You're looking to figure out how much to move the bender to achieve a specific angle in a Chicago bender, similar to using a star on a hand bender for back-to-back 90s. The concept of a "star" in hand bending translates to understanding the advance and gain (or take-up) per degree of bend in your Chicago bender setup.Here's a breakdown of how to approach this

1. Understanding the Goal:
You want to create multiple 90-degree bends in a single length of conduit without cutting and threading, forming something like a series of offsets or a custom configuration. You need to know how far to advance the conduit in the bender between each 90-degree bend to achieve the desired spacing.2. Key Concepts - Advance and Gain



Advance

How much the conduit moves through the bender when forming the bend. For a hand bender, this is what you'd measure with a star. For a Chicago bender, think of it as the distance the conduit travels in the bender shoe to achieve a specific bend angle.

Gain (or Take-Up)

The amount of conduit effectively shortened by the bending process. This is because the bend creates an arc instead of a straight line.

3. Determining Advance and Gain on a Chicago Bender (This is the tricky part, as it depends heavily on your specific bender and setup)



Theoretical Calculation (Less Precise)

While not super accurate, you can start with the bender's documentation. Some manufacturers provide information about gain per degree. However, this might only be for single bends and not multi-bend scenarios. You could estimate using the formula: Gain = Bend Radius (Bend Angle in Radians - sin(Bend Angle in Radians)). The bend radius is the centerline radius of the bender shoe. Radians = (Degrees π) / 180. The problem with this approach is that real-world bending often deviates from the theoretical due to factors like conduit material, wall thickness, and bender condition.

Empirical Testing (More Accurate - Recommended)

This is the best way to get reliable numbers.

Mark a Straight Piece

Take a length of conduit and mark a reference point clearly near the end.

Bend 90 Degrees

Make a single, precise 90-degree bend.

Measure Advance

Very carefully measure how far the conduit moved through the bender to achieve that 90-degree bend. This is your 'advance' for a 90-degree bend. This is NOT the same as the setback.

Measure Gain

Measure the distance from your reference mark to the end of the bent conduit. Subtract this from the original length from the reference mark to the end of the straight conduit. This is your 'gain' for the 90-degree bend.

Repeat for Different Sizes

Do this for each conduit size you commonly work with. The advance and gain will vary with conduit size.

Partial Bends

To find the advance/gain for other bend angles, make a smaller degree bend (22.5°, 30°, 45°) and use proportional math to estimate.

Practical Bending and Adjustment



Start with a Test Piece

Always practice on scrap conduit first.

Bend the First 90

Make your first 90-degree bend.

Advance

Advance the conduit in the bender by the 'advance' amount you calculated for a 90-degree bend.

Bend the Second 90

Make your second 90-degree bend.

Measure the Result

Carefully measure the distance between the two 90-degree bends. This is the critical dimension you're trying to control.

Adjust

If the distance is not correct, adjust your advance accordingly. If the bends are too close together, increase the advance. If they're too far apart, decrease the advance.

Iterate

Repeat the process of bending, measuring, and adjusting until you consistently achieve the desired spacing.

4. Recording Your Results

Create a table for each conduit size. Include columns for: Conduit Size Target Bend Angle (90 degrees initially) Advance per 90 Degrees Gain per 90 Degrees Notes (specific observations about how your bender behaves)

5. Chicago Bender Considerations



Bender Wear

Chicago benders, especially older ones, can have slight variations and wear in the mechanism. This can affect bending accuracy. Regular maintenance and calibration are important.

Conduit Quality

The consistency of the conduit itself (material, wall thickness) affects bending. Use high-quality conduit from a reliable supplier.

Lubrication

Proper lubrication of the bender shoe helps ensure smooth bending and reduces the chance of conduit damage.

Operator Technique

Consistent pressure and smooth operation of the bender are crucial for accurate results.

Example Scenario

Let's say you want two 90-degree bends spaced 12 inches apart on a piece of 1" EMT, and your empirical testing gives you: Advance per 90 degrees for 1" EMT: 6 inches Gain per 90 degrees for 1" EMT: 2 inches1. Bend the first 90-degree bend.
2. Advance the conduit 6 inches in the bender.3. Bend the second 90-degree bend.Now, the distance between the start of each bend should be approximately 6 inches. However, because of the 'gain' you'll have about 2 inches less material, so the end result will be less than 6 inches between the start of the bends. You will have to do the math to add more to the initial advancement of the conduit to account for the gain.Also, the outside bend to outside bend will be different from inside to inside, so you need to plan your bend accordingly.

Important Considerations and Best Practices



Safety First

Always wear appropriate PPE (safety glasses, gloves) when operating a bender. Be aware of pinch points.

Practice

Bending is a skill. The more you practice, the more consistent and accurate your bends will be.

Visual Inspection

After each bend, visually inspect the conduit for kinks, flat spots, or other damage. Discard damaged conduit.

Bending Table

A sturdy bending table with proper supports is essential for accurate and safe bending.

Multiple People

For long runs and larger conduit sizes, it's often helpful to have a second person assist with supporting the conduit.*

Reference Marks: Use clear, permanent markers to mark the conduit.In summary, while there isn't a direct "star" equivalent for Chicago benders, understanding advance and gain through empirical testing and careful measurement is the key to accurately bending multiple 90s in a single length of conduit. Start with test pieces and adjust your technique until you achieve consistent results. Good luck! Flag for review