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Stopping tear out with a plunge cut

1321 Views 9 Replies 7 Participants Last post by  gwilki
I'm trying to form a small bowl for a scoop in silver maple and I'm having trouble with tearout as the cut progresses. I have the wood clamped well to the table of my drill press and I'm running the lowest speed (~500rpm) and it cuts beautifully for the first 3/8" or so of penetration but starts getting quite a bit rougher (the cut & the wood) as the bit cuts deeper. I've tried running it much faster as this is a router bit, but that resulted in alot more chatter & vibration, initially and with deeper cutting. The bit is a 1" radius convex bit and cutting this same wood in a running cut with and across the grain yielded great results (the second tray made with this bit is my avatar), the main difference being the aforementioned cuts were done with a router at ~15Krpm. Any ideas on how to mitigate this a little?

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I'm thinking that your chips are getting in the way of cutting - perhaps a constant flow of high velocity air to keep your cut clean may help.
just mho
I use a similar 1 1/2" bit to make coffee scoops.
I made a jig to use with my router because I always got too much chatter at the drill press. I think it had something to do with router bits being designed to cut at high speed.
That being said, even with the router, some woods seem to chatter and have tear out no matter what I do. It seems sometimes it is a crap shoot as to wether I get a clean cut or not.
I'll be watching this thread though, because I'm always open to trying something new to get the results I need on a more consistent basis.
I tried something similar once, and it didn't work. I never tried to figure out how to make it work. I would think the bit isn't really designed to cut like that and is more at home throwing chips out the side instead of upwards.

Couple thoughts though:

1.) Is the bit sharp?

2.) Do you have a smaller diameter bit you can plunge to depth first? Maybe it's just trying to clear too much at once when you hit full depth.

3.) You could also raise the bit up frequently to clear out the chips and take very shallow passes to see if that helps.
I m thinking that your chips are getting in the way of cutting - perhaps a constant flow of high velocity air to keep your cut clean may help.
just mho

- recycle1943
I tried using a blow gun while cutting and no difference, except for a gi-freaking-gantic mess.
You may be going against the grain right there. Do "back cuts" where you would be going into the grain. Also, take shallower cuts. Just my thoughts. Also, I don't know if you could place a thin dummy board on it, like a throw away pattern board??? Maybe it's just a knarly, crotchety area of wood….........I don't know
Dick makes a valid point about the chips, which is why the router bits running at 15K-22K don't have to worry as much about chip - they fly off or they are much smaller since the rotation is so much faster compared to movement through the wood. And you are stuck in one spot, so even though you might feel it running fast in your drill press, you cannot displace the shavings fast enough to make the next cut and it catches, even with compressed air. Router bits are not equipped with flutes to remove the shavings. I think your bit is just not turning fast enough.
I've experimented a little bit more and the grain issue is the main problem, the second is the bit speed. Different areas of the same board allowed the bit to perform differently so the grain structure is something I'm just going to have to work around. I'll have to see if I can figure out how to very firmly clamp the base of my plunge router to the wood and see if the substantially higher speed is enough to overcome the difficulty I'm having with the grain.
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Here is what I've been using.
The hole in the plywood is cut to fit the router base snug.
Then I lined up one edge of wood being used against a 2×4 and screwed said 2×4 to the underside of the plywood.
I clamp wood between the vise jaw and the 2×4 tight.
Then place the router in the circle cutout and go.
It's worked pretty good so far versus the drill press.
Like I said though, some pieces of wood seem to chatter no matter what.
Next time I get in the shop I can take notes on grain characteristics (straight, wavy, towards one side or the other) and see what I may learn about how that may or may not effect the cut.


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It's hard to tell from the pic, but you are likely getting tear out on the end grain. That's a constant problem for woodturners. One way to lessen it is to flood the end grain with thin CA glue frequently. You take a small cut, then flood, then another small cut. The CA stiffens the end grain so that it cuts instead of being pushed over and torn.

As others have said, that bit is designed to spin much faster than you are turning it.

Finally, that bit looks like it has 2 carbides. If you can find one with 3, you will get better cuts.
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