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Author Topic: Dave's Bandsaw Mill  (Read 4823 times)

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Offline northdesign

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Dave's Bandsaw Mill
« on: November 30, 2016, 11:42:33 PM »
First wanted to say thanks to everyone on this board for providing so much insight into your experiences building mills and trying different designs. Cool to see all of the creative solutions out there and learning.

I'm a designer by trade and hobbyist woodworker. I'm going to take on a mill build and have been studying different designs for a while now. I like to plan stuff out and will research this to death so getting everyones advice will hopefully keep my project moving.

My motivation for building a saw vs buying is mainly for the satisfaction of going through the process and learning, and maybe saving a little money, but I want to build it right. Secondarily looking to improve my welding and fabrication skills.

After a couple weeks of late nights on the internet, here's where I'm heading. Looking for insight on where my plans are flawed.

-36" x 15' log capacity
-18.75" belted sheaves (or larger solid steel band wheels if I can find a decent deal)
-1 1/4" blade
-Acme screws and an electric motor to raise and lower the head
-I already have a nice 25HP Kohler Command engine with electric start off of a retired zero turn mower
-Going to start with a manual feed and maybe add power feed later
-Going to plan so the mill can go mobile eventually
-Will mainly be cutting ash, oak, walnut, maple and cherry

Here are my main questions for ya'll.

1. Do the 18.75" pulleys from Surplus Center work well? Are they balanced well enough? Or should I spend the extra cash and buy actual bandmill wheels from Cooks or another supplier? Are the 18.75" pulleys large enough to handle the size log I'm interested in cutting? Most of what I'll be cutting will be closer to 24" but would like to have the capacity for bigger stuff. I have access to a 50hp Kubota tractor to move logs.

2. Took me a while to figure out the basic design requirements to get the wheels aligned and also to tension the blade properly. I've settled on a drive and idler design similar to the way Cooks mills are set up and have modeled what I'm thinking in CAD.



Any experience with this set up? Seems like a smart design where the wheel can be adjusted in the XY and Z axis to fine tune alignment. I have decent cutting and welding tools and think I can fabricate this without much fuss. Biggest question I have is related to the spring and how much tension/strength it should have. Thinking a 800-900lb spring would do it? I'll buy the springs first and adjust the dimension in the design accordingly but this seems like the area with potentially the most trial and error.





3. Finally, looking for some advice on my lifting design. Thinking about nesting the saw head tubes over the front posts of a 4 post carriage. What do I need to consider to keep the tolerances tight and eliminate any possibility of it binding? Do you try to find the center of gravity for the head before welding the sliding tube on? Seems like too much weight to the front or back would cause binding on the posts. Or should I consider using 4 acme screws instead of 2 to distribute the load?

Thanks for everyones help! Looking forward to documenting my build here.

David


Offline ljohnsaw

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Re: Dave's Bandsaw Mill
« Reply #1 on: December 01, 2016, 12:13:17 AM »
Nice drawing!  Welcome to the Forum.
Just some items I see:

Looks like you have log bunks every 2 feet.  I made mine with cross pieces every 4 feet and my bunks are moveable.  I have 4 bunks now on 22 feet of track and that works quite well.  I plan to make 1 or 2 more when I grow my track to 60+ feet so I can do some long beams for my cabin.

The pillow block set up you have shown - I'd space the bearings as far apart as possible.  There is going to be a LOT of force on those.  What diameter axles will you be using?  Your tension set up, the hinge - make that as robust as possible.  There will be a LOT of side force on that hinge.  I opted for a sliding tube arrangement.  I think you could do it that way as well still using the spring.  I used an Acme thread from a car jack for my tension setup.

Running 1.25" blade (what thickness?), I'd look for larger wheels if you can find them.  The smaller the wheels, the more quickly you fatigue the blade and possibly have a break.

I used car hubs and donut spare tires for my setup.  The tire provides the "spring" in my tension setup.  The hub mounts I made are adjustable to set the toe-in/out.  Blade guides take care of the blade angle.  My tire diameter is around 22 or 23".  I run a 184" band and I have a cut capacity around 32-34".  Biggest cut so far was 26" in dry cedar - tough going with 18hp.  Did some 24" fresh pine and was ok with a sharp blade.
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Offline northdesign

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Re: Dave's Bandsaw Mill
« Reply #2 on: December 01, 2016, 12:49:23 AM »
Thanks ljohnsaw.

=Running 1.25" blade (what thickness?)

Looking for advice from the forum on blade thickness for this setup.

What diameter axles will you be using? 

Was planning on 1 7/16" shaft thickness since that's what those pulleys will accommodate. Is that enough to carry the loads? I think I've seen some mills where they have a 2 inch shaft milled down on one end to fit the pulley. I'm assuming it let's them run a bigger more robust bearing. Based on occasional use, I'm interested to know how well the smaller shaft diameter and smaller bearing will hold up. Related, I noticed huge cost variations for pillow block bearings. Seems the heavy cycle/duty bearings can run as much as $200 each! How much of a difference does it make? Can anyone recommend the best quality/value pillow block bearing?


Offline carykong

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Re: Dave's Bandsaw Mill
« Reply #3 on: December 01, 2016, 01:19:09 AM »
15 foot log capacity? Go ,at least, 16 feet.

Offline fishfighter

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Re: Dave's Bandsaw Mill
« Reply #4 on: December 01, 2016, 04:55:54 AM »
15' and you will be sorry. Have at least room to saw a 16'6" log. Welcome aboard and looking forward to your build.

Offline ozarkgem

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Re: Dave's Bandsaw Mill
« Reply #5 on: December 01, 2016, 05:16:45 AM »
To saw a 16' log on my mill I have to place the log perfect. Give your self some extra room in the length department.  Not much of a fan of the hinge system. Think about it, you use a 1 7/16 shaft for the wheels because of the stress and then go with a shorter smaller shaft for the hinge that has the same stress on it. I prefer something more robust.
I have Surplus center pulleys on mine. Work good. On my mill I found that loose belts on the wheels cause a vibration so I went back to the B56 belts. WM seems to work fine with B57 belts but mine doesn't. Don't know why.
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Offline bandmiller2

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Re: Dave's Bandsaw Mill
« Reply #6 on: December 01, 2016, 07:24:20 AM »
Welcome Dave, no reason you can't build a good functional band mill. First theirs a lot of half truths bantied about most originated from manufactures that want you to believe their mill is ice cream and the next guys is puppy poo. Band wheels 18.75"/ 19" will work just fine, is bigger better, yup but not all that much. Will surplus center pulleys work as well as purpose made, not really, but their not five times better. Many folks even some here will keep parroting these old beliefs. I built my band mill before I even knew about the forums, I looked at many mills and took a little from each  a lot my own design. My mill used the double hinge design and its worked well for about 16 years. Idle wheel pillow blocks are original drive end I just had to replace. Build everything heavier than you think and make everything adjustable ask if your not sure. Frank C.
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Offline Den-Den

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Re: Dave's Bandsaw Mill
« Reply #7 on: December 01, 2016, 08:25:47 AM »
Most of your questions have been addressed.  On the spring rating - I suggest that you plan on having 1000 - 1500 lb of force on the spring.  On the acme rods powered with an electric motor - this is how my mill is set up, it is not the fastest design but is very accurate and repeatable.  I put a home brew set works on mine and love it.
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Offline D6c

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Re: Dave's Bandsaw Mill
« Reply #8 on: December 01, 2016, 09:25:52 AM »
On your power unit I would consider mounting an electric clutch on the crank shaft (similar to what they put on zero turn mowers).  That way you don't have to design any belt tightening mechanism.....just a switch to engage the blade.

I'm assuming your up/down feed will use and elec. motor drive so you'll have power available for the clutch anyway.

If there was room on my LT40 for an elec. clutch I might change it over and do away with the belt/brake arrangement.

Offline pineywoods

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Re: Dave's Bandsaw Mill
« Reply #9 on: December 01, 2016, 10:20:38 AM »
My 2 cents...The hinge and spring tensioner setup will probably be a continuous headache. Go with a slider type adjustment and use the hand pump and ram off a cheap floor jack. Drill and tap a hole and screw in a 0-3000 psi pressure gauge. Pics in arnold113's gallery. The 19 inch pulleys with B57 belts have worked fine on woodmizers for nearly 40 years. For up-down, chains running off a worm drive gearbox are about as bullet-proof as it gets. Lends itself well to setworks later. Plan on power feed, even if you don't build it in initially. Don't skimp on the blade guide rollers. They need to be adjustable in up-down and left-right directions as well as in-out. If you don't know about surplus center, check out their web site for stuff like chains, sprockets, motors, etc. 
Blade length...Check with your blade supplier and design to use one of their standard lengths. Yes, most will make custom length blades, but why make things more complex when you don't have to. Also think about blade sharpening, blades won't last nearly as long as you think..
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Offline bedway

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Re: Dave's Bandsaw Mill
« Reply #10 on: December 01, 2016, 10:45:30 AM »
I think the best help I can give you is to suggest you go to my gallery and review my build. Any questions feel free to ask.

Offline ReinkeFandS

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Re: Dave's Bandsaw Mill
« Reply #11 on: December 01, 2016, 11:54:04 AM »
Just my 2c, but the bunks on my mill are exactly 4ft, and I have had people bring walnut and cherry logs 3'6"-3'11" wanting to salvage 3ft boards for a woodworking projects or whatever. If I had at least one bunk at 3ft near the front of the mill it would have made those projects way easier.
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Online Joe Hillmann

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Re: Dave's Bandsaw Mill
« Reply #12 on: December 01, 2016, 01:30:13 PM »
I think your bunks are too close together.  Most logs are not round and being able to drop a crook or knot between two bunks rather than sitting on a bunk can make it easier to roll a log into the position you want to start cutting.

I don't know if your tension adjustment will be strong enough. I have heard  numbers of wanting 15,000 to 25,000 psi of tension on the blade.  If you are running 1 1/4 blades that are .05 thick and wanted 15,000 psi you would need to put 750 pounds of pull on the blade below the wheels and 750 pounds of pull on the blade above the wheel.  So you would want 1,400 pounds of pressure on your tensioning bolt to get to the lower end of what is recommended.  There are also some companies that recommend doing a flutter test and run with as little pressure as you can without the blade fluttering.  So the pressure possibly could be less if that works for you.  On my mill I personally found that the tighter the blade the better the cut and the longer a blade can go between sharpening.


You plan to use a 1 7/16 shaft.  That MAY be strong enough, keep the front bearing as close to the wheel as you can get.  Just to compare that size bearing to something that is in common use, a 3500 pound trailer axle uses 1 3/8 and 1 1/16 inch bearings and each side has to support 1750 pounds plus the extra force of bouncing over bumps so in reality can probably support several times that weight at least for short amounts of time.

Also if you are ordering from surplus center you may want to order a spare pulley, shaft and bearings because I don't think they always have those items in stock and if you have one of them break and have to order parts from somewhere else a pulley of that size will be much more expensive anywhere other than surplus center.


If you want to be able to cut a 36 inch log that doesn't mean you need to have a 36 inch throat between the blade guides.  To cut a 36 inch log you would be able to cut it if you had 26 in opening between the guides and the blade being able to be raised to at least 31 inches.


Offline Kbeitz

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Re: Dave's Bandsaw Mill
« Reply #13 on: December 01, 2016, 06:06:00 PM »
Most of your questions have been addressed.  On the spring rating - I suggest that you plan on having 1000 - 1500 lb of force on the spring.  On the acme rods powered with an electric motor - this is how my mill is set up, it is not the fastest design but is very accurate and repeatable.  I put a home brew set works on mine and love it.

Do you have anything posted here about your home brew set works?
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Offline bandmiller2

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Re: Dave's Bandsaw Mill
« Reply #14 on: December 01, 2016, 07:51:02 PM »
Dave I'am not a believer in a lot of tension on bands, it leads to early breakage. With compression springs you can nest one or two inside each other for more tension. Over tensioning is a crutch to try and force a straight cut, its sharp and proper set that does that. Frank C.
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Offline KirkD

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Re: Dave's Bandsaw Mill
« Reply #15 on: December 02, 2016, 09:17:52 PM »
Most of your questions have been addressed.  On the spring rating - I suggest that you plan on having 1000 - 1500 lb of force on the spring.  On the acme rods powered with an electric motor - this is how my mill is set up, it is not the fastest design but is very accurate and repeatable.  I put a home brew set works on mine and love it.

Do you have anything posted here about your home brew set works?

KB, I think I found it unless he has more info for us.

http://www.forestryforum.com/board/index.php/topic,81708.msg1244796.html#msg1244796
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Offline barbender

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Re: Dave's Bandsaw Mill
« Reply #16 on: December 02, 2016, 11:23:53 PM »
Northdesign, two things I would stay away from- 1. I don't like the hinge tensioner, it looks to me like as you tighten the blade, the bandwheel will climb vertically. It will make it hard to keep consistent down pressure on your blade guides. 2. From my personal experience with the steel tube in a steel tube, don't do it. There is a tendency to bind, water can get in and freeze, if grit gets in there it binds, if it rusts, it binds. I would use a vertical steel tube with nylon or UHMW slide pads sliding on it.
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Re: Dave's Bandsaw Mill
« Reply #17 on: December 03, 2016, 08:06:53 AM »
Northdesign, two things I would stay away from- 1. I don't like the hinge tensioner, it looks to me like as you tighten the blade, the bandwheel will climb vertically. It will make it hard to keep consistent down pressure on your blade guides. 2. From my personal experience with the steel tube in a steel tube, don't do it. There is a tendency to bind, water can get in and freeze, if grit gets in there it binds, if it rusts, it binds. I would use a vertical steel tube with nylon or UHMW slide pads sliding on it.
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Considering post build alignment, wear and tear...generally, adjustments should be linear in the axis of their action, so as not to provide a rotational or tangential component.  Trying to align or fine tune is much easier when the adjustment has only a single component of movement relative to the mechanism being adjusted.
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Re: Dave's Bandsaw Mill
« Reply #18 on: December 03, 2016, 08:18:00 AM »
Have you considered using a porta-power  type set up for tension ?  I'm no xpert but  spring tension would seem to react to blade entry into the log as well as feed rates .  Nice CAD work !
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Offline ozarkgem

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Re: Dave's Bandsaw Mill
« Reply #19 on: December 03, 2016, 05:08:42 PM »
Considering post build alignment, wear and tear...generally, adjustments should be linear in the axis of their action, so as not to provide a rotational or tangential component.  Trying to align or fine tune is much easier when the adjustment has only a single component of movement relative to the mechanism being adjusted


Man that is deep. I will have to think about that. :D
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Offline AncientTom

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Re: Dave's Bandsaw Mill
« Reply #20 on: January 11, 2018, 05:53:52 PM »
I know this thread is a year old but it is relevant to the questions that I need answered. So, I hope that nobody objects to my hijacking this conversation instead of starting a new thread for the same. I am, as you did at the end of 1916, looking at all the knowledge that I can Google and YouTube before I get started on my build.

Considering post build alignment, wear and tear...generally, adjustments should be linear in the axis of their action, so as not to provide a rotational or tangential component.  Trying to align or fine tune is much easier when the adjustment has only a single component of movement relative to the mechanism being adjusted

Man that is deep. I will have to think about that. :D
I think what he is trying to say is having an axle mount that is hinged at the top of your mounting plate for your tensioning adjustment would also have an effect on the vertical height of your wheel as you try to set tension, not to mention that any slop in the hinge would also throw off your other alignment axises.

I am planning to use a 2" tube sliding inside a 2-1/2" tube for my tensioning adjustment. These steel tubings' dimensions are not exact and so I am anticipating a lot of slop which is to my advantage. With the added space between the tube walls, I do not think that rust will be a problem, especially if I maintain a coat of rust inhibitor on the sliding pieces. I also intend to use a couple of lateral clamping bolts to the stationary outer tube to remove the slop and hold the tensioning slider firmly in place. On the axle mounting surface, I will add what ever scheme I finally decide on to set the toe and camber of the wheel.

My first concern is about Surplus Center's 18.75" O.D. pulleys being used for band wheels. I came here looking to find whether or not a 5/8" urethane v-belt, having the crowned wheel surface being only half that of the blade width, would be wide enough for a 1-1/4" sawmill blade . If this is okay, what effect of the tension riding on only half the blade width have on the blade's longevity? Also along this line, the question of if I need a wheel surface width at least that of the blade width, what effect does the tensioning load have on the blade's teeth holding their position?

My second concern is that of flanged guide rollers. Is there a problem with using a roller that is longer than the band width and allowing the teeth to ride across the surface of the roller or should the flanged rollers be made to match the blade that will be used so that when properly positioned on the blade, the teeth are extending beyond the roller not riding on it?

Any advice or comments (other than derogatory) will be appreciated.

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Re: Dave's Bandsaw Mill
« Reply #21 on: January 11, 2018, 08:04:10 PM »


I don't know if you saw this on you tube , but he is using those Surplus Center 18 3/4"  pulleys. I am using the same, but just recently changed over from tires. So I do not have a lot of experience with them but they are great so far. The band rides with the blade tips just over the edge.  I emailed him to see what size v belts to use (58 or 59, I would be more exact but the mill is 60 miles away) and he said he has successfully cut quite a bit with that setup along with the Cooks 1 1/4" guides.  If that link doesn't work I think his channel is Southeastern Ohio Honeybees. Good Luck. Andy

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Re: Dave's Bandsaw Mill
« Reply #22 on: January 12, 2018, 11:11:03 AM »
19 inch pulleys with B57 Vbelts been working nicely on woodmizer mills since the 1980's. BUT, not just any B57's. Need a flat top, not crowned. Goodyear and browning among others make them. I get mine from woodmizer. You definitely do NOT want the teeth on the blade to touch ANYTHING. Messes up the set on one side = diving in the cut. Never fooled with the urethane belts, most guys who try them wind up going back to standard V belts. They are normally used on shop bandsaws with 1/4 inch blades and nowhere near the tension you will be runing with 1 1/4 bands. Band tensioner, go hydraulic and be done with it. A ram out of a cheap floor jack works great. Plumb a 3000 psi gauge for a tension indicator. Look in Arnold113's gallery for pics
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Re: Dave's Bandsaw Mill
« Reply #23 on: January 13, 2018, 02:13:33 PM »
You definitely do NOT want the teeth on the blade to touch ANYTHING. Messes up the set on one side = diving in the cut...
I assume that this comment is in answer to my question about guide rollers. This is what I thought, that the guide rollers have to match the blade so that the flange would limit the backward thrust of the blade being pushed into the log to keep the teeth from riding back on the roller. I have found nothing across the Internet that mentions this and in fact those commercial suppliers of mills and parts don't even address this.

... BUT, not just any B57's. Need a flat top, not crowned. Goodyear and browning among others make them...  ... Never fooled with the urethane belts, most guys who try them wind up going back to standard V belts. They are normally used on shop bandsaws with 1/4 inch blades and nowhere near the tension you will be running with 1 1/4 bands.
If the saw band needs a flat surface to travel across, what keeps the blade tracking in position on the wheels and how will tracking adjustments of the wheels be effective? With all that I have read, the whole point of a crowned wheel is so that when the blade is tensioned, the blade will attempt to track to where the most force is being applied which is the middle of the wheel. The best tracking adjustment would be to set the tracking to where the blade wants to ride with it's back edge aligning to the back edge of the wheel. I don't think that this would  be possible if the band were riding on a non-crowned wheel. To this end, my thought is that the compression of the surface of the belt when the blade is tensioned will be less in the center of the belt where the belt is thickest causing a sort of a crowning effect. Looking closely at the grooved urethane tires, it looks like the center ridge is slightly taller than the outer ridges to cause a crowning effect. I may be wrong. I'm still looking for definitive and not so obvious answers to these questions.

The reason that I am considering urethane tires is that in order to force regular v-belts onto the wheel, they are just slightly larger than the wheel and they protrude out of the wheel when the wheels are turning. It is said that this effect adds a small amount of instability to the blade while it is cutting. The urethane belts are more elastic to easily be stretched onto the wheel. They are made to fit the wheel groove without any slack. They are created with the purpose of eliminating the problems that exist with using regular v-belts. They are also grooved to help with sawdust buildup on the wheel surface. I have seen in countless videos, this buildup that occurs while sawing which has to be occasionally removed from the surfaces of regular v-belts. My one concern about the urethane belts is the fact that they are elastic and as a result of this elasticity, they might have a mushy surface that may be to soft for proper band tensioning. There are no complaints that I can find across the Internet about this but still, I have yet to have any experience with sawing with a band saw mill so I will be experimenting with all of this.

This mill build will be my first experience in sawing logs so all of my comments here is conjecture and should be construed as an invite to all to point out any misunderstandings that I have and fill in the gaps to anything that I missed.

One more thing. You suggest to use a hydraulic ram with a 3000 PSI gauge to set tension. My head is swimming about using 1000-1500 PSI tensioning to the saw band as it has been suggested. I have no doubt that the blade would snap long before you get that much pressure applied to it. One of the commercial mill manufacturers in there setup video specifies 35 foot pounds of tension for their mill and blade for best sawing. Whereas PSI is a pressure per square inch surface area measurement and foot pounds is a linear measurement, it seems that ft/lbs is a more practical measurement for blade tensioning.

While I am a person, when planning a build like this, will tend to go off the deep end of trying to think of all those things that I would like to see in mine, I have to keep reminding myself of the applicable adage, K.I.S.S. All that candy can be eventually added after I get the basic build running. I view hydraulic tensioning as the cherry on top and the least needed of all the options that I would like to incorporate into the build such as log loading, turning, auto feeding, track extensions, trailering, etc.

Offline Pabene

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Re: Dave's Bandsaw Mill
« Reply #24 on: January 13, 2018, 04:12:02 PM »
About blade tension design.
There is a study performed by a university in Sweden about the best blade tension design for band saws. Maybe it is late to inform you about it in this thread but here it is: The best is to have a spring as the closest component to the wheel bearing assy. It doesn’t matter what you have to preload the spring, hydraulic, screw or a lever. The spring is more forgiving for sudden happenings like when a piece of bark is pinched between the blade and wheel. If the saw frame is stiff, as I hope it is, it is important to allow the tension function to react quickly for such things.
I have a log band saw with a hydraulic, totally stiff (ridged) tension design.
The saw frame is week so in case of such happenings, the saw frame has to take the chock. Some time it ends up in a deformed frame and I have to readjust the blade tracking.
I think Woodmizer has an even better design for this function. It is an air filled pillow, close to the bearing unit, as a last “link” in the “tension design chain”.
This is my opinion, based on hard experiances.
The reccomended blade tension from many manufactures is about 10% of the tension when the blade would breake just by the tension.

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Re: Dave's Bandsaw Mill
« Reply #25 on: January 13, 2018, 06:51:54 PM »
Thanks, Pabene, for this. I will now consider incorporating a spring in the tensioning adjustment. when I purchase my blades, I will ask the manufacturer what they suggest for tension on their blades.

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Re: Dave's Bandsaw Mill
« Reply #26 on: January 13, 2018, 08:03:44 PM »
You might want to look for one of these off E-bay...
You want around 12,000lbs to 15,000 of strain on an 1-1/2" band.

 

 
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Offline Cutting Edge

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Re: Dave's Bandsaw Mill
« Reply #27 on: January 14, 2018, 07:38:50 AM »


You want around 12,000lbs to 15,000 of strain on an 1-1/2" band.

 


Where did you get this information from ?

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Re: Dave's Bandsaw Mill
« Reply #28 on: January 14, 2018, 07:40:35 AM »


You want around 12,000lbs to 15,000 of strain on an 1-1/2" band.

 


Where did you get this information from ?

It's all over the WWW. Some places quote 25-30,000 .

One read up... I hope it's OK to post this link here.

http://www.sawmillcreek.org/showthread.php?251853-bandsaw-tension-guidelines
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Re: Dave's Bandsaw Mill
« Reply #29 on: January 14, 2018, 08:00:10 AM »
12K-15K on an 1-1/2" wide would make for one SLOW cutting headrig.  The "specs" you posted would be lucky to keep a 1-1/4", .035" blade stable in the cut.

There are a couple hobby level band headrigs that are lucky to produce 16K of tension on a band just before the main frame/beam begins to succumb to deformation.  The lumber produced can/is a direct reflection of this.  Just because it resembled a board, doesn't mean that it is what most would consider a usable piece of lumber.

To proof is in the product and low blade tension, regardless of the brand of sawmill, IMO is a crutch to cover up for other shortcomings.  Most reputable blade brands can sustain near twice the tensions that you posted and have a reasonable expected life span with multiple sharpenings.

The weld quality is absolutely critical running at higher tensions.


But if it's  all over the WWW ("12K-16K tension"), it must be true  ???

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Re: Dave's Bandsaw Mill
« Reply #30 on: January 14, 2018, 09:23:08 AM »
Lenox recommends up to 30,000 PSI.
Wood Mizer says 12,500-15,000.
Woodland Mills says 20,000 -30,000
Norwood says 12,500-15,000 PSI.
Hudson says 12,500-15,000 PSI .
Lumber mate says 12,500-15,000 PSI.
TimberKing  says 12,500-15,000 PSI.


Gotta get the info some where...

But if it's  all over the WWW ("12K-16K tension"), it must be true  ???
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Re: Dave's Bandsaw Mill
« Reply #31 on: January 14, 2018, 12:33:33 PM »
Kbeitz,

The majority of recommended tensions you gave, are for manufactured sawmills.  May or may not apply to certain models or even DIY/homemade machines.

I will address one correction, only because the image below is an excellent example.

W-M's recommendations are based on what the machine itself is able to produce and have durability/longevity over it's expected lifetime of components. 

Example:  An LT10 is not built heavy enough to sustain tensions that an LT40 is capable of.  Two completely different machines. 

This information is straight from W-M's instructions for their strain gauge, Part# WMBTG.  LT10, LT15 and LT35 are not listed, so this helps with an approximation of time period.  (Unknown date of actual publication)  Certain models now have more robust components and consistently run in excess of 22,000+ lbs of strain with no issue of a reduction in life of consumables nor blade life.




As you and others can see, there is an extremely broad range of recommended tension, which varies by machine and blade combination.

The reason for posting this is to helps others that are reading this information in the future.  The machine a person has, may not be able to reach those numbers due to the construction (might be a homemade sawmill) and self-destructs (12k-16K).  Or possibly a new owner of an LT70 running literally 1/2 what the machine NEEDs to have a properly tensioned blade (24k-30K).

Again, many blades can exceed what the machine is capable of producing.  Other blades are not, without causing issues with curvature, camber, etc.

Hope this helps.   ;)



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Re: Dave's Bandsaw Mill
« Reply #32 on: January 14, 2018, 01:06:33 PM »
Imo, 12-15k lbs of strain is inadequate for sawing at a decent feed speed.
I routinely run the pressure on my 40 at 2800psi up to 3000psi, thats around 23.5k of strain, thats where it will cut the best,  with no shortening of blade life. At work I have the blade tension at around 27k pounds of strain on the blade and have used as much as 35k lbs of strain. I would NEVER use only 12k of strain for several reasons.  1) lack of blade control,  with that little tension you will push the blade around like a wet noodle. 2) inability to use a decent feed speed, see #1. 3) loss of cut quality see #1. 4) loss of blade life see #2.
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Over 2.5 million bdft sawn with a Baker Dominator and counting.

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Re: Dave's Bandsaw Mill
« Reply #33 on: January 14, 2018, 01:25:39 PM »
I agree 100 percent... When I was building my mill I just googled
for information and thats what I found. After experimenting with
different settings I found what was best for my mill but I used what
I found to give me a starting base.
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Re: Dave's Bandsaw Mill
« Reply #34 on: January 14, 2018, 01:39:45 PM »
I just don't want to see inaccurate info touted as fact.
If someone was to read this and build a mill that can't handle the tension required to cut flat accurate lumber that would give us sawyers a bad rap and people would think we don't know what we are talking about.

There is a fb page for sawmills that is already FULL of misinformation and people don't know what is true and won't listen to the people who actually know because we don't post pictures and comment all the time, we're too busy sawing for that.
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Over 2.5 million bdft sawn with a Baker Dominator and counting.

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Re: Dave's Bandsaw Mill
« Reply #35 on: January 14, 2018, 02:08:42 PM »
I don't see it as inaccurate at all... You should build your mill to tolerate
the tension needed that the blade company's state. So for a 1/1/4"
blade that should be around 12,500-15,000 PSI . I'm thinking to get
the best cut you need this tension.
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Re: Dave's Bandsaw Mill
« Reply #36 on: January 14, 2018, 04:09:00 PM »
The recommended tension for a blade is measured in one part. If you transform that tension to  the force you need to reach that tension, you then have to take that force times two, to see the real load on the wheel bearings. It is also that force as want to “bend” your saw frame. It is also just the static load. When the saw is running there are dynamic load as you have to add in your design.
I have a “tension meter” to check my blade tension in my mill. The blade prolongs about 1mm/1000mm for the tension the blade manufacturer recommends.
I like the possibility to read the real blade tension when I am sawing. If you have a ”hydraulic jack” to pre load your tension spring, it is good to have a pressure gauge in the system. If the blade heats up more than normal it prolongs more and the tension drops.

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Re: Dave's Bandsaw Mill
« Reply #37 on: January 14, 2018, 04:41:38 PM »
That's what I did. I took a hollow hydraulic cylinder and put a pressure gauge
on it.

 

 

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Re: Dave's Bandsaw Mill
« Reply #38 on: January 14, 2018, 04:57:55 PM »

 Without any numbers all I know is if I tension my mill much more that what TK recommends it starts breaking bands fast. Steve
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Re: Dave's Bandsaw Mill
« Reply #39 on: January 15, 2018, 10:35:09 AM »
Wow again on blade tension. With all these new posts on tensioning, I had to re-think what is going on here about blade tensioning being measured in PSI and how it relates to the actual stress that is applied to the blade. I looked at more posts on this subject and found a couple of excellent videos. Within the hour of watching them, I got quite an education.
Bandsaw tensioning: 
Bandsaw setup: 

I had decided that I would just use the way that Woodland Mills tensions their mill blade. They suggest using a torque wrench to a tension on their tensioning screw of 35 foot/lbs. That sounded like a nominally good pull on the blade, so that's what decided to go with. When I saw the 5 digit PSI specs on blade tension, It still blows me away as to how a thin saw blade could take that much stress and not break. But, If that is what it is, then that is what it is. It took me a long time to wrap my head around this but I then started looking at all the variables that had to be plugged into a formula to calculate the actual stress applied to the blade. After doing the math, I can see how Woodland Mills came up with a 35 lb/ft setting on their mill and that it could actually be applying 15,000 PSI to the blade.

After watching the excellent presentation by Carter Products on setting up a band saw, I now have another question to deal with before starting my build. How much offset should I apply to my drive wheel? (as mentioned in the video as all manufacturers do)

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Re: Dave's Bandsaw Mill
« Reply #40 on: January 15, 2018, 11:14:02 AM »
One more quick post to  see if I have the math correct.
A 1-1/4" x .035" blade that is about 1-1/16" to the bottom of the gullet would be; 1.0625×.035x15000 = 557.8125 lbs. linear pull in the blade for proper tensioning. Since it's a circular blade, the force on it has to be doubled (2 x 557.8125 lbs. = 1115.625) to be tensioned properly. That's over 1/2 ton of pull on my wheel. I think that my saw frame will have to be reinforced.

Also, looking for a source for a spring for shock absorption on my tensioning  design.

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Re: Dave's Bandsaw Mill
« Reply #41 on: January 15, 2018, 03:38:19 PM »
Be careful using a torque wrench. One drop of oil on the threads
changes everything. You got dry torque and wet torque .
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Re: Dave's Bandsaw Mill
« Reply #42 on: January 15, 2018, 03:41:20 PM »
I'll be using a tension gauge at first.


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