Bandsaw blade dipping?

[ray299]

Hi everyone, I have a problem. As I run the saw down the track it will cut uniform boards but the cant it leaves behind will be thinner in the middle and thicker at both ends. The blade is equal spacing off of each track run but it seems as it cuts it will dip down and then back up again at the end of the log. Any suggestions on a dipping blade? What to check first?

[york]

Ray,what is this mill ???Need more info....

[Chuck White]

Did you measure the blade height, the full length of the tracks?

Seems something isn't aligned properly.

[ladylake]

Do you have the center of the mill supported good? If not the mill will sag in the middle when the head goes over it causing a thin cant in the middle .  Steve

[ray299]

York- I  have a home made bandsaw mill on a trailer. You're welcome to check out my gallery if interested.
Chuck and ladylake - The height on each one of the racks is equal from rack to blade. When cutting I had it hooked up to the truck still but the tail of the trailer was on trailer jacks. Going to try supporting the middle of the trailer to see if that makes a difference. Thanks for the suggestion.

[carykong]

"uniform boards with a dip in the cant"   The cant would have to lift off the bed to get that result.  Are all your logs yielding this result?  More information please.

[Ox]

Sounds to me like the center of the mill frame isn't supported good enough.

[ray299]

"uniform boards with a dip in the cant"   The cant would have to lift off the bed to get that result.  Are all your logs yielding this result?  More information please.

Yes, I've cut four logs so far and all four had a dip in the center of the cant

[ray299]

Sounds to me like the center of the mill frame isn't supported good enough.

The only support the trailer had was being hooked up to the truck in the front, the suspension in the middle and I had to jack stands supporting the rear bumper. I didn't think the frame would Flex that much but let's hope that's what it was. That's an easy fix. Going to try cutting this afternoon with more support under the frame.

[Ox]

It will make a difference.  You don't think steel would move as much as it does, but it does.  All mills need support on both ends and in the middle.  Spread them out however much, but the 3 points are always needed, as a minimum.

[dustyhat]

Is it your blades dipping ,or just your cants bowing.

[ray299]

Is it your blades dipping ,or just your cants bowing.

I'm not sure...
I just cut another log... I'm new, but what i do is square it up four sides- second to last I cut to width (I'm cutting 3/4 inch thick boards but the width is as wide as I can get it, which is about 9 inches with what I'm working with).... so the last side (fourth cut) is the side with the face of the boards so all I do is take a bark cut and then start dropping 3/4" and cut boards. It seems like the blade dips from the beginning because the cant is not only thin in the middle but the two cuts I take at the beginning make the cant thin in width too. For example, the boards I just cut were 9 inches at the ends but only 8.5" in the middle.
Am I explaining this well? That half inch difference is more pronounced at the end when the cant is thin... it was lifted 1/2" off the bed rails.
Also, I added two more jacks in the middle and put the jack down in front.

[Kbeitz]

An easy way to watch your carraige dip is to hook a laser to one end
of your mill. point it on your carraige and mark the spot with a marker.
The laser light should stay on that spot all the way to the end as it moves.

[ray299]

It will make a difference.  You don't think steel would move as much as it does, but it does.  All mills need support on both ends and in the middle.  Spread them out however much, but the 3 points are always needed, as a minimum.

Ox, what would happen if my blade did not have enough tension? Do they stretch? Is tensioning a blade something to do for regular maintenance?

[Ox]

If your blade didn't have enough tension it would wander all over the place, not thin in the middle over and over again.  I don't think blades "stretch" as they are used.  Regular blade tensioning is something that should be done every morning as you should take the tension off the blade and tires/wheels at the end of every day.  I still say something is settling in the center of the frame as the weight of the carriage rolls over it.  Frame pushes down, cant stays the same and your carriage rides the frame down causing your hourglass figured cants.

[Ga Mtn Man]

Stop in the middle of cut, shut your engine off and take some measurements to see what's going on. 

[Ox]

Thing is, the measurement from carriage/head to frame will remain the same even if the frame is flexing.  Try tying a nice rugged, TAUGHT string from end to end.  Then run your head to the middle of the mill and see if the space between the string and frame changes at all.  This will tell you alot, as well as helping you level and straighten the mill.

[shelbycharger400]

If the frame is supported properly.   90percent chance it's your blade guides , the gap is too wide.  Set em up with a cardboard from a 3 ring notebook for total gap.  Or with blade on, use 2 sheets of paper on either side of the blade. I'm bout fed up with these ceramic guides, and bout to spend $300 or so and buy the old style roller bearings for my Norwood.    When I'm buying high figure logs, I don't want waste from a blade sag.

[ray299]

If your blade didn't have enough tension it would wander all over the place, not thin in the middle over and over again.  I don't think blades "stretch" as they are used.  Regular blade tensioning is something that should be done every morning as you should take the tension off the blade and tires/wheels at the end of every day.  I still say something is settling in the center of the frame as the weight of the carriage rolls over it.  Frame pushes down, cant stays the same and your carriage rides the frame down causing your hourglass figured cants.

Really? What's the purpose of taking tension off the blade end of day?

[ray299]

If the frame is supported properly.   90percent chance it's your blade guides , the gap is too wide.  Set em up with a cardboard from a 3 ring notebook for total gap.  Or with blade on, use 2 sheets of paper on either side of the blade. I'm bout fed up with these ceramic guides, and bout to spend $300 or so and buy the old style roller bearings for my Norwood.    When I'm buying high figure logs, I don't want waste from a blade sag.

Pretty sure I have much more clearance than a sheet of paper. I'll check tomorrow. Thanks

[Ga Mtn Man]

Thing is, the measurement from carriage/head to frame will remain the same even if the frame is flexing.  Try tying a nice rugged, TAUGHT string from end to end.  Then run your head to the middle of the mill and see if the space between the string and frame changes at all.  This will tell you alot, as well as helping you level and straighten the mill.

Unless the cant is bending along with the saw frame, there will be a gap between the saw bed and the cant.

[5quarter]

Ray...it is possible that a log might have enough tension to bow up in the center on all four sides, but not 4 in a row. Your trouble is probably the track flexing as the saw head approaches the the middle. You need to disconnect from your truck and block up your mill at at least 6 points (preferably 10); 2 at the front, 2 in the middle and 2 at the end. optionally, you would do better to have 4 more points of support, at the mid point between the middle and each end, on each side. Do not rely on your tires for support. the combined weight of the log and the saw carriage is likely compressing the tires about a ¼", which seems to be the amount of sag your getting with each cut. Ideally get yourself 10 bulldog trailer jacks and mount them 5 per side to properly level your mill. for now, use whatever is handy; like cement blocks, rr ties or blocking cut out of junk logs. My mill is not mobile. it is bolted down to 10 pilings    (the bottom 5' of power line poles set 42" in the ground with 16" above ground) spaced 4' apart along 20' of track, 5 on each side. I check for level maybe twice a year and occasionally have to make very slight adjustments. I use asphalt shingles and tar paper for shims.
Great job so far...keep up the good work! 

[Kbeitz]

To each his own nut I have never released the tension off my blade since the day I built my mill.nSo far it has not been a problem. I'm not saying it's the right thing to do but I've gotten away
with it so far.

[ladylake]

Thing is, the measurement from carriage/head to frame will remain the same even if the frame is flexing.  Try tying a nice rugged, TAUGHT string from end to end.  Then run your head to the middle of the mill and see if the space between the string and frame changes at all.  This will tell you alot, as well as helping you level and straighten the mill.

Unless the cant is bending along with the saw frame, there will be a gap between the saw bed and the cant.

  That's the easy way to check  if your bed is bowing down in the middle, you most likely will find a gap with the head in the middle then just put more support in the middle until the gap goes away, no need for lasers or strings.  It could be stress but 95% of the time logs stress the other way resulting with the cant being thick in the middle and thin on the ends.  Steve

[Chuck White]

Leaving the bands on overnight isn't the best thing for the longevity of them, or the band-wheel bearings.

The bands will stretch and they will be exposed to the weather (assuming the mill is outside)!

Your bands will RUST too!