Mortise & Tenion Expansion/Contraction

[jteneyck]

Thanks for the info, John.

As much as I wanted to convince myself that 2" tenons were sufficient, I finally had to agree that they weren't.
I took your advice and bought an end mil, so I could do 3 1/2" long mortises. The new end mil is 1/2" in diameter, four flute, and 6" long. It fits my router and the jig I used to make the 2" deep mortises, and is just long enough to make the 3 1/2" deep mortises.

I'm having a problem trying to make the 2" mortises deeper.  I made the original router jig with a center line that lines up with the center of the original mortise, this allows me to put the jig back over the original mortise pretty accurately. 
Every mortise that I have tried to deepen with the new cutter has "caught", severely jerked the router, dug into the side of the mortise, and scared the pee out of me.

 Have any idea what I may be doing wrong?

I've never used a 4 flute end mill, but I would guess it would cut slowly but smoothly.  If that's true, I wonder if you are trying to take too deep a cut.  I typically take cuts of no more than 1/8" per pass, and this becomes even more important with long router bit.  The bit you have is extremely long, so you need to take very small cuts.  

Don't worry about a little tear out.  If you use epoxy to glue up the mortises it won't matter.  

John

[Retiredguy]

I've never used a 4 flute end mill, but I would guess it would cut slowly but smoothly.  If that's true, I wonder if you are trying to take too deep a cut.  I typically take cuts of no more than 1/8" per pass, and this becomes even more important with long router bit.  The bit you have is extremely long, so you need to take very small cuts.  

Don't worry about a little tear out.  If you use epoxy to glue up the mortises it won't matter.  

John

John,
My plunge router (Bosch) has a depth turret that has 8 depth stops, 1/8" each.  So, I'm sure that I haven't made any cuts over 1/8" at a time.
I tried all the obvious things to stop the "catching", like very, very slow feed rate, and being sure the router was always in good contact with the jig, etc.

I'm routing a mortise into red oak side grain. I plunge the router bit into the wood for the first cut.  I move the router away from me on the left side of the mortise.  Then across the end (1/8") and back on the right side (toward me), and across the close end (1/8").  The catches seem to occur most of the time going into the first corner (on the for end), and going into the third corner (on the near end).  In both these locations the bit is cutting uphill end grain, as opposed to down hill end grain on corners 2 and 4.

With that much bit hanging out there, maybe its just not stable enough to cut it cleanly, and therefore, flutters and catches.

Based in one test case, I cut a 3 1/2" mortise in the end of one of the door rails (all end grain) with out a problem.

If I can't think of another solution when doing side grain mortises, I think I will try drilling a hole at both ends of the mortise, then route only the sides of the mortise, thus leaving a smooth glue surface. The hole would probably need to be slightly larger than the thickness of the mortise, but would prevent the cutter from having to cut uphill end grain, and hopefully, prevent all the "catching" that I've been having.

Do you see any merit in this approach?

[jteneyck]

That sounds like a reasonable approach. Have you tried cutting ccw? It's not something I normally do but if the depth of cut is only 1/8" it should be ok and might eliminate the problem. Do you have a link to the end mill you are using? Or post a photo. I'd like to see what it looks like.

John

[Stwood_]

With that much trouble, I'd try a forestor bit in a drill press to get most out of there, then a router cleanup.

[WilliamHodge]

With that much trouble, I'd try a forestor bit in a drill press to get most out of there, then a router cleanup.

I agree. Rough it out, a lot. I use a forstner bit on big stuff, but a 3/16" high speed twist drill will rough out mortises for a 1/4" hollow chisel mortiser.

Routing a mortise like this is hard, because the router bit is essentially working on endgrain.  By roughing out the mortise, you're getting rid of the worst of the wood. The sides present  grain at more of a tangent to the cutting circle.

[Retiredguy]

That sounds like a reasonable approach.  Have you tried cutting ccw?  It's not something I normally do but if the depth of cut is only 1/8" it should be ok and might eliminate the problem.  Do you have a link to the end mill you are using?  Or post a photo.  I'd like to see what it looks like.

John

John,

I don't know how to do pictures or links.  Its on Amazon under Power & hand Tools, Niagara Cutter, N85703, 1/2 dia, 6" long, 4 flute.

Ross

[jteneyck]

I couldn't find that particular end mill, but I looked at other 4 flute ones and they look fine. So the problem is most likely related to the length. Have you tried running really low speed?

John

[rwe2156]

Hmm....I've tried 4 flute end mills and I didn't like the way they cut.  Besides, didn't he say the tenons were already cut? Or did I miss something?

Ret'd Guy:

If you pin the tenons you will be fine with 2 1/2".  Not worth the effort to redo everything.

There wont' be problems with end grain on the tenons it will be glued and sealed up.

What are the panels made of?

If they are solid wood, how big are they and how much are you allowing for expansion?

Also, to consider on the panels is the humidity differential interior vs. exterior.  Major cause of panels cracking.

I've read somewhere that there is a way to construct a panel to alleviate this.