1/4" Diameter Cut, Flush or Pattern Router Bit

[Mike OMelia]

...with a top bearing. Anybody know where I can find one? I could go as large as 3/8", but the slot I am cutting is 1/2". They make 1/2" diameter bits with the bearing on top, but seems to big for a slot of this size... does that make sense?

Mike

[David DeCristoforo]

If you are cutting a 1/2" slot, why can't you use a 1/2" diameter bit?

[Anthony Whitesell]

I didn't dawn on me why you can't find one until I started looking. A 1/4" straight bit with a top bearing would have an 1/8" diameter shaft and a tiny (1/8" ID 1/4"OD) bearing.

I did find 1/4" diameter single flute flush and bevel cutters. They probably wouldn't work for your application, but they guide method gave me an idea. They don't use a bearing as the guideat all , they use the tip or the shaft (or both) as the guide. Could you (carefully) do the same thing with a 1/4" spiral straight bit. Place the spiral bit in the collet, lower the collet as much as possible, and allow some of the shaft to hang out and provide the guide surface? (like the single flute flush trim bits do)

[Mike OMelia]

I guess I could use a 1/2" bit, but I would have to get the "pilot" hole perfect or it won't look right. As of now, I do not own a plunge router. But if I did, that plunge cut past the pattern without a guide surface would be nerve racking.

I could use a spiral bit and use the shank edge as a bearing surface, but burning the slot interior edges would be a problem.

I did not realize that top bearing pattern bits did not come as small as 1/4" (or 3/8"). I sort of see the problem now.

It looks like this process is not suited for a router table. I had someone suggest another solution a while back. Take a 1/8" drill bit blank and create a taper on the end using a grinder. Such a bit in a drill press creates a good cutter at lower RPMs, albiet slower.

Mike

[David DeCristoforo]

There is one thing you can do. Get a 3/8" straight cutter w/ a 1/4" shank and slip a bearing w/ a 1/4" I.D. onto it. The bearing will be a "bit" bigger than the O.D. of the cutter but you can adjust your template to compensate. The bearing should be right against the collet on top (but still be free to spin) and as far down onto the bit as it can go without forcing.

[Chip Lindley]

Mike, I am surmizing you are trying to route a blind slot 1/2" wide. You can always use a 1/4" bit with a 1/2" template collar as for dovetail jigs, in the router base) Make your template slot pattern 3/4" wide with 3/4" diameter rounded ends. (Forstner bit!) If the template slot is accurate, so will be your 1/2" slot.

Drill a 3/8" hole into the workpiece (just shy of finished depth), to allow the bit to start cutting without needing to plunge it.

Template should be thick enough to house the template collar and any unused length of the cutter. Only the depth of cut should protrude into the workpiece. Good Luck!

[Jerome Hanby]

I get confused by top and bottom bearing terms on Router bits. But surfing, it looks like the official definition is top bearing is on the shaft end of the cutting head. If that's what you need, can you not use a 1/4" straight bit with a guide bushing? Not as easy as just laying out a straight guide edge, but...

[Mike OMelia]

Someone who has done it almost has me talked into using a 1/2" flush bit, bottom bearing. I finally understand why they do not make 1/4" top bearing bits.

I am not sure I like the idea about using a template bearing, but I will think about it. At least I could use a smaller bit.

Thanks for all the help!

Mike

[Paul Murphy]

...but it's tiny. 3/16 dia cutter/bearing, 1/4 shaft, but the bearing is on the end.

http://www.amanatool.com/bits-fv/mr0102_mini_bearing_flushtrim.html

[Mike OMelia]

Now that's a nice bit for me! (but not this application). Thanks, think I will get one.

Mike

[Chip Lindley]

Mike, if We knew exactly what you were trying to make, it would make more sense. Curved? Straight? Deep? Shallow? The possibilities could be endless. Please Elaborate!

Meanwhile, don't make it any harder than it has to be! Trial and Error goes a long way to perfect technique. Don't expect perfect results without some practice on scrap pieces.

I was going to mention the tiny 3/16" piloted Amana bit featured on the back cover of this month's Woodshop News, but someone above beat me to it.