Pre-stretching of blades?

[dirtrider73068]

As I was drooling over the vids on youtube of the EX saws one said its best to pre-stretch the blade, he showed on a EX of a new blade, installed showed how loose it was, tightened it down was perfect ran saw about 5 seconds, then all he did was undo the tension lever and it was WAY loose, said he did this for every new blade installed, instead of having to retension part way through a project. I don't know how true this would be, I do find on my craftsman after a new blade and cutting for a bit it seems like the tension gets a tad loose, wonder of this is from the blade stretching, wonder if there is any truth to this or if its a myth.

[cdrover(Clyde)]

I saw the same video about a month ago. I have tried the technique and it does indeed stretch the blade after running it for about 5 seconds. I have not done enough cutting lately to how if it impacts the life of the blade.

[Billy in Va]

Here is what I do on my  Dewalt

Install a new blade and tension to about 4 or 4 1/2 depending on blade

Run the saw and use a smooth Arkansas stone on the back of the blade for a few seconds  to round the edges -  same as I do for band saw blades

Release tension, insert blade into a fret hole, re-tension and start cuting  Most times even if the next cut is a perimeter cut I drill a hole rather that just cutting into the edge.  I think it makes for better stability.

[dirtrider73068]

Does it really stretch the blade? If I was any good at reading a micrometer could measure a new blade then a used blade to see how much it really stretched if any, my saw has a knob at the back so really if I make first cut on the smallest cut that takes 5 seconds then move to next hole my blade would be prestretched by then as I have to turn a knob to tension so I would in theory pre-stretched my blade.

[Kepy]

I think you hit the nail on the head.  I have never had the tension on my 788 higher than maybe 2 1/2 but usually l l/1 to 2.  Even doing straight cutting without have to reset, I have never had to change the tension before changing the blade due to dullness.

[PigsFly]

Just a guess but I wonder if you are really stretching the blades or taking out some slack because of blade slippage in the clamps.  I almost exclusively use FD 2/0 and # 1 spirals so my experience is limited to those blades but I really do not see any additional slack after cutting and loosening the tension.  There could be some oil or other film on the blade end which would permit the slippage.  I dunk the ends in denatured alcohol when opening a new 12 pack and wipe dry and then before using scuff the ends with 220 grit sandpaper which may account for my lack of slippage.

[Billy in Va]

I also clean both ends, both sides of the blade before installing.  When I first got the 788 I used a tension of 2-3.  A friend told me to try 3-4  (or more) and see if I liked it any better.  the higher tension give me better control along with a higher speed.  One of the hardest things I had to (learn/relearn) was that just because the speed was higher, I did not have to cut faster. for me it give better control, especially in small frets.  The larger blades 7, 9 do get less tension than the 1-5 size. 

[Fab4]

If you do any type of fretwork you automatically re-tension your blade on the next entry hole.
This should be tried on an exterior cut to see if this theory is correct.
For whatever reason, I think you do lose a bit of tension on your blade.
May be from stretching, may be from a loose clamp.
Sometimes it doesn't happen at all.
The joys of scrolling...
Fab4

[TripleB]

Hey Dirtrider,

This is Bob, the one who made the video about Pre-stretching blades. Yes blades really do stretch due to metal fatigue, some more than others depending on the brand and how they were forged. Harder blades don't stretch as much if at all, that is why some people do not see any stretching. As I stated in the video the brand I use does stretch, slippage is not the problem, and I just thought I would make a video demonstrating it. As for checking to see the stretch, just lay a used blade next to a new one, granted it wont appear to be much because there is no tension on them at the time, but you should be able to see that the used blade is slightly longer than the new blade.

Thanks to you and every one else that has watched my videos, and for those of you that have not seen the video he is talking about here's the link.... http://www.youtube.com/watch?v=gW-tO2Jx4Gc

Bob

[dirtrider73068]

I use flying dutchman blades now, I did use ones from lowes and tried some from sears, and noticed the ones from lowes tend to break easier once they get dull, kinda makes me wonder they were cheap and would stretch to the point of breaking and then well break, and it was always near the lower clamp. I will find out once my new EX gets shipped to me, should be shipped on thur, I am excited.