Help please - concave cut

[SteveK Senior Member Find all posts View Profile Close SteveK]

I was trying today to cut the puzzle. Box from this month's magazine. The wood was 2"x3"x3" zebra wood. I was using a FD #5 (new) in my DW788.

In cutting the two 2" thick sides the cuts came out concave.

Was I pushing too hard? I didn't think so. Should I have been using a different blade?

Advice please.

[oily IM BACK SORTA Find all posts View Profile Close oily]

Sound like you may have been feeding a little fast and some side pressure.
Watch your blade if it still cuts a little way when you stop feeding you are pushing. Zebra wood is tough stuff and 2" is a chunk that won't hurry.
I wouldn't be afraid of a #5 on that piece.

[3_M Senior Member Find all posts View Profile Close 3_M]

Oily is right.
Have good tension, the blade should not move sideways more than 1/8". have good speed and very slow feed rate in tick wood like that.
FD Mike

[SteveK Senior Member Find all posts View Profile Close SteveK]

Thanks, I will try to proceed. Since these were the outside cuts I could sand it flat.

[DWSudekum Senior Member Find all posts View Profile Close DWSudekum]

There are several reasons for the concave cut. One you probably are forcing the cut a bit and two when scroll saw blades are made they a lot of time have a lip on the backside of the blade this can cause that problem. One of the solutions is to remove the lip on the back side of the blade using a diamond file. Another way is to use a spiral blade that seems to cut thick woods correctly, it is harder to control but will cut straight up and down.

DW

[sawdustus Senior Member Find all posts View Profile Close sawdustus]

Tough to cut zebra wood in any thickness let alone 2". Give it as much tensions as you can without snapping the blade, use a moderate speed to avoid heat buildup, and let the blade do the cutting using the least possible pressure from you. It will increase your cutting time but will be worth it. If you don't mind sanding off fuzzies on the underside, try using a thick wood blade which is designed with only 7 or 8 tpi and rake (a wider kerf than normal) to help clear the chips.

george

[Rolf The WoodMeister Find all posts View Profile Close Rolf]

As you see on the mag cover there are several boxes. The main reason for that was each one I cut had me tweaking the saw a bit more until it was perfect. I found that I was pushing a bit hard and slightly sideways along with my blade being out of perpendicular just a tad.

[handibunny Carole Find all posts View Profile Close handibunny]

There seems to be a prejudice against using the larger blades, but the FD-R #12 is my go-to blade for really hard wood. The #9, R or UR also works really well.

That said, zebra wood is a really tough wood to cut, and 2" is punishing. However, with a really sharp blade and patience to let the blade do the cutting, it should be possible to get a near-vertical cut. Once the blade goes off, however, I've found it impossible to correct--it just gets bent to the shape of the cut. You can tell how you did when it exits the wood.

Thank goodness for sanders!

[Rolf The WoodMeister Find all posts View Profile Close Rolf]

Carole, you know I always go for a smaller than normal blade but for this I actually used a bigger PGT 5 and on one I used a PGT 7 (Olson) I would preffer not to have any reverse teeth for thick wood.
The price you pay for a bigger blade is a bigger kerf and a sloppy puzzle. I cut one of them with a FD Polar blade (#5), that worked well also.

[SteveK Senior Member Find all posts View Profile Close SteveK]

Well thanks for the advice. I tried several different #5 blades (FD, Pegas, Olsen) all were very difficult in the scrap of 2"+ Zebra wood. Then I tried an Olsen #407 thick wood blade. That worked though ran hot. Added clear packing tape which reduced burning. One time I thought I had set wood on fire.

Finished puzzle with 407. It worked though as Rolf said sloppy puzzle.

I will try again with less difficult wood.

Again, thanks.
Steve