Bandsaw 2 of 2 - Blade Tension 101
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- Опубліковано 9 кві 2014
- CarlHolmgrenWoodworking.com
Here is the last word on accurate band saw blade tensioning. I've demonstrated how inadequate the factory tensioning system is, how it can be remedied and how to easily and accurately reset the tension for each of my saw blades which vary from 1/8" to 5/8". The las 1/3 of this video is simply reassembly of saw - you may want to skip. Please subscribe if you find my videos useful and interesting. - Навчання та стиль
Hello Carl. I hope this comment finds you doing well. This video has inspired me and I believe I have figured out a way that you can know the exact amount of force that is being applied to the blade. If a hydraulic ram is installed on the adjustment screw it could be measured very accurately. The ram would need a through hole so it would fit over the adjustment screw with a nut on top. As oil is pumped into the ram it would create a solid block of oil. The force of the spring would react against the solid block and the top wheel which is pulling against the blade. This would effectively give an oil pressure that could be divided by the surface area of the cylinder rod, which would tell you the exact amount of force that is being applied to the spring.
I have worded this incorrectly. The pressure reading on the gauge multiplied by the surface area of the piston or rod would equal the amount of force applied to the spring.
Hi Carl -- Thanks SO much for such a great video. I had been struggling with the tension on my Delta 14" saw and your clear and straightforward approach for measuring the tension was just what I needed. Well done!
Carl you have an eye for detail. And you are very informative. Great video
Dear Mr Holmgren. You are obviously a very methodical Man, and i do feel also a very respectfull and honorable Person. Your knowledge must be amazing, and i did appreciate very much you sharing some of it with all of us. Thank you very much. I have learned something today thanks to you.
Greetings from the Great White North. Thank you so very much for this valuable information. I just purchased a Delta 10 inch Band Saw and I was very curious about the proper tension settings for the blades. I will now check my spring and tension settings as well. I understand the process so much better after seeing this video. Keep up the good work and thanks again.
I use a number 9688K25 from McMaster-Carr on my Delta Homecraft bandsaws which are about the same as your Delta. They are from the same wire as the 9688K35 that I use on the 14" Delta (very close to the Carter numbers).
Interesting video to address a widely known problem for blade tensioning
thanks
James
You Sir are smarter than most of these so called experts. Kindest Regards
Thank you for your time and wisdom, very very helpful.
Very informative Carl, thank you for an excellent demonstration.
a tip : you can watch movies at flixzone. I've been using it for watching a lot of movies recently.
@Ayaan Travis Yup, I've been watching on flixzone} for since november myself =)
Thank you, Carl.
Thanks again. Excellent information
Excellent,thanks for you time
Carl,
I'm guessing you must be an engineer? Great video for reference. Taking ones bandsaw apart could be considered a daunting task. Definitely makes sense as to how and why. Thanks!
Very good info, Thanks
Can you show or explain exactly where you adjusted the tensioner to. Should the top of the nut be be at the mark or the bottom. Thanks
Thanks Carl.
Great job!! Thanks a bunch.
Thanks for the tip on adjusting for drift in video 1. Did you find that you got a better / smoother cut after the tension changes?
+Dysl3xicDog D3D: Not significantly, I think smoothness of cut depends on blade quality. ////Carl
Excellent. Thanks
Thanks for posting. Your measuring device is stretching as you tension up, doesnt that render the measurements different to when a bandsaw blade is installed as it does not stretch nearly as much?
I believe he is not marking movement of the upper axle relative to the bandsaw frame (which axle as you said, moves a lot more when pulling against the measuring device as opposed to when pulling against a band saw blade (because the band saw blade has a much higher spring rate than the spring of the measuring device). Instead, he's marking movement of the spring tensioner relative to the upper axle...the moveable part that is moved upward by the screw adjustment to compress the spring, while the other end of the spring acts to push up the wheel axle; essentially measuring the change in length (due to compression) of his new spring, which will be the same whenever he reaches the same tension between the bandsaw frame and the upper axle, no matter how much the upper axle moves relative to the bandsaw frame.
You did not mention in the video what the brand of the spring was that you replaced on the bandsaw - can you please post the information on getting a replacement spring like you used?
Michael B.
I bought the spring at the local Lee Valley Store; it's a "Carter" brand.
Want to know what mark you are using below the spring when you tension the blade, top of nut or bottom of nut that spring sits on?
+Rick Kaminski Top of the nut (actually the lower end of the tension spring)..
////Carl
There is usually a colored fiber washer between the spring and nut to use as an indicator. I installed a couple washers for spacers above the washer so at 8 turns it lines up with the 1/2" mark. It pretty much lines up with the other appropriate marks also.
Carl,
Would you mind giving the specs for the spring you purchased? I think it would give me (and others) an idea of where to start on our own band saws.
Thank you, David
David W.
The spring is made by Carter, a manufacturer famous for bandsaw accessories. The free length is 2 1/2'", OD is 3/4", ID is 7/16", the wire is 1/8" X 1/8" square cross section.
In the video at 11 mins on is a chart which shows the spring rate, i.e. lbs force at various spring lengths. ////Carl
Eric thank you. I actually found a spring that matched that one that was only $5.
What spring did you buy? I am trying a 3/4 x 2.5 gold (heavy) die spring from McMaster-Carr. Using 8 turns (1/2") for a half inch blade. Max compression for this spring is 10 turns (5/8").
A Carter brand spring from Lee Valley Tools. Square cross-section wire, gold color. It appears that you got the same spring from McMaster Carr
Your chart fits pretty close to my findings using a bathroom scale on the drill press. I am currently looking at borrowing some metric die springs from a local shop to do some testing. McMaster-Carr also has the same spring in a 3" for use on Jet and other saws that take a 3/4 x 3 spring.
Gday mate, nice information, where can i buy one of those springs, cheers
Carter sells them $19.95 each
What is the name of scale you are using to test tension. Where can I get one?
Tom R. Purchased at Farm Supply Store - Princess Auto - SKU No. 8105496 ////Carl
Carl
Never paid too much attention to the "spring thing" and thought that CARTER's ploy is just to sell you "another" expensive and unnecessary item.
I think maybe I was wrong, but, still not totally convinced.
There is a notion of other "experts" that they think that you shouldn't tension your bandsaw too much for excessive wear on your bearings and the wheel tires.
So, I'm a bit confused now, which one is right. (Is the earth FLAT?)
Whatever the verdict is, I find your videos educational and your persistence remarkable. Thanks.
ronin47, Suggest you look at Iturra Designs Catalogue of bandsaw accessories:
dl.dropboxusercontent.com/u/82359640/Iturra_Design_catalogue_2010.pdf
While this is not a current catalog, their discussion of various aspects of bandsaw operation speak for themselves. Refer to page 38 for a discussion of bandsaw blade tension. For me, their catalog is my primary reference for things bandsaw!
Thanks Carl.
Any chance of making that file available again? (the link in the comment is expired)
Plus 1 on the Iturra Design Catalogue. It is a great primer for those really wanting to understand what is going on.
Very interesting.....let me share, as briefly as I can, my experience with my cheaper diy-er bandsaw. Read/watched numerous vids and articles and tried flutter/side movement/twanging (😀) but still experienced very regular blade snapping (wow - that wakes you up every time)....anyway, all the 'experts' kept telling me I didn't have enough tension (including visiting the blade manufacturers factory to discuss) so upped and upped and upped again etc etc.....each time still getting same outcome. I was about to bite the bullet and sell/launch this 'new' machine and spend much more on a new one when by accident I came across a guy who ran a wood turning club and he came and had a look....after approx 30secs he said tension was way too high and immediately took the blade down to less than even the instruction manual.....3yrs later and I still have not snapped one blade and use the thing continually.....don't believe everything you read from experts on the web.
SOL, Thanks for looking at my video and thanks for the report on your experience.
My experience is that lower blade tension, such as obtained with the "flutter test" is fine with thin wood ( up to 1" thick) but when trying to saw thick wood (resawing), a lower tensioned blade will deflect between the guides because there is not enough "beam strength". The "beam strength" can be increased by using a wider blade (I use a 5/8" blade for resawing) or by increasing the blade tension. ////carl
+Carl Holmgren hi Carl...thanks for reply.....don't get me wrong my little machine will not cut huge blocks but has a 5" throat so covers everything I'll EVER want...my problem now is that after a dozen heart attacks (if you've had a blade snap you'll know what I mean) I'm a little anxious about ever increasing the tension again. Ok, I don't get an absolutely perfect cut (I do get a little drift) but do get cuts that I'll, at worst, tidy up on the table saw and, at best, will be fine for my needs. This may not be a practical comment but, as my lecturing wood-turning friend said, don't be afraid to put some horizontal force on the blade as in the worst case you'll simply STOP the blade.....one hell of an improvement to snapping it. Has been brill for 3yrs 😀
Wonderful video. I do have a small suggestion. When I took physics i learned about Hooke's law. Hooke's law is a principle of physics that states that the force needed to extend or compress a spring by some distance is proportional to that distance. Instead of changing the markings you could simply shim the spring to give you the required pressure for your most narrow blade, then the other markings should be correct also. Used to shim valve springs all the time when I worked on race car engines. of course I would get the new spring first.
One of the problems with cheaper saws especially those with cast risers is that they flex at high tensions. One reason you do not see the large saw made for large blades being cast riser but steel frame and risers.. Even the make up of blade; as to hardness and fif same hardness across the width of blade can make a huge difference of tension needed. Harder teeth softer at rear called flex back is what I found to give best duty with average lower cost 14" saw and no thicker than .025 and half inch max.
On steel frame this blade will tension for best cut at less than scale on most saws I have seen.
He is clearly an Engineer
Won't you're readings be off by the weight of the top wheel since that was removed while taking measurements? You will have to tension the spring to overcome the weight of the wheel after it is reinstalled before it can begin applying any tension to th blade, right? I see at the end of your video where you are putting everything back together that your wheel doesn't seem very heavy but for someone else watching, the weight could influence the outcome of this procedure, I think. It may be insignificant but for as much attention to detail you are paying, I would think it is something you should be aware of. Nice video.
+Joseph Cook Good point and of course you're correct. My only defence is that the upper wheel is light aluminium alloy. Compared to other possibilities for error I'd argue that the weight is insignificant. For bandsaws with cast iron wheels, the weight should be considered. //Carl
Cast iron is specifically what I was thinking about.
Thank You so much . I was just about to throw my harbor freight 14 " bandsaw out and buy a more expensive one .
I am not sure I agree with this approach.
The weight (force) the scale experiences vs the distance it stretches depends on the elasticity of the mechanism inside the scale. This is not the same force a band saw blade will experience when stretched by the same distance. The blade has its elasticity modulus that is unlikely the same as that of the scale.
I don't believe this scale can measure the tension of the blade when installed.
@rats arsed The tensioner of a BS is generally a spring made of steel; it is not just steel.
I am trying to figure out where you came up with your 12,000 number and the math.
Seems like fuzzy logic..
Textbook mild steel yield strength: 52,000 psi. On the average, blade manufacturers recommend approximately14,000.I've used fuzzy logic to arrive at a tension of 12,000 (adopting a safety margin of approximately 1/4 of yield strength) and the safe side of manufacturer's suggestion. ///carl
I like your video, but your method depends upon the blades you get being the same length. They DO vary.
Beg to differ Keith, Although blade length can vary 10 cm or more, I'm measuring tension after all slack is taken up. ///Carl
@@CarlHolmgrenwoodworking Sorry, meant to say that your making new markings on the slide won't matter as blades will vary in length. Your method seems sound but not reliably repeatable if blades vary in length. You need a measurement of actual tension from blade to blade. Some sort of gauge in the system, a deflection gauge (can be expensive, but maybe a DIY version?) or a torque measurement on the tensioning bolt.
I think you may have made a mistake multiplying psi by 2. Could you in depth explain your maths?
listen at 2:30 where he says blade has a front and a back component!