means that the BIG drill we may have can be done. The science of the job eg 2, 4, or even 6 facet is another matter ! The only difficult part would be the making of the cams but with CNC this should be possible, or very careful hand work. Food for thought ? Noel.

As Noel says the Brierly is the better and more versatile device. Especially if you need grinds other than basic conical points. Also it’s about the only full spectrum grinder small enough to go in a home workshop.

However if a standard point is fine the Clarkson is, in practice, as fast to set up as a Brierly and equally effective. From a roll your own perspective its lot easier to make if you can find details of the various angles between the parts and will work on any grinder fitted with suitable wheel. A normal bench grinder with a cup wheel on one end being just fine. Effectively becoming the best engineered version of the plethora of swing across the wheel jigs.

Like most folk with larger machines I find the standard 5/8″ maximum capacity a bit limiting. Long term ambition being to make a bigger version able to cope with my MT3 drills. I imagine that maximum size was selected for price / performance / capability reasons. In those days 6 jaw chucks were very expensive. Next size up even more so and, along with the inevitable extra cost of the larger castings needed by a bigger device would probably have pushed the price beyond reasonable for a Clarkson customer.

It’s obvious from the number of tT&C grinders sold that Mr Ckarkson knew his market.

In industrial use drills larger than 5/8 were very likely to have more exotic point shapes requiring at least resetting and, probably, different operating techniques. Not really appropriate for a do it quick, do it now, do it right device intended for less skilled operators.

In its heyday the Clarkson sharpener was quite expensive enough as it was. Which is why they are relatively uncommon given that skilled machinists of that era were expected to be adequately proficient at hand grinding.

Clive