Grab and Hammer

[Giell]

Recently I have been stack cutting 1/4" BB ply. Things work fine when I stack 2 pieces. When I stack 3 I start having trouble with grab and hammer. If I stack 4 it's not worth trying to cut.

After reading through lots of posts here, I have looked at blade size, tight corners, two handed pressure, blade tension and feed rate. I can think of times when each of these have given me trouble, but I don't think any of them is the problem in this case.

I think my blade isn't clearing the sawdust from the kerf and the buildup causes the blade to grab the work. I decided this must be the problem when I noticed sawdust caked against the side of pieces I removed from the work. I only see this on the 3/4" and 1" stacks.

Does this make sense to anyone else? Can anyone point me to anything else I might be missing?

I'm having trouble believing that my Delta scrollsaw is really limited to 1/2" thick cutting or less.

Thanks in advance.

[Gill]

Hi Giell

Welcome to the forum .

What sort of blades are you using? Some blades are better at clearing swarf than others.

Gill

[Rolf]

I have that problem to some degree when cutting thick wood on my Delta and not on the RBI, same blade, I think it has a lot to do with the front to back blade motion on the Delta causing the blade to bind a bit more when making tight turns. You may also need to wait a few more seconds for the blade to catch up before making a turn.
The blade motion on my Delta is almost 1/8 inch. Virtualy zero on the RBI, the blade motion also has a dramatic effect when using spirals.

[SharonW0111]

You didn't mention what type of blade ( reverse, spiral, two-way ) you are using but are you sure you don't have your blade in upside down? Sometimes this can cause us problems like you mention --heck I once had my blade in backwards. Make sure you have the barbs going down - two way and reverse dont't matter they cut either way. on spirals you can feel the sharp points and be sure they go ddown. This may not be the problem but then again it may be.
Sharon

[CanadianScroller]

Hi Giell, it isn't the saw, I have cut maple between 2 and 3 inches thick on a small Delta before.

Some of the reasons you get grab and hammer when stack cutting:

1. the layers of wood flex and in doing so binds on the blade
2. the wood can shift binding the blade
3. the blade size is too fine for the cut causing sawdust to collect in the gullet

When there are only two pieces of ply the binding motion is limited but every piece we add after that the probability of binding increases two fold.
When you are stack cutting several pieces it is really important to make sure they are well connected.
On a previous post in here...I wish I could remember who's suggestion it was.....Someone mentioned using the sticky dots used for scrap booking.
This is an awesome suggestion because it will limit the sideways movement between the stack of wood which is causing your binding.
You may want to try this.
My next suggestion would be using a skip tooth blade.

Good Luck

[GrayBeard Phil]

Giell:

I also welcome you to the forum, I hope you enjoy your visits.

However:

1- Check to make sure your saw table insert is flat with the rest of the saw table. Use metal straight edge if you can.

2- Make sure your saw blade is as close to exactly 90 degrees to the table. Use small machinist squares if you can.

3- as suggested above, use a skip tooth pattern blade for chip removal. Be aware there are several skip tooth patterns, you will need to try one or two to discover which YOU like best.

Phil

[Giell]

It was the movement between layers

Thank you all for your suggestions.

It turned out to be the movement between layers in the stack. My wife scrapbooks, so I "borrowed" some sticky dots and the grab and hammer magically disappeared.

I used to nail everything together, but after reading some suggestions about taping, I have been doing that. Seems to work OK with 3 layers of 1/8" BB ply. With the thicker wood it doesn't work well at all.

I guess I'll start raiding my wife's scrapbooking supplies or nailing my stacks together again.

[Rolf]

My 1/8 BB plywood has been in my basement for a while, not properly stored so it has developed a slight curvature. I make sure that I line those up when I stack cut to eliminate any gaps.