How much beam sag is acceptable?

[Ga Mtn Man]

I fall into the "that's an unacceptable amount of sag" group.

[Joe Hillmann]

If it really is a problem(I have no idea if it is)  Could you run a cable stretched tight under the beam (anchored at both ends), and then wedge a block of wood or piece of metal between the cable and the bottom of the beam?

With a tight enough cable and a tall enough wedge it would be able to pull out any sag that is in it.  I don't know how the head is attached to the beam so the cable and wedge may get in the way of the rollers.

[Left Coast Chris]

If it has 4mm sag with no weight in the middle it makes you wonder if the beam is designed to have 4mm camber upward and it was installed upside down.    Can you flip the beam and see if it makes a difference? 

[barbender]

First, I don't think that is an acceptable tolerance, and I would second checking to see if the beams should have had some positive camber and could be upside down. The cable trick with a block could also work, not something you should have to do but sometimes you have to do what it takes.

[NZJake]

Hi all,

Advised this customer to send the beam back where we would provide a crown to compensate.

Advised that we do have a much heavier duty beam option available. Standard with all larger 4-stroke models now.

Advised this mill's beam would have sag when he purchased. I explained it would be fine.

My opinion... yes 3mm of actual deflection is acceptable. Noting that all beams will have deflection. Just like other swing-blade mills every board is relative to its previous. At each end it needs roughly 1m to support and pivot the blade. So that 7mm of sag (relayed to me) works out to be only 3mm over the log length. Converts too... .118" (7/64)

Our new Galv. beam has only 3/64 sag over the log length with the power-head mounted in the centre.

My advise from timber retailers is what's really important is dimensional accuracy/consistent thickness. A little bow in the length of your timber will be an absolute reality regardless of how straight and tensioned you can make a runner beam.

This is just a reality with beam saws.

Cheers.
Jake.

[RayMO]

If it was mine I would be sawing a few logs and see how the lumber turned out before I got to worried.

[Evergreen Man]

Hi all,

Advised this customer to send the beam back where we would provide a crown to compensate.

Advised that we do have a much heavier duty beam option available. Standard with all larger 4-stroke models now.

Advised this mill's beam would have sag when he purchased. I explained it would be fine.

My opinion... yes 3mm of actual deflection is acceptable. Noting that all beams will have deflection. Just like other swing-blade mills every board is relative to its previous. At each end it needs roughly 1m to support and pivot the blade. So that 7mm of sag (relayed to me) works out to be only 3mm over the log length. Converts too... .118" (7/64)

Our new Galv. beam has only 3/64 sag over the log length with the power-head mounted in the centre.

My advise from timber retailers is what's really important is dimensional accuracy/consistent thickness. A little bow in the length of your timber will be an absolute reality regardless of how straight and tensioned you can make a runner beam.

This is just a reality with beam saws.

Cheers.
Jake.

I didn't want to say nothing as I'm new to sawmills and this forum but I've been working with wood since I was strong enough to hold a hammer.
If he was sawing lumber for me. I would not be concerned about it at all. The boards will all come out the same dimensions.

[golddredger]

Nice to see Jake at Warrior chime in. Sounds like he is willing to get your machine on track and working fine. As I suspected the new models have a heftier beam. I am still considering an 8" myself.

[5quarter]

Jake...Thanks for chiming in. 8mm over 18' might be acceptable for finished lumber, but not green off the saw. It is difficult enough finding the best saw logs, sawing to minimize tension and drying lumber such that it lays flat over its length, without making bowed lumber to start with. Perhaps it may be fine for construction material, but not for hardwood destined for cabinetry or furniture making. It is very good of you to offer to straighten out the situation, so to speak. I hope you guys get it all sorted out. just my 2 pence cents.

[beenthere]

but not for hardwood destined for cabinetry or furniture making

Then again, for cabinetry and/or furniture, cuttings are not often longer than a few feet.

I don't see where bow is an issue, but it is in the eyes of the beholder.

[NZJake]

Hi been-there,

Thanks for your input.

Squarter it's 3mm over 16ft not 8mm FYI. You'll also be very surprised to find that there are realistic tolerances in finished extruded alloy over that length too. So a perfect razer straight edge is pretty hard to find out there in the real world. But we will try our best if and when he get his beam back.

I was also advised I should be making our beams out of carbon fibre in this case too.  :

[RayMO]

I thought a strait line, jointer and planer were used to correct imperfections in lumber destined for cabinetry and furniture .

[giant splinter]

Not sure if its too late but maybe you could set them "Crown Up" like Chris was mentioning.

[5quarter]

I noticed the portable sawmill I bought has close to 10mm sag when carriage is mid span. Beam is 5.6m long.

   My mill has 0mm sag, doesn't matter where the carriage is. If it was showing the sag that kiwibro showed in his video, I wouldn't saw another log until I fixed it, for the reasons I already mentioned. It is already hard enough to produce lumber without defects, especially for someone like myself who does not always have access to the best logs. I certainly wouldn't want to start with bowed lumber, not even a small bow if I can help it.
   What I would like to know is why, on the one hand, you feel that 7,8,10,3 or what ever mm is a perfectly acceptable amount of sag (bow) over 16'; and on the other hand, increase size, weight and rigidity of the monorails on your newest saws in an effort to reduce the amount of sag over the beams length? My guess is that it's not really acceptable to you either.

Ray...many woodworkers have perhaps one of those three shop tools, so the flatter and straighter, the better. My customers Check boards for flatness before they buy. not flat? they don't buy...period.

... for cabinetry and/or furniture, cuttings are not often longer than a few feet.

sure, except for dining room tables, hall benches, built ins, desk tops, doors. etc etc...

I don't see where bow is an issue, but it is in the eyes of the beholder.

Try delivering an order of bowed lumber to a cabinet shop. it'll never make it off the truck. Remember, the beholder is the fellow who writes the checks.  ;)

 

[NZJake]

Hi Squarter,

Everyone is entitled to their own opinions. I guess that's what this forum is about.

I am assuming you have a ground based bandsaw unit (not sure). But the reality is a bandsaw does need to have a very straight runner so that the blade maintains its feed correct and does not dive or rise up as it cuts. Secondary to that the way a bandsaw works is that you need the log rolled to square up your timber. You wouldn't want a thinner mid section beam.

Ground based sawmills certainly have the advantage enabling you to shim your runners. However they get in the way - that's where our design offers some very nice advantages.

All circular mills cut sections off the log with out needing to rotate anything. Every piece of timber is relative to its previous. So naturally we don't get any drawback from sag or crown.

We have built extra long machines where the possibility was maintained that later on down the track the buyer may add a rolling facility so that extra large beams may be sawn (say 16" x 16"). Obviously an extra long beam will have extra sag - so the answer for rolling the log was quite simple. Engineer your log turner bed to have the very same sag to match the beam. That way the beams would remain dimensionally correct all along the length.

Just a couple of scenarios to ponder...

1) Take an 8" x 1" board on its flat 4m long. Lift one end. How much sag do you get from your board?
2) Take an 8" x 8" beam 4m long. Place a support at each end of it and measure its natural sag under its own weight at the centre. You may be surprised. In fact having a slight bow in it could be an advantage to compensate for its own weight if its spanning a certain length.

Timber is unpredictable and will bow according to your sawing pattern - Quarter sawn or flat sawn.

As far as timber buyers rejecting timber 4m long with 3mm sag in it... really??

Cheers.

[NZJake]

I forgot to answer your other questions.

We increased the beam size for the following reasons...

1) We chose to use a much heavier engine with more hp.
2) We preferred offering 7.2m of beam length as standard.
3) Our preference was to remove as much bounce as possible without the use of anti-bounce roller devices (roller and arm that runs on the log).

That being said if someone wanted our lightweight beam with a 13hp Honda engine I would have no hesitation in offering this mill.

We discovered on the first day at the Paul Bunyan show that there was a little more bounce when sawing hard oak then I expected. Specifically with the AUTO unit your not pushing the saw by hand (dampens this effect). So any little resonance became gradually worse. The second day of the show I installed our standard anti-bounce rollers and things performed much better for the remaining 2 days. However personally I felt it needed a little more strength - we had to give away some portability because of this. That's why we now offer the trailer option for ease of transport.

[beenthere]

As far as timber buyers rejecting timber 4m long with 3mm sag in it... really??

Splitting cat hairs here.
Doubt that the footers or base blocking for air drying stacks are that straight, but the fact is that our US and CA lumber grading rules do allow a surprising amount of bow (in softwoods the bow is about three times the allowable crook and the 3mm or 1/10 of an inch is about 1/3 of allowable crook).
In hardwood grades (NHLA) there is only the warp (crook, bow, twist) that will not plane out of the cuttings that make up the grade that enters into the picture, IIRC.

Am thinking the confusion/excitement may be the metric measure and conversion to inches.

[KiwiBro]

With the 1.4m beam extension sold with the mill:

http://youtu.be/EwkMilpn0Zs


Again, turbo have advised they have no problem with this on their beams and such sag is perfectly acceptable. So, I'm asking again, do you guys think that is acceptable?

If I want to spend time and money I don't have getting this back to them, they will crown it.

[beenthere]

So, I'm asking again, do you guys think that is acceptable?

How many more answers do you want?

[uler3161]

I don't have any experience with that kind of mill, so I can't say whether it's acceptable. I think you're right to be a little concerned, but I wonder if you've even ran the mill to see what the lumber is like that comes off it? I think that should be a decisive answer. And if the lumber isn't good, I hope the manufacturer would work with you to make it right.

If I had to guess at what will happen, boards will end up uniform (in terms of the cuts being parallel), but possibly have a bow. I think the bow might depend on how thick the board is and what species. It may be possible to sticker and put weight on your piles to fix that, which is a good idea regardless.

But even with that, I'm curious how the grain of the wood would react. Because it seems like instead of making a straight slice through the log, you're doing more of what I'd call a "scoop". Also, I would fear that cutting beams on this mill would result in the beam taking more of an hourglass shape because of that scoop. And the longer the beam, the skinnier the center is. But as I've never used a mill like this, I have no idea whether that's the case.

[coastlogger]

A mobile dimension saw sure as heck doesnt sag in the middle. AND theyve sold thousands of them that seem to last forever. Give your head a shake Jake. Sorry that just came out. I can see where the lumber may be acceptable,most of the time,but the image of a mill that cuts crooked lumber will be enough to kill major sales IMO

[NZJake]

For those that think there should be zero sag in a beam or 'elevated track' sawmill could prove to me as a fact 'that other manufacturers have zero sag with an unsupported 6m span I will give Kiwibro a heavy duty beam. Place the carriage at the centre of the unsupported span and measure the deflection. I'd like this verified too. I've been from show to show and have compared other mills rails/beams and I know what I've seen first hand.

Also I'd like to note...
This mill was sold 2K lower than list price. A slabbing attachment was also offered with the mill at no charge. Most of the sag shown will be coming from the joiner inserts on the extension. We put a little crown on the inserts which correct it.

So it was a very good deal on the basis that it was our first 4-stroke unit Warrior (close enough to cost price). This model as mentioned earlier was a transitional unit before we upgraded to heavier chains and a heavier Galv. beam that spans 7.2m (23.6ft). Measured deflection with the carriage (22hp Honda) at its centre was 2.5mm (0.0984") FYI. The light weight beam works very well for our chainsaw mills all the way up to our 13hp units. We sell the light weight beams with the 4-stroke in the islands as the mills are usually carried into the bush by hand.

My hesitance to jump at the opportunity to send a new heavy duty beam out to Kiwibro is that I have had numerous emails from him stating that the mill's beam was too heavy and that I needed to design my beam out of carbon fibre to reduce the weight. I explained that we had moved toward a heavier stronger beam and that was our end direction.

Now I'm being told that the beam is actually too light. Well yes it is light (designed to be carried).

Regardless whether I feel its acceptable or not. I have offered to provide a crown. Its a 2 - 1/2 hour drive to our factory??

[NZJake]

Please find footage taken of our Warrior AUTO with the very same beam as being used by Kiwibro. Note that the sawmill is performing very well when sawing. Also note the quality of timber at the end of the video - to me this is acceptable.
I also have numerous videos on YouTube sawing all sorts of hard timber all around the world.

The timber was collected by a local timber retailer with out any negative feed back.

The larger beams were introduced later on.

http://youtu.be/Y1z7lkkpBNk

[Magicman]

Thanks for the video.  That is certainly a uniquely designed machine.

[shinnlinger]

Is it possible to sandwich two stiffeners on both sides of the beam and not affect saw head travel?