What this covers
You’ll have a prototype you can pick up, assemble, and put through a basic bench check, with the problem areas called out early enough to change parts while there’s still time.
Prototype build support gets your CAD to something I can cut, print, and assemble, then proves it on the bench before it matters. If you’re ready, the next step is a quick CAD and deadline review so I can lock a build plan and a slot.
I start by making the CAD buildable, then I pick materials and processes that match what you need to learn on the first build. I fabricate the parts, do a bench fit-up and assembly, then turn every issue into a snag list with clear rev changes so the next cut fixes the right thing.
A bit about me
I’m Tom Hadfield, Prototype builder. I build proof-of-concept and functional prototypes for product teams who need something physical for a gate review, an investor meeting, or early user trials. Most of my work starts with CAD that looks right on screen and needs the hard decisions made before anything gets cut: fixings, tolerances, access, and what will actually take load.
People bring me in when they want a prototype that tells the truth. I’ll point at the first likely failure points, then build in a way that makes those weaknesses show up on the bench instead of in the meeting. I keep the build simple where it can be simple, and I spend time where it saves rework: interfaces, alignment, and anything you have to assemble twice.
Recent work
Here are three recent builds that show the kind of problems I solve before a prototype hits the table.
Portfolio
Handheld enclosure fit-up. Took a CAD enclosure to a buildable split line, added datum faces for repeatable alignment, then printed and machined parts for a full assembly. The first fit-up surfaced two clashes and one fastener access issue before the review.
Bench-test functional rig. Built a functional prototype and a simple test rig to load the critical joint in the same direction it sees in use. The rig made the weak point fail in minutes, not days, and drove one geometry change and one material swap.
Small-batch fit-check build. Assembled a small batch of prototypes to verify stack-up and assembly time before a user trial. Logged every snag during build, then issued a single redline pack so the CAD change set matched what happened at the bench.
“The prototype fitted first time, and the snag list saved us a week.”
Design engineer, a product team preparing a gate review
Build-ready CAD changes
A cleaned-up model or marked-up change set that fixes the things that stop a prototype building: wall thickness, clearances, split lines, fixings, and tool access.
MATERIAL AND PROCESS PLAN
A short plan that names what each part will be made from and how, with one sentence per choice explaining what it proves and what it won’t.
ONE-OFF PROTOTYPE PARTS
The fabricated parts for the agreed build, using foam, MDF, 3D print, and simple machining where it makes sense for speed and learning.
Assembled prototype unit
A bench-assembled prototype with the key interfaces checked, the fasteners and fits proven, and any assembly traps found while there’s still time to change parts.
SNAG LIST AND REV ACTIONS
A clear list of what didn’t fit or didn’t survive, what caused it, and the specific CAD changes that fix it for the next iteration.
PROTOTYPE DRAWING PACK
Manufacturing drawings for the prototype parts that need them, with the dimensions that control fit and alignment called out so the next cut matches the bench.
Pricing
These are starting points. I’ll point you to the right tier based on part count, bought-in lead times, and how many interfaces have to fit first time.
Priced items
Get started
If you want me to hold a build slot, sign below and send the CAD and the deadline you’re working to.
1. Sign the proposal to book the work. 2. Pay the 30% booking invoice within 14 days. 3. Send CAD and requirements so I can start CAD cleanup and the build plan.
Signature
Fee summary
Can you work from my CAD, or do you need to remodel it?
I can work from your CAD. Most jobs need some cleanup to make the first build realistic, so I’ll either edit your model directly or send you a marked-up change list, depending on what you prefer and what your file format allows.
WHAT CAN WE REALISTICALLY BUILD IN TWO WEEKS IN SHEFFIELD?
Two weeks is usually enough for a focused proof-of-concept or a functional bench prototype if the CAD is close and the scope stays tight. The limiting factors are part count, lead times on bought-in items, and how many interfaces have to fit first time.
Where will it break first, and how do we test that quickly?
The first breaks usually come from load paths, thin sections around fasteners, and misalignment that puts stress where you didn’t plan it. I’ll call out the likely weak points, then set up a quick bench check or simple rig that targets that joint directly.
IF IT NEEDS A SECOND ITERATION, WHAT CHANGES COST TIME?
Anything that changes interfaces costs the most time: hole patterns, mating faces, alignment features, and bought-in components. Cosmetic tweaks are usually quick. I’ll flag the time-sensitive changes in the snag list so you know what to lock down first.
Payment
To book the work, I take 30% when the proposal is signed. The remaining 70% is due when I hand over the finished work. Invoices are payable within 14 days of the invoice date.
Changes. If the scope changes, I’ll price the change before I start it. The snag list is for buildability and fit issues found during the build. New requirements or extra iterations are quoted separately.
What I need from you. I need the CAD files, key dimensions that cannot move, and the deadline you are working to before I start. If there are bought-in parts, I need part numbers and lead times.
Bought in items. Lead times on bought-in components can set the schedule. If a critical part slips, I’ll tell you the same day I find out and propose a workaround, substitute, or a revised build plan.
Handover means the assembled prototype unit, the build-ready CAD changes, the snag list with rev actions, and the prototype drawing pack. I’ll send files in the formats we agree before the build starts.
Ownership. Once the final invoice is paid, you own the prototype parts and the CAD and drawing changes I’ve produced for this job. I keep a copy of working files so I can support a second iteration if needed.
Schedule and access. My build schedule is held once the booking payment is in and I have usable files. If I’m waiting on information or decisions, the schedule moves by the same number of days as the delay.
