Setup guide

Lathe automatic feeding device installation and debugging skills

This guide covers the mechanical and pneumatic setup of a bar feeder on a sliding-head or fixed-head CNC lathe. It is written for machinists and process engineers who need the first part to come out correct. By the end you will know which alignment checks matter, what pressure to run, and when a fault points to the bar stock rather than the feeder.

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Bar alignmentGuide bush setupPressure tuningFault checks

Lathe automatic feeding device setup on a fully automatic CNC lathe

On this page

1
Key takeaways
2
What the lathe automatic feeding device actually has to do
3
Preparation and mounting checks before power-up
4
Reading the symptoms during debugging
5
When this setup does not fit the job
6
Installation and debugging, step by step
7
Setup values and fault mapping

Quick answers

Key takeaways

Alignment first, pressure secondA feeder that is 0.3 mm off center will still push bar; it will also wear the guide bush and scrap the first part.

Match the bar to the linerLiner bore should sit 0.5–1.0 mm above bar diameter. Bigger gaps let the bar whip and jam.

Push pressure is a range, not a numberMost 20–32 mm bar runs well between 8 and 18 bar, depending on length and material.

Listen on the first 20 partsRattling at the guide bush or a slow chuck close usually means alignment, not the feeder motor.

Short bars need a different setupUnder 1.5 × spindle bore length, use a reduced stroke or a bar-end pusher.

Before you start

What the lathe automatic feeding device actually has to do

A bar feeder only has three jobs: hold the bar on center, push it a fixed distance, and stop when the bar runs out. Everything in the installation procedure exists to protect those three jobs. If the bar is off center by even a fraction of a millimeter, the guide bush takes the load instead of the cutting tool, and the surface finish tells you about it long before the machine alarms.

Sliding-head lathes are less forgiving than fixed-head machines here. The guide bush supports the bar within a few microns, so the feeder needs to deliver the bar with almost no sideways play. On a fixed-head lathe with a collet chuck and a bar puller, the tolerance window is wider, but bar whip over a long run still shows up as taper and chatter.

Most installation problems are mechanical, not electrical. The feeder can be perfectly wired and still fail because the spindle centerline and the feeder centerline do not agree. Check the mechanical side completely before you touch any parameter in the control.

1
Centerline agreementFeeder axis must match spindle axis within 0.05 mm over the first 500 mm.
2
Repeatable strokePusher stop position should repeat within ±0.1 mm part to part.
3
Clean bar endsBurrs and saw marks cause false bar-end signals and jammed pushers.

Preparation

Preparation and mounting checks before power-up

Level the lathe first, then level the feeder against the lathe, not against the floor. A feeder bed that is level in isolation but tilted relative to the spindle will push the bar uphill and wear one side of the liner. Use a machinist level on the guide tube, not on the sheet metal cover.

Check the bar stock before it goes anywhere near the machine. Bars should be straight within 0.5 mm per meter for sliding-head work. Bent stock cannot be fixed by feeder adjustment; it will chatter, and the guide bush will show a bright wear band on one side after a few hours.

Clean the bar ends. A hacksaw burr of 0.2 mm is enough to trip the bar-end sensor early or block the pusher nose. Chamfer or deburr the leading end on a belt sander, and keep the chamfer under 1 mm so it still triggers the sensor correctly.

Confirm the liner and pusher match the bar diameter before mounting. A 20 mm bar in a 24 mm liner has 4 mm of clearance, which is far too much for a sliding-head machine. The correct fit is snug but free: the bar should drop through under its own weight.

Diagnosis

Reading the symptoms during debugging

Noise is the fastest diagnostic tool you have. A rhythmic knock once per revolution usually means the bar is not centered in the guide bush. A continuous rattle at higher spindle speed suggests the liner clearance is too large, so the bar is whipping. Both are alignment or fit problems, not control problems.

Length variation across a batch is a different story. If diameters are good but lengths drift by more than 0.05 mm, look at the pusher stop repeatability and at bar-end condition. A worn pusher nose, or bars cut at an angle, will change where the pusher contacts the bar and shift the stop position.

A feeder that stalls mid-push on one bar but runs fine on the next is almost always bar stock. Check straightness, check for a burr, and check for a step where two bars were joined or where the bar was previously clamped. Feeder parameters rarely drift by themselves between bars.

Limits

When this setup does not fit the job

Short bars are the most common mismatch. If the bar is shorter than roughly 1.5 times the spindle bore length, the feeder cannot support it properly and the pusher has very little to grip. A bar-end pusher or a short-bar attachment is a better answer than trying to tune pressure.

Small diameters behave differently. Below about 6 mm, bars bend instead of push. Reduce push force, use a close-fitting liner, and keep the unsupported length as short as possible. If the job runs thousands of very small parts, a dedicated small-bar feeder will outperform a general-purpose unit.

Heavy or abrasive stock is the other limit. Cast bar, hot-rolled bar with scale, and bars with deep saw marks all abrade the liner and confuse the bar-end sensor. If you must run them, budget for liner replacement and deburr every bar end. On a sliding-head lathe, the guide bush is the part that pays for it.

Finally, feeder setup only controls bar presentation. It cannot fix a worn guide bush, a misaligned spindle, or a tool that is set 0.05 mm off. If the first part is out of tolerance after the feeder checks pass, stop adjusting the feeder and check the machine.

Procedure

Installation and debugging, step by step

1
1. Mount and rough-align the feederBolt the feeder base to the lathe bed or the floor pedestal, leaving the alignment bolts slightly loose. Bring the guide tube close to the spindle, then set centerline height with a dial indicator on the pusher nose. Target 0.05 mm total indicated runout over the first 500 mm of travel. Snug the bolts in a cross pattern, then re-check. If the reading moves more than 0.03 mm after tightening, the base is not sitting flat.
2
2. Fit the liner and pusher for the bar sizeChoose a liner bore 0.5–1.0 mm above the bar diameter. Push the liner in fully and confirm it does not protrude into the spindle bore. Fit the pusher nose and check that it enters the liner without scraping. For bar under 10 mm diameter, use a reduced-clearance liner and lower the push force; small bars buckle rather than push.
3
3. Set the push stroke and bar-end positionSet the stroke so the bar reaches the part-off position with 1–2 mm of material left for the last part. On a sliding-head lathe, leave enough bar in the guide bush that the last part is still fully supported. Set the bar-end sensor to trip when roughly 100 mm of bar remains in the liner, then adjust after the first run. Too early a trip wastes bar; too late a trip sends the pusher into the guide bush.
4
4. Tune push pressure and feed rateStart low. For 20–32 mm aluminium bar, begin around 8–10 bar; for stainless and steel in the same range, 12–18 bar. Watch the pressure gauge during the push. A spike followed by a drop means the bar is binding. If the pusher slips on the bar end, increase pressure in 1 bar steps, but stop if the bar starts to bow. Never solve a jam with more pressure.
5
5. Dry-run the cycle with no cuttingRun 10–20 complete cycles in single block with the spindle stopped or at low speed. Watch the pusher return, listen for rattle at the guide bush, and confirm the chuck or collet closes only after the pusher has fully retracted. Interlock timing errors here cause the classic crash where the collet closes on the pusher.
6
6. Cut the first part and measureMachine one part, measure diameter and length, then machine five more and measure again. On a sliding-head machine, diameter drift across the first ten parts points at guide bush clearance or bar alignment. Adjust the guide bush in small steps, around 0.005–0.01 mm, and re-cut. Record the setting.
7
7. Log the settings and set the alarm limitsWrite down liner size, pusher type, stroke, pressure and bar-end position for that job. Set overload or jam alarms slightly above the normal running pressure, typically 20–30% above the working value. This catches a bent bar early instead of after a guide bush is destroyed.

Reference

Setup values and fault mapping

Use these as starting points, then adjust to the actual bar and machine.

Symptom	Likely cause	Check and fix
Knock once per spindle revolution	Bar off center in guide bush	Re-check feeder centerline, target 0.05 mm
Continuous rattle at speed	Liner clearance too large	Fit liner 0.5–1.0 mm over bar Ø
Pusher slips on bar end	Low pressure or worn pusher nose	Raise pressure 1 bar, replace nose
Length drifts over a batch	Pusher stop repeatability or bar end	Check stop repeat within ±0.1 mm
Bar-end alarm too early	Sensor position or bar burr	Deburr bar, set trip near 100 mm
Jam on one bar only	Bent or stepped bar stock	Straightness within 0.5 mm per meter
Collet closes on pusher	Interlock timing	Retract fully before chuck close

Align first, tune later

Get the feeder centerline within 0.05 mm and the liner fit within 0.5–1.0 mm of the bar diameter before you change a single pressure setting. Most debugging time is spent correcting pressure when the real problem is alignment.

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FAQs

Questions engineers ask

How do I know the feeder is aligned well enough?

Put a dial indicator on the pusher nose and move through the stroke. Total indicated runout over the first 500 mm should stay within 0.05 mm. Then cut ten parts and watch diameter. If diameter holds within the machine's normal tolerance, alignment is good enough for that job.

What push pressure should I start with?

For 20–32 mm aluminium bar, start at 8–10 bar. For stainless and steel in the same range, start at 12–18 bar. Increase in 1 bar steps only if the pusher slips. If the bar bows or the gauge spikes, the problem is a jam, not pressure.

Why does the bar-end alarm trip with bar still in the liner?

Usually a burr or a saw mark at the bar end, or the sensor set too far back. Deburr the bar ends and adjust the trip position so about 100 mm of bar remains. Also check that the pusher nose is not worn short.

Can I run bent bar if the parts are not tight tolerance?

You can, but expect rattle, length variation and faster liner wear. Keep straightness within 0.5 mm per meter for any sliding-head work. On a fixed-head machine with a bar puller, the window is wider but not unlimited.

How often should the liner be replaced?

Inspect whenever the rattle changes or length drift appears. Abrasive stock and heavy scale shorten life quickly. Keep the liner bore within 0.5–1.0 mm of the bar diameter; once wear opens that gap, replace it.

Do feeder settings need to change between materials?

Yes. Aluminium, brass and plastics need lower push pressure than stainless or steel. Bar weight also matters, so a 1 m bar and a 4 m bar of the same diameter do not run at the same pressure. Log the values per job.