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Discussion Starter #1 (Edited)
Hey all,
I'm getting into making my first mortises on my router table. I have a Whiteside 1/2" spiral upcut bit in the table mounted Triton TRA001, and I am gently lowering the piece onto the bit as it is pushed against the fence. The "plunge" hole sounds like it's being cut smoothly, but when I push and route the mortise, it does not cut smoothly. The piece makes small jumps as I route. When I stop, I get a crappy mortise like you see in the photos. What am I doing wrong?

1/2" deep mortise


1/4" deep mortise


1/2" spiral upcut bit


Thanks,
John
 

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John
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keep it tight against the fence and don't make such a deep cut make more than one pass a lot of guys don't like to perform this procedure on a table I've done it,you got to remember that one side of cut is a climb cut which wants to pull it away from the fence.
clamp a board all the way across your table to hold it against the fence when you are running it. ( make a channel to hold the board in place )
 

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My personal opinion is that it is a bad idea to try it on a router table. Mortices are one of the things that plunge routers were made for. You plunge your way into them, not lower a board onto the bit. That often puts your fingers way too close to the bit and if you lose control while trying to hold tightly onto the board it can drag your fingers into the bit. There are a number of jigs that use a handheld router that will give you very good results. If you have a drill press then I recommend a mortising attachment for it. They aren't that expensive and they are easy to use.
 
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Discussion Starter #4
Could it be the bits? I use tried making a groove with the upcut bit and it chewed up the wood. I did the same thing with a 1/2" straight bit and it was fine. Here's the bit (are those curves supposed to be there at the top?):



 

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I believe that they are cut in like that to increase the rake angle at the outer tip so that they don't tear grain out as easily as they are entering the wood. The increased angle produces more of a shearing cut than a scraping cut. Upcut bits will still tend to rag the edges of a cut because of the cutting action but it's necessary for chip removal. One option that will help is to drill as much waste as possible where the mortise is going before you start routing. That keeps the bit cooler and and gives the chips a better escape route. Routers are not very good at hogging out waste but they leave a much better finish than other tools.
 

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Chuck is corrrrect. Router table morticing is dangerous business.
Moreover, the work cannot be held (x hand) rigid enough for quality cuttings.
The work can self feed etc. don't do it.
Cutter design is a player but not the one you've shown.
Solid carbide cutters are all designed to plunge without even moving the router, (like a drill).

See third picture down (left) for samples when the work is fixed, and the
router is guided by edge guides & stops.
 

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Youre cutting way too deep on the cut. That looks like walnut which is very brittle

That hole should be cut with multiple passes. I just cut some rebates in rosewood on the router table.
Tried to cut 8mm (3/10th") in one pass and the table chewed it up and spat it out.

went back and cut the rest of the pieces in 5 passes 1.5mm (1/20th") a time and it came out smooth and clean.
 

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I have had satisfactory success by cutting in numerous passes i.e. 3/32" max for each pass, not more than 1/8"max.
Be sure you do like has already been mentioned with the board across the whole piece to keep it tight against the fence. The other option is to have it clamped tight to a jog that can be made to hold it tight to the fence. I just use straight cutters with an end cutting flutes.
Herb
 

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Chuck is corrrrect. Router table morticing is dangerous business.
Moreover, the work cannot be held (x hand) rigid enough for quality cuttings.
The work can self feed etc. don't do it.
Cutter design is a player but not the one you've shown.
Solid carbide cutters are all designed to plunge without even moving the router, (like a drill).

See third picture down (left) for samples when the work is fixed, and the
router is guided by edge guides & stops.
Pat what brand of bits are those, never seen the copper colored ones before.
Herb
 

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try a straight bit and shallower passes make sure you are using a decent strong guide fence on both top and side. predrill a starter hole smaller than the finished size
 

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Discussion Starter #12
Brilliant, thanks for the advice all. I will try shallower passes and see how it works out. I watched a youtube video "Cut A Mortise On A Router Table " and thought it would be able to handle larger passes, but I guess the species makes a big difference.

I'm in the middle of making a plunge router mortise jig from FWW Issue 172. In the future I can steer away from table mortising.

The drill press attachment looks nice. For now I'd rather not add another tool to the arsenal though.
 

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Mortising with a router is something the plunge router excells at. You either need to use a long cutter and a guide bush with a template OR two side fences mounted either side of the fence to achieve consistent, neat results
 
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