Tag: Shop

Shop Math 101: 1/100″ = 1/4″

5 May 2021 Darren Young

Does your fabrication shop lack confidence in your drafting/detailing department?

Have you struggled to get buy-in when trying to roll out new processes, technology or deliverables?

Did you wonder why? More importantly, do you KNOW why?

Getting to the Root of Trust Issues

My entire career spanning manufacturing to construction, fabrication shops have had trouble trusting the information they’re given. And there’s good reason. It takes time to master a domain and learn the work. And production staff are busy building and fabricating. They don’t have time to run into the office every time something is wrong. As a result, office staff take longer to train and often persist with producing lower quality work.

But there’s also a lot of reasons that are not good. Downright bad in fact because they’re simple to resolve. Things you’re NOT doing wrong but are causing problems. These trust issues are easily corrected if they’re understood properly. One such issue is fabrication tolerances that I categorize as Shop Math.

The Dynamic Between Tolerance and Rounding

I’ve had trouble explaining this verbally so I figured a more graphic (yet generic) representation would be in order. In basic terms, you need to use a rounding factor 1/2 the amount of your fabrication tolerance to achieve the desired result. As the title of this post suggests, a value of 1/100″ of an inch, can result in a deviation of 1/4″. That’s real Shop Math in practice.

My example uses both fractional inch and decimal to more clearly illustrate the point. You don’t want to get me started in why everyone should use decimal, that’s another post. But decimal also has the same dynamic, it’s just less hidden and more easily fixed. You get a lot less pushback in a shop by adding an extra decimal than by changing the denominator of a fraction to a number the shop says they don’t fabricate to.

Let’s take the following example..,

In this example, lets assume our tolerance is 1/8″ (construction field tolerances, that’s fairly common).

The TOP RED dimensions are all ROUNDED to the nearest 1/8″ to match our target Tolerance. A fairly common practice. The BOTTOM GREEN dimensions are all ROUNDED to the nearest 1/16″ which is half our target Tolerance.

Each graphic shows a line 6″ long. Half that is 3″. We’re going to make a gap and dimension from each end to that gap. Maybe it’s a weld joint in pipe or perhaps a mortar joint in concrete block. Doesn’t matter what to illustrate the problem.

For the graphics on the LEFT (Quadrants 2 & 3), the gap is just shy of 3/16″ of each side of middle to forced the dimension to round UP. For the graphics on the RIGHT (Quadrants 1 & 4), our gap just heavy of 3/16″ of middle to force the dimensions to round DOWN.

Rounding = Tolerance = Confusion = Mistrust

Let’s focus on the TOP RED in the following illustration…

If you take the two parts and add them, they vary by 1/4″. Adding 3/8″ (our rounded gap size) to either of them does not equal 6″ either.

Quadrant 1: 2 3/4″ + 2 3/4″ + 3/8″ = 5 7/8″
Quadrant 2: 2 7/8″ + 2 7/8″ + 3/8″ = 6 1/8“

Between these 2 examples, a mere 1/100″ difference in our gap results in a 1/4″ difference and neither adds up to the 6″ of the total length. This is a 1/4″ TOLERANCE because we set ROUNDING to 1/8″ to match our fabrication accuracy.

If you ever wondered why your shop doesn’t trust your drafting/detailing, this is one reason. The Shop Math just doesn’t add up. They see the sum doesn’t add up to the whole and leads them to question the accuracy of your drawing and your staff.

Rounding = 1/2 Tolerance = Trust

Now lets focus on the BOTTOM GREEN portion of our illustration…

Between the left and right (Quadrants 3 & 4) we’re still making the gap just shy and just heavy of 3/16″ from the center. As you recall, we said our fabrication tolerance target was 1/8″ but here, the dimensions are ROUNDED to 1/16″. This is HALF of our target fabrication Tolerance.

Here, it doesn’t matter of the dimensions round UP or DOWN due to the slight variation in the gap, the dimension are the same. Furthermore, if you add the parts, you get 6″.

Quadrant 3: 2 13/16″ + 2 13/16″ + 3/8″ = 6″
Quadrant 4: 2 13/16″ + 2 13/16″ + 3/8″ = 6″

Same Geometry – Different Clarity

As you can see, we had different results between rounding UP and DOWN when our ROUNDING value equals the Tolerance we’re trying to achieve. When we round to HALF the Tolerance, those small variations are masked and all our numbers add up.

So if you’re dimensioning for the shop, it’s important to realize this little change can mean questioning or trusting your data and staff. Additionally, if you take the time on the shop floor to explain WHY they see these differences, they quickly realize that the information that leads them to question the data (and your people), is also the very same data that’s most likely to be wrong. What IS accurate and didn’t change, is the geometry itself. This is an extremely critical point to highlight if you’re trying to get your shop to use automation and drive machine tools from CAD/BIM geometry.

The model/geometry, is the MOST right data we have. It’s just not human readable and what we provide as human readable is prone to errors such as these. This is one reason you’re seeing terms like “Model Based Enterprise” starting to float around in the Manufacturing space. It’s also a reason you’re seeing more shop go paperless, eliminating dimensions when possible by leveraging automation.

These efforts can be challenging and often require a leap of faith. But if everybody understands dynamics like this, it can be extremely helpful in moving all of your staff to more digital workflows. Because they trust the geometry and you eliminate what’s confusing them.

Shop Floor Computer Tip

2 Jun 2019 Darren Young

We’ve all been there. Moving our mouse around trying to find the pointer on the screen. This can be especially troublesome in a shop floor environment. Computer screens are small. Full of dust and dirt. Poor lighting and perhaps even a poor mouse surface. All of these factors can make use of a computer on as shop environment annoyingly painful.

Beyond the obvious improvements like a larger, regularly cleaned monitor and improved lighting, there’s a couple simple tweaks you can make to keep your staff providing value as opposed to looking for a mouse pointer.

Advanced Mouse Options

Using your Additional Mouse Settings, you can make a couple quick changes that will significantly improve the usability of a shop floor system. Simply press the Windows key on your keyboard and type Mouse.

This should display the Mouse Settings option in the search results, that’s what you’ll want to click. This will bring up the Mouse Settings window. Here you’ll want to click the Additional Mouse Options link.

Now from the Mouse Properties dialog, there’s a few things, you should make adjustments to.

  1. Select a pointer speed – You may want to turn down your pointer speed. It can be hard to find and track a mouse if it’s moving really fast.
  2. Automatically move pointer to the default button in a dialog box – This setting may help depending on the software used on the shop floor. It may also be annoying. However, every time a dialog or window is opened, you’re cursor will be in a predictable location.
  3. Display pointer trails – This leaves a few images of your cursor trailing around as you move your mouse. The longer the trail, the easier it will be to spot your mouse as you move it. Longer trails will have the most visibility.
  4. Show location of pointer when I press CTRL key – You’ve likely seen this trick in software presentations. Press and release the CTRL key and a series of circles will radiate out from your mouse position.

A Word About Machine Controls

A lot of machines now are using Windows based controls. If these systems rely on the use of a Mouse instead of a touch screen, you may want to make these same changes. However these systems can often launch upon startup and make it appear you have no access to the Standard Windows interface. You can often simply plug in a keyboard and mouse into a USB port for quick access. You can then use standard Keyboard tricks to get you to a more familiar interface.

  • Press the Windows key on the keyboard to bring up the standard Windows menu.
  • Press Alt-Tab to gain access to other running or hidden applications.

If the control is running in Kiosk mode, you may not have access to the standard Windows options. In this case, press CTRL-ALT-DELETE to bring up the Task Manager. From the Task Manager, you can launch a new process or run a new program. You can simply type Explorer.exe and this will reload the Windows interface you’re use to allowing you to make the mouse changes.