Key Takeaways
- Bar puller: $500–$2,000, mounts in the turret, pulls bar forward one part length per cycle. Zero footprint, but the operator must reload each full-length bar (~every 10–30 parts).
- Bar feeder (magazine): $8,000–$35,000, stands behind the lathe, feeds 3–6 m of bar continuously. Operator loads 10–20 bars per setup and walks away.
- Bar feeders pay off at >100 parts/day from the same bar diameter. Below that, a bar puller and attentive operator often costs less.
- Remnant waste is the hidden cost: a magazine bar feeder ejects a 150–200 mm remnant per bar; a bar puller can use the bar until 50–80 mm remains. On expensive material (titanium, brass), this difference is material.
How Each System Works
Bar Puller
A bar puller is a gripping device mounted in the lathe turret. After parting off a finished part, the turret indexes to the bar puller position, the device grips the bar and the spindle clamps open, and the Z-axis advances the carriage, pulling the bar forward by the next part length. The spindle re-clamps and the cycle repeats.
The entire operation adds 2–5 seconds per cycle. No external power or air is needed beyond what drives the lathe's collet/chuck. The operator must reload the bar manually when it runs out — typically every 10–30 parts depending on part length.
Bar Feeder (Magazine)
A bar feeder stands behind the lathe on its own support stand. It holds a magazine of full-length bars (typically 3–6 m / 10–12 ft). A hydraulic or servo pusher rod pushes the current bar forward through the spindle bore. When the bar is consumed down to the minimum remnant length, the feeder ejects it, loads the next bar, and re-feeds — automatically, without operator intervention.
Bar feeders come in fixed-channel (single diameter) and hydrodynamic or guide-channel varieties. Hydrodynamic (oil bath) feeders dampen bar vibration during high-speed rotation — essential for bars longer than 3× bar diameter when running above 3,000 RPM.
Side-by-Side Comparison
| Parameter | Bar Puller | Magazine Bar Feeder |
|---|---|---|
| Cost | $500–$2,000 | $8,000–$35,000 |
| Installation | Fits in turret pocket | Aligned behind lathe, rigid connection |
| Footprint added | None | 3–6 m behind lathe |
| Automation level | Semi — operator reloads each bar | High — operator loads magazine (10–20 bars), machine runs unattended |
| Ideal volume | <100 parts/day same diameter | >100 parts/day, overnight/lights-out |
| Bar diameter range | One puller per diameter (2–5 min change) | Each bar feeder has min/max bore range |
| Remnant length | 50–80 mm (very low waste) | 150–250 mm (feeder ejects remnant) |
| Vibration at speed | Not applicable | Hydrodynamic feeder required >3,000 RPM |
| Setup change time | 5–10 min to swap diameter inserts | 10–30 min to re-channel or re-guide |
The Remnant Waste Calculation
On a bar feeder, the minimum remnant ejected when the pusher rod bottoms out is typically 150–200 mm. On a bar puller, you can run down to 50–80 mm before the spindle can no longer grip safely.
Example: 3 m stainless 316 bar, 25 mm diameter. Material cost: $12/kg, density 7.9 g/cm³.
- Bar weight: π × 0.0125² × 3.0 × 7,900 = 14.7 kg
- Bar cost: 14.7 × $12 = $176
- Bar feeder remnant (175 mm): 0.175/3.0 × $176 = $10.27 per bar
- Bar puller remnant (65 mm): 0.065/3.0 × $176 = $3.82 per bar
- Difference: $6.45 per bar
Running 20 bars per day: $129/day extra waste with the bar feeder vs puller. On cheap mild steel this is trivial; on expensive materials it adds up to $30,000+/year — larger than the feeder's capital cost. On expensive material with short parts, a bar puller is the economically correct choice even at high volumes.
Which to Choose
| Situation | Best Choice |
|---|---|
| Short runs, many different diameters | Bar puller |
| High-value material (titanium, brass, stainless) | Bar puller (lower remnant waste) |
| High volume, same diameter, unattended overnight | Magazine bar feeder |
| Swiss lathe with guide bushing | Magazine bar feeder (guide bushing requires pusher-fed bar) |
| Large-diameter turning (>80 mm) | Bar puller or manual — feeders often limited to 65–80 mm bore |