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Daniel

I have written up a sawmill analysis: http://openfarmtech.org/wiki/Sawmill_Analysis

Key findings are:

(1) The current GVCS sawmill is roughly sized for a village of 1250 people if you use conventional construction, more people if you use alternate construction that uses less wood.
(2) A portable bandsaw is a better design overall than the current stationary circular saw design.
(3) Existing log weight specification (3000 lb) is probably too low for the power rating.

Please review and comment either here or the discussion page for that wiki page.

gregor

Bandsaws wear out pretty fast though, and it should be low maintenance.

Dawg

I hate to say it because a band saw is easier to build, but in the long run, a circular saw will pay off I think. The issue is the band blades tend to dull quickly, especially in hard woods. So you find yourself sharpening blades all day instead of making lumber. People tend to have 6 to 8 band blades at the ready to insure they can run all day. Then they spend an hour or more sharpening at the end.

On the other hand, the blades can be sharpened easily and they're cheap. Circular blades tend to have Carbide tips which are harder to deal with and they're expensive. Plus it's easier to remove a band blade than a circular blade.

A dimensional mill that actually cuts finished planks in one go is a bonus but it's operation is more involved.

If I were to build a saw for myself to use, I would still go for a band saw in the end. Much easier to build and operate. Unless you're a trained woodsman, the band saw is the way to go I think.

Daniel

@gregor - A band saw blade has many teeth in contact with the wood, so the heating on each tooth is lower. Therefore you can use steel teeth. Circular blades only have one or two teeth in contact at a time, so the heating is higher, and you need carbide teeth if you are doing high production. I don't think carbides are a village-producible item, while with a laser cutter you could make bandsaw blades locally. So from a product ecology the latter wins.

@dawg - Form personal experience, I agree, blades need replacing pretty often if you are running a 40 hp mill on a production basis. At that scale, an automatic blade sharpener is fairly necessary. They are pretty simple devices for a shop though, apply grinder to tooth, then move blade one tooth and repeat. That can be done with a slow rotating shaft and some cams for both actions.

The argument about cutting finished planks goes to the bandsaw when you actually run the numbers. Assume you have a 16x16 block squared from a log and want to cut it into 32 - 2x4 boards. A dimensional mill takes 31 passes to cut one board with each pass (last one is free). The bandsaw takes 3 passes to cut 4 inch slabs, then rotate and reclamp the slabs, and another 7 passes to make the final boards, so 10 total passes.

Dawg

@Daniel - Well I think the idea is to CNC the machine at some point. Assuming this, then the dimensional machine might be a winner. 31 passes when it runs itself is not a problem really. Like all our designs I feel one model will not be best in all scenarios. You can't design a commercial quality machine for 1200 people and have it cheap and easy to build. Or portable for that matter. So as a category 1 machine, the band saw wins hands down. But as an all out production machine, I think I would go with a dimensional design assuming a microcontroller is involved.

Another point from someone who has done it, is the amount of effort it takes to build the drying stack. We've always stacked green slabs for drying and then used a simple table saw to make the lumber once dry. It's easier to insure nice straight lumber if you stack the slabs. You tend to lose less product that way. Nothing sucks the life out of you faster than to realize you've lost 1/4 of your lumber to cracks and warpage after investing all that energy. Stacking 2X4's is labor intensive and not always successful. I am not a professional woodsman and I'm assuming the majority of people using our designs will be the same.

The Dawg

Daniel

That brings up something I am starting to work on - the information that needs to exist in addition to the hardware. If we have people using a sawmill, for example, they need instructions on what to do with it, including how to effectively load the logs, stack and dry the lumber, etc.

And I agree about having various models for different situations. That's why I am starting to evaluate the machines according to how many people they will serve. The current GVCS sawmill is appropriate for 1250 people or so, and you will need a certain amount of forest to keep it busy on a sustained basis. For a small group of people, something like an Alaskan Mill to slab the log plus a table saw like you suggest to cut boards might be a better fit. Not as efficient, perhaps, but low cost if you have a shop and chainsaw already (which is likely if you are doing any sort of farm).

Dawg

@ Daniel - That is a great idea. No point showing people how to build a mill and then leave them standing there with no clue how to proceed. Ideally, all they need to know from design, sourcing, construction, maintenance, operation and safety would all be there. For that matter, all our projects should follow the same path.

The Dawg

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