Model Engineers' Workshop Magazine March 2024 issue **FREE 20 Page PREVIEW**

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THE UMPELBY ENGINE An ahead of its time machine from Fred Umpelby’s workshop.

THE MAGAZINE FOR HOBBY ENGINEERS, MAKERS AND MODELLERS MARCH 2024 ISSUE 337 WWW.MODEL-ENGINEER.CO.UK

MICRO MILLING Mike Tilby builds a machine for high-precision milling.

CHURCHILL CUB III LATHE Brian Wood extends the rack on a surprisingly modern looking vintage lathe.

AN IMPROVED MINI LATHE CLUTCH A Step-by-Step Guide from Howard Lewis.

D ISSUE: INSIDE THIS PACKE

Mar. 24

 AN A-Z OF METALS FOR MODEL ENGINEERING  CNC CONTROL USING A RASPBERRY PI.  A VISIT TO THE SMEE AT MARSHALL HOUSE.  USING BELT DRIVES.  TOAD5 – ADVANCED CNC CONTROLLER.  OPTIMISING AN OPTIMUM LATHE.  GRAHAM MEEK’S NEW BORING HEAD DESIGN.  TOOL ANGLE GAUGES.  50 YEARS OF THE UNIVERSAL PILLAR TOOL.  ADDENDUM GEAR MODIFICATION WITH FILENGRENE.  PLUS ALL YOUR REGULAR FAVOURITES!

Get more out of your workshop with MEW

Join the conversation at: www.model-engineer.co.uk

EDITORIAL Editor: Neil Wyatt Designer: Druck Media Pvt. Ltd. Publisher: Steve O’Hara By post: Model Engineers’ Workshop, Mortons Media Group, Media Centre, Morton Way, Horncastle, Lincs LN9 6JR Tel: 01507 529589 Fax: 01507 371006 Email: meweditor@mortons.co.uk © 2022 Mortons Media ISSN0033-8923

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On the

Editor's Bench Kitchen Chaos I’ve been fitting a new kitchen, not one of those simple swaps of new doors or units, this is gutting the old one down to stripping tiles and rebuilding the window frames. I truly hope that job is finished, or at least on the final stages by the time you read this.

At least it means playing with lots of fun tools and gadgets. On the one hand my big Clarke wood router is great fun, using it with various jigs to cut room long sections of 32mm worktop to shape with sub-millimetre accuracy. It is rather awe inspiring to use something so powerful as a hand held tool, running a ½” by 75mm tungsten carbide bit at several thousand rpm!.

Yes, googles and a mask were essential, as was working outside, which has been a bit tricky given the weather.

The first cuts happened in sub-zero temperatures, but routing out for the sink has been delayed. I needed to cut my own template, so started by taking the end panel from one of the old units.

Of course when I came to cut that with a jigsaw, it just shrieked – the internal gears had stripped a couple of years ago and I’d forgotten to replace it. By the time a replacement was obtained, a series of storms with endless wind and rain had set in. I must say, the old Black and Decker jigsaw did give me about a quarter century of service, so I

can’t complain. The budget replacement (I only need to make a cut about two metres long) is surprisingly good, and even has variable pendulum and a quick release blade holder.

The old units were made up in the days when it was just chipboard screws through pre-drilled holes. I’ve seen a lot of changes since then, and the latest iteration uses pressed steel cams with pegs that have expanding collets to hold them in place. Combined with a powered screwdriver assembly has become so much easier (and a lot gentler on arthritic thumbs). Lots of other nice touches, such as much easier to use adjustments for door and drawer alignment, little wedges to stop the hardboard cupboard backs from rattling, soft-close hinges and proper adjustable feet. Then there’s the joy that is push-fit plumbing fittings…

It seems a shame to waste such nice units and worktop in the kitchen.

Perhaps I should have fitted them all in the workshop.

Neil Wyatt

This issue was published on 14 February 2024 The next issue will be on sale 15 March 2024

March 2024

3

Contents 9 Extending the Rack on a Lathe

Brian Wood addressed a shortcoming on his 1940s Churchill Cub lathe, and ponders why it might not have been made as long as it could have.

44

13 From the Archives

These two tips from 1926 are just as useful a century later in a modern workshop.

14 Micro-Milling

Mike Tilby looks at the challenges of milling with very small cutters, and discusses some of the design choices behind his shop-built machine for this challenging work.

28 EazyCNC on Raspberry Pi with TOAD5

In his final article, usti yholm explains how he developed a system to allow a Raspberry Pi single board computer to control C C with TOAD5.

20 Addendum modification for involute gears

Jacques Maurel concludes his explanation of addendum modification for making custom gears, with links to many useful videos.

33 An A-Z of Metals

Pull out and keep these pages to create a miniature dictionary of terms relating to metals and their properties, from a hobby engineering perspective. .

39 Upgrades to an Optimum tu2004V lathe

on harp fits cross-slide screw thrust bearings to his Optimum Lathe.

44 Tales from the Workshop eo Theasby tells the story of red Umpelby, the man who pre-empted the Wankel engine.

45 Beginner’s Workshop.

This month Geometer looks at working with belt drives.

46 A Visit to the SMEE at Marshall House

The editor goes through the keyhole at the home of the Society of Model and Experimental Engineers.

48 A New Boring and Facing Head urther details of raham eek’s improved version of his 5 mm

E shop.

LBY ENGIN Umpelby’s work THE UMPE hine from Fred its time mac

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diameter boring head design.

54 Fifty Years of GHT’s Universal Pillar Tool In his final look at the PT, arren Williams describes an integral variable speed drive.

60 Workshop Lighting or the benefit of beginners we take a brief look at current choices for workshop lighting.

61 A Basic Leadscrew Clutch for Mini Lathes oward Lewis o ers a particularly compact solution to disengaging a mini lathe’s leadscrew drive.

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An ahead of

ERS, MAKERS

THE MAGAZINE

AND MODELLERS

MARCH 2024

NEER.CO.UK .MODEL-ENGI ISSUE 337 WWW

FOR HOBBY ENGINE

NG MICRO MILLI a machine for lds Mike Tilby bui milling. high-precision

III LATHE CHURCHILL CUB the rack extends Brian Wood gly modern on a surprisin lathe. age looking vint

MINI AN IMPROVED LATHE CLUTCHe

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Y PI.  ISSUE: A RASPBERR CNC IS PACKED CONTROL USING – ADVANCED EERING  CNC INSIDE TH S.  TOAD5 MODEL ENGIN E.  USING BELT DRIVE BORING HEAD METALS FOR MEEK’S NEW NDUM HALL HOUS  AN A-Z OF  GRAHAM R TOOL.  ADDE SMEE AT MARS UM LATHE. ERSAL PILLA A VISIT TO THE OPTIMISING AN OPTIM S! S OF THE UNIV FAVOURITE  CONTROLLER. ANGLE GAUGES.  50 YEAR PLUS ALL YOUR REGULAR E.  DESIGN.  TOOL ION WITH FILENGREN sation at: FICAT Join the conver r.co.uk GEAR MODI nginee

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in our next issue ver get frustrated by glitchy digital readouts ergus Malcolm has done some research into causes of this perennial frustration.

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Website www.model-engineer.co.uk Why not follow us on Twitter? twitter.com/ ModelEngineers hashtag #MEW

Regulars 3 On the Editor’s Bench

The ditor has been wrestling with at-pack technology.

18 On the Wire

A paddle steamer and narrow-gauge loco in this issue’s round up of news from the world of engineering.

26 Scribe A Line

In this month’s postbag more views on content in as well as some fascinating mystery tools. We are always keen to hear from you – send an email to meweditor@mortons.co.uk.

38 Readers’ Tips

Our winner this month a better way to organise your parallels.

Send your tips to meweditor@mortons.co.uk, you could win a prize.

Another healthy collection of readers’ sale and wanted ads.

ON THE COVER Our cover features Mike Tilby’s shop-built micro-milling machine, see pages 14-17 for more information on this tricky precision operation.

THE UMPELBY ENGINE An ahead of its time machine from Fred Umpelby’s workshop.

You can log on to the new forum using your existing details, you can recover your password to the email address associated with your account. I’m pleased to say that the forum is presently working faster and appears more stable than it has been since the changes. www.model-engineer.co.uk

Hot topics on the forum include: One for the electrical experts How to reverse a brushed shuntwound motor, by Dougie wan.

Repairing damaged thread How to deal with a stripped sump plug,

by John McCulla

THE MAGAZINE FOR HOBBY ENGINEERS, MAKERS AND MODELLERS MARCH 2024 ISSUE 337 WWW.MODEL-ENGINEER.CO.UK

MICRO MILLING Mike Tilby builds a machine for high-precision milling.

CHURCHILL CUB III LATHE Brian Wood extends the rack on a surprisingly modern looking vintage lathe.

A Step-by-Step Guide from Howard Lewis.

Mar. 24

£5.85

INSIDE THIS PACKED

Three Arms … better than Two Some technology unlikely to appear in home workshops for a while, by Michael Gilligan.

Come and have a Chat!

As well as plenty of engineering and hobby related discussion, we are happy for forum members to use it to share advice and support.

Come and join us – it’s free to all readers!

AN IMPROVED MINI LATHE CLUTCH

ISSUE:

 AN A-Z OF METALS FOR MODEL ENGINEERING  CNC CONTROL USING A RASPBERRY PI.  A VISIT TO THE SMEE AT MARSHALL HOUSE.  USING BELT DRIVES.  TOAD5 – ADVANCED CNC CONTROLLER.  OPTIMISING AN OPTIMUM LATHE.  GRAHAM MEEK’S NEW BORING HEAD DESIGN.  TOOL ANGLE GAUGES.  50 YEARS OF THE UNIVERSAL PILLAR TOOL.  ADDENDUM GEAR MODIFICATION WITH FILENGRENE.  PLUS ALL YOUR REGULAR FAVOURITES!

Get more out of your workshop with MEW

March 2024

The Forum has changed!

Putting a square end to a 25mm bar. A beginner’s milling question, by Alexander avin.

66 Readers’ Classifieds

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THIS MONTH’S BONUS CONTENT

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March 2024

Extending a Lathe Rack

Extending the rack on a lathe Brian Wood had an unexpected surprise when he made this useful modification to is urc i u at e

T

he ¾ inch square form rack on this lathe was designed with a few teeth short of taking the carriage the full distance needed along the bed, as a result it ran o the tracks’ when wound up close to the tailstock. It was an irritating fault which became extremely tedious as the carriage had to be hauled back manually into engagement with the rack each time it happened. After nearly four years of ownership since rescue and restoration, I decided to do something positive about it.

1

Plan of attack, phase 1 Photograph 1 is a view of the lathe as it was; the end of the rack is barely visible but is just about level with the end of the carriage. Photograph 2 is a better view of that detail and oto shows the degree of short travel it created. Archive photos of earlier versions of the lathe, from which the Cub III was developed, reveal a much more satisfactory length of rack was fitted, finishing part way under the tailstock position.

OK, the shortage is maybe only half an inch or so in length, and it

2

Close up of the end of the rack.

March 2024

Lathe in current form. automatically prevents a crash into the support bracket for the leadscrew and power shaft, but why the change to this design feature in the first place There is an analysis in the postmortem of the reasons I believe lay behind the thinking.

The rack is 18 DP of 29 degrees pressure angle; to make an extension it needed a cutter I didn’t have. y initial thought was to replace it completely and I approached Halifax Rack and Screw for a quotation. They were very sorry, but they didn’t have a cutter

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Showing the effects of the short length of the rack,

›

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4

20 DP cutter.

5

Toothed ‘splint’ acting as a clamp. either which rather surprised me, their web site implied a wide capability in the supply of DP and metric racks all made on CNC machinery.

Time then for some ingenuity instead, using the 20 DP cutter I did have and shown here in oto I consulted the gearing handbook from HPC I have had for many years for the necessary data.

A 20 DP cutter requires a depth of cut of 0.1125 inches and at the pitch line the tooth width is 0.0785 inches. The

10 www.model-engineer.co.uk

corresponding photos for 18 DP are 0.125 inches for depth of cut and 0.08725 inches respectively. The di erences are + 0.0125 inches for DOC and + 0.00875 inches for tooth width when using a 20 DP cutter to generate an 18 DP rack. The geometry is of course the same and I did o er my cutter up to the short section of rack from the gap piece to see how it looked in practice.

It seemed simple enough, a bit more depth of cut combined with a measured

cutter displacement for a second pass.

I have a full case of precision spacing collars and shims bought years ago from eBay, very useful for such needs, within which I had a shim of 0.008 inches in thickness, close enough for this job. The tooth pitch for 18 DP is 0.1745 inches.

Rounding that up to 0.175 inches it is also close enough and would make easy tabulation of cross slide movements on my Tom Senior mill.

I would be cutting 17 teeth giving a total displacement error of 0.0085 inches over that length. For the few teeth of the driving pinion engaged with the rack at any one time, this error would have a negligible e ect on travel distance.

I wound the carriage along the bed to remove two screws holding the rack which promptly fell o with a clank into the swarf tray. I was somewhat surprised at how short it really was but being keen to press on I thought no more about it at the time. This oversight was to return to bite me later with rather more significance!

The job was duly set up to cut the new rack section into a ¾ inch square piece of brass, chosen to be both easy to cut and present a visibly deliberate addition to the original equipment. I planned to carry out a first pass of . inches in

Model Engineers’ Workshop

Extending a Lathe Rack 6

depth of cut and make a second pass, having removed the shim from behind the cutter, to run through again at the new cutting depth of 0.125 inches.

And as planned, this part of the job went without a hitch, all that remained to do now was to unite it to the Churchill rack. hat could possibly go wrong

Phase 2

The M4 securing cap head screws.

7

End packing piece.

8

The finished job.

March 2024

Photograph 5 is a view (staged and taken after the event) of using the short section rack from the gap piece as a toothed splint’ to help hold the joint alignment for bolting across the joint, having shaved the mating faces to make a snug fit. Photograph 6 is a view of the two cap head screws holding it together and photo 7 the short packing piece, pre-measured weeks beforehand, which I soldered to the end as a support beyond the machined facing for the rack.

All was well and good so far.

The time now came to o er it up to the lathe and mark the new ¼ Whitworth mounting hole with a transfer punch. I rolled the carriage aside towards the chuck, without even noting the irony of using the hand wheel to do so, only to gaze in disbelief at what had been revealed.

There was another section of rack already in place and only then did I realise, with that dreadful sinking feeling, what had gone wrong. I had done all this work on the wrong half of a twopiece rack! Oh, dear oh dear. Talk about a senior moment, Terry Wogan would have hung his head at it all!

In my defence, on all the lathes I have used and owned, I have never found one with a rack in other than one continuous length and took it as read that this was the standard method of construction.

Of course, I should have paid more attention to the warning signs earlier on when I was surprised at how short the rack appeared to be. The other half was then completely hidden from view behind the carriage. hat to do now And here I was indeed most fortunate; Providence had smiled upon me. The two halves of the rack were the same length, even the fixing holes were in the same positions and all I had to do was swap A for B and carry on as if nothing had gone amiss. hat a blessed relief!

To finish, photo 8 is a view of the ›

11

9

Rubber buffer in place.

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The whole rack completed installation, photo 9 shows the impact bu er I cut from a rubber mounting bush for a Landrover shock absorber, split radially to slip over the power shaft. Photograph 10 has been included to show the full rack, with the joint positions marked by slips of paper.

Post-mortem This salutary story reminds me of the rather jaundiced advice o ered by my former boss at Rolls-Royce, Derby. He was the departmental head responsible for the non-destructive inspection of critical parts on aero engines.

It was interesting and rewarding work, intended to find hidden and potentially

12

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dangerous faults on engines prior to operational service.

He always maintained that one should never believe what you were told and only half of what you saw. In this case I expected to find a short rack and did just that! I believe the explanation for the two-piece construction is as follows.

When this lathe was in the design stages, the country was running on a full-time war economy footing and every possible means of avoiding material excess and waste was relentlessly pursued. The redundant end of a rack taken right up to below the tailstock might have been an immediate target for such pruning.

Another target of the time may have resulted in the use of truncated leadscrews, still capable of function of course but with nil points for appearance! These too I have seen, and they look very strange as a result.

The rack halves on this lathe are about 8 ¾ inches in length and just within the 9-inch cross-slide movement of an Elliott Victoria Universal milling machine. Churchill might have chosen to make the racks in batches held in an indexing jig on such a mill to fulfil the economy requirement on this component, and, as a bonus, save the expense of buying full length versions in from a specialist supplier. One length from the batch cut in two would readily supply the sections for the gap pieces with minimal o cut waste.

The e ect of this minor economy’ was clearly noticed not just by me alone.

On closer examination, the end of the rack was bruised, worn and burred in places by frequent re-railing when this lathe was in industrial use. Elsewhere on the lathe, 7-inch lengths of 16 DP rack would easily accommodate the selection guides in the screw cutting gearboxes. Using another jig on the same mill, making batches of these would have been quite feasible.

Despite the unpleasant surprise it gave me, the outcome has been a complete success.

Model Engineers’ Workshop

Model Engineer Archive

From the Archives With over 125 years of Model Engineer magazine and nearly 35 years of Model Engineers’ Workshop in our archives, there’s a huge selection of fascinating and often useful ideas for the workshop to be found.

These handy tips are from from Model Engineer, volume 7 , number 2 , April 7, 3 . ote the rather fancy Art Deco logo used by the magazine in the thirties.

March 2024

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Micro-Milling Mike Tilby describes the construction of a scratch-built machine tool for use with very small milling cutters.

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The micro-milling contraption.

M

icro-milling is the term frequently used to describe the use of very thin endmill cutters. For example, the end mills I mainly use at present have a diameter of 0.5 mm (0.02 inch). Using such micro-milling tools is important for my current project but when I started it, almost 10 years ago, I was unable to find any discussion of this topic in relation to model engineering.

There still seems to be a lack of any information on the topic so I thought that a description of my venture into this field, and the resulting

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contraption, might provide some points of interest (or derision) for some readers. As can be seen in photo 1, this project has definitely not resulted in one of those highly finished pieces of well-crafted machinery of which their constructor can be justifiably proud. owever, it may be su ciently unusual as to provide some amusement and it has proved itself capable of achieving the results it was designed for.

I don’t claim the approach to be described was the best way to have proceeded but, of course, I don’t have to justify what I do since I am not getting

paid to carry out this (or any other) work.

In any case, the project has successfully achieved several important-to-me goals. Firstly, it has enabled me to cut some miniature turbine blades with complex profiles, photo 2. Secondly, it has provided challenges, interest and enjoyment (plus plenty of frustration) for the person doing it. everal years after starting the project I am still finding ways of refining the machine that has resulted.

Thirdly, it has allowed me to make use of many items that were collected over the years because “they might come in handy one day”. (Hence, it was very

Model Engineers’ Workshop

Micro Milling steam turbine with improved e ciency.

To pursue this venture it was necessary to create a large number of very small blades because my hope was to build a multi-stage turbine and I envisaged experimenting with di erent blade shapes. Small blade size is important because the size of a turbine should be in proportion to the desired rate of steam consumption. Turbines can consume steam at much higher rates than reciprocating engines of similar size and so, to achieve both maximum e ciency and modest steam consumption, the turbine and its blades need to be small.

Therefore my aim has been to cut blades that are, at most, 0.06 inch high and 0.08 inch wide. y e orts were inspired by the articles written by Prof. Chaddock whose work on developing miniature steam turbines was described in Model Engineer in the 1950s (Ref. 1) and is represented by models now in the collection of The Society of Model and Experimental Engineers (SMEE) (Refs.

2, 3). Prof. Chaddock made D-type end mill cutters of 0.032 inch diameter by grinding down 1/8 inch diameter high speed steel (HSS). These days one can easily buy proper multi-edged tungsten carbide micro-milling cutters with diameters down to 0.3 mm (0.012 inch) and even smaller sizes are available.

The types of cutters that are commercially available will be described in a future part of this article but first it seems appropriate to discuss the not insignificant challenge of how to use these delicate tools e ectively. In this case that means cutting a variety of smoothly curved profiles.

2

Micro-milling machines Preliminary versions of two types of miniature turbine blade cut using the home-made contraption, co pared to a inch dia eter drill, all at about the sa e agnification. classic e a al profile shol t pe round nosed profile. oth t pes of blade are 0.06 inch high and 0.08 in. wide and were machined using 0.5 mm diameter end mills.

(Photos were taken using an Andonstar ADSM-201 HDMI digital microscope). cheap to build). In addition, it was very pleasing to successfully automate the cutting process using motorised slides that were scratch built and controlled by programs written by myself.

Much of the information in what follows has been picked up from various sources and I don’t claim it to be authoritative. So if any readers with

March 2024

expert knowledge spot errors in these articles or can expand on any points, then I hope they will pass on the benefit of their experience.

The challenge The need to carry out milling of very small components arose from my longheld desire to attempt to build a model

Whilst looking into what machine tools might be useful for working with very small diameter end mills, it soon became apparent that the term ‘micro-milling’ means very di erent things to di erent people. In the realms of milling machines that are aimed at the hobby market, a micro-mill seems to signify any machine that is a bit smaller than some other milling machines. For example the ‘Clarke CMD10 Micro Milling Machine’ has a 10mm capacity chuck and runs at 100 – 2,000 rpm, while the ‘Proxxon FF230 Micro Milling Machine’ is supplied with 6, 8 and 10mm collets and runs at 280 ›

15

All the above factors combine to increase wear rate and load on a cutter, however, its very small diameter makes it extremely delicate and only capable of withstanding small side-ways forces.

Also, I gather that at the very highest speeds even holding tools reliably and accurately becomes challenging because centrifugal forces on the chuck can distort the taper by which the tool is located. Furthermore, it is di cult to measure run-out at the tip of very fine cutters since a dial gauge is not applicable. In industry, specialised (= expensive) laser or capacitative non-contact measurement methods are used.

Figure 1

Choice of spindle

Figure 2 to 2,200 rpm. The ‘Taig 2018DSLS Micro Mill’ is somewhat faster with speeds of up to 10,000 rpm.

In contrast, in the industrial arena, micro-milling seems to generally mean a process done on a machine that uses end mills with cutting diameters well below 1mm. One website says ‘true’ micro-milling uses cutters with diameters less than 0.015 inch (0.38mm) and sometimes down to 0.005 inch. Cutters of this type commonly have shank diameters of 3.125 mm (1/8 inch.) or 4mm and are generally used at very high speeds.

Industrial micro-mills usually run at more than 50,000 rpm, with some running at 100,000 or even 300,000 rpm. In industry, high speeds are important to increase production rates, but they also help by causing swarf to be ung away from the cutting area thereby reducing the risk of the tool clogging up and breaking.

Apart from the need for high spindle speeds, use of very small cutters is associated with some problems that are not relevant to cutters in the more usual range of sizes.

16 www.model-engineer.co.uk

Firstly, when the size of chip being removed becomes very small it is impossible to make a cutting edge that is sharp relative to the chip size since even the sharpest edge appears blunt when seen under su cient magnification ( ee fi ). Therefore, when the depth of cut is very small the e ective rake angle of a very small cutter is likely to be negative and rubbing by part of the cutting edge seems likely. However, I don’t know if this is relevant to the cutters I am using or only to much smaller sizes.

Secondly, cutter run-out is a particularly important issue. Eccentricity of the cutting tip can result from the tip not being truly concentric with the shank of the tool, from errors in the chuck and collet, from errors in the spindle and from vibration of the spindle. With a very small diameter cutter, a normally insignificant degree of eccentricity could amount to a large percentage of the cutting diameter and would result in one tooth doing almost all the work. (See fi 2). Also, under some circumstances runout can lead to other problems, as will be discussed later.

Prof. Chaddock cut his turbine blades using a brilliantly simple home-made tool, photo 3, in which the spindle was a plain shaft running in a ball race. The shaft was driven by an over-head belt running over a pulley located just behind the collet chuck.

As discussed above, it seemed that to use true micro-milling cutters the spindle should be capable of very high speeds and of running very true. The use of a spindle similar to Prof. Chaddock’s did not seem ideal for my project, however I could not find an a ordable mill with a spindle that ran at higher speeds than the hobby machines mentioned above. I did not like the idea of paying a lot of money

3

Prof. Chaddock’s entire blade milling attachment with collet chuck at the near end (From Ref. 1).

Model Engineers’ Workshop

Micro Milling the pros and cons of the design. It will then describe how the spindle is moved automatically by a home made electronics unit based only on simple microcontrollers without the direct involvement of a computer.

To be continued

4

ro on

References

professional drill grinder

for a specialised spindle, especially since the whole project might fail. Eventually I settled on a ‘Proxxon IB/E professional drill/grinder’, photo 4, since I had read comments that they were better made than the ubiquitous Dremels. Also they have a good, machined mounting collar suitable for clamping reliably, they operate at speeds up to 20,000 or 23,000 rpm (the speed increased in later versions) and the makers claimed a high accuracy for the collets. Lastly, if the whole project failed then the tool would be useful for other tasks.

Since building my contraption I saw adverts online for some impressivesounding spindles from China such as one that runs at up to 60,000 rpm, is water cooled and cost just £162.

However, that would need a variable frequency drive and I wonder what could be done when the ball bearings wear out.

(Some expensive high-speed spindles have air bearings - e.g. ref 4).

After I had built the main part of the contraption I joined SMEE and then I soon discovered an interesting article

by Jörg Hugel in a back-issue of the Society’s Journal. This article (ref. 5) reassured me that I’d made a reasonable choice of spindle since it described careful assessment of a Proxxon IB/E in relation to its use for engraving. Also, in a later article Jörg described the design and use of a box chuck for the same machine (ref. 6).

This series of articles will describe the contraption that evolved and discuss

1. Chaddock, D. H. (1950-51). An experimental steam turbine plant - Parts 1-5. Model Engineer 103 (2587): 966 -969; 104 (2589): 17 – 22; 104 (2590): 55 – 58; 104 (2591): 110 – 114; 104 (2592): 126 - 130.

2. Tilby, M.J. (2015) Professor Chaddock’s mystery object. SMEE Journal 23 (3):18—21.

3. Tilby, M.J. (2016) An Experimental Steam Turbine Plant by Professor Chaddock.

Model Engineer 218 (4551): 96 4. www.airbearings.co.uk/en/ 5. Hugel, J. (2010) Cutting and Feed Speeds for Engraving Cutters. SMEE Journal 18 (5):24 – 27.5 6. Hugel, J. (2011) A box chuck for engraving spindles. SMEE Journal 19 (1):28 – 30.1

Next Issue In our

Fergus Malcolm has found an explanation for why inexpensive digital readouts glitch so often, and worked out a cure.

Keith Keen has designed a tool to simplify the tricky operation of trepanning disks.

Coming up in issue 338, April 2024 On sale 15 March 2023 Contents subject to change

Adrian Rawson 3D prints a practical vertical slide.

To pre-order your next copy of MEW visit www.classicmagazines.co.uk or call 01507 529 529 17 DON'T MISS THIS GREAT ISSUE-SEE PAGE 54-55 FOR OUR LATEST SUBSCRIPTION OFFER March 2024

On the

Wire

NEWS from the World of Engineering

Medway Queen Centenary 2024 Paddle Steamer Medway Queen, was built by the Ailsa Shipbuilding Company of Troon, Scotland, and launched on St. George’s Day (23rd April) 1924. Her maiden voyage across the Thames Estuary was on Friday 18th July of that year, under the ag of the ew edway Steam Packet Company. Medway Queen’s standard route was then from Strood and Chatham to Southend, and then back across the estuary to Herne Bay. The excursion service was seasonal, usually starting at the Whitsun Bank Holiday weekend (now the Late May Bank Holiday) and terminating in September. She worked these routes from 1924 until the beginning of September 1939, and again from 1947 to 1963. Variety was created by special excursions and events such as Chatham avy eek and the 37 and 53 pithead aval eviews.

During the Second World War, HMS Medway Queen was a commissioned minesweeper and took part in the evacuation of the BEF from Dunkirk. orking out of amsgate most of the time Medway Queen and her crew made seven return trips to the beaches or

the East Mole at Dunkirk. They rescued thousands of men and seven o cers and crew received gallantry awards.

When her excursion work ceased the ship’s future was extremely uncertain but, in 5, she was purchased to be a club house and restaurant on the Isle of Wight. The “Medway Queen Club” opened in May 1966 and ran in various guises until the end of 1974. All aspects of the ship’s career in all chapters of her history are extensively covered in books published by the Medway Queen Preservation Society.

Medway Queen is moored at Gillingham Pier, and is open to the public on Saturdays from 11am to 4pm (last admissions 3pm) starting on February 17th. The Medway Queen Preservation Society plans appropriate celebrations, and these begin in earnest on Sunday April 21st with a Memorial Service in ochester Cathedral for an invited crowd of people with family connections to the ship at any stage in her career.

To accommodate visitors to the ship over this period the vessel will be open as usual on Saturday 20th April, and she has a second public day on Monday 22nd.

Medway Queen now berthed at Gillinham Pier - Colin Matthews.

Then on Saturday 27th the usual public open day will be enhanced with the added attraction of a visit from some Dunkirk Little Ships and the Chatham Cruising Society. The fund-raising possibilities have not been forgotten and a summer draw is planned with ticket sales from the beginning of April until the end of June and some exciting new merchandise which will be available to personal visitors and also via the society’s website www. medwayqueen.co.uk.

HMS Medway Queen - John Slayford.

18 www.model-engineer.co.uk

Model Engineers’ Workshop

On The Wire

New Clarke MIG103NG No Gas MIG Welder The new Clarke I 3 I elder is ideal for automotive and general fabrication, and as it does not require a gas cylinder, it is much easier to transport and store in the garage or workshop.

The I 3 uses ux cored steel welding wire, a type of wire which produces its own gas shroud as it burns.

This means the welder can weld steel, without gas, whilst providing optimum performance and reliability. This new Clarke unit produces a maximum power

of 90Amps, allowing it up weld mild steel up to 4mm thick.

The I 3 is sold complete with a welding torch, 2 x 0.9mm torch tips (1 installed in torch), 1 x earth clamp, 1 x two piece welding mask, 1 x mini spool of Flux cored wide and a wire brush/ hammer.

The Clarke I 3 is available for £161.99 inc VAT. Visit www. machinemart.co.uk/p/clarke-weldmig103ng-230/ for more information.

Arrival of ‘Fire Queen’ at Vale of Rheidol Railway ‘Fire Queen’ is a unique steam locomotive: it is believed to be the oldest narrow gauge locomotive in existence, having been built in 1848. The locomotive will arrive in Aberystwyth in late January, and will be on public display in the new museum, display & events building when the railway opens for the new season in late March 2024. The Directors Coach is also going on display, prior to a move to the Bala Lake ailway.

‘Fire Queen’, her tender and the Directors’ Coach were on loan to ational Trust Cymru, and were accepted in lieu of tax by HM Treasury in 2021. They temporarily resided at Penrhyn Castle pending permanent allocation.

Ll r ap Iolo, anaging Director of the ale of heidol ailway, said e are grateful to ulian Birley for o ering us the Director’s Coach for short term display until the Bala Lake ailway can exhibit it themselves, and also for recommending us to Cyngor Gwynedd as a possible temporary home for ‘Fire Queen’. It is good that the public can continue to enjoy it, rather than it going into temporary storage behind closed doors. We are excited to have such a historic exhibit to display in our museum, to showcase alongside other rare and unseen rolling stock from our collection.

We are really happy to have ‘Fire Queen’ on public display, until it returns home to where it belongs at Gilfach Ddu”.

This will be a temporary visit, as ‘Fire Queen’ will eventually return to Parc Padarn to be displayed in it’s original

March 2024

shed. This building is set to be restored

by Cyngor Gwynedd, using Levelling Up funding granted by the UK government.

Whilst this restoration work is being carried out, “Fire Queen” will be temporarily allocated for display at the ale of heidol ailway in Aberystwyth.

In addition, the Directors Coach has been allocated to move from Penrhyn Castle to the Bala Lake ailway. It will be temporarily displayed at the Vale of heidol ailway alongside ire ueen’ during the coming season, before moving on to Bala.

The public will be able to view both ‘Fire Queen’ and the Directors Coach at the ale of heidol ailway from late March onwards, when the railway opens for the season. The railway then runs daily until the start of ovember.

19

Addendum modification for in o ute ears art Jacques Maurel explores the theory behind the gear modifications used in his earlier articles about the Filengrene gear design software.

O

n the topic of ‘gear cutting’ I’ll write only about “generating” machines, the tool being a rack or a pinion (using a shaper like cutting movement along the gear axis) or a hob (that can be seen as a rotating rack).

See s etc showing a gear cutting like process, the right gear profile being the envelope of the left one.

For these machines, the gear teeth are automatically generated by the relative movement between the tool and the gear blank. So, any number of teeth can be cut for a given module and pressure angle that defines the tool.

The tooth profile is defined by the “generating rack” (see fi ure u er) whatever the process used. During the cut, the pitch line of the generating rack is rolling without slipping on the pitch circle of the cut gear. ote A cutting rack is di erent from a standard one as the addendum is 1.25 module and the dedendum 1 module (to get the play at the right place) see fi eo .

8

ndercut ro em

the tooth profiles don’t stay tangential and usually the cutting tool bites into the tooth dedendum of the pinion (see etc eft this problem is

For a small number of teeth (under seventeen for a 20° pressure angle, but under 30 for a 14°30’ pressure angle)

0.

4m

1.25m

m

40°

Involute curve

3.14m Standard rack

m

x = 1.4 Pitch circle for x = 0

1.25m

0.

4

20°

x=1 x = 0.5

m

Base circle x=0

3.14m

x = -0.5

Cutting rack

Figure 4

20 www.model-engineer.co.uk

Figure 5

Model Engineers’ Workshop