We caught up with our wide belt technicians, Tony and Chris, to get answers to some of the most common questions they encounter in the field.
Q) What is the ideal tension pressure to run wide belts?
A) Running your wide belt sander with too much or too little tension pressure can cause multiple issues, including tracking problems, belt folding, belt tearing/ripping, joint failure, and more. The proper range for the tension pressure depends on whether your belt is paper, cloth, or Polyester. For paper – 45-55 psi, cloth – 55-65 psi and Polyester – 65-85 psi.
Q) Is there a way to increase the life of the wide belt?
A) Yes! To maximize the life of your belts, make sure, first, to maintain your machine. Then verify that your belts are running at the proper tension, achieving the optimal removal rate, running in the proper grit sequence, that you are using the preferred abrasive material for your application, and that the machine is set to the correct feed rate. All these factors will help to increase the life of the belt.
Q) How much material can be removed in one pass on a wide belt machine?
A) Stock removal varies based on several factors. What grit, or grit paring, you use will make the biggest overall impact on how much material can be removed. Another key aspect is the actual machine, whether single head, 2 head, 3 head, or otherwise.
Wide belts grits are typically paired based on:
1) abrasive plaining (24-40 grit),
2) heavy stock removal (50-80 grit),
3) cutting/surfacing (100-150 grit) and
4) finishing (180-320).
The finishing stage grits, 180-320+ grit, will not remove significant material and should only be used for the final stages and finishing purposes, such as preparing for primer/stain or between coats.
Additional factors that influence how much material will be removed in a single pass include: belt speed, feed speed, machine horsepower and type of sanding head, such as metal roller, rubber roller, platen, orbital discs/pads or brushes.
The best way to determine how much will be removed is to measure the thickness of sample boards before and after running them through as a test.
Q) How many grits can I skip in the sequence?
A) While it might seem like a convenient idea to go from 80 grit to 180 grit to save time, we recommend skipping no more than one grit at a time (i.e. 80, 120, 180, 240 – skip 100, 150, 220). Skipping more than one grit will overwork the finer grains by requiring it to remove a scratch that it’s not designed to remove, thereby leaving a scratch pattern with uneven peaks and deep valleys. This can also result in burning the belt and/or the workpiece, ultimately decreasing the life of the abrasive and leading to a poor finish quality.
Q) What is a segmented platen and what is the benefit of it?
A) A segmented platen is made of small units, like fingers, that work individually along the width of the workpiece to ensure even, proper sanding pressure. The segments are controlled either electronically or pneumatically (air) and are programmed to activate on an as needed basis. A segmented platen is useful for sensitive sanding to prevent break-through, for example with veneer or sealer sanding.
Q) Should sanding be done on a contact drum (or roller) or on the platen?
A) Contact rollers are reserved for surfacing or abrasive plaining, while the platen is designed for finish, or final sanding only. If more than .0004” removal is required, the contact drum/roller is preferred.
Q) What is chatter and what causes it?
A) Likely the most prominent complaint when it comes to wide belt sanding, chatter refers to the faint lines seen across the width of the workpiece, when something is amiss. Chatter can be caused by several factors, and while it’s easy to blame the abrasive, in many cases, it’s the machine. If you have haven’t ever had it happen and suddenly you get it on one head/belt, then it might be the belt, however if you see chatter from every head/belt, then it is likely due to one of many machine issues.
Here are some common areas to check if you’re experiencing chatter:
1) Worn bearings on the contact or idler roller. This typically reveals itself on one side only.
2) Contact roller is too hard (either metal or hard durometer rollers are for stock removal purposes only).
3) Worn or slick conveyor belt. Dress the conveyor or apply a cleaner to remove excess dust/debris.
4) Belt joint is too thick, or improper joint for phase of sanding. Choose the proper joint or ensure that the tape isn’t too thick.
5) Contact roller is out of balance.
6) Belt tension is too low, refer to recommended tensions above.
7) Hold down rollers are not set up properly.
8) If using a multiple head machine, proper grit sequence and stock removal rate should be checked.