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When making mortises, it is possible, with dial caliper level measuring, to make a mortise so perfect that you almost don't need glue. Of course the 3/8" and 1/2" with the 1/2" shaft are going to be a lot stronger, but I will be reserving my use of the 1/4" shaft upward spiral bit only for the most exposed surfaces. Now I have exposed slots that are perfect. I just made some custom router table fences, and I needed to make a 1/4" slot along the backing board of the fence. Also great with a regular hand held, with successive depth adjustments. So they shouldn't last as long.
The problem is that it is not designed for freehand use. Fully burying the bit and going for it is not advisable even in a table. In plain words, I wouldn't be without them. You may say who cares, I use urethane glues, which foam up to fill the gaps, and that would be a valid argument. They are ideal for use with a plunge router with a three step adjustable turret. Simply this: If your creating a pocket, like a mortise, even though you are doing it in successively deeper passes, it will create a perfectly smooth surface, both on the walls, and the bottom of the pocket. Knowing that router collets have a safety factor of needing a second tough release on unscrewing the collet is key. Another consideration is although these bits are solid carbide, I doubt they are the same grade in hardness of the standard double flute straight bits with welded on tips, that are so popular.
As a matter of fact I am adding a 3/8" to my 1/4" and 1/2" bits. These bits are designed to be used in a table, with a fence guiding the work against the bit, or in a jig to make mortises for example. When I just said, "use the heck out of your standard carbide tipped straight double flute bits" I doubly advise you to do that. You may want to for example use doweled pegs only to hold the joint. So why am I buying a 3/8" spiral bit as well.
This review is for upward spiral bits, but the same information applies for a downward spiral bit. In conclusion, I would use the heck out of your standard carbide tipped double straight flute bits, and save these upward spiral bits for your exposed surfaces, or when you want a perfect surface-fit. Even with the great results these upward spiral bits give you, I just broke my third 1/4"-1/4" shaft upward spiral bit. Because I needed a 3/8" slot in the face of a project and wanted to do it with the spiral bit that I didn't have. I wanted it to be even and smooth and look great without any tear out on the edges, so I used the 1/4" spiral bit. For example a 1/2" shaft 1/2" bit, and a 1/4" shaft with a 1/4" bit.
What is often done is the mortise is made with a machine or fixture with a chisel and drill bit at the core, making a pocket that is uneven in its edges, and even more so at the base. So after all of that, why buy an upward spiral bit. When people use the phrase the "break in period" take that literally when you use spiral bits. That way you can make very deep mortises that go beyond the depth of the bit surface.
This review is going to sound funny from someone who broke two 1/4" shaft 1/4" upward spiral bits. That is what a spiral bit does. If you are creating an opening all the way through your work piece, it will create a perfectly smooth wall. Be that as it may, these spiral bits go into your router without any size-fit problems. Additionally the Freud routers were having some problems with the bit fit, some say it is because they were being shipped with metric collets. Downward spiral bits are designed especially for work where you want to go completely through the material. I have routers made by Porter Cable, Fein, Makita and several Bosch models, and each of them receives, both spiral bit size shafts of 1/4" and 1/2" effortlessly.
They slide in without any play and do not bind on the way in or the way out. One other thing worth mentioning, is that it is a good idea to get upward spiral bits with the same size shaft as the head of the bit. Wood mating surfaces can be done to perfection, instead of the standard glue up, and then having to sand out the surface irregularities. I am not knocking mortise and tenon machines, they are great, and quickly usable, because mortise and tenon joints don't show so they don't need to be perfect aesthetically. If you plunge it deep and try to freehand it into some wood, the edges can grab and instantly create a ricocheting effect, which will whip into an instant frenzy and snap the bit.
Highly recommended, I wouldn't want to be without them.***I have come back to add one more comment to this review. If you were doing heirloom antique level joinery with no metal hardware, such a joint would be beneficial. What this spiral bit gives you is the option of building a jig that will fit a range of wood sizes that will give you instant mortises that are perfect, with less time, less effort, and perfectly made, and a lot less expensive than a dedicated machine. I have never had a problem with any of the Freud router bits fitting into any one of my routers. I have to conclude that the additional brittleness that an all carbide bit gives you, leads to an ease of breaking that you will not have with a standard bit.
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