Regardless of feature size: Definition, Symbol, Application and examples [PDF]

regardless of feature size

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 some examples.

What Is Regardless of Feature Size ( RFS) :Regardless of feature size definition

Regardless of feature size is a GD & T concept that informs manufactures to control all tolerances as it is without bothering 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 manufactures to add extra tolerances if the feature is shifting towards LMC or MMC. This is required to reduce the part cost as not features are required to manufacture with 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. In fact, if you don’t show MMC or LMC symbol, the RFS gets automatically applied. So all manufactures 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 below article to understand the concept of MMC, LMC and bonus tolerance. Then only you will understand what is regardless of feature size concept.

Must Read : What is MMC , LMC and Bonus tolerance

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 example so that it is better for everyone to understand

regardless of feature size
Figure: 1

In this example shown in figure 1, the perpendicular tolerance is 0.5 with respect to datum A. What that means is that the axis of the hole needs to perpendicular with respect to datum A and 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 got applied in the above case, no matter at 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 HolePerpendicular Tolerance
10.000.50
10.100.50
10.200.50
10.300.50
10.400.50
10.500.50

Now let us consider an example shown in the 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 in .50 when the hole is produced at MMC. If the hole size is shifting towards LMC, equal amount of bonus tolerance will be added to perpendicular tolerance. Please refer the next level for example.

regardless of feature size
Figure :2
Size of HolePerpendicular 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 that for all dimensions, the regardless of feature size gets applied automatically if there is no MMC or LMC symbol. Having said that, most of the technical drawings has MMC or LMC symbol. So RFS will get applied to only those features which 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 RFS concept 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 part can be made
  • Lesser chance of part rejection
  • Excellent form, fit and function

Drawbacks of Regardless of feature size

  • Increase of 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 to get 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 really need that? Is that feature so critical for function point of view? If not stay away from RFS and use MMC and LMC in your drawing. That will save your dollars and reduce your product cost.

That’ s all I have in this article. RFS is a simple concept and it should not be tough for anyone to understand this. If still, you have any question or query, please do write in the comment section and I will be happy to respond.

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 increases 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


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