Torticollis is a condition where an infant's neck muscle is tight or shortened on one side, causing the head to tilt in one direction. Congenital muscular torticollis (CMT) is the most common form and is typically identified in the first few months of life. Physical therapy with gentle stretching, positioning strategies, and parent education is the primary treatment.

Do you accept TRICARE?

Yes. Lead Pediatric Physical Therapy is an in-network provider with TriWest Health Care Alliance, which administers TRICARE West. Your provider can call 844-866-9378 to enter a referral. We are honored to serve military families in Fort Worth.

Do you offer in-home physical therapy visits?

Yes. In-home and daycare visits are available within a 15-minute drive of our clinic in the 76107 area of Fort Worth. Your child receives the same one-on-one care with Chrissy in the comfort of their own environment.

What is a PCS certification?

PCS stands for Pediatric Clinical Specialist, a board certification awarded by the American Board of Physical Therapy Specialties. Fewer than 3 percent of physical therapists in the United States hold this credential. It requires advanced clinical experience and a rigorous examination focused exclusively on pediatric physical therapy.

How much does a pediatric physical therapy evaluation cost?

The initial evaluation is $185 and lasts 45 to 60 minutes. Follow-up one-hour treatment sessions are $155 and half-hour sessions are $95. Packages are available at a reduced rate. We accept HSA and FSA cards, credit and debit cards, and Venmo.

What should I bring to my child's first physical therapy appointment?

Bring any referral paperwork from your pediatrician, a list of your concerns and questions, and your child in comfortable clothing. If your child is an infant, bring a favorite toy or comfort item. Chrissy will spend time understanding your child's history and your goals before beginning the evaluation.

Posts tagged:

engineering

Personal Projects & Interests

Burning Weeds

Burning weeds is fun. It may also be cost effective, easy to apply than chemicals and just feels more natural. My neighbor once described a brief pass over weeds as “instant drought”. Maybe, but it works well. That is, unless your burner stops working.

The burner hooks directly to a propane gas tank. You just need a regulator, a flow value, and a wand. Light a spark and you have a nice torch.

In my case, I couldn’t get any gas to flow. I messed around trying to dissemble everything and then used compressed air to clear any blockages. This didn’t work. I started looking at new wands. They were > 100$ and repairing this was worth trying, but I needed to understand how this tool worked.

The key insight is that there is a small hole where the gas escapes. Mine was clogged. I put WD-40 on both sides of this hole and used a steel brush on my drill to clean this out and then compressed air until the blockage cleared. Next time, I won’t leave this wand out in the rain. Lesson learned.

The regulator is wrist-watch cool, it’s a mechanical feedback loop

The first part to understand is the regulator. In a typical direct-operated reducing regulator, outlet pressure pushes on a flexible diaphragm while a spring supplies the opposing force. A linkage connects that diaphragm to a valve at a restricted passage. The valve changes the opening through which higher-pressure gas enters the lower-pressure side.

Open the torch’s control valve and gas leaves the downstream side. As outlet pressure falls, its force on the diaphragm falls; spring force moves the mechanism toward a larger opening. When demand decreases, outlet pressure rises and the mechanism throttles toward closed. At a steady demand, it settles near a balance. The regulator responds continuously; it is not a pump or simply an on/off switch.

**Image 1** – You always see this thing, but what does it do?

I can’t follow paragraphs like this, so I built an illustration. Watch the linked diaphragm, stem and valve move together while the spring length changes. Motion is exaggerated to explain the feedback direction; this is not a pressure-response calculation.

Illustration 1 – Regulator

A small fuel outlet inside a much larger cup

Flame Engineering describes a fitting welded to the pipe end with a pin-sized central orifice. This detail was critical to fix this. There is much power in building a 3d model of a part. You can explore exactly how things work and then do a very surgical fix. Professionals gain this knowledge over years in apprenticeships, but weekend hacks like me can get the same wisdom from a model.

First, pressure drives gas through the restricted outlet. The emerging jet transfers momentum to surrounding air, drawing air into the mixing region. Fuel and oxygen then burn, producing a nice focused torch. The large air openings and the small fuel opening perform different jobs.

Illustration 2 – Watch fuel draw air into the burner, mix and form a flame. Use Pause and Speed to explore the flow.

The end of the wand is a mixing chamber, not a safety shield. The torch turns a narrow stream of propane into a broad flow of heat as it mixes in this tube. Pressurized fuel travels down the wand and accelerates through a small outlet into the burner bell, which is 2 inches (about 51 mm) across on the Weed Dragon VT2-23C. The fast-moving jet pulls surrounding air through the openings behind the bell a process called entrainment. The wider tube gives that air and fuel room to mix as the jet spreads. Once ignited, the mixture releases heat, expands, and continues mixing with outside air beyond the mouth, producing a flame much wider than the original fuel jet. The bell helps shape this flow, but the flame’s width and length also depend on fuel flow, air supply, and wind. The drifting haze in the illustration makes normally invisible gas motion visible.

The heat does not necessarily peak at the burner’s face, and it does not simply fall as $1/\text{distance}^2$. Near the torch, combustion, mixing, and the hot gas striking a surface all affect heat delivery. To understand the chemistry and the heat, let’s use NASA’s explanation of flame color. Blue in a real flame comes largely from light emitted by excited molecules during combustion. It is not a “cool” region. Yellow, orange, and red often come from glowing soot particles. Brightness and color alone cannot tell us the gas temperature or how much heat reaches a leaf.

The heat is not maximized at the end of the wand where fuel may still be mixing and burning. It takes distance for the reaction to increase. Farther downstream, the jet spreads, entrains cooler air, and loses speed and temperature. The concept here is heat flux:

q”_{\text{net}} = \underbrace{h(T_{\text{gas}}-T_{\text{leaf}})}_{\text{heat carried by moving gas}} + \underbrace{q”_{\text{radiation, absorbed}}-q”_{\text{radiation, emitted}}}_{\text{net radiant heating}}

Practically, this means you need to experiment on distance.

**Image 2.** Heat and distance from the wand

Why does a short pass of heat kill plants?

The trivial answer is that if you turn a plant into ash, it’s gone. That isn’t the idea here. I’ve learned a light pass that causes just a little wilt is best.

How does a pass of high heat kill a plant? A healthy leaf’s firmness depends partly on turgor: water pressure within living cells pressing against their walls. Membranes maintain the separation and chemical gradients that make normal cell function possible.

Illustration 3 – Watch heat damage the leaf’s cells, then follow its effects on the plant’s ability to recover.

The plant dies when damage exceeds its capacity to sustain itself and rebuild. Loss of support for the roots is part of that process, but damage to the growing points also matters.

Heat damages membranes and proteins, causing cells to lose function and water pressure. Leaves wilt and lose their ability to produce sugars that support the roots and new growth. The plant can recover if surviving leaves and stored reserves sustain it long enough for living buds to produce replacements. If that recovery fails, or heat destroys the growing points needed for replacement, the damage becomes fatal.

The S-curve describes how increasing heat exposure pushes more plants beyond that recovery limit. At low doses, most recover. Through the steep middle, more sustain fatal damage. At high doses, most susceptible plants have already crossed the limit. There is no universal percentage of leaf loss that kills every plant; protected buds and stored reserves change the outcome. Also, a curve measuring reduced growth must not be mistaken for a curve measuring death.

To do it right, pass the heat across the foliage and exposed growing points, the tips or buds producing new leaves. Burning through the stem could work if you really destroy it but that takes too much time.

From my reading on this, a good field check is to let the treated leaf cool, then gently press it between thumb and finger. A lasting thumbprint, dark watery appearance, or easily crushed tissue indicates sufficient heat injury in that area.

Why the same treatment can kill one weed and spare another

Burning doesn’t affect all plants equally. Small broadleaf seedlings are often susceptible because their growing points are exposed. Grasses can protect those growing points near the soil or within leaf sheaths. Established perennials can retain roots, crowns or underground stems that produce another shoot after the visible foliage is injured. A wilted top is not proof of a dead root system. [9] [11]

Nebraska experiments found that response changed with propane dose, species, growth stage and time of day; grasses generally tolerated more flaming than broadleaf species. So a universal pass speed or a single exposure will not kill every weed. [10]

Flaming also has practical limits. It is nonselective, can injure desirable plants, and can ignite dry vegetation or mulch. (Ask my wife about lighting the house on fire.) [9]

The useful question is not “How completely did I burn it?” It is whether enough vulnerable living tissue was injured to prevent recovery, and whether protected growing points can still restart growth. Several fast passes are a good experimental way to find out.

Sources & model notes

October 21, 2026 (updated October 22, 2026) By Tim Booher One Comment

Personal Projects & Interests

Fixing the inlet on my Ryobi Pressure Washer

Some posts I write to inform others of cool stuff. Others posts I write to save someone else time when they google. This post is just a story of frustration, written to look like the second example. You have been warned.

Several years ago, I bought this pressure washer and then let it sit unused for far too long—a bad move. The Ryobi RY80940B, powered by a Honda GCV190 engine, delivers 3,100 PSI at approximately 2.5 GPM, more than enough force for serious cleaning but also enough to punish neglected hardware. For anyone working on one of these, the operating manual is available here: Ryobi RY80940B Service Manual (PDF).

When I finally tried to remove the hose, the metal fitting was stuck. The smart thing would have been to leave the hose stuck in there forever. I didn’t do that. I wanted to get the old hose out and, well, I’m an arrogant engineer and this was a battle of wills not of wits. I’ve spent the better part of an afternoon fighting with a broken brass fitting fused inside the outlet coupler of my Ryobi RY80940B pressure washer. What should have been a simple hose replacement turned into a problem. The brass insert from the old high-pressure hose sheared off cleanly, leaving a ring of corroded metal wedged inside the plastic spindle. I tried everything — prying, tapping, a bolt extractor — but the brass just spun or smeared instead of breaking free.

Eventually, I realized I was wasting time trying to rescue a part that costs less than lunch. The black collar that covers the quick-connect doesn’t unscrew; it slides over a spring and bearing set. Once you see the parts diagram for this model, it’s obvious the spindle (part #642058001) and collar (part #310993003) are meant to be replaced together.

Per the service manual, I first tried an 8 mm hex key to back out the fitting, but it immediately began to strip, producing nothing but a rain of metal shavings.

After exhausting every polite method of extraction, I escalated. Since I knew the brass and aluminum had fused completely, I cut most of the seized coupler off with an angle grinder, then used diagonal cutters to peel the remaining sleeve away from the spindle. With the bulk removed, I applied heat from a torch, clamped a pair of vice grips onto what was left, and added a four-foot cheater bar for leverage. The grips slipped off more than once, but eventually I felt the faint give of motion—the threads finally broke free. Sometimes the “fix” isn’t surgical precision; it’s controlled brutality, executed carefully enough not to destroy the surrounding parts.

Because this took so much work. I’m going to show you two pictures.

Tech Details

So what happened here? The failure wasn’t merely mechanical — it was electrochemical and thermomechanical. The brass hose insert (nominally Cu–Zn alloy, ≈ $Cu_{60}Zn_{40}$) had been pressed into a steel spindle (Fe–C alloy with minor Mn, Si). Over years of intermittent water exposure, this dissimilar-metal couple set up a galvanic cell with the water acting as electrolyte. Brass is more noble than steel in the galvanic series:

$$E^\circ_{\text{Cu}^{2+}/\text{Cu}} = +0.337\text{ V}, \quad E^\circ_{\text{Fe}^{2+}/\text{Fe}} = -0.440\text{ V} $$

The potential difference,

$$\Delta E = E_{\text{cathode}} – E_{\text{anode}} \approx 0.777\text{ V},$$

was sufficient to drive anodic dissolution of iron and the formation of iron oxides/hydroxides.

The local electrochemical reactions were:

Anode (steel):

$$\text{Fe} \rightarrow \text{Fe}^{2+} + 2e^-$$

Cathode (brass surface):

$$\text{O}_2 + 2H_2O + 4e^- \rightarrow 4OH^-$$

The resulting $Fe(OH)_2$ and $Fe_2O_3$ corrosion products expanded volumetrically, wedging the interface tighter. The growth strain of oxide formation can be expressed as:

$$\varepsilon_v = \frac{V_{\text{oxide}} – V_{\text{metal}}}{V_{\text{metal}}}$$

For iron oxides, $\varepsilon_v \approx 1.9$, meaning nearly a doubling in volume. This expansion induced radial compressive stress at the interface:

$$\sigma_r = \frac{E \, \varepsilon_v}{1 – \nu}$$

With $E_{\text{Fe}} \approx 210\,\text{GPa}$ and $\nu \approx 0.3$, localized stresses easily exceeded hundreds of MPa, enough to plastically deform the surrounding brass and produce microscopic cold-welding through diffusion and oxide bridging.

At the same time, dezincification occurred in the brass:

$$\text{CuZn} \rightarrow \text{Cu} + \text{Zn}^{2+}$$

leaving a porous copper-rich layer with high surface energy. Under compression and mild heat cycling, solid-state diffusion across the Cu–Fe interface promoted the formation of intermetallic compounds such as $CuFe_2$ or $Fe_3Zn_{10}$, effectively brazing the two metals together.

The end state was a compound joint bonded both by corrosion-product expansion and diffusion adhesion — a quasi-metallurgical weld. The torque required to shear it loose later had to exceed the yield strength of both alloys plus the adhesion energy of the oxide layer:

$$\tau_{\text{break}} \ge \frac{\sigma_y A + \gamma_{\text{adh}}}{r}$$

where $\sigma_y$ is the yield stress, A the contact area, $\gamma_{\text{adh}}$ the oxide interfacial energy, and r the effective radius. I estimate I needed breakaway torque of in the neighborhood of 80–160 N·m, danger close to the ~200-250 N·m that will break a Grade 8.8 M16 bolt — and this was a thin walled threaded tube. The geometry also doesn’t help. Since brass (CuZn) was threaded into the aluminum/steel pump body at M16 scale, the fine 1.5 mm pitch meant very tight thread flank contact. Over years of water exposure, galvanic corrosion products grew in the tiny 60° V thread roots, effectively cold-welding the joint.

So the “fused” fitting wasn’t rusted in the casual sense — it had become a galvanic, mechanically locked, diffusion-bonded composite system, obeying the same physics that make bimetallic corrosion joints and accidental cold-welds in space so hard to undo.

October 19, 2025 (updated October 19, 2025) By Tim Booher One Comment

Engineering & Code

Shapeoko Troubles

I recently encountered an issue when generating a grid of holes for workbench. I had recently planed down an old workbench from our house in New Jersey. I was planning on 20 mm holes spaced in a grid with 96mm spacing to match the festool MFT table. I’m hoping to use the available array of cool attachments and eventually add the aluminum profile to the side. For example, an MFT table can be used as a bench with a variety of different attachments, such as clamping elements and stops.

Unfortunately, the holes didn’t create a proper grid and the spacing was off. I used a CNC machine to cut the holes, but I noticed that they were off. Just looking at it showed that each row had fairly consistent spacing, but the start of the rows varied in the X direction.

To accomplish a 96 mm grid, the g-code was programmed to start at the bottom of the workpiece and move across in a row. This process was then supposed to be repeated until the entire grid was cut. However, as I mentioned earlier, I encountered some issues with the spacing of the holes and had to troubleshoot the problem.

One theory I became aware of online (thanks gdon_2003, Julien, LiamN, SLCJedi and WillAdams) is that set screws are a part of Shapeoko drive system and a loose set screw can cause this type of behavior. That’s because the set screws transfer motion from the motor shafts to the pulleys, which rotate against the belts. They are intended to be pushed tightly against the flat spot on the motor shaft, causing the pulley to turn with the motor. If the set screw becomes loose, the pulley may turn independently of the motor before snapping into place, which can cause issues with the motion of the machine. This may show up as flat spots on circles or other imperfections in projects. You can see why a loose set screw is bad as captured in the screenshot below from this youtube video by See-N-C.

Screenshot that describes how set screws work

Doing some Math

In order to do some analysis on what happened, I needed to register the image and get the location of the points.

The drawpoint command in MATLAB is a function that allows you to draw a single point on an image or plot. You can specify the coordinates of the point on an image using the mouse to record position. Using drawpoint, I recorded the coordinates of the center point of each circle and put this information in a struct. I then wrote code to turn the struct into two arrays: one for the x coordinates and one for the y coordinates. This allowed me to easily analyze the variance in the x coordinates for each column and the variance in the y coordinates for each row.

I was also able to use the drawpoint command in MATLAB to mark points on the ruler captured in the image. This allowed me to easily record the coordinates of the points and then do the math and convert the distances between the points from pixels to millimeters.

I used the pdist2 function in Matlab to calculate the Euclidean distances between my two sampled points and then converted the distances to the desired units through a conversion factor of 610 mm/523.4087 px.

Since the job started at the upper right and progressed down and across, we could look at the variance throughout the job. The variance in the x direction seemed to increase in the last four columns:

x	1.261	0.3603	0.5854	0.7656	3.2425	3.963

Variance of X in each Column (in mm)

The variance in the y direction was much bigger across the rows and also increased as the job progressed. I used this MATLAB to generate this: makemm(var(y(:,:),0,2))

y	24.7537	24.5736	30.6232	35.2467	36.3425

Variance of Y in each row (in mm)

To generate the ideal points based on a 96 mm grid, I wrote a function that takes in two inputs, iX and iY, which represent the starting x and y coordinates, respectively. The function first initializes two matrices, X and Y, to store the calculated x and y coordinates for each point. Then, it defines a conversion factor, cf, which is used to convert the units from millimeters to pixels.

Next, the function uses a nested for loop to iterate through each column and row of the matrices. For each iteration, the function calculates the x and y coordinates of the current point by adding the starting coordinates (iX and iY) to the appropriate offsets, which are determined by the loop variables and the conversion factor. The calculated x and y coordinates are then stored in the corresponding elements of the X and Y matrices.

To calculate the root mean squared (RMS) error, I subtracted the actual coordinates from the ideal coordinates to find the error in both the x and y directions and then took the square root of the mean of the squared errors in both directions.

	1	2	3	4	5	6
1	0	3.6413	4.8678	12.5796	12.8476	12.0532
2	1.2986	4.7147	4.9236	13.6365	13.8841	12.3934
3	1.604	1.4784	5.262	13.2722	13.5265	13.8716
4	2.6114	2.5362	14.1002	14.2195	14.8988	16.2787
5	6.1564	6.0407	17.3673	17.3558	18.8129	19.6045

RMS errors for each hole

You can see the error increasing as the job progresses, but the major error starts in column 4-6, supported by a big jump in column 3, row 4, which supports the idea that the screw isn’t seating well resulting in slippage.

Overall, doing this math allowed me to see what was really going on. By adjusting for the variance at 4,3:

January 2, 2023 (updated January 3, 2023) By Tim Booher 0 Comments