SN400-SN500-SN630-SN710 longitudinal lead screw half nut replacement

When cutting a lot of threads on your SN400-SN500-SN630-SN710 lathe, the half nuts will wear over time. This is standard, the half nut is a wearable part and needs replacing time to time. Compared to the SN40-50-63-71 the half nut on the SN400-SN500-SN630-SN710 lathes is composed of two parts. The half nuts comes from 1 brass piece, which is divided only after it has been mounted into the holders (brackets). Because the holders are a difficult and expensive parts to produce, you only need to replace the halfnuts. We offer two options for replacing the halfnuts.

Important note: check if the thread pitch on the leadscrew on your lathe has a 6 or 8 mm thread pitch, as the leadscrew comes in these two executions.

We can supply the complete half-nut – a semi-finished product that you have to mount into the brackets and finish it by yourself. See guide bellow on how to proceed.

We can supply the half-nuts, fitted in brackets in exchange for your old holders. Because the holders are not manufactured anymore, we provide this service only in exchange for your old holders. Simply advise us the required thread pitch on your lathe, we will prepare and fit the half-nuts for you, ship us your old holders and we will ship the finished parts for to you. Please note that the holders mustn’t be damaged.

1. Remove the old / damaged half-nuts from the holders.
2. Insert the uncut bronze nut into the holders so that the prismatic base of the holders is aligned in one plane.
3. Through the holes in the holder, drill the tapping holes into the nut and cut the 4 × M8 threads.
4. Fasten the nut with M8 screws, clamp it on the machine together with the holders, and cut it with a milling cutter to the dimension of 16 mm — see drawing.
5. Clamp the separate half-nuts in the holders again and chamfer the edges of each half-nut individually — 30° to the dimension of 19 mm from the axis.
6. Deburr the thread.

Note: The half-nuts in the holder must be marked so that, if they are removed from the holders later, the half-nuts are not mixed up with each other or between the holders. The half-nut and holder must have the same number.