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Author Topic: Can't stop band mill from cutting waves  (Read 1068 times)

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Offline Charles

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Can't stop band mill from cutting waves
« on: November 29, 2019, 12:36:50 PM »
I have  a friend who saws my logs for me. Lately there has been a problem with waveness  while sawing.
The mill is custom made with the blade on about a 15 degree angle with a 40" throat. I had walnut crotches from 24" to 38" dia. that I had sawn and while some cuts were straight a lot had waves in the slabs. He uses the woodmizer double hard 
1 1/2 " blade. Blade tension is about 2100 psi (I read off the gauge) He also cut some small red cedar and there was some waves in them also. When I say waves it is not a continuous up and down maybe one or two small deflections but noticeable to the buyer. He also sharpens his own blades and they seem to dull rather quickly, sometimes two logs and they have to be changed. I have read info on this forum about making sure the tracking is ok after changing a blade but am not sure what that is. He manually pushes the saw head and has tried going slow and going faster but that didn't work. He increased the blade psi from 2100 to 2800 and that didn't work. Nothing seems to worn. The deflection can be up or down  and worst case I have seen is a immediate bad deflection down. If that is not caught right away it is very hard to reverse the blade. To get back on track he pulls the blade backwards and moves forward a little at a time. He has been sawing for me for quite some time and I am not ware of previous problems
Any thoughts


Offline Brad_bb

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Re: Can't stop band mill from cutting waves
« Reply #1 on: November 29, 2019, 12:49:38 PM »
There is a topic just below yours discussing this:

http://forestryforum.com/board/index.php?topic=108521.0

What we learned: waves and blade dives

We need more info.  What HP engine is he using?  The wider you cut the harder it is to cut flat.  I only use 4 degree bands.  Think of it this way. 4 degree band each tooth takes a small bite.  It's like 1st gear in your tranny.  You can climb steep hills in 1st gear.  a 15 degree band is aggressive and wants to take a big bite with each tooth.  It's like trying to climb the hill in 5th gear.  

Knot's and thus crotches can cause issues because of changing grain direction.  Blade wants to follow path of least resistance.  You need to slow your feed rate when you enter significant knots or changing grain direction.  

The reason you have more problems with down dives is that you have nothing supporting the band in that direction.  I imagine he has blade guide rollers on the top side which helps support the band when it tries to go up and the band may catch up and go back down (hence a wave).  

Changing band tension usually does not seem to help with this problem.  Use a 4 degree band, a sharp one, and don't try to feed it too fast.  You can tell by the RPM of the motor.

You said he's done a bunch of sawing for you in the past.  Was it the same type of slabs?  Or was it more like straight logs where this problem would be less likely to show itself?

Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!

Offline kelLOGg

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Re: Can't stop band mill from cutting waves
« Reply #2 on: November 29, 2019, 02:39:46 PM »
Brad_bb got me onto 4 bands and I am staying with them. 8)
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Offline Charles

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Re: Can't stop band mill from cutting waves
« Reply #3 on: November 29, 2019, 02:52:10 PM »
He has a 30 hp diesel . I ment the saw head is on a 15 degree angle not straight across like most mills. But good point I'II check the degree of the blades with him. The blades do mostly want to go down. Even with smaller stuff like 24" the wave is not as bad but does happen. He has tried to go slow through tough areas but it doesn't seem to help. While he is sawing I will watch the blade for him to catch it if it starts to deflect. Wonder if his resharpening is off a little

Offline Just Right

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Re: Can't stop band mill from cutting waves
« Reply #4 on: November 29, 2019, 07:29:54 PM »
Buy him one 4 degree blade and you have it sharpened somewhere else and that will probably show him that he is not doing the sharpening right.  
If you are enjoying what you are doing,  is it still work?

Offline richhiway

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Re: Can't stop band mill from cutting waves
« Reply #5 on: November 29, 2019, 07:52:47 PM »
Make sure his drive belt is tight. If the belt slips it can cause the blade speed to vary. 
Sometimes it is just the log.
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Offline homesteader shane

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Re: Can't stop band mill from cutting waves
« Reply #6 on: November 29, 2019, 09:52:38 PM »
iv had the same problem twice now. slow leaner I guess. I get my bands professionally sharpened. the guy that does my sharping cought it actely. I was talking with him about my bands diving and he told me to bring the mill down to him. he put a device on the mill that shows what angle the band is on. mine was out by less then 1/8. then we put a slide rule on the guide wheels and from front to back they where wore 3/10000. he said "theirs the problem". the guide wheel where just wore out and made the band not run at a 0* angle. making the band dive. unfortunately for me. I turned up the band pressure to composate for this. and intern created to much friction in the band wheels making heat and it took the set out of the bands permitly. 
I put new guide wheels on and haven't had the problem since      

Offline dgdrls

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Re: Can't stop band mill from cutting waves
« Reply #7 on: December 01, 2019, 07:36:13 PM »
I would check the tooth set first.
Wide cuts need more set and the wider they get the more they need.

No need to over-tension the band, its just harder on the wheel bearings.

Curious to know what hook angle he is running,

D

Offline Brad_bb

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Re: Can't stop band mill from cutting waves
« Reply #8 on: December 01, 2019, 09:07:02 PM »
Yes I forgot to mention drive belt tension.  That is a big one.  
1. Sharp bands that are the right degree for the situation.
2. Correct drive belt (not band) tension.
3. The wood grain direction
4. Feed rate
5. Sharp band

Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!

Offline esteadle

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Re: Can't stop band mill from cutting waves
« Reply #9 on: December 02, 2019, 08:00:28 PM »
I would check the tooth set first.
I agree. Check the set of the blades.

If blades dull quickly they might have lost their hardness.
This is usually caused by heat as mentioned in some of the other linked threads.
The best grinding technique uses multiple light passes, and avoids heavy grinding.
Examine the teeth of a sharp blade closely, check:
 - blued tips (loss of hardness)
 - shiny tips (teeth not fully sharpened) 
 - set width (~1/2 of blade thickness as a rough guide)

Are the waves in the same place on each board? 
 - check track surfaces and rail joints / support for stiffness; avoid flexing in cut

Are they in the widest part of the boards being cut?
 - check for blade slippage on bandwheels - (tension helps but you checked that already) 
 - try a lower hook angle blade ( 7 or 4 ). 
 - this also could be the grain of the wood being cut being worst-case orientation (rising upward with the direction of the cut) 
   if so try reversing the log direction to come at the grain from the other direction, and undercut it. 

Small cedar had waves, too eh? That's odd. 
 - check bandwheel for co-planar 
 - check roller guide bearings and ensure parallel with bunks / rails 
 - again, check the rail joints, track surfaces, and supports for any deflections.
 - maybe get a laser level and run it down the length of the track. 
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Offline Charles

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Re: Can't stop band mill from cutting waves
« Reply #10 on: December 03, 2019, 07:01:05 PM »
Found out his hook angle is 10 deg. Definitely going to change that and as well are going to help him go over the mill with all the suggestions you guys gave 
Will keep you posted on what we find
Thanks
Charlie

Offline Charles

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Re: Can't stop band mill from cutting waves
« Reply #11 on: January 11, 2020, 08:41:01 PM »
A little update here
Have been sawing smaller logs 24-30" so can't say about anything bigger yet. But our sawyer started to use a 7 degree hook angle instead of the usual 11 and big difference . He is gradually reducing the angle each time he sharpens and uses the 7 degrees for bigger logs till all his blades are 7 degrees . He is going to try a four degree on bigger logs when the time comes but I believe he is on the right track at this time. 
Thanks for all the great info sure has helped
Charlie


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