What type of part is this? Is it a weldment, a machined part, or a piece of flat steel or whatever.
What type of tolerance are you talking about? +/-.0001 or +/-.001 or +/-.010? Anything less than +/-.001 I would plan on machining after heat treat.
What type of a stress relieve are you contemplating? Heat treat or vibratory? Relieving welding stress cause some movement of the parts.
Heating most metals into the stress relieving range reduces the strength of the material and if not held properly in the furnace may change shape. Atmosphere control must be used.
Heat treatment of gears and splines typically cause and external gear or spline to grow in size and depending on the repeatability of the heat treat process can be repetitive. All bets are off if you use differing heat treaters from batch to batch. The amount of growth is based on experience and usually is not calculated.
These are weldments: base plates (with premachined holes) and risers, some with plates welded to the top of the risers. Stress relieving will be after welding, by heat treatment. My concern is with how it will affect the spacing between the holes. The fixtures are about 2' x 4' in size.
The amount of movement really depends on the amount of residual stress after the welding operation and the geometry of the item. It would be complex to predict (as point out by BillPSU) the movement but some educated assessment could be carried out by looking at the longest spans and sectional variations. In the past, to prevent this kind of thing I've used a variety of restraints for the item when in the furnace. These have varied from custom jigs to just large scrap pieces placed at appropriate places on the item. In all honesty though not all of them worked and some final rectification m/c was needed. Hope this helps.
