scoring cuts on a RAS

[Cooler]

I have a new Freud blade for my table saw and it leaves cuts on plywood that is nearly 100% free of splintering.

I can't say the same for my radial arm saw.  The bottom of the board is clean but the top has some tear out.  I use the RAS mostly to cross cut on solid wood and plywood.  I can't recall ever using it for a rip operation. 

I recently saw a video where the woodworker was making "scoring" cuts on a table saw using a sled.  He made a very shallow cut pulling the stock back instead of pushing it into the blade.  He then raised the blade and made the final cut.  The cut looked very clean.

I am not sure about how safe the process is, however.

And that brings me to my RAS.  I could easily make a scoring cut by setting the depth to a very shallow cut and pushing the blade instead of pulling it.  I could then lower the blade for a full depth cut and finish the cut by pulling it like a normal cut.  

Questions:  

Will this actually work?

Is it advisable?

Is it dangerous?

I don't use a sled on my table saw primarily because I have the RAS and I have a track saw, so I never felt the need for one.  I think I would find it very awkward pulling the stock towards me on the sled.  

Any thoughts?

[jteneyck]

Your problem is indeed odd; I've never heard nor seen of a RAS producing tear out on the top of the board, only the bottom.  The only way I can picture that happening is if you are using it like a sliding miter saw and pushing the saw through the work, back towards the fence which would be incredibly dangerous, too.  

What blade are you using?  Got any photos of the problem?  

John

[Cooler]

Your problem is indeed odd; I've never heard nor seen of a RAS producing tear out on the top of the board, only the bottom.  The only way I can picture that happening is if you are using it like a sliding miter saw and pushing the saw through the work, back towards the fence which would be incredibly dangerous, too.  

What blade are you using?  Got any photos of the problem?  

John

Yes, I have that backwards.  So the scoring cut only makes sense for the table saw or if I make the cut and flip it over on the RAS.  I doubt I would get perfect registration after flipping it so it does not make sense there either.  

Thanks for the reply.

[jteneyck]

Yes, I have that backwards.  So the scoring cut only makes sense for the table saw or if I make the cut and flip it over on the RAS.  I doubt I would get perfect registration after flipping it so it does not make sense there either.  

Thanks for the reply.

So is the problem tearout on the bottom of the board?  If so, put a piece of 1/4" plywood, etc. under the board for critical cuts where you want perfection on both sides.  A HI-ATB blade will inherently give cleaner cuts, too, but the real key is backing up the board on the exist side.  

John

[Bill Wilson]

Theoretically, if you are using a stop block, you could get duplicate registration to make a scoring cut on the bottom, then flip it over and make the through cut, but I don't know if I'd trust it.  John's idea of a sacrificial backer is the best.  Think of it like a zero clearance throat plate in your table saw.

Also might try putting painter's tape on the bottom.  Probably not as good as a sacrificial backer, but may improve your results.

[Cooler]

Thanks for the replies.  A zero clearance panel (1/4" MDF) would be easy.

There are limited selections of blades for the RAS as they have to have a negative hook angle.  Happily the negative hook angle, while cutting slower tends to make a good, clean cut.  

I will try the zero clearance board thing.  I almost never make angle cuts on the RAS so the zero clearance should last a long time.

[Eurekan]

I've used my RAS faithfully for 30+ yrs and there are some other things to consider for your splintered cuts. Are you sure your cutting head (blade) is parallel to the direction of travel? The cutting head swivels and if not locked in place correctly will easily splinter your cut. Make sure the head is locked corectly into position. I've also found different blades give different results. I have one blade that always cuts smoothly but will splinter when returned to the back. With that blade I move the cut piece or stop the blade before return. Is the the board flat? A slightly bowed board will fall into the blade path when cut and easily splinter on the return stroke.

Just some other things to consider.

[BloomingtonMike]

Is the cut line still somewhat zero clearance? That cut should be mostly supported underneath by the table. Time to change the table surface?

[jteneyck]

Thanks for the replies.  A zero clearance panel (1/4" MDF) would be easy.

There are limited selections of blades for the RAS as they have to have a negative hook angle.  Happily the negative hook angle, while cutting slower tends to make a good, clean cut.  

I will try the zero clearance board thing.  I almost never make angle cuts on the RAS so the zero clearance should last a long time.

When I want as close to perfect as possible on every cut I move the sacrificial piece of plywood/MDF/etc. underneath for each cut.   

John

[Pirate]

If you get tear out on top on a ras, I would guess the blade isn't aligned properly, causing the teeth coming up thru the back of the cut, to cut into the side of the cut, already made with the leading edge of the blade. You could make a 12" cut and stop the saw, and see if the tear out in the part of the cut, that has only been cut by leading edge of blade, has tear out.

If you have a powerful enough ras, self feeding without using a neg. hook blade is not that much of a concern. Assuming a sharp blade.