How much beam sag is acceptable?

KiwiBro · January 17, 2015, 09:34:03 PM

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?

POSTON WIDEHEAD · January 17, 2015, 09:35:24 PM

I don't know my M's. say_what

thecfarm · January 17, 2015, 09:36:30 PM

Close to an inch??

Den-Den · January 17, 2015, 09:38:02 PM

That would not be acceptable to me.

rasorbackQ · January 17, 2015, 09:40:11 PM

If you think the builders are wrong then jack up the middle.

mikeb1079 · January 17, 2015, 09:46:35 PM

if my conversion is right 10mm is just over 3/8", that does seem a little excessive...can you post some pics? perhaps that would help with ideas?

Magicman · January 17, 2015, 09:50:12 PM

Any sag is too much if you know it is there and do not correct it.

YellowHammer · January 17, 2015, 09:52:23 PM

Yeah, that's a little less than 0.4 inches over about 18 feet. That's a pretty long unsupported span and will saw some not so straight lumber. I'd block it up or otherwise add some mid span support.
YH

wetdog · January 17, 2015, 10:05:12 PM

0mm is acceptable, any more than that is considered excessive in my opinion. I would add more support.

KiwiBro · January 17, 2015, 10:15:20 PM

Thanks for the replies. I put a string line on it and shot a video with my phone but am not able to upload such a large file until I find a better internet connection. Will get a photo later today and see if I can figure out how to get it uploaded here.

I have to drive about 10mins to get phone coverage at the mo so might not get back on until tomorrow.

When I saw the sag I freaked out, rang the manufacture who said it's fine and go ahead and start milling as it won't be an issue in use. Well, I have milled one deliberately short log and it is an issue and does transfer into the cut.

I am keen to establish what others would consider acceptable. Some beam sag is going to happen. That's fine but approx 10mm? Maybe I am being too demanding relative to industry standards or what most consider acceptable.

PC-Urban-Sawyer · January 17, 2015, 10:22:55 PM

Upload video to youtube, then post link to it here.

logboy · January 17, 2015, 10:30:56 PM

Quote from: KiwiBro on January 17, 2015, 09:34:03 PM
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?

You said carriage, midspan, you're talking about a 5.6 meter beam, and your name suggests you're down under. I'm guessing you're talking about a swingblade mill with aluminum rails, not a bandsaw, correct?

KiwiBro · January 17, 2015, 10:36:30 PM

It is a turbo warrior swingblade mill with 16hp engine. The design isn't using any supports mid span. Here's a link to their site for reference:
http://turbosawmill.com/weekendwarrior/

I tried a ratchet strap and a mid span can under the beam but couldn't get much if any sag out. Given the manufacturer thinks this sag is fine, then if others in the industry do too then I'll have to accept I'm being unrealistic and will just have to cut my lumber waaay oversize. But I would not have bought this if I had known about the beam sag. Perhaps I should have asked about it but I just never thought that much sag would ever be on a mill beam.

Pretty dissapponted.

dean herring · January 17, 2015, 10:42:34 PM

What mill did you get? I am looking for a mill and might not want that brand if the manufacturer is o.k. with that much beam sag.

logboy · January 17, 2015, 10:43:01 PM

If thats the machine I think it is, I saw one operate in Ohio at the Paul Bunyan festival last year. Does the machine hop when you are cutting?

Are you saying the beam is sagging all the time, or only when the powerhead is on it? I cant remember, is that a once piece beam or a bolt together?

golddredger · January 17, 2015, 10:52:19 PM

I would call the weekend worrior guys Jake in NZ again and talk this out. I would suspect they would have put some crown in the beam so when the weight of the cutting head made it,s way it would be a flat cut. This will turn into a pissing contest real fast here and I do not think worrior deserves that. I am not affiliated at all but I have done a good amount of research on swing mills as I am looking to buy one myself. The owners I have spoke with have been happy and results are good. I would like to think you diid not talk to the owner and maybe a dealer that does not know. I would call weekend worrior direct right away. Did you get the mill second hand or brand new? Maybe it was bent during transporting and shipping? I cannot imagine him saying 3/8 or 10mm off is acceptable. My home built bandsaw cuts with a 1/16 or 2mm.

KiwiBro · January 18, 2015, 02:52:41 AM

I too couldn't imagine he'd be happy with that much sag and I also am not interested in a slanging match. But having emailed and talked to him about this, he is quite adament it is OK and no problem in actual use. But disagreeing with what must be many decades of milling experience between him and Carl is not a stance I take lightly, hence me trying to establish what others consider acceptable.
On a few occasions already I have deferred to their greater experience on a few things, but this one I need others opinions on.

Here's a video:
https://m.youtube.com/watch?v=ByOKlAzPTFU

golddredger · January 18, 2015, 03:01:36 AM

Kiwi your video is set "private" on youtube so un check that and make it public so we can view it. ;)

KiwiBro · January 18, 2015, 03:12:27 AM

Sorry, hopefully sorted now? Not sure how to delete my double post above sorry.

golddredger · January 18, 2015, 03:29:16 AM

Yep video works now good job! 8) Wow I am not sure what I would do about that sag. I am now very curious to know how much other warrior owners are seeing and also would like to see what a lucas mill with the carriage in the middle is showing for sag? Maybe a lucas owner could set up the same string test with the motor in the middle of the tracks and give us an idea of how they stack up. I wonder if you could add a U section of channel inside of the original extrusion that would help lift the center up. You could even put a slight bow up in the channel prior to putting it in to create some up pressure in the middle. Would add a little weight and I think it is a bum thing to have to deal with but at this point you need a solution. I would look into an aluminum I beam or U beam that will fit inside the original warrior beam if for nothing more than your piece of mind. Keep us posted.

golddredger · January 18, 2015, 04:27:15 AM

Well you got me poking around a bit now. I am looking at the warrior web site and it looks like your mill uses the same beam as the original chainsaw powered versions use. The new 8" with a 20hp Honda have " new heavy duty beam with centre split as standard" Which looks much beefier than the other model. I suspect your 16hp model is an early model and they used the lighter duty beam that was used with the chainsaw power head. I am sure that Honda and the saw head look bigger and heavier than the chainsaw model. Which probably is a bit to much for the original beam style so they upgraded to the "new" split beam for the heavier 4-cycle head rig. You may have gotten a "good deal" on yours as it was a transitional model. It has the lighter duty beam not the new one. If you go to there site you will see the chainsaw models use the same frame and beam you have but the 4-cycle models all use the new heavy duty split beam. It looks like you could easily slide a channel or I beam inside yours to add more strength. I would be doing that and I would put some arch upward to the channel before you slide it inside to create a bit of upward preload.
Only good thing I will say is the new split beam model is a stronger beam so the issue has been addressed already and if you bought a new 8" or 10" it has the new beam and should be a solid unit. Bummer is you got one with the lighter duty beam. But I suspect that is why you got a great price to.

Nomad · January 18, 2015, 06:01:44 AM

Kiwi, your video is working now. I wouldn't be happy with that sag either. Does it droop like that without the weight of the head on it, or only when it's loaded? If the beam strength is insufficient, it would be interesting to see what it does when it's in a cut.

longtime lurker · January 18, 2015, 06:45:38 AM

over that sort of distance I don't think any sag in the beam is acceptable, but it might not be the end of the world either. So long as the sag is consistent from cut to cut the timber should come off at a consistent thickness. It would however have about 10mm of bow cut into it, which over that sort of distance would be within the acceptable limits of most grading standards for rough sawn timber.
Having said that, I think most of us can get enough bow with a beam that doesn't sag - getting more from a design or production or freight problem sounds like a poor deal to me.

If the timber is coming off thick in the middle it's not beam sag that's your issue - to me that sounds more like a log tension issue. Face cut on your next log and see what happens: ie drop the power head 5 mil or so after you've taken your deck of boards, and "plane" the top of your sawn face with the blade to remove the hump where tension is bending your log.

Don't think you're the first person who can't talk with Jake either, he'd have sold me one of the big ones several years back if he didn't know what I needed better then I did. Great designs, but built too light for the roads I travel.

KiwiBro · January 18, 2015, 03:52:55 PM

Golddreger, I had concerns pre sale and Jake was adament the beam would be fine. I only learned a few days ago our ideas of fine don't match so why I'm asking what others think is acceptable. the price for an ex demo unit was great but I don't feel that justifies problems I was assured would not be problems.

Have tried to tension and cam the underside but only have ratchet straps onsite in .middle of nowhere and it didn't help.

Beam sags about 4mm when carriage at the ends, so the sag about doubles when carriage gets mid span.

I need this like a hole in my head at this point of the season.

Swatson · January 18, 2015, 04:16:45 PM

I would be curious if it has that much sag while it is cutting or if maybe being in the wood provides a little bit of support? It seems as if there is a good bit of area to add extra support. A plate of steel (albeit heavy) or aluminum could probably take the negative sag out if it was the length of the beam and was bolted into place with a bit of positive "sag".

Just an opinion...I have no experience with a swing mill. Good luck.