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Using a quorn to grind single point involute cutters

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John Rutzen21/09/2020 20:13:33
255 forum posts
12 photos

Hi, I have a Quorn and am trying to figure out how to grind a tool bit to an involute form with it. Has anyone done this? It should be possible but how exactly?

Emgee21/09/2020 22:52:47
1695 forum posts
225 photos

By using a wheel shaped to the involute form will be one way.

Emgee

Bazyle22/09/2020 00:27:36
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5454 forum posts
206 photos

I assume you mean translate the method used for making them on a lathe by cutting on the grinder with an equaivalent prepared wheel. That is a grinding wheel dressed to a circular profile (no funny quips about it being a wheel please). This would be prepared using the part of the tool holder normally used for putting a radius on a tool.
However for a tool you put the tool tip closer to the wheel relative to the axis of rotation of the holder and grind the tool in a series of passes while advancing the tool into the wheel. But in this case you put a diamond back away from the axis by the radius you want, then very slowly move it into the wheel while rotating the holder abut its axis and it generates the curve on the wheel. You only need to do one corner of the wheel if you are prepared to work out how to invert the tool bit to do the other side.
Once you have a curved wheel edge you treat it like the button style cutters for preparing a tool in the lathe ie with respect to infeed and width of the tool blank. You obviously don't have two buttons simultaneously cutting each side at the correct spacing so you need to pick up a refernce on the edge of the tool blank. I think it is a bit tricky to set the two key dimensions, infeed and button separartion as the Quorn only has one micrometer dial and feed screw.
There are som extra complications if you want to use the curvature of the wheel to provide the cutting edge clearance,

not done it yet22/09/2020 07:12:31
4989 forum posts
20 photos

A CNC Quorn would seem to be the obvious requirement? Not so easy in practice, I would think?

John Rutzen22/09/2020 08:06:39
255 forum posts
12 photos

I've been trying to accomplish this by setting the rotating table on the Quorn to the button radius using the setting micrometer. The lack of any scales on the Quorn is a problem though. The great advantage would be of course that you can use square HSS tool bits. I've done this a few years ago when I made some extra changwheels for my Harrison lathe but I'm unable to remember how I did it! The gears turned out fine.

Michael Gilligan22/09/2020 09:08:39
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16342 forum posts
712 photos
Posted by John Rutzen on 22/09/2020 08:06:39:

I've been trying to accomplish this by setting the rotating table on the Quorn to the button radius using the setting micrometer. The lack of any scales on the Quorn is a problem though. The great advantage would be of course that you can use square HSS tool bits. I've done this a few years ago when I made some extra changwheels for my Harrison lathe but I'm unable to remember how I did it! The gears turned out fine.

.

Forgive me if I am being thick, John ... but am I right in assuming that you are not needing to grind an actual involute curve, but only the circular approximation ?

i.e. for making cutters by the ‘button’ method.

... if so, it should be relatively simple.

MichaelG.

John Rutzen22/09/2020 09:17:29
255 forum posts
12 photos

Yes Michael, I'm only trying to reproduce the "button" method on the Quorn. I'm afraid I didn't realise it's only an approximation to the true curve. The gears I''m making are only for a bending rolls, not a very exacting task. They are 2 inch diameter pinions in aluminium.

John Rutzen22/09/2020 09:19:56
255 forum posts
12 photos

Bazyle, sorry, I wasn't ignoring you. I think that would be a good method, in fact I could use a worn 4 inch grinding disc for the wheel, I've got one of those somewhere .

Michael Gilligan22/09/2020 09:26:31
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16342 forum posts
712 photos

It’s a very practical approximation, John yes and widely used !!

The gist of what you need to do is to position the centre-line of the blank on the rotation axis of the table, and create the radius by offset.

If you angle the blank upwards slightly, it will also produce the rake.

Sorry, I don’t have a Quorn so details are sketchy ... but I know a man who does this very successfully [by milling] on a little Hauser jig-borer.

MichaelG.

Michael Gilligan22/09/2020 09:37:43
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16342 forum posts
712 photos

Not of any great importance, but; here is a very clear illustration of how an actual involute curve is generated, and some interesting notes: **LINK**

http://www.cartertools.com/involute.html

MichaelG.

Bazyle22/09/2020 14:55:18
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5454 forum posts
206 photos
Posted by John Rutzen on 22/09/2020 08:06:39:

I've been trying to accomplish this by setting the rotating table on the Quorn to the button radius using the setting micrometer. The lack of any scales on the Quorn is a problem though.

I was suggesting dressing the wheel to the required button radius. You are perhaps using the sharp corner of the wheel to grind the curve. I see the problem of getting the centre of rotation to the right point realtive to the wheel as it is effectively inside the wheel itself.

John Rutzen22/09/2020 15:22:11
255 forum posts
12 photos

Hi Bazyle, yes I was trying to use the corner of the wheel to grind the curve. You can set the radius easily enough with a setting micrometer but as soon as you move the cutting head to adjust the infeed or offset you alter the radius. I can't work out how to do it without altering the radius so I think dressing the wheel edge to the button radius would fix that aspect of the problem. It's a bit wasteful of expensive wheels though.

Edited By John Rutzen on 22/09/2020 15:22:43

Michael Gilligan22/09/2020 18:12:17
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16342 forum posts
712 photos
Posted by John Rutzen on 22/09/2020 15:22:11:
.

Hi Bazyle, yes I was trying to use the corner of the wheel to grind the curve. […]

.

Apologies ... evidently I mis-understood

It appears that you want to grind the cutter profile directly [as opposed to grinding the “button” to use as a form-tool to produce the cutter on the lathe].

MichaelG.

John Pace22/09/2020 21:56:22
197 forum posts
185 photos

Grinding a form tool like this on the Quorn rotating base would be
difficult the largest wheel that would fit and clear the part of
the casting that holds the work head support bar on the
rotating base is 2.750 inch diameter ,with all the attendant
problems of aligning both sides of the tool and the correct
spacing of the 2 radii to produce a tool there would be no
clearance behind the cutting edge when it was done.

A simpler method is to use the same as can be seen in the
book gears and gear cutting Fig 95 page 118 in which an
arbor is used to form a single point cutting tool by turning, a similar
approach could be used by form grinding the radius on the grinding
wheel and making a suitable arbor for the work head ,in this way the
work is facing along the length of the Quorn bars so the adjustment
micrometer can be used to set the distance .Once one side is
ground the tool is turned around and the other side is ground,
since the arbor is a fixture the distance to be ground in from
each side can be set with some accuracy.

John

quorn grinding.jpg

John Rutzen23/09/2020 08:08:54
255 forum posts
12 photos

Thanks John and Michael, yes it's always seemed a long way around to make the tool using buttons when i've got a cutter grinder. Also hardening tool steel is a bit hit and miss though I've done it plenty of times. Thanks for the sketch John, I can see how that could work. But if you could get the tool set up you would think you ought to be able to grind the form by rotating the Quorn head around a grinding wheel?

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