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blade tension...

Started by mrcaptainbob, March 08, 2010, 12:28:55 AM

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mrcaptainbob

looked through past postings about blade tension and liked the many ways and suggestions. The best one was clamping the dial caliper to the blade and measuring like that. Similar to the store-bought. But....how much stretch per inch is correct? I'm sure it depends on blade width and such, but as a start point, what's a dimension? Is there a table to go by?

John Bartley

Quote from: mrcaptainbob on March 08, 2010, 12:28:55 AM
looked through past postings about blade tension and liked the many ways and suggestions. The best one was clamping the dial caliper to the blade and measuring like that. Similar to the store-bought. But....how much stretch per inch is correct? I'm sure it depends on blade width and such, but as a start point, what's a dimension? Is there a table to go by?

There is no "table" as such. Each supplier has a different recommended amount of strain for their bands. To do your own stretch calculations you'll have to learn about "Youngs modulus of elasticity", and then find out from your band supplier how many pounds of "strain" they recommend. Once you do that the calculations are pretty straightforward. When you're doing your calc's, remember that strain is force, not pressure, it's in pounds, not pounds per square inch, and you need to use twice the cross sectional area of the band because it's a loop, not a length. I always buy the same bands (Hakkansen), so once I got it figured out and knew how many PSI it took to get the correct strain, I forgot the stretch figure and stuck with the PSI.

cheers

John
Kioti DK35HSE w/loader & forks
Champion 25hp band mill, 20' bed
Stihl MS361
Stihl 026

bandmiller2

Cap Bob,on the two bandmills I've operated I haven't found the band tension to be critical,you have a useable tension range.Sufolk machine [timberwolf bands] says tighten til theirs no flutter,then a little tighter,check their procedure.Myself I have a heavy spring and know how much to compress it,usally by counting the number of turns on the handle.The cats pooper is hydraulic or air with a gauge.Try it, then find a way to repete what works for you.Frank C.
A man armed with common sense is packing a big piece

sdunston

Just got my WMBTG last week, WM says blade tenision should be around 2800 lbs on the dial.I have not had to get out and try it yet because of all the snow but will report when I do.
Sam
WM LT28, American fordge 18x8 planer,Orange and white chainsaws, NH TC33, IHT6 dozer, IH-H tractor and alot of other stuff that keeps me agravated trying to keep running

Precision Wood Products

I've found if I don't keep the tension Around 2600 I can tell a drastic change in the quality of my cut. I can cut faster when it is tensioned properly.

MartyParsons

We have been testing the WMBTG Wood-Mizer blade tension gauge. I get out servicing a few mills each month. It is an eye opener when you show a customer where he has been running the tension and where it should be. I can really put the tension up on a LT28 or LT15. Cross section of the blade changes with thickness, and width of the blade. If you check a mill with a .045 thickness blade and then change the blade to a .055 blade you will need to raise the tension to get the same reading or stretch of the metal band. I would assume that if you have poor bearings or a weak bearing you may find it. I think some mills were not designed to run the blade at the tension we like to see the blade perform at.
I give advice to owners of other manfactured mills not just WM, you may adjust the tension then take a mallett or move the wheels and see the tension lower. You can see this on the hydraulic gauge on the WM but lots of mills just have a spring or other method of keeping the blade tight.
I am not saying the other guys are incorrect I am just telling you what I have seen.

Hope this helps.
Marty
"A pessimist sees difficulty in every opportunity; an optimist sees opportunity in every difficulty." -Winston Churchill

John Bartley

Quote from: MartyParsons on March 08, 2010, 10:05:21 PM
We have been testing the WMBTG Wood-Mizer blade tension gauge. I get out servicing a few mills each month. It is an eye opener when you show a customer where he has been running the tension and where it should be. I can really put the tension up on a LT28 or LT15. Cross section of the blade changes with thickness, and width of the blade.

Hope this helps.
Marty


Marty,

Does Wood-mizer give out the strain information for their bands? The gauge is likely calibrated for Wood-mizer bands, but with the amount of strain known, anyone using Wood-mizer bands can do the calc's and use a dial indicator.

cheers

John
Kioti DK35HSE w/loader & forks
Champion 25hp band mill, 20' bed
Stihl MS361
Stihl 026

coastlogger

captainbob, Im not sure if this will help but I went thru same question last year, followed John Bartleys advice on modulus research,concluded that 15000 (psi?) of strain was a realistic # for a band and that this would give 2.5 thou of stretch over 5 inches. I did this test on my mill and concluded that the 2500# of HYDRAULIC pressure I had been running at gave 2 thou of stretch over 5 inches or app.12000 psi of strain.(clamped a vernier to blade)This seemed fine (a bit less than the researched optimum) to me so I stayed with my 2500# hydraulic pressure. I never did confirm any of this with any experts but am getting good cuts and blade life.
As an afterthought I have been tracking my blade width and a blade of mine loses over 10 % of its width by  repeated sharpening so I guess an old blade should run with 10% less strain/pressure to give the same "strain" and hence stretch, as a new wider blade.
clgr
clgr

mrcaptainbob

More great info, and more great help. I can do Young's Modulus and plan to use that to help neighbor in the design of this unit. Great info, and again, thanks so very much for the help.

sdunston

Quote from: MartyParsons on March 08, 2010, 10:05:21 PM
We have been testing the WMBTG Wood-Mizer blade tension gauge. I get out servicing a few mills each month. It is an eye opener when you show a customer where he has been running the tension and where it should be. I can really put the tension up on a LT28 or LT15.

Hope this helps.
Marty

Marty.
      On an lt28 what tension have you found to be the optimum. I got my WMBTG last week,reason beining that I put a new blade on and it was diving, cranked up the tension a full turn and all was fine. That was the deciding factor on the guage purchace(and the money off thanks for the calender in the month of march) And my thinking was to check blade tension prior to sawing and after every blade change
Thanks Sam
WM LT28, American fordge 18x8 planer,Orange and white chainsaws, NH TC33, IHT6 dozer, IH-H tractor and alot of other stuff that keeps me agravated trying to keep running

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