negative rake blade?

[Selwyn]

Got a dewalt radial arm blade and not sure if its negative rake or not. How can I tell?

 

[chipmunk]

If you put a straight edge through the centre of the blade out to the cutting edge of one of the teeth and compare the aligment of the cutting edge with it, a positive rake will leave a gap on the inside of the circle (AKA agressive cutting) and a negative rake will have a gap on the outside of the teeth (AKA a trailing edge at the tip).

HTH
Jon

 

[Selwyn]

Ah very helpful thanks.

Been looking everywhere to understand. I think mine is neg rake - need to find someone to sharpen it for me now!

 

[matthewwh]

It should be negative on a radial arm saw, the rake ensures that the cutting action forces the wood down onto the table and back against the fence.

On a tablesaw where the blade comes through the table you want positive hook to hug the wood down onto the surface.

If it's an industrial blade (proper big lumps of carbide rather than the little dots that they put on replaceable blades) and you don't have anyone local, you could try Atkinson Walker in Sheffield for sharpening by post.

0114 275 2121

 

[Selwyn]

Nope mine wasn't negative. Explains why cutting was scary! Will get one

 

[blackrodd]

It should be negative on a radial arm saw, the rake ensures that the cutting action forces the wood down onto the table and back against the fence.

The negative rake is for severing the wood fibres, as in the cross cutting action, tends to give a cleaner smooth finish.
It wasn't designed to keep the wood in place. This happens because the saw cuts from above and from the fence end,
and the cutting action of the blade, A Rip saw blade will do the same
The positive rake tooth is for ripping along the grain and it's variations, knots etc,
The different shaped and bevelled tooth is designed for either ripping, cross cutting and man made boards.
Best not to try, but any attempt at ripping with a negative raked tooth will be quite dangerous, snatching and even burning the timber,
You would need both types of blade with the RAS. As it was designed to do both operations.
Personally, I would never rip with one, I don't like the ripping action but it is a first class cross cut.
Regards Rodders

 

[Peter Sefton]

Ripping on a cross cut is a dangerous and best avoided.
Using a positive hook blade for cross cutting is also dangerous as the blade will grab into the timber and either stall an underpowered machine or run the blade violently over the timber towards the user on a powerful machine.

Some crosscuts do use blades with up to 5 degrees positive for smaller section timber, where the grab factor is minimal.

Cheers Peter

 

[Jelly]

With Regards to ripping on the RAS, it isn't any more dangerous than any other circular saw.

It does give you more opportunity to set it up incorrectly and create a dangerous condition... That's down to the operator not the machine.

This Post covers the issue in great detail.

The essence is this; if you're not going to commit to setting the RAS up correctly when ripping, don't use it for ripping; the same principle applies to all wood machining though, poor setup is always dangerous.

Using a positive rake blade on an RAS to crosscut, IS dangerous, and will at the very least scare you witless, even a negative rake blade can ride forward at you if not properly controlled, I shudder to think how forcefully an inappropriate blade would do so.

 

[Zeddedhed]

Using a positive rake blade on an RAS to crosscut, IS dangerous, and will at the very least scare you witless, even a negative rake blade can ride forward at you if not properly controlled, I shudder to think how forcefully an inappropriate blade would do so.

From experience I can tell you that it can be forceful enough to actually knock you over!!

I bought a DW 1501 (I think that was the model number) several years ago and had no idea about blades and all.

Merrily fired it up and started to pull it across a 350mm wide slab of Oak. Next thing I know I'm on my arse amongst the sawdust.

So I learned a bit about blades.

 

[Selwyn]

One of these will do for my 1251 dewalt RAS won't it? Don't want to pay too much as its not used that much. They both seem to have negative rakes don't they? (pictures don't match blades)

http://www.ebay.co.uk/itm/Makita-B-0906 ... SwstxVB1S0

http://www.ebay.co.uk/itm/TREND-CSB-CC2 ... xyBPZTg6l6

 

[Jelly]

One of these will do for my 1251 dewalt RAS won't it? Don't want to pay too much as its not used that much. They both seem to have negative rakes don't they? (pictures don't match blades)

http://www.ebay.co.uk/itm/Makita-B-0906 ... SwstxVB1S0

http://www.ebay.co.uk/itm/TREND-CSB-CC2 ... xyBPZTg6l6

You might be surprised to see how cheap a "proper" one is...

Those are the Atkinson-Walker resharpenable TCT blades which the sawmill I used to work in used, albeit smaller and made available to the public slightly more easily by matt. Both a tad cheaper, and IMO one of the best products on the market.

 

[Selwyn]

Ah splendid. Thanks jelly I didn't know workshop heaven had them