Member postings for Duncan Munro

Wow! That's some machine Thanks for posting.

Thanks again for spotting that. I made sure that bit had been double checked, so not sure how I managed to make a mess of it... Spreadsheet and web page should now be corrected.

Norman and David, thank you for the warm welcome

Re: the Quorn, I bought the castings in 2006 although they sat there for an appreciable amount of time doing nothing. I saw a statistic somewhere (and this is probably an awful misquote from memory) but it was something like 60% of people who buy the Quorn castings die without doing anything with them!

That shocked me into action; I worked out that my productivity was pretty low but would would go down even more after death

Anyway, I did make it during 2007 with the exception of the spiralling head which I don't have a massive need for so that's another job on the "to do" list. I did, however, make a square toolbit holder and an ER25 collet holder for it which do get regular use. SInce the construction of the Quorn I've also converted it to a poly-V belt as the frustration of the band-a-belt regularly snapping was too much to bear.

I did find it a challenge to make, but I can honestly say I learnt a lot from it and found the exercise very enjoyable. Some pics and details of the build here **LINK**

Regards,
Duncan

Thanks for spotting that, I've update the website page and the spreadsheet.

Regards,
Duncan

Hi there, my name is Duncan Munro and I've just started posting here. I did know about the website being a subscriber to MEW, however I hadn't dipped into the forum until another poster brought it to my attention.

I've had an interest in model engineering for about 15 years now, as it's that long since I bought my ML7. With no knowledge of engineering, or indeed how to use a lathe, I've relied heavily on books from G Thomas, Radford, Chaddock et al to fuel my "apprenticeship" plus the generosity of those on other forums and groups who have helped by answering my frequent questions.

What have I made? Very little as it turns out! Real life seems to leave very little time for my hobbies, so things tend to be done in bursts. I have however made a number of tools for use in the workshop, culminating in the construction of a Quorn tool and cutter grinder which I could now not survive without.

My current hobby horse is 3D printing - this started with the construction of a homemade Prusa Mendel iteration 2 in August 2013 followed by the purchase of a Flashforge Creator Pro in July 2015. It's getting used for printing fixtures, packing pieces and prototype items. Getting things wrong in plastic is much more fun than getting them wrong in metal

I do a little bit of metal casting and will be employing the 3D printer to make patterns that will be encased in investment plaster then melted out in the style of lost wax casting. It will probably all go terribly wrong, but if you don't try...

Regards,
Duncan

Hi Gustav, I now have the diagrams and spreadsheet which may be easier for you than the English text? There is a link at **LINK**

This now has a spreadsheet hobber_differential_2016_02_29.xlsx which has diagrams and text explaining how the gears interact, and also the calculations to allow the non-prime gears to be made. Hope this is of some help to you.

Hi Gustav, I've found some emails from 2003 to a chap called Michael Durkin where we tried to work out the hobber workings and some of the numbers around it. He kindly dug out some of the following pictures for me which he took at the Harrogate show. He also gave me the following explanation of how the differential worked. I'll have a deeper look for the spreadsheet as well, but with the picture and the description it should hopefully be enough to make your own differential. I'll try and dig out the calculations as well as that will get you to a point where you can cut the primes from non-prime gear sets.

"...I have figured out the differential. I noticed that the gear being cut has 36 teeth, so I tried a teeth counting exercise on the photos and tried to add everything up to arrive at 36 teeth on the blank.

I did so in this manner (you need to look at the photos at the same time!):-

Input from the motor drives the big gear behind the one with the differential, (I think they are on co-axial spindles, but not coupled), this has 60 teeth.

I think this gear is coupled to one of the differential wheels, the rear one, facing the one visible on the hob drive shaft. It also drives an idler (don't care about teeth on this) which you can just see 4 teeth of, and then onto a 60 tooth Acetal gear. This latter drives the worm and wheel, which seems to be a 36 tooth job.

The 60 tooth Acetal gear is coupled to a 30 tooth Aluminium gear and via another (Acetal 60 tooth) idler, drives the 30 tooth gear which also forms the differential cage.

I did the "mind game" involved with this differential and if the rear gear is driven at, for example, 100 rpm c.w., then this would drive the visible differential gear at 100 rpm a.c.w. if the cage was static. With the fitted gears, the cage is also driven at 100 rpm c.w., which would drive the visible gear at 200 rpm c.w. if the rear gear were static. The differential acts as a summer and the final speed of the visible gear (and the hob) is the sum of the two resultant input motions, 100 rpm c.w.

Of course, by playing with the ratios of the train between the big gear and the differential cage, you can play with the speed of the hob and the speed of the worm.

The worm acts as a 36 to 1 reducer and would have an input of 100 rpm, so the blank would rotate at 100/36 rpm. This is exactly right for the gear we look to be cutting.

I set this up in an Excel spreadsheet and played with the available change gears in a Myford set (maybe 2 sets for some ratios). It will generate lots of different outputs. If you change the worm gear, this adds even more.

I intend to analyse it further, because I think some interesting possibilities arise. This is because the differential is used to sum two speeds and end up with a third speed which can be prime. For example, if you input 200 rpm and 500 rpm (actually 250 rpm multiplied by 2 in the differential) you get 300 rpm...."

The above quoted bit was from Michael Durkin, following is the images that he used to go with the description above. More soon when I dig out the spreadsheets... Regards, Duncan.

Hello there, I think this is the first time I've posted on here and is definitely the first day of my retirement so don't beat me up

I've received an email from Gustav asking about the CES hobber and the differential gears and he has pointed me to this thread. When I get back home tonight I will dig out a spreadsheet I did some years ago in conjunction with a chap who had sight of a Jacobs hobber with differential gear. That will maybe help with his question in some way and provide some numbers to show how the primes ratios are formed from normal non-prime gearsets.

Also some great replies on the thread on different ways to do things, and thinking outside of the box. If the 127T gear is for metric cutting on an imperial lathe it may be possible get some really good approximations using standard gears that can exceed the cutting accuracy of the machine without going to primes.

As I'm getting incredibly lazy as I get older, rather than try and concoct some fancy solution to cut a gear I need but will only use once or twice, the 3D printer often gets a workout.

I've attached some pictures, hope they show up. There's a couple of shots of a spare 60T gear on the Myford ML7 printed in ABS and a 127T gear for the same printed in PLA. I'll post again tonight when I've tracked the spreadsheet for the differential down.

Regards,
Duncan