Burn from sander/thicknesser

Hi folks. Ive got a Performax sander/thicknesser and i an trying to sand fiddleback eucalypt,but i keep getting burns on the wood. I am doing light & fast passes, using 120 grit , after using 40, then 80 grit. I clean the sandpaper every pass with a rubber block and when or if i get burnt sawdust engrained into the paper, i flex the paper by hand as well as use a steel brush. I notice the burn in is particularly visible on the wild grain areas of the fiddleback eucalypt. Ive wondered about using Oxalic acid perhaps,to get rid of the burn, but i have a feeling a cabinet scraper will unfortunately be the answer. . Any suggestions are welcome



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I also have the same problem with fiddleback and i think it's because the timber is much more dense in the figured areas so it retains heat seeing the fibers are closer. Wild grain fibers can also be considered end grain which burns easier than long along grain. Next time you pass the timber through the sander compare the temperature of the wild and straight grain areas.

I also find i get burn more often when the weather is humid, not sure if that has anything to do with the glue in the sand paper or the timber swelling?!

In situations like this i usually do the rough grits by independent machine and then from 120 onwards use a hand held orbital sander or sand by hand only. It does take much longer but you get a better result with crazy timbers.

You could try passing the timber through in the opposite direction pending the grain won't pull up too much.

A scraper on wild grain sometimes causes pecking and undulations, as the density changes so much in a small areas a scraper digs in more in softer areas. I have machined HSS power hacksaw blades in to scrapers about 20cm wide and in wild grain areas constantly change my direction of travel keeping an eye on pecking and grain lift.

Hope this helps

Dan

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Originally Posted by ChrisHo

Hi folks. Ive got a Performax sander/thicknesser and i an trying to sand fiddleback eucalypt,but i keep getting burns on the wood. I am doing light & fast passes, using 120 grit , after using 40, then 80 grit. I clean the sandpaper every pass with a rubber block and when or if i get burnt sawdust engrained into the paper, i flex the paper by hand as well as use a steel brush. I notice the burn in is particularly visible on the wild grain areas of the fiddleback eucalypt. Ive wondered about using Oxalic acid perhaps,to get rid of the burn, but i have a feeling a cabinet scraper will unfortunately be the answer. . Any suggestions are welcome



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Thanks. Just remembered a tip to dampen the wood before thicknessing. Might also work for sander thicknessing

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I get this a lot with blackwood in the drum sander. A brand new belt seems to be the best solution. I think we all keep belts going longer then we should.

Tendancy to burn varies greatly, some blackwood isnt a problem but some is near impossible. I think the stuff that burns is softer and more resinous.

Also coachwood.

Cheers
Arron

You probably are right there ,regarding hanging onto the belts too long, though even a new 120gt belt didnt take long to burn into the wood. My neighbour mentioned to me he cleans the resin off his sandpaper belts with kerosene, so that might be a way to rejuvenate old belts with resin all over them.

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Originally Posted by WIGdj

In situations like this i usually do the rough grits by independent machine and then from 120 onwards use a hand held orbital sander or sand by hand only. It does take much longer but you get a better result with crazy timbers.

Dan

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I've never worked with Fiddle Back but I have heard it can be a bit difficult to get along with.

I have to agree with Dan, Once you get it flat and smooth, start using a GOOD ROS.

I have a Metarbo with 2 orbit sizes. I would be inclined to work up to say 240 on the large orbit, & then start at 240 again on the small orbit. I particulary like the Metarbo as the large orbit really works fast & the fine orbit is fantastic or finishing off.


Steve

The burns are happening because the finer paper is getting clogged too easily and too quickly.

One solution would be to slow down the sanding speed (this is one reason why I am using a 3 phase motor and a VFD on a sander I am currently constructing) and the other would be to use stronger or more vigorous dust extraction

It would be interesting to know what dust extraction is being used as most machines use 4" outlet which restricts air flows to ~400 cfm more or less irrespective of the DC being used. Uisng 6" duct extraction will pull ~1250 cfm which is more likely to keep the belt clean.

To assist with the run time cleaning of the belt I have often thought about using what is called a push pull system such as is used on Festool ROS.
This could be done by arranging a ~10 mm diam metal pipe at right angles across and just above the belt. The pipe would be plugged at one end and perforated with a line of holes or jets for the section crossing the belt and the other end connected to a compressor. The air jets would be angled so they impact at shallow angle to paper surface and the glanced air flow and loosened dust would be directed immediately into a DC inlet. This would have the effect of keeping the paper cleaner much better than current systems.

Quote:

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Originally Posted by ChrisHo

You probably are right there ,regarding hanging onto the belts too long, though even a new 120gt belt didnt take long to burn into the wood. My neighbour mentioned to me he cleans the resin off his sandpaper belts with kerosene, so that might be a way to rejuvenate old belts with resin all over them.

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I find the best way to clean a belt is with Oven cleaner. Blast them with a water blaster to get the dust out, let dry, use the oven cleaner, then blast again. Works well and comes up clean though if worn out nothing will save them.
I find that if you buy mediocre belts then they will blunten with about an hours use. Top quality abrasives are much better.
If you buy your own rolls and cut your Own belts then you will get much better abrasives and much cheaper belts. The Sandpaper Man sells 25 metre rolls for $75 - out of which you will get 11 or so belts - so even an old stingebag like me doesnt feel the need to keep them going to long.

I dont agree that dust clogging is the sole reason for burning. Bob does raise two important points though - dust extraction needs to be top notch which usually means modifying the machine; and the fundamental problem with drum sanders is that they spin too quickly for the finer grits.

I have a machine like yours and I have a love-hate relationship with it. I've wasted many hours on it, trying to get it to do what it just isnt designed for. I now think of it as a surface treatment. - never as a way to thickness stock. Still, it can do things that no other sandwr can so I stick with it.

All pretty good points

I think you're better thicknessing with a thicknesser and sanding wth the sander

I also wondered whether you might have been taking too much in each pass

but then I had smoke coming out of my dusty from the sander yesterday, dunno why

I neglected to mention i am making solid wood edge trim for 12 & 18 mm plywood,so sanding with a ROS ,could round over the edges. Due to tear out while machining, i am forced to thickness with 40 grit to remove the tear out,then progress to 80, then 120 grit. Thanks so much for the input, fellas! Sone great advice and information.