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Quality Control Troubleshooting Guide
Automatic Screw Machines
It often takes years for a new machinist to learn all of the likely causes for the various quality problems that will arise. These troubleshooting algorithms can help your personnel by giving them the benefit of years of experience at the click of a mouse. Select the Quality Defect in the list below, then follow the links (if applicable) to learn the most likely causes.
Select Quality Defect:
Select the statement that best represents the situation:
- ALL the parts are Too Short.
- SOME of the parts are Too Short.
- ALL the parts are Too Long.
- SOME of the parts are Too Long.
ALL the parts are Too Short
- Check the Stock Stop and readjust if required.
- Check for dull end-working tools which might be pushing the bar back into the collet.
- Check to be sure the Stock Feed Stroke is set to cause enough feed to reach the Stock Stop. Adjust the Stroke or replace the Stock Feed Cam.
- Overfeeding can cause the end of the bar to bounce off the Stock Stop before the collet closes. Adjust the Stock Feed Stroke or replace the Stock Feed Cam if overfeeding is occuring.
- Check for a tool striking the bar end during the Approach portion of the cycle.
- Be sure the correct size Collets, Pushers and Feed Fingers are installed.
- Be sure the bar stock is the correct size.
SOME of the parts are Too Short
- On Multi-spindle machines, take sample parts form each spindle to identify the spindle or spindles that create short parts.
- Check and adjust the Collet gripping pressure on the Spindles identified as required.
- Check that the Collet opens properly during the Feed Portion of the cycle and that it closes fully at the end of the cycle. If not, remove and clean or replace the collet.
- Check that the bar is not rusty, twisted, or bent.
- Check the Feed Fingers to see if they are cracked, worn or broken.
ALL the parts are Too Long
- Check the adjustment of the Stock Stop.
- If a facing tool is used, check the position of the tool.
SOME of the parts are Too Long
- Check for flat spots on the Center Tool Slide cam roller.
- Check for a loose Center Tool Side cam.
Select the statement that best represents the situation:
ALL Parts have the Same Diameter Error
- Identify the tool position that causes the diameter errors.
- Check the tool for sharpness and replace or sharpen as needed.
- Check the Cross Slide positioning at high point and adjust to the correct depth of cut for the position.
- Readjust the Positive Stop screw to achieve the correct amount of stop pressure on the Cross Slide at High Point.
- Be sure the Form tool is not contacting the end working tool at the High Point of the stroke.
- Check that the tool geometry is correct to be sure efficient cutting occurs and the tool does not push the workpiece away during the cut.
SOME Parts have the Same Diameter Error
- Sample Parts from each Spindle to see if a single Spindle position causes the error.
- A single Spindle location creates the diameter errors:
- Check that no chips or debris intermittently come between the Positive Stop Screw and the Compensating Screw on the cross slide during the machining cycles.
- Check the Compensating Screws at the Spindle location for damage or looseness.
- Have maintenance adjust the Compensating Screw for the Spindle Position.
- No single Spindle position causes the diameter errors:
- Be sure the Cross Slide tool of the tool which creates the dimension is not contacting a Drill at the high point of the stroke.
- Check for flat spots on the Cross Slide cam for the tool which creates the dimension.
- Check for a flat spot on the cam roller of the Cross Slide which creates the dimension.
- Check for a loose Cross Slide cam on the Cross Slide that creates the dimension.
- Check for an improperly adjusted Gib on the cross slide.
Select the statement that best represents the situation:
- Chatter Marks CAN be Traced to a Single Tool.
- Chatter Marks CANNOT be Traced to a Single Tool.
- Chatter does NOT appear on ALL parts.
Chatter Marks CAN be Traced to a Single Tool
- Be sure the tool installed is the correct tool.
- Be sure the tool is on-center with the bar stock.
- Check the sharpness and condition of the cutting edge.
- Be sure the tool was honed after sharpening to eliminate a too sharp edge.
- Be sure the tool is firmly mounted to the Tool Holder.
- Be sure the Tool Holder is firmly mounted to the Cross Slide.
- If a drill is the cause of the chatter, rotate the drill 90 degrees in the drill collet.
- Ask maintenance to check the gib adjustment for the cross slide.
- Be sure the correct Cross Slide cam is installed.
- Because vibration can pass through the floor into a machine, check for an external source of the vibration both inside and outside the shop.
Chatter Marks CANNOT be Traced to a Single Tool
- Be sure the correct feed and speed gears are installed for the job.
- Check for a loose Stock Reel Tube.
- Check to be sure the correct size Liner is inside the Stock Reel Tubes to support the bars.
- Check the size and type of bar stock to be sure it is correct.
- Be sure none of the bars of stock are bent.
- Check to be sure the machine is securely mounted to the floor.
- Because vibration can pass through the floor into a machine, check for an external source of the vibration both inside and outside the shop.
Chatter does NOT appear on ALL parts
- Sample each Spindle to locate the Spindle which creates the chatter.
- Be sure the bar of stock is not bent or is the incorrect size.
- Be sure the Stock Reel Tube is secure.
- Be sure the bar is fully supported along its length inside the Stock Reel Tube.
- Check to be sure the correct size Pusher Spool is installed in the Pusher.
- Check the Collet tension to be sure the bar is properly gripped.
- Check the collet jaws and their operation, and remove clean and or replace collet as required.
- Check the collet chucking components for worn or broken devices.
- Ask maintenance to check for a bad Spindle bearing or cracked Collet Seat.
- Check for a dull, burned or chipped cutting edge.
- Be sure the coolant is reaching the cutting edge during the cutting cycle to remove chips and heat.
- Be sure the tool is on-center with the bar stock.
- Be sure the finishing tool is not required to remove more material than it is designed to handle.
- Be sure the correct speed and feed gears are installed.
- Check to see that the correct Cross Slide cam is installed.
- Check for flat spots on the cam roller.
- Be sure the drill is the correct size diameter.
- Check to be sure the drill is sharp.
- Check for a bent drill.
- Inspect the length of the cutting edges at the drill point to be sure they are the same.
- Check to be sure the Cross Slide tool is not contacting the drill at high point.
- Check to be sure the Drill Holder is securely mounted to the Tool Slide.
- Be sure the Drill Holder is on the centerline of the Spindle.
- All Parts have Same Depth Problem:
- Reset the Drill position in Drill Holder at high point.
- Reset the Positive Stop tension on the Center Tool Slide.
- NOT All Parts have Same Depth Problem:
- Take samples to isolate the problem spindle.
- Check Collet Tension to be sure bar is not being pushed into Collet by drill.
- Check drill sharpness to eliminate pushing of bar.
- Be sure the drills which precede the Final Drill are of the correct size.
- Check to be sure the Final Drill is not dull or burned.
- Be sure coolant reaches the drill point and into the hole during drilling.
- Check the drill to be sure it is not bent.
- Be sure the Drill Collet is clean and properly aligns the drill with the centerline of the hole.
- If chips are not being removed easily during the drilling cycle, replace the drill with a coolant hole drill or chip breaker drill.
- Check the Spot Drill for dull, worn or broken edges.
- Be sure the Drill Collet Nut is secure.
- Check the Drill Holder and Drill Collet to be sure it is not cracked, broken, or has burrs.
- Check the Drill Holder Seat to see if it is broken.
- Check the alignment of the Drill Holder on the tool slide to be sure it is properly aligned with the Drill Saddle.
- Check the Drill Saddle to be sure it is properly aligned with the centerline of the Spindle.
- Make sure the drill does not contact the part during the Approach portion of the cycle.
- Check to be sure a Cross Slide tool is not dull or damaged and is pushing the part during machining.
- Check the Positive Stop tension of the Center Tool Slide to be sure it is properly set.
- Be sure the Cutoff Tool is not dull, damaged or incorrectly mounted.
- Be sure the Cutoff Tool is not above center (tip) or below center (burr).
- Check to be sure the correct type of Cutoff Tool is being used.
- Check the stroke of the Cutoff Tool Slide to be sure it completes the Cutoff.
- Check the timing of the Pickoff Attachment to be sure it does not begin to retract before cutoff has been completed.
- Be sure the Pickoff Attachment is securely holding the part during Cutoff and Back Machining.
- Check the Back Machining Tool to be sure it is sharp and properly aligned with the part during the Back Machining portion of the cycle.
- Check the Pickoff Collet to be sure it is properly aligned with the Spindle centerline.
- Diameter or Pitch of Threads:
- Check to be sure the tap is the correct diameter and thread pitch.
- Be sure the drilled hole is not oversize.
- Damaged Threads:
- Make sure the tap is sharp and coolant is reaching into the hole to clear chips during the cycle.
- If a floating holder is used, make sure the proper amount of float occurs and that the holder is properly aligned with the workpiece.
- Make sure the Trip Dogs cause the speed change to occur soon enough to allow the tap to back out of the hole before the Tool Slide retracts.
- Make sure the Start Spring cushions the force of the Kicker Cam when the tap first enters the hole.
- Be sure the Kicker Cam only applies pressure to start the tap into the hole.
- Be sure the clutch controlling the tapping spindle is reset to the correct speed before the tap begins each new cycle.
- Make sure the Auxiliary Slide on which the tapping attachment is mounted moves freely during the complete tap cycle.
- Make sure the threading spindle on the attachment is rotating freely.
- Tap is Broken:
- Make sure both the depth and diameter of the hole are correct before tapping begins.
- Check the timing of the speed change causing the tap to back out of the hole to make sure the tap does not bottom-out.
- Make sure coolant is washing the chips clear as the cycle is performed.
- Make sure the clutch controlling the tapping spindle is reset to the correct speed before the tap begins each new cycle.
- Make sure the slide on which the tapping attachment is mounted moves freely during the complete tap cycle.
- Make sure the Return Spring is attached to pull the attachment away from the work spindles after tapping is completed.
- Diameter or Pitch of Threads:
- Check to be sure a matched set of Chasers are installed in the Die Head.
- If the Chasers are preset, make sure they are correctly set and firmly mounted.
- Be sure the diameter of the piece is correct before threading.
- Be sure the Chasers are mounted in the correct numerical order in the Die Head.
- Make sure the Die Head is fully closed before threading begins.
- Damaged Threads:
- Make sure the Chasers are not chipped or broken, or are dull.
- Be sure the diameter of the workpiece is correct before threading.
- Be sure the Die Head is properly mounted and aligned with the workpiece.
- Be sure the Chasers are mounted in the correct numerical order in the Die Head.
- Make sure the Start Spring cushions the force of the Kicker Cam when the Die Head first contacts the workpiece.
- Be sure the Kicker Cam only applies pressure to start the Die Head.
- Be sure the Yoke, or other opening mechanism, opens the Die Head before the Return Stroke begins.
- Make sure the Auxiliary Slide on which the Die Head attachment is mounted moves freely during the complete cycle.
- Make sure the threading spindle on the attachment is rotating freely.
- Diameter or Pitch of Threads:
- Check to be sure a matched set of Thread Rolls of the proper specification are mounted in the correct arms in the Roll Head.
- Be sure the Roll positions are properly matched by looking at their alignment markings.
- Be sure the diameter of the piece is correct before rolling the thread.
- Make sure the Positive Stop tension is properly set on the cross slide.
- Check the distance between the rolls to be sure it is correct for the thread being rolled.
- Check the vertical alignment of the Roll Pins in each arm.
- Make sure the Rolls stop at the centerline of the piece and dwell for the correct time.
- Damaged Thread Rolls:
- Be sure the diameter of the workpiece is correct before threading.
- Be sure the Thread Rolls are properly matched and positioned in the head.
- Be sure the Roll Head is properly mounted and aligned with the workpiece horizontally and vertically.
- Check the vertical alignment of the Roll Pins in each arm.
- Make sure the correct Thread Roll cam is mounted and properly secured.