Router bit for cross-grain rebating. - Router Forums
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post #1 of 25 (permalink) Old 11-14-2019, 02:53 PM Thread Starter
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Default Router bit for cross-grain rebating.

I make small boxes. I am usuing a simple router bit (no fancy profile, it just cuts a rectangular slot with sides at right anges to eachother), in a router table, hardwood. I cut a rebate on all four edges on both the top and on the bottom before setting in and trimming a piece of hardwood (for decoration). When cutting parallel to the grain there is no problem, but across the grain the tearout on the face of the workpiece is very noticeable. It makes no difference whether the two box faces, or the sides and edges, are flat on the router table when routing. I have thought of cutting acros the grain with a sharp cutting tool but it seems impossible to get it in just the right position.

Any ideas please? Thanks.
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post #2 of 25 (permalink) Old 11-14-2019, 03:06 PM
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Hi, Steve; welcome!
I feel your pain!! Pretty sure most of us have experienced that issue. Some of the factors are type of hardwood, depth of cut, whether you're doing the cut in one or more passes, and especially whether the bit is extremely sharp.
You could try honing your mortise bit with a diamond card and see if that helps(?).
Just google 'honing router bits' for You Tube vids.
The diamond hones aren't expensive.
https://www.sharpeningsupplies.com/D...pener-P19.aspx
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post #3 of 25 (permalink) Old 11-14-2019, 03:16 PM
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What Dan said, and...I may be misunderstanding what you are doing but if you're using a straight bit, might a spiral bit work better for you...?

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post #4 of 25 (permalink) Old 11-14-2019, 04:17 PM Thread Starter
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Thanks. Here is a web site that offers a spiral bit for rebating. Is that what you mean?

Unfortunately, it states "...in HS steel- optimally suited for softwood applications". However, my boxes are in hardwood.
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post #5 of 25 (permalink) Old 11-14-2019, 04:28 PM
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Quote:
Originally Posted by stevekirk View Post
Thanks. Here is a web site that offers a spiral bit for rebating. Is that what you mean?

Unfortunately, it states "...in HS steel- optimally suited for softwood applications". However, my boxes are in hardwood.

I didn't see the web site you referred to but here is Freud example...

https://freudtools.com/explore/route...al/down-spiral

You may already have a favorite manufacturer but all make the spiral bit in up and down configuration. You will want to pick the right one so that it cuts scissor fashion with the important edge.
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post #6 of 25 (permalink) Old 11-14-2019, 04:55 PM
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I have found that cutting very small cuts, slowly, works for me.

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post #7 of 25 (permalink) Old 11-14-2019, 04:59 PM Thread Starter
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DaninVan: The wood is in this case Sapele but I would be using other hardwoods such as beech, oak and mohogany.

The bit is new, use only for, perhaps, a total running time of 20 mins. However, some people say that tool bits are not as sharp as they could be out of the box.

Do you think doing that cut in more than one pass might help?

Alternatively, do you think strengthening the face where the tearout occurs with a tape of some sort stuck on? Perhaps the brute force of the cutterwould still tear out fibres.

If I can't solve this problem I will have to confine any decoration (by inserted contrasting hardwoods) to cuts along the grain. Quite a design limitation.

A totally different aproach would be to make the top and bottom pieces slightly smaller all round, effectively providing when fitted the same slot for the hardwood strips. It would be easy to get the eges of the top and bottom to the correct size without tearout, perhaps by finish planing the long edges of the top/bottom by hand and sanding the short (cross grain) ends (sanding does not cause tearout). When gluing on the top/bottom, it would have to be very accurately centred, otherwise the hardwood strip, when finish sanded to size in place, would vary in width. Hum!

Or perhaps I'll stick to plain boxes.
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post #8 of 25 (permalink) Old 11-14-2019, 05:10 PM Thread Starter
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Quote:
Originally Posted by JOAT View Post
I have found that cutting very small cuts, slowly, works for me.
Seems a good idea. Perhaps the first cut could be exceptionally shallow, since it is the cut that cuts the troublsome wood fibres on the face
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post #9 of 25 (permalink) Old 11-14-2019, 07:43 PM
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Try using a backer strip/push block behind the part to support the outer fibers as it exits the bit, I think that you'll find that this will pretty much eliminate the blow-out - you can use the same one for the whole project as it just needs to support the wood in the area being routed. Another suggestion would be to cut the end grain at both ends of the part first, the edge cut along the grain would tend to remove any minor splintering. Of course, a lighter cut won't hurt either.
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post #10 of 25 (permalink) Old 11-14-2019, 08:24 PM
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what are the dimensions of your cuts..
what brand of bit are you using ..
which style of rebate are you making...

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