Doin' my best just to change my yesterday, Then I won't have no more errors of my way.

by Ivan Hamilton 4/21/2008 12:53:00 PM

Spin motor left, spin motor right. Easy enough. The next step is to get positional feedback by mounting an encoder on the motor shaft. Sounds easy enough, doesn't it? But since my motors don't have a shaft on either end, I'll need to add an extension.

Luckily someone much better than me has already done this, and put nice instructions on the web. How hard could it be? It would also be my first real piece of work on the new mill.

What I needed to do What I did
Machine flat the raised area where the encoder will mount. Fixed the endplate to the mill table on top of only two standoffs.
The plate wasn't flat, and halfway thru gouged below the non-raised face.
Refix the workpiece using 3 points and machine flat (hoping the circular valley won't matter).
Drill a slighly oversize hole in the center of the end plate. Drill an off center hole, and then roughly open the hole in the direction of where the hole should be.
Drill a hole straight down the center of the motor shaft. Drill a hole angled down the center of the motor shaft.
Machine a 4mm bar for the shaft extention. Machine a 3.9mm bar which is too small for the encoder wheel to grip.
Machine a new 4mm bar, but thin up one end so it can sit straight in the angled hole.
Add glue and insert shaft extension until the glue rises to just ooze a fillet above the end of the rotor shaft. Add too much glue before inserting shaft extension.
Dab at glue with paper towel to remove glue until shaft extension can be inserted without glue flowing over the bearing.
 Drill and tap 2 x M2.5 holes for mounting screws. Don't check the screw size. Eyeball the screw and match against the smallest tap in your set.
Drill and tap 2 x M3.0 holes for mounting screws. Scratch your head when the M2.5 screws just fall out.
Bore out the encoder board and base to 3mm to fit M3.0 screws.
Realise you don't have suitable M3.0 screws.
You have to go out to buy M3.0 screws, so you may as well buy a M2.5 tap and use the right screws.
Abandon your 2 x M3.0 holes.
Drill and tap 2 x M2.5 holes for mounting screws.

It didn't go completely smoothly, but no fatal mistakes were made. A couple of cubic millimetres of material were removed that didn't need too... and a bit of extra glue.

At the end of the day... I'm fairly happy with the results.

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Mechanics | Pragmatism

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