Linear guide rail length determines whether an axis can reach its full stroke while every moving block stays supported. A correct profile size alone cannot prevent travel loss, end-hole conflicts, or interference with sensors and stops. Therefore, the final rail drawing must combine the motion envelope with the selected model’s mounting-hole pitch and end distances.
1. Linear Guide Rail Length vs. Working Stroke
Working stroke describes the required movement. By contrast, linear guide rail length describes the fixed support that keeps the block on the raceways throughout that movement. Therefore, the rail normally extends beyond the working stroke.
Rail size requires a separate decision. A designation such as 15, 20, 25, or 35 identifies the nominal profile family, while rail length defines the physical cut length. First, choose the profile, block type, and block quantity. Then confirm the linear rail profile size from load, moment, and mounting space before calculating the final length.
| Term | Engineering Meaning | Why It Changes the Decision |
|---|---|---|
| Rail size | Nominal profile family, such as 15, 20, 25, or 35 | Sets rail section, block family, pitch, ratings, and installation envelope |
| Rail length | Total physical length of one rail or one matched rail set | Controls usable travel, mounting-hole layout, shipping, and installation |
| Stroke | Required movement of the carriage or machine table | Forms only the travel portion of the total rail length |
| Block-group envelope | Full length occupied by every block moving together | A two-block carriage needs more rail than one block at the same stroke |
| End clearance | Planned space between the moving group and each rail end | Prevents collision and leaves room for stops, sensors, covers, or service access |
| Pitch P and end distance E | Mounting-hole spacing and distance from the nearest hole to the cut end | Convert the motion estimate into a rail that can be manufactured and mounted |
Why a 500 mm Stroke Does Not Mean a 500 mm Rail
A moving block occupies physical space on the rail. At either travel limit, the raceways must still support the block, while the moving plate must remain clear of stoppers, sensor brackets, covers, and nearby machine parts. As a result, a 500 mm rail normally cannot provide a true 500 mm working stroke.
However, no universal safety allowance fits every axis. A slow inspection slide may use controlled end margins, whereas a fast transfer axis may need more deceleration distance and larger mechanical stops. In addition, bellows, telescopic covers, and lubrication hardware can reduce usable travel.
Use the Actual Moving Envelope, Not a Nominal Allowance
Avoid adding an arbitrary value such as “40 mm” to every axis. Instead, calculate linear guide rail length from the exact block drawing and the real machine layout. For example, a long block, an added scraper, or a second block can increase the occupied length substantially. The final check must include the moving plate and its attachments, not only the bare carriage.
IMTEK TechTalk: Why Stroke Alone Is Not Enough
This short IMTEK TechTalk provides a visual introduction to stroke, block length, and end allowance. Use it as the concept check, then use the model-specific calculations below for the final drawing.
2. How to Calculate Linear Guide Rail Length for One or More Blocks
First, calculate the motion envelope. Do not round the result to the nearest catalogue length yet, and do not choose the end-hole position. This first calculation simply proves that the required stroke and the complete moving assembly fit inside the available rail and machine envelope.
Linear Guide Rail Length Formula for One Block
| Symbol | Meaning | What to Measure |
|---|---|---|
| Lpre | Preliminary rail length | Minimum length required by the motion envelope before hole-layout adjustment |
| S | Working stroke | Actual operating travel, including any required process overrun |
| B | Block length | Overall block length in the travel direction from the selected model drawing |
| CL / CR | Left and right clearances | Space for full support, stops, sensors, covers, and safe travel limits |
| A | Additional allowance | Any extra space not already included in the left and right clearances |
Rail Length Formula for Two or More Blocks
Blocks attached to the same moving plate travel as one group. Therefore, replace the single block length with the complete block-group envelope. Before you apply the formula, determine the required block quantity and center spacing from load position, moment demand, support span, and available travel.
For two identical blocks defined by center distance K, the complete group envelope is:
For two blocks defined by a clear gap G between their facing ends, use:
Case 1: TOH25CA, One Block, 500 mm Stroke
This example uses an IMTEK TOH25CA block. According to the 2026 catalogue, the block is 84 mm long, while TO25 uses a 60 mm rail-hole pitch and a 20 mm standard end distance. Here, the TOH heavy-load square guide serves only as a dimensional example; the project still needs a separate load and rigidity review.
| Input | Value | Reason |
|---|---|---|
| Working stroke S | 500 mm | Required process travel |
| Block length B | 84 mm | TOH25CA catalogue dimension |
| Left clearance CL | 20 mm | Planned end margin |
| Right clearance CR | 20 mm | Planned end margin |
| Additional allowance A | 0 mm | No separate sensor or cover allowance in this example |
This motion envelope needs at least 624 mm. Next, apply P = 60 mm and E = 20 mm. An 11-hole layout gives:
Case 2: Two TZH35CA Blocks, 600 mm Stroke
A heavy or overhung platform often uses two blocks on each rail. In this example, two TZH35CA roller blocks move together at a 220 mm center distance. The catalogue block length is 124 mm. The TZH roller-guide block geometry creates a larger moving envelope than a single compact block, even though the working stroke remains 600 mm.
| Input | Value | Reason |
|---|---|---|
| Working stroke S | 600 mm | Required table travel |
| Individual block length B | 124 mm | TZH35CA catalogue dimension |
| Block center distance K | 220 mm | Support span defined by the carriage layout |
| Left / right clearances | 20 mm each | Planned end margins |
| Rail pitch P / standard E | 40 mm / 20 mm | TZ35 catalogue hole layout |
A 25-hole layout gives:
3. How Pitch and End Distance Set Linear Guide Rail Length
The preliminary calculation proves that the motion fits. Next, convert that result into a workable mounting-hole pattern. The selected series and size determine rail pitch, so the designer cannot choose pitch freely after setting the length.
Use the Symmetric or Asymmetric End-Distance Formula
When the distance from each rail end to the nearest mounting hole is different, use:
When both end distances are equal, the expression becomes:
| Symbol | Meaning | Drawing Check |
|---|---|---|
| L | Final physical rail length | Must be equal to or greater than the required motion envelope |
| n | Total number of rail mounting holes | Do not confuse hole count with the number of pitch intervals |
| P | Center distance between adjacent mounting holes | Use the selected rail model’s catalogue value |
| E1 / E2 | End distances at the left and right rail ends | Confirm both values when the rail is not cut symmetrically |
Stock Length and Pitch-Compatible Custom Length Are Not the Same
A catalogue-listed standard length appears in the series length table with a defined hole count. Therefore, it can simplify procurement and repeat replacement. However, always confirm current stock before placing the order.
By contrast, a pitch-compatible custom length follows the hole-pitch equation and uses acceptable end distances, yet it does not appear in the standard-length list. Therefore, IMTEK must cut it to the approved drawing. Meanwhile, an arbitrary requested number may fail the pitch check or leave an unsuitable end distance.
| Length Type | What It Means | Procurement Consequence |
|---|---|---|
| Catalogue-listed standard length | Length and hole count appear in the catalogue table | Simpler repeat ordering; confirm live stock and end configuration |
| Pitch-compatible custom length | Length follows P and acceptable E values but is not listed as standard | Requires custom cutting and final drawing approval |
| Arbitrary requested length | A length is stated without checking pitch or end holes | May need revised E1/E2, a different hole count, or a changed total length |
| Existing replacement length | Rail must fit a previously machined base and hole pattern | Measure both end distances and every mounting-hole position before ordering |
Case 3: TTH20CA, 300 mm Stroke, Custom 400 mm Rail
The TTH20CA block is 69.1 mm long. Assume a 300 mm stroke and 15 mm clearance at each end.
TT20 uses a 60 mm pitch and a 20 mm standard end distance. Seven holes produce:
The 400 mm result is pitch-compatible and keeps E at 20 mm. However, the TT20 catalogue’s nearby standard lengths are 340 mm and 460 mm; 400 mm is not listed as a standard length.
Why Final Hole Position Matters in OEM and Replacement Projects
A total length alone cannot fully define a replacement rail. For example, two 735 mm rails may place the first mounting hole at different positions. If the base plate already exists, provide the full hole pattern or at least P, E1, E2, fixing direction, and the original drawing. For an OEM batch, approve one controlled production drawing before IMTEK repeats the length across machines.
4. How IMTEK Series and Block Types Change the Length Decision
The calculation method stays the same across IMTEK series; however, the input values change. Use the exact series, size, and block type to obtain block length, rail pitch, standard end distance, available standard lengths, and maximum single-piece length. Never transfer the dimensions of one size-25 family to another simply because both use the number 25.
Model-Specific Data Used in the Four Worked Examples
| IMTEK Model | Block Length B | Rail Pitch P | Standard E | Example Final Length | Catalogue Single-Rail Maximum* |
|---|---|---|---|---|---|
| TOH25CA | 84 mm | 60 mm | 20 mm | 640 mm standard length | 4,000 mm |
| TTH20CA | 69.1 mm | 60 mm | 20 mm | 400 mm pitch-compatible custom length | 4,000 mm |
| TZH35CA | 124 mm | 40 mm | 20 mm | 1,000 mm standard length | 4,000 mm |
| TGW12C | 46.1 mm | 40 mm | 15 mm | 270 mm standard length | 2,000 mm |
*Values shown are from the IMTEK Linear Guideway Product Catalogue 2026 used for these examples. Confirm the latest model drawing, current supply capability, and shipping constraints before ordering. Special project capability may differ from the catalogue table.
Long Blocks Increase the Required Rail Length
A long block can improve the support span or moment capacity, but it also consumes more rail. For example, TOH25CA is 84 mm long while TOH25HA is 104.6 mm long. Changing to the HA block adds 20.6 mm to the preliminary motion envelope before any change to stroke or end clearance.
In addition, a sealing package, metal scraper, self-lubrication unit, or special end component may increase the complete block assembly length. Therefore, freeze the ordered block code before you approve the final rail drawing.
Case 4: TGW12C Miniature Wide Guide, 180 mm Stroke
Miniature rails use smaller pitches and tighter end geometry, so a few millimeters matter. The TGW12C block is 46.1 mm long. Assume a 180 mm stroke with 10 mm clearance at both ends.
TGW12 uses P = 40 mm and standard E = 15 mm. Seven mounting holes give:
What Changes Across TO, TT, TZ, and TG Applications
| Series Direction | Typical Length-Planning Effect | What to Freeze Before Calculation |
|---|---|---|
| TO heavy-load ball guide | Standard and long block options can change the occupied envelope | Exact CA or HA block and sealing package |
| TT low-profile ball guide | Compact height does not remove the need for full block and end allowances | Block type, restricted machine envelope, and stock-versus-custom strategy |
| TZ roller guide | Larger blocks and wider support spans often increase total rail length | Block quantity, center spacing, preload, and base rigidity |
| TG miniature guide | Small pitch and minimum end material make hole position especially sensitive | Exact TGN/TGW model, E minimum, sensors, and mounting-hole drawing |
For an external technical comparison, the THK HSR official product page also separates standard rail lengths, maximum lengths, and joined-rail use. In addition, ISO 14728-1 covers dynamic load ratings and rating life for linear motion rolling bearings. These references reinforce one practical point: length planning does not replace load-life verification.
5. Choose a Standard, Custom, or Butt-Jointed Linear Guide Rail Length
After the calculation, choose the supply format. A standard, custom, or butt-jointed linear guide rail length should match the machine envelope, repeat-order plan, single-piece capability, shipping limit, field handling, and base-preparation accuracy.
Three-Way Rail-Length Decision
| Option | Choose It When | Main Advantages | Main Checks |
|---|---|---|---|
| Catalogue-listed standard rail | The machine can accept a listed length and hole pattern | Simpler drawings, repeat ordering, and replacement planning | Confirm live stock, usable stroke, and final end clearance |
| Pitch-compatible custom-cut rail | The base length or existing hole pattern is fixed | Fits a tight envelope and can match an OEM drawing | Approve L, n, P, E1, E2, fixing direction, and tolerance |
| Factory-matched butt-jointed rail | Required total length exceeds practical single-piece supply or must be divided for shipping | Supports long travel and modular handling | Segment sequence, joint end distances, reference sides, base continuity, and field alignment |
When the Required Length Exceeds One Rail
For the four catalogue examples in this article, the tables list a 6,000 mm single-piece maximum for TO, TT, and TZ and 2,000 mm for TGW12. If the calculated total exceeds that value, divide the requirement into controlled segments rather than treating each piece as an unrelated rail.
When a long-travel axis needs multiple segments, specify factory-matched butt-jointed linear rails. IMTEK can then identify the segments and preserve the joint sequence, while the installer controls step, lateral offset, and reference continuity.
Complete the total-length calculation before planning the segments. Afterward, define joint locations, segment numbers, rail-end tolerances, packaging sequence, and the installation reference. Where possible, keep a joint away from the position where the block repeatedly stops under its highest load.
Long and Dual-Rail Axes Need a Separate Alignment Check
Rail length does not create accuracy by itself. Instead, a longer rail magnifies base flatness error, burrs, shoulder error, bolt-sequence effects, and differential alignment between parallel rails. If the design uses two rails or a long moving table, align the paired rails across the full travel with a dial indicator after you approve the length and mounting-hole layout.
Finally, perform the installation check after the length decision. Do not use alignment work to compensate for an incorrect hole pattern, weak end support, or a carriage envelope that does not fit.
Final Drawing and Order Checklist
| Check | Information to Confirm | Common Failure if Missing |
|---|---|---|
| Working motion | Stroke, home position, overrun, and emergency-stop allowance | Requested travel cannot be reached after assembly |
| Moving group | Exact block model, quantity, block center distance or clear gap, and attached hardware | Rail is too short for the real carriage envelope |
| End clearances | CL and CR measured from the complete moving assembly | Collision with rail end, sensor, stopper, or cover |
| Hole layout | L, n, P, E1, E2, and top- or bottom-fixing design | Rail holes do not match the machine base |
| Supply format | Standard, custom, or matched jointed set | Unexpected lead time, replacement difficulty, or field assembly risk |
| Long-axis installation | Base flatness, reference side, rail sequence, joint position, and alignment method | Binding, noise, or inconsistent resistance |
| Documentation | Approved revision drawing and rail identification | Wrong length or hole pattern repeated across an OEM batch |
What to Send IMTEK for Length Confirmation
Frequently Asked Questions
Is linear guide rail length the same as stroke?
No. Stroke defines the required travel. Linear guide rail length must also include the complete moving block-group envelope, end clearances, and space for stops, sensors, covers, or lubrication hardware.
How much longer should a linear rail be than the working stroke?
There is no universal fixed amount. The extra length depends on the exact block model, block quantity and spacing, left and right clearances, and accessories. Calculate the motion envelope rather than applying one general allowance.
How do I calculate rail length for two blocks?
First calculate the complete two-block envelope. For two identical blocks defined by center distance K, Bg = K + B. Then use Lpre = S + Bg + CL + CR + A before adjusting the result to the rail pitch and end distances.
What is the difference between a standard rail length and a pitch-compatible custom length?
A standard length appears in the catalogue length table. A pitch-compatible custom length follows the mounting-hole pitch and acceptable end distances but is not listed as a standard length, so it requires custom cutting and drawing approval.
Can the left and right rail end distances be different?
Yes. Use L = (n − 1) × P + E1 + E2 and show both end distances on the drawing. This is common when a replacement rail must match an existing base-hole pattern.
When should I use butt-jointed linear rails?
Use a matched butt-jointed set when the required total length exceeds practical single-piece supply or when shipping and field handling require shorter segments. Complete the total-length calculation before defining the segment plan.
Does a longer rail improve positioning accuracy?
Not by itself. Positioning and running quality still depend on rail accuracy grade, base preparation, mounting, parallelism, preload, drive accuracy, and thermal behavior. A longer rail can make installation errors more influential.
What information is needed before ordering a custom rail length?
Provide the exact guide model, block quantity and spacing, stroke, total length, hole pitch, hole count, E1 and E2, fixing direction, base drawing, accessories, and whether the rail is single, paired, or butt-jointed.
Conclusion
A reliable linear guide rail length decision uses two checks. First, confirm the motion envelope from stroke, the complete block group, end clearances, and accessories. Next, match that envelope to the selected rail’s pitch, hole count, and end distances. Finally, choose a catalogue-listed standard rail, a pitch-compatible custom cut, or a factory-matched butt-jointed set.
The four worked examples show why model-specific data matters: the same method produces different results for TOH25CA, TTH20CA, TZH35CA, and TGW12C. Before production, approve one drawing that identifies the exact block code, linear guide rail length, hole pattern, and supply format.