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Wide Belt Chatter

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Chatter is probably the most common wide belt problem encountered in the field today.  The abrasive is usually where blame is assigned first because our reps don’t charge to come out and inspect the problem.  Machinery techs can charge anywhere from $70 a call to over $200 a call.  Relatively speaking, we are the easy out.  Realistically speaking, if there are at least 15 different causes of chatter, the odds that the belt is going to be the culprit every time are pretty low.  And those odds get even lower when you hear things like “I’m getting it on all the belts”.  In my 20 years I have yet to run into an instance where a customer was buying multiple grits for sanding in sequence, buying multiple belts in each grit, and every single belt chattered as a result of a manufacturing error.  It just doesn’t happen.  So let’s take a step by step look at the questions you should be asking when you encounter a chatter complaint. 

First, you need to see if it’s a multiple head machine.  If it is, you need to isolate which head the chatter is occurring on.  This is achieved by running a test piece through the machine with only one head at a time lowered.  If the first head runs clear, raise it for the next pass and lower the second head and so on until you find the head where the chatter is being created.  If all the contact rolls are run with no chatter, that leaves the platen as the cause on a chatter complaint originating with the belt. 

Chatter is most commonly found on the platen due to improper materials, joints and grits being run there. Platen sanding is by its nature designed to do 10% of the work done to a piece moving through the machine.  It is strictly for finishing grits (normally 150 & finer although some 120 grit is seen) and it’s purpose is to clean up any stray scratches left behind from the intermediate sanding grits prior to putting down stain or sealing.  Platens should be raised on single head machines until the finishing grits are reached in the process sequence and only then lowered.  Platens should be covered in felt (to cushion) and graphite (to reduce heat) and both of these materials should be on a maintenance schedule for replacement. Gouges, raised or flat spots on either of these will telegraph through the belts and onto the work pieces.

KLINGSPOR recommends that all platen sanding on wide belts be done with paper materials made with a #1 joint where possible.  The finish will be finer and the belts less expensive so there’s nothing not to like about that situation for the customer. The tolerance on a #1 joint in paper belts should fall between +/- 1000.  Joints outside this range are out of spec and may indeed be causing chatter. (If, due to machine age, poor maintenance, dust collection or operator experience, cloth needs to be run on the platen sanding step be sure to put a T joint on the belts.  This will help with joint thickness and head off any chatter problems that might ordinarily occur due to the thicker cloth backing.)

Chatter originating on a contact roll is normally found to be a machine issue.  Some of the reasons you may get chatter on a contact roll would be a contact roll that’s too hard (steel) or too aggressive (serrated), contaminated or damaged.  Poor dust collection results in piles of dust that accumulate where the heat is being generated which is between the contact roll/belt/work piece.  Some other causes of chatter can be oscillation mechanisms that are out of adjustment, static electricity buildup, excessive PSI or excessive out-feed hold-down shoe pressure.

I’ll include here the listing out of your Woodworking Reference Guide that involves chatter.  Cut it out and put it in your car.  Tape it to the visor or into your catalog, put it in a briefcase pocket or anywhere else that you can get to it easily and the next time you get a chatter complaint from a customer….refer to it.  Share it with them.  Makes you look helpful, knowledgeable and interested.  All good things if you’re trying to sell him our products.


Chatter Marks

 1.)       Worn bearings or journals on contact roll or idler roll.  Normally shows up as chatter on one side of panel only. Check bearing temperature and listen to bearings with mechanic’s stethoscope if possible. 


 2.)       Sanding pressure too low.  Increase pressure.  Marks normally show up in spots.


 3.)       Contact or idler roll out of balance.  Marks caused by vibration are regularly spaced and clearly defined. Have wheels/rolls checked periodically.  


 4.)       Contact roll too hard. Steel and/or serrated contact rolls should be used for removal applications only.


 5.)       Belt splice defective or incorrect for the application.  Marks are normally narrow,  regularly spaced and clearly defined.  Try a different belt on machine to compare.


 6.)       Machine vibration due to improper anchoring of machine to floor. Regular maintenance should include checking mounting of machinery.


 7.)       Belt tension too low.  Results in belts to contact roll slipping. Increase PSI.


 8.)       Hesitation in feed or drive mechanisms.  Chatter marks are irregularly spaced.  Have machine tech evaluate the mechanism.


 9.)       Grit too fine for application or contact roll. Do not try to dimension with finishing grits and do not use finishing grits on serrated or steel contact rolls.


10.)      Drive belts too tight or too loose. Check V-belts and adjust as needed.


11.)      Abrasive belt too stiff for application. Check for other materials in this grit available in lighter weight backings suitable for belts.


12.)      Glazed conveyor belt. Results in workpiece to belt slipping. Replace or re-surface.


13.)      Hold-down rolls or pressure shoes incorrectly set up. Can cause work piece to move thru machine unevenly. Have machine tech evaluate and adjust as needed.


14.)      Dust build-up on conveyor rollers or underneath conveyor belt. Be sure draw on dust collection is operating at optimum capacity and collection containers, filters etc are clean and regularly emptied.


15.)      Loose motor coupling, guards or cover plates. During routine maintenance check for any loose nuts, bolts, guards or fittings resulting from machine vibration.

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