Problems with perpendicular scroll sawing

[oldjohnevans]

I have a 20" DeWalt scroll saw that I like very much. But I am haing problems getting perfectly perpendicular cuts.

1) Testing for perpendicular cuts - Take a block of wood 2 inches thick and cut a short cut. Turn the block over and make another cut in exactly the same place. If when you examine the cut face you can only see one cut your saw is perfectly perpendicular, theoretically.

2) I take a 3/4 inch piece of pine and cut a complex wiggly cut with a #3 blade. The pieces separate perfectly. OK everIything is going great, I think however --

3) In order to cut a "Shape Shifting Jigsaw Puzzle" I have to make 3 critical cuts of a stack of two layers of 3/8th inch Baltic Birch plywood. (see my thread "How to make a Shape Shifting Puzzle" 2nd try with pictures, (by
oldjohnevans) which 66 people read but no one responded to,)
Now I have 4 pieces of plywood. The left hand top piece now fits loosely with the right hand bottom piece, but the right hand top piece is too tight to fit into the left hand bottom piece. This is a real pain in the butt.

It anyone can come up with a solution to this problem I would really appreciate it.

[CanadianScroller]

That is a tough one!
Some dewalts have a slightly concave table, but it sounds like you have checked that out by text cutting the block and flipping it over.
My next thought would be that the feed rate was a little too agressive which would cause the blade to bend slightly.
Since the bottom of the blade will not flex in as much as the top of the blade the fit will be tighter on one piece than the other.
You could try slowing down the feed rate of the wood.
Make sure the stack of wood is tight and does not shift..
I know some people will cringe at the next suggestion..... try a spiral blade.
I was talking to an old timer at a craft show who stack cut much of his stock. he had issues with the blade bowing as he cut until he swiched to spiral blades. I havent tried it yet but it is worth a try.

My last suggestion would be to make a plywood table to slip over the dewalt table. That way you know it is true.

I recently made some zero clearance inserts for my saw, only to find the material I used was too thin. The slight depression left in the center of the table made it impossible to cut annything square.

I hope these suggestions help

[GrayBeard Phil]

John:

Your method for setting the saw table to be perpendicular to the blade may have too much room for error for your specific needs. That method is great and sufficiently accurate for the VAST amount of scroll saw work.

The next level up in accuracy is an engineering square, and a strong light method. Set a small try square up next (just lightly touching) to the back of the blade and shine a strong light from behind and adjust the table so an equal amount of light is shining thru the entire length of the try square. Your needs may require this method of setting the perpendicular. I suggest the following (These links are for example only, I tried to look for examples that would sell to UK residences. )
http://www.dick.biz/eindex.htm and search for: mini square, item 707274

or
http://www.leevalley.com/wood/page.a...01&cat=1,42936
and look at the 2" or 3" precision try square.

(Aside: The try square method depends a lot on the definition and measurement of the saw's table being 'FLAT' and uniform when you make your adjustment. The effect of the table insert may throw your adjustment off. You may have to 1st make your insert flat with the flat table. )

The next level up in precision would be to measure the vertical error of the blade, and try to get the error to be less than say 0.004 inches (less than 0.10 mm) over 3 inches (76 mm) on the blade mounted on the saw. This method can get very expensive for just working with wood. (And we would have a nice long argument with the metrology / precision measurement folks about if any such measurement has any meaning if you undo the blade and re install another in the blade chuck.)

Phil

[jigsue]

In a recent UK woodworking magazine, they tested the scrollsaws sold in UK and the Hegner was the only saw that came out with a straight table, so what Carl and Phil said was probably true. At the International Woodworking Exhibition a couple of weeks ago, I did notice one scrollsaw user with a complete false table on top of the saw's own table. Howver, this would mean having ensure that this false table was exactly flat, too - another engineering feat.

I stack cut quite a few puzzles and, although I test the table and the blade every time, there are occasions where the puzzles pieces are not interchangeable - this is much the same problem as you have, The error is down to a number of reasons and explained above - there are just too many variables for consistent 100% accuracy as I see. My only suggestions would be to cut them one at a time!

Sue

[3_M]

To see that the blade is square with the table is not that hard. Take a piece od 3/4" wood, cut about 1/16" into the wood, then try to put it in the back of the blade. If it fits, you are square to the table.
Very imported is the tension, if not enough, the blade will start cutting with a bevel. The blade should give a nice high ping sound or it should not move side ways more then 1/8".
Do not push too hard into the blade, let the blade do the cutting or the blade will cut with a bevel again. I don't like to slow the speed too much, a blade cuts better with a higher speed. If too low, the blade starts to grab the wood.
Mike

[AC_Scroller]

I had a problem with my 788 not cutting exactly square, and no matter how many times I squared the table to blade I couldn't fix it. I finally figured out that the table wasn't completely flat (convex) so I took it to my Dewalt rep. and they replaced the table under warranty.
Try laying a straight edge across the table; if it rocks at all or has gaps under it at all you may have a table problem. Also, lay your straight edge from front to back of the table for the same test.

Tom

[oldjohnevans]

I think (I hope) I have found the problem. I was using Flying Dutchman two way cut #3 blades. They were tracking a lot to the right. On a hunch I switched blades to a German blade (Make Unknown) Double tooth TPI 24 #3. Like magic I got perfect cuts.

I got these blades from an Intarsia site in Canada that I have had good luck with.
Garnet Hall
Box 1339
Estevan, SK
Canada S4A 2K9

E-mail: intarsia@sawbird.com

http://www.sawbird.com/contacts.htm

[3_M]

The blades Garnet sells are the same as the FD blades.
They come from the same German company.
Mike

[CanadianScroller]

I used Sawbird blades quite some time ago, I didnt know they were the same as yours Mike, Thanks for the info.

[oldjohnevans]

Maybe I am stupid but I cannot find "Home of the FD blades".