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Discussion Starter · #1 ·
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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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/DMT-Diamond-Card-Sized-Sharpener-P19.aspx
 

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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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Discussion Starter · #4 ·
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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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/router-cnc/straight-spiral/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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Theo
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I have found that cutting very small cuts, slowly, works for me.
 

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Discussion Starter · #7 ·
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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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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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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If you build a slotted frame to shove that end into that fits tightly around the end and sides then that should help with the torn grain at the edges. The up cut spiral should do a better job as mentioned. If possible I prefer to do that type job on a table saw using a backer board to push the piece past the saw. It does a better job in my opinion.
 
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What Charles said, especially if you have a bunch of pieces the same. I like the routerf(handheld, not in a table) for cuts in big pieces like cabinet gables. Bringing the tool to the work rather than the work to the tool.
 

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Discussion Starter · #14 ·
Stick486:

The cut I want to make is along the edge of a piece, across the grain. I think it is called a rebate. I would remove some wood from both surfaces at that edge of the board, like the one in your first image, the piece about to be fitted in. The cut will be made along the four top edges of a box and along the four bottom edges. I will insert a square-section contrasting wood about a mm wider in both directions, glued and trimmed. A high degree of accuracy is required to ensure that all mating surfaces are very snug.

I have two problems:

1. At present I find that the geometry of the rebate made on my router table is not quite accurate enough, leaving unacceptable gaps in some points at the interfaces with the contrasting wood. The cutting must be made when the box is complete so using feathers is not possible - only hand holding.

2. Each box will be made of a different hardwood. I have experimented so far with softwood (as a trial) and sapele. With sapele (not the softwood surprisingly) the edges of the top and the bottom which have been cut across the grain shows tearout. I will try the suggestions made (tape and making the cuts (especially the first) very shallow but the tearing defeats me, so far.

On problem 2 (tearing) I have researched spiral bits and am told that a down spiral bit (either in a router table or with a hand-held router) will give a clean edge (in my case no terouut on crossgrain) on the upperside of the workpiece (router table setup - my setup) or on the lower side (hand-held setup).

I have therefor ordered a down spiral bit and will report results.

Do you think that will solve the tearout problem? (Which still leaves problem 1 which will require practice - any ideas??).

Thanks.
 

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Discussion Starter · #15 ·
A few photographs may help to bring more ideas.
Sapele (unlike the softwood in the trial wood boxes) has many quite deep pores on its surface, so any tearouts are very difficult to see and impossible in a photo. That's fine fp#or sapele but the same amount tearout in a closer grained wood be noticeable. That would become clear with more experiments.
 

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Steve you can post pictures or a sketch that has been scanned into a jpeg or some other suitable file format and then post it on here by using the Advanced Post option. In the Manage Attachments section it will tell you what file formats our site accepts. The more clearly we understand the problem the better we can answer.
 

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I use a dado blade to cut those joints for drawers...
my pieces are generally over width and then ripped to final..
when I can't rip I use a backer board to prevent tear out...

how thick is your material...
do you have a glue line blade and a cross cut blade...

two table saws???
 

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Discussion Starter · #19 ·
I use a dado blade to cut those joints for drawers...
my pieces are generally over width and then ripped to final..
when I can't rip I use a backer board to prevent tear out...

how thick is your material...
do you have a glue line blade and a cross cut blade...

two table saws???
The sides and ends are 10mmthick abd the top and bottom are 6mm thick

As for a glueline blade, I had never heard of them until your post. I think that might solve my problem.

Only one table saw with an as-bought 40 tooth blade.
 

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Mike
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For what you are doing the downcut bit should work. You mentioned using tape and it would help a little. You can also score the edge of the cut with a sharp knife, like an xacto knife so the fibers are already cut. Hold the straight edge down over the good part of the box so if you git off the line you are cutting in the waste area that will be cut away .
 
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