Platen Use and Depth of Passes on Wide Belt Sander

[Alan Lightstone]

The other post today about wide-belt sanders reminded me that I wanted to ask about this, but didn't want to hijack his thread.

What is the typical depth of each recurring pass that people use on their wide belt sanders? Mine is a Grizzly G0445 24" Wide Belt, which comes with a 10HP, 3-phase motor. So not a massive industrial beast, but not a featherweight either.

I typically sand 0.01 inch per pass, as I've noted that going much larger (0.03 in) can cause burning on boards.

Also, second question, I really don't use the platen. I think I probably should be. How should this be used, and when? I'm thinking final passes on the project. And what is its real purpose?

And while I'm at it, how about feed rate adjustments? My previous drum sander did this automatically (though not well). On my wide-belt, I've used the setting it came with and haven't adjusted it as its worked well at that feed rate.

[Kris Cook]

Alan - no experience with these machines but have been researching for my own use. This thread has a good explanation of the platen, I believe.

https://sawmillcreek.org/showthread.php?207724-Drum-vs-Wide-Belt-Sanders/page2

[Ron Selzer]

15" wide belt open one side
36-60 can raise 1/2 turn and stay under on amps. can do full width on 36 with one full turn on popular and cherry. amps will be at max
80-120 1/3 - 1/4 turn and maxing amps on 100-120, will make two passes before changing on 120
150 and higher rarely do. two passes every setting and 1/4 or less each time raising
have not taken the time to figure out exactly how much one turn is equal to
platen is down and never changed
not certain why coarse grit takes less amps then fine even though taking twice or more each pass. sure fills the dust bin when running 36
Ron

[Jeff Roltgen]

I was taught to pay close attention to grit size. EG: 180 grit should be maximum .007" per pass, based on the actual size of the particles of grit. Any more, and you will get excessive loading of the abrasive, leading to premature belt wear, poor finish, and even burning as mentioned above. The particles cannot grind off anything larger than themselves.

As for platen use, if you are using coarse 50-80 grit, with more of a thicknessing approach, you want to use just the drum, as the small contact area of the drum will more quickly abrade and grind down more aggressively.
As for the platen, use it for finish sanding, starting at about 120 grit and finer. My planer has helical carbide head, so I almost exclusively use 180 and the platen. This means, plane to ~15 thousandths over thickness, one pass each face at ~.007", and you arrive at a precise thickness with a finish sanded face using minimal passes.

Try this as an illustration: run a sample piece through your sander repeatedly without changing thickness setting. You may be surprised to find how much stock is still being removed, even after 2-3 passes as you check with a set of digital calipers. This generally can indicate whether you are taking off too much in one pass, overdriving the grit size.

.030" per pass is almost certainly overdriving the medium-coarse grits.

*All of the above is done assuming you have a DRO, factory or aftermarket, in order to change thickness setting in these increments.

jeff

[Kevin Jenness]

Here's a good explanation of the basics, including recommended maximum stock removal per pass relative to grit size. https://surfprepsanding.com/the-ultimate-primer-on-single-head-wide-belt-sanding/

If you operate you sander using coarse grits for stock removal, and subsequent grits to remove the high points of the previous grit pass your belts will last longer and you results will be better. Platens are designed to be used on the last pass to lengthen the scratch pattern. The drum contact alone is more aggressive and suited to initial passes. Heavy passes with high grits and dull belts generate a lot of heat, not what you want.

You need to find the balance between stock removal per pass and feed rate to keep the heat down. If you are burning the material you need to clean your belt, change to a new one, take a smaller cut or increase the feed rate.

The maximum stock removed per pass will depend on the grit used, hardness of material, width of stock and power available. 10 hp on a 24" machine is not a lot, but adequate if used correctly.

[Jonathan Jung]

I have this very handy grit removal chart stuck to my wide belt for reference:

https://surfprepsanding.com/wp-content/uploads/2020/05/Wide-Belt-Stock-Removal-Chart-2020-3.pdf

With my SCMI wide belt, I've found the platen not needed at all. In fact, it can leave a scratch pattern of a sine wave, with the oscillation. The finish is very good with the right abrasive at P220 right off the drum, so I never use the platen.

[Dave Cav]

I have this very handy grit removal chart stuck to my wide belt for reference:

https://surfprepsanding.com/wp-content/uploads/2020/05/Wide-Belt-Stock-Removal-Chart-2020-3.pdf



I have a text version of the same chart taped to the door of my widebelt.

More information here: https://www.woodweb.com/knowledge_base/The_Ultimate_Primer_on_Single_Head_Wide_Belt_Sandi .html