Thin Kerf vs Full Kerf

[p8ntblr]

This may have been discussed before but I can't seem to find the thread. If it has and you know the link pls post the link and disregard the thread.

Is there a substantial difference between how much power needed and/or the feed rate when using a thin over a full kerf blade? I've heard that with 3HP + saws it doesn't matter as much but with saws like mine (ie 1.5 or below) it's a big difference. Is this true? Now I'm assuming full is .125 and .100 is thin. I'm having a hard time seeing how 1/40 " can make such a difference. On the flip side I've also heard that thin kerfs are more prone toflexing.

I have a 22114 saw and know at least a few members here have one as well. What's been your experience with either kerf blades. Have you found a huge increase in feed rate capability when going with thin. Any flexing problems with KF blades? Main reason I ask is I have WWII Full on hold with Amazon and am debating on whether I've made a mistake in not going with the thin.

[leehljp]

"flexing": Forrest as well as others recommend blade stiffeners to keep the blades from "flexing." The real reason, IMO, is that they want to cover themselves for people who have inadequately set up saws or if a saw has some built in vibratrion. The reason that "I" say that is because many many BT3x00 owners use the thin kerf withOUT the blade stiffeners (against Forrest's and other's recommendations) and have absolutely NO problems with flexing. That truth can be determined by the glass smooth cuts that would not be so - if the blade was flexing.

This little bit of truth is hard for some people to grasp and some simply do not buy it, rather they chalk it up to a cultic brand loyalty and reality distortion. I have two BTs, one in Japan and one in the US. Both give glass smooth cuts and I don't own any stiffeners to add to the thin kerf blades if I wanted to. I am not partial to Ryobi or any brand as a brand, but the on performance of the BT with TK blades.

BTW, TK blades can be 1/32 to 3/64 thinner than regular kerfs and it can make a difference in cuts when the blade begin to wear. A truly sharp, finely sharp blade will decrease the drag. A full kerfed very sharp clean blade will cut using less power than a TK if the TK is dull or has resin built up on it. IMHO.

However, if both are equally sharp, the TK will slow down less on hard wood than a full kerf - on low powered saws.

[Knottscott]

Hi Paul - That's a good question IMHO, and I've often wondered how many people have personally experienced issues with TK's using a high quality blade on a reasonably good saw....an arbor with high runout is asking for trouble. Leaving cheap or lower quality blades out of the discussion, and focusing only on 10" blades or smaller, I've always found the TK's to feed noticeably easier than their full kerf counterparts. (12" TK's have significantly larger spans, so if the body thickness is the same as a 10", I'd expect a higher chance of flexing). The feedrate makes less of a difference while crosscutting, but it sure shows up on rip cuts. The improved speed isn't even usually the important factor to me...it's the ease of feeding which allows better control and less pushing (feels safer), and lower strain on the motor. If you consider that a 1/8" full kerf blade is 1/32" thicker than a 3/32" TK, it's literally 33% thicker, and the difference is pretty significant from that perspective....it's just a matter of physics so long as the blade is stiff and runs true.

To date, I've tried a fairly significant number of both kerfs....somewhere near 25 TKs and over 10 full kerfs, and have never had a deflection, flexing, or vibration issue with either....I've never noticed a difference with or without a stiffener, so there should be no need for one as long as the arbor's runout is low enough. I also can't tell a difference in the cut quality between the kerfs. I've read of both of the afore mentioned issues with the TK's, but never experienced them personally whether testing a blade or just using one for project work. It's my opinion that the manufactured quality of the TK is pretty important in this regard. Some folks judge quality by brand name, which I think is an oversight in many cases.... there are several brands that offer multiple quality levels...You don't necessarily have to go absolute top shelf to get high quality, but I think it's important to at least avoid the entry level lines to insure better quality.

Modern alloys, designs, and manufacturing techniques are better than they've ever been...it's quite possible that many of the horror stories we hear about were pertaining to older technology, cheaper blades, or saws with high runout. It's also logical that work load plays a factor....if you're cutting hundreds of linear feet in succession without much pause, it's more likely you'd overheat a TK than a full kerf....typically a non-issue for a hobbyist.

I've switched primarily to TK's with my 1-3/4hp saw, b/c I always notice the improved feedrate, which equates to the perception of more power, ease of cutting thicker woods, less burning, etc, and I know my motor is straining less. Until I encounter enough situations to dispute the data I have so far, I'm staying the course with TK's on smaller saws. The full kerfs work ok on a smaller saw mind you, but the TK's have always fed easier and cut comparably, therefore are attractive to me. If I had a full 3hp cabinet saw, then there would be far less reason to use TK's so I'd likely go to full kerf.

p.s.: Not meaning to hijack Paul's thread, but I think it's pertinent to the discussion. For those interested, back in July I updated a chart of the blades I've tried. It shows my perception of cut quality and feedrate, along with comments and other bits of info. The feedrate was a significant factor in the overall rating of many of the blades, and the TK's repeatedly rated higher in that aspect.

[Ken Massingale]

FWIW Paul, I called Forrest when I first got a WW II and they suggested that a stiffener isn't needed on a TS3650, I feel the same is true with your TS. I'm not clear on why he asked which TS I had and why that would make a difference, but he did.

[sweensdv]

I primarily run FK blades on my contractor saw and have never had an issue with the saws motor not being up to the job. I purchased a TK rip blade just to see if there really was a big difference and I couldn't find a big difference. There was a slight difference in the feed rate with the TK but not enough to say the TK is significantly faster. As far as I could tell, there was no difference in how the motor performed as there wasn't any indication that the motor bogged at all when the FK was installed.

[Knottscott]

FWIW Paul, I called Forrest when I first got a WW II and they suggested that a stiffener isn't needed on a TS3650, I feel the same is true with your TS. I'm not clear on why he asked which TS I had and why that would make a difference, but he did.

Ken - I'd hazard a guess that the Forrest rep was trying gauge the amount of vibration or runout on your saw when he asked, but I don't know for sure...makes sense that it would be more beneficial on a saw with poor runout and high vibration. From a vendor standpoint, the stiffener is one of those things that's "more right, than wrong", regardless of whether it's necessary for a particular saw, and oh BTW...there's bound to be a pretty good margin on those things!

I borrowed the sig line below with permission from forum member on another site...it pretty much sums up my view of stiffeners/stabilizers:

"In my small mind I want it to make a difference because I paid 24 dollars for it ......"



.

[LCHIEN]

Most of the above posts indicate that the use of TK vs FK results in a satisfactory, if not equal cut. If cut quality is not a problem then, I'll attempt to show why TK improves your life.

Assuming the friction forces on the side of the blade are negligible then the simple reduction of plowing or cutting .100 wide path vs. .125 wide path is a 20% reduction in effort or work.

If you assume some portion of the effort is side friction then the net reduction in force for the same feed rate is somewhere between 0 and 20% for going to a thin kerf blade.

I've tried to explain it before, but the forces encountered and the motor power may make a great deal of difference in you woodworking ease.

Two factors set the appropriate feed rate:
One is the fact that if you feed too slowly you burn the cut.
Two is the fact that if you feed too fast then the motor bogs down and stalls, an undesirable condition.

I've made a chart illustration this compromise.
In the first chart (you may wish to click on it to enlarge and read the detail) I show the relationship between feed rate and material.
If the relative hardness and or thickness of the cut material increases, then the cutting effort increases. Also the tendency to burn increases. As you can see, yellow area shows the tendency to burn, too slow (to the left) and increasing hardness/thickness contribute.

On the right, the red are shows the area where the motor stalls. As the thickness/hardness reduce the you can feed faster and not stall the motor.

The slanted lines labeled FK, 3HP motor stall, TK, 3HP motor stall etc. indicate that the feed rate at which it stalls is a function of the TK vs FK and the motor HP. A thinner kerf presents less load and will permit a higher feed rate. A higher 3HP motor will also permit higher feed rates.

A working range in green is where the saw operates best, no burning and no stalling - that's what you want. The range of feed speeds indicated by A for thin, soft material is wide. But as you go to thicker and harder material (more work to cut) the range of speeds is much less, more critical and harder to feed. At the place indicated by "B" you have to keep a steady feed rate with little margin faster or slower to keep from either burning your wood or stalling your saw.

In the first plot the green are is indicated for a full kerf, 1.5 HP saw.
The Gray area represents the possible improvement of using thinner blade or more powerful saw.

The second plot shows what happens when you go to a higher power motor and a thinner blade. The green working area becomes much larger.
The range of working feed rates for A is much greater. The previously small range of acceptable speed for B is now wider (you can go much faster), and for material of a hardness and thickness indicated by "C", this saw/blade combination will cut it whereas the full kerf, 1.5HP motor could not properly cut it at all.

[pecker]

Nobody is saying what it is they are cutting. A 3/4" piece of poplar that's 2ft long and has been jointed square and planed will cut fine with a TK blade.

An 8ft yellow pine 2 x 10 won't. A SK blade won't flex as much on a job like that. Also, dense, figured, or thick lumber is harder to get a glue-up edge and will highlight any flexing issues.

[LinuxRandal]

With carefull planning, this won't come up. But occassionally, if your close on your board requirements, you can squeeze out that extra piece, due to the thinner kerfs, not eating up as much material.

[Knottscott]

Most of the above posts indicate that the use of TK vs FK results in a satisfactory, if not equal cut. If cut quality is not a problem then, I'll attempt to show why TK improves your life.

....snip...

Hey professor...wow! That's an impressive piece of work you just put together!

____________

... Also, dense, figured, or thick lumber is harder to get a glue-up edge and will highlight any flexing issues.

The thicker and denser materials also highlight the weakness of a smaller motor, and that's where I tend to see the most difference with the feedrate of the TK's....YMMV.


.

[Sawduster]

I have noted maybe 1/64" or less of deflection when making bevel crosscuts in woods such as Black Walnut, White Oak, Mesquite and Pecan with all of the TK blades I have, even freshly sharpened and cleaned. The first time I noticed it I went nuts trying to figure it out. Checked the SMT fence to the blade, checked that the SMT was sliding parallel to the blade, checked the blade for run out and wobble.

A dirty and/or dull blade exascerbates the problem, but even clean and sharp I can check the cut workpiece against the same square used to check and set the fence and can discern a bit of difference. I generally notice it the most when I am making a bevel cut right at the end of a piece as opposed to a cut made several inches in from an end.

I noticed the same thing on my Griz cabinet saw.

Anyway, I ordered a Systimatic combination blade which cuts a kerf .133" wide as opposed to the normal .125". It should be in tomorrow.

I will likely put a good thin kerf blade on when cutting the strips for the next rocking chair runners as that added kerf thickness adds up when cutting 1/8" thick strips of $10+/ bdf mesquite.

[p8ntblr]

Very informative posts and diagrams guys.
Loring, That's a very useful diagram in understanding the different results of kerf thicknesses. The most important thing I got from that was probably how important a consistent feedrate is with thicker/denser woods.
It seems like the consensus is that with higher quality blades, flexing is not a problem and there is an increased feed rate. But the importance seems to be more for rip cuts and since I'll be using the WWII for cross cuts I think I'll stick with it and just get at TK rip blade.

[JimD]

I use and like both 1/8 and thinner kerf blades. I believe the difference in feed rate is often overstated, however. The type of blade makes far more difference than it's thickness in my experience. How clean it is also makes more difference. How sharp it is also makes more difference. I have cut 3 1/2 inches thick in hardwood and softwood with my BT3100. I did it in oak the first time with the original Freud blade. It required a slower feed rate than my more recently purchased Freud full width ripping blade. With the ripping blade, I can cut pretty quick with less force required but I have to be careful to not push too fast because it creates swirly marks on the wood - I think it is the sawdust becoming trapped in the cut when I cut too fast. With all around blades, thin or not, I do not have this problem but my feed rate is even slower because the saw seems to be straining.

If you want a blade for thick rips, I would get a dedicated ripping blade - I like my Freud. If you can find one that is thin and want to use it, it may work better than my full width blade but I like mine. I cross cut sometimes with it and the cut quality is better than I expected. It is a very useful blade.

My other favorite blade is a 4atb with 1 raker 50 tooth all purpose blade - 1/8 inch kerf. I have a Frued and a DeWalt with this tooth pattern. I do not have difficulty with the saw straining with these blades but I normally switch to the ripping blade when going over 2 inches deep.

My only complaint with thin kerf blades is most of them are ATB blade grind. That is OK but not optimum for ripping. If you can get the appropriate grind in a thin kerf, it should require a little less effort from the saw.

Jim

[Knottscott]

Jim - Freud's LU87R010 is a 24T FTG (flat top) ripper with a 20 degree hook in a TK. AFAIK, its configuration is the same as the LM72R010 24T full kerf ripper (which sounds like it might be the rip blade you use), but in a thinner version. Infinity, HO Schumacher, Leitz/Irwin, CMT, and DeWalt (to name a few) also make 10" 24T FTG TK rippers.