Category: Machine Shop

Mechanical widgetry

Shrinking Heat-shrink Tubing to a Specific Diameter

Shrinking tubing on a mandrel

I needed some black plastic tubes with several different IDs, which usually calls for some tedious machining. Then I realized I could just shrink some heat-shrink tubing around mandrels.

Drill rod worked fine, as did a socket wrench. The only catch was avoiding the engraved lettering, which tends to lock the tubing firmly in place.

In a pinch, I suppose you could turn a rod to the right OD and make a mandrel. That would likely be faster than machining a tube from solid stock, at least for me.

Chuck the mandrel in the lathe, lean a box cutter against the tubing, turn it by hand, and cut to the right length with nice flat ends. Pry it off by sliding a fine needle between the tubing and the mandrel.

You knew that already, right?

2010-07-07
Constraining a Sewer Snake

Constrained sewer snake

Had the occasion to run the flexy snake through a kitchen drain that turned out to be not as plugged up as I expected, which is always good news. Replaced the cleanout plug, hosed off the snake, coiled it up, and applied the usual three nylon cable ties to keep the snake together.

It took me years to figure out that last step. None of the old-school tricks work for me; I can’t tie knots in string / twine / rope while simultaneously holding those coils together and the snake resists any attempt to weave the loose ends into the bundle.

Mercifully, I don’t use the snake all that often and I don’t feel at all bad about tossing three cable ties each time.

You figured that out long ago, right?

2010-07-05

HT GPS + Audio: Battery Pack Contacts the CNC Way

Faced with the daunting prospect of converting half a dozen 4-40 brass screws into battery contacts by hand filing, I did what I should have done in the first place: turn it into a CNC project.

It’s quick-n-easy:

mill the head flat and 0.5 mm thick
shave off the sides

I grabbed the screw in the Sherline vise, touched off XY on the head (close enough to being concentric for this purpose), and touched off Z on the nut supporting the screw. For the next few, I’ll eyeball the Z touchoff at the bottom of the head, rather than the nut, because the heads don’t quite sit flush on the nut.

They dropped right into place, without any filing or fiddling! Well, the second one did. I had to tweak the dimensions slightly to make the answer come out right. But that’s one of the advantage of hammering out simple G-Code like this: change two lines and wham you’re done.

The heads show some tool marks, but that’ll just make the silver solder stick better. Right?

Herewith, the G-Code…

(ICOM IC-Z1A battery pack shell)
(Battery pack contacts)
(Ed Nisley - KE4ZNU - June 2010)
(Vise clamping on threads, XY orgin on central axis, Z=0 at *bottom* of screw head)
(Tool table used just for Axis previews and to activate "manual" changer via M6)
(Tool change @ G30 position above length probe)

(-- Global dimensions & locations)

#<_Traverse_Z> =        5.0
#<_Cutting_Z> =            0.0

(-- Get started ...)

G40 G49 G54 G80 G90 G92.1 G94 G97 G98        (reset many things)

M5
(msg,Verify XY=0 on screw axis)
M0

(msg,Verify tool touched off at Z=0 on *bottom* of head)
M0

(debug,Verify vise clearance around head)
M0

#<Contact_Width> =        4.1            (X axis metallic contact - minus a smidge)
#<Contact_Head_Dia> =    5.5            (recess for 4-40 head)
#<Contact_Head_Radius> = [#<Contact_Head_Dia> / 2]

#<Contact_Head_Depth> =    0.7            (recess depth - plus  smidge)

#<Mill_Dia> =            1.98            (end mill diameter)
#<Tool_Num> =            20
#<Mill_Radius> =        [#<Mill_Dia> / 2]
#<Mill_RPM> =            5000
#<Mill_Feed> =             50

(debug,Verify #<Mill_Dia> mm end mill)
M0

(debug,Set spindle to #<Mill_RPM>)
M0

F#<Mill_Feed>

(--- Flatten the head)

G0 Z#<_Traverse_Z>

#<X_Step> = [0.5 * #<Mill_Dia>]
#<X_Limit> = [3 * #<Mill_Radius>]
#<Y_Limit> = [#<Contact_Head_Radius> + #<Mill_Radius>]

#<X_Coord> = [0 - #<X_Limit>]

G0 X#<X_Coord> Y[0 - #<Y_Limit>]
G0 Z#<Contact_Head_Depth>

O<Head_Trim> DO

G1 Y#<Y_Limit>
#<X_Coord> = [#<X_Coord> + #<X_Step>]
G1 X#<X_Coord>
G1 Y[0 - #<Y_Limit>]
#<X_Coord> = [#<X_Coord> + #<X_Step>]
G1 X#<X_Coord>

O<Head_Trim> WHILE [#<X_Coord> LT [3 * #<Mill_Radius>]]

G0 Z#<_Traverse_Z>

(--- Trim the sides)

#<Arc_Radius> = [#<Contact_Head_Radius>]
#<Half_Width> = [#<Contact_Width> / 2]
#<Angle> = ACOS [#<Half_Width> / #<Arc_Radius>]
#<Half_Height> = [#<Arc_Radius> * SIN [#<Angle>]]

G0 Z#<_Traverse_Z>

G0 X[0 - #<Half_Width>] Y[0 - #<Contact_Head_Radius> - 3 * #<Mill_Dia>]
G0 Z#<_Cutting_Z>

G41.1 D#<Mill_Dia>
G1 X[0 - #<Half_Width>] Y[0 - #<Half_Height>]

G1 Y#<Half_Height>
G2 X#<Half_Width> I[#<Half_Width>] J[-#<Half_Height>]
G1 Y[0 - #<Half_Height>]
G2 X[0 - #<Half_Width>] I[-#<Half_Width>] J[#<Half_Height>]
G1 Y#<Half_Height>

G0 Z#<_Traverse_Z>

G40

G30                    (back to tool change position)

(msg,Done!)
M2

2010-07-03

Repurposing Tomato Cages

Bending tomato cage wires

Mary wanted to convert some old tomato cages into flower supports and deer protectors (until the flowers get big enough), by the simple expedient of flipping the cages over with the large end down. She figured we could chop off the wire ends that normally anchor the cages to the ground, then bend them into hooks for secure ground anchors.

I deployed the linesman’s pliers, which only showed that my wire size estimation is grossly underdeveloped. The high-carbon steel wires required bolt cutters… but a few minutes of twang effort scattered two dozen really stiff wires across the patio.

I ran a marker across the pile at the bend point, grabbed two random steel rods in the vise and, in short order, bent up a stack of ground anchors.

Not every job requires G-Code …

2010-07-02
Zire 71 Button Protector

Zire 71 button protector

I carry around an ancient Zire 71, from the time before PDAs merged with phones and PCs to become fashionable objects of desire.

Anyway, it turns out that the buttons on the front are remarkably easy to squash in your pocket: the poor thing spends a lot of time turning itself on and off. I machined a plate with two holes for the four buttons and a lengthwise recess with two notches for the joystick selector. The whole affair slides into the pouch Mary made for it and works fine.

I tweaked the thing a bit when I got a replacement Zire a few months ago; the grippy tape I put on the sides seemed to be just large enough to force the joystick against the protector while sliding it into the pouch. Now that’s not a problem.

Zire 71 protector in place

This is in the nature of documentation, just in case I need something like this ever again. I found these pix while looking for something else …

2010-06-28
HT GPS + Audio: Case Dimensions

Having obtained eyeballometric measurements from the case, the next step was to doodle some shapes on graph paper and pencil in the dimensions. My motivation for not using CAD is simple: it’s easier (for me, at least) to doodle using a pencil.

The outside of the case had pretty much the same features.

Pack Layout – External

The inside, of course, bore no resemblance to the battery pack; the shoulder and whatnot will support the circuit board.

Pack Layout – Internal

The original battle plan was to build the case in at least two layers, simply because it had to be so deep the Sherline couldn’t reach to the bottom with any rational end mill. It would probably make more sense to glue up four sides on a machined bottom, but that requires actual skill.

This became the Front layer, with Front and Rear faces. The Rear layer attaches to the back of this one. In this picture, the Front layer is on the bottom, taped to the radio.

ICOM IC-Z1A with GPS+Audio Interface

The two layers peeled apart, with the Front layer to the right. You can barely see the internal shoulder and external tabs.

Interface – top and bottom surfaces

2010-06-27
ICOM IC-Z1A and W-32A: BP-171 Battery Pack Dimensions

Early on, I decided that the whole APRS + voice interface for our bikes had to fit on the back of the radio, which meant it had to look a lot like a BP-171 battery pack. The first step was to get all the relevant dimensions from an existing pack.

I laid a (rebuilt) pack on the scanner and took its picture. There’s a lip on the bottom (top in the image), so I held it level with the end of the calipers you can see near the bottom. That puts it slightly above the scanner’s focal plane, but it’s close enough.

Then I scanned some graph paper (remember that?) with 10 lines per inch, overlaid that on the pack image, rotated to line it up with the pack, scaled the grid so that the major lines were 1 cm apart on the pack in both directions, and that gave me a nice 1 mm grid to eyeball the measurements.

Printed the image out at about twice real size and there you have it:

Battery Pack Dimensions

The doodles around the bottom give the Z-axis dimensions for tabs & contact slots & suchlike.

The notes near the top were a first pass at how to mill the thing; two years later, the actual G-Code bears little resemblance to that.

I put the origin at the lower-left corner of the part that fits into the radio body, 2.4 mm inside the left edge that mates with the outside of the body. That was probably a mistake, as it meant I had to touch off the final part at X=-2.4 rather than just 0.0.

We live & learn.

2010-06-26