How does one decide when to change blades (as in dull)

[Robert R]

Another question, at least I have not broken any blades.  So, when am I using a dull blade?  I think I have a tendency to change blades to a new one too often, as when I take it out it doesn't feel a lot different than when I first put it in the holder and that can be several hours latter.  I've used the same blade now all day today and seems to still cut quite well.  Perhaps I should be checking the cut itself for particularities and if so, what?

Edited July 23, 2023 by Robert R
spelling

[Scrappile]

The minute it feels like you have to push the wood into the blade as opposed to it "melting" into the blade, or you start have difficulty controlling the blade, time to change.  And like all things there are a lot of factors.  You cannot put a time limit on it.  What your are cutting, What wood you are using, what type blade you are using.  I Probably, and I have never timed it, just a guess, but I would say on average I may get 20 minutes out of a blade.  But again I do not set a timer, when I feel in the slightest that I am having to work to get the blade to go where I want, it is time for me to change.  Right now I am cutting in 1/2" Monkey Pod, a little harder than Popular, maybe, but what I am cutting I want to be  precise, I am using a #1 size blade and I have probably changed the blade every 10 minutes at the most.  That is just me, your mileage may vary as they say.  You may not want to go by what I say,, I have broken lots and lots of blades! But I am often trying different blades, different technics, different woods..expect to break blades.

Edited July 23, 2023 by Scrappile

[aussiescroller]

For me its when i start over-forcing the piece into the blade instead of letting the blade do the cutting. I will also speed up the cutting 25-50% to what i had when i originally started cutting with the new blade. That's the hint its getting dull. They go in the "used" test tube for use on another day when my supplies get low

[Robert R]

Well, just reading what both of you have offered, I'm overdue. First thing tomorrow I'll put a new blade in. I have a feeling I will feel the difference as soon as I start.  Thank you, I'll get back tomorrow.

[BadBob]

The longer you cut the duller the blade gets and the slower it cuts. When it becomes too slow or hard to control I switch blades. I seldom break blades.

 

[Bill WIlson]

For me, it's when I see smoke rising from the cut. 

Seriously, as the others have mentioned, it's more of a feel thing than any sort of measurable condition.  I suppose, under controlled testing circumstances, one could arrive at some sort of objective standard as to when a blade arrives at a particular state of dull, but there are so many variables at play, that this would prove difficult to measure, in practical terms.  Most scrollers learn to gauge it by how the blade is performing, in the moment.  Blades aren't always consistent.  Sometimes a brand new blade will seem to last indefinitely and sometimes a different blade, from the same pack will under-perform almost right away.

[BadBob]

19 minutes ago, Bill WIlson said:

For me, it's when I see smoke rising from the cut.

That will do it. I forgot about the smoke.

[Robert R]

48 minutes ago, BadBob said:

That will do it. I forgot about the smoke.

that would do it for me as well, but that I have not seen.  I'm about to go out and see how a new blade feels as opposed to my yesterdays blade.   

Edited July 23, 2023 by Robert R

[dgman]

For me, it’s easy. When the blade no longer cuts the way I want it too, it gets changed. It has nothing to do with time, or distance, if it isn’t cutting the way it was when it was new, I change it. Like was mentioned above, I have even changed a brand new blade because it did not cut the way it should.

At the very least, I replace the blade before starting another project, I replace blades after each session, I replace the blade when the cut starts getting ragged, I replace the blade when it won’t track properly. This is why blades are sold in bulk…. Packages of 144 or a gross.

I think once you start changing blades more often, your scrolling will become more enjoyable.

[Wichman]

For me and the blade I use the most ( FD Polar #! ) I use the following criteria:

1. feed rate slows down

2. blade won't track right

3. blade won't make tight turns

4. blade "wanders"

5. when changing holes the blade is either bend front to back or has a noticeable kink side to side

6. when changing hole I will gently run my finger against the teeth, if I can feel a difference in the sharpness from where the blade is cutting and what does not cut.

    

[BadBob]

11 minutes ago, Wichman said:

6. when changing hole I will gently run my finger against the teeth, if I can feel a difference in the sharpness from where the blade is cutting and what does not cut.

That's a good one. INTOT

[Robert R]

6 hours ago, BadBob said:

That will do it. I forgot about the smoke.

that would do fit for me as well, but that I have not seen.  I'm about to go out and see how a new blade feels as opposed to my yesterdays blade.   

 

Ok, so the last 5 hours I've been having fun and YES, a new blade really makes a difference. I even had the blades to use, but you all gave me a good sense of what to look for.  I changed blades twice sense I restarted this morning, I guess three times as I put a spiral blade in for some of it.  I'll try to add my practice project when I'm done here.

 

 

Edited July 23, 2023 by Robert R

[James E. Welch]

Absolutely agree with what's been said so far.  

Before buying the hegner I rarely broke a blade. I would notice it not cutting as well and change it. The hegner has a learning curve apparently and I'm working through that curve as we speak. It's getting better but for a while there I heard the twang and rattle of a blade breaking in my sleep...  Lol   it still startles me every time it breaks one. 

[crupiea]

I use them over and over until they break or are too bent to use anymore.

Sometimes you will notice that a blade just doesnt seem to be working the way you want so when that happens I swap it. 

I have some blades I have used for years.  They are all rusty and old looking but hey, they are still cutting so I keep using them. These I just use to cut pieces to size and stuff like that, not for the more technical work. 
 

I think it equals out when some days I will break like 6 in about a 10 minute span for some reason. 

[MarieC]

This thread has been helpful for me as well.  I pretty much have figured out how to tell now when I need a new blade and as others said, some I need to change out quite quickly while others seem to last much longer and they are the same brand and same size blade.  Not sure why that is.  I also found that if my blade it newer I can put it in the clamp below the table of my EX 21 a lot easier.   

[Robert R]

6 minutes ago, MarieC said:

This thread has been helpful for me as well.  I also found that if my blade it newer I can put it in the clamp below the table of my EX 21 a lot easier.   

Funny you say that, I also like to put it in the bottom clamp first, and with my machine I've been able to do that. It just seems to line up better that way.   

[TAIrving]

When my blade stops cutting well, tracking well, etc, the first thing I do is reset the tension.  If that doesn't work, then I replace the blade.  

[Robert R]

On 7/22/2023 at 7:32 PM, aussiescroller said:

For me its when i start over-forcing the piece into the blade instead of letting the blade do the cutting. I will also speed up the cutting 25-50% to what i had when i originally started cutting with the new blade. That's the hint its getting dull. They go in the "used" test tube for use on another day when my supplies get low

Are you saying that you start out cutting at 50-75% at machine cutting speed and then speed up cutting the additional as your blade dulls?  I have been using my machine on full speed for everything I've been doing, it seems any slower and the wood wants to jump and it is more accurate at higher speeds.

[BadBob]

8 minutes ago, Robert R said:

it seems any slower and the wood wants to jump

In my experience, if the wood is jumping I am feeding too fast, the blade is dull, or maybe the blade I am using is not appropriate for the material I am cutting.

[rafairchild2]

For me it is a few things.  I hear a tonal change in how the wood is cutting, I also find that the blade starts to drift more and becomes more difficult to control, and I also find that I am pushing harder, or I have to turn the speed up more. 

Really, it is something that comes the more you cut.  Just talk to yourself as you cut, and note how the blade works when new, and after so many inches or minutes of cutting (depending on wood hardness too).

 

[Robert R]

OK, so a lot of great suggestions to consider, actually I'll consider all of them. I'll start with slowing both speed of the machine and my push speed, cause, I know I push too hard. It's not right to think this, but I figured the faster I went the straighter the line would be, but them I would come to that corner or circle and I'd slow way down, so go figure why I figured I had to go fast in the first place. The magnifier with light should be a big help, I have found myself with my glasses I'd say almost nose to blade holder to see what I was doing. I am thinking the jumping is coming when I lighten up so much holding it. One of the biggest things I need to change the blade more often, I think I've been trying to use one blade for an entire cutting, that really made a difference this morning when I put the fresh blade in.  So, I thinking I need to go back out and do some more cutting and trying to put all I've learned so far together.  

Thank you. Don't stop I'll take any knowledge you all can give me.  

Oh, the wood I've been working with so far is Light Premium MBF as the Baltic Birch I had been using had voids in it.

Edited July 24, 2023 by Robert R

[MarieC]

17 hours ago, Robert R said:

Funny you say that, I also like to put it in the bottom clamp first, and with my machine I've been able to do that. It just seems to line up better that way.   

Robert, I did not mean that I start the blade at the bottom.  On my EX 21, I put the blade in the top clamp first and then in the bottom one.  It is when I am threading it through holes that I sometimes have difficulty putting the blade in the bottom clamp, especially the super small blades 2/0 for example I will then sometimes switch the blade out.  This is probably because I bent it a few too many times.... 

[Sycamore67]

This is just my thoughts.  I typically cut thick woods which are 3/4" and even thicker.  I do mainly Intarsia and accuracy is the primary concern so that fit is tight.  I aim at cutting half of the line.  Also, some of the woods are difficult to cut.  I change blades quite often as a dull blade results in inaccurate cuts.  I really do not care about the price of blades. I may only cut one piece with a blade and make no attempt to reuse a blade. I use either FD Polar #3-#5 blades.  I also use PS Woods SuperSharps. My saw is a Hegner

I can tell when I am pushing too hard just by the feel.  I have had blades go dull in just two inches.

The point of all this is that the type of project makes a huge difference.  I might have a difficult time knowing when a blade is dull on a fret work project or other thin wood with different blades.

What blade to use and how long it lasts depends on your saw, blade type, material type and thickness, your style and a bunch of other things.  One needs to experiment and carefully watch how your blades  are reacting.  There is no secret formula or rule.....just lots of experience.

[aussiescroller]

14 hours ago, Robert R said:

Are you saying that you start out cutting at 50-75% at machine cutting speed and then speed up cutting the additional as your blade dulls?  I have been using my machine on full speed for everything I've been doing, it seems any slower and the wood wants to jump and it is more accurate at higher speeds.

Usually i cut around 60-70% speed (mainly cause I'm a newbie) but different blades will perform differently depending on material/thickness etc. Ive never cut at max speed but I'm also mainly using softer woods plywood,birch,pine,sometimes oak at 1/4,1/2,3/4 inch thickness.

[Puzzleguy]

A couple of things 

I can tell when its dogs out - when it starts to fight me -

and i look at the teeth of a blade , if they start getting bluish or discolored

( just where it cuts ) its worn out

Edited July 27, 2023 by Puzzleguy