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NEMA17 Motor and Bearing Mounts

As part of coaching a student (and his father!) on their incredibly ambitious build-a-plotter-from-scratch project, I suggested stealing using HP’s grit-wheel paper drive, rather than fiddling with guide rods to move either the pen carrier or the entire paper platform. Dremel sanding drums seem about the right size and they had an 8 mm shaft harvested from a defunct printer, so a pair of mounts moves the project along:

NEMA17 and Bearing Mounts - Slic3r preview

NEMA17 and Bearing Mounts – Slic3r preview

The motor mount code is a hack job from my old NEMA17 mount and the code has a lot not to like. The bearing mount puts the bearing on the proper centerline using brute force copypasta and depends on friction to hold it in place. The two models should be integrated into the same file, the shaft centerline shouldn’t involve the printed thread width, and blah blah blah:

NEMA17 motor and bearing mounts

NEMA17 motor and bearing mounts

I had him turn the shaft adapter from an aluminum rod in the mini-lathe: he’s hooked.

The OpenSCAD source code as a GitHub Gist:

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Mini-Lathe Tailstock: Alignment

After dismantling the tailstock to apply the tweaks, it was grossly out of alignment, as seen from the top:

Tailstock - initial H offset

Tailstock – initial H offset

Seen from the side, the tailstock center is way too high:

Tailstock - initial V offset

Tailstock – initial V offset

No surprises there.

The object of the game is to make the tailstock bore collinear with the spindle bore in all four degrees of freedom:

  • Front-back
  • Up-down
  • Yaw angle
  • Pitch angle

The first step is to match those two points, then measure the angular error.

Loosen the (new!) screws holding the tailstock top & bottom castings together:

Tailstock - modified screws

Tailstock – modified screws

I set them snug enough to prevent casual motion and loose enough to allow adjustment with gentle taps from a plastic hammer. Tapping the top casting forward lined up the dead centers horizontally, leaving only the vertical alignment.

Then I clamped the tailstock’s bottom casting to the lathe bed:

Tailstock - clamp for shimming

Tailstock – clamp for shimming

Loosening the screws a bit more let me tilt the top casting to the left and slide a brass shim between the two castings, adding just a little more height to the left side to move the tailstock center downward.

This could do any or all of:

  • Correct a pre-existing pitch angle so everything is fine again
  • Pitch the tailstock ram axis out of line with respect to the spindle axis
  • Confuse the issue

I started with a 6 mil = 0.15 mm shim that didn’t quite do enough and a 16 mil = 0.4 mm shim was a bit too much. Pinching a brass shimstock snippet between the centers show how they match front-back and don’t match up-down, with the tailstock center now too low:

Tailstock - alignment too low

Tailstock – alignment too low

Some back-and-forth fiddling showed a 10 mil = 0.25 mm sheet came out about right:

Tailstock - perfect point alignment

Tailstock – perfect point alignment

With the two linear degrees of freedom accounted for, measure the yaw angle by comparing the position of the tailstock ram’s far end:

Tailstock - vertical angle measurement - 1

Tailstock – vertical angle measurement – 1

With its near end:

Tailstock - vertical angle measurement - 2

Tailstock – vertical angle measurement – 2

Note: measure the offset by sliding the tailstock along the ways, not by retracting the ram. Reassuringly, the ram slides out parallel to its axis.

Measure the pitch angle, similarly:

Tailstock - vertical angle measurement

Tailstock – vertical angle measurement

As it turns out, the far end of the ram is 5 mils down and front from its base near the tailstock. Over 1.5 inches of travel, 5 mils works out to 0.19°.

Although it’s a small angle, the huge Jacob chuck supplied with the lathe puts a typical drill 125 mm from where you see the tailstock dead center’s tip. In round numbers, the drill point will be 16 mils low-and-front,  about 25 mils radially off-center, which agrees reasonably well with what I actually see:

Tailstock - misaligned drill chuck

Tailstock – misaligned drill chuck

Because I don’t do much turning between centers, I retinkered the alignment to put a point held in the drill chuck on center. Deep hole drilling won’t work quite right, because the ram extends along those 0.19° angles, but it’s Good Enough for now. It’ll be much easier to correct the yaw misalignment than the height mismatch.

Those of you who read image metadata surely noticed the pix aren’t in ascending temporal order. Verily, this was an iterative process, with pix happening all along the way.

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Mini-Lathe Tailstock: Cleanup

Filling the mini-lathe’s tailstock ways with epoxy made it slide easily and lock firmly. Some upcoming projects urged me to perform The Canonical Mini-Lathe Tailstock Upgrades, as shown nearly everywhere on the Intertubes and detailed in various HSM articles.

For unknown reasons, the screw clamping the tailstock’s top and bottom castings together threads into the top casting from below:

Tailstock way repair - blue Sharpie

Tailstock way repair – blue Sharpie

Although it’s faintly possible you could adjust it by reaching up from below the bed, it’s easier to just drill out the threads for a clearance fit around a 5 mm SHCS:

Tailstock - drilling clamp screw clearance

Tailstock – drilling clamp screw clearance

The drill went through the tailstock so easily I think the hole had been capped with body filler, which would eliminate the need for a bottoming tap.

Then build a square nut from a slice of 7/16 inch square stock:

Tailstock - drilling square nut

Tailstock – drilling square nut

… and be done with it:

Tailstock underside - square clamp nut

Tailstock underside – square clamp nut

If the tailstock ever needs more adjustment range, I can knock those corners down a bit.

The screw clamps the castings vertically, with a second screw under the tailstock ram handwheel forcing the top and bottom not-quite dovetails together horizontally. I replaced both with 5 mm socket head cap screws:

Tailstock - modified screws

Tailstock – modified screws

Tightening a cup-end SHCS against the square not-a-dovetail tends to shift the upper casting; the original screw had a narrow pin end to reduce the torque. Having brass rod close at hand, this seemed easier than machining the screw:

Tailstock slide lock screw

Tailstock slide lock screw

The little tip comes from using a square-ended cutoff tool. Purists will dress the tool at a slight angle to cut off one side first. Of course, which way one dresses it depends on whether you want the remaining stub on the stock or the cut-off part. Sooo, I still have a square tool.

The tailstock has a cam lock handle clamping a square-ish plate against the bottom of the bed ways. Unfortunately, the manufacturer cut the plate with a dull shear, producing two beveled edges:

Tailstock clamp plate - OEM bevels

Tailstock clamp plate – OEM bevels

Flipping it over dramatically improved the clamping action, although I must eventually scrape the paint and grunge off the bottom of the ways. While I had it off, I turned a small aluminum bushing to replace the pair of washers:

Tailstock - clamp plate bushing

Tailstock – clamp plate bushing

The plate hangs lower toward the rear because the clamping bolt isn’t in the middle. The tailstock originally had a mighty spring holding it level, but the spring tended to snag against the front side of the bed, so I removed it.

The lever handle actuating the tailstock cam lock had no stops and rotated freely counterclockwise when loosened. The tailstock casting had enough meat for a 5 mm threaded brass insert in a useful location, so I drilled a suitable hole:

Drilling for tailstock lever stop

Drilling for tailstock lever stop

The vacuum hose slurped up the cast iron dust, which is a Very Good Idea.

Butter up the insert with JB Kwik epoxy, slide into the hole, wipe off most of the excess, then pause to admire the result:

Tailstock lever - insert installed

Tailstock lever – insert installed

The lever stopper won’t win any design awards, even though it’s a dramatic usability improvement:

Tailstock lever bumper - installed

Tailstock lever bumper – installed

The finger-tight nut serves to lock the SHCS in place against the lever’s impact. I conjured a small bumper around the head from a rubber foot intended to fit under a random box of electronics.

Pushing the lever leftward to the stop lets the tailstock slide freely and pushing it to the right clamps the tailstock to the bed. The cam’s limited rotation keeps the plate close enough to the underside of the bed to prevent it from tipping left-to-right as the tailstock slides, so it no longer snags.

While I had the tailstock up on jackstands, this is what the ram thrust bearing looks like:

Tailstock ram screw thrust bearing

Tailstock ram screw thrust bearing

The flange over on the left bears against the steel disk on the right, with no real thrust bearing to be seen. A dab of grease improved its disposition.

Now, to realign the thing …

 

 

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Monthly Image: Google Pixel XL HDR at Wappingers Falls Bridge

We walked over the bridge in Wappingers Falls on our way to a play:

Wappingers Falls Bridge - Google 3D Overhead - 2017-09-22

Wappingers Falls Bridge – Google 3D Overhead – 2017-09-22

As always, we paused near the center to admire the view (clicky for more dots):

Wappingers Falls Bridge - Pixel XL HDR - 2017-09-22

Wappingers Falls Bridge – Pixel XL HDR – 2017-09-22

That’s from the PixelXL, braced on the bridge wall, facing downstream toward the Hudson River.

A dot-for-dot crop of the penstock, showing off the RGB LED garland:

Wappingers Falls Bridge - Pixel XL HDR - Penstock crop - 2017-09-22

Wappingers Falls Bridge – Pixel XL HDR – Penstock crop – 2017-09-22

Contrary to what you might think, the gorge underfoot appeared almost black to the eye, particularly against the glare from the floodlights, so the HDR works very well:

Wappingers Falls Bridge - Pixel XL HDR - Gorge crop - 2017-09-22

Wappingers Falls Bridge – Pixel XL HDR – Gorge crop – 2017-09-22

The JPG compression on those images doesn’t materially affect the results; the original image has most of the artifacts.

The EXIF information:

Wappingers Falls Bridge - Pixel XL HDR - Photograph EXIF - 2017-09-22

Wappingers Falls Bridge – Pixel XL HDR – Photograph EXIF – 2017-09-22

The “1/10 s shutter speed” probably has very little to do with any physical event. AFAICT, the Pixel camera records 30 images/s for the on-screen preview, then uses various images before-and-after the shutter click for motion compensation and HDR processing. If so, “1/10 s” corresponds to three images.

I had the Pixel location tracking in “battery saving” mode with the GPS turned off:

Wappingers Falls Bridge - Pixel XL HDR - GPS EXIF - 2017-09-22

Wappingers Falls Bridge – Pixel XL HDR – GPS EXIF – 2017-09-22

In reality, the bridge is about 90 feet above sea level. The “GPS Time Stamp” and, presumably, the date, use UTC. We’re in UTC-4, with Daylight Saving Time in full effect, so we were comfortably early for the 8 PM show.

The camera doesn’t produce DSLR-with-big-glass quality images, but it fits in my pocket and it’s better than my old Canon SX-230HS for most purposes.

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Bathroom Sink Stopper Rod

After swapping the corroded steel rod end-for-end twice, I expected this would happen:

Bathroom Sink Stopper Rods

Bathroom Sink Stopper Rods

So now we know a chrome-plated steel rod will survive 16 years in a bathroom drain, at least if you’re willing to coddle the fool thing far more than seems reasonable.

I eased a slug of epoxy into the brass tube to seal the wet end. Given how little use the stopper gets, I hope it lasts forever …

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SRAM Shift Indicator Repair: Polypropylene Sheet

Over the course of a few weeks, both of the indicators in the SRAM grip shifters on my bike snapped off. Having recently touched my parallel jaw clamp assortment, it occurred to me I could mold snippets of polypropylene sheet (saved from random clamshell packages for just such a purpose) around the nose of a clamp and come out pretty close to the final shape:

SRAM Shift Indicator - shaped replacements

SRAM Shift Indicator – shaped replacements

A hot air gun set on LOW and held a foot away softened the polypro enough so a gloved thumb could squash it against the jaw. Too much heat shrinks the sheet into a blob, too little heat lets the sheet spring back to its original shape.

The flat tab of the original indicator is about 1 mm thick. I found a package of 47 mil = 1.2 mm sheet with one nice right-angle bend and ran with it.

Because I expect sunlight will fade any color other than black, that’s the Sharpie I applied.

They don’t look as awful as you might expect. The rear shifter, minus the cover:

SRAM Shift Indicator - rear detail

SRAM Shift Indicator – rear detail

The front shifter, with cover installed and HT PTT button below the still-good Kapton tape:

SRAM Shift Indicator - front assembled

SRAM Shift Indicator – front assembled

The transparent covers press the OEM indicators down and do the same for my homebrew tabs. I expect the Sharpie will wear quickly at those contact points; next time, I should tint the other side.

They’re rather subtle, I’ll grant you that.

Now, to see if they survive long enough to make the worry about a brighter color fading away a real problem…

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More Tommy Bar Handles

Having used a nail for far too long, this is a definite step up for my machinist vises:

Tommy Bar - machinist vise

Tommy Bar – machinist vise

The vise knob has a hole just barely passing a length of 3.4 mm = 9/64 inch mild steel rod from the Small Box o’ Cutoffs.

While I was at it, I made a handle for the parallel jaw clamps:

Tommy Bar - parallel jaw clamp

Tommy Bar – parallel jaw clamp

Those knobs pass a 3.0 mm = 1/8 inch rod, similarly sourced. Inexplicably, one clamp expected no more than a 7/64 inch rod; a brief introduction to Mr Drill Press persuaded it concerning the error of its ways.

I should have made the handles distinctively different, because they’ll get mixed up in the box of vises & clamps. Next time, fer shure!

The Tommy Bar handles use the same solid model as the Sherline Tommy Bars, with hole diameters as noted. Cyan PETG is definitely easier on the eye than red PLA, although it does fade into the background clutter around here.

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