Continues from Thread Dial Indicator.

To get a visual idea of the finished unit, here’s a photo of the fully assembled unit:

As can be seen, there are 3 separate gears (14, 16 and 20 teeth), which are brought into
mesh with the leadscrew by mounting the indicator upon a stud fitted to the side of the
saddle assembly via the appropriate hole.

A lock screw then clamps the indicator to the stud once correctly installed.

The gear to be used is determined by which thread pitch is desired using the table on the previous page.

Construction Drawings

The body is milled from 40mm aluminium stock.

A pocket is required to house the gears.

A longitudinal 6mm hole is drilled to accept the shaft that holds the gears and top indicator dial.
Note that this hole should extend the full depth otherwise it is extremely difficult to later dismantle.

3 cross holes are drilled to fit the unit upon the saddle and mesh the appropriate gear.
Note that these are progressively offset from the front edge so the unit remains plumb when engaged on any gear.

A 30mm wide, 7mm deep pocket is bored upon the top surface to house the indicator dial.

The 6mm shaft was sourced from an old dismantled printer as it had a nice polished finished.
Flats should the milled in 3 places to prevent the grub screws on the dial and gears leaving burrs and making disassembly difficult.,

The indicator dial should be cross drilled and tapped to M3 in line with the “2” indicator.

The gears were machined from brass, using a module 1 gear cutter.
This is not an exact perfect fit onto an acme leadscrew, but as power is not being transferred it meshes fine for the purpose.

The 14 and 20 tooth gears each have a large hub within which a grub screw is fitted.
These grub screw holes should align with a tooth on the gear, which then fit up to the flats on the shaft to prevent burrs from affecting disassembly..
This also maintains the alignment of the gears with the “2” indicator mark.

As the 16 tooth gear is too thin, it is pinned to each neighbouring gear.
These pinning holes must also be aligned so that the “2” on the indicator dial will align precisely with the teeth on all 3 gears in that position.
I recommend drilling the pinning holes 180 degrees opposed to the grub screws, thus also directly inline with the teeth on that side.

The diagram below in the plan view shows the pinning holes in each gear.
Note that the side view shows the pinning holes 90 degrees to the grubs. This should be ignored.

Once fully assembled, the unit was offered up to the side of the saddle meshing one of the gears with the leadscrew.

A transfer punch was used to mark the side of the saddle, and an M6 hole was drilled and tapped.

A 10mm shaft was prepared with a short 6mm thread at one end and a central relief to prevent the locking knob
from burring the shaft and making it hard to remove the unit from the saddle.

Finally the spacing from the side of the saddle needs to be determined so the gauge can be readily
moved from hole to hole and retain the correct drop in point alignments.

Recall that the tips of all the gear teeth align with the “2” position on the indicator.
What we need to do is get the dial indicator to align with the “2” mark when the half nuts are engaged.
This will require a bit of judicious juggling of the saddle position relative to the leadscrew, engaging
the half nuts then nudging the unit along the mount until the correct alignment appears.

Once this location is determined, the space between the saddle and unit is measured using bits of stock, feeler gauges etc.
A spacer is then made up to match this sizing and slid down the mounting shaft.
You can see the black plastic spacer which I found suited the space I required in the photo above.

To test the final installation, engage the 16 tooth gear and try and drop in upon any line.

If this succeeds, then try the 14 tooth gear.
This should only drop in exactly on the “2” and “6” positions as all other indicator marks do not correctly align with the gear teeth.

Finally test the 20 tooth gear.
This should only drop in on any numbered line. Once again the unmarked lines do not align with a gear tooth with this gear.

A PDF file of my original turbocad drawing is available. This should provide clearer rendering than some of the images above.

Final Thoughts

As the BV-20 latch does not have a slotted power feed shaft, the dial indicator will also be very useful when used in the 16 tooth position.
Here the leadscrew can be engaged on any line, or even the imaginary lines between the marked lines.

If you have any queries with the construction, please feel free to drop me line at web@mrjones.id.au