Better moulder finish quality

Eliminating snipe on mouldings. August 13, 2002

We make moldings to go with our architectural interiors. We bought a Wadkin GD220 about two years ago, and still do not get the quality we would like with it. There is a lot of snipe and waste in the expensive hardwoods that we use (cherry primarily, and poplar secondarily).

The salesman set us up with 20 degree heads and suggested that two knives would be sufficient. We spend too many hours sanding our moldings to try and remove knife marks and snipe. Sometimes this is an hour of work for each piece of molding! The machine is always run at its slowest feed (20 fpm) and we make dado relief cuts on the table saw to try and reduce the deep cuts required for some casings and crowns. Still, when we go to a job site and see other moldings supplied, they seem much better with no snipe right to the ends.

On the next job, we will try four knives to see if that will help. Does anyone have suggestions for the ultimate finish? Does anyone run moldings through twice on a five-headed molder? Is the pressure foot too tight on the front of the upper head, causing snipe when a board does not follow right after? We believe that trying to hold the wood down better will give a better finish. Different cutting angle heads?

Forum Responses
Four knives in the head will not help improve the finish, but will actually cause more problems.

The sniping is caused by inadequate hold-down. I suggest the use of a special felt hold-down shoe material that is available from MSI. There are many other possible problems, which could include: pressure shoe not parallel to the tables, spring tension on the pressure shoe too tight, too much gap between the head and the pressure shoe and chipbreaker, wrong belt, improperly balanced tooling, bad bearings.

You might have a top-quality technician visit to help you with your problem. The Grinderman's Association also offers telephone support for its members. You may find this Association to be of great help to you.

Dave Rankin, forum technical advisor

A feed rate of 20FPM will not be sufficient chip load removal to keep the knives cool. Result will be premature breakdown of the knife steel. Dave is right about the problems you are having. I suggest getting back to the basics. Make sure your tooling is set correctly to the machine. Even a machine that is set perfect will not totally eliminate end snipes. Material needs to be prepped both in width and thickness and fed the proper way to eliminate end snipes. If you want to keep your 20 FPM, I suggest using carbide tooling. What type of profiles are you trying to run on this machine? Your machine might not be able to handle what you are asking it to do. There are realistic limitations besides the capacity of the equipment. For example, a Profimat with a 9" capacity - anything over 4" wide would be a quality gamble. The snipe you mentioned normally appears when the piece behind it is thinner and the chip breaker snaps off the end of the board.

You might be running too much hook angle in your heads. I think you would need to run a shallower hook, like 10 to 15 degrees, in the hardwoods. I know this won't help with the snipe at the ends, but should with the surface finish.

Hook angles depend on moisture content, wood density and several other things. In general, hardwoods (hard to machine) use a 10-15 degree hook. Softwoods (easy to machine) use a 20-22 degree hook.

There are some exceptions and these usually require talking with a technician that has actually run tools with the parameters that you are experiencing. Technicians or other operators have first hand knowledge where many sales companies do not.

Dave Rankin, forum technical advisor

When working with cherry, maple and other hardwoods, a 12 degree hook angle head will provide better finish quality than the 20 degree you are now using. Wadkin offers a XS dual angle combination hook cutterhead that has 2 wings at 12 degrees and 2 wings at 20 degrees. Forest City Tool, Michael Weinig and other companies also offer dual angle heads. A straight 10 or 12 degree hook head will work fine as well. These are available from about any tooling supplier. On your GD220 unjointed moulder, 2 knives in the 12 degree pockets should provide a suitable finish with the feed rate of 20 to 60 feet per minute. You would need to run filler knives in the unused pockets of any cutterhead to maintain proper balance and to keep from distorting the head. The use of a 12 degree hook head will dramatically improve the finish quality of your cherry out of the moulder.

I agree with Dave on your snipe issue. Are the snipes from the top or bottom head? There are a few differences in troubleshooting snipes between top and bottom heads.

From the original questioner:
We set the "pad pressure" as the Brits call it in the manual to just hold the wood down at the exit of the top head by putting a dollar bill between it and the wood and then turning the spring pressure until you can just withdraw the dollar without tearing it. We felt this would keep people from screwing down too hard because they use their dollar.

The pad pressure is always pulled in as close as we can get to each knife. The infeed hold-down we don't seem to change much. What are the parameters here? The knives are ground by a very reputable company in the area and check from 1-3 thou in concentricity.
We only run the machine at 20 fpm, figuring that will give us more knife cuts per inch and thus, smoother work. Why wouldn't four knives improve matters? I always bug the guy about the knife balance and spot check with a scale occasionally. Usually within 1/3 1/2 a gram.

We did burn out a couple of belts, by the operator trying to start the top head with the knives stuck in the wood during setup. We were surprised that the breaker didn't blow. We did replace the belts with one ordered from Wadkin. There is a slight roughness (more a loose than tight feeling) when the shaft is turned by hand. The pulleys were scrubbed with MEK to remove any of the smoked belt before replacement, however. I would be surprised if the bearings would be burned out, as this machine probably hasn't run 3500 feet of wood yet. Our company does run big mouldings such as 6" casing and 8" crown, however. (What's the extra 5" for if it will only run 4" moldings?)

The first issue to address is the setup of the moulder. Control of the material while it is being cut is the most important area in order to produce a quality finish. The top head chipbreaker and pad pressure must have control at all times, and sometimes have to be "modified" to suit a particular profile. The lack of control is the single biggest reason for poor quality finishes.

Assuming the snipes are on the leading and/or trailing end of the top surface, this would tend to indicate that the top head chipbreaker and/or pad pressure are either not being correctly set or they are out of alignment with the bedplates.

You mention that you sometimes make relief cuts on the table saw prior to running the material through the moulder in an effort to ease the cut. Depending on the profile and the amount of material removed, you may be making the control of the material more difficult.

Running the material through the moulder at 20 ft/min is also not helping you produce a good quality finish, because at this feed speed the knives are spending more time rubbing than cutting, which will compress the wood fibers rather than cut them. The feed speed needs to be increased to 30 ft/min in order for the cutters to cut the material efficiently.

The 20 degree cutting angle of the tooling is not really contributing to the present poor quality of finish, but with the other issues addressed and if grain tear out is your only quality issue, a 12 degree head will eliminate or reduce that problem.

While larger profiles are generally run with more ease and efficiency on moulders with two top heads, with attention to detail and care, a five-head moulder should be capable of producing a good quality product. This is mainly because a machine with two top heads has the potential for larger horsepower motors, pre-planing and pre-relieving capabilities, and generally better control over the material being profiled. Pre-planing the material prior to feeding it into a machine with only one top head is normally the most beneficial. Pre-relieving on a table saw can work against you!

Forget the dollar bill routine. The bill is acting as a shim as well and I suspect that, once removed, you may not have enough pressure.

You should align the shoe with the minimum radius of your tool, then lower it approximately .015". When jogging the first piece through, you should be able to easily see the leading edge engage and slightly push up the shoe. There is probably a spring tension adjustment as well. You should also check alignment. Maybe I'm reading something into your post, but it sounds like your primary problem is chatter, not snipe (snipe is a "bite" on the first or last couple of inches of the board only).

If you have a snipe on the top surface at the leading end, the pressure going into the spindle is too loose. If you have a snipe on the trailing end, the pressure going in may be too tight. Loosen it and tighten the exiting pressure some and also run your work pieces back to back. They should be consistent in thickness or you will hardly ever get rid of the snipe at the trailing end... that's where you need a top pre-cutter. If your material is too inconsistent, I suggest running it through a square molding process to true it up first.

If you have a snipe on the bottom surface, the cutter is probably not properly set - it needs to be set with a straight edge. Also, one thing I have seen is that sometimes you might move the bed plates around for cutter clearance or whatever, and they will get wedged up by trash under the plate, causing improper molding. This also happens at the fence near the side spindles. Any time a fence or plate is moved back, it should be taken off and cleaned.

I think 20 fpm is much too slow and I don't know how much material you are removing, but if you are taking off a lot, I think four knives would help out, but only with more speed.

The dollar bill would not be enough pressure in any application I have seen. And stay away from carbide if you are concerned with surface quality - you will most likely produce some fuzzy parts, as the carbide will last but provides less desirable finish quality.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor T:
I have found some snipe on the trailing end can be blamed on the nature of a throughfeed moulder. The last roller(s), usually rubber, sometimes want to pull the workpiece out of the machine, creating a small gap in between boards between the last two heads. The profile cutter is trying to basically lift the workpiece off the table and can be your cause of sniping. First, make sure your blanks are of even size if you don't have roughing cutterheads. Second, check to see if the shoe is actually in contact with the workpiece in at least one or more points. Third, if you're still having problems, raise up the last roller(s) so they contact the workpiece but do not pull it out of the machine till you want it to.

Comment from contributor J:

I have the same Wadkin moulder from which I get awesome results. When I do get snipe, I have always been able to correct the problem. For front end snipe, check the following:

1. Are your top head knives sharp and clean?
2. Is your depth of cut on your top head excessive?
3. Have you adjusted your top head chip breaker slightly below the thickness of the material entering the top head and adjusted the spring tension?
4. Is the material you are feeding into your moulder a fairly consistent thickness? If not, plane first or make continuous adjustments on your first bottom head.
5. Is your bed waxed and oiled.
6. Have you adjusted your beam height for maximum control?
7. Are you butting your material carefully?

For trailing end snipe, check the previous comments and add the following:

1. Set the top head pad height lower and adjust the tension.
2. Adjust the final two rollers.
3. Make sure as the material exits the moulder it remains level or slightly elevated and smooth.
4. Adjust air pressure to around 40 lbs.

My moulder runs best at about 31 feet per minute.