Blades for Felder FB710

[Van Huskey]

This was confirmed with 2 Lenox tension meters and via stick + .0005 dial indicator. In my testing the 'clamp a digital caliper' over 5" was not accurate or repeatable compared to a dedicated tension meter.

This is one of the reasons that a lot of "our" discussion about tension stays in the theoretical realm. If we all had load cell based strain gauges we could get into the minutia. I have one for 14" cast saws but it isn't useful for these high psi discussions.

I have found over the years that both the commercial strain gauges and DIY methods for measuring strain vary a lot in their precision as well as accuracy. Because I have the load cell based strain gauge for small saws I can get an idea about the accuracy of different methods (at least at up to about 15kpsi). I use a particular Lenox gauge (out of the 3 Lenox, 2 Starrett, an Iturra and the caliper method using both calipers and dial indicators) because it was the most precise (repeatable) and close to being the most accurate, again checked using the load cell. In the end, MY 30k psi is likely to be different than everyone else's 30K psi.

In reality, this is just a fun (for some) internet discussion since our numbers are just too unreliable to compare. It does produce good anecdotal information regarding what blades will work well on what saws and it reinforces the fact that large (for us) carbide and bi-metal blades need a lot of tension which requires a stout frame and a hefty spring and tensioning mechanism to control the spring.

[John TenEyck]

Dennis, assuming your tension meter was accurate, those measurements were real, independent and undiminished by the deflection of the frame. Compression springs don't have a perfectly linear response at low or high compression, only in the middle 75% or so. It would be quite normal for actual measured deflection to be greater than an ideal model unless the model was created from the exact spring you used. In any case, you are one of the few to post actual data and are to be commended for doing so.

I've used quite a bit of Sapele and if Sipo is similar I know what you mean. I've had a few boards that did all kinds of wonky things when I ripped or resawed them. I finally concluded, rightly or wrongly, that if a Sapele board has any amount of twist in it in the rough it's likely to give me problems when I rip it, whether or not I first jointed and planed it flat. I've even ripped wide boards in two, or three, jointed and planed those flat and true, and still had problems when I ripped those narrower pieces. That twist must mean that there are internal stresses in the board and it gets released every time the board is cut narrower. So now I will not buy a Sapele board with any amount of twist in it, and haven't had any problems since. Fortunately, my lumber supplier lets me pick through his stacks and take only what I want.

John

[Denis Kenzior]

Van,

I'm curious, how much variability did you experience across the 6 tension meters you used? I would have expected all of these to be within 10% or so. So if my gauge reads 25k, I could see how someone would get 27 or 23, but I'd be surprised if there was more variance than that. Hence why I'm curious.

Here's a shot of my 2 Lenox gauges.
IMG_2498.jpg
As you can see they're of different vintage (small manufacture differences, different paint job, etc), but they read almost dead on compared to each other. A good quality dial indicator should also be a good way to measure strain. Over 15" range, each .001 is roughly equivalent to 2000 psi. So with a .0005 indicator I would expect one to get pretty accurate readings. In my testing, it was close but admittedly I was not very thorough cross-checking this method since I had the tension meters.

On the other hand, a typical 6" digital caliper is speced as repeatable / accurate to roughly .001. So using that method you could only count on getting to +/- 5000 psi, which is not very accurate.

[Van Huskey]

First, I will admit I never recorded the exact numbers go it will be going on memory from over a period of time. I also could not measure over 15K psi safely on the 14" saw and that was with one of Louis Iturra's beefed up wheel hinges. The worst was always the caliper method which for me no matter how much I tried always read high and the level of precision was low, I measured up over 18K psi several times. The rest all read low between 10 and 13K psi. The Lenox I ended up keeping and use now is the only strain gauge I bought new and it read about 12.5k psi at what my load cell said was 15K. The other Lenox gave similar results (always a little lower) but the precision was lower as well. The Starrett read in the 12k range with similar precision so I could have easily picked it but the resell was higher. The Iturra I was never able to get to work correctly as I was never able to get any level of precision, my thought was that it has more friction which I suspect was the problem with all of them.

The entire time I was basing everything on the idea the electronic tension meter was accurate. I now consider 30k psi to be 36k psi on my Lenox how accurate that is I honestly don't know but it does seem to be in the sweet spot since if I drop to 30k on the scale I can see (or convinced myself I can see) a degradation in quality of the cut. I still have the ETG but don't have a 14" Delta or clone currently so I can't play around with it currently. There is a guy that built a nice loadcell based one around Rasberry Pi and it reads in psi directly, I keep thinking about building one but it would be for pure knowledge since I am happy with my current state of affairs when it comes to setting tension.

[David Kumm]

I had two Starrett, one Lenox, and one Iturra. Initially I had trouble with the iturra and sent it back to Louis. He reworked it as he had some issues with some indicators. Whatever he did fixed the problem. All four were within 1000 psi of each other. It did take some experimenting to load them properly since they were all slightly different and if not preloaded properly you got garbage out. Once I knew they all worked I kept two. I don't know if they are necessary ( my old saws don't have reliable gauges ) but 190" Carbide blades are expensive and the meters have paid for themselves. I think all of mine were bought used for about 1/2 price. Tension meters often are bought and used a few times on new saws until the gauge on the saw can be marked and then stored away so every one i've bought looked to be in new condition. Dave

[Wakahisa Shinta]

...
BTW I noticed I referenced a 3/4" Trimaster in my other post, must have been a brain fart, the 1" 2/3tpi or 1" 3/4tpi would be my choice for that saw.

How will the cut quality of the 2/3 vs 3/4 tpi 1-inch blade above be different? I am also sourcing blades for a FB710 for resawing and making veneer.

[David Kumm]

Generally the wider the board the fewer teeth. Blade speed is also a factor but cost is usually related to number to teeth so fewer costs less. That is partially why the CT 1.3 is well liked. Dave

[Wakahisa Shinta]

Another issue to consider is how stiff the spine is. As you tension the blade, the frame of the saw will start compressing, in effect applying less tension on the blade.

I was reading this thread a second time to finalize blade purchase, came across that sentence and wonder if anyone ever welded additional iron (flat stock, C channel, U channel, whatever) to the spine of their bandsaw to add more strength to the frame/spine?