Moulder Blade Sharpening and Touch-Up Tips

      Here's extensive advice about moulder knife sharpening and touch-up and other issues that can affect knife edge quality and moulding appearance. October 18, 2011

I have a 5 head Weinig moulder. I am wondering how to achieve a little better finish on my product after running mouldings. I am using a good high grade of high speed steel for the knives in the profiles I run. I run all lumber through mostly at 15/16" hit and miss.

What I run into is after I have a set re-sharpened, I will get a good run on say 1500-2500'. Then the next knife I have re-sharpened it never fails that I start seeing some light lines in the mouldings. Now I will take samples and put stain on them and usually they don't pull out, are these normal machining lines? I feel I need to sand these lines out by hand roughly, and most of the time it's only in the flat areas of a profile. Iím trying to figure out how to be more consistent when running mouldings. I have seen carbide do this also.

Forum Responses
(Architectural Woodworking Forum)
From contributor G:
If you are staining it you should be sanding it. Maybe us a Superbrush.

From the original questioner:
I agree, but I am running into competition that is beating me and their product is not even close to what I run even if I rough sand mouldings before deliver, and I might be $.10 higher. Stainers love how I run stuff, but not all stainers will sand if I let some of the line go if not real bad. Does anyone have good experiences with moulding sanders? Do they work?

From contributor M:
First off I don't agree all stained wood should be sanded, at least not by you. The bottom line is the process of making moulding is it is cut by a knife and that leaves knife marks. The key is to maximize the quality of cut and how visible the knife marks are.

The first thing for us is we never put straight 15/16 lumber into the moulder. We always surface it to remove the dirt and grit from the mills and we also end trim the leading edge going into the moulder. This helps the life of the knives and allows us to run longer. This is particularly true for abrasive planed lumber.

The second part of the equation is good knife grinding skills. This means watching balance, backgrinds, pocket angles, knife projection, head distortion, so on and so on. One tip is you may try using a secondary bevel so touching up on the grinder is easier and more precise.

The last part is we sand all our flat stock e2e, or any moulding that has a wide flat surface using the overhead sander. It requires a little planning so as you generate new profiles leaving the detailed section lower than the flat. We personally don't sand the detail portion of any moulding but we don't do any stain work either. That of course doesn't mean specialty products, radius, handrails, etc. The next thing you could look into is a profile sander.

From contributor U:
Contributor M is right about getting the lumber "clean" prior to the wood hitting the cutting blade. It does not matter how well you sharpen your knives when all it takes is some grit to make for a bad day. When we ran a Weinig, we precut both ends of all lumber. It is amazing how dirt and sand can get imbedded into the open end grain of a board. To speed things up we kept a Skil saw and pair of sawhorses by the infeed area for cutting the ends. Also if the surface was dirty we would also resurface and let the straight knives clean up the wood rather than the moulding blades getting nicked.

From contributor Y:
I'm not sure I understand which direction the "light lines" are on the board. Across the board or lengthwise? If across the board it's a machining defect: head balance, knife grind (too much land, no secondary bevel, flat area not parallel to bed, incorrect primary back bevel), machine setup: last bottom head not cutting even with the outfeed bed plate. Crap under the bed plates. Chip breakers not set right on top head, pressure shoe over last head not tight enough or not parallel to top of molding or there is so much profile that the shoe isn't contacting enough of the molding (make a counter shoe.)

If the lines run lengthwise it is most likely either a knife defect or there is something imbedded in the top pressure shoe. Check the knives before you put them in the head. Is there a wire edge still on them from grinding? (You can knock it off with a piece of hardwood drug along the edge). Was the last grind done with a course wheel at too slow of rpm? Was the last grind forced too fast, not enough coolant flow? Was the secondary bevel not enough (skips) or too much? I'll assume you are not running a jointed molder.

If all else fails start from scratch. Go back to the tooling bench, remove the knives and clean the head slots and knife corrugations. Put the knives in and torque bolts progressively, go to the profile grinder and make sure your template is supper smooth and the flat parallel to the axis. Do a careful primary grind with lots of coolant then shift the wheel speed to high and do a very slight secondary grind at the correct angle. Check for the wire edge and get rid of it. Go over your molder setup process very carefully. All of this isn't of much value if you run dirty boards (one of the values of a 6 head).

One of the things we do for longer runs is use double back carbides in alternative slots for the flats. You can grind them on your profile grinder with a diamond wheel even if your grinder doesn't have axial adjustment. It may take some fiddling to get the levels of the steel and carbide knives to line up well. The double back knives have very fine corrugations which helps. Feed speed for single knife cutting and nice quality: 30 to 35'/min.

From contributor W:
To the original questioner: Are you making your own knives or ordering them in. Are you re-sharpening your own knives?. What grade and brand of steel are you using? What species of wood are you running and what is the average total length of run? How many feet per minute on your moulder?

What confuses me is youíre saying you get about 1500-2500' good feet on a new set of knives but when they get re-sharpened you start getting lines. You should get the exact same footage if the guy sharpening the knives is the guy making the knives. I donít know, maybe Iím missing something.

From the original questioner:
As I stated, I have a Weinig 5 head moulder. I usually buy 15/16" hit and miss lumber to mill up the jobs I get. I have bought my knives from several places and have since been mainly using one of them as my main source (Mirror Reflections). If I need new knife I usually buy a black nitride or the endurance grade of high speed steel. These hold up very well with the variety of woods I run. I feel he does the best job with re-sharpening, servicing, and overall knowledge of moulders and how to troubleshoot them if I run into problems or general questions.

I rip all my blanks for the job. I set the moulder up and run some test pieces. Now it could happen with new knives or even just re-shaprpened knives that I see these light lines going with the grain. They look like very small nicks in the knives. Now I have seen them in products where the manufacturer is using carbide on high speed machines.

Again, if I hold up in light, they are there but only someone trained will see them. Now other times they can be really visible and for sure have to hand sand the mouldings before I send to customer. Now this can happen within the first 50' or fewer or it can happen after 1000 or 1500'.

As I stated before, am I being too picky if I hand sand the light line even though when I take the sample and put stain and varnish on it it is not visible? My competitors are beating me up on price but they also are running mouldings that you clearly see these lines bad once stained. Iím looking for a cost effective way to do less sanding and running a better moulding. I run everything around 27fpm. I do see on some profiles that have a few bumps due to the hold down but otherwise I get great comments all the time. Just looking for insight if a moulding sander really works or not. My next purchase when cash is available is a knife grinder.

From contributor Y:
Knife steel: our runs are usually short, less than a thousand feet. We touch up knives before every run on our profile grinder. We used to use a harder steel that would hold an edge longer but found that they developed small chips very easily (your long lines.) We went to a M42 steel and pretty much eliminated the chipping problem. The disadvantage is they will start to show signs of dulling by 1500 or 2000'. Not a big deal to just put them on the profile grinder and take a very light secondary grind. Put them on the measuring stand and back on the spindle, set with the digital indicator and run.

From contributor W:
I think the solution to your problem may be as simple as learning how to use honing stones. Basically a honing stone (slip stone) is used to manually polish a knick off a blade as soon as you see it. With some practice it can take as little as 1-2 minutes to refresh the edge of some blades and remove the small nicks.

A little warning though, anything that can fix and edge can also damage it. It can take a good six months of practice for someone to learn to hone with consistent results but is a very useful skill. Iíd suggest practicing on dull blades at the end of a run when your timeline is not crucial.

From contributor M:
I tend to lean towards Contributor Yís thinking with the steel. We have also tried all the super hard grades and other than being tough on grinding wheels achieved nothing for increased run times. I feel it is just too brittle. The lines you see are nicks in the edge of the cutter and as stated earlier by Contributor W can normally be honed out by hand. We use good old M2 steel for all our moulder work.

I will reiterate, it takes one piece of wood with a little dirt and grit on it to make your knives do just what youíre describing. Clean wood is paramount, standard hit and miss mill lumber can be sitting around for a long time out in a dirty dusty yards and that is pure abrasive. If you don't have a planer, have your supplier send it to someone who does and have them surface it for you. Then don't do what I caught one of my guys doing, use a piece of sticker material for a setup stick!

From contributor N:
All the advice about cleaning the material is probably the most helpful thing to eliminate the problem. Beyond that you might try harder steel. Properly sharpened M3 will outlast M2 in my experience. I have a Whirlwind jointer that I occasionally use for long runs. It joints the knives off the machine (in the head of course). This is not as good as a jointed molder, but it helps.

From contributor O:
Moulders are temperamental at best, I make my own templates and knives then run up to 10,000 lf of red oak on a SCMI 23 Superset at 60 lf a minute between sharpenings. To sharpen I make sure to dress the grinder stone first to match the profile of the knife, an undressed stone is the main cause of the lines you are experiencing. Second, check lumber for staples used for tagging lumber bundles. One staple can send you back to the sharpener. Third, do not feed through a knot, this will give the knives a very short life. Other than that do your setup correctly and you will not have a problem.

From contributor Y:
I'm not a fan of honing for two reasons. It takes longer than putting the head back on the grinder for a touch up grind and too often have seen people swipe the stone from side to side instead of perpendicular to the edge. Mineral in wood is a killer, best off turning those boards into pallets.

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