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Aaron Cake: I was looking at lapping tables in McMasterCarr and figured well all it has to be is flat... my housings are flat why not make one a lapping table for the other surface, let em lap eachother.
It sounds like you basically built the lapping jig I've had in the back of my mind for a few years now. My sticking point was that I wanted to use a drill press as the motor to rotate the eccentric shaft and drill presses with that much depth are huge and expensive, even used, and the ones that I would find cheaply were three-phase. I don't even have 220v service in my garage.
'Course, I think I found a better way of doing it anyway. And a whoooole lot of bad 12A side housings to experiment with. I don't think any of them are usable since the hardening is flaking out in spots on most of them (didn't know that could happen!) and I'm loath to have to lap all the way through.
The nice thing about lapping one surface against another like that is that, as long as the motions are at all randomized, flatness is self-generating. Any high spots/waves/curves will wear down first. Is why I want to use an eccentric shaft for orbital motion instead of any kind of purely linear or rotating motion.
Works a treat! About 250-ish rpm, with lapping compound and lot's of WD40 in between. The top housing slowly rotates as it's moving in a circular motion. I checked the progress, and relubed every few minutes, sometimes adding lapping compound.
It does take a while, I ground the bad housings down a few thou first, and I made sure the total amount of material removed per face was under 0.05mm, otherwise the waterseals get compressed too much. I use viton o-rings for waterseals, they are a bit more forgiving to lapped housings.
John, do you know how to make a single lip cutter? If you do, it's so simple to make a water seal deepening tool. Start with an unsplit carbide blank, grind the diameter first (you'll to make two) from a nominal stock to fit a collet (you may get lucky here you being in metric land and all and just grab off the shelf or end of an end mill).
Now when you split it, you want it on an angle for chip clearance. Start at about a millimeter at the cutting edge and taper deeper but not so deep as to clear the top of the existing groove, come back now and relieve it so you have an edge but be careful not to get into the diameter too deep (it's what guides the tool). Have a land diameter above the cutting edge and cleared back to guide the tool like a router bit.
Easiest is to stone the table of the vertical mill (around here, Bridgeport) real good, chuck the tool, set a zero and a way to control depth (knee). Be careful plunging, may need a stop in the tee slot. Once the depth is there just push the plate around by hand, you'll get the feel on the feed.
I've made a plate that goes on the end on my 90 degree grinder, use my step mic to set the depth, but it's runs too fast. Worked though... I tried my wood router, I had to make metal foot for it and some other mods to set depth accurately. It spins at a better speed though.
Given the propensity of the seal lands to break out at stock depth, I'd be leery of making them deeper. If need be, I'd just use a slightly thinner O-ring material. I think McMaster sells it in .2mm increments.
I was talking restoring depth of ground/lapped plates. It's usually only a few thousandths so, there really isn't much pressure. You can push it around by hand, just go in the direction to climb against the inside.
07-04-17, 01:12 PM
