# Small diameter circles.



## NewMontanaWorkshop (Sep 10, 2004)

I have a couple of home-made trammels that I use for routing arc's in various projects, but now I want to route a circle into a piece of 1/2" ply to mount my PC690 router in to. (2 pieces of 1/2" ply will be glued together).

The trammels that I have appear to me to be too large to route a circle the diameter of the PC690 base. Any suggestions?


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## Richard Wey (Sep 10, 2004)

You could route a circle Larger than the 690 base plate, in some scrap material.
Make the circle large enough so the 690 base will fit in the center of the large circle.
Remember to allow for the diameter of the bit. Then you will be able to use the large circle as a template to route your two 1/2" plywood pieces. They could be cut together, by temporary nails or double back tape. Good luck.

Richard wey


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## Joe Lyddon (Sep 11, 2004)

... and that's the Wey to do it!!


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## NewMontanaWorkshop (Sep 10, 2004)

Richard Wey said:


> You could route a circle Larger than the 690 base plate, in some scrap material.
> Make the circle large enough so the 690 base will fit in the center of the large circle.
> Remember to allow for the diameter of the bit. Then you will be able to use the large circle as a template to route your two 1/2" plywood pieces. They could be cut together, by temporary nails or double back tape. Good luck.
> 
> Richard wey


 Hmmmm, 
Thanks for the suggestion. I'm trying to picture this. If I route a larger diameter circle (than the PC690 base) for a template, then I need to get another bit of some sort -- all I have now is a flush trim bit -- in order to get the diameter of the circle in the ply back to just large enough for the 690 base to fit into.

Thanks.


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## Rattie (Sep 16, 2004)

For circles smaller than a trammel will allow, best to make a custom subbase with a centre pin around which you can rotate the router. This pin goes off to one side of the cutter obviously, with the cutter projecting down through a slot.

The nicest version of this can be slid along the standard subbase, and locked off in any position, providing an adjustible radius. For this you need to cut T-slots on the custom base, to accept bolts which go up through the mounting holes in the router base.

Most router jig books have plans of such things.

To use the fixture to cut a circle, you would drilla hole in the centre of the circle-to-be, pop the centre pin into it, then route out the circle. It helps to hold the workpiece down with double sided carpet tape. That way, the central offcut doesn't go ballistic as you finish the cut.

Have fun

Martyn

(spelling of centre - UK style BTW)


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## kp91 (Sep 10, 2004)

If I understand what you want to do, an easy way to do this would be to make a small router compass. The smallest one I use for inside cuts is a piece of 1x6 poplar with a 1" hole for a template guide. Then mark off your radius on the compass and drill a tight hole for your nail. On small inside cuts, where the piece is going to be pretty much covered up by the router the whole time, I like to double stick tape the parts to my cutting board, so that the center piece won't bounce around when cut free.

I like using the thick boards for compasses because they don't flex, they don't wobble on the pivot hole after a couple of uses, and because some of my template guides are kinda long.

The only other way I could think of doing it would be to use your existing plate as a template, but unless you had a spare plate that can use guide bushings, that might be more work than necessary.

For making small outside cuts, I have a base plate for my router table that I have drilled as a compass, and it works pretty well for small circles if you rough cut the circle out on the bandsaw first. (good for plaques, toy parts, etc.)

Hope these ideas help,


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## NewMontanaWorkshop (Sep 10, 2004)

Thanks much for the tips, will be giving the ideas a run this weekend and see how it works out.

Thanks agian.


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## loststevie (Sep 13, 2004)

try the circular router jig made by jensen.. ,, varies in sizes from 1' to about 8 '
i use one in my 690 and have good luck in makin small circles for wheels etc.


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## NewMontanaWorkshop (Sep 10, 2004)

*690 Base template.*

Guess I wasn't considering all the options when I first posted this question, after a few replies and a bit of shop time -- the solution was painfully obvious. Used the trammel to route the larger diameter circle in 1/2" MDF, the rest was easy.










Thanks for the replies.


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## NewMontanaWorkshop (Sep 10, 2004)

*PC690 baseplate circles.*

This is what I ended up with. Used the trammel to cut a template, then used the template to route the 690 baseplate size into some plexiglass.


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## template tom (Sep 18, 2004)

Snowshoe said:


> This is what I ended up with. Used the trammel to cut a template, then used the template to route the 690 baseplate size into some plexiglass.


Snowshoe 
I am sure there must be some out there wondering how you calculated the size of your template
Tom


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## NewMontanaWorkshop (Sep 10, 2004)

template tom said:


> Snowshoe
> I am sure there must be some out there wondering how you calculated the size of your template
> Tom


I think I can come up with a description. Here goes.

I started out with some 3/4" plexiglass that was a 'found item'. Rather than seeing it find it's way to the local landfill, I grabbed it and stocked it away for a rainy day. Deciding that I needed a dedicated router table rather than the accessory table mount in my table saw that I had been using, I pulled out the plex and started.

I am putting a PC690 with fixed base in this table, so I grabbed a piece of scrap 1/2" MDF large enough for the template and centered the round baseplate for the 690 in the center of the MDF and marked around the outer edge.

Then I set the router on the MDF with a trim bit mounted. The bit was located to just touch the inside edge of the first circle drawn on the MDF. A mark was then made on the outer edge of the base away from the center of the circle. This was done in 4 different spots. The marks were then measured from the center of the first circle and averaged.

This measurement was set on the trammel and the hole was then cut in the MDF creating the template.


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