This page discusses long, straight saw blades used in up and down sash
sawmills, including blade profiles, sharpening, and hanging the saw in
the frame (sash). There are many 19th century references available online with discussions of straight mill saw blades listed on the reference page of this website
- for example, see The Sawyer's Companion
written in 1857 by Sanford Parsons.
Profiles of Blades Used at Ledyard Mill
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Blade # 1 (Tracing made in about 1998 by Alan Ganong)
87 to 88 (2 to 3) degree rake angle
Blade is 72" long
Tooth spacing is 1.75"
Tooth height is 1.25"; height has been reduced by repeated sharpening; needs gumming
Tooth face filed at 90o to long axis of blade
Thickness = ??
Width = ??
Number of teeth = ??
TPI = ?
Toothed section length = ??
Maximum log diameter = ??
Length of stroke
The above drawing is based on a trace of one of the saw blades in Ledyard Sawmill collection. It was made from teeth at the end of the blade which only enter the largest logs, and consequently are not sharpened as frequently as those at the center. When a blade is sharpened, tooth height is reduced and may reach a point where the gullets become too shallow, reducing the saw's ability to clear sawdust from the cut. If sawdust is not cleared, it increases the friction between the side of the blade and the wood, robbing power from the saw. This saw blade needs to be reshaped with deeper gullets, the rake angle made more aggressive and sharpened. Grinding a blade to increase gullet depth is called gumming.
We are now using Blade #2 for cutting. Just before Blade #1 was switched out, it was cutting poorly, requiring that we reduce the log feed rate to prevent the saw from stalling. Most likely this was due to dulling of the teeth and friction from sawdust.
Blade # 2 (Tracing made in 2010)
78 (12) degree rake angle
Blade is 69 1/2" long;
Thickness 5/32"; this corresponds to a 9 gauge according to Parsons
Width = 6";
Teeth spacing is 1.9" from tip to tip; tooth height is 1.5";
Tooth face filed at 90o
In Progress: Profiles of other blades to be added as tracings are made.
In April, 2010 this blade was used to cut red oak that was 13" square. At a sash stroke rate of 100 oscillations per minute, the blade cut one linear foot per minute, producing essentially one board foot a minute. The blade was mounted so that the top front edge (where teeth are) was about 3/8" forward (overhang or blade, not tooth, rake) compared the bottom. This was too aggressive, probably due to 78 degree rake angle of teeth. Consequently, excessive vibration was created on the downstroke, causing the side rails of the carriage to oscillate and the mill floor to "bounce." Decreasing the overhang, reduced the vibration but did not affect cutting rate.
Profiles of Blades Used at other Sash Sawmills
Gunton Mill, England
Drawing below was prepared by David Durst from a rusted blade found in sawdust pit of Gunton Up/Down Mill (http://www.norfolkmills.co.uk/Watermills/gunton-sawmill.html)i n Norfolk County near London. Mill operated from 1825 to 1915 serving the needs of large estate. After being restored in 1988, the mill is currently operated by volunteers who provide demonstrations of sawing timbers. Ten pages of photos and videos of the Guntom Mill can be seen http://pets.webshots.com/album/578088011JiVuSh?start=0 Check page 4 for videos of the saw in action. Note the short stroke compared to the Ledyard saw.
During the restoration, new blades were made from modern materials using measurements and a tracing of an old blade (shown below) as a reference.
Blade has 27 teeth per inch over 52.5 inches, yielding one tooth every 1.94 inches. Overall length of toothed section limits the size of logs to be cut to ----- inches, given that stroke length is ------ inches.
Rake angle of teeth is 81 (9) degrees as measured from traced teeth in drawing
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The following notes are excerpts from correspondence with David Durst, a Gunton volunteer:
"A far as I am aware, there is only one complete and workable up-and-down saw in the British Isles. Gunton Park Historic Sawmill is located" ... " some 120 miles due north of London. It was built in 1825 on a large well-wooded estate for their own use, and continued to serve them for 90 years. The building is thatched, and the waterwheel draws from an artificial lake, previously made for its scenic appeal. "
" In the 18th and 19th Centuries there was an excess of labour in England so secrecy ruled the day, whereas the colonies all wanted to get moving. Hence we know relatively little about the machines that were displacing the pit-sawyers in this country; but there were books on how to do it in America. I have a reprint copy of Oliver Evans "The Young Millwright & Millers Guide (Philadelphia 1795 onwards). You mention that the top of your blade has to be set forward by about half an inch; Evans said the same thing; we found out the hard way before reading his book.
An old letter has survived which suggested that when our saw first came into use at least eight pairs of pit sawyers were displaced No wonder the local mob tried to burn the place down in 1833, but they were frightened off by an assembly of game keepers who normally looked after the estate sporting rights."
"The man, named Hase, who built the sawmill in 1825 was a blacksmith by upbringing, and with his brother ran a foundry; hence we have more metal than your mill. The cast iron crankshaft carries a 2-ton flywheel, and the sawframe (or sash) weighs nearly a ton. Burdened with an engineering background, I find the stresses in it are all quite terrifying, but we do not tell the old girl and she keeps on going. Fortunately all the framing on which the crankshaft sits is heavy duty oak (windmill technology): this cushions the cyclical stress reversals. If the mill had been built 20 years later I expect they would have been able to get 4 or 5 foot diameter circular saw blades, and integral saw benches for them, but they stuck with the known methods. Then in 1864 they bought such a thing, and drove it from a second identical water wheel, co-axial but independant. That got used for smaller scantlings, while the old saw was best for breaking down. Parts got lost from the circular saw, and are not worth replacing because there would then be too much of our conjectures based on flimsy evidence; there are plenty of historic circular saws around for people to go and hear."
"Our mill was neglected for over 60 years, then rethatched and made safe. An expert millwright was employed to rebuild the machinery. The iron parts only needed a clean up, but most of the timber was soggy, so was measured and replaced like-for-like. The only blade found was down in the sawdust pit; we hoped it was not a reject, so had it copied in modern materials. I made a sketch which I have just unearthed, and hope to include as an attachment to this e-mail.. A firm who make bandsaw blades made us 4 replicas which we use in turn; when blunt or losing set we exchange them, and have them sharpened and reset by a local firm who work on bandsaw blades. Our blades are clearly very similar to those used by the old pit sawyers, and seem to be thinner than yours.
Not having the skill to do our own sharpening the old [saw} vice in the nearby workshop is not used. During restoration a new concrete floor was put in this shed, so the vice is now too low. and wobbly. The shed is too cluttered for a good photo. It was clearly made by the local estate blacksmith to fit our blades. The jaws are made from iron plate 4" x 1/2", chamfered to their lips,each 60" long. The fixed jaw is backed by 4" x 4" timber which sits on two 6" x 4" wooden legs 36" apart anchored in the ground. The front jaw has two drop bars also 36" apart welded to it; these run down the front of the legs to pivots about 20" below the lip. Set into each leg is a 9" x 3/4" bolt about 7" below the lip, which then passes through the drop bar, and by tightening their nuts the vice is closed. "
"The stop-go advancing of the carriage is usually done with pawls and a ratchet wheel. I see from your video clip that yours is somewhat similar. Ours is different, being a friction grip onto a smooth wheel-rim; we think this was a system devised (or re-invented) by the man who built our saw: he was a blacksmith by upbringing. Our saw, like many I have seen moves the carriage forward during the downward (cutting) stroke, and keeps it still for the upward (return) stroke. I am interested that yours does the opposite."
"In thirty years we have never had a dried out pond, but we have had the dam overtopped on several occasions. We hope that we now have better precautions. We run at around 60 strokes a minute, and advance about 1/8 " per stroke. The carriage is returned by muscle-power. There is provision for multiple blades, but that would set us scrounging more lumber which is not easy. We cut whatever we are given, often oak or chestnut of no commercial value, but also softwoods."