Lead error

[[Da...]]

Is lead error a form check? Or does it relate to the centerline of the part ?

[[Ch...]]

Typically it is Fß in Gear Pro, Total Lead Error, extreme high to low point within Eval range.

ffb is form error
fhb is angle error only.

It is essentially how "straight" your gear tooth is. It is also sometimes referred to as "parallelism" (in gear data blocks); and more recently as "helix" (even when nominally straight).

[[Da...]]

Please sign in to view this quote.

So...Straight to the Centerline of the bore ??? Or, to the rest of the teeth ? What is the datum for this measurement ?

[[Ch...]]

The Datum depends on the drawing and gear/part function.

Most of our drawings say lead/parallelism error WRT (with respect to) Datum -A- for example. This would be the datum feature to use.

If it is not presented so clearly, check the gear/spline data block. If it has a runout hanging off of the pitch diameter, this means the Gear P.D. must run true to this datum, so all other gear characteristics are typically inspected to this Datum as well. The majority of the time the gear is referenced to Either Datum A or B, primary or secondary datums on the drawing or combination of both if A is a plane and B is a surface.

Let us know if you need further help. Good luck.

[[Ma...]]

In the strictest sense "Lead error" means the error in the actual lead from nominal. Lead is the distance along the axis of rotation required for the tooth of a gear to make one full rotation. The "Lead error" would then be the difference between the actual lead and the nominal lead. In the case of a spur gear (nominally infinite lead) a rather large lead error may be a very small error on the actual tooth.

In common use the term "lead error" can mean a number of different things also many mentioned in other replies. It's no wonder this term is not used in any modern gear standards. As mentioned "Helix" is the preferred term these days. The three main relative deviations are slope, form, and total. There are also standard symbols for Crown and end relief deviations.