How to machine an ellipse

[JasonBModerator @jasonb]

This shows one being done as per Dave's sketch

[DalboyParticipant @dalboy]

There is a jig that woodturner make which will turn an eclipse whether it could be adapted for use on an metal working lathe I do not know. I am sure that I have a book in my library that has a jig in it if I can find it I will let you know

[John HaineParticipant @johnhaine32865]

This might be of interest

**LINK**

[DalboyParticipant @dalboy]

I found the jig but I don't think that it will be what is needed. Here is the diagram of it can not show any more.

[HopperParticipant @hopper]

Yet another way of doing it is with steel filing buttons made up, one large pair that fit over the centre part, and two small pairs that fit over a screw through each stud hole. Often the buttons need flats filing on the them where they meet so they fit the space. As often happens, takes way longer to make the buttons than to file the little bit of brass down to the resulting shape. But works well for multiple flanges. By rocking the file a bit, a good elliptical shape can be achieved, rather than the flat sides between the three radiuses. If you make the buttons from silver steel you can even harden them. Otherwise, I sometimes use mild steel and file carefully so as not to damage them. I don't have a mill so this method is handy for me.

Edited By Hopper on 17/07/2018 10:15:56

[Mike PooleParticipant @mikepoole82104]

To machine an ellipse that is a true shape and accurate size you may have to go for CNC. For most practical purposes the solutions offered for an approximate ellipse would be completely satisfactory. The cross and pin jigs for routing work very well but the solution doesn't seem to have an equivalent for machining metal. I suppose that prior to NC a copy mill and a template would be used, it seems that an ellipse is not often machined and just left as cast where it does come up in a design. CNC does allow complex curves to be accurately machined and the need to do this from the aircraft industry provided the force to develop Numerical Control and funded mainly by the US military it was soon making parts.

Mike

[Tim StevensParticipant @timstevens64731]

A simple way to draw an ellipse without doing complex sums (etc) is this:

Draw out a circle on graph paper using a pair of compasses, with the centre on one of the major crossing points on the paper, and the radius to the size of the longer diameter required – or some handy multiple of it. Your circle will be divided into strips by the lines on the paper, and we need to look only at the more heavily printed ones, and only those which run up and down the page. Take each such heavy line in turn, and measure the length between the ends where the circle cuts it. This can be done without a ruler or calliper by counting the squares on the paper (but not quite so exactly). Divide this distance by 4. Yes, that is a sum, I know, and a calculator makes this bit quicker. Measure this 1/4 distance up from the equator of your circle, and make a dot, and then do the same down from the equator. Do this for each of the heavy vertical lines, and you will produce an oval ring of dots. Join them up and there is your ellipse.

It doesn't matter whether the diameter of your circle fits exactly with the squares on the paper, or even whether the starting centre is exactly lined up with a heavy line – the method I set out above does not need these details, but it does make the job quicker as the four quarters of the ellipse can then rely on the same measurements each side – you can even fold the first quarter over and mark through, if you are a precise folder. And if you have no graph paper, use lined writing paper with the lines going up and down, and a ruler for measuring.

The result is an ellipse with the vertical diameter just half the horizontal. If you need a different proportion, don't use half the vertical distances, but some other fraction or decimal to do the calculation. If your fraction is larger than 1/2, the ellipse will be more nearly round, and if your chosen fraction is smaller the ellipse will be more pointy-ended.

Useful, sometimes, if for example you need to make a tidy looking car Nationality Plate for a trip abroad (as I did, you might guess).

And while I am writing, you can generate a true ellipse using a 'trammel' comprising a pair of followers (like T-nuts) running in two right-angle slots in a cross-shaped construction (one in each slot). Join the two followers with a bar (which can stick out each end if you like) and any point on the bar will move in an ellipse as you slide the two followers along. Winding the handles of your manual mill to trace the correct outline keeping the followers in the slots would make an interesting exercise – rather more difficult than scratching your head and patting your belly, I reckon. Hours of untrammelled joy …

Regards, Tim

Edited By Tim Stevens on 17/07/2018 16:26:21

[JasonBModerator @jasonb]

As most on here will be using a computer to post it is also very easy to just draw out what you need, print and stick it to your material. No need for fancy CAD, something like Windows Paint will do ellipses

[Keith RoweParticipant @keithrowe57572]

BIG thank you to you all, JasonB I have download your PDF many thanks.

If the house next door comes up for sale I will post it here in the hope one of you will move in !!

[BazyleParticipant @bazyle]

If you are after a curve rather than a true ellipse have a think about a steam engine connecting rod. One end goes in a circle and the other end goes in a line. In between you get points following a curve (asymmetrical). A little ingenuity with a rotary table on a mill should achieve the required effect.

[duncan webster 1Participant @duncanwebster1]

Posted by Bazyle on 18/07/2018 13:39:08:

If you are after a curve rather than a true ellipse have a think about a steam engine connecting rod. One end goes in a circle and the other end goes in a line. In between you get points following a curve (asymmetrical). A little ingenuity with a rotary table on a mill should achieve the required effect.

angularity of the con rod results in an asymmetric ellipse, sort of egg shape. If the con rod were long enough it might not matter.

[BazyleParticipant @bazyle]

You would just turn it round after doing one end.

Another candidate is a rose engine although that sort of assumes you have a master ellipse.

Industrial users might have had an Armag profiling tool, but again a master is needed.

Edited By Bazyle on 18/07/2018 17:47:36

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bazyle on 18/07/2018 17:42:18:

Another candidate is a rose engine although that sort of assumes you have a master ellipse.

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Really ?

MichaelG.

.

Here is a concise explanation: https://chestofbooks.com/home-improvement/workshop/Turning-Mechanical/Advertisements-Vol-3-Part-2.html#.UQxbQmtYCK0

… and someting a little more complex: http://ornamentalroseengine.com/rose/rose2/holtz.php

Edited By Michael Gilligan on 18/07/2018 18:22:33

Edited By Michael Gilligan on 18/07/2018 18:30:46

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Derek Lane 2 on 17/07/2018 09:48:06:

I found the jig but I don't think that it will be what is needed. Here is the diagram of it can not show any more.

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Thanks, Derek

I've located the web-page that describes it : **LINK**

http://www.aawcontentsource.org/aaw_cs1_pdf/AW3006p28-35.pdf

The design appears to be a wood-turners version of the Holtzapffel Ellipse Chuck : **LINK**

http://www.ornamentalturning.co.uk/ellipse_chuck.pdf

MichaelG.

[BazyleParticipant @bazyle]

MG is correct, I think a rose engine using a thin rectangle pattern and a large diameter disc rubber will work. I was thinking of a simple rubber just following the pattern.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for your gracious acknowledgement, Bazyle.

Prior to seeing that, I did suddenly wonder if you were being devilish by mentioning a 'master ellipse' [the circle being, of course, a 'special case' of the ellipse].

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

I've just found this page [with interactive diagrams] which describes the properties of an ellipse much better than I can: **LINK**

https://www.mathsisfun.com/geometry/ellipse.html

MichaelG.

[Brian HParticipant @brianh50089]

I've just dug out a book I have entitiled "Machine Construction and Drawing" that dates to around 1895 to 1900 judging by the sample City & Guilds exam questions and this shows that drawings for stuffing boxes and glands consist of a large circle around the rod and 2 smaller circles around the studs, joined by straight lines.

The proportions of all the dimensions are derived from the diameter of the piston rod.

I can copy the relevant pages if anyone is interested.

Brian

[JasonBModerator @jasonb]

Muncaster also gives a table of suitable proportions for "oval" glands in his book. You will also find this in Westbury's series of articles that are dotted about on the web. Note he calls them oval and not elliptical.

The straight edges ones don't see to be as common as the oval when you look at both full size and model.

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