Idea: a Sawmill with No Frame?

      Forumgoers kick around the concept of a "gantry" bandmill that would roll on wheels on a slab, instead of sliding on a steel frame. October 3, 2009

Question
Well, I'm back with a daft question. Does a horizontal sawmill without rails exist? Imagine just a wheeled gantry with the saw attached via posts screws, like a car lift, nothing underneath, on the ground level. The wheels of the gantry would be powered by a motor and worm/gear reductor of some kind, linked by an arbor and two chains and sprockets. No differential. And this would be used on a flat (ish) concrete slab, or if need be two leveled I profile steel beams. The saw would be powered by something like a 40HP diesel motor. Raising and lowering by electric motor. Don't know about the feed turning the wheels, either the engine or another electric motor, depending on convenience. Most of the parts are readily available - saw's body, and a modified car lift for the gantry.

What do you think - does it already exist, or have I got a new idea?

Could be used on a good car park or hangar concrete slab or anything flat enough over the length of the tree to cut. And it's even easy to check for plane, with a piece of string. I don't think 5mm over 5 or 6 metres would matter much; my boards are that bent out of the wood shop next door. And that's what a jointer is for. At my workshop, I would obviously use two rails or a concrete slab flat enough.

Forum Responses
(Sawing and Drying Forum)
From contributor B:
I saw a basic mill sort of like what you describe. It consisted of a concrete slab with 3" angle iron embedded in the concrete, point up, running down each side. Wheels about 3 feet apart rolled on the angle, 2 on each side, supporting towers connected by a light bridge about 6 feet off the concrete, tying the two towers together. An all-thread screw system in each tower raised/lowered the support for a Stihl 090 power head in each tower. The two powerheads were connected with an 8' bar.

He was sawing very large cypress logs into flitches. This was a 20hp chainsaw mill -pretty impressive. It was homemade.



From the original questioner:
Thanks. Means I'm not the only one with weird ideas!


From contributor N:
Sounds like a large version of the TK B-20 to me.


From the original questioner:
Nope, it's not really like a Timberking. What I'm planning is something without rails, if I can do without. My idea would be to use car wheels to wheel the gantry. And use it on a concrete slab. If need be, if I go cutting somewhere else, I would carry two I profile steel laid flat so the wheels would run in the side groove. I would obviously level the steel profiles. What I want to do is be able to roll the wood on the slab, then cut it.


From contributor N:
If you used 2 -3" angle irons to lay flat on the concrete, connected by flat bars between them at say 4' OC, you would only have to roll the log over a 2" high angle. The wheels would only have to be 4" pulleys to roll on the angle.


From contributor T:
One problem will be keeping the unit going in a straight line; any error in wheel alignment will cause it to drift. Also after the first cut you will have sawdust on the floor, which will lift the unit slightly and cause uneven cuts. It will get worse unless sawdust is constantly cleaned up. Tire pressure and style will cause problems as they will give unequally and the unit will not stay aligned with the floor. There are many other problems that would show up, such as vibration from the motor on pneumatic tires, etc. Sawdust/chips under log would add to unevenness of cuts. As size of log was cut down, you would need some way to hold it stable for final cuts, etc. The rails and solid wheels exist for many reasons.


From contributor E:
I'm with contributor T. I keep picturing sawdust buildup under the wheels. Pneumatic tires have a big footprint and even a small buildup will cause a problem. That's the reason most mills use a knife edge approach that both sheds well and allows the concentrated weight on the rollers to cut/smash the sawdust off.


From the original questioner:
Well, I had an idea watching an alternative sawmill... The thing has a frame, a blade moving alternatively from one side to another. And it looks almost like a car lift! The big saw, attached horizontally on a car lift. I wonder, hydraulic or screw car lift? But that'd be a good solution. With a railed chariot moving under fed by a capstan winch. Okay, not mobile.


From Professor Gene Wengert, forum technical advisor:
Frame saws have been popular in the past. A variation is to put several saws in the frame (called a sash gang saw) so that several pieces of lumber are produced with one pass. In fact, logs with high internal stress (we have none of those species in North America) can be sawn only with a frame saw (or multiple saw arrangement) that cuts lumber from both sides equally at the same time. This keeps the stresses balanced.

It is well to remember that the older saws were developed when logs were cheap and plentiful. So, wasting wood in favor of high production was justified. Each 1/32" of extra thickness in a 4/4 piece of lumber is a loss of 3% in yield. With the high cost of logs and our concern (and responsibility) to conserve our natural resource, we cannot use all the old saw designs today. We must make sure that they are appropriate for today's world.



From the original questioner:
Thank you. Well, I'm not planning to build a frame saw, but rather use the same arrangement for a bandsaw, in a gantry like this (actually a car lift) and move the chariot underneath with a capstan winch and two pulleys.


From contributor D:
Have you looked at the Keener Built sawmill? It has an overhead track that is pretty unusual. If nothing else, it might give you some ideas. I wrote a review of one for Sawmill & Woodlot Management magazine, and the sawyer was pretty pleased with it.

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