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Shuswap Pat
06-26-2011, 12:26 PM
I see a thread on alignment, and I will try and post a simple tool I built that mimics that Starrett tool. It is a piece of ½” square aluminum tube about 5" long, that clamps parallel to the blade axis, to check with a square. I built 2, and then I clamp one on by each guide to check the alignment – with the two. You can see “twist’ in the blade easily, on both horizontal and vertical saws. Another issue is making sure the wheels are ‘Co-planer’ (another topic – more for vertical saws}. It doesn’t matter is if is a 6’ diameter – 250hp band mill in a sawmill, or a 6 x 9 ½ Hp saw at home – principles are the same.

Has anyone got a sketch for a simple tension gage? The commercial ones are a nice, but time is more available than cash for some of us. They basically measure the strain by the amount of 'stretch' over a given distance, relative to the cross sectional area - got all that. Layman’s terms - pull on the blade it stretches, for a given amount of pull, a thicker blade stretches less, and a thicker blade stretches more.
The blade manufacture (Lenox, Starrett, Morse, etc) will give you the suggested strain ( PSI or Kpa), so your blade will cut ‘Optimally’. Also on the blade note – make sure you ‘Break it in’. You will get much longer life – see blade manufacturers web sites.

Pat

lazlo
06-26-2011, 12:29 PM
Pat, I've always been told that for the smaller horizontal bandsaws, like the 4x6 and the 7x12, just tighten the tension as much as you can by hand.

I'd love to see your alignment tool :)

Shuswap Pat
06-26-2011, 01:40 PM
I finally figuired out how to post the picture.

Here is a pair of simple blade alignment tools. They don't say Starrett, but they work fine.

http://i1094.photobucket.com/albums/i451/shwswap_pat/Bandsaw%20Alignment%20tool/Constructionstuff001.jpg

Mr Fixit
06-26-2011, 02:04 PM
OK here goes some of those not so smart questions. Don't the guide blocks or small wheels(bearing guides) on my machine do the same thing or am I missing something here. Are these for straightening a bent blade? Do you install them and leave them when you cut or remove them? OK enough of those not so smart questions I will sit back and wait for the answers from the grumpier ones "LOL" or not.

TX Chris :)
Mr. Fixit in the Family

RWO
06-26-2011, 02:20 PM
The Starrett tension gauge is not too hard to clone. It's just a simple block with an embedded dial indicator. The plunger of the indicator is depressed by one end of lever arm pivoted near the middle with the other end clamped to the blade.

It indicates blade stress in PSI, by measuring the blade stretch(strain). Many blade manuf recommend 10K PSI as optimum. Blade cross-sectional area is not a factor in the measurement since we need load per square inch. Narrow and wide, thin and thick blades stretch the same amount for any given blade stress. The variable is tension.

I made a clone of the Starrett gauge some years back, but have lost the calculations. On my version, it boils down to .001" indication on the guage with any blade is equivalent to 10K PSI stress. Rather than recreate the calcs, I could measure the critical dimensions on my gauge ( there are only 3) and indicate them on a sketch if anybody is interested.

RWO

tyrone shewlaces
06-26-2011, 02:37 PM
Has anyone got a sketch for a simple tension gage?
Pat

I wonder if something as simple as this would work:
http://i240.photobucket.com/albums/ff201/rgpimage/Blade.gif

You would use a torque wrench to screw the bolt against the blade until you reach the required tension (have to do some math to figure out what that would be) and just read the deflection on the dial indicator.

Not high-precision, but if you could establish a reference to compare to or be good enough with your math, maybe this would be enough to work in a home shop?

Shuswap Pat
06-26-2011, 04:53 PM
Fixit - The two gages clamp on to the saw blade (when shut off/locked out) then you can check to see that they are parallel - no twist, and sguare to the bed of the saw. This will allow your saw to cut straignt and square.
Pat

Duffy
06-26-2011, 07:25 PM
Somewhere in the distant past, Fine Woodworking had an article on band saw tensioning. I know, metal saws are tensioned more, (maybe,) but the recommendation was to tension the blade to a given pitch, using a tuning fork. The important point here, I think, is that, once you have the blade tensioned to a given note, AND it cuts just fine, then you can repeat the process without ever knowing WHAT the actual tension is.It sticks in my mind that high C was the note.

Lew Hartswick
06-26-2011, 07:39 PM
Somewhere in the distant past, Fine Woodworking had an article on band saw tensioning. I know, metal saws are tensioned more, (maybe,) but the recommendation was to tension the blade to a given pitch, using a tuning fork. The important point here, I think, is that, once you have the blade tensioned to a given note, AND it cuts just fine, then you can repeat the process without ever knowing WHAT the actual tension is.It sticks in my mind that high C was the note.

That will depend on the spacing of the contact points (distance between the wheels)
and the cross section of the blade AND even on the material of the blade.
So even perfect pitch operators will need a LOT of calibrating first.
:-)
...lew...

Bill Pace
06-26-2011, 07:45 PM
Fixit

To add to Pats explanation of the gages and a possible answer to your question --
The blade guides are - obviously - guides for the tracking of the blade and therefore occasionally need to be re-tweaked. When loosened, the bolt/screws that holds the two guides will have some "play" in them, allowing fine tuning of the blades tracking. The gages are an aide in seeing when the blade is 'square'. A slight deviation out of 'square' will make for really crappy cuts.

DATo
06-26-2011, 07:54 PM
Has anyone got a sketch for a simple tension gage?


Check it out.

http://bbs.homeshopmachinist.net/showthread.php?t=21171