Reaming Allowance: A Finishing Tool Needs a Defined Preceding Hole

Keep the preceding hole with the reamer

Harvey describes reaming as a finishing operation following a pre-drilled hole. The material remaining before that pass is part of the preparation record. Primary reference: Harvey technical explanation.

Compare fictional local stock

Assume a fictional finished diameter of 10.00 mm and a concentric circular pre-hole of 9.80 mm. Diametral stock is 0.20 mm, corresponding to 0.10 mm radial stock under this ideal geometry.

Now retain that diameter but offset the pre-hole center by 0.04 mm relative to the intended finished center. On the opposing line through both centers, radial stock becomes 0.06 and 0.14 mm. The same nominal diameter therefore hides unequal local engagement. These invented values are not an acceptable reaming allowance or a predicted correction of position.

Review the actual preparation map

Keep diameter, roundness, taper and center location with the pre-hole evidence. Record which finished geometry the subsequent tool is expected to establish and whether that expectation is supported by the actual process.

Do not turn a supplier-specific percentage for a particular reamer into a universal allowance from this article. Use the stock map to ask whether the finishing operation encounters the intended material around its full boundary. Actual tool, material and cutting evidence remain necessary; nominal diameter subtraction alone cannot establish the finished tolerance or repair every preceding-hole error.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: Harvey technical explanation