Aluminum Gearbox Bearing Seat CMM & Datum RFQ Guide

# Gearbox Bearing Seat CMM Datum RFQ Checklist

Gearbox and reducer housing RFQs often look simple at first: send the drawing, ask for an aluminum casting quote, compare tooling and unit price. In practice, the bearing seat and datum scheme can decide whether two supplier quotes are comparable at all.

If one supplier assumes only raw casting supply and another assumes CNC machining, CMM inspection, bearing-bore cleanup, cover-face flatness checks, and sample documentation, the cheaper quote may not be the cheaper sourcing path. This checklist is written for buyers who need a practical way to describe bearing-seat and CMM requirements before approving a gearbox housing supplier.

For the matching quote path, review Bohua's gearbox housing OEM quote guide and gearbox housing manufacturer page. This article focuses on what should go into the RFQ package.

Why bearing seats should be defined before quote review

The bearing seat is not just another machined feature. It controls shaft alignment, noise, vibration, service life, and assembly repeatability. If the housing casting moves during heat treatment or if the machining stock is not planned correctly, the bearing bore can still be machined to size while the surrounding relationships are wrong.

That is why a useful gearbox housing RFQ should identify:

• •which bores are bearing seats
• •which faces control cover assembly
• •which holes or pads locate the housing in the final assembly
• •which dimensions need CMM reporting at sample stage
• •which dimensions can be checked by gauges in serial production

The RFQ does not need to solve the inspection plan completely. It should tell the supplier which features drive function so the quote can include the right review work.

Start with the datum reference frame

Many quote problems begin when the buyer and supplier read the same drawing but imagine different measurement setups. A datum scheme should answer three questions:

• •What surface or feature establishes the primary orientation of the housing?
• •What feature controls the bearing axis or shaft centerline?
• •What feature prevents rotation or controls the mounting relationship?

For a gearbox housing, this may involve a machined mounting face, a bearing bore, a locating pin hole, or a split-line cover face. If the drawing already defines datum A, B, and C, include the drawing revision and ask the supplier to confirm the inspection setup. If the drawing is early and datums are still under review, say that clearly in the RFQ.

A simple note is enough:

> Please review whether the proposed datum scheme supports CMM inspection of the bearing seats, cover face flatness, and shaft-center relationship. If another datum sequence is more practical for casting plus machining, please flag it before tooling quote.

Separate casting risk from machining risk

Gearbox housings are often quoted as a combined casting-plus-machining part, but the risks are different.

Casting-side review should cover wall thickness, shrinkage-prone zones, ribs, bosses, draft, gating, risers, and expected stock allowance around functional faces.

Machining-side review should cover datum access, clamping stability, bore cleanup, cover-face sequence, fixture concept, tool reach, and inspection method.

When these two scopes are mixed into one vague line, buyers lose visibility. The RFQ should ask the supplier to separate:

• •raw casting assumptions
• •heat treatment or aging assumptions if relevant
• •machining stock and datum strategy
• •CMM or gauge inspection scope
• •first-article documentation
• •production sampling plan

This makes supplier comparison easier because the buyer can see whether each supplier is quoting the same technical workload.

What to ask for in the CMM report

A CMM report can be useful or almost useless depending on how it is defined. For a gearbox housing first sample, buyers should ask for a report that includes the features that affect assembly, not only dimensions that are easy to measure.

Useful CMM scope often includes:

• •bearing bore diameter and roundness
• •bore-to-bore distance
• •concentricity or positional relationship to the datum system
• •cover-face flatness
• •mounting face flatness
• •threaded or locating-hole position
• •critical wall or boss location if it affects machining stock

If the part will be checked after machining, state that the CMM report should use the final machined datum scheme. If the buyer also needs casting-stage inspection, ask for a separate as-cast check so the two stages are not confused.

Include tolerance risk in the RFQ language

Some dimensions are routine. Others drive fixture design, machining time, and inspection cost. The supplier should know which is which.

Instead of saying "all dimensions must meet drawing," add a short priority note:

> Critical-to-function features are bearing seat diameter, bearing-seat position to datum A/B/C, cover-face flatness, and mounting-hole true position. Please quote CMM inspection for these features at sample stage and state which items require production sampling.

This does not replace the drawing. It helps the supplier understand which features deserve engineering attention before quote release.

Ask how heat treatment or stress relief affects datums

If the housing uses A356-T6 or another heat-treated alloy, the buyer should ask how heat treatment may affect flatness and bore relationships. Heat treatment can improve mechanical properties, but it can also expose distortion risk in thin walls, long flanges, and asymmetrical ribs.

The RFQ can ask:

• •Is the housing quoted as as-cast, T5, T6, or another condition?
• •Are datums machined before or after heat treatment?
• •Which faces receive stock for post-treatment cleanup?
• •Is any stress relief or aging step assumed before final CNC?
• •How will first samples be checked for distortion?

These questions help avoid a quote that is technically complete on paper but under-scoped for dimensional stability.

Minimum RFQ package for a bearing-seat housing

A strong gearbox housing RFQ should include:

For broader drawing preparation, see the casting drawing requirements guide and quote readiness checklist.

Supplier questions before approval

Before selecting a gearbox housing supplier, ask:

• •Which datums will your CMM program use for the first sample?
• •Which features will be machined from casting stock rather than held as-cast?
• •How much machining stock is reserved around bearing seats and cover faces?
• •Will the quote include CMM reporting for bearing-seat position and flatness?
• •Which features are checked 100% and which are sampled in production?
• •How will you handle dimensional drift between T1, T2, and pilot batches?
• •What information is still missing before you can quote confidently?

The last question is important. A qualified supplier should be comfortable naming missing information instead of pretending the RFQ is complete.

Practical buyer takeaway

For gearbox housings, the best RFQ is not the longest RFQ. It is the one that clearly identifies bearing-seat function, datum strategy, machining scope, and CMM inspection expectations before price comparison.

If your team is preparing an aluminum gearbox or reducer housing RFQ, send the drawing, STEP model, alloy target, annual volume, bearing-seat requirements, and CMM scope through Bohua's RFQ form. Bohua can review the package and help clarify which assumptions should be fixed before quoting.

FAQ

Should a gearbox housing RFQ include CMM requirements?

Yes, when bearing seats, cover faces, or mounting datums affect assembly. The RFQ should identify which features need CMM reporting at first sample and which can be handled by production gauges later.

Is the bearing seat usually checked before or after machining?

The final bearing seat is normally checked after machining because it is a functional machined feature. Some programs also check casting-stage stock allowance before machining to confirm the raw casting supports the final geometry.

What makes gearbox housing quotes hard to compare?

Quotes become hard to compare when suppliers assume different machining scope, datum strategy, CMM documentation, heat-treatment condition, or production sampling level. Buyers should define these before comparing price.

What files should I send first?

Send a 2D drawing with datum references, a 3D STEP file, annual volume estimate, alloy or temper target, machining scope, and the list of bearing-seat or flatness features that require inspection evidence.