Deep hole drilling machines are specialized equipment. When a part fails, you can’t always get a replacement quickly. Having the right spares on hand can mean the difference between hours of downtime and days.
Here’s what I’ve learned about stocking spares.
Critical Spares
These are parts that fail without warning and cause immediate downtime:
| Part | Why It Fails | Cost | Lead Time |
|---|---|---|---|
| Rotating union seal | Wear, normal | $50-$200 | 2-5 days |
| Coolant hose | Burst from pressure cycling | $100-$500 | 1-3 days |
| Guide bushing | Wear, normal | $50-$200 | 1-5 days |
| Spindle drive belt | Fatigue | $100-$300 | 2-5 days |
| Door interlock switch | Coolant contamination | $50-$150 | 2-5 days |
I keep at least one of each of these on hand for every machine.
Consumables
These are parts that are replaced regularly:
- Guide bushings in common sizes
- Coolant filter elements
- Seal kits for rotating unions
- Wiper seals for steady rests
- O-ring kits for coolant connections
I stock these based on usage rate. A machine that runs three shifts needs more stock than a machine that runs one shift.
Long Lead Time Parts
Some parts have long lead times and should be ordered before they fail:
- Spindle bearings (6-12 week lead time)
- Ball screws (4-8 weeks)
- Hydraulic cylinder seals (2-4 weeks)
- Control boards (2-6 weeks)
I order these when the machine is new or during a major rebuild. Having them on the shelf saves months of downtime.
What I Stock
Here’s my recommended spare parts inventory for one mid-size gun drilling machine:
| Item | Quantity | Estimated Cost |
|---|---|---|
| Rotating union seal kit | 2 | $300 |
| Coolant hose set | 1 set | $400 |
| Guide bushings (common sizes) | 3 each | $600 |
| Coolant filter elements | 6 | $500 |
| Door interlock switch | 2 | $200 |
| O-ring assortment | 1 kit | $100 |
| Spindle drive belt | 1 | $200 |
| Total | $2,300 |
For a shop with multiple machines, the total is less than buying for each machine individually. Many parts are common across machines.
Storage
Spare parts need to be stored properly. Seals and O-rings degrade in sunlight and heat. I store elastomeric parts in a cool, dark cabinet.
Guide bushings and bearings are stored in their original packaging until needed. Once opened, they can collect dust and debris.
Key Takeaways
The most important spare part is the rotating union seal. It’s the most common failure on gun drilling machines, and it’s cheap to stock. A $50 seal can prevent $5,000 in lost production time.
I’ve also learned to check the inventory quarterly. Consumables get used and not replaced. A quarterly review catches the gaps before they cause downtime.
Building the Relationship with Suppliers
Having parts on the shelf is only half the solution. I also maintain relationships with suppliers who can ship critical parts overnight when my inventory runs short. I keep a list of part numbers and supplier contacts for every machine in the shop.
For older machines, I check whether the parts are still available from the original builder. Some builders discontinue support for machines after 10-15 years. When I find a part that is going obsolete, I buy several extras while they are still available. I have seen shops unable to run a machine because a $100 sensor was discontinued and no substitute existed without rewiring the control cabinet. For more on parts that commonly fail, see Sealing Technology.
Key Takeaways
- The rotating union seal is the most critical spare — it is the most common failure and costs under $200.
- Stock critical spares: union seals, coolant hoses, guide bushings, drive belts, and interlock switches.
- Order long lead time parts (spindle bearings, ball screws) when the machine is new.
- Store elastomeric parts (seals, O-rings) in a cool, dark cabinet away from sunlight.
- A recommended spare parts inventory for one gun drilling machine costs about $2,300.
- Review inventory quarterly and maintain relationships with suppliers for overnight shipping.