Spiral upcut router bits

[jarhead]

I am looking to buy a spiral upcut bit to practice cutting mortices with a new jig I just built. What is the most common size bit for cutting mortices?
From what I have seen, the spiral bits are very expensive compared to your everyday bits.

[LarryG]

What is the most common size bit for cutting mortices?

Correct me if I'm wrong, but it sounds like what you're actually asking is, "What is the most common size of mortise?" Is that right?

If so ... although there are no hard and fast rules, the tenon that will go into the mortise is usually 1/3 to 1/2 the total thickness of the piece on which its cut. For example, a 3/4" thick table apron might have a 3/8" thick tenon with 3/16" shoulders, or a 1/2" thick tenon with 1/8" shoulders. (Both examples assume equal shoulders, but the tenon doesn't have to be centered ... yet another variable.) With a thicker piece, you'd increase the size of the tenon accordingly, most of the time.

So as usual it depends on what you're building. If you mostly work with 3/4" material I'd say get a 3/8" bit. That'll cut the mortise's full width in one pass. If you need more width, you can make multiple passes with the same bit.

[Otter]

I am looking to buy a spiral upcut bit to practice cutting mortices with a new jig I just built. What is the most common size bit for cutting mortices?
From what I have seen, the spiral bits are very expensive compared to your everyday bits.

Yes they can be more. I am not sure of a standard but I have 3 of them, 1/4", 3/8" adn 1/2" that I use based on stock thickness and such. MLCS has a them for what I think is a resonable price.

http://www.mlcswoodworking.com/shops...iral_up_anchor

[vaking]

The mortise sizes I use the most (in the order of frequency used) are:
1/4"; 5/6";3/8" and rarely 1/2". As a reference take a look at common sizes of floating tenons - quick substitute for real tenons.
Here is the link at LV:
http://www.leevalley.com/wood/page.a...at=1,250,43217
I follow the rule of 1/3 usually - 3/4" stock gets 1/4" mortise.
If your budget only allows one size - make it 1/4" upcut bit.
I like bits from Lee Valley but some of their bits may require adapters as they make shank the same size as bit. For 5/16 and 3/8 that means using an adapter.

[LCHIEN]

The mortise sizes I use the most (in the order of frequency used) are:
1/4"; 5/6";3/8" and rarely 1/2". As a reference take a look at common sizes of floating tenons - quick substitute for real tenons.
Here is the link at LV:
http://www.leevalley.com/wood/page.a...at=1,250,43217
I follow the rule of 1/3 usually - 3/4" stock gets 1/4" mortise.
If your budget only allows one size - make it 1/4" upcut bit.
I like bits from Lee Valley but some of their bits may require adapters as they make shank the same size as bit. For 5/16 and 3/8 that means using an adapter.

I'd suggest following Alex's advise - if you only buy one to start, get the 1/4" They run cheapest about $15 and you can make multiple passes to widen a mortise if you need.

[LarryG]

One potential problem with 1/4" bits, though ... they break more easily, so even though they're cheaper it could be a false economy in the long run.

[Tom Miller]

How about a mortising router bit as opposed to a spiral bit? Aren't they (mortising bits) less expensive? Anyone who's used both care to compare/contrast?

Regards,
Tom

[Holbren]

How about a mortising router bit as opposed to a spiral bit? Aren't they (mortising bits) less expensive? Anyone who's used both care to compare/contrast?

Regards,
Tom

Tom,

Those bits are for hinges not plunge mortising.

[LCHIEN]

How about a mortising router bit as opposed to a spiral bit? Aren't they (mortising bits) less expensive? Anyone who's used both care to compare/contrast?

Regards,
Tom

well, the mortising bits are generally straight bits with straight flutes and carbide cutting edges. The spiral upcut bits are straight bits made of solid carbide and a spiral cutting flute(s) so they are much more expensive due to the carbide construction and maybe the more complex flute.

In return the spiral bits clear the cutting trough/dado/groove/mortise like a screw conveyor, pulling the chips up out of the slot making it easier to see and cut. Further the slanted face of the cutting edge shears the fibers, making (it's claimed) a cleaner cut.

Actually it seems to me that the downcut spiral shears the fibers down into the wood so you don't get the fibrous hairs on the top edge and that's the clean cut, but it also ends up packing all the chips into the bottom instead of cleaning them out.

[Tom Miller]

Tom,

Those bits are for hinges not plunge mortising.

I guess where I'm confused is whether or not a mortising bit can be used for plunging. It seems that I read a description of such a bit somewhere that said it was excellent at chip ejection, so I pictured it being plunged.

Otherwise, is the general consensus that the upcut spiral is best for a traditional "pocket" mortise that you'd find in M&T construction?

Regards,
Tom

[LCHIEN]

I guess where I'm confused is whether or not a mortising bit can be used for plunging. It seems that I read a description of such a bit somewhere that said it was excellent at chip ejection, so I pictured it being plunged.

Otherwise, is the general consensus that the upcut spiral is best for a traditional "pocket" mortise that you'd find in M&T construction?

Regards,
Tom

some straight bits are designed only for cutting in from the sides, like hinge mortising bits. The cutters are on the outsides of the bit. They lack a cutter in the middle of the bottom of the bit so if you plunge it it will get stuck on a pillar in the middle of the bit.

Plunge bits actually have a cutter in the bottom center so it removes material in the entire area under the bit. If you compare illustrataions in the MLCS catalog at straight and plunge cutting straight bits it becomes real clear:

http://www.mlcswoodworking.com/shops.../bt_plung.html

http://www.mlcswoodworking.com/shops.../bt_strai.html

[Wood_workur]

I would go with the 1/4" bit, because then you can cut the mortises perfectly centered, and adjust the width of the mortise precisely. (Imagine if the 3/8" bit was JUST oversized.)

[Holbren]

I would go with the 1/4" bit, because then you can cut the mortises perfectly centered, and adjust the width of the mortise precisely. (Imagine if the 3/8" bit was JUST oversized.)

Either way will work fine. For me, fine tuning your router fence would be a pain. If you have a jig, no big deal. If you make your own floating tenons too no big deal if the hole is too large, you can make the tenons to fit.

[drumpriest]

I use a 1/4" solid carbide cutter for most of my mortises. It works great. Adjusting the fence "can" be a pain, depending upon your router fence. I now have a bosch microposition edge guide, which works great for doing this hand held.

Larry, I've not broken a 1/4" solid cutter yet, but I'm not too aggressive with the cuts. Now more than 1/8" at a time, and probably less than that often times. I do loose tenons, and it's a breeze. Even if you don't have the tools, you can get 1/4" oak from lowes for tenons.

[jarhead]

Correct me if I'm wrong, but it sounds like what you're actually asking is, "What is the most common size of mortise?"...

Larry,
Yes, I did not phrase my question correctly. I also found this chart on Woodcraft's web site that gives mortise and tenon dimensions. I was comparing prices for 3/8" bits at Woodcraft and almost fell of the chair.

Onsrud HSS Bit, 3/8" Cutting Dia., 3-3/4" Overall Length, 1-1/4" Cutting Length, 1/2" Shank - $20

Whiteside Solid Carbide Bit, 3/8" Cutting Dia., 3" Overall Length, 1-1/4" Cutting Length, 1/2" Shank - $54

For someone who is not going to be cutting a lot of mortices, is an Onsrud HSS bit good enough?