How do I machine this groove?

I'm currently building the Quorn Mk3 and am working on the spindle assembly. The threaded end caps to the spindle assembly incorporate an annular groove as part of the labyrinth seals, machined into the face of the caps, that is 1.6mm wide, 4.9mm deep. I've never machined anything quite like this before. What's the best way to achieve this ? To machine it on the lathe would require a special cutter with considerable clearance which I think would be quite fragile.I am thinking of maybe milling it with a slot mill on the rotary table....

A nice stiff bar with a bit of HSS ground to suit and clamped in it will cut these quite easily. To cut it on a milling machine and RT would require a small Woodruff key cutter if you can get one that small or are willing to grind one down. An internal grooving tool will probably be something you can use for future jobs.

Martin C

I don't follow you there Martin. The groove is on the face of the part, not in the bore. There are some grooves in the bore as well which are easy....

Sorry, thought you were talking about the internal grooves. The external ones require a trepanning tool. Should be plenty of references in the forum or the internet.

Martin C

Thread on grinding a trepanning tool

Link added

Edited By Martin Connelly on 01/06/2020 16:15:01

You could also make a tool like a hole saw out of Silver steel, turn to 20.6mm and bore to 23.9 adding a tiny amount of relief if needed by setting the topslide over a degree or two. Then cut some teeth in the end, I would just have a few so you can get a good gullet to clear swarf.

The groove is 1.65mm wide and 4.9mm deep. Is a face trepanning tool really going to work do you think? The tool would be very fragile.

Unless the design has been changed this is well covered in the book.

I could post a photo of the cutters I made for the job if this would help.

I like that idea.

I don't have the book, just the drawings!

Yes, pics of your cutters would be great.

25mm Rotabroach mini cutter. 20.5mm internal diameter, depth of cut 6.3mm max. Could be ground to required dimensions if you had one. This is the sort of cutter Jason is suggesting, OD and bore not as Jason suggested 

Martin C

Edited By Martin Connelly on 01/06/2020 16:48:12

I put it down to bad dimensioning of drawing

The Mk I, whch I built more years ago than I care to remmber,has the same feature. Although Prof. Chaddock covers the machining of the spindle at some length in the ME articles, he doesn't mention this groove. Presumably run of the mill, (pardon the possible pun!), to him. I can't remember my method, it certainly wasn't a trepanning tool. Most probably a silver-steel lathe tool, used with trepidation.

I see that the MK3 drawings are metric; DHC's design was, of course, imperial and he specified a (double-ended) cutter with one end 0.940" OD x 0.810 ID, the other 0.815" x 0.685"; I opted to make two cutters which seemed easier:

IIRC, I marked the teeth out in the lathe and filed them by hand with a neutral front rake. I think the through hole was to facilitate holding the tool for hardening and tempering.

Surprising, as the book is very much the same as the ME articles; another good reason to stump up for the book!

The OP just has the drawings; if they came from Hemingway without instructions it seems likely that they assumed either the articles or the book would be available. I realize that a competent machinist ought to be able to reproduce a part from a drawing bit I like to have a bit of help by way of instructions!

Hi Ifoggy - the proper tool is a Face Grooving Tool. Try searching eBay and you will find them with inserts.

It’s basically like a parting tool, but the sides are curved to fit the groove.

Easy to grind from HSS blank, especially for one-offs

Cheers - Will

I would cheat and use the mill and rotary table with a 1/16" end cutting tool. But I have the patience to go round and round for a very long time. I wonder how tight the tolerances are, or even if the piece could be made from two parts Loctited together?

Posted by lfoggy 01/06/2020 14:30:08

I'm currently building the Quorn Mk3 and am working on the spindle assembly.
The threaded end caps to the spindle assembly incorporate an annular groove
as part of the labyrinth seals, machined into the face of the caps, that is 1.6mm
wide, 4.9mm deep. I've never machined anything quite like this before.
What's the best way to achieve this ? To machine it on the lathe would
require a special cutter with considerable clearance which I think would
be quite fragile.I am thinking of maybe milling it with a slot mill on the
rotary table....

Hi lfoggy

Unfortunately this is one of the chicken and egg type moments when building
a Quorn grinder ,if you had a Quorn grinder the tool to do these would be
easy to grind .The were a right pain to do when i made mine 35 + years ago,
the slot has to be concentric with the thread and also the inner bore and
inevitably requires a turnaround 2nd operation which has to be clocked in,
hole saws and the like are just asking for trouble as this part has to run true
for the complementary other part of the labyrinth on the front of the
spindle and also the pulley hub.

I have just recently completed 3 off grinding spindles similar to the
Quorn spindles. They do share some similarities with the Quorn spindles but
i have altered the construction thoughout so that each part can be turned as
a single operation and the part that you describe is now made in two parts that
eventually are loctited together to form one.The slot that you describe
is no longer trepanned but is formed by boring on one part and OD turning
on the other.This is a much easier method of construction but still requires
some careful machining.
The photo here of these three spindles in the lower right hand corner and top
left you can see the end caps reasonably clearly, the end cap and the
inner part that forms the labyrinth seal.It may not appeal to some doing
this but these spindles run very well to above 30,000 rpm.

John

Thank you everyone that is very helpful.

I already have a Deckel SO clone grinder which is quite versatile so I am going to try and grind a suitable curved single-point face grooving tool and see how I get on with that. If that doesn't work I will make a cutter like ega's pictures.

You may well ask why I am building a Quorn if I already have a decent tool and cutter grinder. I don't really have an answer to that....