From: patter@dasher.uucp (24224-guthrie)
Subject: Re: Trouble Ripping Hardwoods
Reply-To: patter@dasher.cc.bellcore.com
Organization: Bellcore, Livingston, NJ
Distribution: na
Date: Sat, 25 Jul 92 02:19:04 GMT

In article <1992Jul25.000451.8483@adobe.com> bennett@adobe.com writes:

>24224-guthrie writes
>> Assuming that the distance *is* the same, then you may be extending the
>> blade too much. It's not a good idea to extend the saw blade much past the
>> surface of the wood. 

>Wrong. The exact opposite is true. By not extending the blade past the work, 
>the teeth stay in the cut longer, causing the teeth to get hot from rubbing 
>against the wood more. In addition, sawdust can't escape and is rubbed into the 
>work by the teeth, increasing friction and heat.

I've found that the wood is usually expanding a little after it leaves the
cutting teeth. It may not be as dry as it should be. This gives you the same
effect as the "few thousandths of an inch" fence difference you mention,
Bennett.

Easy way to tell. Extend the blade several inches and make a cut partway down
a board. Then raise the board rapidly off the blade and look at the cut. If
the area behind the blade is burnt, but the area where the center and front
of the blade was is clean, the back teeth are burning the wood. If not,
Bennett's right.

>
>> If you extend the blade too much, the rear teeth may burn the wood a little.
>
>If lowering the blade is reducing burning, then the rear of your rip fence is  
>almost definitely closer to the blade. Let's say the fence is one degree out of  
>kilter. Think of two lines crossing each other at a one degree angle. As you  
>move further from the intersection the distance between the two lines becomes  
>greater. What lowering the blade does is decrease the distance of the rear  
>teeth from the front teeth, thus reducing the offset distance, which is what  
>causes rubbing. And rubbing causes heat. Heat causes burning. Another thing
>lowering the blade does is reduce the chance of having the blade's body
>contact the wood.
>
>The proper fix is to align the rip fence exactly, or at least make sure the 
>back of the rear is slightly further away from the blade, and then raise the  
>blade.

Correct. However, if the wood expands a little immediately after cutting you
may get this with a parallel fence. If both pieces of the ripped board are
burnt, that's your problem. If that's the case, as Bennett says, make the
rear slightly further away.

>> Take it slow with a 60. 
>
>Wrong again. The slower you go the longer the teeth rub in the kerf and so the 
>hotter they get. Take an extreme case where you actually stop pushing the wood 
>part way through the cut. If you've been having a tendency to burn, this will 
>produce a definite burn mark. As brisk a pace as you can safely perform is
>the ticket. 

I should have said that you'll *have* to take it slow with one. The saw
will let you know how fast you can go.

>> A 60 tooth planer blade (for example) would not be the best choice.

>Right. Most of the blades with high numbers of teeth are made are made for 
>crosscutting, where burning isn't as much of a problem. On some Freud crosscut 
>blades, for instance, the tolerance between the teeth and blade body is so 
>close that they've coated the blade with teflon to try to reduce friction and 
>heat from the blade's body.

In fact, Freud recommends a 40 tooth in their carbide blades, though they
say the 60 I'm using is adequate. First I've heard about the Teflon. I
would think it wouldn't last very long. Isn't that stuff sort of delicate?

>- Bennett Leeds

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                    |
George Patterson -  | He who is not a revolutionary at 16 has no heart.
                    | He who is a revolutionary at 60 has no head.
                    |                          Lord Chesterfield
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