1. Does the supplier ask about datum strategy first?
The first engineering question on any fixture project should be: which surfaces are you locating from, and why those? A supplier who jumps to price after reading a drawing has not read the drawing. In practice we look at four things before quoting: the datum callouts, the wall thickness at the clamping points, the tolerance stack between locating faces, and how the part sits in the machine envelope.
A useful test: describe the part in two sentences and see whether the reply repeats your datum assumptions back to you, or challenges them. Suppliers who challenge them have usually built fixtures for parts like yours before.
2. Can they explain what happens when the fixture is loaded wrong?
Every fixture gets loaded wrong eventually — by a night shift, by a new operator, by a tired setter. The difference between a good and a mediocre design is whether a wrong load either fails visibly or physically cannot happen. Poka-yoke features cost very little: an asymmetrical locating pin, a clearance cut that only one orientation fits, a proximity sensor on the clamp.
Ask directly: "What prevents this part going in backwards?" If the answer is "training", keep looking.
3. Do they show the clamping force and its effect on the part?
Clamping force is where thin-wall parts are lost. A supplier quoting hydraulic clamping should be able to state the clamping force per clamp, the resulting elastic deformation at the weakest wall, and whether the fixture needs sequenced clamping or pressure reduction for the finishing pass.
| What is asked | Weak answer | Credible answer |
|---|---|---|
| Clamping force | "Standard hydraulic clamps" | Force per clamp, pressure setting, and a deformation estimate at the thinnest wall |
| Clamp sequencing | Not mentioned | Which clamps close first, and why the finishing pass runs at reduced pressure |
| Chip clearance | "We add coolant" | Where chips pack, and how the fixture geometry or coolant-through clamps avoids it |
4. What does the quote actually contain?
A fixture quote that is one number is not a quote. A comparable one lists: fixture concept, number of stations, locating scheme, clamping type, materials and surface treatment, hydraulic or pneumatic circuit scope, tooling assumptions, lead time in working days, and the price split between design and build. Ask for the split — it tells you whether they are selling engineering or metal.
5. Can they show inspection records, not certificates?
A CMM report on one fixture proves nothing about the next one. Ask for the inspection plan instead: which features are measured, at what frequency, and what happens when a feature drifts. For workholding, the measurement that matters is repeatability at the locating faces — the same part loaded ten times, ten results. Any competent builder can produce that in an afternoon.
6. Do they understand your machine, not just your part?
A fixture is a machine accessory. The relevant questions are spindle reach, the table T-slot pattern, the through-spindle coolant rating, the pallet interface on a horizontal machine, and the control's ability to drive a hydraulic or pneumatic sequence. A supplier who cannot say how the clamp sequence is triggered from your control has not built many fixtures for your control type.
7. How do they handle the first-article cut?
The trial cut is where a fixture is proved or exposed. Insist that it happens on your machine, or at minimum on a machine of the same model, with your cutting parameters, and that the outcome is documented: dimensions measured, cycle time achieved, any vibration or chatter observed, and the parameter changes made. A supplier who treats the trial as a formality is telling you the fixture was never at risk.
8. What is the lead time made of?
Custom fixtures from China typically run four to eight weeks: one week for concept and sign-off, two to four weeks for machining and assembly, one week for hydraulic circuit build and pressure test, and one week for trial and packing. If a supplier quotes three weeks, ask which of those steps they are skipping. If they quote twelve, ask what is queued.
9. Will they tell you not to buy?
This is the check most buyers never run and the one that predicts the relationship. A fixture only pays if the batch size covers its cost. For a run of 200 parts, a twenty-thousand-yuan hydraulic fixture is usually a bad investment and a two-thousand-yuan manual fixture is right. A supplier who runs that arithmetic out loud — and tells you the answer is no — is a supplier worth keeping.
Where this leaves the decision
None of the nine checks requires travel. All of them can be run over email, a drawing and one video call with a fixture on a bench. The signal you are looking for is not polish; it is whether the engineering conversation is specific to your part.
Liuzhou Dongben Machinery Equipment Co., Ltd. builds custom CNC fixtures in Liuzhou, Guangxi, and answers these nine questions as standard practice before quoting — including when the answer is that a fixture will not pay back in your batch size.