Micro-Milling Machine

A watchmakers lathe is a good starting point owing to the precision of the slides and spindles, but it lacks the z-axis. In more recent years kits became available to convert Chinese-made watchmakers lathes into small vertical milling machines, but the milling table on them is arranged in a conventional way.
In my stock of watchmakers lathe bits and pieces I have collected over the years parts for several D-bed lathes of variable state of conservation. Some ‘scrap’ was also bought on purpose. From this parts I now want to construct a micro-milling machine with as little work as possible.
As design specifications I decided that the mill should be able to machine in a space of u 20 mm x 20 mm x 20 mm. This requires movements along the x-, y-, and z-axes of around 40 mm. There should be a fourth axis with a 360° rotation, that should be able to rotated under load. This axis should also be able to be moved from the vertical into the horizontal (5th axis). All those movements should be realised with parts from watchmakers lathes, so that no dove-tail slides need to be machined from scratch.
The back-bone of the mill will be a special D-bed that I obtained recently. It was originally meant for the conversion of a lathe into a small precision pillar-drill. Its lower end is turned down to a diameter that fits into a lathe foot. The foot that I am going to use probably came from a British Pultra-lathe.
Another key part is an old and somewhat battered cross-slide from a Lorch, Schmidt & Co. D-bed lathe. This will be the x- and z-axis of the new milling machine.
The y-axis will be constructed with the help of a nearly scrap lower-slide from the cross-slide of a Lorch, Schmidt & Co. WW-lathe that I was able to buy cheaply. The spindle and micrometer-dial will have to be made from scratch. A 6 mm-grinding spindle of unknown make will serve as milling spindle. This limits somewhat the maximum diameter of cutters that can be used to ones with about a 4 mm-shaft, but the machine is meant for light work after all. On the other hand, many years ago I made an adapter for 6 mm end-mill for use in the lathe together with a vertical slide (before I owned a milling machine).
The fourth and fifth axis will be formed by the dividing head that I made some years ago from a 6 mm-watchmakers lathe grinding-spindle. For the moment it will be simply screwed onto the cross-slide as for use with a lathe. This gives considerable flexibility for the positioning at any angle between vertical and horizontal. The setting will be a bit time-consuming and has to be done with templates.
So far the existing parts that need to be re-conditioned somewhat at a later point in time.


In order to mount the y-axis to the column, an adapter is needed. This adapter is fashioned from a small aluminium-block that was bored for the 20 mm column. The top-side was milled to a close fit on the lower slide from the WW-lathe, which is clamped down with a bolt. In this way the lower slide can be moved by about 15 mm, giving a greater depth of throat, if needed. It was planned to use a rectangular key to lock the adapter to the column. However, it appears that the two set-screws lock it sufficiently secure to the column. Practical experience will show whether this is true.

The 20 mm-hole was drilled and bored on a face-plate in the lathe to ensure that it is exactly vertical to the top and bottom of the adapter block. The aluminium-block was srewed down onto the face-plate using a 6 mm hexagonal bolt. Luckily, a suitable hole was needed anyway for the locking bolt of the slide. Other hexagonal bolts prevent the block from moving during the machining operations and act as counter-weights. After the functional machining was complete, the adapter was 'beautified' by giving the edges a half-round camfer. For occasional jobs on aluminium like this, I use cheap woodworking router bits ... don't tell any real mechanic.

The Lorch, Schmidt & Co. milling attachment will be held between two angle-irons screwed-down onto the slide. The locking will be effected by an excentric bolt acting as a cam. I had hoped to use the threaded holes that a previous owner of the slide had made, but they did not fit the angle-iron I had in my stock, so new holes had to be drilled and tapped. The pair of angle-irons was squared and trued on the mill using a fly-cutter. The above picture shows also the drive unit made for the toolpost-grinder of the WW-lathe, which in fact looks very similar to what the future motorised milling head will look like.

Hick-ups: While working on some part, the Sherline-motor of the mill suddenly broke down. It had some problems before, but I thought with new brushes these were resolved. However, the new carbon brushes had been eaten away very quickly. I took the motor apart and found that several pads on the commutator had been ripped out and leads to the coils cut. Probably a write-off ...

Set-up for cutting the thread on the y-axis spindle		The first pass	Almost finished thread	Calibrating the thread using a die	Finished spindle	Set-up for drilling out top-slide	Milling top-slide extension	Top-slide extension

While sorting out a replacement motor for the mill, I turned my attention to making the spindle for the y-axis. Most WW-lathes seem to have the odd thread of 4.5 mm x 1 mm pitch. The spindles from the old cross-slide I am using were missing, but must have been thinner, probably 4 mm. As I have both, a die and a tap for the usual left-hand thread, I decided to adapt the cross-slide for this. First the spindle was made. Unlike on the lathes, it will have two ball-races as thrust bearings, but otherwise the design will be similar. The ball-handle crank is a commercial product. I started out with a 5 mm rod and turned it down to 4.5 mm and then set-up the lathe for cutting the left-hand thread. This means cutting proceeds towards the tailstock. As the torque on the lathe transmission system is too low, the thread was cut by hand-cranking. For this purpose I had made an adapter for a ball-handle crank already a long time ago. The thread was cut with full cuts until it was about 90% complete. The final cut then was made with a die in the tailstock die-holder to calibrate the diameter, which might have been a bit bigger in the middle due to the flexing of the long spindle. In order to eliminate the effect of flexing, the cutting bit was run along the thread several times without adavancing it into the work, until no material was taken off anymore.

The long hole for the spindle in the cross-slide was opened up to 5 mm using the Dixi horizontal miller as a boring mill. However, the travel of the slide was too small, so an extension was made to give the slide a travel of around 50 mm, allowing the milling spindle to reach across a face-plate mounted in the dividing attachment on the mill. The extension is a fairly complex piece, fashioned out of a block of aluminium. This is jointed to the existing top-slide with two location pins and two countersunk screws (the holes used were already made by a previous owner).

To it screws the housing for the y-spindle bearing. Watchmakers lathes usually have simple sliding bearings there, the end-play of which is controlled by a nut with a very fine thread. The elements of this arrangement would have been ground to give a smooth sliding. I decided instead to use miniature thrust-bearings with I.D. of 5 mm and an O.D. of just 10 mm. Two are needed, with the thrust-collar on the spindle in between. This gives an arrangement of 12 mm in length. The bearing-housing was made from a piece of 15 mm x 15 mm aluminium bar. The section was centred in the large 4-jaw-chuck on the lathe and the stub turned on. The piece then was reversed and taken into a 3-jaw-chuck so that the face that screws down onto the slide extension could be turned flat and perpendicular to the axis. The through-hole was drilled and reamed for the spindle. In the next step the seat for the bearings was bored out to exactly 10 mm diameter and a tad unter 12 mm depth . Finally some cosmetic milling operations gave the bearing housing a more elegant shape.

Top-slide extension	Centering y-slide spindle-bearing in large 4-jaw-chuck		Turning stub for spindle-bearing		Reaming bearing for y- spindle	Boring-out seats for thrust ball-bearings	Bearing plate	Spindle parts	Topslide extension and spindle in place

The original spindle-nut seems to have had a left-hand thread of 4 mm x 1 mm, so it was drilled out 3.7 mm for the 4.5 mm x 1 mm thread and the thread re-cut with the appropriate tap. The odd digs and dents were removed by a light cut on both ends in the lathe. A test assembly showed that everything worked as planned.

The next piece to be tackled is the micrometer-sleeve, which will be turned from brass. The original sleeves were split and had a friction seat on the polished spindle. I will be deviating from this design and cross-drill the sleeve for a tapped hole for a headless screw that will act through a pressure pad on the spindle. With this the zero-ing resistance can be set. The original micrometer-sleeves have a knurled ring, but the knurl is convex.

Making Concave Knurls Today, concave knurls to produce such patterns are obtainable only at prohibitive costs. Therefore, I embarked on making my own knurl, encouraged by a few examples on the Internet. Knurling wheels normally have to have a certain diameter in order to prevent their bore from being distorted under the stress of the knurling process. I choose a blank of only 10 mm diameter for a bore of 6 mm in order to reduce the mass to be heated, when attempting to harden the knurl with my rather limited heating capabilities. I also had a cut-off from a Schaublin collet-blank available, which I assumed would harden nicely. The proposed process of creating the knurling wheel employs an ordinary threading tap as an improvised hob. This, stricly speaking, would result in a 'rope' knurl, but the helical angle of a, say, 0.4 mm pitch tap is barely perceptible. The easiest way to hold the blank for cutting seemed to hold it in the knurling-holder for the watchmakers lathe that I made a few years ago. This means, however, that the process could not be done on the lathe, because it would have been not so easy to mount the holder on its side. Cutting the knurl on the lathe would have been better, as the end of the tap could have been supported in the tailstock to eliminate flexing. Unfortunaly, the DIXI horizontal mill does not have an overarm, which then would make it the ideal machine for the job. So the job was done on the vertical mill. The blank was drilled and reamed for the arbor of knurling tool holder. Some polishing ensured that it spun freely. A M2 tap was chucked in a collet as short as possible and  offered to the blank with its uppermost end in order to keep flexing to a minimum. Initially, the mill was run at slow speed and with a small feed. After each incremental feed, the blank was allowed to make several revolutions until no chips were produced anymore. Once the pattern was created, the mill was run at a somewhat higher speed and the amount of incremental feed increased from around 0.03 mm to 0.05 mm. Every time blank and tap were flooded with WD40 in order to wash out the chips that then were wiped off. A first failed trial showed, how important it is to wash-out chips. The second attempt was successful.   Hobbing a concave knurling wheel Finished knurl Knurl in holder Knurling tool in action After the machining, the knurl was hardened by heating it to a cherry-red colour and quenching it in ice-cold water. As I don't have a very strong torch, the knurl was pre-heated to 450°C using the hot-air soldering gun and then brought to temperature with the gas-torch. The knurl was also rubbed in soap to prevent scaling. After some cleaning, the hardened knurl was tempered to a straw-yellow colour using the the hot-air gun. A test with a file showed that the hardening was successful.

For the dial I had a piece of 21 mm diameter brass to hand. This was faced in the 3-jaw-chuck, drilled and reamed for the 5 mm spindle, an then bored out to fit over the spindle bearing-plate. The blank was the mounted on an arbor with a 5 mm stem in order to be able to turn the outside shape. At one end there is the notorious convex knurled ring. For this a ring of 1.2 mm width and 1 mm height was left standing with slightly chamfered edges. For the next machining step the knurling tool with the concave knurl was mounted to the cross-slide. The knurling tool was fed slowly into the slowly rotating blank. It catches quite quickly at the edges and the pattern evolves fast. While generously lubricating with WD40 the knurl was fed into the faster rotating blank until the pattern had developed fully.
The blank on its arbor was then transfered to the dividing apparatus on the milling machine for engraving the dial. For this a 15° engraving bit was used. in the same set-up the hole for the friction brake of the dial was pre-drilled. The numbers were stamped in a make-shift set-up in a vice. In order to ensure that the number-stamps were applied exactly radially a purpuse-made guide-block was used. Finally, the dial was mounted back on the arbor and the burrs from engraving and stamping cleaned up with a couple of light cuts in the lathe. The two parts were separated on the lathe with a jewelers saw substituting for a parting tool.


The dial then was degreased and the engravings laid out in black enamel paint. After the paint had dried, the dial was rubbed in the lathe with very fine wet-and-dry emery paper to remove the excess paint. The dial finally was provided with a friction brake, which consists of a short piece of Plexiglas that is pushed onto the spindel with a set-screw.
The milling spindle will be secured in its place between the two brackets by a lever-actuated excentric bolt that pushes it down. I found a rough excentric bolt in my scrap-box of odd lathe parts, but it would have been as easy to start from scratch. The excentric was worked over holding the bolt in the 3-jaw-chuck with a brass-shim to give the off-set. The head was turned with the help of the shop-made radius-turning tool. The tool-bit diameter was chosen to match the neck and shoulder of the bolt. The turning operation was followed by smoothing with wet-and-dry paper and steel-wool of various grades. Finally it was polished with polishing paste.

Parts of the spindle	Assembled spindle	Spindle at its working place	Method of excentric turning	Shaping the head of the excentric bolt using a radius-turning tool

The ball-end lever for the locking bolt was fashioned from a short piece of steel in several steps: first the stem that will be a push-fit in a hole of the bolt was turned; chucking the material with this stem, then the main part of the lever was turned conical, leaving a part cylindrical for the ball-head; the conical part was given a waist using the free-hand turning rest; and finally the ball-head was formed using the radius-turning tool. The tool-bit in this case was a 2 mm HSS-bit in a special holder that allows to form a sphere with a sharp edge at the stem.

Steps in forming a ball-end lever using a free-hand and a radius-turning tool						Locking bolt

A while ago I had been able to purchase at a good price a 'left-handed' Lorch, Schmidt & Co. cross-slide, which is what was needed for this project. In Germany, watchmakers for some reason traditionally worked with the headstock to the right, and not to the left as is common practice in virtually all other lathes. Some older watchmakers still seem to work like this, but I gather the majority nowadays, prefer to have the headstock to the righ. In consequence, cross-slides that are meant to be mounted to the left of the headstock and operated mainly with the left hand are relatively cheap to come by. The one I received looked a bit worn on the outside, but mechanically was still in a good condition. Spindles and spindle-nut were tight. However, the nickel plating was chipped and peeling off. I completely diassembled the cross-slide and ground-off the remaining nickel with fine wet-and-dry paper and polished the surfaces. Then all parts were thoroughly cleaned. The spindles have the 0.75 mm pitch commonly found on cross-slides for D-bed lathes. Not very convenient for calculations, but I got actually used to it on my D-bed lathe. The dial on the y-axis (the future z-axis of the mill) was actually graduated with 15 divisions, giving the diameter reduction when turning, though it has the same pitch as the x-axis. On the mill this graduation would be confusing and I also wanted to have a conical dial on the z-axis. So I moved the x-axis dial to the y-axis, which is the future x-axis of the mill, and made a new dial for the future z-axis. For this, a 20 mm piece of brass was drilled and reamed for the 4 mm-spindle. It was then taken onto a 4 mm-arbor for further machining. The lathe top-slide was off-set by 45° for turning the conical shape. In the same set-up the lines on the dial were engraved using a pointed tool-bit - the lathe head-stock, as for all watchmakers lathes, can be used for simple dividing. There are 60 stop-holes, which was convenient for the 15 stops needed here. The engraved dial was then moved to a special jig I made some years ago, that allows to punch numbers onto conical dials. After punching, the dial was moved back to the arbor, the exact position had been marked before removal, and the burrs thrown up by the engraving and punching were removed by a light cut, leaving behind crisp lines and numbers. As for the other dial fabricated, a pressure pad provides for an adjustable friction stop. The outside rim was also given a treatment with the concave knurling tool described earlier. The engravings on all dials were filled-in with black paint and when the paint was dry, the dials were slightly rubbed-over with fine wet-and-dry paper to leave crisp black engravings on a satin surface. 

Disassembled cross-slide	Taper-turning dial	Engraving dial in the lathe		Jig for punching numbers	Cleaning-up the dial	Knurling the rim		Finished dial at its place	Re-assembled cross-slide

Some time ago I purchased a 12V motor from a Chinese source that is supposed to run at a nominal speed of 3000 rpm. Considering is length of 71 mm and a diameter of 51 mm with an 8 mm drive shaft I expect it to have sufficient torque for the purpose. The data given by the seller were rather cryptic. The mounting of the motor caused me some head-scratching. The original intention was to use a bracket similar to the one used on the lathe toolpost-grinder I showed above for the mock-up. This would have resulted in a self-contained drive unit. However, the motor would have fouled the cross-slide, when the y-slide is fully run out. Making the bracket longer would have solved this problem, but I was afraid of the vibrations this long lever might transmit and the distortions to the y-slide. Another possibility would have been to mount it upside-down over top of the y-slide, but this would have raised the centre of gravity of the whole machine considerably and transmitted vibrations to the system. In the end I make, for the time being, a simple bracket that uses the two screws with which the extension of the y-slide is screwed down.
The lathe and grinding spindles were meant to run at maximum speeds of around 4000 to 5000 rpm. Therefore, a slight stepping-up compared to the motor speed would be permissible. As the motor bracket does not provide for any adjustment of the belt-tension, I copied the pulley on the grinding spindle for use as a motor pulley as exactly as possible. It will be put upside-down onto the motor, so that the belt can be shifted for stepping up (1 : 1.4) or stepping down (1 : 0.7) speeds without the need for adjusting the tension. Most of the speed control will come from the electronics in the power-supply. The pulley on the grinding spindle has a 75° V-groove for 3 mm round belts. A V-groove can be cut by either setting over the top-slide, or using a pointed tool with the appropriate angle. I had to grind a HSS-toolbit with this angle, checking it against a template. The two grooves were cut using a stepping method. Cutting it full depth would not be possible. I order to ensure concentricity between the pulley-bore and the groove, first the step in which the set-screw is located was turned and then the piece turned around for drilling/reaming the bore and cutting the grooves in the same set-up. For cutting the grooves the pulley was supported with a revolving tailstock centre.

Drive mock-up	Steps of turning the motor pulley			Finished motor pulley	The two drive pulleys	Motor mount	Masked, primed, and painted parts			Dissambled milling spindle

I would have preferred to leave the parts in their bright, nickel-plated finish. However, the plating on the foot, for instance, was coming off in large flakes. In addition, the parts fabricated from aluminium have a rather different colour. Therefore, I spray-painted most parts in my favourite bottle-green (RAL 6007).
The milling spindle was disassembled and given a thorough clean and generously oiled before being put together again. I also replaced the slotted worm screws that lock the pulley in place with Allen ones. Not original, but more functional. These milling spindles are intended to be operated horizontally and, therefore, have only a simple oiling hole with no cover. In order to ensure adequate oil supply to the upper bearing surface, I fabricated an oilder that rises to the level of the upper bearing. A piece of 4 mm brass was turned down for a press-fit into the oiling hole. An 1 mm-hole was drilled part-way from this side and a 3 mm-hole from the opposite side. The resulting tube was cut at a 45° angle and the two pieces silver-soldered together to form a 90° knee. From a short piece of brass a cap was turned and bored for a sliding-fit over the oiler. Since the convex knurling worked so well, I applied this also to the cap.
The milling spindle was missing the draw-tube. A new one was turned from a piece of 8 mm tube with a 5 mm bore. One end was tapped 5.1 mm x 36 tpi for the collets, for which I am lucky to have tap. The other end was serrated to provide a positive lock for the hand-wheel. For this machining operation, a pointed tool was mounted with the cutting face vertical in the QCTP and the draw-tube indexed in the head-stock of the lathe. The original hand-wheels were made from black or dark-brown Bakelite, a materials that is not easy to buy anymore these days as round stock or thick enough plates. I had to resort to a piece of black POM. As it turned out to be too complicated to set up the radius-turning tool for this, the torus-shaped rim was fashioned by free-hand turning. The POM is rather soft and was best finished with a fine file and steel-wool. The finished hand-wheel was loosly taken into a 3-jaw chuck and the draw-tube, that was held in a collet in the lever-tailstock was pressed in.

Various steps in fabricating the oiler for the grinding spindle				Completed spindle	Grooving the draw-tube for the hand-wheel		Turning the draw- tube knob	Finished draw-tube and an original one

As indicated at the beginning, the machine will be provided with a fifth axis for rotary milling and dividing operations. Some years ago, I fashioned a geared dividing head from an old Lorch, Schmidt & Co. grinding spindle. This mounts onto the cross-slide of a 6 mm lathe, such as the one used in the milling machine. These grinding spindles were meant to be bolted down onto the cross-slide using the latern for the turning bits. While this reduced the number of bits and pieces to be provided for the lathe and to be taken care of, it seems to be a rather strange economy. In the present circumstances this method of bolting is also not very satisfactory, as the angle of the spindle, as well its position in the T-slot have to be adjusted at the same time. Too many degrees of freedom. Therefore, a mounting bolt was fashioned from a normal M6 screw with a hexagonal head. These fit perfectly into the T-slots, but their heads have to turned thinner. Over the bolt a sleeve with an internal M6 thread screws down, thus keeping the bolt in place. Now, the dividing head can be rotated around the bolt without movement up and down in the T-slot. The dividing head is clamped with an standard M6 cap-nut (a nice polished stainless steel one though) and a large washer. The latter also is a commercial stamped product that was cleaned up on the lathe and given a nice polish for aesthetics sake.
The rotating spindles, such as the main spindle and grinding spindles on watchmakers lathes have a knurled sleeve in brass that is meant to prevent dirt from entering the bearings. The one for the grinding spindle used as dividing head was missing. Using an original one as example, a replacement was fashioned from a piece of round brass. After facing a short length of brass it was drilled 5 mm and taken onto a respective arbor for turning the outside to size. A rim was left standing that was given a round knurl. Back on the 3-jaw-chuck, the inside was bored to a tight fit to the body of the milling spindle. The front part was given a concave bevel with a form-tool. 

Geared dividing head	Mounting bolt for geared dividing head			The various steps of shaping a new dust-sleeve for the milling spindle					Original (right) and copy	Sleeves in place

Several years ago I had constructed a micro-vise that was intended to be hold in a collet e.g. in the upright collet-holder on the larger Wolf, Jahn & Co. milling machine. The stem has a 5 mm diameter, which was chosen so that it also fits into the largest regular collet of a 6 mm-lathe. While the collet thus can be mounted in the dividing head, this may not always be convenient. Therefore, a small holding block was fashioned from a piece of steel. This holder allows to rotate the vice around the clamping bolt, but also in the mounting hole. With this arrangement and the tilting capability of the vice itself, it can be offered to the milling spindle in any conceivable angle.

Micro-vice	Steps in machining the holder for the micro-vice				Parts of  the holder for the micro-vice	Holder and micro-vice	Various ways of positioning the micro-vice

The motor also needs a housing, so that the electrical connections can be adequately installed. I wanted to make the supply cable detachable in order not to have it hangig around, when the mill stored away. Unfortunately, the motor has the somewhat odd outer diameter of 51 mm and it was not so easy to come by a suitable pipe. Finally, I chanced upon a can from a weird drink that pretended to be an alcohol-free Bellini-cocktail. In this way the overly expensive can somewhat amortised. I shortened it to suit with a diamond saw in the hand-held electrical drill. A lid was cut and turned from a piece of 5 mm Plexiglas™. Three fastening holes were pierced with a needle and opened up using cutting broaches in the very thin and flimsy drinks can. The lid was drilled and tapped for M2 screws. A 6 mm hole for a 3.5 mm mono-socket was pre-drilled with a small drill and then reamed to size into the bottom of the can. The housing was given a base-coat and painted to suit the rest of the machine.

Motor housing before painting

The completed micro-milling machine

Different work-holding options from the arsenal of spindle-tools of the 6 mm-lathe

Small table for clamping flat objects

Small fly-cutter

The dividing head offers a wide variety of work-holding options using the spindle-tools from the 6 mm-lathe, such as 3- and 6-jaw-scroll-chucks, independent 4-jaw-chucks, ring- and step-chucks, face-plates, as well as the whole range of collets from 0.3 mm to 14 mm diameter. Collets for work-holding are particularly useful, as a wide variety of small parts can actually by milled from round material of various diameters and then sawn-off from the stem held in the collet. The dividing head can be set at any angle, from vertical to horizontal, offering the possibility for instance to mill multiple facets onto material, or to drill into bevelled surfaces. Longer, delicate work can also be supported by the over-arm for the dividing head that takes the various types of lathe tailstock-centres.
In addition to the micro-vise shown above, I also made a small table for clamping flat objects to be held in the 5 mm collet or in the inclining holder for the vise.
Collets for the milling spindle, a holder for standard 6 mm end-mills, arbors for slitting saws, a small fly-cutter, as well as a small boring-head are stored in a fitted antique box.

Different positions of the dividing head		Dividing head with supporting over-arm mounted					Table- stop	Collet- box	Swarf accumu- lation	Graduated sleeve replacing th  dust-sleeve

Addendum 24/02/18: unfortunately, milling operations with the dividing-head in the upright position leads to the accumulation of swarf between the spindle-head and the dust-sleeve. Also it was felt useful to have some kind of indication of the angular position of the spindle when using the indirect dividing gear. In order to overcome both problems, a graduated dial was manufactured, that has a friction-fit to the spindle-head. With its round-knurled ring it can be zeroed. Because of its tight fit to the spindle and its shape, it sheds the swarf away from the spindle.

And finally a few video-clips showing the machine in action:

Click on images to play videos