HANDWHEEL DIAL FOR EMCO 7 AND 8

Part one by Graham Meek

My first lathe after starting my apprenticeship was an Emco Unimat SL, purchased via a mail order catalogue. This served me well for a number of years and when the Unimat 3 was introduced this too was added to the budding workshop. Over the years our expectations grow and so do the size of the models we would like to build, it was soon realised that a larger lathe was needed. Given my already largely Emco workshop it will come as no surprise to the reader that the next lathe I decided to purchase was a new Compact 8, this was not the very first machines which had chrome finished handwheels.

Measuring the length of a workpiece on the Unimat lathes was never a problem as the longitudinal feedscrew was always engaged. When the Compact 8 first appeared it had no longitudinal or leadscrew dial. This was only added when the milling facilities were added, which if I remember correctly was first started with a vertical slide and later followed by the adaptation of the Compact 5 milling and drilling unit at the back of the lathe bed.

Accurate measurements were, therefore, restricted to the use of the topslide, provided they fell within the range of the topslide movement. Measurements beyond this relied on the use of a good rule and my eyesight, which I have never considered good and it is after all just a comparator. It is a bit like reading the old vernier scales of the pre-digital calipers, the measurement to a degree is open to interpretation, especially if the vernier is between lines.

Some means of measuring off distances accurately was required, similar to that which I used in my day job in industry via the use of the Apron handwheel dial, this I thought ought to be possible. One day while following the tool along a stationary workpiece with a rule to set out a length and operating the apron handwheel at the same time. I suddenly realised that the handle of the handwheel was at the 12 o’clock position on 22, 44 & 66 mm readings on my rule, the penny finally dropped, was 22 mm per rev the answer to my problem. Further investigation with a measurement taken over 10 turns of the handwheel showed it was too near to 22 mm not to use this as the basis for my dial.

The reader will appreciate that this is a long time before I designed the Super 7 Handwheel dial with it’s internal gearing, (EiM March 2007 to May 2007, & “Projects for your Workshop Vol 1” pages 8290).

At his time gear cutting was something to be fought shy of, mainly because I had not done any gear cutting at that time. However all this was about to change as in order to fit a handwheel dial to my Compact 8 I would have to make a new

Original shorter prototype handwheel pinion shaft.


handwheel pinion shaft. The reason being the standard Compact 8 handwheel is retained by a cross pin, and this retaining pin method would be inaccessible under the friction dial when this was fitted to the handwheel boss.

The handwheel proper would have to follow the same method of fitting as the tailstock handwheel, ie a 3 mm wide woodruff key, (Emco Part No ZFD 88 0337 WOODRUFF KEY), and an M8 self-locking or Symonds nut for endwise play adjustment. While it would be possible to drill and tap the end of the existing shaft to provide a means of adjustment the shaft would really be too short for the handwheel as the dial design also introduced a backplate for the dial index mark, more on this later. Luck would have it that the boss on the Compact 8 Apron handwheel had been machined to the same diameter as the Tailstock handwheel. Thus it was this diameter that formed the basis of the internal diameter of the dial being 22 mm.

Those who have made the Myford Super 7 dial will also note this, too, is 22 mm diameter. This is no coincidence as originally the dial friction spring used on the Compact 8, (Emco Part No B2A 000 080 FEED SPRING), was to be the source of the friction on the Myford S7 version, and this was how the prototype unit was built. However, in use this friction spring was felt to be ineffective as the larger mass of the Myford dial would carry on moving after the handwheel had stopped due to the flywheel effect under manual usage.

This, however, was never a problem with the Compact 8 design as the dial is considerably smaller as well as much lighter. At the time this dial was made there were no photographs taken of the actual build as I had never in my wildest dreams ever thought that I would one day write about my work. As an aside it is interesting to note that it was in response to a letter that appeared in EiM on the Hemingway Myford Super 7 dial and this dials internal workings that started me off writing for EiM which is now almost 10 years ago.

Thanks to Neil Hemingway there does survive a rather poor photograph taken by me in the days of Zenith E’s and colour film of a display item made to promote this dial series at a Model Engineering exhibition in the South of England, I think it was Woking but I am not sure. The better photographs were sent to Neil and one was used in the catalogue of the day. The dials in the picture were to be supplied finished like the Super 7 versions by Neil and made by myself. The design featured two different types of construction as well as the two measuring systems. One design the “Standard” featured an “Oilite Bush” centre bearing in the  backplate. While the other, the “DeLuxe” version featured two radial ball bearings, (the terms Standard & DeLuxe were added by Neil as a way of promoting the product and ordering from me).

Obviously there was a price advantage with the simpler “Standard” construction of the Oilite bush. Many years later when Neil decided to sell his business he returned this demo model and other Emco enhancements to me. I have been able to take some photographs of the few parts that I have retained, but these are the parts belonging to the prototype.

The original had no Oilite or ball bearings and showed up one or two pitfalls to my first ever (naïve) design. The play in the apron bearing would allow the handwheel to move up and down as the handwheel was rotated, this in turn would allow the dial to contact the top and bottom of the backplate. This contact introduced a stall in the rotation of the dial relative to the handwheel and with it an error in the distance measured. As a stopgap to designing what would become the production version the prototype backplate was bored out to receive a single ball race and this is the one shown in the photograph. While the single ball race went some way to eliminate the problem, adding the Oilite bush or the two ball races totally cure the play problem.

Rear view of modified prototype backplate.
Front view of modified prototype backplate with single ball race.

The other problem was that after a useable band of knurl was machined on the original 10 mm wide dial the the room available for graduations and numbers was very small. In fact the first dial was not that dissimilar to the Emco tailstock dial only larger in diameter, but extremely difficult to read at arms length. Adding the additional ‘bearing’ arrangement allowed for a wider dial to be fitted as the dial could also overhang the bearing housing extension now present on the backplate. One of the ‘Demo’ handwheels did find it’s way onto my friend’s Emcomat 7 so I know this design fits this range of lathes as well. The dial should also fit those lathes designated Emcomat 8.4 and 8.6 which superseded the Emcomat 7, as all these lathes use the same apron assembly, but it is always wise to check before hand. I remember well the differences with the MiniLathe handwheel dial of recent months.

The new pinion shaft was, as I said earlier, my first foray into gear cutting and to ensure I did not go too deep on the gear I first of all dismantled the apron of my Compact 8 and measured over 2 off 3/32” dowels placed in the pinion gear. This measurement was 17 mm and is carefully recorded in my shop notes for that year as well as the cutter depth of 2.25 mm which was using a standard Emco Mod 1 gear cutter.

This first attempt at gear cutting is all that I needed to get me started into an interesting subject in itself and believe me even after 40+ years in industry I am still learning things today about gears and gearing. I also had the advantage just after making this new pinion shaft of spending 3 months of my apprenticeship on the Gear cutting section at Dowty Rotol, Gloucestershire, which helped to fill in some of my knowledge gaps.

The Circlip groove in the pinion shaft is only required on the DeLuxe version as this allows a degree of preload on the radial ball bearings, but without trapping the handwheel pinion against the inside of the apron. This preloading does not want to be overdone as these are only small ball races, it should be sufficient just to take any play out of the bearings and no more.

Original modified handwheel.


The modification of the Apron handwheel at first appeared to be a problem with some purchasers of the dials who sought to purchase a ready finished part from Emco instead. This option might still be available today but I would check first with ProMachine Tools Ltd as regards the availability. This would also apply to those

constructors who do not want to make their own friction spring and woodruff key.

Bought-in items.


There is no real problem in modifying the Apron handwheel as the Tailstock handwheel can be used on the Apron when the dial parts are finished while the modifications are carried out the Apron handwheel. The only things that need to be done to the handwheel are to reduce slightly the end face of the boss, provide an undercut for the friction spring to fit in and to cut the 3 mm wide keyway.

This last item was also my first attempt at cutting an internal keyway when I made the initial dial conversion on my Compact 8 lathe, if I remember correctly. I am sure that this last operation was what put so many people off modifying their own handwheel, the actual modified handwheel off the prototype is shown in the photograph. I do remember that I used a boring bar with an inserted 3 mm diameter HSS tool bit probably from the shank of a broken drill.

The boring bar was held in an eccentric holder similar to those later advocated by George Thomas, in his article on Boring Tools, but this is many years before this article appeared. This type of boring bar holder can be found in GHT’s book “The Model Engineers Workshop Manual” and using this technique makes getting the tool bit dead on centre height easy. It then becomes a simple matter to rack the carriage to and fro while applying a cut with the cross slide of about 0.025 mm per stroke. Every few passes it pays to any spring out of the bar by doing a few passes with no increase in cut depth.

Engraving the first dial with 110 divisions did present me with a slight problem. In that my Emco dividing equipment at the time only used dividing plates to give fixed numbers that were divisible into 24, 30 and 36. I finally overcame the problem by providing a paper scale that fitted around my Compact 8 chuck body with 110 spacings. This was made in those days at the traditional drawing board with a T-square, set square and compass, but the technique is dead easy to perform these days with the aid of AutoCad or similar.

Using this scale and a fixed pointer attached to the bedways, (that also served as a stop for the carriage), engraving proceeded using various drill shanks to control the different lengths of the engraved line that were required. As regards the lengths of the engraved lines initially I just copied those on the tailstock dial just to keep things neat. There are only two lengths needed anyway as each graduation equals 0.2 mm of movement, so there is one long line for the full millimetre and the shorter ones are for the 0.2 mm increment. The length of lines adopted for the “production dials” followed those of the Myford S7 simply because I used the same multiple stop and the width of the dial face was the same. The line lengths are just for reference 2.5, 3.0 & 3.5 long and the dial was stamped every two millimetres. For graduated lines I use a tool with an included angle of 40⁰ which is laid on it’s side in the toolpost. It will pay to stone a small radius on the tip of this tool, taking a single cut even 0.15 mm deep will eventually take the point off a dead sharp tool anyway, usually this happens before the dial is finished. The subsequent lines after the breakage being much rougher and not so wide. As regards getting the curls of swarf off afterwards I use a piece of scrap brass pulling the curls back towards the beginning of the engraved line. I also leave about 0.15 to 0.2 mm on the dial diameter to allow a small clean up cut to be taken after the stamping operation. This needs to be remembered when setting the depth of the engraved line. While I use a toolpost grinder now for much of this type of work these days the originals would have been finished turned, using HSS and dressed with a Dead Smooth file. If this is done with the spindle stationary with the file incrementally fed around the periphery in a slow rocking motion while applying gentle forward pressure, the finish afterwards is not unlike a good ground finish. If the file is not rocked then all that will be produced is a series of small flats. Do not be tempted to polish this surface, the edge of the dial as well as the graduations will become rounded and the glare from

the polish will make reading difficult.

The Imperial version is a bit of a compromise and without internal gearing it was always going to be as 22 mm in imperial units works out at 0.86614”. This is not the easiest dimension to work with when doing multiple turns of the handwheel. It is not the easiest dimension to provide a scale for either, unless the dial is engraved every 0.005”, but even then the dial is a “thou” short Thus it was that Neil and I agreed that 86 divisions or 0.860” per revolution of the handwheel was a much more logical calibration. However given these days the advantage of AutoCad then a similar scale to fit around the chuck with 173 divisions will give a dial with 0.865” that is more accurate than first envisaged. If a simple spreadsheet is made using this 0.865 dimension and kept by the lathe then the required “full” measurements, eg 1.5” can be read of the spreadsheet. If the spreadsheet is constructed with a little thought this can be such that at the required dimension the actual dial reading can be provided. I have done a similar sheet to this with my Maximat Super 11 lathe. This lathe has 19 mm per revolution of the handwheel, (this is as supplied by the factory). If I should want to move say 50 mm then from my spreadsheet I now it is 2 full turns and “12” on the index.

When I was younger with the Compact 8’s 22 mm dial I could do all this in my head but these days as I am getting older it pays to play safe as the memory sometimes plays tricks on me lately. The spreadsheet can also be configured to accommodate the shortfall of 0.001” per rev if so desired, although this is only really significant I feel after 5, 10 or more turns.

When the decision was made to make these dials for sale, then a more direct means of indexing was derived to fit my Maximat Super 11. This setup is shown fitted with the 100 division wheel in use for another project I am working on and the means of fitting this to the lathe. The system devised only allows one tooth to pass at a time therefore saving considerable time and any chance for a mistake. I understand that Steve Tracey who has taken over the manufacturing rights to all my “Dials” has rigged up a more modern system which is fully automatic using Stepper motors. I also understand from Steve that he intends to provide a kit of parts for the design submitted here. He can be contacted by searching Google for Steve Tracey Tooling Services Ltd, I would like to add that I no longer have any connection with this venture financially.

The fitting of the backplate to the lathe apron requires two M4 tapped holes to be drilled and tapped. As these are intended to be cheese head screws then 4 BA could be substituted. These can be spotted through from the backplate once the new pinion shaft has been fitted to the apron. Try to get the cutout in the rear of

the backplate symmetrically disposed about the rack pinion bearing. The backplate does not want to foul this shaft when fitted permanently to the apron as this may mean the apron and carriage cannot be moved when refitted to the lathe. Also take care when readjusting the fingers on the apron that make contact with the underside of the bedway. These only need to just touch the bed and should not provide any drag.

A simple way to ensure a return to the same setting is to mark the cap screw with a small scribed line and a temporary pencil mark on the saddle casting. To avoid smudging the pencil line out I usually use a piece of masking tape for the pencil or ballpoint mark. It goes without saying that reassembly needs to carried out with extreme cleanliness, any swarf trapped on the mating surfaces will disrupt these fine settings.

Endwise adjustment needs to be carried out with some degree of care especially if the “Standard” version was constructed. If the M8 self locking nut is over tightened then the whole assembly will lockup solid. This is something that cannot happen with the DeLuxe version, but it is still possible to permanently damage the ball races if this is overdone. Just remember that during any zero setting of the handwheel dial the handwheel needs to be urged gently in the direction of travel to ensure there is no backlash in the system.

Also during machining under longitudinal power feed the carriage is in advance of the dial, because the leadscrew is pulling the gearing along. When nearing the desired dimension all that is required is again just gently urge in the direction of travel, so that the dial has caught up with the carriage.


FOR DRAWINGS  SEE PART TWO HERE.


Escapement pivot fitted into cover securing tapping.


How the division gear is fitted to the end of the lathe spindle.


Escapement on the pivot pin.


Escapement pawl and return spring in position.


Modified Maximat bed stop with S - M - L stops for the length of the engraved lines.