Hour Glass cuts

[BT9212]

Hello all, I have a mill I purchased from a local guy that builds them. It's 30ft long and 5ft wide. I'm running woodmizer blades brand new with a 50/50 mix of RV antifreeze and wd40 or diesel depending on what I have in bulk on hand. The blade tension is built based off of a PSI gauge which i'm running at 3-4k which is how it was made to be run. I'm also sawing pine/white oak that that range from fresh drops to logs that have been down for months. I'm marking out my pith and trying to template my logs to have the grain going in as close to the same direction as possible. I have my mill level, It could be moving since it's on blocks ( I am building a perm frame as I go ). I am placing my dogs down low on the log once I have atleast 3 sides cut. My problem is I seem to be getting an hour glass on my top cut and everything after that. I'm looking for tips to try, I don't feel like it's tension in the wood based on how common it is on every single log across 2 species. Any tips are appreciated and welcome as I am very new to this.


Edit: The pictures of the mill on poles are from when I purchased it, it now sits on blocks on the ground as I didn't know where I wanted to place it.


Update, I found the gallery and the rules. Took a warning since the rules are not pinned to the top of each page as I am used to but I think I have it all going correctly now. I appreciate the direction for them.

[doc henderson]

pics will be the best form of communication.  there are threads on this forum.  a little bit of learning curve.  good luck and welcome.

[SawyerTed]

Welcome to the Forum! 

Is the mill flexing as the head travels down the rails? 

A tight string run the length of the mill in the center of the bunks should allow you to see any flex.

[thecfarm]

Are in a cold climate?
Meaning logs froze?

[maple flats]

A string works quite well, but I get the best results when I place my auto level laser n one bunk and measure every bunk, each end from there. It seems to get adjustments perfect faster. The only other thing I've got to offer, a good sharp blade cuts best.

[BT9212]

Are in a cold climate?
Meaning logs froze?

We are in the South East, temp at time of cut today was around 75. I switched to the WD40 thinking maybe a
gummed up blade.

[BT9212]

Welcome to the Forum! 

Is the mill flexing as the head travels down the rails? 

A tight string run the length of the mill in the center of the bunks should allow you to see any flex.

I have not seen any flex but it's entirely possible that the frame is flexing, I don't think the head would flex as beefy as it is. I'll run a string or a laser and see what happens when I run it on both the head and frame to double check.

[barbender]

 When we talk about frame flex, what commonly happens is your support feet flex when the weight of the head passes over them. What can happen is that the weight of the mill is supported on the ends, or the middle. It is harder to get the weight evenly distributed than one would think. 

 When I set up my Woodmizer (different brand, but the principles are the same) there are 4 jacks along the main rail. I first set the two inside jacks down. Then with the head sitting between those two inside jacks, I then set the two that are on the opposite ends of the mill. What I am looking for, is to get the jacks down to the point that they aren't loose if I give them a kick, but yet not lifting up the frame. If I tighten them down too much, the frame will have a smile shape to it more or less. If they aren't tight enough, then the flame will flex in a frown. 

 Don't discount log tension either. Every log has tension in it, some just have more than others. If you have an incorrect sawing procedure, you can make most If not all of them misbehave.

[BT9212]

When we talk about frame flex, what commonly happens is your support feet flex when the weight of the head passes over them. What can happen is that the weight of the mill is supported on the ends, or the middle. It is harder to get the weight evenly distributed than one would think.

 When I set up my Woodmizer (different brand, but the principles are the same) there are 4 jacks along the main rail. I first set the two inside jacks down. Then with the head sitting between those two inside jacks, I then set the two that are on the opposite ends of the mill. What I am looking for, is to get the jacks down to the point that they aren't loose if I give them a kick, but yet not lifting up the frame. If I tighten them down too much, the frame will have a smile shape to it more or less. If they aren't tight enough, then the flame will flex in a frown.

 Don't discount log tension either. Every log has tension in it, some just have more than others. If you have an incorrect sawing procedure, you can make most If not all of them misbehave.

I appreciate the reply, I am going to do some serious looking at the frame and have someone watch as close as possible while I pass over. I am planning on setting the entire mill about 6" off of the ground for ergonomics on 12x12 post ( it's just what I have an abundance of) and plan to have around 10 post in all set under each support . I'll also keep reading up on the tension, I am trying to plan each log out before I cut, it takes me a ton of time to cut one but I don't want to waste the trees I have if possible.

I will attach a picture of some more of the aweful cuts I have managed to make.

[rusticretreater]

Go down each side with a long level and a short level.  You will probably find a low spot or two.  Then you also need to check across the bunks for level too.

Then check the mill head for side to side freeplay and the blade being level and also square to the bunks.  Also, ensure there is proper blade tension.

Its usually a combo of things that make really bad cuts.

[Ljohnsaw]

Every board when cutting fro the top down? Or are you flipping the cant? Have you tried flipping the cant after each board to relieve the log stress?

[jpassardi]

It looks like you're set up permanent. One simple option is to make 12" x 12" x width of mill cribbing and place it under each cross (across, not lengthwise) bunk, level then fasten the bed to them. I've had mine set up this way for several years and no issues with bed movement.
With them placed 90 to the bed you can still easily clean debris out from under as well.
By fastening to them you allow some movement when placing logs but it can move some if hit hard.

[WELumberjack]

@BT9212, Can you show a picture demonstrating this "hourglass cut" you're describing? How much of a thickness difference?

Yes, there's variable tension in every log, but if you've tried several different logs and a couple species as mentioned in the initial post, and still get boards with consistent waves (or thick on the ends and thin in the middle as one goes along the surface of the board), then it may be how your mill is setup + your sawing technique. You said that sawmill has changed from its original location and pictures may have changed. Which is your current mill setup?  Like IMG_8223 in your original post? What is the base supporting the horizontal tubing the sawmill runs along? or is that still in-process?  Do you know the weight of the sawhead from the builder? What are the dimensions of your metal tubing along the sides?  Since it is a local build, it depends on the R&D that went into the build.  If your supporting posts (vertical 12x12s) are _x_ feet apart, is the mill flexing as the sawhead passes in-between (like a roller-coaster) and/or the heights of the posts are not all the exact height, then your support base may be part or all of the problem.  I gather that you're still in the process of building a permanent base for your 30-foot mill.  But the base has to be consistent height all the way along the mill.  Finding single pieces of 12x12 that are 30+ feet long to put under each of the side rails to completely support it uniformly will be difficult. If the sawmill is set out in a field that you think the ground is completely level, the frame may still flex as you go down the rail.  If you have the chance, set you mill on a big flat concrete slab, and see if you have the same problem, to take out the base variable.

Like @barbender described with a cantilevered Woodmizer mill, there is a rigid tube 2x8 or 2x10 with a solid rod above and below that the 1,500-2,000# sawhead runs along. If not properly supported, even that tube can "flex" a bit and give variable thickness boards as a result.

Updating your location in your profile helps give a geographic background/framework to any advice given or if anyone else is nearby to visit to give in-person advice.

[doc henderson]

are the boards thin in the middle and thick on the ends?  it would seem if it is in the set up, that after the first cut, the mill would cut along the same path and be equally thick along the board, even though sawing in a curve.

[ladylake]

 
 If your cant is thin in the middle put more pressure on the middle jacks or supports, If the ends are thin put more pressure on the ends.  No need for strings or lasers .  Steve  

[barbender]

I've never had strings or lasers out on mine either. I'll use a level when setting up just because I like my sawhead running uphill just a touch when cutting, and I want the loader side just a touch high, too. So I use a level, to make my mill not level😁 Coplanar is what you are going for.

[BT9212]

Every board when cutting fro the top down? Or are you flipping the cant? Have you tried flipping the cant after each board to relieve the log stress?

I have only flipped one one log and it had the same results as the rest. I have not been able to get back home yet but I have decided to just build a permanent 12x12 frame under it with 10-12 beams.

[BT9212]

are the boards thin in the middle and thick on the ends?  it would seem if it is in the set up, that after the first cut, the mill would cut along the same path and be equally thick along the board, even though sawing in a curve.

correct, thick at ends and maybe a 1/4" thinner in the middle, my 4ft level showed I was good but I Have got to be off from reading up, I have decided to just build a permanent frame, I will update with results once that is done.

[ladylake]

 When you get it set up again get a long board and skim off 1/2 " off the top to eliminate  any stress, turn it over and it should touch all of the bunks,  if not it needs more  support where it doesn't hit.  Steve