CNC Machined Bolt Manufacturer
Most bolts are forged. A die shapes the head hot, and the part is threaded afterwards. That is the right way to make thousands of a standard size, but it depends on a die existing for the size and head form you need. Where it does not, the bolt is turned from bar instead.
S.R. Forgings machines bolts from 20 mm to 75 mm diameter in property classes 8.8, 10.9 and 12.9, on PLC-controlled turning machines. Threads are rolled rather than cut, so the grain follows the thread form instead of being severed across it. Under-head radius and undercut are machined on a dedicated PLC machine, which matters on a highly stressed bolt because the under-head fillet is where fatigue cracks start.
We machine both before and after heat treatment. Turning after heat treatment is slower and harder on tooling, and we do it where a customer asks for it: it leaves a bright, clean surface, so the bolt arrives on site looking like the finished article rather than a scaled forging.
Machined Bolts
Size: 20 mm to 75 mm diameter
Property class: 8.8, 10.9 and 12.9
Thread: Rolled, metric coarse and fine, UNC, UNF, BSW
Finish: Self colour, black, zinc plated, hot dip galvanised or zinc flake
Fitted Shank Bolts
Where the drawing calls for the shank to fit the hole rather than clear it, the shank is turned to size and left parallel over the grip length. Machining is the practical way to hold a shank tolerance, because a forged shank carries the tolerance of the bar it came from.
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Supplied as Sets
Machined bolts are supplied complete with matching nuts and washers where the connection needs them, so the assembly arrives lot matched from one supplier with one set of test certificates.
Send EnquiryWhen a Bolt Is Machined Rather Than Forged
Four situations account for most machined bolt orders:
- The size is outside standard tooling. Large diameters, or a head sized differently from the thread, where no stock die applies.
- The quantity does not justify a die. On a small lot, cutting a new forging die costs more than turning the parts. Machining lets a short run be made without that tooling cost passed on.
- The shank has to be held to a tolerance. Fitted and fit bolts, where the shank locates the connection instead of the bolt clamping it.
- The part is made to a drawing. Special head forms, stepped shanks, drilled heads, non-standard thread lengths.
Related products: drift pins, also machined from bar, and forged high tensile and HSFG bolts for standard sizes in quantity.
Ordering Machined Bolts
Send the drawing if you have one. If not, we need the diameter, the overall length, the thread length, the property class and the finish, plus the shank tolerance where the shank is fitted. Quantities can be small — machining is the process that makes short runs practical.
Send your drawing for a quotation or use the bolt weight calculator to estimate weights before you order.