Machining question

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hi when putting a piece of 6x2 hrough a planing machine [thicknesser they call it] i notice that at the start of the board after it pulled through that there is a depression at the front of the board like the knves really dug in for the first couple of inches then the rest is pretty flat all the way along. They guy who was showing me how to use it said thats normal [community access wood workshop].
is it normal?? or is it a badly set up or low quality machine??
I have some very high quality mahogany i want to machine and dont really want to waste that leading edge if i can help it
also is it beter to do the edges with a jointing machine or a bench router and fence??
as you can see i know very little so thanks for answering my very basic question zz
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This is called snipe. On most machines the cutter head is above the wood and supporting the end that is out away from the machine and even lifting up slightly on it will help. What you are seeing is for the first 3-4 inches the board is only being held down to the planer's surface by the roller in front of the cutter head. Until the board travels through the machine far enough to contact the back roller the board can tilt or lift up into the cutter head causing more wood to be removed from the leading edge. The same thing can happen at the trailing edge if the board is not supported when it comes out of the machine.
Eric

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It could be both. However almost all planers do this. You can help prevent this by lifting the trailing edge as the leading edge first goes into the planer. Additionally you can help prebent the trailing end from doing this by lifting the leading end as the trailing end goes through the planer.

The jointer was specifically built to to this operation but only to straighten or flatten one edge or surface of the board. Use a table saw to make the opposite edge parallel to the edge straightened by the jointer.
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If you know the length of the area with the "snipe" then allow for it by using a longer board and cutting off the "snipe".

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Yes, maybe, maybe.
Even the best of machines can give a little snipe at the front and rear edges if it is no perfectly flat when going through the rollers. Be sure th e machine is set up perfectly, feed the board and keep it supported, and when it exits, keep it supported also.
While my planer is generally snipe free, I do not cut the final length utill it is thicknessed as one little bungle on my part can cause the snipe. I leave room to trim it off if needed.

Yes, you joint one edge, then run it through the table saw with the jointed edge against the fence. If you don't have a jointer, you can make a sled and do both edges on the table saw. Depending on what equipment is availalbe, choose accordingly.
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Some claim it's normal. Mine doesn't do it nor would I stand for it if it did.

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CW wrote:

Bingo. CW knows how to set up a machine.
Depending on the make of planer, you've got chipbreaker, infeed roller, pressure bar, outfeed roller - all holding the board down. If you are getting snipe on the leading end of a board, it's the infeed area that's at fault. The only time you should get any snipe is if the board is too heavy for the machine - then it's a simple matter of supporting the end of the board until it's past the outfeed roller.
John Martin
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here's a way to work around snipe when working with a particularly nice or valuable piece of wood: run through with it a second piece of wood, the same thickness as your nice one, but a foot or so longer and made of something cheaper. if your mahogany is wide, your second one might be two narrow ones, one on either side, or it might be two short wide ones, one running through immediately before the mahogany and one immediately after. and I mean immediately- you'll be pushing one board through with the other. what this does is move the snipe from your valuable board to a lesser, sacrifical board.
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thanks i especially like the idea of the sacrificial board zz
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bridger wrote:

Really don't see how this will have any effect at all on snipe. Unless the boards are glued end to end.
I'll sometimes run boards end to end on my 12" Parks, or overlapping side by side. The reason I do that, though, is that when taking heavier cuts the boards will sometimes stop when they hit the front edge of the chipbreaker. There's a handle on the front of the chipbreaker to allow you to lift it slightly when that happens, but it's easier to feed side by side to keep wood under the chipbreaker at all times. Also makes use of the full width of the cutters and table.
Snipe at the start of a board, though, is caused by the chipbreaker or infeed roller being set too high, or by the springs on those not being heavy enough to keep the front of a heavy board from lifting. Running boards end to end will have no effect on that.
John Martin
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I don't know, but I was taught to do that and I've never had a bit of snipe when I did. Could be a religious issue or something.
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It's a force issue and, yes, it works.
wrote in message

snipe
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CW wrote:

a major cause of snipe is the load on the board as it is fed into the planer. You can minimise this by setting up an infeed and outfeed roller stand to support the board.
Some of the small benchtop planers benefit from an additional table such as an 8' piece of particle board shelving.
You can also reduce it somewhat by using a very fine initial cut.
the sacrificial board ia also an excellent option, it can be a small piece of 1 x 2 nailed to the edge of your board.
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snipped-for-privacy@yahoo.com wrote:

Right on all points, except that he was talking about a sacrificial board not attached to the workpiece. Why that would work I can't imagine.
John Martin
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I don't own a planer, but I'm guessing that a sacrificial board end to end with the working piece would negate the sudden introduction of the to the blades, eliminating most if not all of the snipe.
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Upscale wrote:

Now I understand why I never get any snipe.
You see, I always leave my boards next to the planer for at least a week before I mill them. With really difficult species, I'll sometimes move them halfway across the shop first. I'll monitor things for a few days and, as long as I don't hear any fighting or arguing, I'll move them a bit closer. Then I'll say, in a quiet voice, "Mr. Planer, I'd like you to meet Dalbergia nigra. He's visiting us from down south - from Brazil, actually. Nigra, this is Mr. Parks." I wouldn't think of introducing them suddenly.
Sudden introduction has nothing to to with it. A good planer that is correctly set up and properly used will not give you any snipe. Period.
John Martin
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On planers with adjustable rollers You can lower the bottom outfeed rollers and let the stock run on the bed. You will have to keep wax on the bed so the stock will slide easy.

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A jointer is a much more reliable method for the edges than a router. The jointer will inherently be more accurate because you are referncing a longer cast iron surface, compared to the very short (and possibly wood) router fence.
Bob
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No.
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BillyBob wrote:

Unless, of course, your router "fence" is a straightedge on top of the workpiece rather than a true fence on the edge of the workpiece (for example, see http://www.rd.com/americanwoodworker/articles/200009/farmtable/page3.html ). In that case, your cut line will be as straight as your straightedge, which is easy to make as long and accurate as any jointer bed.
In fact, one company even makes a fancy version: http://www.thewoodshop.20m.com/jointabillit.htm
Since a router bit will cut the wood at *much* higher revolutions per inch, the cut will be, correspondingly, much smoother.
Limitations are: 1) set-up not as easy as a jointer that's ready to go, 2) careful prep to make sure your router is making an exact 90 deg. cut (flat surface, calibrated straightedge, good machine, good bit, and good control), and 3) you're limited to about a 2-3" cut. Even a 3" bit on a router is stretching it, and it had better be a good quality bit.
If you can live with those limitations, then a router can theoretically make a better cut, and it's infinitely more portable. Moreover, if you're trying to joint a few items that are significantly longer than your jointer's bed, then the router set-up is much easier than trying to make longer infeed/outfeed beds for your jointer.
Been doing this on-site for years with good results, H
...if you have a router table, it's even easier (http://www.woodshopdemos.com/rtrplnr.htm )
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