Swing mill build questions

[Arvynet]

Hello all,
First post on the forum, been lurking around and reading for quite some time, found out lots of interesting things.
Now I decided it's time to ask for some opinions. 😉
I am building a compact swing mill for personal use, as I have allot of 15-20 year old pines I have to cut down and put to good use.
I took inspiration from a russian sawmill builder on youtube, link to the saw:

Initially I thought I will use a Bondiolli and Pavesi 1018 90 degree gearbox and build the frame similar to the video above.
Recently the russian builder posted a new video with a very interesting transfer from the engine to the blade, using v-belts. Link to new video:

What do you guys think of this idea? I am thinking this would save some initial investment but probably cost more on replacement belts as they surely will wear quicker, than in the setup with a gearbox. Do you think it is worth giving it a try since this mill is not going to be in a comercial operation whatsover?

On another note, I still need to get a blade. The blades I have been able to locally source (Europe) are similair to the blade in the first video of the mill. They have quite a lot more teeth than most swing mill blades. I can order a custom made blade with 5-6 teeth that most commercial sawmills use.
What is the benefit of the latter?
As far as I read main difference is in the speed and ease of sharpening.

Thank you for your insights! 😉

[longtime lurker]

Less teeth = less load = lower power requirement.
You can have more teeth but it can't cut faster because of it unless you have more power andif you have more power you get more weight and then it stops being portable.

Opteco may be worth an email, they are a saw manufacturer in Australia and OEM supplier for several swing blade mill companies. It may be cheaper to post saws internationally then it is custom manufacture them

https://opteco.com.au/product-category/opteco-saw-blades/portable-mill-blades/

A gearbox would be a better way of transferring power than belts in this case IMHO. But belts will surely work

[Ianab]

The cutters on a swing blade mill work more like the teeth on a larger circle mill. They take out large chips of wood with each pass, for fast cutting. But it takes 2 or 3 hp per tooth to drive them efficiently like this. So a big saw with ~50 cutters, probably needs ~100 hp to drive it. A small mill like mine a 6 cutters, and 13 hp, so the power available to drive each cutter is similar. This style of blade doesn't make "sawdust", it makes small wood chips.

A table saw type blade has many more cutters, but it's for a more precision cut, rather than speed. Each time a tooth passes through the wood, it takes some power to cut through the wood fibres, even for the finest cut, so the high tooth count simply won't have the power to take a decent "bite". It will be scraping out fine sawdust, and not throwing large chips of wood. 

The finish from the lower count blade is going to be rougher of course, but it's "rough sawed" by definition. Even if your mill could cut perfect "glue line" cuts, the wood is then going to move, either from tension in the log, or uneven shrinkage while drying. So even "perfect" boards off the mill are going to need jointing and planing later, to keep them perfect. And that process takes out the rough edges left by the original sawing. 

[Arvynet]

Thank you for the insights.
I will be running the mill on a 16hp gasoline engine so 6-7 cutters would be the way to go. What would be the optimal diameter?
I will have to make a custom ordered blade as I can't seem to find one like this here unless I find one for a good price abroad. I think the custom one should set me back around 100-150, so I doubt I will be able to source one abroad for cheaper than that and then shipping cost on top.
Regarding the belt drive, the biggest issue I see is when the belts are twisted, but I mean lots of lawn tractors and other equipment uses similair setups without issues. I thought it was a fascinating idea when I first saw the video as I had not even thought about the possibility of running like that. I just wonder how long the belts would last..

[Don P]

You do understand that the tips intersect at the same point vertical and then swung horizontal. That point is determined by the diameter of the blade and the pivot point. You need to be able to saw, swing 90 and saw to create an inside corner with no under or overcut and no adjustment to the height or width.

[Ianab]

What would be the optimal diameter?

How wide are the boards you want to be able to saw? The standard swing mills tend to be 6-8-10" inch cut depth. So a 6" cut needs 2 x 6" + ~4" for the hub, =~18" dia. Larger blades tend to need a bit more power, and blade design / tension become more important. My mill for example is a 6" cit, 13hp and 6 cutters, it runs fine, but 18hp wouldn't go amiss on the deeper cuts. 

As Don P mentions, your swivel mechanism has to be designed to match the blade size. So when you swivel, the cutting tips end up in the same place in the log, but because the blade has swivelled, you are effectively using the other side of the blade, so the cutting direction through the log is the same (No climb cutting allowed)  

Another thing to consider is sharpening. Depending on what you are sawing, you might need to do this a couple of times a day. The carbide tips need a diamond sharpening wheel on some sort of grinder, and a jig to align it with the blade for sharpening. The tips will eventually wear out (or break if you hit metal), so you will want either a local saw doc, or the gear to replace the tips yourself. 

[Arvynet]

Mainly I will be cutting soft wood, and it would be nice to be able to get a 2x8 out for rafters and the like.
Regarding the swinging mechanism I am well aware and will be designing it accordingly.
Sharpening is one thing I have not yet put thought into. I have a friend that can sharpen the blade at his work but that will not be optimal if I wont be able to get through a day without sharpening. Replacing the teeth most likely will be left to the professionals as I am not sure if I will be able to do so myself. (Even though I am handy and could figure it if need be.)
Could you elaborate on climb cutting as I see in most videos on youtube people sawing horizontally in one direction and then flipping at the end of the log and cutting vertically on the way back. Wouldn't that be a climb cut?

[Arvynet]

Could you please explain vlimb cuts and why they are a no no?

[Woodside Kai]

A climb cut is when the saw blade is rotating the same direction as if it were rolling along the log.  ( think clockwise rotating blade feeding from left to right)

The reason it is a no no is the blade will pull itself into the log rapidly and disaster will strike.   If the blade is rotating the opposite direction it will pull itself out of the cut if no feed force is applied. 

Which direction your blade swings is what will determine if your blade will rotate the correct way to edge on the return pass of the carriage. 

[Joe Hillmann]

I had planned to build a swing mill kind of like the one in the second video.  The reason I though of going with belts was to save money compared to a gearbox.

One issue I had while designing it was the corners of the blade have to meet up at the same point as Don P pointed out. 

But at the same time the pulley blade shaft has to be in line vertically and horizontally  with the engine when the blade is up and down .

And it needs to be in line horizontally when when the blade is horizontal.

And the pivot mechanism has to be out of the way in both positions.

I found in order to keep everything lined up I needed to use a short shaft between the blade and the pulley(about the same length has half the blade diameter.

And the pivot point had to be in line with the engine pulley and blade pulley.  And since there can't be a pivot point between the engine and blade(belts will get in the way)  So the pivot point has to be one sided(like in the video) which requires a much stronger pivot point.  Or it has to have a pivot point that spans from one side of the engine pulley to the other side of the blade pulley.

I don't think the twisting would wear the belts too much faster than a non twisted belt.  Although with the twist if the pivot point isn't perfectly in the center of the v pulleys one belt will be doing all the work and the other will be flopping loose.

A lot of stuff that needs to be very strong needs to fit in a pretty small space where the lumber you are cutting also needs to fit.

[beenthere]

And that intersecting point must change with every sharpening of the blade ?? or so it seems will need an easy adjustment to compensate. 

[Don P]

You're sharpening the face of a small carbide tooth so the diameter does not change enough to be... too much of a problem before the blade needs retipping. Before I tried to make a swing blade I think I'd make a 2 blade more like a mobile dimension/Lucas mashup. The intersction point is then fixed and the rails take care of vertical adjustment and the carriage cross slide takes care of horizontal adjustment. That would require more engine though.

[Arvynet]

Deffinately makes sense now that I played around with a saw blade in my hand, regarding the climb cuts.
I would love to make a two blade machine but I have already purchased a 16hp engine and I doubt that will handle two blades at once, so I will be sticking with the swinger.
Where as for the gearbox I decided it will make life a little simpler to just use a gearbox and not the belts.
My frame is almost done just have to get the hard part done, getting blade geometry and such correct..
Too bad I don't have an oxy acetalyne torch would have made everything easier, as my metal kept warping..
Thanks again for the insights.