wide belt burn

[Mike Hollingsworth]

I got a burn spot on my wide belt today and couldn't find that rubber thingy to clean the belt. Found that if I ran some lumber cross grain it would clean it right up.

[Jim Andrew]

That is interesting. How did you burn it. I was warned to not try sanding 3/4" wide pieces with mine, because it would burn a strip.

[Mike Hollingsworth]

rarely happens on my wide belt. Thought it might be of more interest to those with drum sanders.

[Ira Matheny]

Mike,
I sand a lot of Western Maple on my 37" x 60" Lobo wide belt. I frequently burnt belts. Then I learned the following system would reduce the burn problem by about 90%.

I always start at the roughest grit necessary to get to the thickness desired.
First pass thru the sander is at a level that removes very little surface.
Second pass is a cutting pass, but I index the lumber at about 20 degrees off straight. I then adjust the cut to a new level, usually about 0.0025 to 0.0015 of cut. I then send the lumber thru again, this time 20 degrees off straight to the opposite direction. Then, without adjusting the cut level, I send the wood thru straight. Some times I send it thru several time at the same setting.

I tend to start with a 50 grit on rough sawn lumber, or 120 grit on S4S lumber, progressing to a maximum of 180 grit. I use this same system with each grit. The finer the grit, the smaller the changes to the cut. Each machine and each different wood may benefit from a different sequence and amount of changes to the cutting/sanding levels

I find the following results: [1] no burning of the lumber [or at least a great deal less] [2] better and quicker sanding, [3] significantly less burning of the belt and therefore, significantly longer belt life.

When I do get a burn on a belt, I attack the burn with my pressure washer. I usually can clean it off the burn with a few minutes of careful pressure washing.

Ira

[Kevin Jenness]

Mike, that is an interesting method. I have seen people use a crepe rubber eraser to clean a wide belt while it was running, but the risk of having the machine grab it and possibly a hand incline me more toward cleaning the belts off the machine. We use Renuzit, a scrub brush and water rinse to extend the belt life considerably unless the burns are severe in which case it's not worth the effort. We find the fine belts (we usually stop at 150-180) tend to develop some chatter from the process, so stick to cleaning the rougher belts used for stock removal.

Ira, are your figures correct? .002" seems like a very light cut indeed. With an 18 hp motor I would be taking off more like .015" at 50#.

There is a very useful discussion of wide belt sanding procedures here: http://surfprepsanding.com/2014/02/28/the-ultimate-primer-on-single-head-wide-belt-sanding-2/

[Mike Hollingsworth]

Mike,
I sand a lot of Western Maple on my 37" x 60" Lobo wide belt. I frequently burnt belts.
Ira

Western Maple was the culprit here also.

[J.R. Rutter]

Are you guys using cloth belts?

[Mike Hollingsworth]

I do use cloth belts, but I've never thought of giving them a bath.

[Kevin Jenness]

Sorry, the stuff we use is actually called Reuzit. I gather some people use Simple Green and other products in the same fashion.

[Martin Wasner]

If you're burning, you're removing too much material, moving too slowly, or the belt is shot. Depending on the feet per minute of the head, some machines are just hard on abrasives. The second head in my widebelt runs 180g and has a platen in it, it is moving at 4800 ft/min, and it's just plain hard on abrasives.

Kicking everything you can at an angle is important to for a few reasons.
1. Less load on the motor. Not a big deal if you are running a narrow pieces at random intervals, but when you have something that's 70% of the belt width hitting all at once, it creates a spike in the load.
2. Running long material at the same spot on the drum or platen, (or both), will create a hot spot. Heat kills belts. It will also make the belt more prone to loading which will cause more heat.
3. You're using more surface area of the belt, for more even wear of the abrasive.




I've pressure washed belts when I've loaded them up removing paint, but it's never gone well for me.

[Ira Matheny]

WOOPS. Got the decimal point in the wrong spot. I usually take 0.015 to 0.025 on each subsequent pass. Once I have is done, I end with several 0.002 passes. Give a good final product.
And yes. Western Maple is undoubtedly a major contributor to burning belts.

Indexing any wood to 15-20 degrees will help several issues. Belts run coolers. Evens the wear on the belt and the platen. Make the sanding marks much less pronounced when moving to next finer belt, therefore fewer passes required.

[J.R. Rutter]

And grit matters a lot, of course. Taking too heavy a pass with too fine a grit is the #1 reason for burning, IME.

https://lh4.googleusercontent.com/-EdI1YNWLwoc/USvBW-KJ__I/AAAAAAAACYI/E4jnls6OmLY/s865/scratch%2520depth.png

[Martin Wasner]

And grit matters a lot, of course. Taking too heavy a pass with too fine a grit is the #1 reason for burning, IME.

https://lh4.googleusercontent.com/-EdI1YNWLwoc/USvBW-KJ__I/AAAAAAAACYI/E4jnls6OmLY/s865/scratch%2520depth.png

Wish I could remember how the tech set up the heads and platen on my widebelt. I go from 13/16" to .788 in one pass, then to 0.760 on the next using 120 grit on the first head and 180 grit on the second.

[Kevin Jenness]

Martin,

That must work for you, but it's very different from the way we run the single head Sandingmaster I am familiar with.If your figures are correct you are taking .024" with 120# and following with a.028" pass at 180#. That is far more than I would ever take with either grit- I max out at about .012" for 120# and .004" at 180#. Why are you removing so much material at the sander? We run an SCMI 20" planer with onboard grinder which gives very clean cuts with all but highly figured woods, and for general use I plane to .030" over final thickness, then sand off .010" on each face with 100# to make sure of removing the occasional snipe or tearout and .005" with 150" to remove the 100# scratches. Once milling or assembly defects are removed with a coarse belt there is no reason to do more than refine the scratch pattern with subsequent grits. There is a good table here http://surfprepsanding.com/2014/02/2...elt-sanding-2/ (http://surfprepsanding.com/2014/02/28/the-ultimate-primer-on-single-head-wide-belt-sanding-2/)giving maximum recommended cuts with various grits as well as the minimum cut to get down below the scratches from earlier grits. Not saying your method is wrong, but it differs a lot from the way I have learned to run our machine. How much power do you have to work with on each head? What sort of belts are you using, and how much life do you get from them?

[Barry Richardson]

You may all be aware of this, but I will throw it out there anyhow. On a Timesaver (not sure about others) There is a height adjustable bar across the front. You can adjust it so the board just fits under at the optimum sanding height, if the bed is raised too high which would result in too aggressive of a pass, the board wont fit. We reduced our burning problems to almost zero after we figured this out...

[Martin Wasner]

Why are you removing so much material at the sander?

I get material at 13/16", I want the doors to finish a bit over 3/4" One pass per face, boom. Done.



How much power do you have to work with on each head?

25hp on the first head, 20hp on the second. It's a 43" I kinda wish I would've upped the power a bit more. Running full width table tops, once they are knocked flat with courser grits, I can take a max of about .015" before she is really hammering the amperage meter. Even then, you kind of alternate. .010 on one pass, .015 on the next, .010 next, etc.



What sort of belts are you using, and how much life do you get from them?

I use the 3M cloth backed purple belts. About 8-10 hours of run time. Depends on what is being sanded.



I'm running it the way the factory told me to. I was planning on using it with 80/120 on a first pass per face, then swapping the belts out to 150/180 for a second pass per face. Basically they told me that was dumb. lol The reason I can hog as much as I can has to do with a few things. I'm running the medium length belts, 75" which run cooler though I should've sprung for the longer 102"? belts, and the abrasives run at a ridiculous rate of speed. The first head is something like 3800 feet per minute, the second is pushing 5000 feet per minute. My old widebelt, which was a Timesavers "Speed Sander", the belt traveled around 2500 fpm I'm told. If I were to switch to paper backed abrasives, it'd leave a finer finish sand, but the belts would have less than half of the life that I'm currently getting.

When I'm doing drawer parts, they get planed to 11/16", and a 1/32" gets sanded off per pass. Factory said no problem, and I'm happy with the speed and results.

[Kevin Jenness]

I see now what you are doing. I thought from your earlier post that you were going from .812" to .760" in one pass, whereas you are actually taking two passes at about .026" each. With two heads at 25 and 20 hp that makes sense- with only 18hp on our single head unit we are much more restricted on stock removal. I still wonder if you are actually set up to take more material off with the second head than the first, and if so what is the rationale. By the way, we are using the same belts; they give the least amount of chatter of the belts we have tried with reasonable longevity. Thanks for responding.

[J.R. Rutter]

It is good to read what other people are running.

I have a lighter duty 44" x 75" 2-head that shares a 30 HP motor for both heads. 3150 FPM abrasive speed, and 15 FPM feed speed. It is set up with 120/180 paper belts (or 220 2nd head, depending on customer) and goes from 0.860" to 0.812" in two passes (one per side). I set it up to take more with the first head (steel drum). The second head (45 shore) is set to just remove the scratches from the 120 grit completely. I have a 2" wide platen as well, but find that the shorter scratch pattern from the rubber drum is easier to random orbit. We tried cloth and paper belts and found that for us, the paper lasts almost as long and is cheaper overall for a better finish. The second head has an oscillating blower to keep the abrasive clean, so that helps. We have never torn a belt in the 5-6 years that we've had it. Of course, cabinet doors are an easier load than slabs, and I keep some coarse cloth belts for leveling big glue-ups before finish sanding.

[Martin Wasner]

Horsepower is huge in a widebelt, you almost can't have too much. My feed rate is 21.5 feet per minute typically.