Do you know that if you want to manufacture your parts with tight tolerance, you should go by using ” Regardless of feature size ( RFS) material condition for features?
Many of us may not know much about RFS as it is applied by default to all our engineering drawings. Let’s learn more about ” Regardless of feature size” and find out its definition, symbol, application, and examples.
What Is Regardless of Feature Size ( RFS): Regardless of feature size definition
Regardless of feature size is a GD & T concept that informs manufacturers to control all tolerances without bothering about the size of the feature or considering any bonus tolerance.
We all know that we use MMC and LMC in GD & T control frames which gives flexibility to manufacturers to add extra tolerances if the feature is shifting towards LMC or MMC.
This is required to reduce the part cost as no features are required to manufacture with a very tight tolerance. Right? If we start making all parts with tight tolerance, the part cost will be too high.
In cases where tolerance is critical, we use RFS. If you don’t show the MMC or LMC symbol, the RFS gets automatically applied. So all manufacturers should assume that, if there is no MMC or LMC symbol, they have to consider the tolerance as RFS and should take extra care to meet the tight tolerance.
Before heading forward in this article, I would request you to go through the below article to understand the concept of MMC, LMC, and bonus tolerance. Then only you will understand what is regardless of the feature size concept.
Regardless of feature size symbol
Before 2009, there was a symbol for RFS, which is nothing but capital R. But after 2009, we don’t need to show any RFS symbol in manufacturing drawings. The RFS gets automatically applied if you don’t show any MMC or LMC symbol.
Regardless of feature size Examples
Let us define and explain regardless of feature size with some examples so that everyone will understand
In this example shown in Figure 1, the perpendicular tolerance is 0.5 concerning datum A. What that means is that the axis of the hole needs to be perpendicular concerning datum A and the tolerance is 0.5.
You may have noticed that there is no MMC or LMC symbol next to the perpendicular tolerance value. So, in this case, the RFS gets applied by default.
Since RFS was applied in the above case, no matter what size the hole is produced, the perpendicular tolerance remains the same. Let us look into the below table. You noticed that the perpendicular tolerance remains the same irrespective of the size of the hole.
| Size of Hole | Perpendicular Tolerance |
|---|---|
| 10.00 | 0.50 |
| 10.10 | 0.50 |
| 10.20 | 0.50 |
| 10.30 | 0.50 |
| 10.40 | 0.50 |
| 10.50 | 0.50 |
Now let us consider an example shown in Figure 2. You noticed that an MMC symbol is there next to the perpendicular tolerance. What that means is that if the hole size departs towards LMC from MMC, extra tolerance gets added to the perpendicular tolerance, which we call bonus tolerance. This is the beauty of MMC or LMC, which gives bonus tolerance to manufacturers.
As per the feature control frame shown in Figure 2, the perpendicular tolerance is .50 when the hole is produced at MMC. If the hole size is shifting towards LMC, an equal amount of bonus tolerance will be added to the perpendicular tolerance. Please refer to the next level, for example.
| Size of Hole | Perpendicular Tolerance |
|---|---|
| 9.5 ( MMC of the hole) | .50 |
| 9.6 | .50+.10=.60 |
| 9.7 | .50+.20=.70 |
| 9.8 | .50+.30=.80 |
| 9.9 | .50+.40=.90 |
| 10 | .50+.50=1 |
| 10.10 | .50+.60=1.10 |
| 10.20 | .50+.70=1.20 |
| 10.30 | .50+.80=1.30 |
| 10.40 | .50+.90=1.40 |
| 10.50 LMC of the hole) | .50+1=1.50 |
Regardless of feature size application
As I said before all dimensions, regardless of feature size get applied automatically if there is no MMC or LMC symbol. Having said that, most of the technical drawings have MMC or LMC symbols. So RFS will be applied to only those features that are critical to form, fit, and function.
A typical application of RFS is parts of aircraft, medical equipment, automobile industry, electronic boards, etc.
But don’t assume that all parts of these industries are made following RFS. What I want to say is that those industries use more amount of the RFS concepts in the technical drawing due to the criticality of the product.
Benefits Of Regardless Of Feature Size
- Feature tolerance can be independently controlled
- Precise and tight tolerance is achievable
- High-quality features and parts can be made
- Lesser chance of part rejection
- Excellent form, fit, and function
Drawbacks Of Regardless of feature size
- Increase in part cost
- High-end measuring equipment required
- Proficient technician required to accurately measure dimensions
- Longer cycle time for part manufacturing
- The overall product cost increase
Conclusion
No doubt, RFS in GD & T is an excellent concept for getting high-quality parts. But RFS also increases part cost or product cost. Before you apply RFS in your drawing, you need to ask a question,
Do I need that? Is that feature so critical from a function point of view? If not stay away from RFS and use MMC and LMC in your drawing. That will save you dollars and reduce your product cost.
Frequently Asked Questions ( FAQ)
What is regardless of feature size?
Regardless of feature size is a concept used in engineering drawings to inform manufacturers to build the part with specified tolerance without adding any bonus tolerance or tolerance due to feature size deviation
Does Regardless of feature size increase part cost?
Yes, It does
What is the regardless of feature size symbol?
There is no symbol for regardless of feature size.
When I should use RFS or Regardless of feature size?
If the feature or part is critical to form, fit, and function, then only we should use RFS
