Gentlemen,
How do the folks (like me) who have to set tension on their blades manually accomplish this? I have a big bolt that pushes the wheel outboard when tightened, and I use a torque wrench to apply the pressure. How much do you tighten a 221" blade? It is a long way between guides, so is 70 ft/lbs out of the question? When working on aircraft rigging, there is a tool to measure tention from the rigging cable. Any such animal?
Feel free to talk amongst yourselves....
My Norwood has got a spring that you compress ,keeps the tension right when the band streches
My 18" "economy" Hudson mill requires 40 to 60 lbs torque. I usually use the 50 to 60 range with good results. The blade is 132 " if that matters.
Hope that helps
Rick
Beerguy,
If you want to spend the $$, the big saw companies (Simond ) have a tension measuring device that clamps on to the blade and measure the stretch in the blade with a dial indicator. I thought about buying one for my manual mill, but the cost were about equal to the price of hydrualic components to build a hydrualic tensioning system.
that thing is a tensiometer. I use one checking the rigging on airplanes as well (KC-135E models as a matter of fact) They work quite well. If you really think you need one, I may be able to dig one up around here. Let me see what I can find!!!
My mill also has the screw spring adjustment and in the beginning it was a guessing thing. Then I found out about the fluddering test and it work out well for me.
I put some tension on the blade, start the motor and slowly get the fpm up to max. I then tension the blade until the fludder is gone and turned the tension screw one full turn. After that I shut it down and counted how many turns it took to back the blade off to slack. As for mine it takes 7 turns. I run a 14 ft 6 inch blade. Hope this helps.
EZ
Twoodward15:
I too have used the tensiometers on the C-130 aircraft rigging cables. It was the same as the one we used on the transient KC-135, C-141- C-5 aircrafts.
I may be wrong, but I dont think the ones we use on cables is going to be sufficient for band blades. I would bet a tensiometer for a band blade would be much wider than a cable tensiometer. It would have to be wide enough and deep enough for the tension device to be applied to the center of the balde width.
I bet that the brand of those meters are stamped on them somewhere and if so, the company that makes them for cables may have also made them for other applications.
I no longer have access to a cable tensiometer (Retired AF) but if you do check the brand name and and we could try to contact the company that made it. If you cant find the company name I may be able to contact some of my friends at Little Rock AFB and get the info.........provided they are back from Iraq.
If you want to make a dirt cheap tension gage, you can clamp a 6" dial caliper to your blade. You can get the correct stress to run your blades from the blade manufacturer. Open the caliper to 6.000", clamp in place, and then tension your blade until the blade strains the correct amount over over the original 6". I could help with the calc's if anyone wants to try this. I'll just need the blade width and thickness and gullet depth.
Duh, I don't need all those dimensions. :P Strain is strain. Get that dusty old engineering book out engineer boy! All I need is how many psi the band manufacturer recommends.
The cheapest dial calipers can be found at http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=47257
(https://forestryforum.com/images/03_21_04/47257.gif)
Only $15.99 for a 6" digital caliper.
OK, guess it's me. How does this work?? Where do you clamp it, and what reading do you get ???
Lets say that I want 1600 PSI on the blade tension.???
I gave Simonds a quick call and they said their Red Streaks should be stressed 25,000 to 30,000 psi.
Thus:
Stress = E * Strain
25,000 psi = (29,000,000 psi) * Strain
Strain = 0.00086 in/in
Having a distance of 6" gives 6" * 0.00086" = 0.005" deflection.
So, clamp the caliper, opened to 6.000", on your band with zero tension. Then tension your band until it reads 6.005". This will give 25,000 psi in the band.
For 30,000 psi your caliper should read 6.006"
Hope this helps,
Gilman
I called Woodmizer this morning and was told I needed to talk to John Storm to find out how many psi their blade should be set at. Unfortunately he is in meetings this morning. If anyone gets info from Munks or other band manufactures, please post it here. I'll do a quick little chart for the group.
Ran outside and did a quick test. I'm running 0.042" x 1 1/2" bands, but the strain should remain the same no matter what thickness or width.
Mounting the caliper, Don't try to get exactly 6.000", way too difficult, just get it close and then add 0.005" to it.
(https://forestryforum.com/images/03_21_04/Copy%20of%20DSCN2136.JPG)
Band set to Zero tension.
(https://forestryforum.com/images/03_21_04/Copy%20of%20DSCN2138.JPG)
Band tensioned.
(https://forestryforum.com/images/03_21_04/Copy%20of%20DSCN2139.JPG)
Caliper reading after tensioning. I got 0.0045" of deflections, thus I guess I need to be running in the high red with the 1 1/2" bands.
(https://forestryforum.com/images/03_21_04/Copy%20of%20DSCN2140.JPG)
Hope this helps out.
Gilman
Good method. and cheap too. (IMO)
Seems one could just clamp the digital caliper to the band at 6 ", and then zero it out at the "untensioned" starting point, and then read the 'stretch' needed when tensioned.
Saves trying to set exactly at 6.0000" to start, and just use the direct reading of 'stretch' needed to get the desired reading.
That's a good idea, it will also increase your accuracy.
I like it. Thanks for the idea. Now if I could just remeber which blades are which. LeeB
Thanks for the lesson, Gilman. I will try that in reverse next time we go to the camp. 8)
Thanks, guys. This takes the mystery out of it. My torque wrench has been out of calibration for some time, and I have the tools for this measurement.
Gilman,
I found your information on blade tension which was very informative. I had calculated my needed blade tension and bought a proper die spring when I built then mill some 6 years ago. Since I have lost my calculations. I like the dial indicator method, thanks.
Maybe I'm thinking of a different thread...but I believe this method was only for those people who had actual bandwheels or sheaves. I though I remembered reading that it didn't work for guys like me who used trailer tires.
Jim
Mike from Mr Sawmill gave Bill instructions on tensioning using 1 revolution on the pull bolt, back off 1 to change, return to original setting. Now I know he said the blades are accurate, but how can they be sure each and every blade is exactly the same length? I think the caliper idea is an easy and effective way to do it.
hay what was the hyd guage lb reading
I think the discussion on blade tension is about as wide as it is long. I am not saying that I am an authority but I have seen things and like to share others ideas. I have built several saws over the past twenty years and I always go to the Lennox engineers for info such as wheel size, spacing, etc. My first bandmill was in 1999. At the time I had the proper data and designed accordingly. Since that time I have lost this data in swapping from a gazillion computers. To me the importance of this thread is that is gives a basis for one to do his own checking of tension versus his idea of his tension.
I read where this guy says that he has to use xxx ft/lbs of torque, or xx lbs of hydraulic pressure. For those with homemade or some store bought mills, the design is different such torques, and hyd pressures. There is a spring out there sold by Danly Die Set, www,danly.com . They sent me two catologs with all of their springs in them. You can get a spring that gives exactyy so much pressure for each 1/10" of compression. I think MSC Supply carries some of these springs. The kicker is that one needs to know and calculate the distance from the pivot point of the wheel bracket, center of the axle, and the point the spring is placed. I believe that this was for a 1 1/2' blade and one needs to find out what one needs for an 1 1/4" blade.
I have never been around any mills that run rubber tires so I am not sure how this will work for them. Since I have gotten this mill back in the shop after some years, I have been experimenting with many different things. There was a thread that mentioned tightening the blade until the flutter came out then thighten a little more. I think I have found that this is a good way to do it. I want to compare this tension with a dial indicator.
Thanks to everyone. This forum is really good.
I guess I really don't know what I'm doing or just DanG lucky.I just tighten the blade until I think it looks good,than take my thumb and push down on the blade and I can tell how tight the blade is in this manner.I run the blade and I make sure it's running smooth,no flutter.I haven't sawed 100,000 bf,but I've sawed quite a lot and this works for me.
Thecfarm,
It is in what works. That is kind of what I do.
thecfarm, that is my gauge on my homemade also.
Will
Jim,
The nice thing about strain is that it doesn't care or know the difference. You can use this method with goat hair wheels if that's what your running your blades on.
You're very welcome Highpockets
Lennox replied to my question and said 0.0025" on 5" test.
I pluck it with my wrench and listen for the thrum.m.m.
Works as good as anything else I have tried. I borrowed a tension meter from my blade source but broke blades when jacking it up to the recommended tension. I have tried keeping track with a torque wrench too.
I can cut flat lumber without those things but there was a learning curve. A lot of broken blades and wavy lumber due to improper tension at first.
I think the proof is in the pudding. I am still a little confused in what I read and what little I can calculate. Ken told me that he had a 1" cylinder on the WM Mill tensioner. I think they recommend some 2,000 p.s.i. of pressure. To me this calculates to some 1680 (calulator not handy) lbs of force on the shaft. If you divide that by two, I don't see where the 15,000 lbs of (Lennox recommendation) strain come from.
To be honest, I started out trying to run by these large numbers. I broke probably 30% of my blades. Since I started pulling the flutter out and tighten a little, I can cut good woood and have not broken a blade out the last 14.
I agree with Brucehuggins. I would pluck the blade on my vertical bandsaw and you could hear a note. Do it enough times and you'd know when you were getting tight enough.
I'll try it on the mill whenever it stops working perfectly! :D :D :D
High Pockets,
I think Lennox was referring to pressure lbs/in^2 the band experiences, not lbs of pull.
Assuming you have 1 1/4" blades x 0.045" thick and 1680 lbs of pull
pressure (stress) = (1860lbs/2)/(1.25" x 0.045") = 14933 lbs/in^2 (psi)
Gilman, I am certainly glad you are around. I am getting old and my thinking does not seem to be what is used to be. That sounds about right, now you mention it.
I had alot of problems at first with blade tension on my mill. I now put 48-50ft lbs on the bolt with a torque wrench. If you have to keep tightning its because your blade is hot and stretching because its dull. If you don't sharpen the blade its going to start cracking. I debark and use keosene for lube, this helps my blades run cooler, don't use much, if your blade hydroplanes bad news. Kerosene will ruin the tires on some mills. I have much better luck with my blades now.
How we can find out tension in a circular saw 10 mm Thick 1500 mm diaby A STRAUGHT EDGE WHICH HAVE
A ROUND BOTTOM???
What is this straight edge for?
For thinner saws you can use ALLEN GAUGE.
Wonder what note on the scale the blade will give when plucked at the right tension? If that is what it takes, seems that with a pitch pipe, blade tension could be 'tuned' to the correct note. Anyone know what that note might be? Any violinists on the forum? or maybe even a trombonist ;D or string plucker ::)