Appearance
Deep hole drilling produces 80–95% of removed material as chips — far more than conventional machining. A damaged way cover lets chips and coolant infiltrate the guideways, causing accelerated wear and loss of positioning accuracy. Cover maintenance is accuracy maintenance.
Way Cover Types for Deep Hole Drilling
| Type | Protection Level | Chip Load Capacity | Best For |
|---|---|---|---|
| Telescopic steel | Excellent | High — handles heavy chip impact | BTA drilling, heavy chip loads |
| Bellows / accordion | Good | Low — for fine chips only | Gun drilling, light chip loads |
| Roller blind | Good | Medium | Machines with limited clearance |
| Armoured bellows | Very good | Medium–high | Large machines with extended travel |
Telescopic Steel Covers
The most common choice for deep hole drilling machines. Steel interlocking sections slide over each other as the axis moves.
| Feature | Specification |
|---|---|
| Material | Stainless steel (1.4301 or equivalent) |
| Wipers | Polyurethane or felt, replaceable |
| Slope | 15–30° for chip shedding |
| Travel ratio | Typically 1:5 to 1:8 (cover length : axis travel) |
Bellows Covers
Used where telescopic covers are too heavy or take too much space. Suitable for gun drilling with fine, broken chips.
Warning: Bellows covers are not suitable for BTA applications. Stringy BTA chips catch on bellows folds and tear the fabric. Use telescopic steel covers for any machine producing long or stringy chips.
Common Damage Modes
| Damage Mode | Cause | Detection | Consequence |
|---|---|---|---|
| Dent from chip impact | Large hot chip hits cover | Visual — visible dent | Wiper seal failure, chip ingress |
| Fold tear (bellows) | Stringy chip catches on fold | Visual — fabric tear | Chip ingress through tear |
| Wiper wear | Normal wear, abrasive coolant | Reduced wiper contact | Coolant seepage under cover |
| Cover jamming | Debris between telescopic sections | Axis movement noise, stalling | Axis drive overload |
| Corrosion | Water-based coolant on steel | Rust spots on cover | Structural weakening |
| Guideway scratch | Embedded chip in wiper | Linear scale reading noise | Scored guideway surface |
Inspection and Maintenance
Daily Inspection (Every Shift)
- [ ] Visual check of all way covers for dents, tears, or misalignment
- [ ] Listen for unusual scraping or grinding sounds during axis movement
- [ ] Check wiper condition — should contact the cover surface evenly
- [ ] Remove any visible chips from cover surfaces
Weekly Maintenance
- [ ] Clean between telescopic cover sections with compressed air or coolant spray
- [ ] Inspect wiper edges for wear — replace if torn or hardened
- [ ] Check bellows folds for trapped chips
- [ ] Verify full axis travel is unobstructed
Monthly Maintenance
- [ ] Remove telescopic cover sections (if possible) and clean inside cavity
- [ ] Inspect guideway surface underneath for scoring or wear
- [ ] Lubricate cover sliding surfaces with light oil
- [ ] Check cover mounting brackets for looseness or cracks
Replacement Criteria
| Condition | Action |
|---|---|
| Dent deeper than 2 mm that impairs wiper contact | Replace individual cover section |
| Bellows tear longer than 10 mm | Replace bellows immediately |
| Wiper no longer contacts cover surface | Replace wiper strip |
| Cover jams or sticks during travel | Inspect and clean; replace if damaged |
| Corrosion perforating cover material | Replace affected section |
Extending Way Cover Life
| Strategy | Benefit |
|---|---|
| Install chip deflector shields above cover | Reduces direct chip impact by 50–70% |
| Use stainless steel covers (not painted steel) | Eliminates corrosion from coolant |
| Add secondary wiper at cover entry point | Double seal keeps chips out |
| Maintain positive air pressure inside cover cavity | Prevents coolant ingress through wipers |
| Replace wipers proactively every 12 months | Catastrophic guideway damage is prevented |
FAQ
How often should I replace way covers on a deep hole drilling machine?
With proper maintenance, telescopic steel covers last 5–10 years. Bellows covers last 2–4 years in deep hole drilling applications. Replace when wipers no longer seal effectively.
Can I repair a dented telescopic cover section?
Small dents (under 2 mm deep) can be hammered flat if the cover is removed. Larger dents require section replacement. A dented section that still seals is acceptable temporarily.
What is the cost of replacing way covers?
Telescopic cover set: $2,000–8,000 per axis depending on travel length. Bellows replacement: $500–3,000. Compare this to guideway replacement at $15,000–40,000.
Do way covers affect machine accuracy?
Yes. A cover that jams or drags creates axis loading that affects positioning repeatability. Damaged covers that allow chip ingress cause guideway wear and progressive accuracy loss.
Should I upgrade from bellows to telescopic covers on a BTA machine?
Yes. If a machine with bellows covers is used for BTA drilling, upgrade to telescopic steel covers. The cost ($3,000–8,000) is justified by preventing guideway damage from stringy chips.
Way cover requirements vary by machine model, chip load, and coolant type. Consult the machine manufacturer for cover specifications. This article reflects industry practice as of 2026.