Another 4X6 Bandsaw Modification

That wimpy little plastic knob for tightening the blade on my band saw was too small to get the proper tension on the blade without using the large channel loks. So ....... I made a new adjustment handle using a 2" diameter piece of CRS , drilled and reamed .500" holes for handles 180 degrees apart. I loc-tite the 1/2" rods in the holes, put on a nifty set of rubber grips I had left over from other projects, and loct-tie some 3/8" all thread in a tapped hole.





The handle works great. I can easily tighten the blade to proper tension by hand. This mod only took about an hour to make (looks good too).

The hole in the saw casting was tapered (draft angle) when cast, so I used my 4 1/2" angle grinder to grind it flat so the handle seats properly against the casting.

Wow, great looking handle Mark, but it's size leads me to ask this question. Just how tight do you like to have your blade ?? You must be feeling better, and I'm glad about that. JR49

The handle is 6" across. Not really that big, but heavy duty . ( I made it from scraps I had). I am actually afraid to tighten the blade to what several blade manufacturer say it should be. The specs say .00034" stretch over a specified distance. I make mine about 2/3 of that spec and it is TIGHT. With the proper tension, the saw cuts straighter faster and a smoother finish. I was amazed how much better my saw performs just with the proper blade tension. This handle made it so much easier to adjust the tension.


Oh ..... and I am getting better, I think

Some of this malarky is over my head, but there is a table that says the factor of stretch relating to tension in various materials is called "Young's Modulus" The young's modulus for steel is 29,000,000 .

Using a blade tension gauge ( as I made in another thread) or by using two small c clams and clamp a dial caliper to the saw blade (functional but not as fancy), measure the physical stretch of the blade when tightened.

(amount of stretch) .0003" / 4.00 (span of stretch) = .00075
multiply that by young's modulus .00075 x 29,000,000 = 21,750 PSI (of tension). (this is what I set my blade to.)

To convert that to actual tension in pounds, multiply the cross section of the blade in square inches times the PSI tension.

(blade width) .500" x .025" (blade thickness) = .0125 square inches

.0125 x 21,750 = 271.875 pounds


What it amounts to is I tighten my blade to stretch it .0003" on the gauge and it works great.

Wow! That seems overly complicated for my feeble brain. I tension mine til it " feels good". Seems to work.

So, Mark
First, glad you're getting better & hope you continue improving.
Second; since you had to use channel locks to get proper tension on your saw does that mean that I can (and maybe should) crank the little stock knob about tight as I can? I don't have any experience with band-saws and have always been scared to crank the knob anywhere near what I can get by hand. I also don't have any idea how tight it is or how tight it should be.

Would it be possible, and would it even work, for you to use a guitar tuning software to find the pitch of your blade when struck? Then I can "tune" mine to the same pitch, which should equal the same tension (I guess we would need to be using the same blades - but maybe it would be close). One such free PC guitar tuner program is http://www.nch.com.au/tuner/index.html. A plug-in earbud with a microphone works good enough to pick up the tone.

(My Ducati motorcycle uses this method to set the tension of its valve timing belts.)

mark_f said:

Some of this malarky is over my head, but there is a table that says the factor of stretch relating to tension in various materials is called "Young's Modulus" The young's modulus for steel is 29,000,000 .

Using a blade tension gauge ( as I made in another thread) or by using two small c clams and clamp a dial caliper to the saw blade (functional but not as fancy), measure the physical stretch of the blade when tightened.

(amount of stretch) .003" / 4.00 (span of stretch) = .00075
multiply that by young's modulus .00075 x 29,000,000 = 21,750 PSI (of tension). (this is what I set my blade to.)

To convert that to actual tension in pounds, multiply the cross section of the blade in square inches times the PSI tension.

(blade width) .500" x .025" (blade thickness) = .0125 square inches

.0125 x 21,750 = 271.875 pounds


What it amounts to is I tighten my blade to stretch it .0003" on the gauge and it works great.

Click to expand...

Mark, I was having the same kind of issue on my 7x12 horizontal bandsaw so I added a needle bearing thrust washer below my plastic tension setting knob and now its real easy to get the right tension without using a cheater. Great wright up. Jack

Groundhog said:

Would it be possible, and would it even work, for you to use a guitar tuning software to find the pitch of your blade when struck? Then I can "tune" mine to the same pitch, which should equal the same tension (I guess we would need to be using the same blades - but maybe it would be close). One such free PC guitar tuner program is http://www.nch.com.au/tuner/index.html. A plug-in earbud with a microphone works good enough to pick up the tone.

Click to expand...

Way back before things seemed seem to get very complicated there was a following of woodworkers who did this. The blade was plucked, and supposedly (if I remember correctly anyway) the desired tone to hit was "F". I still do it on my wood saw although I couldn't tell you what actual note I'm hitting!

-frank

Gonzo,

I used to think that. My saw cut and it cut straight and it worked. I thought it cut a little slow so I talked to several "blade" professionals. Now my saw is a "metal eating machine". I always used a bi-metal blade. Setting the proper tension made it cut faster and the finish improved greatly. Instead of a "sawed" look, my cuts look almost machined. It cut a lot faster by using the correct tooth combination blade. I went to a 6 - 10 tooth combo blade for most cutting. I keep a 8-12 combo blade for lighter materials. The guy that made my blades said the combo tooth pattern self cleans better (tooth count changes every three teeth). I also start a cut slowly until the cut is started good. This keeps from breaking a tooth. ( Rule of thumb is to have at least 3 teeth in the material being cut.

Groundhog,

Everyone has a different amount of strength, but I tightened the knob as tight as I could by hand an then gave it another turn with the Channel locks. Even this was a little less than the gauge recommendation but I am scared to tighten it more. It plays a nice note when plucked and it does cut better. I do not know if the guitar note would be the same as the blade, but it might work.

Jack,
I though about doing that. I have the bearing but it would change the feel of tightening the blade. If I put the bearing in, I will definitely have to use the gauge to set it up. A blade lasts a year or two ( and I cut a lot). I have been told proper blade tension will make the blade last longer and also to "break"in a new blade to make it last longer.

I want one!