Knife Sharpening Frequency

How many times can you sharpen moulder knives, and how do you know when it's time to do it? January 9, 2008

Question
At what point can you tell your moulder knives need to be sharpened? On average, how many times can you resharpen the knives? Is it best to send back to the place the knives come from for resharpening? Is it best to buy multiples of the most popular knives?

Forum Responses
(Architectural Woodworking Forum)
From contributor J:
This is the big box of worms that comes with the moulder. Besides the obvious (knicks), you can tell by burning on the wood or sometimes a wire edge where the edge of your moulding will be raised or rough feeling. Most people who buy a moulder will also buy a profile grinder for the ease of in-house resharpening. If you're going to be running a lot of stock, this is the way to go. There are a lot of sharpening services out there to serve you as well. Russ at Mirror Reflections I recommend highly. It's nice to have someone like him with years of moulder experience work on your tooling. If you're not going to be running a lot of L/F, this might be just as cost effective, but it would be nice to have backup knives to use while the other ones are shipped out for service.

---

From contributor L:
Depends on what quality you are selling. The longer you run, the more compressed the fibers of the wood and the more spring back the grain as the wood absorbs moisture from the air. We try to provide a quality molding, so our knives go back on the grinder before every run. Depending on what steel you are using, you can get 1000' to 3000' un-jointed, more on a jointed molder. The slower you run, the faster they dull. Walnut and maple with mineral streaks are a knife killer, almost instantly! You will need carbide for wood with high mineral content.

---

From contributor R:
Sand, mineral, staples, as mentioned, will knock the number right out. You should be able to get 25 - 50 or more times sharpenings if you don't knick or chip the knives, and if the person who cut the steel used the right width from the start. If they use a smaller width than needed, you just lost many sharpenings, probably 1/4" worth.

---

From contributor L:
1. When your wood's finish is unacceptable, burnished, or burned are the default methods. However, I have seen some people install an amp meter to their motors. This meter can indicate worn or dull knives through an increase in the amperage drawn. When you correlate your finish quality with the reading on the meter, you can change out your knives before they are excessively worn. This can benefit you in additional sharpenings on your knives due to the lack of overuse.

2. There is no way to put a number to this. Depending on the height of the knife originally, the care taken to not overuse, and the species being cut, anyone would be hard pressed to give an accurate number of sharpenings.

3. Yes, the original manufacturer will have the correct profile, knife geometry, and compensation specifications. However, many companies can duplicate these accurately from an existing knife. You can help this along if you send a wood sample.

4. Buying multiple sets of knives will depend upon your usage of said profiles and your method of sharpening. If you are running the same profile every day, then you should have multiple sets. Usually enough to make it between your sharpener's turnaround time. If you self-sharpen, then you may only need one set if you are proficient at sharpening.