Troubleshooting Nicks in Moulder Knives

Newly ground knives can be damaged right away by hard mineral deposits within some hardwoods. Here's advice on knife material choices that could help avoid the problem. June 11, 2010

We mill a lot of maple mouldings and our knives are Weinig M3+ Steel or M2. It is not uncommon for us to get sizeable nicks in the knives after only a few boards go through the moulder. There are sometimes little black marks in the maple and those black marks are very hard and can nick the knives. This can be very frustrating, obviously, as we have to hone the knives after just a few boards.

Honing is a last ditch effort to finish a run; it should not have to be done to a pair of knives that have just been sharpened on a profile grinder. Would we have better success if we were using Weinig's Supre 18 grade steel? It is a harder steel, I believe.

Forum Responses
(Architectural Woodworking Forum)
From contributor L:
Yes, same problem. The mineral streaks also occur in walnut. Whenever possible we use red maple instead of hard maple. Since we always do a light grind on the profile grinder before starting a run rather than honing, we will go back to the grinder and take a very light cut, measure and reset the readouts for the diameter loss. For flat or S4S we run the double back system using carbides. Lots of moldings have a large percentage of their area just flat, so we will run the carbide in the other two slots and the profile in the opposite slots. We rarely get long runs to do, so having custom carbide profile knives made doesn't pay. We have a Weinig 950 grinder so we can only do the straight carbide knives on it, not profiled.

From contributor R:
A very common problem, not just with Weinig M3+ products, but with many others. Your comment about the mineral streaks is right on the money. The minerals are very hard and they nick the knives. The Supre steel is better and you should test it. I use a steel called Endurance from Global Tooling and have had very good results. Dr. Dave Rankin has a steel he developed, DKG, that is supposed to be real good as well.

My suggestion would be to buy a bar of each and see what works best for your application. Others might have something even better.

From the original questioner:

Thanks for the feedback.

Contributor L, how do you like the red maple? Do you find it has similar appearance to the hard maple? How do you like the double back carbide knives?

Contributor R, glad to hear this problem exists elsewhere. It can be very frustrating. We do not grind in-house; we outsource. So, once I get a set of knives back (and spend sometimes up to $50.00 for a pair to be sharpened) and then have a nick occur with just a few boards through the moulder... Ahhh! You know what I mean? Then, by honing them, I am in essence ruining the edge by removing the nick. I can hone pretty good but not as good as a profile grinder. I will check out the steel you recommend.

The tooling company I use for sharpening and knife production is willing to grind other steel; if I purchase a bar they will make them into knives for us. Do you find it is much more difficult to grind Supre or the Endurance Steel vs. M2 or M3+? Does it take much longer? Do you need a different type of grinding wheel?

From contributor R:
It is a bit more difficult to grind, but not much. I would suggest you use a 120 grit borazon wheel for the finish grinding on all the better quality steels. They are a bit harder and more prone to chipping if you use a 100 vitrified wheel.

From contributor C:
Nicks can often be caused right off the bat with knife steel that is radial finish ground across the bar width, rather that lineal ground along the bar's length. Under magnification, these create miniature Grand Canyons on the surface of the knife. In radial ground stock these grooves run the entire width.

A fair amount of the knife steels mentioned in this discussion are radial ground materials. Other things to consider are hook angles, especially in hard maple. Hard maple (heavier mineral content in general) harvested in Western NC (where I'm located) machines much differently than hard maple harvested from Michigan (lower mineral content), for instance. We have used 10 degrees and even as low as zero degree hook angles on occasion.

WKW offers a diamond back coated steel that we've used on mineral streak issues. More often, carbide ends up being used on rock maple.

From contributor R:
Contributor C brings up some very interesting and true comments about the surface grinding from the manufacturers. If you're interested in the diamond coated, that will work as well. When you call Global ask them about their RW coated steel. I use this type of steel as my M-2 and it works very well.

From contributor L:
I like the double back system. The one that Weinig sells (made by someone else) has quite thin carbides that are subject to breakage if everything isn't maintained really well or if a hard knot comes loose. They stay sharp and continue to give an excellent cut quality long after steel dulls, especially if there is any mineral. European tooling also sells a thicker system that I haven't tried. Unfortunately the corrugation spacing is different than the Weinig, so you have to use one or the other or buy two sets of backer plates. One problem with employees honing the edges is they like to run the hone along the length of the edge (easier). Problem is that creates small grooves that are parallel to the edge so they allow the edge to break back and become dull quickly. If you look on the back of your Weinig steel you'll see they grind it correctly, across the bar rather than along its length.

I've also found that Weinig heads are more accurately ground than the DML heads we have. For the first bottom spindle we run a segmented insert head. The inserts run a long time. But if one breaks it will usually wipe out all the inserts that follow it. It also runs a lot quieter than the straight knife heads. Have you considered buying a profile grinder? We have a Weinig 950 that is okay (for a small shop) but lacks the adjustability to grind profiles with a diamond wheel. We do grind the double back carbides using a straight diamond wheel on it. If you look for a used grinder, donít buy a Weinig 925 - thatís what we had first. Profile grinders require a take-apart and good cleaning periodically.

From the original questioner:
Thanks. Contributor L, you give good insight into the double back system; may be worth trying.

We outsource our grinding and I am happy with the excellent service this company provides. At some point I may be interested in a grinder but for the time being I feel that outsourcing is our best solution; there are not enough hours in the day as it is. The company we use has excellent customer service and they always do what they say they'll do. If they say you'll have the knives for this Thursday, you'll have the knives for this Thursday. The company is Galt Wood Tool from Cambridge Ontario; I have been using their services from day one (about 14 years now).