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Thick and thin

Started by Neil_B, October 25, 2003, 12:07:57 PM

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Neil_B

As always, I don't have much to offer but have lots of questions ;D

I'm cutting cedar and when the cant gets down to a couple inches thick, the end of the board lifts off the bed of the mill.
This results in a thicker board on top and thinner on the bottom at the end. This is happening with the blade in the cut so it's lifting as it's cutting. The first lengths of the boards are fine.

I've tried increasing my hook angle ,12deg, but it didn't help. The blades I am using have a really heavy set though. 32 thou on most of them. My feed speed was lowered as well thinking this could be the problem but it didn't help. I've also checked the guides to make sure they were parallel to the bed.

Aside from going through and resetting all the teeth, is there anything I'm overlooking?

Thanks as always
Neil
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Fla._Deadheader

  Sounds like stress???  Have you tried turning the cant at 3" and taking a board and then turn back to finish the cant???  This would be more of a check to see if there is stress causing the problem.

  Is there evidence of the cant bowing at the ends or in the middle, so it's not sitting flat on the bunks???
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

D._Frederick

New sawyer,
I agree with Deadhead, You have a stress problem. On my manual mill, I have log rests every 40 inches that I can clamp a cant down before sawing. All my board are the same thickness, but they still will warp because of the stess. If a log is not straight, or the pith is not centered, it most likely will have stress in it. Depending on what the lumber is to be used for, you can saw to minimize the effects of stress.

Percy

Im not familiar with the clamping system on your mill but if the ends are lifting everytime and turning the cant doesnt help, you may have some downward pressure from your clamp causing the board ends to lift when the cant gets thin and is able to bend.  The other day I  was splitting a clear 2 X 6 for a guy  and applied a little down pressure with the clamp to get the board to lay flat. I applied a bit too much  and noticed the ends of the board lifted slightly. I imagine the farther your bunks are apart, the worse this could be. Just graspin at straws but ..... ;D
GOLDEN RULE : The guy with the gold, makes the rules.

Neil_B

I had wondered about stress but the cant stays flat until the blade comes toward the end. It's almost as if the blade is diving into board but instead it's just lifting the end up because it's not that thick. I always seems to happen when I'm down to the last 2".

Do I make any sense ???.

I remember reading somewhere here that if you direct the blade slightly upward with the guides it will help it run truer. Am I remembering that right. I'm going to go double check that it's not angled down slightly on the front as I usually make sure it's parallel to the bed with levels as guides.
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Neil_B

Hey Percy,
Didn't see your post, must have been typing the same time.

I'll make a mental note of that but usually all I do is drop the clamp to the height I need, so I don't try to cut it, then move it into the cant so there shouldn't be any down pressure.

I'll keep a watchful eye though. Thanks
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Tom

No,no.  Don't put lead in the blade. That's like toeing out the left front wheel because the right front wheel is toed to the right andpulling to the right.  You make one thing wrong to compensate for a problem and then you have to make everything else wrong to compensate for that.  Don't even go there.!!!

Read the article I wrote on stress that is in the knowledge base.  That might give you some idea of what is going on.
"cutting stress out of a cant link"

I've experienced the same thing and it usually ends up being a slight set problem or a dulling problem   It lifts the cant because it is diving and overcoming the weight of the cant where the clamp is not holding it down.  A new sharp blade will usually solve the problem.  The problem with the old blade will go away when it is resharpened.  

Gumming on the top surface of the blade will cause it too. Does the inside of the blade feel sticker to the touch than the outside of the blade?  Gumming is a heat problem so look for lubrication or set or dullness to solve it.

What you are experiencing is a common problem.  It can sometimes be resolved by turning the cant and pulling the center down against the bed with the clamp before making the last cut.  That puts a little more downward pressure on the ends of the boards.

Hook angle should have nothing to do with this problem.  If your set is 32 thou. on each side and perfect then it probably doesn't hurt either, though 32 thousandths is too much for a 42 thousandths thick blade.  If you set your blades to 21 or 22 thousandths then their combined set will make a kerf close to the size of the thickness of the blade and will help to control the blade.  Kerf actually performs a function.  It's not functional when the blade wallers around in a big open gap behind the teeth.  It loses function when the body of the blade rubs in it too.  You have to find a happy medium which will help guide the blade.

Neil_B

QuoteNo,no.  Don't put lead in the blade. That's like toeing out the left front wheel because the right front wheel is toed to the right andpulling to the right.  You make one thing wrong to compensate for a problem and then you have to make everything else wrong to compensate for that.  Don't even go there.!!!

Thanks Tom, I thought I had something wrong with that info.

I went out and rechecked the alignment. I had too much deflection in the blade so I started from scratch and brought everything back into place. Left the blade parallel with the bed as well. Maybe it was a case of too much downward pressure so will see tomorrow if that changes anything.

It was a freshly sharpened blade so that can't be the problem. Still wondering if that amount of set, 32thou, may be the issue though. I'll try again tomorrow with the same blade and if it still does it, I'll try one of my hardwood sets and see what happens.

I might still be overlooking something though.

One thing I did change recently was lowered the rpms of the motor. I was running at 3000 and reduced to 2600 but according to the sfpm calculator, I'm still over 5000sfpm.
Reason I did this was to bring the engine closer to it's torque curve which is highest at 2400rpm. Maybe if all else fails I will bump back up to 2900 or 3000 on the motor again.
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Kevin

Quotethe board lifts off the bed of the mill.

The board lifts off the bed or off the cant?

If it's the cant I might say stress, if it's the bed I might say clamps.
Right now I just don't know what to say.  ;D

Neil_B

Yep, off the bed. The clamp is tight but there is only one of them and it's in the middle :(. I don't have anyway to clamp it closer to the ends unfortunatly.
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Kevin

Quotethere is only one of them
Can we add a couple more?

Tom

My opinion is Solve the blade problem and board will lay flat.

This really is a pretty common fault that is almost always blade specific.

Neil_B

So I should look at dropping the set down? I hate the thought of having to go through 20 blades bending the teeth back but I guess I'll have to.

Speaking of which, when you guys order blades with a particular set do you get them or are they just whatever the manufacturer sets them to.

Something else I just thought of. The blades I'm using have a really shallow gullet. Could this be the problem, gullets filling to much? There is always a lot of sawdust on the board but I always figured it was because of the extra set. Maybe I'll just bring the set back and see what happens first ::)

Kevin, I have it in the plans to add another clamp in the future. Mostly for the long stuff though. This didn't start doing it until recently so I still gotta figure out what is going on with it.
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Kevin

I usually run into that when I try to resaw a board later on.
Lay the board on the bed and it's up on one end.
Pull that end down and it pops up on the other.
I take woodworking clamps and clamp the board to the bed then set the mill clamps.
I haven't encountered what you are experiencing when milling other than see a board raise off the cant due to stress.
I have three clamps on my mill and use all three when I can.

D._Frederick

New-Sawyer,
You did not tell the length of lumber you are sawing, but if you are sawing 10-12 ft boards and only clamping in the middle, you have 5-6ft end that can go anywere. If you are ripping cedar boards to 3/4 inch, vibration from the saw teeth can cause the board ends to shift. When you slow your engine rpm and still feed at the same rate, your chip size will increase and the spill-out will decrease. If your blade has the gullet size reduced during sharpening, you should reduce your feed rate, when the gullets are fill will cause blade deflection.

Fla._Deadheader

  This is an interesting quote, "D".  ". When you slow your engine rpm and still feed at the same rate, your chip size will increase and the spill-out will decrease."  
  
  Being as how we are using 1 drive belt, I will have to try your idea and see if that will help with "spill out".  
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

Neil_B

D_F,

It is most noticable on the 12 footers sawing at 1" thick. These blades have a shallow gullet and I've been gradually deepening them each time I sharpen. I also tried slowing my feed rate, way slow for cedar, and still made no difference.
 I certainly wish I could get the other clamp done right away for the longer pieces but at this point, I have no time. :(

If it ever stops raining, I will be out to try different blades to see what happens. These ones are Lenox, 1" pitch, 38 thou thickness with a 32 thou set from factory.
I have some good Vikings, 1" pitch, 45 thou thick and set to 18 thou. They have a deep gullet.

Both brands are 2" wide blades.
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Tom

New Sawyer,
Is the 32 thou. set something that Lenox printed on the box or that you measured across the entire blade?

Usually set is stated as the distance on one side of the blade.  

21 thou. set would equate to 42 thou. Kerf.
32 thou. set would equate to a 64 thou. Kerf.

64 thousandths is a heck of a lot of wood for a 38 thou. thick blade to remove.

If you are measuring across the entire thickness of the Kerf to get 32 thou. then the set would actually be 16 thou.

I'm only questioning this so that we are on the same page.  That's more set than I would want to run on my 42 thou. thick blades, even for softwoods.   :)

Stump Jumper

kerf = band thickness + right set + left set
Example: band thickness .042
               right set           .021
               left set             .021
               equals             .084 kerf
Jeff
May God Bless.
WM LT 40 SuperHDD42 HP Kubota walk & ride, WM Edger, JD Skidsteer 250, Farmi winch, Bri-Mar Dump Box Trailer, Black Powder

Neil_B

Tom,
That's only on one side of the blade not the full kerf. That's why I questioned about the specs when ordering. Seems like a lot. Kerf is average .100 thou. I think my other blades are .080 - .085

The way I measured is with dial calipers on the thickness of the blade first then measured the tooth to the outside edge and came up with 70 thou. 70 - 38 for the thickness of the blade = 32 set on one tooth. Am I thinking this through right?

Just so you get a visual in your head at what I'm seeing, if I look down the tooth when it's in the sharpener, the inside edge of the tip is almost in line with the outside edge of the band. Does that make sense?

These blades were originally ordered for hardwoods and when I realized they were too heavily set then I put them aside to use for softwood but then the gullets are probably too shallow for this.

Let me know if this isn't making any sense :)
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Neil_B

Hey stumpjumper,
You posted when I was typing so I missed your's.
That's the way I thought it was supposed to be measured and as you see in the above posting, I'm getting .100 + on my total kerf. :o
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Stump Jumper

I am not sure what machine you are running but my blades are only a 1 1/4" wide  by .045 and I run a set between .019 and .023 depending on the wood.  So my kerf goes up to .091 - .092.  As for the cants moving off of the bed that is caused by stress in the cant.
Jeff
May God Bless.
WM LT 40 SuperHDD42 HP Kubota walk & ride, WM Edger, JD Skidsteer 250, Farmi winch, Bri-Mar Dump Box Trailer, Black Powder

solidwoods

NewSawyer

Set should be around .022 +- a few  for a few specific uses.
My guess is too much set on your blades.
Was the Cedar you cut dry?
Are there are black skid marks on the top of the cant (the finnal "lifiting cuts")?
Check, make sure your blade is running parallel to the cut path, or "flat",,not front up or down.

A blade with way too much set will do wild but predictable problem cuts. I think the blade is trying to drift up, and it is pulling the cant with it.  
Are you seeing the blade back pop off of the end of the log when the cut is complete (log/cant is too heavy to be picked up by the blade).  This could also have a concave or convex cut on the cant/board face.

After allignment check, run a blade with .022 - .025 set for a check.
JIM
Ret. US Army
Kasco II B Band mill
Woodworking since 83
I mill & kiln dry lumber, build custom furniture, artworks, flooring, etc.
If you mill, you'll be interested in some of my work in one way or another.
We ship from our showroom.
N. Central TN.

Neil_B

Did not notice any skid marks, not on the wood anyway ;D. The cedar is still fairly green. Did all the alignment checks, solidwoods. Will try my other blades tomorrow and see what's happening.

Near as I can tell, there is no stress in the cant as all the boards are flat. There is no bowing or cupping after sawing.

I was thinking about D_F's comment with the heavier chipping and thinking that I have to speed up the blade to reduce chip size when using a shallower gullet. It makes sense because it started doing it shortly after I reduced the rpm's of the machine. Will also try that tomorrow.
Timberwolf / TimberPro sawmill, Woodmizer edger, both with Kubota diesels. '92 Massey Ferguson 50H backhoe, '92 Ford F450 with 14' dump/ flatbed and of course an '88 GMC 3500 pickup.

Tom

New sawyer,
When the setter is zeroed, you use a flat piece of metal and zero the edge that is closest to the dial indicator.

When you bend the tooth to 21 thou.  It is hanging over the outside edge of the band by half the blade width.  The inside point of the tooth  would line up with the middle of the band.

adding the thickness of the blade to the set to get kerf is proper.  I mis-spoke.

To quote the instructions for my woodmizer setter:

A maximum set of .017 for .035 blades and or .021 for .042 blades is recommended for most cutting operations.  The set should not vary more than .001 from tooth to the other.

---------------
While I have increased set a little to get around difficult situations, I find that going much over the .021 on a .042 blade causes instablility and decreased blade life.

The tooth height should be at least 3/16, measured from the to of the transitional curve into the gullet..  Some of the newer designs are  higher even yet.

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