Workshop Fitting Out & Project Pages.

An Electric Chainsaw Mill (Part 2).

Designing the jig

When operating a chainsaw mill there are several methods for mounting the mill above the timber to be cut.

Chainsaw Mill 1^st cut using a ladder for rails.

The usual option is to securely attach a ladder along the top of the wood and simply push the mill along the top of it as shown in this photograph. These ladder rails ensure a first reasonably flat cut.

Photograph by "Bongo Drummer"

Chainsaw Mill using the first cut surface as a guide.

Chainsaw Mill 2^nd cut using the first cut surface as a guide.

Once the first cut has been made the ladder guide can either be re-attached as a guide for the next cut, or alternatively the rails can be removed completely and subsequent slabbing cuts made simply by pushing the chainsaw mill along the flat surface made during the first/previous cuts.

Photograph by "Bongo Drummer"

DESIGN IDEAS

For my small-scale mill I decided to try and design a jig where the mill ran on rails both supported and strictly kept on track by means of a set of eight small furniture castors. The gauge (distance) between the rails was governed by the length of the chainsaw guide bar and the width of the Royston 24" Mill. The resulting design is shown below.

(Click on image for animated view)

Figure 1. Sketchup drawing of a jig designed to support the Royston Portable Chainsaw Mill with Oregon CS 1500 Chainsaw. Note that the chainsaw powerhead has been omitted in this drawing.

With this design there are five main sets of components (Shown above in Figure 1):

The Royston 24" Portable Chainsaw ("Alaskan") Mill...
...supported on a wooden carriage which runs by means of eight castors on....
...two angle-iron rails supported by....
...a wooden Base Frame the whole supported & firmly gripped by...
...two Workmate portable work benches used in bench-vice mode.

Detail of mill supported by castors running on rails.

(Click on image for larger view)

THE ADVANTAGES OF CASTORS RUNNING ON RAILS

Figure 2. Detailed drawing of the mill on its wooden carriage supported and guided by 6 visible (& 2 hidden) castors running on the two angle-iron rails. The main advantages of castors running on rails are:

Reduction of friction, and thus the amount of effort needed to push the mill through the cut & along the rails
Elimination of wear and tear on the base struts of the mill frame by avoiding pushing them directly over the rails or directly over the wood surface
The rail/castor combination keeps the chainsaw on a straight and narrow course (preventing deviation and maintaining the best orientation of the saw for cutting)
Production of boards consistent in thickness

THEORETICAL CAPABILITY OF THE JIG

The theoretical specifications of the jig (given in the table below and in sketch figures 3 & 4), are for a chainsaw with a 450mm (18") long chainsaw guide bar. A longer guide bar would significantly increase the capabilities as regards both width and potential length of cut.

THEORETICAL CAPABILITY OF THE JIG ILLUSTRATED IN FIGURES 1 & 2.
Guide bar effective length (before mounting in the mill)	Distance between the two points of attachment on the chainsaw guide bar	Max width of cut when the chainsaw is mounted in the mill	Length of rails (of the illustrated jig)	Max length of cut (when using the illustrated jig)
450 mm (18")	355 mm (14")	320 mm (12⅝")	1,500 mm (4' 11") (See Figure 3)	945 mm (3' 1¼") This depends on the length of the metal guide rails. (See Figure 4)

The maximum width and depth of cut will depend on how irregular the wood is in shape. A regular cylindrical shape shown diagrammatically in Figure 4 is rarely seen in nature and is further complicated by any boughs or other irregularities such as burrs on branches and trunks. In practice some trimming by means of free-cutting with the chainsaw will be necessary before the timber can be mounted into the jig.

(Click on image for larger view)

Figure 3. Drawing showing the theoretical maximum width of cut and the possible maximum diameter (about 453 mm or 17¾") of a roughly cylindrical piece of trunk or branch. Using the jig to carry out initial cutting along the cylinder on four sides would result in a slab of wood within the 320 mm width limit of the jig.

(Click on image for larger view)

Figure 4. Drawing showing the theoretical maximum length of cut with the jig running on rails of length 1,500 mm. Longer rails are possible but bear in mind that they have to support the weight of the mill plus chainsaw without flexing. Flexing of the rails during cutting would result in an irregular/uneven cut rather than a straight tabular one.

Building the jig

MATERIALS

l already had all the wood required for the project and only needed to purchase additional metal components.

WOODEN CARRIAGE COMPONENTS
Quantity	Material	Measurements	Comments
1	12 mm plywood	300 mm x 370 mm	Top of carriage. Could also be constructed using MDF
4	Softwood laths	165 mm x 40 mm x 20 mm	Sides of carriage
8	Wood-screws (Countersunk heads)	5 mm x 35 mm wood screws	Used to fasten the plywood top of carriage to the softwood laths (carriage sides). Could be self tappers
8	Small furniture (fixed plate) castors	30 mm length x 17.5 mm depth x 17 mm width x wheel diameter 15 mm	*Castors by Hafele* (product code 661.23.322) are ideal for this.**
16	Pan-head self-tapping screws	4 mm x 12 mm (Imperial size 8 x ½")	Used to fasten the castors in place.

ANGLE-IRON RAIL COMPONENTS
Quantity	Material	Measurements	Comments
2	Mild steel angle iron rails	40 mm x 40 mm x 3 mm thick and 1,500 mm long	If opting for longer rails, bear in mind that they are only supported at each end and have to bear the weight of the mill, the wooden carriage plus the chainsaw itself without flexing. The combined weight of the Royston 24" Mill plus the Oregon CS 1500 chainsaw is in the region of 14 Kg (30 lb)
3	12 mm plywood (sleepers)	272 mm x 100 mm x 12 mm	These form the sleepers of the track and determine the outside distance between the two angle-iron rails. This distance must equal (or be 2-3mm less and certainly not exceed) that between the two sets of castors on the bottom of the wooden carriage (in this instance 280 mm)
6	Softwood blocks	100 mm x 68 mm x 44 mm	These screw to the plywood sleepers and are attached to the support laths (connecting the rails to the Main Frame)
12	M4 countersunk head bolts (with washers and nuts)	70 mm long	These bolt together the angle-iron rails, the plywood sleepers and the softwood blocks to secure the rails in place
12	M4 self-tapping screws	30 mm long	These screw the plywood sleepers to the softwood blocks

BASE FRAME COMPONENTS
Quantity	Material	Measurements	Comments
2	softwood planks	95 mm x 45 mm x 1,605mm	Longitudinal sides of the frame.
4	Softwood connecting planks	95 mm x 45 mm x 183 mm	Connecting braces for the frame sides
2	Softwood lugs	44 mm x 36 mm x 45 mm	These lugs enable the base frame to be gripped by the bench vices
16	hexagonal-headed turbo-coach screws	6 mm x 90 mm	These fasten the cross-braces to the longitudinal base frame timbers

WORKMATE PORTABLE WORKBENCHES
Quantity	Material	Measurements	Comments
2	composite	610 mm (length) x 601 mm (width) x 775 mm (height)	2 of these (or something similar, there are many similar designs available) are ideal both for holding the lugs on the base frame of the jig firmly in position and thus maintain the whole jig at a reasonable working height when in operation.

MISCELLANEOUS MATERIALS
Quantity	Material	Measurements	Comments
9	M12 threaded steel rods	500 mm	Used to assemble and hold the components of the jig together	A jig support lath
9	M12 nuts	-
9	M12 wing nuts	-
18	M12 washers	-
6	softwood support laths	44 mm x 25 mm x 460 mm
1	Lockheed Brake Fluid Reservoir	-	Used as an auxiliary chainsaw oil reservoir (oil piped through plastic tubing from the nozzle on the bottom of the reservoir)	Auxiliary oil reservoir
1	Fuel shut-off tap	-	Fuel tap used here to control the flow of oil from the auxiliary chainsaw oil reservoir (oil piped through plastic tubing)	Fuel tap

CONSTRUCTING THE CARRIAGE

MATERIALS
12 mm plywood board 300 mm x 370 mm
5 mm x 35 mm wood screws (Countersunk heads)
2 Pine laths 370 mm x 20 mm
8 small furniture castors
16 pan-head self-tapping screws, 4 mm x 12 mm (Imperial size 8 x ½")

(Click on image for larger version)

Figure 5. Sketch plan of the wooden carriage constructed for supporting the portable chainsaw mill
This bottom view of the carriage shows the HAFELE© 15 mm diameter fixed castors (Part number 661.23.322). These castors (which allow the jig to run on rails), are ideal for this project and are readily available to purchase on-line. The positioning of the castors is crucially important and must be attached in such a way as to enable the carriage to run smoothly along the angle-iron rails.

ADDITIONAL DETAILS OF CARRIAGE CONSTRUCTION & ASSEMBLY

(Click picture for larger view)	Figure 6. Sketch plan showing the chainsaw mill in place on top of the wooden carriage. The Chainsaw mill sits on top of the carriage and is held in place both by its weight and by two v-shaped indentations cut out on either side of the carriage through which the mill guides pass. (Click thumbnail images for larger and animated views)
(Click picture for animated view)
(Click picture for larger view)	Figure 7. Photograph of the carriage as constructed. Photograph of the bottom of the carriage (viewed upside down), showing the castors. (Click thumbnail images for larger views)
(Click picture for larger view)	Figure 8. Assembling the Mill & the carriage - part 1 Before assembly ensure that the chainsaw mill frame is adjusted to the width between the chainsaw bar guides (320 mm). The annotated photograph shows the correct distance and the locking nuts which are loosened to enable the frame member to be slid to the correct width as required. When the correct distance has been set, the locking nuts are tightened. (Click thumbnail images for larger views)
(Click picture for larger view)	Figure 9. Assembling the Mill & the carriage - part 2 Assembly is very easy! First place the chainsaw mill guides attached to the chainsaw guide bar on a flat surface. Lift the wooden carriage into place, sliding the guide bars into the v-slots on each side of the carriage. Finally, lift the mill frame into position and slide down the guide bars and into position. Lock in position by tightening the nuts on the u-bolts. (Click thumbnail images for larger views)

CONSTRUCTING THE RAILS

(Click on image for larger version)

Figure 10. Sketch plan of the angle-iron rails
The rails are secured by countersunk headed bolts to ensure that the castors of the carriage run smoothly over the top.

USING TWO STEEL TABLE SUPPORTS INSTEAD OF THE TWO ANGLE IRON RAILS

Sketch showing actual rails used for construction.

(Click picture for larger view)

Sketches and photographs showing my plan for using table support rails (instead of angle-iron rails).

I did not use angle-iron rails as I had two metal rails which were originally part of a scrapped dining table support frame. As it happened, these were exactly the correct length (1,555 mm), size and shape for this project.

The plywood sleepers and softwood wooden blocks were cut to size, drilled and corresponding holes drilled in the rails (see sketchplan for details). The components were then bolted together using 12 countersunk headed M4 bolts, 70 mm in length.

Note the M12 threaded rods in the lower photograph. These were used to fasten 6 wooden removeable supports which connected the rails to the lower mainframe of the jig. (See below for details).

(Click thumbnail images for larger and animated views)

(Click picture for animation)

Photographs showing rails as constructed.

(Click picture for larger view)

TEST RUN OF THE CARRIAGE ON THE RAILS

(Click picture for larger view)

Testing the carriage on the rails.

The rails were placed on two Workmates and the carriage placed on top to see if it ran smoothly and easily on the rails.

(Click thumbnail images for larger animated view)

CONSTRUCTING THE BASE FRAME

No hard and fast rules with this but the base frame timbers have to be fairly sturdy in construction to support the weight of the rails with carriage and chainsaw, plus the timber being sliced. If the lumber is green then it may be extremely heavy. The only constraints are the overall width and length of the frame which must match those of the rails (See assembly description), to ensure the linking supports will match. As regards the timber components, I had two 2 metre lengths of 95 mm x 45 mm of pine left over from a previous project which were ideal for this project.

BASE FRAME COMPONENTS

(Click on image for larger version)

Figure 11. Sketch plan of the base frame rails
The base frame components were fastened together using 16, 6 mm, 90 mm long hexagonal headed woodscrews.

(Click picture for larger view)

Base frame components ready for assembly.

The main components were screwed together using 6 mm (diameter) hexagonal headed woodscrews, 90 mm in length.

(Click thumbnail images for larger view)

(Click picture for larger view)

Screwing the components together.

Base frame components held securely in position with a G-cramp whilst a ratchet spanner is used to screw home the hexagonal headed wood-screws.

(Click thumbnail image for larger view)

(Click picture for larger view)

The completed base frame.

Bottom view of the completed base frame showing the attachment lugs and inserted M12 threaded rods used to connect the frame to the overlying carriage rails.

(Click thumbnail image for larger view)

CONNECTING THE RAILS TO THE BASE FRAME

To incorporate a "Chainsaw Mill Easy Loader" function a total of six supports were used for this. Two (the pair of central supports) are only used when the mill carriage is being loaded on the rails, and are removed before operating the mill. It's important that all the supports are easily assembled and disassembled from both the rail and base frame units. To facilitate this a series of 9, M12 threaded rods are used with nuts and wing-nuts. These pass through a series of pre-drilled holes in the 6 supports, rails and the base frame.

Sketch showing how the rails are supported above the base frame.

(Click on image for animated version)

Figure 12. Sketch showing how the six supports are utilised, supporting the rails above the base frame.

Click HERE to return to the Home Page.