How to Cut a Log Lengthwise With a Chainsaw (Mill, Chain, Safety)

You can cut a log lengthwise with a chainsaw, but a freehand rip wanders and wastes wood. A chainsaw mill riding a leveled first-cut rail, with a ripping chain, gives flat boards, and every pass turns about 1/4 inch of log into sawdust. Ripping chain is not for handheld use. This guide covers setup, the first cut, kerf loss by board thickness, and the safety gear to wear.

What You Need to Cut a Log Lengthwise

Cutting along the grain is called ripping, and a chainsaw does it very differently from the crosscuts it was designed for. The chain drags a long, wide kerf through the log instead of severing short fibers, so the saw works harder and the cut tries to drift. That is why the standard method for boards is a chainsaw mill: a frame that clamps to the bar and holds it at a fixed height above a flat reference surface.

Here is how the realistic options compare. The details come from the mill maker’s tag on the product above, Stihl’s product page, and the hobbyist write-ups named in each row.

Method	What it gives you	Main limit
Alaskan-style mill (frame on the bar)	Consistent thickness along the whole log; first-cut rail, then the mill rides on the flat face	Needs a powerful saw (70cc-plus is the usual advice) and a ripping chain
Small log mill (bar attachment)	Cheaper option for short, narrow logs; Granberg’s G777 is listed for 16 to 20 inch bars	Limited log width and bar length
Freehand with a guide board	No extra hardware; Woodgears.ca cut a 5-foot log this way with a guide board bolted to the bar	Rough surfaces, wandering cuts, and sawdust packing in the kerf
Wedges and a maul	Splits along the grain for firewood or rough stock	Follows the grain wherever it goes, so it is not a way to make flat boards

Bar length sets the widest log you can mill. Granberg’s tag on the G778-36 says it fits bars up to 36 inches and cuts up to 32 inches wide, so the cut width is somewhat less than the bar length. Bigger saws also cost more to run: one milling write-up notes that bar oil use nearly matches fuel use during milling, so keep the oil tank topped up. If you run a gas saw, our guide to 2-stroke chainsaw fuel covers the fuel mix.

Weighing up cost and saw size before you buy anything? Our cheap chainsaw mill guide breaks down what a budget setup really costs, and the chainsaw size for milling guide compares engine sizes.

Ripping Chain vs Regular Chain

A standard chain has top-plate cutters ground at roughly 30 degrees for crosscutting. Stihl’s ripping chains use a 10-degree top-plate angle, which Stihl says helps clear chips and sawdust from the cut. Stihl sells them for cutting your own lumber with a saw-mounted mill, on a saw of preferably 70 cc or more. Its listed options are the 33RMX (3/8-inch pitch, .050 gauge) and the 46RCX (.404 pitch, .063 gauge), so check your saw’s pitch and gauge before ordering.

The safety point is the one people skip. Oregon’s RipCut ripping chain page states that the chain is for ripping cuts only, is not for hand-held use, and that the yellow-labeled chain does not comply with low-kickback requirements. So a ripping chain belongs on a saw locked into a mill, not on a handheld saw used for felling or limbing. Our ripping chain guide covers how to tell the chain types apart.

Can you rip with the chain already on your saw? Milling write-ups say yes, only slower, and Woodgears.ca reported that stringy wood such as silver maple caused shavings to clog around the sprocket. If you try it, expect a rougher surface and more time between passes for the saw to cool. Treat that as a workaround, not a setup to invest in.

Set Up the First Cut

The bark and shape of a log are not flat, so the first cut needs its own straight reference. Once that first face is flat, the mill rides on it for every later cut. This is the step where most crooked boards start.

1. Secure the log: chock or clamp it so it cannot roll, and support it at a height where you are not working bent over. Popular Woodworking notes wedges or hooks to stabilize a log and recommends two people for the first cut.
2. Mount a guide rail: fasten a straight ladder, board or rail kit along the top of the log with screws or lag bolts. Newton Makes uses lag bolts and cuts under them.
3. Level the rail: check it across several points along the log, not just at the ends. A rail that twists gives you a twisted first face.
4. Set the mill height: set the cut deeper than the fasteners so the chain never touches metal.
5. Make the first pass: run the mill along the rail at full throttle with an even, steady feed, letting the chain cut rather than forcing the saw.
6. Remove the rail: move the mill onto the freshly cut flat face and reset the height for your board thickness.

Before the first pass, check the log for nails, fencing wire or embedded metal, which can wreck a chain and throw hot fragments. A log that has stood in a yard for years is the most likely to have some.

Milling the Rest of the Log

After the first face, work down the log one slab at a time. A few habits from the sources make the difference between clean boards and a mess.

• Keep the kerf open: Popular Woodworking inserts wedges every few feet so the cut does not pinch the bar as the slab settles.
• Use shallow passes on tough wood: Woodgears.ca found that multiple shallow passes gave smoother surfaces and less tracking trouble than one deep cut.
• Mill through the pith: Newton Makes cuts through the center of the log to reduce splitting risk in the boards.
• Keep the chain sharp: a dull ripping chain heats up, burns wood and pushes the bar off line. Sharpen before the pass, not during.
• Leave thickness for surfacing: cut about 1/2 inch over your target so a planer or sander can clean up the saw marks.

Speed varies a lot. Woodgears.ca reported a 5-foot, 10-inch-deep cut in about 2.5 minutes with a Stihl 026, while Newton Makes mills with a 36-inch bar on a Stihl 661 and reports roughly 10 to 15 minutes per cut depending on log size. Species, chain sharpness and saw power all move those numbers.

Milling means running a saw under load for long stretches, and fatigue is a real hazard. Our chainsaw noise guide explains decibel levels and hearing protection.

How Much Wood You Lose to Kerf

This is the number most guides skip. Wikipedia’s chainsaw mill entry puts the kerf at about 1/4 inch, which it describes as wide compared with a bandsaw or circular saw mill, so roughly one inch of log turns to sawdust for every four cuts. Actual kerf varies with your chain and bar, so measure a test cut. The table applies a 1/4-inch kerf to common board thicknesses (my own arithmetic: kerf divided by board thickness plus kerf).

Board thickness	Kerf lost per cut	Share of log turned to sawdust	Whole boards from 12 inches of log height
3/4 inch	1/4 inch	25%	12
1 inch	1/4 inch	20%	9
1.5 inches	1/4 inch	14%	6
2 inches	1/4 inch	11%	5
2.5 inches	1/4 inch	9%	4

The last column ignores the slab lost to the first cut and to bark edges, so real counts run lower. The lesson still holds: a chainsaw mill wastes far less wood on thick slabs than on thin boards, which is why hobby millers favor slabs of about 2.5 inches for tabletops and benches, and why thin stock is better bought or cut on a bandsaw.

Fresh slabs also need drying. Popular Woodworking cites a traditional rule of one year per inch of thickness for air drying, stacked on 1-inch stickers, though Newton Makes considers that too long. Seal the end grain with paint or log sealer so the ends do not dry faster than the middle and crack.

Chainsaw Safety for Ripping Cuts

Ripping does not make a chainsaw safer. The rules below come from OSHA’s logging standard, 29 CFR 1910.266, and the milling sources above. OSHA’s standard applies to professional logging, but it is a sound baseline for a home shop.

• Chain brake and kickback devices: OSHA’s standard requires a chain brake and says no kickback device may be removed. Never remove or defeat either one, and test the brake before each session.
• Leg protection: OSHA calls for cut-resistant leg protection such as ballistic nylon covering the thigh to the boot top. Popular Woodworking still recommends chaps when the bar is enclosed in a mill fixture.
• Head, eye and face: wear a helmet with a face screen or mesh visor. Popular Woodworking recommends a full-face shield rather than glasses alone, because milling throws a great deal of chips and dust.
• Hand and ear protection: use snug work gloves and hearing protection, since milling runs the saw under load for long periods.
• Dust: Newton Makes lists a respirator or mask among its milling gear, sensible when cutting dry or moldy logs.
• Keep the kickback zone clear: kickback comes from the upper tip of the bar, and a mill fixture does not remove the risk. Stay out of line with the bar and keep bystanders well back.

No source I found gives a safe technique for freehand ripping with a ripping chain, and Oregon’s warning is unambiguous, so I am not describing one. If you need boards and do not own a mill, freehand ripping is not the place to save money.

Two Outdated Tips About Ripping Logs

Older versions of this advice claim you should run guide rails along the whole cut, and that you adjust depth gauges to control how deep the cut goes. Both are muddled. A rail is needed for the first pass only, and after that the mill rides on the flat face it just cut. On a chain, depth gauges (also called rakers) set how much wood each cutter bites, not how deep the cut is, so board thickness is set by the mill’s height, not by filing rakers.

Frequently Asked Questions

Can you cut a log lengthwise with a regular chainsaw?

Yes, but it is slower and rougher. A standard chain is ground to cut across the grain, so ripping with it tends to clog and run hotter. Without a mill or guide the bar wanders, and the boards come out uneven. A chainsaw mill and a ripping chain are the reliable route.

Do you need a ripping chain to cut a log lengthwise?

Not strictly, since some milling write-ups say a regular chain works, only slower. A ripping chain is ground for cutting with the grain and clears chips better. If you buy one, read the label: Oregon marks its RipCut chain as not for hand-held use and not low-kickback.

What size chainsaw do you need to mill a log?

Stihl says its ripping chains are meant for saws of preferably 70 cc or more, and Granberg’s Alaskan mill tag also recommends 70cc-plus. Smaller saws can mill short, narrow logs but run hot and slow, and the bar has to be long enough to clear the log’s full width.

How thick should you cut boards when milling a log?

Popular Woodworking’s example cuts slabs at 2.5 inches so they finish near 2 inches after surfacing. For 1-inch boards, cut about 1.25 inches. The wide kerf means thinner boards lose a larger share of the log to sawdust, as the table above shows.

How long does it take to cut a log lengthwise?

It depends on saw power, log length and species. One hobbyist reported a 5-foot, 10-inch-deep pass in about 2.5 minutes with a Stihl 026 and a guide board, while another mills with a 36-inch bar on a Stihl 661 in roughly 10 to 15 minutes per cut. Expect longer on dense hardwood.

Conclusion

To cut a log lengthwise with a chainsaw, use a mill, a leveled first-cut rail and a ripping chain, and keep that chain on a saw that is locked into the mill. Plan around the 1/4-inch kerf by cutting thicker slabs, and wear leg, face, hand and ear protection every time. For more on choosing a saw, see our saws guide.