Consider an inspection camera that must move 120° around a fixture at a 300 mm radius. Its reference point travels about 628 mm. That number alone does not tell you how much rail to order. The carriage needs room at both ends. The camera bracket may follow a different radius, and its offset adds a moment load. You can use this example to work through a fixed-radius curved linear rail selection and then check an IMTEK TTH-ICR drawing against your machine.
Quick answer: A curved linear rail guides a carriage along a defined arc. You choose its radius and segment angle from the required path, then check the carriage’s real end positions, load and moment, mounting, and drive. Arc length describes a reference point’s path; it does not state usable carriage travel or a product’s order length.
When Does a Fixed-Radius Curved Linear Rail Make Sense?
Your camera must stop at several points around a stationary fixture. A curved rail gives the carriage one path between those points. You might use the same idea to guide a sensor around a part, carry a tool beside a round workpiece, or move a small platform around a machine opening. The rail locates the moving assembly while the rest of the machine provides the drive, stops, and cable route.
You should draw the camera, bracket, and carriage at the start, middle, and end of travel. The lens must still see the part at each point. The bracket needs clearance from the fixture, and the cable needs a safe route. A carriage usually turns as it follows the arc. If the lens must keep one fixed direction relative to the machine, you need another means to control its orientation. A rail radius alone cannot solve that task.
Check whether the center can hold the support
You may be able to support a large rotating platform with a central rotary bearing. You may also use a ring guide near its perimeter. Sketch both layouts if the platform is wide. Check where the payload sits and where the drive and services fit. The useful choice depends on the whole machine. A small camera moving along part of an arc does not need the same layout as a full turntable.
One requirement changes your options early. If the same carriage must leave a straight track and enter a bend, ask for a guide system made for that transition. A fixed-radius curved segment does not prove that it can accept a straight section. You should confirm the matched carriage, joint design, and path limits in the exact system drawing before using one continuous axis. For one documented example, THK identifies its HMG model as a straight-and-curved guide.
For a replacement project, start with IMTEK’s linear guide cross-reference checklist, then verify the curved rail geometry and load ratings for the exact models separately.
How Do You Specify Radius, Angle, Usable Travel, and Load?
The camera example uses a 300 mm radius and a 120° sweep. Those numbers describe a usable path only when you and the supplier measure from the same points. You should place the rail, carriage, tool, and fixture on one drawing before selecting a segment.
Put the reference points on one drawing
Mark the center of the arc, the carriage reference point, and the camera’s working point. The lens may sit farther from the center than the carriage, so it follows a larger radius. The bracket may reach toward the fixture and set a smaller clearance radius. You need these different paths on the same view. You also need to label the feature on which the supplier defines its nominal rail radius. Two drawings marked R300 may use different reference lines.
| Drawing item | What you mark | Why it matters |
|---|---|---|
| Rail reference | The supplier’s stated radius datum and arc center | You can match the catalog geometry to your base. |
| Carriage path | The block reference point at both end angles | You can check travel and stop positions. |
| Working path | The lens or tool tip and the outer bracket edge | You can check coverage and collision clearance. |
Calculate the path, then locate the carriage endpoints
You can calculate the nominal arc length at the carriage reference point with arc length = radius × angle in radians. A 120° angle equals 2π/3 radians. At a 300 mm reference radius, the path is 300 × 2π/3, or about 628 mm. You can also use 2π × 300 × 120/360. Both give the same path length at that one reference point.
You cannot treat 628 mm as the rail order length or usable carriage travel. Draw the complete block and bracket at the required start and end angles. Allow space for the block body, stops, cable attachment, and any drive hardware. A segment that covers exactly 120° on paper may leave too little room for the assembly to reach both views. The same check applies when your design uses more than one segment; you need an approved joint arrangement and a smooth passage under load.
Add load direction and the offset moment
Suppose the camera and bracket exert a 60 N force, and their center of gravity is 120 mm from the carriage reference point. If that force acts at a right angle to the offset, the simple static moment is 60 N × 0.12 m = 7.2 N·m. This is one load case, not a product size. You need to show the direction of the force, the offset, and the positions in which the carriage works. If the arc is vertical, gravity’s pull along the travel direction also changes with position.
You should next check start and stop forces, tool contact, speed, and any second support block. At the same speed, a smaller radius raises inward acceleration, so your chosen path can affect the load on the assembly. Use the selected supplier’s rating definitions and life method for the final check. Before applying a model’s rating, calculate the load and moment on the most demanding guide block for your real layout. The 7.2 N·m example has no safety factor and assumes a perpendicular force.
Which Curved Guide Design Fits the Motion Path?
Your camera needs one fixed arc, but several guide types can produce it. They do not use the same contact parts or mounting rules. You should compare the actual carriage and rail pair, rather than assuming that every curved guide with the same radius will carry the same load.
| Guide design | What you should check | Typical design question |
|---|---|---|
| Recirculating-ball curved guide | Defined radius, block envelope, rail segment, ratings, and lubrication | Does the selected block meet the load and moment cases? |
| V-wheel track or ring | Ring or segment size, wheel setting, support, drive, and free space | Can you support and adjust the full moving assembly? |
| Polymer sliding curved guide | Sliding material, friction, wear, environment, and maintenance | Does the contact design suit the speed and duty? |
A product family can contain several carriage designs, so you should read the model drawing rather than rely on a brand name. A roller guide does not always outperform a ball guide, and a sliding guide does not always suit a dusty site. Your load, speed, mounting quality, and service access decide the useful comparison. If your station later gains a straight return path, repeat the architecture review. Your new axis now has a transition requirement that the original fixed arc did not have.
What Must You Design Around the Rail?
A guide can match your CAD radius and still run badly after installation. The mounting base can distort the arc. A bracket can pull across the block, and a cable can become tight at the last camera position. You should check these interfaces while you can still change the machine layout.
Set a base datum and inspect the joints
You need a clear mounting reference for the 300 mm path. Mark the location face and the surfaces you will inspect after machining. You should remove burrs and raised areas before installation, then follow the selected guide’s mounting drawing and torque instructions. If you need more than one segment, ask whether that size supports joints. You should inspect any step or side shift at a joint while the carriage, camera bracket, and drive pass through it.
Route the drive, cable, and stops through the full arc
The guide carries and locates the camera; the drive supplies motion. You should check the pull direction at the start, middle, and end. Run the same three-position check with the cable bundle fitted. Leave room for the end stops and sensors without taking away the required view positions. If you are planning a wider automated axis, the split between guidance and drive in an automation system helps you assign each part its job.
Plan protection and first-run checks
You should describe dust, liquid, temperature, and cleaning practice at the rail. Conditions at the camera may differ from conditions at the block. Ask for seals, lubricant, and service intervals for the exact chosen model; an option offered on a straight guide may not exist on a curved one. During your first run, note the angle at which drag or noise appears. That observation can direct the first inspection.
| What you observe | What you check first |
|---|---|
| Drag at one angle | Base seating, bracket clearance, cable route, and drive alignment there. |
| Click at a segment joint | Joint height, side alignment, and any part crossing the joint. |
| Drag along the whole arc | Specified clearance or preload, seal drag, lubrication, and assembly distortion. |
| Change after fitting the camera | Center of gravity, bracket stiffness, and drive force on the loaded block. |
These checks are starting points. They do not diagnose a specific IMTEK product. You should follow the maker’s handling instructions before removing a carriage from its rail. Some rolling-element blocks need a transfer rail or another handling method. A rushed removal can damage the assembly or release internal elements.
IMTEK TTH-ICR: From an Application Drawing to a Product Check
IMTEK uses TTH-ICR as the name of its curved rail series. You can use the marked-up camera layout to check a proposed configuration. Start with the actual TTH-ICR drawing and the approved data for the exact size and segment. Your example dimensions explain the method; they do not state that an R300, 120° part is in stock or supported by every size.
- Geometry: Does the offered radius use the same reference as your layout? Can the approved segment arrangement carry the block between both required camera positions?
- Interface: Do the block envelope, rail section, hole pattern, and location face fit your base and bracket? Do your drive and stops still clear the moving parts?
- Duty: Do the published load and moment ratings, speed limits, lubrication arrangement, and available protection suit your worst operating case?
You can review the TTH-ICR curved rails product page for its current series information and available drawings. You should still request confirmation of the exact configuration before you release a machine design. A picture, family name, or nominal radius cannot replace an approved drawing.
If you are replacing a guide from another brand, include its full model code and drawing. A matching nominal radius does not prove that the mounting holes, block height, rail datum, travel, load definitions, or seals match. For example, THK lists specific HCR curved guide models; their codes are not TTH-ICR interchange codes. You should compare dimensions and rating methods side by side and then test fit the proposed assembly in your CAD layout.
You can send IMTEK your annotated application drawing with the load, end positions, duty, and existing part number. This gives the application team enough information to review the carriage path, mounting interface, and demanding load case for a specific offer.
Frequently Asked Questions
Can a curved rail form a full circle?
Some guide systems offer rings or approved joined segments. You should check whether the exact size supports your full circle and how many carriages it can carry. The circle still needs a suitable support, drive, and service route.
Can one carriage move from a straight rail onto a curved rail?
You can do this only with a system designed and approved for the transition. You should not assume that a standard fixed-radius segment joins to a straight guide with the same nominal rail width.
Can TTH-ICR replace a THK HCR guide?
You can ask for a drawing comparison. You should not assume a direct swap. Check the radius datum, segment angle, usable travel, block and hole dimensions, rating methods, and required protection for both exact models.
Is a 628 mm arc the travel I can use?
No. You calculated 628 mm for one reference point on a 300 mm radius over 120°. You must place the full block and bracket at both endpoints and allow for stops and clearances before you state usable travel.
Conclusion
You can select a curved linear rail more reliably when your drawing shows the arc center, the carriage and tool paths, the real end positions, and the load direction. Use the 300 mm camera example to organize those checks, then compare your own layout with an approved TTH-ICR configuration. Your final decision also needs the mounting, drive, cable, and service details that make the whole axis work.