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Discussion Starter · #1 ·
I've been working on making a ships ladder for my granddaugther's fort. For the hand holds, I am making templates for using a circular saw for the straight parts of the cutouts and a router for the radii at the ends and for finishing the sides and edges. The router template needs to have a large radius for the router base, to create a template radius of 3.394" which will, in theory, create a radius of 1.5" at each end of the hand holds.

I was thrashing about trying to figure out how to make a circle cutting template for my router (Bosch 1617). I was in a woodworking store recently and saw some really cool circle cutting templates and normally I wouldn't hesitate to buy one. But, money is tighter right now than usual, so I refrained. The jigs I looked at in the store rely on using a 1/4" router bit for establishing the radius that the jig will cut. The jigs had series of radiating 1/16" holes allowing radii to be set at increments of 1/16". One reason I refrained from buying one is that I remembered I'd bought the Bosch edge/circle guide jig (RA1054) about the time I bought the router. I realized I didn't need to buy anything and digging it out when I got home proved that correct.

The Bosch jig has a cool little circle pivot point tab for inserting a 1/4" dia. rod located either in the workpiece or by using a provided suction cup with a 1/4" pin protruding. The radius I need puts the pivot tab too close to the router base to use the suction cup, so I needed to come up with a different method. Either way, I needed a way to set the radius of the router/jig. I reasoned that a 1/4" pin securely mounted in the pivot tab could be used along with calipers and a similar 1/4" pin in the router chuck for setting the radius, subracting half the pin diameter of one of the pins. I set about making a somewhat fancy one, but I realized that a partially threaded 1/4" bolt could do the job satisfactorily. I tried it and it does, but made the fancy one anyway.

Bolt Pivot Pin (head would need to be cut off and the shaft shortened)
Product Auto part Wheel Bicycle part Clamp

Auto part Bicycle part Wheel


Brass Pivot Pin
Auto part Bicycle part Metal Tool Aluminium

Auto part Wheel


Bolt pivot mounted in the jig
Electronics Machine Machine tool Scientific instrument


Brass pivot mounted in the jig
Product Machine Machine tool Tool Milling


Setting jig for 3.394" finished template radius.
Electronic instrument Electronics Machine Brake Metal


It appears that the bolt would work every bit as well as the fancy brass pin, but I do like the brass one better. I haven't tried either one out yet and I expect to encounter some glitches, perhaps in how well the caliper does in setting the right radius. It will likely take some trial and error, sneaking up on the desired setting. Even with a bit of fiddling, if it works, I'll consider it a success. I expect to set it shy of my final desired dimension for roughing it out and then setting it for a final light pass.

Rick
 

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Good thinking, Rick...I assume you'll be cutting the head off the bolt and use only the shaft...?
 

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Discussion Starter · #3 ·
Good thinking, Rick...I assume you'll be cutting the head off the bolt and use only the shaft...?
Thanks. If I were going to use the bolt, I would cut the head off, yes.

But, I will use the fancy brass one that I made. The shaft that inserts into the jig tang was machined to be a snug slip fit and the shoulder created by the hex brass stock is 1/2" dia., giving a fairly positive - square mounting. I trust it a lot more than a mass produced bolt, which are typically undersize by up to 0.010". The pivot hole through the tang is 0.254". The shaft on the brass pivot pin is 0.2535".

Rick
 
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Thanks for the idea, Rick. It looks like with a little thought, the capability could be added on to edge guides which do not have the tab for the centre pin. Might need to invert the edge guide, in order to clear the workpiece. I am sure @JOAT could come up with something.

I would not be able to achieve the tolerances you quote, but then again I probably would not need to.
 

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Thanks. If I were going to use the bolt, I would cut the head off, yes.

But, I will use the fancy brass one that I made. The shaft that inserts into the jig tang was machined to be a snug slip fit and the shoulder created by the hex brass stock is 1/2" dia., giving a fairly positive - square mounting. I trust it a lot more than a mass produced bolt, which are typically undersize by up to 0.010". The pivot hole through the tang is 0.254". The shaft on the brass pivot pin is 0.2535".

Rick

...can't get better than that...have fun...
 

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All of the posted methods work great, even the Jasper jig that you found in the store. I have used all of them at one time or another, and they all do a good job. Adding the 1/4" pivot pin to your edge guide is yet another good, and cheap, way to cut arcs and circles. Kudos for coming up with a cheap (free) solution.

Bobj3 modified his Jasper jig so he could use it with a router bushing some years ago and posted pictures here. I thought it made the Jasper jig even easier to use, just in case anyone is interested. A search on this site should find it easily.

Charley
 

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Rick, it looks well thought out and as some of said the precision of the tool might be greater than actually required. I do think it was prudent that you did try to hold close tolerances for the tool itself, but please don't get too picky when working with wood to try to hold very close tolerances because you will lose some of the joy woodworking gives you.
 
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Discussion Starter · #10 ·
Rick, it looks well thought out and as some of said the precision of the tool might be greater than actually required. I do think it was prudent that you did try to hold close tolerances for the tool itself, but please don't get too picky when working with wood to try to hold very close tolerances because you will lose some of the joy woodworking gives you.
Thanks, to you and the others, who have commented about the precision being a bit much. I appreciate that it is, where working with wood is concerned. As you allowed, it may be good to have held that for the tool itself. I agree. We'll see how well that translates to actually working with wood.
 

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All of the posted methods work great, even the Jasper jig that you found in the store. I have used all of them at one time or another, and they all do a good job. Adding the 1/4" pivot pin to your edge guide is yet another good, and cheap, way to cut arcs and circles. Kudos for coming up with a cheap (free) solution.

Bobj3 modified his Jasper jig so he could use it with a router bushing some years ago and posted pictures here. I thought it made the Jasper jig even easier to use, just in case anyone is interested. A search on this site should find it easily.

Charley
Yes Charlie, Bob's version was a BIG improvement on mine.
 

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Rick,

The only suggestion that I can make about your router circle jig is to be certain that you have all of the thumb screws good and tight before cutting the circle.

I was using my CRB7 jig and DeWalt 618 router to cut circles from 3/4 cabinet birch ply and my thumb screws were tight, but apparently not tight enough, and my first circle suddenly began to diminish in diameter as I was cutting it. I saved the day by deciding that this piece would now be the smaller of the two diameters that I needed. The smaller diameter circle needed to be 4" in diameter smaller than the large one, and I had luckily been trying to cut the larger one first.

After cranking down on the thumb screws at both ends of each guide rod for each circle setting, my circles in both pieces turned out perfect. They became the two layered lid to attach my Dust Deputy to my metal 20 gallon re-purposed grease barrel.

No matter how good we get at woodworking, there still seems to be a woops every once in a while, and this was one of mine.

Charley
 

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The instructions Pat Warner's router circle jig has pretty much identical instructions for setting the pivot pin to router bit distance - he claims that, with care and experience, the circle diameter can be set within a couple of thousandths. His jig, shown in the attached photo, uses a .185" diameter pin (I believe that this is a section of #13 drill bit) which gives a close but workable fit on a 3/16" drilled hole - you can just make out the pin to the left of the clamp knob. I wish now that I'd thought to ask Pat about making the center hole in the plate for a snug fit on a 3/4" guide bushing - I don't know what the actual hole size is but it's quite a bit larger than the biggest standard size - somewhere in the shop I have a circle guide that I made years ago with a 3/4" center hole; to use, I just mount a 3/4" bushing in the router, drop it in the hole and cut the circle. The router doesn't rotate as you cut the circle and so the power cord doesn't wind itself into a know, no matter how many rotations you make to get to the required depth. Pat's jig is a dream to use, very easy to adjust, and I guess I could modify a guide bushing by shrinking a brass/nylon ring on the OD of a guide bushing and using it that way.
 

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Rick,

Nice first design. I've attached Pat Warner's circle jig which I have found to the be the best out of all the circle jigs I've used. Unfortunately Pat passed away and his web site is unavailable, but I used the Internet Archive to get a previous version.

3/16" or 1/4" dowel pins make for better pivots and are cheap. You're correct about a bit of trial & error on the radius because the router armature and collet have a bit of runout. Also the router bits have a small tolerance.

I copied Pat's design in MDF. I would suggest cast acrylic because it's super handy to see thru the base. My base has seen quite a bit of use and the couple of coats of thinned polyurathane varnish is holding up well. Some paste wax on the bottom helps too. Below are a couple of pics of the build.
 

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The instructions Pat Warner's router circle jig has pretty much identical instructions for setting the pivot pin to router bit distance - he claims that, with care and experience, the circle diameter can be set within a couple of thousandths. His jig, shown in the attached photo, uses a .185" diameter pin (I believe that this is a section of #13 drill bit) which gives a close but workable fit on a 3/16" drilled hole - you can just make out the pin to the left of the clamp knob. I wish now that I'd thought to ask Pat about making the center hole in the plate for a snug fit on a 3/4" guide bushing - I don't know what the actual hole size is but it's quite a bit larger than the biggest standard size - somewhere in the shop I have a circle guide that I made years ago with a 3/4" center hole; to use, I just mount a 3/4" bushing in the router, drop it in the hole and cut the circle. The router doesn't rotate as you cut the circle and so the power cord doesn't wind itself into a know, no matter how many rotations you make to get to the required depth. Pat's jig is a dream to use, very easy to adjust, and I guess I could modify a guide bushing by shrinking a brass/nylon ring on the OD of a guide bushing and using it that way.
Lucky you to have an original. I don't quite understand the 3/4" bushing vs using a 3/4" bit as the OD's are different and how you are doing the setup. That said the Porter Cable guide bushing specs are:
  • Thru hole: 1 3/16"
  • Flange: 1 3/8"

The 1 3/8" counterbore is a bit expensive if you work w/acrylic or jig plate.

And yes, you can set the radius to a couple of thou on first try.
 

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Hi Rick. I made mine out of MDF and it works well. It provides a huge range of circle diameters. Looking at what you did I went back to my trim router accessories and worked out I can produce up to a 13 inch diameter circle with the bits provided with it:shout: Oh well practice I suppose.
Great job mate.
 

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Lucky you to have an original. I don't quite understand the 3/4" bushing vs using a 3/4" bit as the OD's are different and how you are doing the setup. That said the Porter Cable guide bushing specs are:
  • Thru hole: 1 3/16"
  • Flange: 1 3/8"

The 1 3/8" counterbore is a bit expensive if you work w/acrylic or jig plate.

And yes, you can set the radius to a couple of thou on first try.
Sorry, didn't make myself clear. When using a guide bushing on the router mated to the corresponding hole in the circle guide, the router is NOT bolted to the circle guide. What this means is that the router doesn't rotate with the jig as you sweep the circumference of the circle being cut ie the router stays in the same position relative to the operator so the guide bushing is rotating inside the hole in the circle guide. This means that the power cord and vacuum hose, supported from above to stay out of the way, stay in the same relative position and don't end up twisted in a know, no matter how many times you need to go around the part to cut through.

Cutting a circle in plywood is a snap, cutting a circle in wood is somewhat of a problem as, depending on the direction of rotation, some segments are being cut against the grain - the solution then is to cut the circle in 4 segments so that you're always cutting with the grain and don't wind up with chip-out.
 

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What was the advantage of machining(?) the brass hex "head" verses just cutting the threads longer and having a regular nut on both sides? Actually I bet I know after asking, it was probably because the nut that should be fixed might move while loosening the other nut, and that would cause slight variances in the distance the pin protruded.
 

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Discussion Starter · #20 ·
What was the advantage of machining(?) the brass hex "head" verses just cutting the threads longer and having a regular nut on both sides? Actually I bet I know after asking, it was probably because the nut that should be fixed might move while loosening the other nut, and that would cause slight variances in the distance the pin protruded.
A couple reasons. First, it is like why dogs lick their... Because they can...

Kidding aside, I had the brass hex stock and I wanted the pin to be as secure as possible. With nuts on both side the pin can actually be angled. Turning the shoulder on the brass hex stock ensures to a greater degree that the pin will remain perpendicular. Also, I have not looked at it in a while, but I suspect the stock screw can be undersized. My brass pin is a slip-with-no-slop fit. Overkill, but that is how I like doing things.

The way I've made the brass one, there can be no variation in how far the pin protrudes.

Rick
 
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