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Keep gaining thickness

Started by True North, June 02, 2009, 11:49:32 AM

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True North

When I am sawing cants with our TH, I made some charts working from the bottom up (shown below for 1 3/4 and 1 inch).

1 13/16               1  1/8
3  5/8                2  3/16
5  7/16               3  1/4
7  1/4                4  5/16
9  1/16               5  3/8
10  7/8                6  7/16

When I am working down through the log, each board is a little fatter than the previous one. Not a big deal on small cants but makes a difference on a larger one.  Would anyone know what the problem is and how to correct it?

I have a job coming up, and the guy wants full one inch and two inch thickness on spruce and pine. Would anyone have any suggestions on how to do this using the TH?

DR_Buck

I'm not familiar with your mill, does it have a calibrated scale?   Does the scale include kerf?

It looks like from your numbers you are not properly accounting for kerf and you keep "adding" to your target thickness with each successive cut.   

If you don't have a scale on your mill, I'd suggest getting one.
Been there, done that.   Never got caught [/b]
Retired and not doing much anymore and still not getting caught

True North

Yes, it has a scale and I am accounting for 1/16 kerf.

By the way, the job is cutting pines and spruce up to 30" diameter.

Dan_Shade

does it drop a preset amount, or do you position it manually?

also, the kerf is closer to 1/8 than a 1/16th.  (actually, it's probably on the plus side of 3/32)
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

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Sprucegum

If your boards are getting 1/8" fatter you are working on the wrong side of your kerf.

Try adding 1/16 each time instead of subtracting  ??? or should I say subtract instead of add  ::) whichever way you are going now - go the other way  :)  :)

sgschwend

Your scale has a larger step at the bottom on the one inch board, that should be the only thicker board.  No matter what value you use for the kerf as long as you use the same step size you should obtain the same size board from the cant.  If they are getting thicker there is something wrong.

I prefer to list the values with the larger numbers on top, just like what the scale looks like, and the order that I will use them.



Steve Gschwend

sjgschwend@gmail.com

moonhill

Recalculate the number using 1/8" start with the last board left on the bunks, 1" add 1-1/8 the thickness plus the kerf =2-1/8, 3-1/4, 4-3/8, 5-1/2, 6-5/8, 7-3/4, 8-7/8, 10, 11-1/8...........

Tim
This is a test, please stand by...

Brad_S.

The dial is measuring the distance off the top of the bunks. Your last board against the bunks should read 1" on the dial. If your actual board thickness is 1" but the dial is reading 1 1/8", then you need to recalibrate the dial.As stated, allow 1/8" for your blade kerf, 1/16" allowance is too thin. Granted, it really isn't a full 1/8" thick, but it is a better number than the 1/16th.

Though I would like to see you use the 1/8" kerf allowance as per the numbers Moonhill laid out, your math as outlined for 1/16" is correct (except for your starting point, which should be 1", not 1 1/8"), so that is not the reason your boards are getting thicker. Unfortunately, it is not a problem I ever had, so I am not sure what to tell you to look for. 

Possible areas of trouble could be one or both of the chains transfering the up/down motion of the head to the dial may be loose (I keep them as tight as possible using a spreader clamp) or one or both of the right angle gears on the dial assembly may not be meshing correctly. These problems would more likely cause uneven board to board thickness than a growing thickness problem but it's the best I can offer at the moment.

When setting the head for the next cut, always arrive at the number by coming down. If you overshoot the mark and go to low, raise the head up higher and come back down again, don't try to teak in by raising the head slightly if you went to low. That keeps the chains tensioned the same for every cut. Again though, that would be a board to board problem.

Moonhill laid out your 1" scale, your 2" scale will be 2, 4 1/8, 6 1/4, 8 3/8, 10 1/2, 12 5/8, 14 3/4, 16 7/8, 19, etc.

If you can't get to the root of the problem, you may want to try calling CMS, one of our sponsors to the left here, and see if they can help. They are very knowledgeable about TH equipment and can get pieces and parts to keep you running true.
"Life is what happens to you while you're busy making other plans." J. Lennon

DanG

I'm not a bandmiller, but I read a lot of this stuff out of boredom, as well as to keep up with what my friends are up to.  I've noticed a bit of talk about the set in the blades.  I know it wouldn't be much difference, but wouldn't the set of the blades have an effect on the kerf, making the scale less than accurate?  Of course, we all need to make our customers realize that we are working with a sawmill, not a planer.  There is going to be a small variation from board to board, and even more difference as the lumber dries at different rates.  That is why a finished one inch board measure's 3/4 inch.

What is the difference between your minimum and maximum sets, and what would that add up to in slicing up an 18" cant into 4/4 boards?  Would it make a noticable difference?
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

LeeB

If I understand what you're asking DanG, it wouldn't make any more diference than you changing the set on your blades. The first and last board may be off, but as long as the drop is consitant the rest of them would be the same.
'98 LT40HDD/Lombardini, Case 580L, Cat D4C, JD 3032 tractor, JD 5410 tractor, Husky 346, 372 and 562XP's. Stihl MS180 and MS361, 1998 and 2006 3/4 Ton 5.9 Cummins 4x4's, 1989 Dodge D100 w/ 318, and a 1966 Chevy C60 w/ dump bed.

LeeB

Just a thought for True North. Is the scale you're using in true inches or is it set for ther kerf? Measure it with a trusted tape and see.
'98 LT40HDD/Lombardini, Case 580L, Cat D4C, JD 3032 tractor, JD 5410 tractor, Husky 346, 372 and 562XP's. Stihl MS180 and MS361, 1998 and 2006 3/4 Ton 5.9 Cummins 4x4's, 1989 Dodge D100 w/ 318, and a 1966 Chevy C60 w/ dump bed.

DanG

B-b-b-but if you have a scale for drop+kerf, ain't yer kerf gotta match the scale, lest ye run out of wood before ya gets through cuttin'?  Don't yer kerf change if ya change the set in the blades?  It would be ever so slight, but it would be there.

The set on a circle mill don't change, except for the microscopic reduction with tooth wear.  I don't worry about that, cause I ain't trying to use it as a planer. ;)
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

Tom

True North, I'm a little confused as to your question.  Do you mean that you think your scale is off?

There is another thing that will affect the thickness of boards, and the only thing that I know of that would do it randomly.  The cant moves.

If you are cutting through and through, without turning the cant, it might be rising off of the bed as you relieve tension from the top.  One thing to look for is daylight widening beneath the cant.

You should also measure your board's thickness on each end and in the middle, not just in one spot all of the time.  This will indicate a moving cant.  It might be, if it's the ends of the boards rising, that the middle of the board is the correct thickness most of the time and the ends will be thick.  If the middle of the cant is rising, middle of the board will be thicker and sometimes the ends will be thin.

If you find that this is your problem, there are some threads on the forum that discuss how to remove the tension.

Brad_S.

For those asking about the scale including the kerf, on a Timber Harvester, there is only a dial indicating how far above the bed the blade is.You either have to figure the cutting thickness manually and include the kerf in your measurement, which Truenorth did in his post, do the math in your head as you saw, or use a second pointer hand to show you where your next cut should be.
Sorry DanG, the amount of set shouldn't be what is plaguing TN.
The height of the head is transfered to the dial by a series of chains. Somewhere along the line, Truenorths head drop is moving at a greater distance than the dial actually is, therefore his boards are getting thicker as he gets nearer to the bottom when sawing through and through.
Truenorth, check and see if the sprocket that the chains wrap around above the top flat iron chain anchor is bent. it is on an unsupported shaft that is easy to bend. I will try and get a photo of it tonight to show where I mean.
"Life is what happens to you while you're busy making other plans." J. Lennon

ellmoe

  If the indicater dial is off it should be easy to check. Without a log, start at the top and start dropping a even number, say two inches, and compare a tape rule to the dial indicater.  If the gauge is the problem , it will show up. Since there is no kerf involved the numbers should stay the same.

Mark

Thirty plus years in the sawmill/millwork business. A sore back and arthritic fingers to prove it!

True North

Well, I changed the scales to allow for 1/8" instead of 1/16" as per Moonhill and Brad's directions. Also, I was not rotating the cant after a few cuts so I started doing that. Also made sure that I was always stopping as I came down and not going back up.

It is cutting perfect now!!! 8) 8) 8)

I guess the kerf allowance was the biggest problem I was having. I must say that without the advice from you guys on this forum, I would be up a creek without a paddle or a properly working saw to make a paddle with!!??  This was just in time, since we have our first custom job tomorrow!!

Thanks :)

moonhill

It sounds like Truenorth is up and running. 

When I check my scale I measure from the lowest set tooth on the band to the bunk, this measurement should equal what the scale says, providing you have the proper perspective, don't stand up on the mill 12" from the scale and read the number, you have to stand back where you typically do while sawing.  I have to sit in the chair and look up at the scale, when I stand up it is not right or if someone much taller than I sits in the chair it is off by as much as 1/8" easily. 

Tim
This is a test, please stand by...

Jeff

True North,  Your mill isnt set up on a side road just off of 129 north of pickford  is it? Say around 20 sumpthin mile road?
Just call me the midget doctor.
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Commercial circle sawmill sawyer in a past life for 25yrs.
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True North

Hey Jeff,

That wasn't me. I saw that mill too, but did not have a chance to stop. I was actually sawing for someone on West 20 mile road on Friday and Saturday. The mill worked great. We cut about 2200-2400 bf of 1" and 2" pine and spruce, plus about 16 4x4's in 11 hours of sawing.  Since we are just starting out, I was wondering if those numbers were decent for production. Any thoughts?

Fla._Deadheader


Unless you had 10 workers, I would say that's pretty good, if you are just starting out.
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   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

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True North

I was just working with the landowner, and my Dad helped for half a day.

Meadows Miller

Gday

True north those figures sound pretty good on a bandmill w/o edger Mate  ;) ;D ;D 8) 8)

With the gaining Thickness Dad says that he reckons i get Thicker every year but i dont thinks its the same problem you have somehow Mate ;) :D :D :D :D :D :D

Regurads Chris
4TH Generation Timbergetter

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