Band saw marks

[dadiOH]

I was surfacing some rough poplar yesterday with my drum sander. The boards had been band sawed from the log and, naturally, they were quite rough and the saw blade marks were obvious. A few passes through the sander and all was nice and smooth but the location of the band saw marks was still evidenced by lighter colored stripes about 1/4" wide and at about 1" intervals across the board. Further sanding and they disappeared but they were at least 1/16" deep.

I should say that once the board was smooth, the stripes differed from adjacent wood only in color...no disruption of wood fibers, I looked with a

10x glass.

I've seen this before but never on anything except poplar and then on only the sap wood, never on heart wood. Anyone have a clue as to what causes it? The only things that come to my mind are heat and/or pressure from the blade but I wouldn;t think that would/could cause the regular interval of the stripes.

[Leon]

Probably not this but is there any sun light hitting the surface, perhaps thought something like shutters or blinds? Poplar will sun fade/ tan in a matter if a few minutes.

[dadiOH]

Nope, no sun. Even it there were, the areas are too regular to be from that; they are definitely related to the band saw blade in some manner. Next time I encounter them I'll take and post pix.

[Leon]

A head scratcher there. I could understand telegraph marks that underlying fibers were changed from the blades but color changes is really strange.

[Dr. Deb]

While I agree with Leon, there is one other possibility. The steel the ban dsaw blade may well have reacted with the popular. All it would take is fo r one tooth to have some trace element in it that reacted with the moisture in the wood to give you the staining you are currently seeing.

Deb

[joeljcarver]

....

Since the marks appear at regular intervals, I would first suspect it has to do with the blade. Maybe changing blades and making some trial cuts could help pin it down.

[Swingman]

Something to do with the blade/or saw setup/ feed rate would also be my guess.

Since the wood was apparently wet when sawed from the log, I would suspect momentary blade friction that heated up the sap in that area with each rotation of the blade just enough to cause a very slight "burn" in those areas as the stock was pushed through the blade.

Perhaps a combination of feed rate and blade friction?

Simply a wild ass guess ...

[dadiOH]

I found a board that hadn't been skinnied down all the way that shows the marks. The board started out about 1 1/8" and has been rough sanded down to a bit more than 7/8", equal amounts from each side so the marks are greater tan 1/16 deep. When I take it down to 3/4 or 13/16, all or most will be gone.

Here's a link to the pix, both same board, one close up...

[Jerry.Osage]

Alas, it appears that we must wait for the definitive answer from the Electric Comet...

[John Grossbohlin]

Another possibility....

Due to the regularity they seem more like marks from a pressure roller than from a saw blade... Any chance something is embedded in the pressure roller on the sander or that the pressure roller is damaged? This symptom would likely be more evident if you are taking heavy sanding "cuts" when you start and taking lighter "cuts" for the final sanding..., i.e., greater pressure roller during the heavy phase.

John

[Electric Comet]

i would bet on heat causing this

the sudden heat application created steam from the water and resin content

the cells burst on expansion

the discoloration came from the resin cooking

[dadiOH]

Nope, not that. If it were, all boards would show them and it should be everywhere, not just on the sap wood.

Good thought though

[dadiOH]

Actually, I'm thinking along the same lines myself.

[Sonny]

Yep. I see it often when the bandsaw bade becomes dull. Its cuts become " wavy" when it gets dull. By wavy, I mean it doesn't cut parallel along the log, so one saw mark is slightly deeper than others.

Once you have different depths of saw marks.... some deeper than others.... the wood weathers at those deeper intervals. IT's the weathered colorat ion you are seeing as different shades of "color".

When a bandsaw blade hits metal, wire or a nail in the wood, the blade goug es the wooddeeper, at intervls of/from the "hit" spot. At those deeper spo ts, albeit small, the wood will weather deeper at those spots and the resul t is the discoloration at those lines of cut across the board. You might n ot think that small of difference depth is significant, but it is. You're witnessing it when you see the shade/color difference.

Do a test yourself: Gouge the surface of a board, with a heavy knife... go uge it fairly deeply, alloy it to weather for a month, then do your regular sanding. Compare the shades of "color".

Weathered coloration can be as deep as 1/8". In gouged or low spots, it wi ll seem deeper.... meaning it IS deeper than an adjacent higher spot.

Sonny

[John Grossbohlin]

It still strikes me as being too regular to be saw related...

Wood hardness variance across the sap/heart wood and across boards could explain the variance you describe...

...or perhaps a power feed is being used on a resaw that has some irregularity that pauses the board with each rotation and causes what amounts to localized case hardening from heat build up.

I hope you figure it out as this is an odd one!