Multi-position carriage stop.
This multi-position stop was designed primarily for graduating dials on the lathe. It is often the case when graduating a scale that most of the lines are small but every fifth mark is a little longer and every tenth mark is longer still. This makes the scale easier to read. Marking using the top slide to move the scribing tool is slow and at every fifth and lenth line it is necessary to remember to increase the line length by a certain amount. This little gadget speeds things up because the lines can be scribed by moving the carriage and the line length for the primary, fifth and tenth lines can be preset. It is only necessary to remember when to increase the line length.
The stop is also useful in making repetitive parts with shoulders.
The photo above shows the completed multi-position stop. It comprises several parts. On the left is the clamp that fixes the stop to the lathe bed. Attached to the clamp is a revolving cylinder which has four screws protruding. These can be set at different protrusions and locked in place with lock nuts. On the right of the photo can be seen a stop block that is attached to the saddle. By rotating the cylinder different screws can be located to hit the stop block. The cylinder is scribed with the numbers 1 to 4 that can be lined up with a scribed line on the clamp to bring each of the screws to the stop position.
The stop is also useful in making repetitive parts with shoulders.
The photo above shows the completed multi-position stop. It comprises several parts. On the left is the clamp that fixes the stop to the lathe bed. Attached to the clamp is a revolving cylinder which has four screws protruding. These can be set at different protrusions and locked in place with lock nuts. On the right of the photo can be seen a stop block that is attached to the saddle. By rotating the cylinder different screws can be located to hit the stop block. The cylinder is scribed with the numbers 1 to 4 that can be lined up with a scribed line on the clamp to bring each of the screws to the stop position.
This photo shows the clamp. The top half is made from 1/2" x 3/4 steel bar and the bottom half from 1/2" square bar. The 90 degree vee section is milled out with an end mill. The clamp screw is M5. On the left hand side is a 4 mm pin forced into the top half. There is a 4.1 mm guide hole in the bottom half. Between the two halves, on the pin, there is a washer that sets the separation of the gap when the clamp is tightened onto the lathe bed. The hole in the top half is drilled and tapped M5 for the cylinder pivot screw.
This shows an end view of the cylinder. It is made from 25 mm round bar and drilled out centrally to 6 mm. A 10 mm recess is cut around the hole with an end mill. This recess is to accept the head of the pivot screw. Equally spaced around the hole are four holes tapped M4 for the screws that define the stop points.
The cylinder is knurled and chamfered at the right hand end and scribed at the other end with equally spaced line and numbers.
The pivot screw is turned from a piece of 3/8" round bar. The central portion is made a good sliding fit in the cylinder. The left hand end is threaded M5. The head is slotted for a screw driver blade.
This shows the completed assembly without the stop screws.
The stop block on the saddle is a piece of 10mm hexagonal bar, 25 mm long, that is turned down at one end to 6 mm and threaded M6. This screws into a tapped hole in the saddle. This hole was originally drilled in order to mount the head of a toothbrush that wipes the leadscrew. The tooth brush head (white) can be seen in the header photo, immediately below the stop block.