Chainsaw Mill – What Size Bar To Use?


A chainsaw mill brings convenience and portability to anyone needing to mill lumber on a small scale. To use a chainsaw mill, you will need a portable chainsaw with an appropriately sized bar. How do you size the bar for your chainsaw so that you can make effective use of the chainsaw mill?

The recommended minimum bar size for a chainsaw mill is 20-inches, but 24-inches is preferred. Larger bar sizes can be used depending on the power of your chainsaw and the size of the timber being milled. Bars of 36-inches or longer are commonly used with mills requiring two people to operate.

A chainsaw mill is an extremely useful jig that can be attached to a standard handheld chainsaw and allows you to mill trees down to usable lumber for your building projects. When using a chainsaw mill, some limitations apply to the saw, and the length of the bar fitted to the chainsaw. Several factors will play a determining role in the bar length you can use on your chainsaw.

Photo 228891064 / Chainsaw © Valdis Muiznieks | Dreamstime.com

How To Size The Chainsaw Bar For Your Chainsaw Mill

The factors that contribute to the correct sizing of the bar fitted to your chainsaw are important to get right. They will affect the size of the timber you can mill, how safely you can do the milling, and the wear and tear the process puts on your chainsaw.

The main factors that play a role in sizing the right chainsaw bar are as follows.

  • Minimum bar size
  • Saw size
  • Mill size
  • Timber size

Minimum Chainsaw Bar Size For A Chainsaw Mill

While there is no theoretical reason to have a minimum bar size for using a chainsaw mill, the restriction is usually due to the minimum size bar the chainsaw mill can accept.

A chainsaw with a short bar of under 20-inches can theoretically be used to cut appropriately sized timber, but if the chainsaw mill jig cannot accept a bar that short, it will not be possible to use the chainsaw in the mill.

The generally accepted minimum chainsaw bar size that is recommended for chainsaw milling is a 20-inch bar.

Most mills would be able to mount a saw with this bar length as a minimum and any bar larger than this. Before you go out and buy a 20-inch bar to fit onto your chainsaw for milling, you need to read the other requirements for sizing the bar. You may need to buy more than a longer bar!

Another factor that makes the 20-inch minimum bar length appropriate is that you lose some bar length when you fit the chainsaw to the mill. Consequently, the size of timber that can be cut with a shorter blade in a mill probably does not warrant being cut using a mill in the first place.

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Chainsaw Size To Establish Bar Size For Milling

Most people familiar with chainsaws and their operation know that these saws come with different-sized motors, which determine the saw’s power.

If you are new to chainsaws, you may not know that minimum and maximum bar sizes can be fitted to a saw of a certain power.

If you fit a bar too long for the chainsaw, the under-sized motor will struggle to drive the chain through large logs. This will cause frequent jamming of the saw and wear out your chainsaw motor very quickly!

Most chainsaw manufacturers will give a minimum and a maximum bar size that can be used on the chainsaw. Chainsaws with smaller motors will only be able to drive chains on shorter bars.

The following table can be used as a guide for bar length for saw size, but you should always consult the chainsaw user manual for the correct bar limitations for your saw.

Chainsaw Motor SizeRecommended Bar Sizes
Under 25cc10 to 12-inches
35cc12 to 16-inches
45cc14 to 20-inches
60cc16 to 24-inches
75cc18 to 28-inches
90cc20 to 32-inches
100cc24 to 35-inches
115cc26 to 50-inches
Greater than 115cc28 to 84-inches

Selecting the right type of chain for your saw will get you the best results when using a portable chainsaw mill. Check out our recent article on choosing the best chain for your chainsaw mill for help.

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Mill Size For Determining Chainsaw Bar Size

Most chainsaw mill manufacturers will indicate the minimum size chainsaw bar that is safe to use in their mill.

The most common minimum bar size for chainsaw mills is 20-inches because the bars that are shorter than this have other characteristics that make them unsuitable.

Shorter bars are not only short but also thinner than larger chainsaw bars. Thinner bars make it difficult to clamp the bar in the mountings on the mill without pinching the rail, causing the chain to jam on the mill’s bar mountings.

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Timber Size For Chainsaw Bar Size

The size of the timber you intend milling will be a significant determining factor in the bar size you need on your chain saw.

One of the factors you should bear in mind when sizing the chainsaw bar for the timber is that you lose up to 4-inches on the length of the bar when you mount it in the mill. This is because the mountings on the mill for the chainsaw bar are roughly 2-inches from the base of the chainsaw bar and the bar’s tip.

The size of the timber has a bearing on the length of the bar required on the saw and the size of the chainsaw.

Large logs will need higher-powered chainsaws to drive the chain through a log with a larger surface area. The larger the surface area of the log being cut, the greater the friction resistance on the chain. Thus, a chainsaw with a more powerful motor is necessary to cut through larger diameter logs.

The following table can be used as a guideline for sizing the chainsaw motor according to the diameter of the timber.

Chainsaw Power For Timber Size
Chainsaw Engine CapacityTimber Diameter
55cc to 65ccUp to 18-inches diameter
65cc to 85ccUp to 36-inches diameter
85cc to 120ccLarger than 36-inches diameter

What can be seen from this is that the timber size governs the length of bar needed and the power of the chainsaw required to cope with the size of the timber.

Conclusion

From our discussions, it is clear that you cannot simply put any length bar on your chainsaw for mounting it in a chainsaw mill.

To operate the mill safely and without placing too much strain on the chain and the chainsaw motor, all the factors for sizing the bar must be considered.

In some cases, this may include purchasing or borrowing a larger chainsaw to handle the longer bar and cope better with larger diameter logs.

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