Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Using superglue, or ideally acrylic cement, you’ll want to attach the spacer feet to the bottom of the supports.
As it turns out, though, the tabs on the Support sides stand just a bit proud of the Bottom plates, so that any attempt to glue the Feet in place will simply attach them to the side tabs and nothing else. Not what you want…
So I rubbed the Bottom plates on a sheet of coarse sandpaper until everything was nice and flat:
Flattened Plastruder Support bottom plates
Then the spacer feet glued neatly in place:
Gluing Plastruder feet
I tried to keep the acrylic cement off the tabs, so it’s theoretically possible to dismantle the whole thing, but I suspect that’ll never happen.
So I finally noticed that the water wasn’t nearly as soft as it used to be, which usually means I forgot to dump a bag of salt in the tank. This time, the water was halfway up the tank, which usually means something’s broken.
The usual cause: crud clogging the filter screen upstream of the venturi that sucks brine out of the tank. The usual fix: rinse the screen.
This time, however, the screen was clean. Pulling the gasket off the nozzle assembly revealed a collection of particles and chunks inside the fluidic channels; this is what the gasket looked like after I sorted everything out.
Original gasket and venturi
The gasket has at least three layers: a stiff red backing, a compliant green middle layer, and a white surface layer with molded channels matching the red nozzle. The two black cylinders are metering plugs with precisely shaped orifices that control the 0.1 and 0.3 gallon/minute brine and rinse flows.
The green and white layers evidently disintegrated into chunks that blocked the nozzle. With no flow through the venturi, the tank could fill until the float valve limited the flow, but the brining step had a very, very low flow and the resin bed eventually ran out of capacity.
I ordered a replacement nozzle and gasket assembly, figuring that Sears (actually, its OEM supplier) might have changed things in a non-compatible way. The old part numbers, which will get you the new equivalents:
Gasket: 7163663
Nozzle + gasket: 7187772
The new parts looked like this:
Replacement venturi and gasket
Surprise! The fancy molded gasket is no more; the replacement is a flat rubber sheet with the appropriate alignment notches and holes. The nozzle assembly might have come out of the same molding machine on the same shift.
I reassembled all the fiddly parts, manually set the softener to its Brine stage, let it suck a few inches of salt water out of the tank, and then returned it to automatic operation. At this point, the water heater is full of hard water and it’ll take a few repetitions of that cycle to get back to normal.
Given the limits of the gasket’s resolution, I’m sure the Batman icon is completely coincidental and sincerely regretted…
Having had to look up ball bearing sizes far too often, here’s the table…
Bearing
ID
OD
Thick
603
3
9
5
623
3
10
4
633
3
13
5
683
3
7
3
693
3
8
4
605
5
14
5
625
5
16
5
635
5
19
6
606
6
17
6
626
6
19
6
608
8
22
7
629
9
26
8
The first digit is something like the bearing type; I think 6xx = miniature bearings.
The second digit has something to do with the overall size, but is a code rather than an actual dimension.
The last digit is, hal-lay-loo-ya, the actual bore diameter.
[Update: Shows what I know; an excellent explanation of the numbers lives there. The short summary:
First digit: bearing type, 6 = single row deep groove
Second digit: series, 0 = extra light, 2 = light, 3 = medium duty, 8 & 9 = thinner
If three digits, third digit = ID in mm
If four digits, last two = ID/5, except 00-03 = 10/12/15/17
Moral: always verify everything you read on the InterTubes!]
Of course, a randomly chosen eBay listing will list the bearing size as:
ID x thickness x OD
OD x thickness x ID
ID x OD x thickness
and be wrong in at least one dimension
Of most interest to Thing-O-Matic hackers: a 635 bearing ought to fit a NEMA 17 stepper shaft (pay attention if you’re buying surplus: not all are 5 mm) and slip into the same hole as a 626 bearing.
Alas, there seems to be no 5 mm ID bearing equivalent to the 606 bearing in the MK5 extruder head, but a 0.5 mm = 20 mil shim around the outside would adapt a 625 to that hole. Might take some careful forming, though.
This should be obvious, but don’t reach across the build platform of your Thing-O-Matic with the extruder at 215 °C: you might bump the nozzle with the back of your hand.
Scorch mark from TOM nozzle
It never really hurt, but the nozzle tip made a nasty punch mark in the middle of a disk of scorched skin.
This is a better view of the alignment process that I endure once a year when I haul my Sherline mill back from Cabin Fever. The whole thing depends on a laser level that I’ve gutted and clamped to the floor joists over the mill, as described there.
The first step uses a plumb bob to position the hacked laser level lens directly over the Sherline’s spindle bore. I’ve shimmed the countertop under the mill to be pretty much level, so a vertical line from the bore determines where the lens must be.
Then I fiddle around to get the beam directly in the middle of the spindle bore, using a slip of paper to figure out where it’s going. The top picture shows the result.
Having done this a few times, the laser level starts out pretty much aligned, but the first setup required quite a bit of back-and-forth twiddling of the screws.
Then I put a mirror flat on the Sherline’s table / tooling plate to reflect the beam back up the spindle. More fiddling around gets the reflected spot pretty close to the outgoing beam; this picture shows the spot just off-center near the top (actually, toward the base of the laser level’s frame) of the aperture.
Reflected spot near laser aperture
When the outgoing and reflected beams converge, then I put the bushing (without the polarizing filter) in the top of the spindle bore to reduce the beam size and fine-tune the positions & angles.
Surprisingly, it stays in position quite solidly. I do twiddle it every now & again, but as long as the beam gets through the bore it’s close enough.
A display across the aisle from the CNC Ghetto at Cabin Fever featured a nice Laser Center Edge Finder with their new polarizing attachment. I played with it for a while and decided that, although my crude lashup gave similar results, I just had to have a polarizing filter, too.
I’d already made a bushing to fit the top of the spindle bore with a small aperture that aids in lining up the laser, so I just added a small recess for a disk of polarizing film. I have, for reasons that should not require any explanation by now, a lifetime supply of polarizing film…
Anyhow, the new polarizing filter sits neatly atop the spindle. The main laser beam lights up the middle of the filter, with junk light spilling on the bushing to the front and rear.
Polarizing film in upper bushing
Getting a good photograph of the spot size poses some problems, but here goes. This is the original, un-attenuated spot on a scale with 0.5 mm divisions: in round numbers, it’s half a millimeter across.
Normal laser spot size
Cross-polarizing the beam produces this attenuated spot on the same scale: it’s 0.25 mm in diameter, maybe a bit less. Call it 10 mils.
Attenuated laser spot size
Obviously, what you’re seeing are overexposed more-or-less Gaussian spots, so their diameters aren’t fixed numbers. But at this level, the inaccuracies of my Orc Engineering lens mount are comparable to the spot size, so reducing the spot any further isn’t going to improve the overall positioning accuracy.
It’s worth noting that the spot size isn’t the same as the positioning accuracy: you can visually align a workpiece mark to less than 1/4 the spot diameter. Claiming 1/10 the diameter would be more brag than fact, at least for me, but somewhere around 2 mils is close. That’s good enough for most of what I do.
Here’s how you measure the height of the extruder head over the build platform to calibrate the Z-axis travel: a taper gauge.
Home the Z stage, zero the readout, move the stage downward by known increments until it’s less than 4 mm above the platform, then slide a taper gauge under the nozzle until it touches. Read off the actual nozzle height above the platform, add that to the distance you moved the nozzle from its home position, and you have the total Z axis travel.
For example, right now my TOM Z axis travel is 115.3 mm. Plug that into the homing routine in start.gcode and you’ve got perfect nozzle height control.
Here’s a Starrett No. 270 taper gauge showing the nozzle 1.65 mm above the platform. One might quibble with the last digit, given the bit of snot hanging from the nozzle, but it’s pretty close.
Taper gauge below nozzle
Nice things:
You won’t accidentally ram the nozzle into the platform
The gauge flattens out small belt waves
You don’t squint at tiny vertical differences
Bad things:
Assumes a flat platform, which really should be true anyway
Seriously spendy (see below)
The gauge has inch divisions (0.001 in) on one side and metric (0.05 mm) on the other. I’ve put plenty of hours on the metric side in recent weeks.
Starrett 270 Taper Gauge – inch side
Fortunately, I’ve had that gauge in my tool cabinet forever; I’d be reluctant to cough up the C-note required to buy one these days. That Enco page gives some other choices, none of them, alas, inexpensive. If the link has rotted out, search for Starret No 270 taper gauge and you’ll get close.
I think you could construct something similar by gluing or soldering layers of brass shim stock: 8-mil (call it 0.2 mm) shim stock would probably stack up in 0.25 mm increments under sufficient pressure. You could measure the resulting steps to get pretty good accuracy, even if they’re not regularly spaced. Perhaps a gauge that measured 1.00 to 3.00 mm in steps of 0.25 mm, stacking eight thin layers atop a sturdy 40-mil / 1 mm base strip?
The Smell of Molten Projects in the Morning 