new mill - first cuts- different size on 6x6

[OH Boy]

I finally got my new Norwood LM 29 up and running. beautiful to see it all put together, with other projects going on it took me about 3 mos to get it all built. it's a serious upgrade from my previous Lumbersmith mill I started with, where all I really cut was flat boards without turning the cant. So, I got my first couple of practice logs done yesterday, dead Elm that had fallen and i had a 14" log and a 10" log, both 8 footers.

The new saw ran fine, I managed to get the blade running true the first try, so it cut fine. I followed the Norwood book first suggestions to make some 6x6 's and stickers. everything ran great, didn't hit the log dogs or anything. cut the four sides and rolled each time as suggested. the rolling of the cant is new for me, not a big deal, I just have to learn how to get the most out of a log now. what I did see and need some help with from your experience is this. The 1 in. boards I got off the sides of the cant cutting down to the 6x6 look pretty good, even through the length as far as I can measure. But, when i got it down to the 6x6, the ends came out pretty close to 6x6 inches ( maybe an 1/8 inch off) but the middle of both of them wasn't 6x6. I ended up where, in the middle of the 8 ft length of the timber it was about 5.5 inches. wierd. both ends came out decent at 6x6 but not the middle. like the blade was dipping down a bit in the middle of the cut, then rising back up at the end.

what would cause this? blade not tight enough? I don't know this saw well enough yet so judged the blade tightness which seemed to me to have very little bounce, maybe 1/8 to  1/4 in. depending on how hard i push down. should it be tighter than that?

I have quite a few more logs to practice on, both hardwood Oak and softwood spruce, before i dig in to the nice walnut logs i have set aside. want to get it figured out so those come out good. Thanks for any comments.

[Southside]

Elm is a twisted grain wood, as such it's one of those that will walk off the mill by itself as you saw it.  Basically your cant raised off the bed from the stress being released and being, well Elm.  Offset pith, field edge trees with the crown all on one side, leaners, twisted grain types (Elm, Gum, Sycamore, Hickory) are more prone to this but even boring Southern Yellow Pine will do it.  

Did you notice any of the boards happen to have a larger gap between them and the cant as you were sawing them? If so you were observing what happened to your cant.  Turning the log as you did is often the only option you have, sometimes a log isn't destined to give you what you plan to get out of it so you need to adjust your plan.  

[arky217]

Hello OH Boy, congratulations on getting a Norwood LM29.

The most important modification you can make on
an LM29 is detailed in the post that I made on 6/30/2020.

The link to that post is   https://forestryforum.com/board/index.php?topic=111236.0

[RAYAR]

It seems like your track has a 1/4" dip in the middle, or maybe it dips in the middle when the weight of the carriage passes over that section. Is your track level (straight) by string line or sighting. How about when the carriage is on that area of the track? Does the track have adequate support in the area where the cant is thinner? (5.5") These are things to check and to be aware of.
Also, is there a 1/4" gap between the cant and the bunk after it is flipped? ... possibly when the carriage is over that section of track.

[Ianab]

I'm with Southside on this one. The log is probably "hogging" slightly as you saw it and tension is released. You don't notice on each board, because it's less than maybe 1/16", so no reject boards, and the top of the log gets levelled off and "reset" each cut. You don't notice the underside of the log, because it's still sitting on the bunks correctly, and being un-sawed you can't tell if it's banana-ed  1/4" or more. Now if you just kept cutting to the deck, each board is still in spec, and any remaining error is left in that bottom slab and never noticed. 

But when you take off 4 boards, then flip and do the same on the other side, you balance out that tension that's been "corrected" on the previous side. The cant straightens up again, and that original face is now banana-ed. 

This is why we dislike logs with too much tension, but the best option is to flip more often. Take 2 boards, flip, take 2 more... Repeat. It's more work, and no one likes that. But that way you keep that tension more balanced, and the size error doesn't accumulate. 
  

[ladylake]

 

 The easy way to check if it's the mill or the cant is to take a long 1" board, stand it on edge and take 1/2" off the top,  flip it over and take another 1/2 " off.  If this board is narrow in the center it's the track sagging. If nice and even from one end to the other your just dealing with stress  Steve

[Patrick NC]

I had a similar issue with my hd36 when I first put it together.  When I pulled a string across the bunks it was perfectly flat, but when I checked the rails it was sagging about 3/16" in the center.  I took all the bunks out, loosened the track bolts, and with the help of some strategically placed jackstands got the rails perfectly flat. It took a whole weekend of loosening bolts and retorquing,  but I haven't had any problems since. The rails are hard to check with a string line unless you make some blocks that fit over the t-rails to pull the string across and elevate it above the rails a little.  

[YellowHammer]

It's important to separate the unknowns of the sawmill from the behavior of the logs.  

Its critical to make sure the bed is perfectly flat, I use a piece of 10 foot long extruded aluminum, or a minimum 7 foot long level, put it on the bed and start making sure the bed rails are dead flat from end to end, and front to back.  If everything is fine, this will only take a couple minutes, longer than it takes to find a piece of metal to do it with.  Also, use this to make sure all your backstops line up.  I've not had much luck using a string unless you block it up as Patrick mentions, even a little sag will make a difference.

Then use a speed square, or a block with a tip, or something solid a few inches tall, and place it on each bunk, push the saw head with a tensioned band down the rails and do the same with each bunk.  Don't use a tape measure for this, use a stationary block that sits on the bed.  This makes sure the saw blade is perfectly in plane with the bed.  Of course, while you have the block out, double check the alignment of the band, with a blade guide alignment tool or similar, clamped to the band.  These adjustments should be checked anytime the mill is suspect, but I may go many weeks or even months before I repeat them if the mill is running fine.

After these are right, there are still things that can go wrong, but this will eliminate lots of unknowns.  

Log stress is a real issue, it can easily cause 1/2" miscuts, but you'll be able to recognize it when its happening and correct for it.

[OH Boy]

Wow, thanks all, that's a lot of info and I have a lot to learn. Makes sense to check the middle of the rails, I do notice a little hitch there on some cuts so will check and adjust. I did just get it all together and started cutting. Didn't know Elm was tricky either. I have some nice dead Ash I can try. Most of my logs right now have been sitting around for a while waiting on the mill, glad to have a few to practice on.  
My plan is to build a saw shack first, and have 4 or 5 nice black locust logs, thinking they won't rot as quick as posts. Any pointers on digging in to locust?

[DesertHobo]

What blades are you running? Seven degree? Be ready to change blades often, locust is hard and gritty. Go slow through the logs and take your time.

[OH Boy]

Well I bought an extra box of 10 blades and as near as I can tell they are 10 degree. Does that sound right? I may have to dig for the receipts. I can see I have a lot to learn about what blades go for what wood and cuts. Is there a sticky on this site I haven't seen that is a primer on blades?

[DesertHobo]

Norwood only carries 10 degree and 7 degree, so there's a very good chance you ordered 10 degree. If you go slow it might go ok, you'd be better off with 7s or even 4s in hardwood like locust though.
Search "hook angles" and you'll find an encyclopedia's worth of information here. There's also a few different posts written recently that are discussing hook angles.
Another thing for you to consider if you haven't already, remove the bark off the logs before milling. You'll get twice as much run time on a blade before it needs changing.