This newsgroup has been a great help to me. I sincerely appreciate the helpful and courteous responses that I have received to my few, but important previous posts.
I remember seeing this addressed in some woodworking magazines in the past. But, I can't remember what the answer is.
So, here is the age-old question. What is the best way to significantly reduce the amount chipping that occurs on the underside of boards when cross cutting with a radial arm saw?
I think that part of it may have to do with the setup of the saw, but the rest of it has to do with the blade that is being used.
Use a sacrificial layer of hardboard (masonite) or plywood on top of the saw table. It's basically the same idea as using a zero-clearance throat plate in a table saw. When the kerf in the hardboard becomes too wide to prevent chip-out, remove it and replace with a new piece.
Attach it using small brads, being very careful to keep the brads out of the path of the blade.
1 - sharp blade (I know it's obvious, but ...)
2 - new table or sacrificial sheet of mdf (my favourite is 4mm) or whatever; I replace my table & fence regularly.
3 - type of sawblade - more & smaller (carbide) teeth = less chipping
4 - speed of cutting
5 - make sure both the sawblade AND the arm are exactly at right angles to the fence. If the arm is at right angles but the blade isn't, chipping at the rear of the sawblade is virtually guaranteed.
5.1 put engineer's square against fence
5.2 check against sawblade for alignment - adjust as necessary
5.3 keeping the engineer's square in contact with one sawtooth, slide the saw forward and backward on the arm - the tooth should not move away from or into the square. Adjust arm as necessary. Return to step 5.2 and repeat the sequence as often as necessary.
5.4 after this the movement of saw and blade are in one plane and it should no longer chip out, both on square AND mitre cuts.
With A RAS it is extremely important that the blade is parallel to the path it travels. No blade will correct this problem if the blade is not aligned properly. After setting the saw up properly you can then consider a better blade if necessary.
The cheapest, most consistent way to stop/reduce chipping is to forcefully apply masking tape and saw in the middle of the tape. Some woods, especially plywood, may still chip a bit when the top layer is cross cut. As Doug M says, you also need a good sacrificial surface and it needs to be changed when the saw groove widens, but that may take a long time depending on what blades you switch between.
You were reading correctly. Negative rake blades reduce chipping. As heretical as it seems, using the saw opposite the way Norm does will also help. Push the blade through the work and chipping, a product of the same motion that produces loss of control evidenced as climbing and self-feeding will be diminished.
Note that the tape goes on top when the saw is pushed, bottom as it is pulled.
Other common problem also gives fuzz and zing when crosscutting solid wood. That's called "heel" in my manual, and Peter alludes to it, though without naming it. This is making sure the blade is parallel to the line of travel along the arm. We use the fence to help verify this, but it's not really a part of the problem.
Before someone jumps on it, POWER OFF. Guard off, and use your carpenter's square with one leg against the fence to set the travel of the blade square to the fence. Pull it along the square as Peter suggests to make sure it's square to the fence. Fingertip, not death grip, because you'd be surprised how much you can push some otherwise accurate saws. Then raise the arm of the square and use, not the arm adjustment, as you did for squaring to the fence, but the head rotation adjustment to get it parallel to the blade of your square. It's ass-backwards of the way you do your tablesaw, by first getting the blade parallel to the miter gage grooves then squaring the miter gage to the blade, but you're doing the same set of operations and for the same reason. It's a two-measure or two-fiddle operation in my experience, since the two are somewhat dependant on one another, so after the first heel adjustment verify square again. Sometimes you'll find yourself a bit off. Sometimes you'll find a lump in your fence that makes the result differ on the right versus left of the blade.
Kids were tough on the old Dewalt at school, so it was a fairly regular adjustment. The Monkey Wards in my basement tends to stay in adjustment even when it goes through a couple of binds and climbs occasionally.
I use laun ply as my heel check for both table and radial. The splinters should be symmetrical if there. One-sided means heeling. Perhaps you could put a metal strip in the table to hold your dial indicator so you'll know how far you're off rather than just knowing you are and to which side.
Just make sure they really _are_ brass and not the brass plated steel that is often sold as "brass" these days. Brass tacks also work and won't damage the blade.
Thank you to all of you posters for your suggestions and recommendations. I can't wait to get my lazy butt out to the shop tomorrow to work on my RAS. Wife gave me three more picture frames she wants made for people for Christmas.
Interesting, I bought my MW in 1973 and the shop teacher at the school where I taught said they had to readjust their radial arm (don't remember if it was a Dewalt or other but heavily built) every time it was used. My MW took a bit of fiddling to set up but it stayed correct.
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