Want to get the Gage Report in your e-mail? Click here.
ST-7001
RSC Pin Standoff Gage ST-7001 with standard
ST-7002
RSC Box Standoff Gage
ST-7002
Back to the Basics:
Finding Standoff with Pitch Diameter
What’s My Standoff?
Because many shops control the manufacturing process inside the machine exclusively using Pitch Diameter or Functional Diameter Gages (JSS PD, MRPs, Roll Gages)…the operator needs to know how much each incremental change in pitch diameter or lead will ultimately affect the standoff.
These operators often ask us, “If I’m reading a +0.002″ on my MRP, then what’s my projected standoff?”
But before we answer that, let’s take a quick look at standoff. Standoff is used as an indicator to determine if a part’s size is within the allowable tolerances. API defines standoff as “The distance between faces of gages or gages and product reference planes when mated.” Simply, it is the gap between the ring or plug gage’s face and the connection’s face or shoulder. For example, an external thread that is cut too large would have a greater standoff than a properly cut part.
Standoff, Taper, and Pitch Diameter
Now, back to the question “What’s my standoff?”
First of all, we need to know the taper per foot (TPF) of the part. The specified taper is used to correlate the standoff with pitch diameter. So once we know the taper and the pitch diameter we can calculate the standoff from nominal.
We need to know the taper because standoff is a function of taper and pitch diameter. To find the deviation needed to locate standoff, divide 12 by the TPF and then multiply the result by the pitch diameter value. Simply stated as: (12/TPF) X PD. This value is the amount of material needed to be removed to bring the part to the proper standoff tolerance.
Here’s Your Standoff
To answer the question, “What’s my standoff?”, we’ll use an 8 Round thread with a taper of ¾” TPF (0.75″) and the +0.002″ pitch diameter value. Tolerance for a ¾” 8 Round thread is +0.125″ or 1 turn.
Using the formula, we get: (12/0.75) X .002 = +0.032″. The standoff of +0.032″ is within the allowable tolerance +0.125″. So, any required ring gage should achieve the correct standoff
Finally, remember the less steep the taper, the greater effect that a change in pitch diameter has on the standoff. For instance, every 0.001″ of change in pitch diameter for a ¾” TPF thread affects the standoff by 0.016″. While on a 2″ TPF RSC connection, every 0.001″ change in pitch diameter affects the standoff by only 0.006″.
75TPFTubing & Casing Standoff Change
2 tpf standoff
RSC Standoff Change
Do I Need to Worry About Standoff?
ST-7001-and-ST-7002
ST-7001 with
standard
ST-7002
For API products, standoff is required in the specification for thread measurement. Your product will not be in tolerance otherwise. However, how you measure standoff is not specified. Calipers, Go/No Go gages, or special standoff gages are all used to varying degrees of success. For inspecting standoff on rotary shouldered connections, Gagemaker recommends our standoff gages, the ST-7001 for pins or ST-7002 for boxes.
For non-API governed products, the reason for inspecting standoff is the same as the reasons behind API’s requirement, simply that improper standoff means you have an out of tolerance functional diameter (i.e., oversized boxes or undersized pins). Also, your part’s specifications may require the inspection.
What can you do to help minimize the effects of an incorrect standoff?ST-7000-on-Tool-Joint-
Check your parts before they are removed from the machine
Inspect your lead
Inspect your pitch diameter
Inspect your standoff
Ensure the part and gages are at the same temperature
Ensure your machine is running properly
Check your inserts on the machine
Look out for more on the relationship of standoff and lead soon!
Thread Height Gages
Functional Thread Size Gages
Pitch Diameter Size Gages
Thread Lead Gages
Thread Profile Templates
Functional Rolls
Pitch Diameter Ball Contacts
TDWIN Thread Calculation Software
MIC TRAC 3000 Series
Eliminate Calibration Headaches
Calibrate In-house Today
Dim lights Embed
Today, calibration systems should offer more than just calibration. As systems are customizable, they can be as simple or as complicated as you need. Generally, companies have various gages and tools, from handhelds to permanent fixtures, which all need calibrating, setting, and zeroing.
Historically, calibration has been viewed as a financial headache and a logistics nightmare. The expense of tracking, scheduling, shipping, instrument downtime, and the actual calibration service really adds up. Currently, companies who implement in-house calibration find that the systems pay for themselves in short order.
For in-house calibration and gage setting, you want accurate, repeatable, reproducible results from a versatile, cost effective, easy-to-use system. With Gagemaker, finding your perfect system can be achieved in just 4 easy phases….
Click here to learn more!
Look out for more videos on the way in 2014!