How much sag is acceptable in a sawmill beam??

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KiwiBro

Mill 'em, nails be damned.
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Setting up over first log I noticed the portable sawmill I bought has close to 10mm sag when carriage is mid span. Beam is 5.6m long.

Manufacturer says that's acceptable. I say it ain't right. What do you guys think?
 
I would think it needs a jack or blocks in the middle to hold it up.
I don't think it should be off that much.
Cha d
 
It's a turbo warrior swing blade with 16 HP engine. Here's their site for reference

http://turbosawmill.com/weekendwarrior/

So you will see it is just one beam and not really much opportunity to support mid span.

I am OK with a few mm. I expected there'd be some sag but this much seems wrong. Just trying to gauge if I am being unrealistic or if people in the industry think there's a fault or flaw in the mill beam and this much sag is too much. Of the few people I have asked so far, nobody thinks this much sag is OK, but I need to ask more people to be sure.

I put a stringline on it and took a video but nowhere near a good enough internet connection to upload yet.
 
I would turn it over and see how much its off then.
If you can jump on it a bit and bend it the 10mm. I would put some blocks up to stop it from going too much till you get a feel for it. It may not be straight when your doing it but when you turn it back over you would be flat.
Chad
 
Managed to upload a video:



Am I being unreasonable in thinking it's not right?
 
I also think 10mm is quite a bit of sag for that standard length beam. Maybe 4mm absolute max sag considering its just a single beam supported only at the ends.
From memory the new 4-stroke models have a larger steel beam to support the heavier engines. I also remember reading somewhere that they are considerably stronger than the "chainsaw mill" alloy beams and should therefore provide less sag.

Jake may have to do you a good deal on a new steel beam, that would help for sure.
 
I think it comes down to the product, with a 10mm sag is it still producing near perfect wood? If yes run it. If no fix it.
 
Saw some wood, see how the lumber comes out. You might try posting same thread in the forestry forum, lot more sawmill boys talk over there.
 
Yup, try it and measure the lumber. If the lumber runs out too much, I'd NOT be happy... If the lumber is acceptable, then who cares how it looks!!

SR
 
Setting up over first log I noticed the portable sawmill I bought has close to 10mm sag when carriage is mid span. Beam is 5.6m long.

Manufacturer says that's acceptable. I say it ain't right. What do you guys think?

Will it sag that much when it is actually in the cut? Would think the kerf might tend to support it
 
I think 10mm over 16ft is to much. That being said, if the unit is second hand, and you are getting what you want from the blade, it wouldn't be a problem for me. Must run a few cuts to see how much the sag really is.


394xp w/ 33" & 42" Bars - Full Comp Full Chisel - 36" Granberg Alaskan Mill
455 Rancher w/ 20" Bar - Semi Chisel
Husqvarna Forestry Helmet & Full Wrap Chaps
 
Other than sawing your own crown into the lumber, I'm guessing as my slow Internet connection wouldn't download the vid. ...That you'll have to use a reduced feed rate to keep the bounce under control when coming back in the vertical mode.
 
Having traded emails and phone calls with turbo, he was adament close to 10mm sag is acceptable and wouldn't be a problem in use and I should go ahead and start cutting. So I did that log in the video and yes it does translate into the wood. Fine if flat sawing off the top quarter of log because the tension helps straighten the board, but that works against me on the bottom side of the log. I Cut a 6x6 and had about 4mm of curve over 2.6m. Could cut oversized but on rigid posts where people are wanting to leave rough sawn I'm stuffed.

I've a heap of logs to cut full length but this sag is going to mean cutting way oversized.

Yes, there's bounce on the vert cuts unless I go real slow. Also on the horizontal cuts. If trying to hoz cut say 6" I tried 2 passes of 3". The first is very bouncy because the blade anti chatter/bounce device doesn't extend out far enough. The second pass is much better.

I too have concerns about the beam not handling the weight and quizzed Jake hard but pre sale Jake was quite adament it would be fine and I relied on their years of experience and assurances. I later learned they went to the steel and longer beam because of problems but I have been told multiple times it's not the weight of the 16hp manual option like mine but the larger engine with all the automation gear was too much for the Ali beam. Somehow after my experience I don't agree.

Right now, I'm just trying to figure out if I'm being unreasonable expecting less beam sag and being unhappy about this.

I tried ratchet strap and mid cam on bottom side of beam to see if I could get enough tension to bring it up some but no real difference. Needs more tension than I can sort out on site in middle of nowhere.
 
I remember going to a show and a guy was milling with a swinger... It started hopping and you could see it in the lumber. He put a roller of some kind ahead of the blade that supported the motor/blade weight and got it to stop... I wish I could remember more, but it was a lot of shows ago...

A mill has to be pretty accurate for me, or I'm NOT a happy camper! So, I completely understand your frustration!

Like yesterday, I milled out some "stickers",

standard.jpg


If my mill couldn't keep decent accuracy, how could you get decent stickers like this without planning them, or resawing them on a tablesaw??

standard.jpg


There's a few 7/8" x 2", but almost all of them are 7/8" by 7/8" and I expect them to be within 1/32"...(I'll pull out the wider ones later, and use them in the garden for stakes)

I hope you find a solution to your problem!

SR
 
I think you are right in being concerned with that much sag...If you bought this new (recently) you might consider taking it back for a swap or for them to fix.
If you have had this for awhile, you might try getting a hold of some welders/machinists that have alot of experience under there belt, to ask them if they can heat treat the sag out of the beam. I have zero experience with aluminum but with Steel it is straight forward and I would suspect in capable hands aluminum would be the same.
Good Luck
G Vavra
 
Will it sag that much when it is actually in the cut? Would think the kerf might tend to support it
I don't think it sags as much in the cut, but it still does. That it doesn't sag as much might mean the blade is doing more work and subject to more heat than a straight beam blade would. I don't know if that will become an issue or not. I'd rather not have to find out.

I guess the bandsaw guys can crow about their thinner kerf being much thinner while mine is probably bigger than advertised.
 
I think you are right in being concerned with that much sag...If you bought this new (recently) you might consider taking it back for a swap or for them to fix.
If you have had this for awhile, you might try getting a hold of some welders/machinists that have alot of experience under there belt, to ask them if they can heat treat the sag out of the beam. I have zero experience with aluminum but with Steel it is straight forward and I would suspect in capable hands aluminum would be the same.
I don't think his beam is bent. The beam is probably straight but sags under its own weight (they all do that) and more so when the weight of a power head is added. To maintain a straight beam over that length would need the bean to be made with a bend in it to be able to take the power head weight into account - not so easy to do.

I tried ratchet strap and mid cam on bottom side of beam to see if I could get enough tension to bring it up some but no real difference. Needs more tension than I can sort out on site in middle of nowhere.
You will need many 10's of tons of tension to remove that degree of sag over that length. As a guide, the amount of tension needed to reduce the ~3/8" sag in the middle of a 60" bar to 1/16", is around 13 tons.
 
Hi Guys,

Jake Peterson here. I have advised that he should send the beam back to us where we can crown it slightly so that it settles straight if it's an issue.

Noting that the beam may be sagging 7mm but the reality is the ends where the saw pivots is not relevant. So the actual sag that may be relevant in the timber is only about 2-3mm.

I have spoken to other sawmill merchants today and they have agreed that it would be very hard to find a piece of timber that is within 5mm tolerance over 4m length.

I also advised that we do have larger steel beams available. 7.2m long with 2.5mm deflection. Although this moves away from the super light weight beam idea. The 16hp is very close to the limits but completely ok in terms of the quality of timber it produces.

I've used this saw and know that it cuts dimensionally accurate timber.

The mill was sold at a very good price. The galv. Beam option is still very available if it's needed.

I will do a very good price on the heavy duty beam if out of preference needed.

Cheers
 
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