Set Named Formulas

i want to do I have a list of data like this

Machine Date Value

A 1 1.1
A 2 1.2
A 3 1.3
B 1 1.1
B 2 1.2
B 3 1.3
C 1 1.1
C 2 1.2
C 3 1.3

This is imported from else were and AutoFilter by machine then number and value every time a new record is added to the list.
I want to have three charts in the sheet (one for A, one for B and one for C) and i need to be able to set the data source ranges dynamically.

I have a macro i mind that will search the first column cells one at a time. something like:

Sub marco1()
'find A limit
range("a1").select
For row=1 To 100 Step 1
If cells(row,1).value<>"A" Then
ARowFin = row-1
exit For
End If
Next row

End Sub

This will find the last "A" cell's reference by index numbers as cell(ARowFin,1) But i can't find how to then use this format to select a range.

The "range" function only uses A1 notation for multiple cell selection. How do i use index notation to set a range?

If i can work this out then i can set: r1 = that range and a second range r2 in a similar fashion, then set the data source range as a union of these ranges.