# Guidance for bit selection



## myronhale (Mar 6, 2005)

Can someone give me advice on what diameter of pattern bit to use for different applications. For instance, when making a 1/4 inch plywood pattern would I use a 1/2 inch diameter bit, a 3/4 inch or a 1 inch.
Second issue I need help on is what bit to use when using the router to cut through wood. For instance when cutting a 12 inch circle from a plywood sheet. Have several router books but can't seem to find the answers.
thanks
myron


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## -Sam- (Sep 24, 2004)

myronhale,

That's an easy one! Use 1/2 inch diameter flush trim bit for the patterns. And to cut through wood, use the 1/4 inch diameter spiral bit. Later...

Boricua


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## myronhale (Mar 6, 2005)

Thanks Borica for the info. I am still a little unclear as when to use the larger diameter pattern bits. Must be a use for them since many are larger than the 1/2 inch you recommended. 
myron


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## Mike (Nov 22, 2004)

Myron, let me take a stab at this. You have a piece you want to duplicate, lets call it an oval. You want to create a jig because you just know you will sell 97 of these things as fast as you can make them. You start out by making a pattern the exact size you want the finish piece. Since your jig must allow for a guide bushing it has to be bigger than the pattern. We will use a 1/4" bit for making the cut because the less wood you are trying to remove the easier the cut. For the sake of explanation we will use a 1" guide bushing. This will give us an oval cut out which is 1/2 the diameter of the guide minus 1/2 the diameter of the bit larger than our pattern. In this case it would be (1/2" - 1/8" = 3/8" larger than the pattern on both sides) Now we have a template which is actually 3/4" longer than our finish piece should be.(3/8", both sides)
To make our piece come out the proper size we will use the same bit but change the guide bushing size. We reverse the process, 1/2 the diameter of the guide plus 1/2 the diameter of the bit will equal our finished size.(In this case 1/4" + 1/8" = 3/8" on both sides. Since 1/4" is half the diameter of the guide we would use a 1/2" guide bushing with our 1/4" bit) I went through this explanation because a jig is usually easier to work with for a lot of repetition. If you know you are only going to make a couple of these ovals you can get by making just the pattern and using a flush cutting pattern bit. These bits come in many sizes, and the only important factor in choosing which one to use is that it is not larger than any of the area's you need to trim. 1/2" is a popular size for this type of bit, and it will cut most anything you throw at it. You will get more wear out of a larger bit, and it will be stronger than say a 1/4" bit. Remember you are not cutting the full width of the bit so a smaller bit is not the big advantage it is in making a through cut. One last thing, if you are making a pattern out of 1/4" thick material try using Masonite.(hardboard) It is usually cheaper than plywood and easy to work with. There are no voids which could create snags on your edges.


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## myronhale (Mar 6, 2005)

Mike, thanks for taking the time for giving the advise. It makes sense to me. I have been doing woodworking for about a year after my retirement and enjoy it a lot. And if I spend my time making things for my family, I don't have to work as much in the house. The router is such simple tool and at the same time there seems to be no end to the tasks it will perform. I mostly have done edge forming with it and some other small jobs. I have two PC routers and really like them but what I thought was a substantial investment in them turns out to be small in comparison to quality bits for them. That was the basis of my questions - trying to decide which bits to buy. Thanks again to you and Boricua. I need all the help available.
myron


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## jerrymayfield (Sep 25, 2004)

First of all a flush trim bit has the bearing on the bottom,a pattern bit has the bearing on the top(above the cutting edge). If you are using either type bit to trim to a pattern or what ever,use the largest diameter bit you have. Check Pat Warner's site or read some of the router books available. Do not expect to get all you information from this or any other forum. The late Dr. Roger Cliffe used to say "want to be a better woodworker - do more woodwork.

Good Luck
Jerry


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## Mike (Nov 22, 2004)

That is true Jerry, and both a flush trim bit and a pattern bit are flush cutting bits.


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