Snipe Problem with a Four-Head Moulder

      A mis-adjusted upper pressure bar is probably the source of trouble in this sniping story. November 18, 2006

Question
I have a Mattison 4 head moulder. I use it to cut all types of woods from 15/16" (H) x 1 5/8" (W) x 12' (L) down to 3/4" (H) x 1 1/2" (W) x 12' (L). Most of the time, it works great. My problem is that when I am feeding the moulder, if the second piece isn't right up against the piece ahead of it, then the end of the first piece basically pops up in the air, and that leaves a huge cut in the wood, almost as if a big chunk had been scooped out of the wood. Which then, of course, makes that portion of the wood worthless. I have looked/tried everything related to the moulder, but have now thrown up my hands and am looking for advice. Does anyone else have these issues? If so, any ideas on how to fix them?

Forum Responses
(Solid Wood Machining Forum)
From contributor G:
Elevate your infeed and outfeed tables or rollers.



From Dave Rankin, forum technical advisor:
It is always recommended to feed a moulder end of wood to end of wood. If you do not do this, then you can expect some loss of control. With that said, to reduce the snipe I would first check the gap between the pressure bar and the top cutterhead. From your post, it appears that the snipe is happening on the top head. This gap should be as close as possible. Most pressure bars are made of wood or UHMW. These materials can be cut by the top head, so you should be able to close this gap to less than 1/8".


From contributor R:
Excessive pressure at the chipbreakers will also cause this problem. Why are you not feeding butt to butt? You should expect to have problems if you are not, particularly on a push feed molder. If the piece is allowed to stop, which it surely will if there is a gap between the one following it, the other cutterheads in contact with it will mar or burn the product.


From the original questioner:
Thanks for the feedback. I do feed them butt to butt, however sometimes a piece doesn't get right up to the piece in front of it or it gets caught a bit when feeding and leaves a small gap, thus resulting in the huge cutout I get. I assume then from everyone's feedback that the key is getting them exactly up to each other, which 90% of the time I do.


From contributor C:
I would suspect that the pressure bar is not properly set. If you get bites on the trailing end, it is almost a given that it is a pressure bar problem. What happens is that as the piece leaves the top head chipbreaker, the piece kicks up because there is too much clearance between the pressure bar and the machined piece.

Why does it do that only when the pieces are not butted? Probably because on a push feed machine, there is a really powerful end pressure between the two pieces. If you have a gap, the first piece stops and is just sitting there. Then you put the second piece under the feed rolls and, BAM! The second piece collides with the first piece with force and forces it up.

Get the pressure bar against the knives, be certain it is just a hair tighter at the point of cut than further along its length. That will give you a snug fit at the point of cut without too much friction or drag. If the material is wide, you can groove the pressure bar so as to reduce friction when using adequate pressure. And be sure that the brackets, metal shoe, etc., are in good condition and not shifting under pressure.



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