fill formula down to the last row in every inserted columns and clear the error value

[calif]

Hi guys,

I tried to insert columns every two column i.e. column A, D, G...last column and fill it down with the formula to the last row, which suppose to make it faster and clear the error value from the formula.
I have been thinking something like this, but do not know how to define the last column and last row to make the formula work.

With range
For i = lastcolumn - 1 To 1 Step -2
  For r = 1 To .Rows.Count
    ws.Columns(i).Insert
    Range("i" & r).FormulaR1C1 = "=LEFT(RC[1],FIND("":"",RC[1])-0)"
  Next r
Next i
End With

Cells.Replace What:="#VALUE!", Replacement:="", LookAt:=xlPart, _
        SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
        ReplaceFormat:=False

I thank you in advance for your help.