Introduction: A Versatile Watchmaker's Milling and Drilling Attachment
I own a watchmakers lathe and I want to use it for the construction of clocks and watches. However, watchmaker's milling attachments that allow wheel and pinion cutting are not only prohibitively expensive but also difficult to find. I also own a Myford Super 7 and have access to a Dore Westbury milling machine, so I decided to design and make my own milling attachment.
I designed the attachment to be as versatile as possible. I can use it for wheel and pinion cutting, or very easily convert it into a drilling attachment to enable drilling of off-centre holes in the watchmaker's lathe. And finally, I can even convert it into a boring head for use on my larger machines.
In this instructable, I outline the design and manufacture of the attachment and demonstrate it in use.
Step 1: Design
The main body is dimensioned identically to George H. Thomas's small boring head as detailed in "The Model EngineersWorkshop Manual". I recommend purchasing the book for dimensions if you wish to reproduce this project.
The total travel is only around 15 mm and while this is plenty for use as a small boring head, as a vertical slide on a watchmakers lathe, it is restrictive. Rather than machining a longer dovetail slide, I simply included 3 mounting positions for the bearing block which holds the spindle. I mount the bearing block onto the dovetailed slider and chose the position according to the job. This method has worked well.
I used high tolerance ball bearings for the spindle mounting to minimise sideways slop in the spindle. The spindle is made from 6 mm diameter silver steel rod, so if an odd cutter needs to be mounted, machining a spindle specific to that cutter is very easy.
The whole dovetailed assembly is mounted to an angle bracket which can be bolted to the topslide on the watchmaker's lathe. The dovetailed assembly can be rotated about both the longitudinal and vertical axes to allow an angled cutter advance.
To convert the milling attachment to a drilling attachment, the milling spindle is replaced with a chuck-mounted spindle and the whole attachment is rotated by 90 degrees about the vertical axis.
To convert the milling attachment to a boring head the following steps are taken. Firstly, the large brass bolt holding the main body to the angle bracket is removed and replaced with a MT2 arbour (or appropriate). The bronze dovetailed part is then removed and replaced with one for boring. Finally, the jib strip may need some adjustment.
Step 2: Machining the Main Body
Firstly, a block of steel is sawn (and milled, if required) to size. If you are lucky, you can use a powered bandsaw for this. I used a hacksaw. The steel is drilled in the 4-jaw chuck to allow clearance for the feedscrew. The back face is then bored and screw-cut, also in the 4-jaw chuck. To form the dovetail slideway, I started by hacksawing out as much material as possible to reduce wear on my milling cutters. I then roughed out the rest of the slideway on the milling machine. By tilting the head and using a small milling cutter, I roughed out the dovetail before finishing with a dovetail cutter. I hand scraped the dovetail to exactly 60 degrees and ensured the dovetail was parallel. Non-critical faces were draw-filed.
Step 3: Machining the Dovetailed Slider
The dovetailed slider was roughed to shape from bronze using the milling machine. The dovetail was then machined and hand-scraped. The feed nut was machined as part of the slider and was drilled and tapped (in my case, M6 x 0.75). Threaded holes and a keyway for fitting and aligning the bearing block can be included later.
Step 4: Fitting the Slider
A jib-strip was made from gauge plate and hand-scraped flat. Holes for the jib-strip adjustment screws were drilled and tapped in the main body, including a larger one in the centre for the lock. The jib strip was dowelled to prevent movement of the jib-strip, which may cause the bronze slider to jam. Final scraping was completed so the slider was a smooth consistent fit with no sideways play.
Step 5: Machining the Bearing Block
The bearing block was cut and filed to size. It was then drilled through the centre, and bearing recesses were bored in the 4-jaw chuck. Note that I retrospectively tapered the ends to allow more clearance for the workpiece when the attachment is in use. Location slots can be milled as seen in step 16, image 2.
Step 6: Feedscrew
I would highly recommend taking the time to set up for screw-cutting the feed screw. By all means, screw-cut slightly undersize and finish the thread form with the die, but the initial thread profile needs to be straight and accurate and this is best done in a screw cutting lathe. Support the end of the feed screw with a half-centre when machining. Ideally, the feed screw should be machined between centres, but holding one end in an accurate collet will suffice (as I did).
Step 7: Feedscrew Collar
The feed screw collar prevents the feed screw from being pulled upwards, out of the plate. The collar is machined and tapped. It is cross-drilled and tapped to accept a grub screw; this allows the collar to be locked in place. It is essential the inside face of the collar is square to the inside thread. This is best done by screw-cutting an arbour with the same thread as the feed screw. Without removing the arbour from the lathe, fit the collar to the arbour, tighten the grubscrew and skim the face rubbing against the brass plate. The diameter in contact with the brass plate can be reduced to reduce friction (see the last image).
Step 8: Brass Plate
The plate containing the feed screw is cut and milled to size. The central hole is drilled and reamed and the bolt holes are counterbored. Make the holes for the bolts in the plate slightly oversized to allow a small amount of float in the plate. This ensures that the plate is exactly in the right place when the bolts are tightened after the rest of the slideway has been assembled. The threaded holes in the main body to hold the plate in place can be marked out with the plate in situ. The plate is positioned by assembling the rest of the slideway.
Step 9: The Angle Bracket
The angle bracket is easily made from steel or aluminium L-section. All faces were milled square. The main hole can be drilled and bored to size either with a boring head or in the 4-jaw chuck. The two outside faces were scraped flat and square. Holes to mount the bracket to the watchmakers lathe can be simply marked out and drilled on a pillar drill or coordinate drilled with a milling machine.
Step 10: Brass Bolt
The brass bolt can be machined from hex bar (or circular bar and the bolt head machined on a milling machine). I used hex bar. The bar is held in a 3 jaw chuck, machined to diameter and screw-cut. The bolt is reversed in the chuck and the head is machined and chamfered. It is important to protect the threads so they aren't damaged when the bolt is reversed in the chuck.
Step 11: Washer
Turn a thick steel washer to go behind the brass bolt head.
Step 12: Spindle Pulley
Machine some aluminium pulleys to fit on the spindle. It could be a single pulley; however, I turned a dual pulley to allow more speed options. Make sure you leave a stub on the end of the pulley block for grubscrews (or you could put the grubscrews in the centre of the pulley groove if required). The spindle pulley can be used as a spindle collar too but I machined a separate collar from steel just to make sure the spindle wasn't going anywhere when cutting gears.
Step 13: T-Nuts
T-Nuts are easily machined on a milling machine to fit your specific watchmaker's lathe.
Step 14: Guide Pulley Arrangement
I've tried two guide pulley arrangements for wheel cutting (drilling required no guide pulleys, see the second image). The first arrangement was an overhead pulley system as suggested by George Daniels in 'Watchmaking'. Personally, I found this did not work satisfactorily due to lack of rigidity. It is likely that the design is fine, just my construction was flimsy. Having said that, I much preferred running the belt underneath the bed. Although perhaps less versatile, the system was far more rigid and the belt was not as obtrusive.
Machining the guide pulleys themselves was a trivial turning operation. I machined them from Nylon but almost any reasonable material is fine. I bored the pulleys out to take ball races to reduce drive system friction.
Step 15: In Use - Drilling
Off-centre drilling is now possible on the watchmaker's lathe. The offset is measured using the cross slide dial. The attachment in this configuration will prove useful for making lantern pinions.
Step 16: In Use - Wheel and Pinion Cutting
The system works well for wheel and pinion cutting. An example 0.65 module 12 leaf pinion cut with the attachment is shown as well as a larger wheel.
Step 17: Further Work and Conclusion
The next step to improving the milling attachment is the inclusion of a dial on the feed screw advance as well as angular graduations on the main body stub. I hope you enjoyed this article. If you have any comments or questions, please feel free to contact me.
Thanks to my father, Alastair Godfrey, for his help with the design of this project.
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