Bit deflection when cutting tabs.

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benaroh
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Joined: Thu Oct 10, 2013 1:57 pm

Bit deflection when cutting tabs.

Post by benaroh »

I often find myself cutting profiles that require tabs. I am typically using a 4flute upcut bit (they are cheap and work well).
I use the plunge tool on my profile cuts, however it will not plunge after cutting the tabs & as a result the bit deflects. See the attached picture.

Is there any way to prevent this? My plunge speed is set fairly low.
Attachments
Deflection.jpg

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Bob
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Re: Bit deflection when cutting tabs.

Post by Bob »

Try the 3D tabs. I use them to eliminate this defect.
tabs.JPG
Bob
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Consultingwoodworker
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Re: Bit deflection when cutting tabs.

Post by Consultingwoodworker »

3D tabs are one answer. When using them, add a bit to the tab height because you lose a bit of the strength with the ramp.

Check too to be sure that your bit is not cutting a disk as it plunges through the bottom face. This disk can get cut free then spins under the bit rather than being cut and ejected. (You may have experienced this drilling in plywood with a spade bit) This can cause deflection AND throw off the Z axis.

The reason yours are deflecting is that your bit does not like to plunge. Four flutes is a LOT when turning at the speeds of a router, you are generating a lot of excess heat.

Freud's 1/4" single flute straight cutter is my preferred bit. It is a great bit and under $20.00, around $14 I think. A single flute makes larger chips. Larger chips have more mass, so they fly farther away from the cutting area taking heat with them. They also are not being re-ground causing more heat. And the single flute generates less heat from friction because there is only the one flute.

Proper chip load and ALWAYS ramping your plunges are the two secrets to long bit life.

benaroh
Posts: 28
Joined: Thu Oct 10, 2013 1:57 pm

Re: Bit deflection when cutting tabs.

Post by benaroh »

Thanks both of you!

I agree about bit life! Some my my bits seem to last forever! Im excited to try the 1/4 strait bits, ordering some now!

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Consultingwoodworker
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Re: Bit deflection when cutting tabs.

Post by Consultingwoodworker »

HD now carries the Diablo router bits from Freud. I just bought one for $17.00.

Also, use short bits for thin materials, longer bits for thicker as needed. But remember that the longer the bit, the more it will deflect and the louder it will be cutting. I always try to use the shortest bit possible.

Ralph

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