Back to some milling.

**BobL** · 13th April 2021, 05:38 PM

Due to some health issues over the last few years the only milling I've been doing has been with my small chainsaw mil,l but today I used the 36" bandsaw mill at my tree lopper mate's (Jeff) yard for the first time in about 4 years.

No one had been using the BSM mill for at least two years and it took some resurrecting. The fuel lines were brittle and had split so those and the battery needed replacing but worst of all someone had backed into it and the mill and rail tracks had moved off its concrete pad. I envisaged several hours with a crowbar but Jeff pulled the truck with the Hiab up alongside the pad and we lifted the mill off its tracks and then lifted the tracks back on and put the mill back on the tracks - easy enough - I wish. Someone has also dropped logs onto the cross beams between the tracks so these are slightly bent!

So lots of checking alignments and parallelisms of the tracks and mill, constantly walking the 60m back and forth from the mill to the shed to fetch and return tools. Lots of bending and standing up and over the mill, stepping over rails and logs etc. I only worked half days and it really tired me out.

Anyway - short version - 3 half days later I was ready to cut and that was this morning.
First cut I took nice and steady and it went fine.
IMG_4893p.JPG

Second cut I got a bit greedy and really pushed it and before I knew it the blade dove in the cut. This happened a number of times when we first got the mill back in 2014. This time I managed to back out of the diving cut (blade has to be moving to do this) without the blade coming off the wheels and ruining the blade. What happens is that sawdust builds up behind the blade and prevents it from being able to move it back through the kerf. I keep a long bow saw blade to stick down the kerf to drag some of the jammed sawdust

This gave me a chance to practice cut recovery and I managed to get it cutting straight in the same kerf by slowly going backwards and forwards in teh kerf just before it starts to dive
This meant the slab being cut was OK but the one under it was not as it contained the diving cut. I trimmed the diving cut off by cutting a 25 mm thick slab and took that one to the mens shed where they make can use even a butchered slo like this as the make all sorts of small things like cutting boards and boxes etc.

By taking it easy I managed to cut the next two slabs OK but the fork lift wouldn't start so I called it a (half) day because these were too thick/heavy to move by hand.
The slabs might look nice but one end has a termites nest that has been invaded by black ants and there are some slightly pukey bits in as well - it might all end up at the mens shed ye.
IMG_4894p.JPG

I really need to go back and reset the track geometry (make sure everything is parallel etc), then the mill geometry, and then the blade geometry and hopefully this will cure the diving issue.

A few weeks ago I found out can just do half days work. If I do a full day but that wipes me out from doing anything for a couple of days.
Anyway I plan to use this mill about 2-3 half days a week.

**Old Hilly** · 14th April 2021, 05:59 PM

Bob, we had hells own trouble with the blade diving and/or rising with our mill. In the end it turned out we just didn't have enough tension on the blade. I had to actually measure the stretch in the blade as it was tensioned with a set of digital callipers that were clamped to the blade then transfer that to the amount of torque that we applied to the tension screw.It drove us crazy for a while.

**BobL** · 14th April 2021, 08:20 PM

Originally Posted by Old Hilly

Bob, we had hells own trouble with the blade diving and/or rising with our mill. In the end it turned out we just didn't have enough tension on the blade. I had to actually measure the stretch in the blade as it was tensioned with a set of digital callipers that were clamped to the blade then transfer that to the amount of torque that we applied to the tension screw.It drove us crazy for a while.

Thanks OH - I will give it a try.
The mill has a hydraulic piston pushing the wheels apart and a pressure gauge that reads the pressure. The fella we bought the mill told us what to set it at but I will up the pressure a bit to see what happens

**Old Hilly** · 15th April 2021, 07:11 AM

Bob, it may be worthwhile you doing a bit of research on bandsaw blade tension. I wandered around a few of the US forums looking for info, eventually going to various bandsaw blade manufacturers web sites. Then I wandered to a bloke in Canada who made his own bandsaw out of wood (wood gears.ca I think) who had a less complex idea of measuring tension of bandsaw blades. Then I fumbled around with a calculator and got some numbers that confused me so I got help from a bloke that does complex maths for a living. He agreed with my figures of, I think, .002" stretch over 4" for the saw blade we were using which equated to 35FtLbs torque on the tension knob. A similar process applies to the little bandsaws that we use in our sheds for slicing up bits of wood. It comes down to some blokes "Modulus of elasticity".Good luck.

**BobL** · 15th April 2021, 08:29 AM

Originally Posted by Old Hilly

Bob, it may be worthwhile you doing a bit of research on bandsaw blade tension. I wandered around a few of the US forums looking for info, eventually going to various bandsaw blade manufacturers web sites. Then I wandered to a bloke in Canada who made his own bandsaw out of wood (wood gears.ca I think) who had a less complex idea of measuring tension of bandsaw blades. Then I fumbled around with a calculator and got some numbers that confused me so I got help from a bloke that does complex maths for a living. He agreed with my figures of, I think, .002" stretch over 4" for the saw blade we were using which equated to 35FtLbs torque on the tension knob. A similar process applies to the little bandsaws that we use in our sheds for slicing up bits of wood. It comes down to some blokes "Modulus of elasticity".Good luck.

I did some checking out of this when we got the bandsaw. The former owner of the mill recommended 2000 PSI on the gauge, for a 2" x 0.05" blade that works out to 20,000 psi across the blade dross section. The hydraulic ram that provides the tension has a cross section of about 1 sqin so that equates to about 2000 lbs or just under a ton of tension. Some websites recommend 25,000 psi but that seemed high to me but I have to remind myself that the band could easily hold a couple of tons under tension.

**Old Hilly** · 15th April 2021, 10:10 AM

I had seen that figure bandied about on some US forums but I got the impression that they were using narrower blades but anyway, I went for the measuring thing simply because we didn't have hydraulics on our home made mill. Good luck with the sawing. It's always nice when a board comes off the mill all straight and true.

**19brendan81** · 23rd June 2021, 04:29 PM

Hi Bob, good to see you back in action. I am also having issues with diving blades in my bandsaw which is giving me the . i havent used it in a while but plan on going and spending a few days with it soon to see if i can nut it out. I suspect it may be issues with tension - i think you can buy gauges to measure it for memory.

**Old Hilly** · 23rd June 2021, 04:54 PM

Originally Posted by 19brendan81

Hi Bob, good to see you back in action. I am also having issues with diving blades in my bandsaw which is giving me the . i havent used it in a while but plan on going and spending a few days with it soon to see if i can nut it out. I suspect it may be issues with tension - i think you can buy gauges to measure it for memory.

Yes Brendan, you can purchase such a device but when I looked they were frightfully expensive for what they were. Some research and almost endless wanderings led me to this gentleman, "woodgears.ca", who seemed to have had some success with a plain old digital caliper and a couple of spring clamps. $29.95 at Creepycheap Auto beat the few hundred dollars the yanks wanted for something that did the same thing: it measured the stretch in the bandsaw blade over a set distance and thus the tension was calculated. But I have the feeling that the calculations were for the larger blades, those over the 1" mark rather than the more common hobby blades used by us mere mortals. Well, except my mate and I when we cut Paulownia, then I get to play with bigger toys.

**BobL** · 23rd June 2021, 05:10 PM

I'm still having problems with the bandsaw mill.
Have replaced the tyres, played around with the tension, rebuilt the hydraulic ram that tensions the blade, and realigned everything multiple times - only to realise several of the settings (eg wheel tilt) have been wrong for the last 5 years. So had to do a hard reset of everything, only to find the throat gap arm is bent as is one of the log support rails ! ARRGGHHH !

I've avoided going near it for the last two weeks but will have to grin and face it soon.

**Old Hilly** · 23rd June 2021, 05:24 PM

So the machine has had an easy life and was well maintained by a fastidious previous owner? Or perhaps not by the sound of things.

**Bushmiller** · 23rd June 2021, 05:30 PM

There are a number of aspects that will cause the blade to dive including blade tension. However, too much tension and the band breaks! A second issue is that these mills are horizontal and sawdust does not clear easily from beneath the blade compared to a vertical band mill where saw dust is easily ejected. The build up of saw dust combined with cutting creates heat and heat is an enemy.

Most horizontal saw mills employ water on the blade at both the entry and exit points to the log to combat this. The problem is that if the blade is allowed to heat, the tooth edge through expansion becomes longer than than back of the blade and now without effective tension on the tooth edge it is free to wander.

Regards
Paul

**BobL** · 23rd June 2021, 08:14 PM

Originally Posted by Old Hilly

So the machine has had an easy life and was well maintained by a fastidious previous owner? Or perhaps not by the sound of things.

It's never been they same since someone at the yard hit the frame it with either vehicle or large logand pushed it off the concrete slab. Ive spent about a week in total trying to sort it out.

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