Wolf, Jahn & Co. Model A Milling Machines

This restoration had a number of surprises in store. The main spindle has a thrust ball-bearing, but during an earlier restoration a few of the balls seem to have disappeared. The size of the balls is a rather awkward 3.155 mm rather than a more logical 3.175 mm or 1/16". I could not get such replacement balls and fitted for the time being 1/16" ones - have to monitor the bearing. Unfortunately one half of the bearing was machined into the upper headstock bushing, so one cannot simply replace the whole bearing. The designers some 100 years ago had a lot of trust in the longevity of their material!

In fact, the machine seems to have suffered some not so professional maintenance and repairs. Whoever at some time took the x-spindle of the table apart seems to have had no idea how the spindle anti-backlash arrangements work in a watchmakers lathe-type cross-slide. Fitting it the wrong way around he must have found the spindle to be too long and cut it off !

Both table spindles have a rather unusual thread of 7 mm diameter with a 1.4 mm pitch. I had planned to replace them with one of the discouraged, but standard M7x1 thread. This pitch gives a rather slow feed, but it is easier to make feed calculations then. However, I could not find a company (in Vienna) that would machine for me such spindles at a reasonable price. Prices quoted for the two spindles were in the same order of what I paid for the whole machine ...

So in the end I settled reluctantly on commercial, threaded M6x1 bar. The spindles were made to extend the full length of the slide. Previously, only a little more than a quarter of the table could actually be reached without rotating the table. This is probably sufficient for watchmaking and die work, but not for my model engineering purposes. The later BCA millers have the casting of the x-slide extending the same distance left and right of the rotating table, while the one on the WJ&Co. is asymmetric. A pleasant surprise was the split-nut on both cross-slide spindles that can be tightened with two screws to make up for wear and to reduce backlash. They were replaced with new ones fashioned from bronze and modelled after old ones, but with the M6x1 thread, of course.

A common feature on tightening nuts of similar cross-slides is the badly worn knurl. Using a pair of pliers to tighten them seems to be very tempting. Admittedly, I also use pliers, but I first put a wooden clothes peg(!) over the knurl. As interim cosmetic solution, the knurl on the original nuts was restored using the geared dividing head fitted to the hand-shaper.


The original spindles and micrometer drums	Knurling the new drums	Engraving the drums	Stamping the numbers using punches in a jig		New micrometer drum	Restored cross-slide

When I eventually replaced spindles, the rather worn and coarse original micrometer drums, which would not work with the new spindle pitch anyway, were replaced with much larger and better engraved ones. They were modelled after the old ones, but became a positive lock for the zero point using a small knurled screw. The knurling, engraving and stamping processes in their manufacture are illustrated in the pictures above.

The table is not very ingeniously designed. It appears that it is not actually meant to be turned under load, i.e. for milling pieces round. All bearing surfaces are cylindrical, thus not permitting very precise centering when the table is unlocked. In addition the lock, a bolt with an excenter turned on, just pulls down the central pivoting bolt. For this reason, the bolt does not turn with the table, making the centering of the table a bit awkward.

During an earlier repair effort someone replaced the worm driving the table with its arbor and crank etc.. The balanced ball-handle crank was a rather crude imitation and the arbor was made without understanding the cone bearing into which it would be drawn with a nut, secured by a lock-nut. As this brass replacement worm was already rather worn, I replaced it with a newly made on in steel as the original one. A compassionate owner of a similar miller kindly supplied me with pictures of the dismantled worm, so that I was able to replicate the parts. Originally hexagonal nuts were fitted, but I found this rather unelegant and used nuts to be tightened with a C-spanner.

A somewhat awkward feature of the T-slots on many early precision machines is that they are not actually T-shaped, but dove-tailed. On top of it, in the present case they have the rather unusual angle of 65 deg. Making a set of matching T-nuts was the first job to test the hand-shaper under fire.

The machine is driven by a Sherline motor with variable speed control. The top speed of this excellent motor is around 6500 rpm, which is somewhat above the rating of 5000 rpm given for the headstock by the manufacturers. It is mounted in a plywood housing as for the lathe.

A shop-made(?) counter shaft that I acquired some time ago is mounted behind the machine and allows 4 x 3 = 12 different speed ratios in both, upward and downward direction. The large primary pulley reduces the motor input by a factor of 4.5. This counter shaft consisted of some rather rough aluminium castings that were cleaned up on the milling machines before carefully painting them.


Cutting a new worm for the rotary table	Boring out of the relieving holes in the large pulley.		The DIXI mill doubles up as a facing lathe for large items.

Restoring the Wolf, Jahn & Co. Model 'A' Milling Machine