I’ve been thinking for a while that a useful piece of equipment to have would be a portable band saw milling set-up.
I’ve seen lots of home-built examples, most of which are of a two or four post design. Whilst thinking about this, it seemed to me that a single post design would offer the operator greater access when unloading the mill as each board is cut.
Today I began to put some of my ideas into action, and I have begun to design a mill of a single post design. I’ve given lots of thought to the stability of the vertical movement and how this might be simply achieved, including an electronic control system which would enable boards of a pre-set thickness to be cut once a reference datum has been established, as well as longitudinal cut control.
I offer here a couple of preliminary renderings, and would appreciate any comments (via the link below), should any experts have any feedback they’d like to offer. I hasten to add that I am not an expert in this field at all, I just think it is an interesting design project. When I’ve completed my design work, I will offer a complete set of drawings for download should anyone else be interested in the idea.
I will try to post regularly over the next few weeks as the concept progresses.
This image shows my first thoughts with regard to the post and vertical carriage arrangement. 8 ‘V’ rollers run on hardened tracks, with the carriage being raised and lowered by a pin which itself runs in the slotted post. My thoughts here were that the lifting could be actuated by a cable or chain from a worm-drive gearbox mounted either at the head or foot of the post. Should the post be of substantial construction it ought-not to flex when the torsional loads of the cutting operation are applied. I have a cunning solution for adjusting the rollers to enable very accurate tramming-in of the movement or to take up wear, I’ve just not shown it on this drawing yet.
Another configuation being considered, and an idea I’ve not seen elsewhere is shown here. In this example I’ve placed the drive motor out-board of the cutting frame to help balance the assembly. I’ll mount a water tank for the blade lubrication here also to further stabilise the frame. I’ve added a track and rollers to provide the longitudinal travel. Not shown here, but soon to be added, will be additional rollers running on an track under the guide rail to prevent tipping.
This is how I have chosen to mount the axles for the band wheels. Self-aligning bearing take up units are used with draw bolts to adjust the toe-in of each wheel, ensuring they run true to each other. In practice a straight edge held across each wheel would allow for the necessary adjustment. Each take up unit is held in its own frame which is bolted to the drop arm on the bow. Minor adjustments to the vertical alignment can be achieved by adjusting just one of these frames relative to the other. However careful fabrication of the bow should ensure accuracy in this respect.
The arrangement of the ‘V’ rollers to the vertical axis can also be seen in this picture. The inner and outer plates will be joined in due-course to create a stiff box like structure to which the bow will be connected.
I’m still considering the rise and fall mechanism for the bow, and am tending to favour a rack and pinion mechanism at the moment.
The design of the bow provides plenty of opportunity for additional strengthening, which I will add later when I have more fully considered the cutting forces, and the anticipated load of the blade guides and guarding. However, for now the principle design intention is there.
My next task will be to develop the cutting ‘table’, for which I’ve had what I think may be an original idea. Recently when making the village sign for Peasmarsh, I had the problem of machining a very slender taper to the oak post. As this was beyond my means to achieve, this task was contracted to a local joinery shop, (please see my village sign page). This experience got me thinking about designing the bed of this machine to tilt. This would enable such a taper to be cut with ease.
Now, it would be quite a simple matter to prop the end of already ‘squared’ piece of timber up on a block such that the mill would cut the taper. However, for the purposes of this design exercise I think it would be interesting to incorporate a hydraulically tilting bed with a clear scale which displays the angle of the cut in terms of degrees and also fractions of inches/foot, or the metric equivalent. I could see this being especially useful when cutting firing strips for flat roofing projects. Indeed a whole batch of could be cut at once.
There may be a perfectly good reason why other similar machines don’t incorporate this feature, and experienced sawyers may think it unnecessary, however it seems to me like a good idea and worth investigating fully at this stage. Again, comments with regard to this would be very welcome.