Tools / Machining allowance
Machining Allowance Calculator
Leave too little stock and the face cleans up in one corner only. Leave too much and the machining time doubles. This gives you a defensible starting range to put on the drawing and to discuss with the quoting shop.
Your part
How to use the number
Put the range on the drawing as a note, then let the quoting shop tell you if it wants more on a particular face. A shop that welds and machines parts like yours every week has a better answer than any formula, and asking the question at quote time costs nothing.
What the tool is doing
Published practice puts machining allowance on weldments in a band of roughly 3 to 6 mm on faces, with more on long or flexible sections. The tool starts at 3 mm and adds for the four things that actually move the number: part length, weld volume, how much the material moves for a given weld, and whether the residual stress is taken out before cutting. A bore gets roughly half the face figure on the radius, with a floor, because material is removed all round rather than from one side.
It does not know your joint layout, your restraint, your weld sequence or your tolerance. Those matter, and they are why the output is a range rather than a number.
This is not an engineering calculation
It is a starting point for a conversation, built from published practice rather than from your part. Nobody here has seen your drawing. The responsibility for what goes on the drawing stays with you and the shop that quotes it.
The reasoning in full is in machining allowance and tolerances on weldments, and the stress relief decision is covered in when a welded frame needs stress relief.
Want a second opinion on the actual part?
Send the drawing. We will tell you what it needs and match it with shops that weld and machine it in house. Free for buyers, reply within 24 business hours.