Question about radial arm saw and dado

[Dave adamson]

Has anyone used a dado blade on a radial arm saw? If so, would it be safer to push the carriage over the board rather than pull to avoid self feeding of the carriage. I picked up a used arm saw and have only used it a few times with a regular blade.

Thanks in advance for our help.

[Todd Burch]

Intuition says that would work, and it would be my primary choice for a method of cutting, but it's not a good idea if you follow through the process. "The process" being:

1) turn saw on
2) pull saw towards you
3) insert board between fence and 130 MPH spinning blade and micro-align the blade to the cut to the best of your ability
4) push blade through with ease
5) remove board
6) loop back to #2 and repeat process

#3 is the clincher.

Could you turn the saw on between 2 & 3 and and off between 4 & 5 - sure. And if that is how you want to do it - then that is fine. IMO, I would do the turn on/push cut/turn off method. I'm not a fan of upcutting with a dado blade on a RAS.

Do what's right for you. Some people freehand complex curves on a bandsaw - it works for them. You'll never see it documented in a user's guide, though.

Todd

[HANK METZ]

My technique is to do a pull cut as normal, but make the dado width in two or more passes to avoid grab. You can do this in one of two ways; limit the depth of cut or decrease the maximum set width, make multiple passes to final dimension. The issue really stems from the blade design, since far and away the majority of users do it on a tablesaw, sets are optimized for this machine type. It is also advised you use a stack dado set as opposed to an adjustable (wobble) unit.

[phil harold]

Dont use a wobble blade on the pull
damhik

[Jerome Stanek]

What I do is pull the saw out as far as it will go and lock it there slide the piece in start saw and release the lock push though and shut saw off.

[Steve Rozmiarek]

Always pull a RAS through the cut. Also, and a serious qualifier, understand which blades you should use one which saws. A proper chop saw, RAS type of blade is a negative hook, which pushes the material away from the blade slightly. Dado's should be of a proper design to be used on the RAS as well.

RAS's are designed to rest behind the fence in a "safe" zone, while you work in front of the blade to adjust the cut. Most miter cuts are repetitive, and having the carriage out while moving the stock is dangerous. One slipped board that hits the blade, and you have a ruined piece at least, assuming you are like most people and take a shortcut and don't shutoff and wait for a blade in an extended carriage to stop at each cut.

A push cut also reduces your cutoff capacity by several inches, depending on blade diameter, maybe 4-5", a tradeoff that seems a bit silly to me.

[Stephen Cherry]

Plus, the pull (climb) cut is pushing the top layer into the plywood- almost ensuring that there will be no tearout. Can you adjust the preload on the bearings? If you load it up a little, it will be less anxious to self feed.

[Dave Cav]

I used to cut tenons and dados on a RAS for years. I agree, pull cut, control the feed, keep your arm and shoulder stiff and don't let the saw self feed, DON'T push cut, DON'T use a wobble dado. Scoring the stock on the cut line will help control tear out. Using a stop clamped to the fence will help you make very accurate repetitive cuts as long as you keep sawdust and swarf out of the stop block area. A small, well set up DeWalt MBF, 925 or similar saw is perfect for this kind of work.

[Dave adamson]

Thanks for your help. i will try out a Freud 8" D208M Dado later today. looks like it has negative rake.

[Jim Mackell]

In my experience, I pull the saw out, insert the wood in the proper position and then make the first pass as a push cut. From then on the saw can be travelled back and forth as necessary to widen the dado to the marked lines. I've found from experience that a pull cut with dado blades as a first pass has the saw trying to jump at me! Obviously there are as many different opinions as there are users! In a similar manner, if I'm cross cutting heavy stock I'll push the saw into the work as I can control it much easier. My 2 cents for what it's worth.

[Steve Rozmiarek]

Plus, the pull (climb) cut is pushing the top layer into the plywood- almost ensuring that there will be no tearout. Can you adjust the preload on the bearings? If you load it up a little, it will be less anxious to self feed.


Exactly, and a negative hook blade will actually try to back the saw out of the cut, not over it. A weak saw that allows bending at the arm probably contributes more to a saw self feeding than anything.

[Steve Rozmiarek]

Thanks for your help. i will try out a Freud 8" D208M Dado later today. looks like it has negative rake.

Dave, that one sure looks ok. I don't see that it has the chippers filed with a negative hook as well, some do like the Forrest dado king, but it'll work fine. What saw are you using?

[Myk Rian]

If nothing else, make darned sure the table is properly adjusted. Especially front to back.
Any mis-adjustment there will show in the dado depth.

[John Gustafson]

Myk's point is well taken but also there is an issue with arm deflection. Unless you are dealing with one of the old cast Iron machines the arms on most recent RAS
are made of aluminum or worse. What happens is that as the saw head is moved out away from the post, the weight of the head causes the arm to deflect down. The result is a change in depth of cut over the length. It's the nature of the beast, some worse than others.

[jack forsberg]

the negative rake is not generaly what these saw where made to use. Chip limiting tooling would serve you better. the climbing cut is the nature of the saw and it holds the wood to the table and fence. If you push through you are lifting the wood off the table by nature and could get a major kick back if this happens.

the older saws where the heads where so heavy had the mass to overcome the self feeding blades. here is my buddy making fun of the 2" wide dado stack in My wadkin 18" RAS.
http://i927.photobucket.com/albums/ad111/tool613/wadkin/wadkincc008_zps630e36fa.jpg (http://s927.photobucket.com/user/tool613/media/wadkin/wadkincc008_zps630e36fa.jpg.html)

Wadkin also make some scary looking tooling like there trenching head that has a very positive rake and cuts very well do to its chip limiting design. you can see that the body of this cuter by the side nickers limits how much the tooth can take. in the case of this head you have a very clean cut but don't climb


http://i927.photobucket.com/albums/ad111/tool613/wadkin/wadkintrenchinghead025_zpsa748dcaf.jpg (http://s927.photobucket.com/user/tool613/media/wadkin/wadkintrenchinghead025_zpsa748dcaf.jpg.html)


http://i927.photobucket.com/albums/ad111/tool613/wadkin/wadkintrenchinghead028_zpsa8ad7ab4.jpg (http://s927.photobucket.com/user/tool613/media/wadkin/wadkintrenchinghead028_zpsa8ad7ab4.jpg.html)

here it is cutting in a small Delta RAS

https://www.youtube.com/watch?v=qiIYHs-nNTU&list=UUI6jpIs2zjN9DmVvK2ZAWXA&index=2


so really what you want is chip limiting tooling so the tooth rake is made to cut clean but does not let the blade climb

here is a dado stack with positive rake but chip limiting design.
276074

[Dave adamson]

Thanks for he extensive help with this saw. I will definitely use all your advise. I never considered the kickback when pushing saw carriage.
The saw is an 80s sears craftsman 10" RAS. Picked it up for $50.
Used it to cut the top and bottom rail tenons in the fir door I built over the weekend.
Door turned out ok, had some issues with the tongue and groove. could not find router bit tall enough to cut the tongue on the 1.5" thick boards, so i used the dado initially on my cheap Ryobi table saw for this.
Dave
Dave