--- title: "Drill jig and fixture design considerations" subject: "Manufacturing and Production Processes" chapter: 10 key: "semester_4/manufacturing_and_production_processes:drill-jig-milling-fixture-design-principles" source: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/drill-jig-milling-fixture-design-principles site: BCT Engineering --- # Drill jig and fixture design considerations Manufacturing and Production Processes · Chapter 10: Jigs and Fixtures for Machine Shops - Asked in: year not given, 5 marks - Video: [Drill jig design considerations/ important/ hindi](https://www.youtube.com/watch?v=hN4cweQU6xI) — EW - INDUSTRY SOLUTIONS - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/drill-jig-milling-fixture-design-principles - Whole chapter: https://www.bctengineer.com/md/semester_4/manufacturing_and_production_processes/chapter-10 ## Question List the principles to be considered in the design of jigs and fixtures. Describe any three types of drill jigs and the main elements (locators, clamps, bushes) used. Briefly describe a straddle-milling fixture. ## Short answer Design uses 3-2-1 location from machined datums, clamping over supports, rigid bodies, chip clearance, foolproof loading and economy. Drill jigs include template, plate, box or leaf types, with locators, clamps and hardened bushes. A straddle-milling fixture mills two parallel faces with spaced cutters and uses a set block with feeler gauge for positioning. ## Answer #### Design principles 1. **Location:** use the 3-2-1 principle; locate from machined datum faces; locators should be hard and replaceable. 2. **Clamping:** the clamp must hold the work firmly without distorting it; clamp directly over a support; use quick-acting clamps (cam, toggle, hinged strap). The clamping force should push the work against the locators, and the cutting force should be taken by the locators, not by the clamps. 3. **Rigidity and strength:** the body should resist cutting forces without vibration; use ribs and short overhangs. 4. **Chip clearance:** allow chips and coolant to escape; avoid pockets where chips collect; provide openings for cleaning. 5. **Foolproofing (poka-yoke):** the part can be loaded only in the correct way. 6. **Ease of loading and unloading,** operator safety, and light weight (for handling). 7. **Economy:** use standard parts and cast or fabricated bodies; keep the cost low for the batch. #### Types of drill jigs | Jig | Description | Use | |---|---|---| | Template jig | Plate with holes laid on the work; no clamping | Few parts, light work | | Plate jig | Plate with bushes and clamps | Parts with holes in one plane | | Box (tumble) jig | Box with bushes on several sides; the work is turned over | Holes on several faces | | Leaf jig | Hinged leaf swings open for loading | Small parts | | Channel jig | Channel-shaped body holding the work between its sides | Simple, small work | **Elements:** locators (pins, V-blocks, pads, buttons), clamps (strap, screw, cam, toggle, quick-acting), and **drill bushes** - fixed (press fit), renewable (with a liner) and slip bushes, made of hardened steel, which guide the tool. #### Straddle-milling fixture In straddle milling, two side milling cutters mounted on one arbor and spaced apart by collars mill two parallel faces in one pass (e.g. the two flats of a bolt head). The fixture holds the work on the table with a V-block or a vice-like clamp, and a **set block** fixed on the body shows the cutter position; a feeler gauge (usually 2-3 mm) is placed between the cutter and the set block to avoid contact. Tenons on the underside locate the fixture in the T-slot. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is a clamping principle? A. Clamp far from locators B. Clamp with large force on thin sections C. Clamp near the support and resist cutting force without distorting the work D. Clamp against the cutting force only Answer: C. Clamping force should act toward locators and be close to support. (Key point: Clamping) 2. Which jig suits holes on several faces? A. Template jig B. Plate jig C. Leaf jig D. Box (tumble) jig Answer: D. Work is turned over in a box jig. (Key point: Box jig) 3. What is the function of drill bushes? A. To guide the tool; they are made of hardened steel B. To clamp the work C. To locate the part D. To clear chips Answer: A. Fixed, renewable and slip bushes. (Key point: Drill bushes) 4. How is cutter position set in a straddle-milling fixture? A. By tenons B. Set blocks with a feeler gauge of 2-3 mm C. By dial gauge D. By drill bushes Answer: B. The feeler avoids contact; tenons locate the fixture in the T-slot. (Key point: Straddle milling) ## Related in Manufacturing and Production Processes - [Jigs and fixtures: purpose and 3-2-1 principle](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Ajigs-fixtures-purpose-locating-principles) — Manufacturing and Production Processes, chapter 10 - [Milling, shaper and drilling machine operations](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Amilling-shaper-drilling-machines-operations) — Manufacturing and Production Processes, chapter 7 ## Related in other subjects - [Locating principle and design of a drill jig](https://www.bctengineer.com/question.md?key=semester_2%2Fworkshop_technology%3Ajig-locating-principle-design) — Workshop Technology, chapter 12 - [Jigs and fixtures: purpose and differences](https://www.bctengineer.com/question.md?key=semester_2%2Fworkshop_technology%3Ajigs-and-fixtures-purpose-differences) — Workshop Technology, chapter 12 - [Principles of surveying; scales used](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aprinciples-and-scales-used) — Surveying I, chapter 1 - [Main characteristics of 3d transition elements](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3A3d-characteristics) — Engineering Chemistry, chapter 5