Help with Blade size for wood thicknesses.

[NLAlston]

 

Yesterday, I applied myself to scroll cutting more of the 'Christ with thorns' portrait patterns'.  I had done two, before, with one of my sisters getting one.  She liked it so much that she wanted two more, as gifts to her two children.  I'm not a seasoned scroll sawer, and (largely because of the number of internal cuts) I thought it would be nice to batch cut the portraits.  So, I secured three pieces of 16"x12"x 1/4"  plywood together, and began with the project (the third one was supposed to be a gift for someone else).

 

I encountered two problems.  The first one could be remedied by the use of a 'sacrificial' bottom board, for what is resulted from the cutting characteristics of the blade, on that bottom piece.  Had I used one, on this project, the stock thickness would have been raised another 1/4" - giving me a 1" total to push through the blade.  

 

Now, the blade I was using is the Olsen #4 Spiral blade, and I had never broken a blade before - not until this project.  I actually broke 4-5 blades and, for those that hadn't suffered breakage, they (more than a few times) kept slipping out of the lower blade holder.   I had read, somewhere, that it wasn't good to really torque down on the blade holders, so I had always just gave them good tightening.  But, I wonder if (just maybe) I was using the wrong size blade for the thickness of that project.

 

I've bought all of my blades locally (Rockler), and they have only stocked the Olson #4 Spiral blades (as far as I've known).  I've been hearing great things about the Pegas blades, and think that I am going to make them my supplier.  But I would really appreciate it if someone could enlighten me as to what number Spiral blade I would need for cutting thicker stock (3/4" & 1").

 

As always, your input would be greatly appreciated.

[NLAlston]

I also wonder if my issue has more to do with tensioning, as opposed to anything else.  At the Pegas website I ran across some info which put the #7 Spiral blade as a worthy candidate for 3/4" (and even somewhat greater) thicknesses of plywood stock.  But, it just may be that there are two elements - tensioning, and speed - which may need addressing.  Trial and error episodes, I guess, just may be of the order. 

[NLAlston]

By the way, my scroll saw is the Dewalt 788, and the blade tensioning position had been set at the 3.5 setting. 

[SCROLLSAW703]

First & foremost, imo, ditch the plywood! Get yourself some good 1/4" baltic birch ply. It will be easier on your blades, and less headaches for you, especially when it comes to your inside cuts. Next, put the spiral blades on the back burner for right now, & invest in some #1, #3, & #4 polar blades, ultra reverse, & skip tooth blades. If you have plans of going the route of stack cutting, and if your experience is limited to this point, I would use two pieces of baltic birch with a 1/4" backer. In this particular case, I would use #3 polar blades for the good percentage of the project, and #1 polar blades for your tight inside cuts. The reason I personally recommend polar blades is because they leave a clean cut, and are easy to maneuver around sharp corners & tight turns, & leave a look like no other.  Make sure you drill entry holes through your stack and into your backer. Some forget that!

The next thing I would be concerned with is your blade speed. The breed of your saw makes no difference. They are all designed to the same thing. Remember, you are cutting 1/4" baltic birch, which is a far better quality material than plywood. And the faster your blade speed, the faster you're going to destroy your project. So easy does it. I'd start out between 1/2 & 3/4 on your variable speed until you get used to the blade and how it handles. Then, if you feel comfortable, speed up a little.

Last but not least, your blade slippage. DO NOT OVER TIGHTEN! That doesn't accomplish anything! Take your thumb screw out of the blade holder & look at the blade side. I'm willing to bet it's goin' to be smooth as a baby's butt! To fix that issue, get yourself a 4" x 4" piece of 100 grit sand paper, and take that thumb screw and rub it over your sandpaper. What this does is rough up the holding part of the thumb screw. I would touch up your top blade holder, too. This should solve part of your issue. Do not over tension! That could be part of why you're breaking blades. Your blade should have just a high "ting" sound when it's plenty tight. Stop there! But continue to check your tension until you change out the blade. You can go to woodenteddybear.com and order all sizes of flying Dutchman & Olson blades. My apologies for the length, but hope it helps you. Sawdust.

Edited August 10, 2018 by SCROLLSAW703

[kmmcrafts]

I've never used 1/4 plywood for portrait work..  I usually use 1/8" Baltic birch plywood.. much stronger and higher quality than a normal plywood.. with 1/8" you can stack cut 4-5 boards together at one time.. I've never used a spiral blade any larger than a #3.. and that is pretty rare.. Typically use a #0/1 or a #1 .. I mostly use flat blades but will use spirals from time to time.. 

I like Flying Dutchman spiral blades.. usually the "New Spirals" I bought a sample of Pegas spirals.. I do like Pegas blades.. I think Pegas blades run on the small side from the other blades I've used n spinals anyway.. Most online places that sells blades have a recommended usage description.. also a size chart for each size blade to get an idea.. not all brands and styles of blades use the same size by number configuration.. so a #4 Olsen blade will most likely be a different size blade that a #4 Pegas or other brand / style.. blade...

Making portraits from 1/8 BB ply and then adding a 1/8 backer still allows the portraits to still fit in many picture frames.. You can paint the backers if using the same wood.. or use a regular 1/8 plywood from a contrasting color.. if the piece isn't too fragile.. you can also use a foam sheet or colored paper to ad color to the background of the picture..  

[heppnerguy]

My opinion is 1 inch of wood is pushing things pretty hard, especially for a beginning scroller. I would back off to 2 sheets macs and enjoy the cutting without the struggles you will be putting in front of you with that many layers. The saw can handle that much OK but for you,  I think I would not try to cut them as discribed

Dick

heppnerguy