I am taking Garmin Data from small planes, and exporting that data to a shapefile.
From that shapefile I am exporting the attributes to excel.
In excel I am retaining all the fields from the shapefile, and doing calulations based on those fields.
After I have completed my calculations, and try to join the new table with the shapefile it says my table has no OIDs, it does the same thing if I do this process from a feature class.
Is there anyway to fix this? So I can join my tables?
I would advise using Excel to Table prior to creating the join.. solves the problem and you have an arc* file if you save the table in a geodatabase. If you need a dbf, just be aware of the field name limitations (and a few othrs)
Is it really necessary to do the calculations in Excel? I'm sure most calculations can be done in ArcGIS too, without the need to do double conversions and the need to join them back later. What calculations do you have to do?
...and exporting that data to a shapefile.....
...does the same thing if I do this process from a feature class...
So what is it; a shapefile or a feature class? There are a few things in life I try avoid: one is my ex-wife. Another is shapefiles. Yet another is Excel when it comes to anything but my taxes and invoices. OIDs are a nifty feature in ArcGIS, but I like to avoid them for key items in relationships; I prefer to add a long int field called something like JoinID. Calc JoinID to equal the OID, and you've got a persistant unique key field.
As Xander (Xander Bakker) mentions, it seems like you should be able to do any calculations within ArcMap that you can do in Excel. What type of data are you collecting with the Garmin? What is your procedure to convert it? ArcGIS has a builtin utility that you should be able to import your Garmin data directly into a feature class: How To: Convert Garmin GPS data to feature classes or shapefiles . Have you given that a try?