Aluminum plate carries residual stress from the quench. Machine more off one face than the other and that stress rebalances, and the part bows. This calculator models the stress the cut releases, predicts free-state bow in thousandths, and returns a symmetric roughing and finishing sequence with the stock to leave per face.
Last updated July 2026
Removal is one-sided. Rebalance to 0.250" off the top and 0.250" off the bottom.
Consider 5000 series cast tool and jig plate instead. Same cut, predicted bow 0.0126" against 0.0648" for 6061-T651. Cast and thermally stress relieved, essentially no residual stress.
Predicted bow is for one reference cut: a 24 by 12 inch piece taken from 1.000 inch down to 0.500 inch with all of the material removed from one face. It is the same model the calculator above runs. Peak core residual stress values are indicative figures calibrated against commonly reported shop outcomes, they are not spec values and no mill certifies them.
| Alloy and temper | Peak core residual stress (psi) | Modulus E (10^6 psi) | Stress relieved by stretching | Predicted bow on reference cut (in) | Note |
|---|---|---|---|---|---|
| 6061-T651 | 1,500 | 10.0 | Yes | 0.0648 | Stretched 1.5 to 3 percent, the standard machining plate |
| 6061-T6 not stretched | 8,000 | 10.0 | No | 0.3456 | Sheet-route or re-heat-treated, avoid for machined plate parts |
| 6061-T4 / T451 | 1,500 | 10.0 | Yes | 0.0648 | Low strength but stable |
| 7075-T651 | 3,000 | 10.4 | Yes | 0.1246 | About twice the movement of 6061-T651 for the same cut |
| 7075-T6 not stretched | 14,000 | 10.4 | No | 0.5815 | Worst case, do not machine plate parts from it |
| 7075-T7351 | 1,800 | 10.4 | Yes | 0.0748 | Overaged, SCC resistant, about 12 percent less strength than T651 |
| 7050-T7451 | 2,000 | 10.3 | Yes | 0.0839 | The thick-section standard, holds properties to 6 inches |
| 2024-T351 | 2,500 | 10.6 | Yes | 0.1019 | Stretched after solution treating, highest modulus of the group |
| 5083-H321 | 2,000 | 10.3 | No | 0.0839 | Cold-work stress, not quench stress |
| 5052-H32 | 2,000 | 10.2 | No | 0.0847 | Cold-work stress, not quench stress |
| 5000 series cast tool and jig plate | 300 | 10.3 | n/a | 0.0126 | Cast and thermally stress relieved, essentially no residual stress |
| Band | Bow per foot of length (in/ft) | What it means on the floor |
|---|---|---|
| Low | under 0.005 | A normal finish pass takes it out |
| Moderate | 0.005 to 0.020 | Rough both faces, rest, re-indicate, then finish |
| High | 0.020 to 0.060 | Symmetric removal is mandatory, consider a more stable temper |
| Severe | over 0.060 | Change material or start from a thickness close to finished |
| Bump rule | asymmetry over 0.50 | One band worse, the cut is lopsided |
| Bump rule | slenderness over 120 | One band worse, the part is too thin for its footprint |
The plate is treated as a beam of unit width carrying a self-equilibrating parabolic residual stress profile. All work is in inches and psi, with z measured from the mid-thickness of the as-received plate, running from -T0/2 to +T0/2.
F is the released force per inch of width and M is the released moment per inch of width, both taken over the slabs that get machined away. Re-applying the negative of that force and moment to the section that is left is what bends it. The stock to leave figure is found by running the model twice, first with 0.015 inch left on each face, then again with the result of that pass, and rounding up to the nearest 0.005 inch.
The model is elastic and one-dimensional. It does not cover clamping distortion, heat from the cut, thin-wall deflection, or the through-thickness anisotropy of heavily rolled plate, so treat the number as a ranking and an allowance, not a flatness guarantee. Need the stock to cut these parts from, get an instant quote on 6061, 7075 and 7050 plate cut to your size, with mill certs on every order so you know which temper you are actually machining.
Rolled and quenched aluminum plate carries a self-balancing residual stress profile, compressive at the two surfaces and tensile through the core. When you machine one face you remove part of that balanced system, and the stress that is left has to find a new equilibrium. It does that by bending. The bow is not caused by heat or by clamping, it is stored energy from the quench being released, which is why the part looks fine on the table and moves the moment you unclamp it.
Leave at least 0.015 inch per face, and about 1.5 times the bow you expect after roughing when that is larger. For a typical 24 by 12 by 1.000 inch 6061-T651 plate coming down to 0.500 inch, that works out to roughly 0.030 to 0.040 inch per face. For 7075-T651 on the same cut, plan on 0.060 to 0.080 inch per face. The point is to leave enough that the finish pass can machine the bow back out instead of following it.
Yes, just far less than unstretched T6. The 51 in T651 means the mill stretched the plate 1.5 to 3 percent after solution treating, which knocks the residual stress down by roughly 80 to 90 percent. That is why T651 is the machining temper. It still moves on a heavy one-sided cut, typically a few thousandths per foot rather than a few tens of thousandths, so you still rough both faces and rest the part before finishing.
Remove material symmetrically and in stages. Rough both faces to equal depth leaving stock, unclamp the part and let it rest, re-indicate it in its free state, then take equal finish passes off each face. Never take the whole allowance off one side. If the part is pocketed on one face only, add a balancing skim on the back. When the geometry forces one-sided removal, buy 5000 series cast tool and jig plate or an overaged temper such as 7075-T7351 or 7050-T7451 instead of fighting it.
5000 series cast tool and jig plate. It is cast rather than rolled, thermally stress relieved and machined on both faces, so it carries almost no residual stress and stays close to its as-supplied flatness after you cut it. The tradeoff is strength: cast tool plate runs roughly 23 ksi tensile against 45 ksi for 6061-T651, it welds poorly, and it anodizes blotchy. Use it for fixtures and baseplates, not for load-bearing parts.
Yes, roughly twice as much movement for the same cut. 7075 is quenched harder to reach its strength, so even after stretching it retains about double the residual stress of 6061-T651, and its higher modulus does not make up the difference. Shops report that even 0.010 inch off one side of a large 7075 plate will move it. If the part allows it, 7075-T7351 or 7050-T7451 are overaged and noticeably more stable.