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New Circle Jig For Router.


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This week's project was to make myself a new circle cutting jig for my router. The old one was a hastily made MDF jig that I made for a job at work, but it relied on holes being drilled in it to fix the pivot point and there's always the matter of having to either subtract or add the radius of whatever sized cutter was in the router...depending on whether you are cutting a disc or cutting a hole. The existing holes had started to wear and it wasn't accurate any more.
Router circle jig.

Router circle jig.

As I still have some 8mm acrylic left over from the router table project, I will use that to create a jig that uses a sliding pivot point and so will be infinitely adjustable. I cut a piece of acrylic 450mm x 150mm which will be long enough to create circles from as little as 75mm dia. (any smaller, and I'll use a hole saw) up to 600mm. I can never see me needing to go bigger unless I decide to create a table top!

The piece is marked out and the fixing holes drilled. l used masking tape so I could draw my lines on it.
Router circle jig.

The counterbores are drilled with a 12mm Forstner bit, then drilled right through with a 5.5mm bit.
Router circle jig.

Router circle jig.

Once this was done, I fixed the acrylic to the router and plunged a 6mm cutter through as a guide for the hole saw.
Router circle jig.

Router circle jig.

At this point the sheet is still rectangular because the next job is to route the central slot for the slider. First a 19mm slot, 3mm deep that the slider will travel in, then an 8mm slot for the bolt and slider knob. This was done on the new router table. I had to go quite carefully and slowly, especially with the 19mm cutter to avoid melting the acrylic. I found it best to make several shallow passes rather than try to do it all in one go.

Router circle jig.

Router circle jig.

Onto the slider, and I used a piece of 3mm aluminium cut from the end of this strip...
Router circle jig.

It's marked out and centre punched, ready for drilling the holes for the bolt and pivot point. These are going to be offset so that by rotating it, the slider can go to both extremes of the slot.
Router circle jig.

Router circle jig.

Once drilled, the holes are tapped to take the bolt (a short piece of 8mm studding) and the pivot point (made out of a cut down 5mm screw)
Router circle jig.

Router circle jig.

The pivot point was made by holding the 5mm bolt in my drill (I don't have a metal working lathe) and spinning it against a file to make a 2.5mm point. I tried doing this on the grinder, but couldn't get it accurate enough.
Router circle jig.

Router circle jig.

Finally, I rounded the ends of the slider so it can get right to the ends of the slot in the acrylic.
Router circle jig.

The bolt and pivot are fixed into the slider with blue Locktite.
Router circle jig.

Here you can see how the pivot can reach right to the router end of the slot...
Router circle jig.

...then by turning it, it will go right to the opposite end.
Router circle jig.

Finally, the edges of the jig were cut and smoothed to a nice shape.
Router circle jig.

You will have noticed that there is no scale on this jig. I find it much more accurate to mark out the radius I require, drill the pivot point hole, then slide the jig so that the cutter edge is against either the inside of the arc (for a hole) or the outside of the arc (for a disc).
Mark the radius with a compass and draw an arc.
Router circle jig.

Drill the 2.5mm pivot hole.
Router circle jig.

Now put the pivot in the hole and slide the jig until the edge of the cutter is either inside or outside the arc...here to cut a hole...
Router circle jig.

...and here to cut a disc.
Router circle jig.

Old and new...
Router circle jig.

That's it for this week. The rail saw and router sled are both under construction at the moment and will be put here when complete.

 

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You have been busy, very nice indeed. :thumbsup:

I'll wager that tap handle is older than both of us!. 

I've done the same in the past using a drill as a lathe. A small bench lathe is next on my list of major purchases. 

I could fit a Warco 180 on my end bench but would prefer shoehorning a 240 in there. 

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@BobJ  I made that small tap wrench, and a bigger one when I worked in the maintenance dept. at CompairBroomwade back in the seventies...

large.20180910_172245.jpg.fd53657bc0705bd7aa8ebab867d0eb72.jpg

A small lathe would be nice, but I just don't have the room.

There was a thread about old tools of the trade...I'll see if I can find it, as I did a post in it.

 

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A very useful and simple tool (as demonstrated by the mdf) and a great upgrade with clear acrylic.

I must admit to butchering with a strip of mdf pinned on with nail or screw with the head removed and just plunged the router straight through at the appropriate dimension then affixed. Your more elegant solution certainly gives better results.

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