V5.4 - RAS-choose the best blade

More of our on-going discussion about the Radial Arm Saw… Let’s see, where were we?... oh yes, we ended up talking about Positive and Negative blade hook angles.

My best description of how to check a sawblade’s hook angle was the ‘intersecting line method’ that I outlined last week. My second-most used visual to help understand this is that of a swimmer’s hand. If the hand is scooping the water, he is using a ‘positive hook angle’, but if the hand is laid back and just slapping water, it is a ‘negative hook angle’ effect. The swimmer won’t go anywhere using a ‘negative hook’ hand angle, but such is not the case with a spinning sawblade. It still cuts just fine when a negative hook angle is used, but because it is not digging or scooping, the operator has maximum control over the head and blade.

High-speed steel sawblades (those without carbide tips) are not really described in terms of ‘hook angles’ because a HSS blade truly cuts through the wood, whereas a carbide-tipped blade ‘scrapes’ its way thru.

Years ago, on any saw where the blade was suspended over the workpiece (ex: a miter saw; Delta’s “Sawbuck”, a sliding miter saw, or even a sliding compound miter saw) one would never see any blade on it, other than a negative hook. For some reason, that has changed. Now, one might see a 12 to 15degree positive hook blade installed on one of these saws, right out of the factory. While I am not going to speculate as to why the manufacturer’s decided that they could do this, I will say that I, personally, am not comfortable with it. As I told about in my example of testing, a negative hook blade offers the user so much more control over the sliding head, that to use any positive hook blade just invites ‘climb-cutting’.  

On miter saws, where the head does not slide, a positive hook blade could be used and it still be as safe as using it in a table saw (which is another discussion entirely) because the head is ‘locked in’. There is no sliding movement as there is on a Radial Arm Saw or a sliding miter saw. With this in mind, I can understand it, but on a sliding miter saw? Not for me.

Hopefully, from our discussions, you have a better understanding of some of the techniques of a Radial Arm Saw’s blade needs. Next week, we’ll take a look at the different styles of RAS’s and get a tip or two about how to go about properly aligning a RAS

Send your questions or comments to:

Toolsmartz@bellsouth.net and we’ll see what we can do to help you

V5.3 - Radial Arm Saw-How’s your Hook?

Last week, we started a discussion about the Radial Arm Saw and I covered a couple of the reasons as to why I am a member of the ‘pull the blade through the workpiece’ camp. We’ll continue the discussion this week with reason #3.

Third, IF the proper negative-hook sawblade is used, the operator has complete control over the force of the blade thru the wood. Now, IF a positive-hook blade is used, the blade will try to ‘climb’ thru the workpiece and make the operator push back against it. ALWAYS use a negative-hook sawblade on your Radial Arm Saw.

I did some testing years ago and it really is true. Using the ‘pull-through’ method, with a 20 degree positive-hook blade, I had to push back against the saw head slightly to keep the blade from trying to ‘run’ towards me. On the other hand (again using the pull-through method), when I used a 15 degree negative-hook blade, I could use one finger to pull the blade thru the wood and it did not try to climb at all. In fact, I would let the head stop every couple of inches and just let it sit there…and it wouldn’t move, even though the blade was spinning at 3450rpm and buried in the wood.

This might be a good place for a talk about negative and positive blade “hook angles” because they do have an effect on how smoothly a RAS blade can pass thru a workpiece. For this discussion, we are talking about carbide tipped blades. Picture, if you will, a circle. On that circle, we draw a straight line vertically and a straight line horizontally - with the intersection of the two lines dead center in the middle of the blade’s hole. Now, we give that circle some blade teeth and let’s say that the ‘blade’ is going to rotate, and cut, counter-clockwise. Align one particular tooth right on the vertical line.

With that picture firmly in mind, here are your three ‘hook angle’ definitions:

If the flat of a tooth is exactly aligned with the vertical line, that blade is a ‘zero hook angle’ blade.

If the flat of the tooth has its upper tip tilted in the cutting direction (in our example, that would be counter-clockwise) this blade is a ’Positive hook angle’ blade.

If the flat of the tooth has its upper tip tilted AWAY from the cutting direction (in our example, that would be counter-clockwise) this blade is a ’Negative hook angle’ blade.

We’ll pick up here, next week.

V5.2 - The mysterious Radial Arm Saw

OK, let’s get back to the task of learning more about our many shop tools and machines. This week, we’ll take a look at one of the most versatile machines, but also one of the most dangerous.

The Radial Arm Saw. Sometimes, the very words can make a grizzled woodworking veteran recheck his hands to make sure he still has all of his fingers and thumbs. This machine requires THAT much caution when using it.

But, as with most machines, if you respect it and realize what it can do to you in a heartbeat… you simply must be careful.

Just so that we are all on the same page, let’s outline a few parts of the saw.

The “head” is the part of the saw that holds the “sawblade” and slides fore and aft on the “track”. The “track” is the “arm” of the saw that holds the “head”, which is sometimes also called the “carriage”. The “fence” is the barrier that the workpiece is held against while laying on the “table” which references the workpiece, prior to being cut. The “off” position of the head/blade is when the head is fully retracted towards the rear of the saw, behind the fence.

Alright, now let’s take a look at one of the more frequent questions that I’ve been asked: “Should I pull the blade thru the wood, or push it through?” While I am sure that I may get some pushback, I will state my case and the reasons that I believe as I do. In my opinion, the blade should be pulled thru the workpiece. Here’s why.

First, when the blade and head are at rest, they are retracted behind the fence, away from the operator. That is a good position to then start the saw up, without it being hung out in space next to the operator.

Second, the proper blade rotation is over the top towards the operator, and down and under and away from the operator. Given this, if the head is retracted behind the fence and turned on, then pulled into the wood, the first contact the blade has with the stock will be pushing the stock down into the table and towards the fence. That places all of the cutting force downward towards the table, and rearwards towards the fence – both are very good things because they properly brace the workpiece.

If the blade were to be pushed into the stock, the first blade contact would tend to lift the workpiece…NOT good.

Next week, we’ll tell you more about the Radial Arm Saw.

Send your questions or comments to:
Toolsmartz@bellsouth.net and we’ll see what we can do to help you