10ee Tachometer Disassembly

I took some pictures of the guts of a 10ee 2500 RPM tachometer from a 1942 machine. The pictures show a few things that may not be obvious. The bezel is removable without removing the tach, if the glass is broken or the tach needs to be serviced. The glass is held in place betwen a pair of fiber gaskets, and the bezel wedges into the outside chrome trim piece that attaches to the tachometer. I imagine that there was a puller that could grip the outside of the bezel to remove it; this one was removed by prying a few times, the marks show.

The dial and needle have been removed, so the assembly that has the balance shaft and spring is visible and there are several pictures that show it. The rotating cup (aluminum) is attached to the balance shaft with a brass nut (looks like a small gear) at the center. There is a steel shim between the cup and the brass nut, which I assume would be all that needs to be replaced to convert this to a 4000 RPM tach (replaced by a smaller size shim, so that the rotating assembly would be less affected by the magnetic field). The cup is balanced (the three cuts show on the underside), so I assume the shim would need to be balanced as well, although it is not round (it has arms that bend up around the cup center support).

Below the balance shaft assembly is the magnet that is driven by the spindle (with the number 100 pencilled on it).

-Dave

Some additional pictures:









One thing that is sort of amazing about this tach is that it came from a parts machine that had been sitting outside in the weather for years, and the glass on the tach was half missing, but there is no hint of rust inside.

-Dave

Dave,

Thanks for posting this.

What did you have to go through to get the tach off the machine?

Cal

What did you have to go through to get the tach off the machine?

Click to expand...

Cal,

You don't need to remove the tach to service it, but to get it off, there are a pair of studs on the back of the mechanical tach that stick into the headstock cavity. So remove the nuts from inside the headstock, remove the gear on the tachometer drive shaft (it has a small setscrew), and use the studs alternately as points to apply force with a lever. Its can be a tight fit if it has been in place 50 years...

If you want to service the tach in place, the bezel has a ridge around the circumference, which you can use a lever to work against. A suitable puller could be made.

-Dave

Thanks Dave,

I'm in the process of painting the headstock and I was thinking about pulling the tach so I could get the old paint off the bezel. I'm not sure I want to risk dropping the screws into the headstock, however.

My tach seems to be working fine. Is there anything about it that requires periodic maintenance?

Cal

There is an oil cup on the rotor assembly, and there are a couple of bearings that support the balance shaft (which would be lubricated with sperm oil by 1940's - 70's specs; not sure what the modern replacement is). If the tach is working leave it as is. The wartime models had non-plated bezels, so the bezel should be painted semi-gloss black. You should be able to scrape the paint off with a knife or similar and a razor blade on the glass. But watch out, some of them have plexiglas.

Original photos that got deleted from this thread are below:

More photos: