Cutting Birch and Oak 3/4" Plywood

[vswla1@bellsouth.net]

Since I am new to the world of shopbot I am asking for any and all the assistance I can get.

I am cutting 3/4" birch and oak 7 and 9 ply plwood and am running into problems with broken bits and "feathering" of the top of the boards.

History: I purchased the whole machine from shopbot. table, vacuum, routers, a axis, even their dust collector. It is a great machine and I am proud of it. I use it to make engraved signs and computer worstations that our employees with disabilities sand, stain, assemble and sell.

Currently I have the routers set at 19000rmp and normaly use a 1/4" bit. My feed rate varies from about .75 to 1.25. I tried slower rates down to .3 but the bit breakage and feathering continues.

I would appreciate any help on how to prevent or atleast reduce these problems.

Thank You

[gerald_d]

Many things:

Feathering can be solved with a spiral-down bit (or an orbital sander)

If you are trying to cut 3/4" in one pass with a 1/4" bit, then you are asking a bit too much. (pun?)

You can go much faster than 19000rpm with a really good sharp bit.

Good spiral bits give a MUCH better result than cheaper straight bits.

[rgbrown@itexas.net]

Jeff,

My first thought is "What the heck bit is he using." Except it wasn't heck I thought.

The "feathering" or fuzz might be cured with a down-shear bit if it is on the top. I could be a spiral-down or 'compression' bit.

What this leads to is we only have the parts for part of your problem. To solve it, more information is needed - probably the bit/material interface, since that appears to be where the problem seems to be.

Ron

[Jeff Johnson]

First off I want 2 apologize for the double post, computer glitched and I didn’t know I did it, and thank you for your posts.

Trying to answer your questions:

The feathering does occur on the top of the board.
From what I have read in other posts a spiral down bit has a tendency to get under the wood and break the vacuum. I do not know if this is true or not, nor have I tried one yet.
I am trying to get away from having to sand the feathers off before we put edge banding on.

I may be asking a “bit” much as I am trying to make the cuts in one pass.
I have tried a spiral up bit
it broke. (PorterCable ¼” dia straight bit, 1”cut depth, ¼” shank)
I tried a carbide tip double fluted bit
broke 2. (Rockler ¼” dia straight bit, 1”cut depth, ¼” shank)
I tried the cheaper bits and haven’t broke but 2 of those, but they wear out quickly.
Since these broke at or near the collet I’m wondering if my move speeds are to fast.

The plywood I’m using is the same as you find at any major lumber dealer. It is not a special type.
My routers are Porter Cable with 5 speed settings from 10,000 to 21,000 rpm.

I’m not sure what else to tell you. Ask and ye shall be given answers oh wise ones.
Thank You

[twiles]

A 1/4" bit is the wrong tool for the job. Check your E-mail, I sent you some info on compression spiral bits.

TW

[rgbrown@itexas.net]

I would tend to agree a 3/8" or 1/2" "compression bit" might be a good choice.

[beacon14]

Make sure your collet isn't part of the problem. They do wear out and are only expected to last a certain number of hours before being replaced. (Many hours, true, but not forever) We had a similar problem with broken 1/4" bits; the problem went away when we replaced the collet. (Not before we pissed off a supplier by complaining that his bits kept breaking!)
It's also possible to ruin a collet if you crank down when tightening the bit and don't realize there's a piece of debris or dust inside, or a burr on the bit shank.
You can also try going up to a 1/2" shank, they are much more durable.