Product type
A dial indicator converts a small linear movement into the rotation of a pointer across a graduated face. It does not measure an absolute dimension in the way a caliper does; it measures how far something has moved, or how far a surface departs from a reference, which is what makes it the standard instrument for run-out, flatness and alignment.
A dial indicator converts a small linear movement into the rotation of a pointer across a graduated face. It does not measure an absolute dimension in the way a caliper does; it measures how far something has moved, or how far a surface departs from a reference, which is what makes it the standard instrument for run-out, flatness and alignment.
The distinction matters because most dial indicator work is comparative. The instrument is set against a reference or a nominal position, and the reading is the departure from it, so the quantity being judged is usually a tolerance on a departure rather than a size. A shaft whose indicated run-out is within a stated band is accepted; the same reading would be meaningless as a diameter.
Three figures settle the choice: the measuring range, which has to cover the movement expected without the plunger running out of travel; the graduation, which sets the smallest departure that can be read reliably; and the mounting, because a dial indicator is only as good as the stand holding it.
Inside the body a precision rack is cut along the plunger and drives a pinion train that turns the pointer. The gearing multiplies a small linear movement into a large angular one, which is how a travel of a few millimetres is displayed across a face large enough to read. The same train drives a second, smaller hand on a concentric dial, the revolution counter, so that more than one turn of the main pointer can be followed.
The mechanism is a comparison device rather than an absolute one, and it is set to zero wherever it is convenient. The bezel carrying the graduations can be rotated so that the zero mark is brought under the pointer at the reference position, after which every reading is a departure. That is why a dial indicator does not have to indicate a true dimension: it has to be consistent across its travel and to return to the same reading when it does.
Because the instrument responds to movement, the mounting is part of the measurement. A magnetic base or an articulated arm that flexes under the measuring force allows the indicator body to move, and the reading then includes that movement. A rigid stand, the plunger square to the surface, and a measuring force low enough not to deform the part are the conditions under which the numbers mean what they appear to mean.
Most of the specification is fixed by these decisions rather than by the accuracy class. Each one constrains the next, which is why they are settled in order.
| Configuration | Options to fix | What it actually decides |
|---|---|---|
| Measuring range | A short range such as 0 to 3 mm, or a longer one such as 0 to 50 mm | Whether the movement being checked can be followed without running the plunger to the end of its travel, and how large the body has to be to contain it. |
| Graduation | Typically 0.01 mm on a dial indicator, or 0.001 mm on a dial gauge | The smallest departure that can be read with confidence, and whether the tolerance being judged is coarse enough for a 0.01 mm face. |
| Revolution counter | A second hand that records full turns of the main pointer | Whether travels longer than one turn of the pointer can be read at all, which above about a millimetre they usually must be. |
| Dial diameter | A small face for confined work, a large one for reading at a distance | How easily the pointer can be read in the position the work puts the instrument in, rather than how accurate it is. |
| Plunger travel and measuring force | The travel available beyond the range, and the force the spring applies | Whether the indicator can reach the feature being checked, and whether the force is light enough not to deflect a thin or soft part. |
| Mounting and contact point | A magnetic base, an articulated arm or a fixed bracket, with a range of contact tips | Whether the body stays still while the part moves, which decides how much of the reading is the measurement and how much is the stand. |
| Contact tip form | Flat, spherical or roller tips in different materials | What the indicator can be run against: a flat face, a curved surface, or a rotating part the tip has to ride. |
| Factor | Why it decides the answer | How to settle it before enquiring |
|---|---|---|
| What is being judged | Run-out, flatness, alignment and a direct dimension each place different demands on range and travel | Describe the check: a shaft run-out, a face flatness, an alignment, or a size. |
| Tolerance to be read | The graduation has to be fine enough that the tolerance can be read as a number rather than estimated | Give the tolerance, so that a 0.01 mm or a 0.001 mm graduation can be settled. |
| Movement expected | The range has to cover the departure with the plunger still on its travel | Give the largest departure expected, not the nominal dimension. |
| Access to the feature | The dial has to be visible and the plunger able to reach the surface squarely | Describe the position of the feature and the space around it. |
| Holding the indicator | The mounting decides whether the body moves under the measuring force | State whether a stand is already held, and whether it is rigid enough to be trusted. |
| Environmental conditions | Water and dust reach the movement on machine-tool and workshop duties | State whether a sealed or dust-protected instrument is needed. |
| Whether a certificate is required | A traceable calibration certificate is a separate deliverable from the instrument | State whether readings are relied on for a customer drawing and have to be traceable. |
If any of these are still open, send what is known. A quotation can be issued against a duty description and refined once the gaps are filled.
These are the types an enquiry for a dial indicator usually turns out to be, and the point at which the choice is genuinely decided.
| Nearest alternative | What separates it from a dial indicator |
|---|---|
| Digital calipers | Read an absolute dimension directly and can measure inside, outside and depth, which a dial indicator cannot. Where the requirement is the size of a feature rather than its movement or departure, the caliper is the instrument and the indicator has no part to play. |
| Micrometers | Measure a single dimension to a fine resolution with a screw, and are the instrument for a size held to a tight tolerance. They are read against an absolute scale rather than zeroed to a reference, so they answer a different question from the one a dial indicator is used to answer. |
| Measuring gauges | Include the dial indicator in its comparative role alongside the stands, fixtures and contacts that make comparative measurement repeatable. Where the question is how to hold and present a part rather than which indicator to buy, the gauge is the wider answer. |
| Depth gauges | Reference a surface and read the distance to a feature below it. A dial indicator can be pressed into that service with the right base, but a purpose-made depth gauge presents the reading and the reference in one instrument. |
The commonest error here is choosing on range alone. An indicator that covers the movement but sits on a stand that flexes reports the stand rather than the work.
The first reply can be a quotation rather than a set of questions if the enquiry carries these. Where a figure is not known, send the duty description and we will confirm what it implies.
Available products
Dial Indicators
Mechanical dial indicator and dial gauge for comparative measurement, in 0.01 mm and 0.001 mm graduations with dial diameters from 42 to 80 mm.
Also in Dimensional Measurement
Every type we quote for under Dimensional Measurement. A type with no link yet is still quoted for - it is described on the Dimensional Measurement overview, and gets a page of its own as soon as a model is published against it.
Frequently asked
The graduation, in most cases. An instrument reading to 0.01 mm across a comparatively long range is normally a dial indicator; one reading to 0.001 mm over a short range is normally a dial gauge. The distinction is one of resolution rather than of construction, and both are comparative instruments, so the choice is settled by the tolerance that has to be read.
Because the indicator measures movement, and anything that moves other than the feature also appears in the reading. A base that slips, or an arm that flexes, contributes its own displacement to the pointer. The error is not obvious on the dial, since the instrument is behaving correctly; it is the body that is not. A rigid mounting is therefore part of the measurement rather than an accessory to it.
It can indicate a dimension if it is set against a reference of known size, but that makes it a comparator against that reference rather than a measuring instrument in its own right. For a size read directly, a caliper or a micrometer is the appropriate instrument. A dial indicator is best used for what it does without a reference: showing how far something moves or departs.
What is being judged and against what tolerance, since those fix the graduation and the range; the largest departure expected, so the plunger stays on its travel; how the instrument will be held and whether a stand is already held; the environment at the point of use; and whether a traceable certificate has to be issued. The dial diameter and the contact tip follow from where the work has to be done rather than from the measurement itself.
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