How much sag is acceptable in a sawmill beam??

[Turbosawmill]

Hi Ian,

That's a stiffener that's attached to our standard alloy beam for all 8" model chainsaw mills. With the 6" model the blade pivots up into that area so it can not be fitted.

 

[Haywire Haywood]

Ah, ok. Good looking mill.

 

[Peterson Miller]

Turbosawmill. But that's the thing, I don't need a string line as the sag issue just isnt there. Period. This is because there are center supports and levelers down the track all pegged in (as well as minimizing the side to side movement. Especially with the hi/lo setup). Whereas your beam only has the end support and nothing in the middle, so there will always be sag. So I take it you dont try to obtain a criss-cross pattern on the log with the blade, instead you adjust the blade to the beam (which would be fine if it was completely straight and had no sag). My concern for kiwibro (and I may be wrong here), is that if I was to adjust my blade out 10mm (as per kiwibros beam), my mill would be cutting very inefficiently and cause blade issues. Would you not agree?

So if theres "no magic formula" as to how much you crown a beam, how do you know if you are crowning it the right amount? Is it just guess work? But then you go on to say "we just try to get it as straight as we can". But wasn't kiwibros beam straight until you put the engine and cutting unit on?

You also say in your last post, that "if you choose you can crown our Gladiator beams at the centre just by adding washers at the join". I thought you were the expert, why should you leave it up to the customer to try and band-aid the sag issue, instead of fixing it initially? It seems a bit absurd to me that you knowingly sell the mills with sag in the beam, letting your customers be the guinea pigs to see if they notice the issues and then fix it or up-sell them on a stronger "heavy duty" beam.

Maybe I am a bit over the top here, but Chris at Petersons (who trained me) always told me to make sure the tracks are straight and level, read the log and the marks on it to ensure blade adjustments are correct and then you know everything is sweet. If the mill gets hard to push, or the blade heats up, or the blade makes a "shing" noise when it exits the log, the first thing i do is check the log to make sure its stable and hasnt moved and check to make sure the levelers or track skids arent sinking (sometimes happens due to soggy ground).

 

[rwthom279]

IMO, Peterson Miller has summed it up very well. There are a few of us with swing mills that have discussed this issue/thread "behind the scenes" and also have the same feelings. I'm unsure how many reading/contributing to this thread actually have experience operating a swinger, but I'll say this... It is a different animal all-together when compared to using a CSM or bandmill. Different technology and MUCH different sawing techniques to produce good lumber. BUT, one thing I feel is paramount with any sawmill... the track, ladder, frame, beam(s) etc. must be straight to produce straight lumber... PERIOD. Best example that comes to mind is using a 20ft 2"x4" for a ridge beam and hanging rafters from it...

Getting straight and true lumber is a challenge in itself. With the downward sag of Kiwi's beam and the log raising upwards due to internal stress within the log, I just cannot see how a sawyer wouldn't get stomach ulcers trying to figure out how to compensate to get lumber that is within an "acceptable tolerance". Even with add'l skim cuts, in an attempt to get the face flat again, compensating for that much beam sag would be near, if not, impossible. Might get close sawing 1x's, but 2x's and thicker just release to much stress in the log. The farther down you go, the worse the stress gets.

How would Kiwi be able to resaw material for himself or a customer?? IMHO, that ain't gonna happen in any capacity.

I do hope that Kiwi gets a mill that performs as one would expect... and it appears that is the direction things are now going.

 

[Turbosawmill]

Turbosawmill. But that's the thing, I don't need a string line as the sag issue just isnt there. Period. This is because there are center supports and levelers down the track all pegged in (as well as minimizing the side to side movement. Especially with the hi/lo setup). Whereas your beam only has the end support and nothing in the middle, so there will always be sag. So I take it you dont try to obtain a criss-cross pattern on the log with the blade, instead you adjust the blade to the beam (which would be fine if it was completely straight and had no sag). My concern for kiwibro (and I may be wrong here), is that if I was to adjust my blade out 10mm (as per kiwibros beam), my mill would be cutting very inefficiently and cause blade issues. Would you not agree?

So if theres "no magic formula" as to how much you crown a beam, how do you know if you are crowning it the right amount? Is it just guess work? But then you go on to say "we just try to get it as straight as we can". But wasn't kiwibros beam straight until you put the engine and cutting unit on?

You also say in your last post, that "if you choose you can crown our Gladiator beams at the centre just by adding washers at the join". I thought you were the expert, why should you leave it up to the customer to try and band-aid the sag issue, instead of fixing it initially? It seems a bit absurd to me that you knowingly sell the mills with sag in the beam, letting your customers be the guinea pigs to see if they notice the issues and then fix it or up-sell them on a stronger "heavy duty" beam.

Maybe I am a bit over the top here, but Chris at Petersons (who trained me) always told me to make sure the tracks are straight and level, read the log and the marks on it to ensure blade adjustments are correct and then you know everything is sweet. If the mill gets hard to push, or the blade heats up, or the blade makes a "shing" noise when it exits the log, the first thing i do is check the log to make sure its stable and hasnt moved and check to make sure the levelers or track skids arent sinking (sometimes happens due to soggy ground).

Simply put... when you measure from the beam and adjust to the blade. You get criss-cross.

Regarding the straightness scenario... I have expressed my opinions and arguments thoroughly on the forums. Kiwibro's mill has a light weight beam. It cuts perfect timber even with that sag. No blade problems, no lack of criss-cross. If you the customer feels that the sag is too much, you have the ability to counter it.

You are incorrect with your assessment. The blade simply is not out 10mm. A blade out 10mm would dive into your log and stop cutting. This is what your trying to portray. A blade out .5mm will dive into the log too.

The blade is running true to the beam. So if your trying to understand what the blade is doing with a 'hypothetical' excessive sag scenario here it is...

As both sides of the blade are equal to the beam, the carriage raises and lowers (equally) as it moves through the log. A banana beam would mean you lose a little hp as it saws having a slightly wider kerf (its a consistent transition from one end to the other). Timber will still be straight and equal, you'll still get criss-cross. Even with Kiwi's 'more than normal' sag the amount of sag he's talking will not have any noticeable effect. All my arguments and points still stand as previous.

Your training regarding setting up your mill, likely is more about getting your tracks parallel. I also am quite aware that your tracks need to be propped up over 8m to remove 'major' sag. Why don't you put a stringline on your single groove side track and let us know what you get (as you normally setup the mill). Side bow is the same result as sag.

Beam saws/elevated twin tracks work. I can certainly understand the perception of an issue without understanding it.

Hope this helps.

PS
Who would have thought that such a wide carriage frame would still pull straight through the cut. Well its proven to do so over so many years.

 

[Turbosawmill]

Just had to point out a couple of things.

First of all nothing is straight (its not possible).

A 20ft 4x2 that's straight-ish ?? Unheard of. Timber bends either under its own weight or due to growth tension. The longer the length the more its going to sag. Timber is placed and nailed true.

I think this argument will have trouble being summed up so easy.

 

[Peterson Miller]

You are incorrect with your assessment. The blade simply is not out 10mm. A blade out 10mm would dive into your log and stop cutting. This is what your trying to portray. A blade out .5mm will dive into the log too.

I beg to differ. If your blade is running true to your beam, and your beam is not straight, then how can your blade run true to cut accurate boards??? This is pure logic. Agree?

As both sides of the blade are equal to the beam, the carriage raises and lowers (equally) as it moves through the log. A banana beam would mean you lose a little hp as it saws having a slightly wider kerf (its a consistent transition from one end to the other). Timber will still be straight and equal, you'll still get criss-cross. Even with Kiwi's 'more than normal' sag the amount of sag he's talking will not have any noticeable effect. All my arguments and points still stand as previous.

So kiwi will never cut straight lumber, he will always cut lumber as per Figure A in the picture below:

So if you don't eliminate the sag in your tracks/beam, then you will always be cutting boards as per figure A. But then we have the tension of the log as well, so if you are still getting the curved boards and you KNOW your tracks/beam isn't sagging, then it has to be the tension in the log. Nobody can get around this, so then you can compensate for it. Trust me, I have spent a lot of time talking with Chris at length about this. So to say "I can certainly understand the perception of an issue without understanding it", is like saying that "you don't know what you are talking about, so just believe what I say" LOL.

So if your trying to understand what the blade is doing with a 'hypothetical' excessive sag scenario here it is

There isn't a "hypothetical" excessive sag scenario, there is sag!!! LOL Your timber will not be straight and equal, as the blade will pull down if there is sag and then rise up again once you go past the middle of the beam and are getting to the end t-frame. As per the picture above. Then when you add the extension on to the beam, its only going to get worse.

Yes I agree that my tracks sag over the 8m length. But that is exactly why there are track levelers put in place to ELIMINATE that problem. So that point is invalid. Its like saying that "oh you are going to get wet when driving in the rain if you have your window down". You put the window up, you eliminate the problem lol

I also agree that this debate will have trouble being summed up so easy. But hey, that's what forums are for

 

[Turbosawmill]

Hey Peterson Miller good diagrams. Your really taking the time out to show us your perspective.

Your points in order...

1) I'm a little confused regarding the diagram and text... bow = sag in tracks (what about all the other variables?)
2) .001 is closer to logic 10mm is just flat out incorrect.
3) Hypothetical is a scenario that your beam is so bowed that it actually makes a difference.
4) You are incorrect. The timber will remain true (both by dimension and width) along the full length.
5) Its only a problem if you make it a problem.

What I don't understand is how a carriage being around 2m wide is able to maintain a true and uniform cut all the way down a 6m log. Surely it all depends on where and how you pull it right??

All mills have weakness one way or another. I have listed why I think Kiwi's mill is fine as it is. I believe I have made a strong and valid argument.

However...
I have offered to correct the sag regardless of my opinion.

Noting...
Our standard heavy duty beam has 2.5mm deflection with the carriage mounted at the centre over a 7.2m span. That's with our largest Warrior motor and model.
Our super light weight beam has 3mm deflection over its full standard length with 8" carriage mounted at its centre.

If that's not bearable you have two options.
1) Buy some other ground based mill and meticulously string line the rails.
2) Ask to get it crowned at our factory.

This debate really sounds like its turned into 'who makes the better sawmill'. If your interested in who makes a better mill or which has more advantage give me a call. I'll provide you with what I believe to be true and you can weigh up against what you've heard from the others. No use trying to skew facts here as its on record. Yes that's the great thing about these forums.

Jake.

 

[Haywire Haywood]

If the boards in figure A are stickered and weighted or strapped, won't they cure out straight?

 

[Peterson Miller]

If you say your light weight beam has 3mm deflection and kiwis mill has 10mm as per the videos he posted, I would say that is out of spec from the manufacture, so it is a problem. So when you say "its only a problem if you make it a problem", if something is out of spec, then it is a problem, isnt it? But thumbs up to you for offering to fix it.

I am sure you understand quite well, about how a 2m wide carriage can maintain a true and uniform cut all the way down the log. You obviously use the pull handle located on the center unit. You have, after all, worked for Petersons and have done shows for them in Australia as per a previous comment of yours. Your sarcasm amuses me.

FYI I have never used a string line. Never had sag, so never needed to. But if it makes you feel better, I will do it for you sometime.

I guess if you can put hand on heart and say you have never had anyone return their mill because of beam issues or inaccurate boards, I say well done. Because anyone with an ounce of logic would surely see this as a problem.

Well I can see this is going to keep going around in circles, maybe we should agree to disagree? I think this whole thread reinforces the fact that before buying any sawmill (or anything else of significant investment), you need to run one for yourself and put it through its paces. Because watching a bunch of videos on youtube simply doesnt cut it. In fact Petersons offered to put me in contact with a bunch of Peterson sawmill owners to talk to them, talk about being totally transparent and honest...

I don't think its turning into a "who makes a better sawmill" debate. I invite any other swingblade manufactures to get on here and share their opinion about rail/beam sag not making a difference when it comes to accurate boards. Any Lucas owners out there??

 

[Peterson Miller]

If the boards in figure A are stickered and weighted or strapped, won't they cure out straight?

The boards in the picture are bowing out sideways when laying the 6 inch wide surface on the ground. If they bow up at the ends with the 6 inch surface on the ground, then yes weighted and strapped would help. Clear as mud?

 

[Haywire Haywood]

Ah, just sticker them standing upright then. LOL

 

[rwthom279]

Just had to point out a couple of things.

First of all nothing is straight (its not possible).

A 20ft 4x2 that's straight-ish ?? Unheard of. Timber bends either under its own weight or due to growth tension. The longer the length the more its going to sag. Timber is placed and nailed true.

I think this argument will have trouble being summed up so easy.

Turbo,

The point of using a 2x4 as an example you confirmed with your own reply. If it already has a sag/deflection under it's own weight, then adding more weight will only compound the problem.
Yes, timber is placed and nailed true... so is what is Kiwibro to do then??
So yes, in a sense, it can be summed up so easy.

As for a straight 20ft 2x4, or "straight-ish" as you put it. Yes, it can be accomplished and I've done it many times, but with the bandmill. Perfect.. no. When checked with a stringline, All were less than an 1/8" crook over 20'4" length, some showed no deviation (perfect??) Yes, it took extra time/extra cuts to balance the tension, but it is not "unheard of".

Yes, forums are a great way to discuss and share information. But to keep on point, I don't think Peterson Miller is trying to turn this into a comparison of brands. I believe he is trying to enlighten/educate all who read this thread. He has went the extra mile to illustrate the effects of what the original topic was all about. I imagine he came about this by his own experience and felt compelled to back up what he stated in a previous post.

Disclosure: This post was not to be taken as aggressive or to "smear" any names. Read it however you may, take it however you want.

If the boards in figure A are stickered and weighted or strapped, won't they cure out straight?

Yes, it is possible. But its lumber... sometimes it has a mind of it's own.

 

[rwthom279]

Any Lucas owners out there??

 

[Turbosawmill]

No offence taken at all. I'm just here to state facts from my point of view. Take them as you will.

Peterson Miller - I need to clarify (the lightweight beam deflection of 3mm was measured against our 8" chainsaw mill). Kiwi's mill was new territory for us as we moved up to the 4-stroke, hence the ultimate move to Galv. steel.

Nope no one has come back to me yet other than Kiwi. For a lot of people a small amount of deflection is not a problem, obviously for others it is. Not the end of the world, its sortable.

I will always correct false statements such as...
The blade being out by 10mm or that we have blade life issues. Not true.

I've already asked on the other forums for results from other (single beam/twin high track) saws showing likely sag over a 6m span. No one has come back to me. If there are defined standards out there in the industry I would be happy to work within them.

Jake.