# cutting archs/circles (what bit to use?)



## mcbradford (Jan 2, 2005)

I have been cutting archs with my Bosch jigsaw. I do okay, but I am following a pencil line, so they are not perfect. I purchased a plunge router in addition to my fixed base router. I have also purchased a circle jig for the router. What bit should I use? This will be my first plunge routing experience - any tips/cautions?


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## Mike (Nov 22, 2004)

Plunge bits are different from other straight bits. The end of the bit has cutting edges to bite into the wood as it is lowered. The less wood you are actually cutting means the easier the job, so a 1/4" bit is what I use. This has the added advantage that 1/4" diameter bits are less expensive than larger sizes. Spiral cutting straight bits tend to make a better finish cut than a simple straight bit, more of a slicing action as opposed to a scraping action. They also help eliminate the slight burns, bumps and tear out that can occur at the end of a circular cut. The spiral bits are either up or down cutting, depending on which way you want to eject the chips. Remember to make your cuts in small passes, ie... no more than a 1/4" depth at a time. Again, the less wood you are cutting means an easier cleaner cut.


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## x372sailor (Dec 24, 2004)

*Use a Template*



mcbradford said:


> I have been cutting archs with my Bosch jigsaw. I do okay, but I am following a pencil line, so they are not perfect. I purchased a plunge router in addition to my fixed base router. I have also purchased a circle jig for the router. What bit should I use? This will be my first plunge routing experience - any tips/cautions?


Another option you have is to make a template (from 1/4" material), carefully sanded to "perfect" the arch. First you would rough cut the arches on your jigsaw to within about 1/8" of the line. Then you can use a straight bit (with a bearing) or a spiral bit (with a template guide) to get a perfect replica (or slightly offset, in the case of the t.g.) of the template. You probably have to make a number of arches so they will alll be identical relatively easily.

I always prefer the template approach and have good experiences with it.

This is not really a plunge operation as I picture it. Perhaps I misunderstand the operation you have in mind. 

Brian


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