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post #1 of 19 (permalink) Old 11-03-2011, 10:13 PM Thread Starter
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Default Circle trimming

I am trying to make some 4 section trays to give as xmas gifts and I am trying to figure out a way to get them to be perfectly circular. My original idea was to draw a line to be the outside edge of the circle, then bandsaw and sand up to it, but I tried it and the results weren't very good.

I also thought about using a circle jig on the bandsaw, haven't tried that, but I don't think it would be as good as I could do with a router.

What I think I would like to do is first bandsaw staying close to but outside of the line, then use some sort of a jig combined with a router and a straight bit to do the final trim. I think this is probably as close to perfect as I can realistically hope to get.

Now my question is how to go about doing this. Most of the circle cutting jigs I have seen want you to put a hole for a guide pin in the work, but it seems like those are designed with the inside of the circle being the waste piece. In my application, the inside of the circle is the part I want to keep. I know I could flip the workpiece upside down and drill a shallow hole there, but I'm not sure how to go about getting it exactly centered.

I know you can use a square to find the center of a circle, but that requires you to have a perfect circle to start with. I also know I could start with a square blank and mark the center on both sides, but the template that I'm using doesn't have a center marker, so I'm not sure how to go about getting the template exactly centered even if I know where the center of the workpiece is.

So my thought about how to actually trim the circle is to just use a simple piece of MDF about the same length as the diameter of the circle. I would drill a hole at one end and mount the router so the bit protrudes through that hole, then use a pin to attach the MDF to the center point on the workpiece. Then plunge down and work all the way around. Am I on the right track?

Any info or suggestions on any of the questions I asked would be much appreciated.
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post #2 of 19 (permalink) Old 11-04-2011, 05:24 AM
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Fred,
This is probably what you mean, I have used this very successfully many times, you do not need to make hole through for the centre pin, just use a small panel pin and don't go in too far,
Cut one decent one and sand the edges, then use as a pattern, attach with double sided tape or hot melt glue to a piece of board , then trim within a mm. or so and finish with a flush trim bit, this way you will have exact replicas as often as you wish.

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post #3 of 19 (permalink) Old 11-04-2011, 10:19 AM
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Originally Posted by derek willis View Post
Fred,
This is probably what you mean, I have used this very successfully many times, you do not need to make hole through for the centre pin, just use a small panel pin and don't go in too far,
Cut one decent one and sand the edges, then use as a pattern, attach with double sided tape or hot melt glue to a piece of board , then trim within a mm. or so and finish with a flush trim bit, this way you will have exact replicas as often as you wish.

circle cutter.jpg (1.5 KB)
This shot is just to illustrate Derek's suggested method. For the male template it matters not what size hole the circle jig requires. so far as the photo goes, just forget the pins and wing nut, double sided tape is used to hold the material to the template
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post #4 of 19 (permalink) Old 11-04-2011, 10:39 AM
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Hi Harry

I think I will stick to the safe way with the plunge router no center holes needed

Trend Pivot Frame Jig
Trend Pivot Frame Jig - YouTube

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post #5 of 19 (permalink) Old 11-04-2011, 10:49 AM
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There's nothing wrong with that method Bob except that you still need to make a template and either have engineering skills to make the jig or spend big dollars buying one. Derek and I, and I thought you also didn't have the funds to spend BIG in our early days of woodworking!

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post #6 of 19 (permalink) Old 11-04-2011, 11:31 AM
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HI Harry

I made the Trend Pivot Frame Jig for peanuts. if I recall it was about 10.oo bucks or less and no template needed with this type of jig..once you have the jig made all that's need to is to cut out a hole in some scrap stock, that's it the norm..that the jig can do easy// >> just slip off the one beam and cut the cir.out..the threaded rod in the center of the beam is not needed the norm it's for the fine adjustment..and a locking device..so to speak..the Trend T4 router has a 6mm hole in the base plate just for the rod to fit in, I didn't have any 6mm rod so I used some 1/4-20 rod and rethreaded it to 6mm about 1/2" long... easy stuff..


Pop bottle caps for knobs and some rod from any hardware store.. easy stuff..the beams can be anything you have in the shop.


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Quote:
Originally Posted by harrysin View Post
There's nothing wrong with that method Bob except that you still need to make a template and either have engineering skills to make the jig or spend big dollars buying one. Derek and I, and I thought you also didn't have the funds to spend BIG in our early days of woodworking!

ping


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Last edited by bobj3; 11-04-2011 at 12:13 PM.
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post #7 of 19 (permalink) Old 11-04-2011, 12:30 PM
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Quote:
Originally Posted by Vrtigo1 View Post
I am trying to make some 4 section trays to give as xmas gifts and I am trying to figure out a way to get them to be perfectly circular. My original idea was to draw a line to be the outside edge of the circle, then bandsaw and sand up to it, but I tried it and the results weren't very good.

I also thought about using a circle jig on the bandsaw, haven't tried that, but I don't think it would be as good as I could do with a router.

What I think I would like to do is first bandsaw staying close to but outside of the line, then use some sort of a jig combined with a router and a straight bit to do the final trim. I think this is probably as close to perfect as I can realistically hope to get.

Now my question is how to go about doing this. Most of the circle cutting jigs I have seen want you to put a hole for a guide pin in the work, but it seems like those are designed with the inside of the circle being the waste piece. In my application, the inside of the circle is the part I want to keep. I know I could flip the workpiece upside down and drill a shallow hole there, but I'm not sure how to go about getting it exactly centered.

I know you can use a square to find the center of a circle, but that requires you to have a perfect circle to start with. I also know I could start with a square blank and mark the center on both sides, but the template that I'm using doesn't have a center marker, so I'm not sure how to go about getting the template exactly centered even if I know where the center of the workpiece is.

So my thought about how to actually trim the circle is to just use a simple piece of MDF about the same length as the diameter of the circle. I would drill a hole at one end and mount the router so the bit protrudes through that hole, then use a pin to attach the MDF to the center point on the workpiece. Then plunge down and work all the way around. Am I on the right track?

Any info or suggestions on any of the questions I asked would be much appreciated.
You can make a trammel out of mdf as you pointed out. You do not need to cut the material close to your circle then try to center it over your cut out. The bit will plunge thru the material centering your circle off the pivot. Just make sure your bit is in contact all the way around. You can mount your trammel with a finish nail & route from the bottom. Then when you turn your piece over there will be no hole.

I made this quikie trammel out of 1/4" mdf to cut a 60" round table top. Rip the mdf as wide as the base plate on the router (just makes it easier to center up router). Drew a line down the center of the length to use as my measurement. Drew another cross reference line down from one end where the center of the bit will be. Drilled a hole large enough for the bit to clear at this intersecting point. Took the base plate off & lined it up flush with the sides & one end. Your hole should be centered in the base plate. Counter sink screw holes & use original base plate srcews to fasten it to trammel.

Used base plate as template for mounting holes. Mounted router to trammel without base plate. Measured down center line from bit to size circle I wanted. (Far side of bit for an inside circumference. Close side of bit for outside circumference). Measure down your line & use a finish nail for your piviot. This quik trammel was made for a Porter Cable 690 router witch is not a plunge router. For thick material make a few passes adjusting deeper for each pass.

This is one off many ways to do the same task.
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post #8 of 19 (permalink) Old 11-04-2011, 02:12 PM
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This shot is just to illustrate Derek's suggested method. For the male template it matters not what size hole the circle jig requires. so far as the photo goes, just forget the pins and wing nut, double sided tape is used to hold the material to the template
Thank-you, Harry for elaborating on my post, I don't know what all the kerfuffle that followed is all about, this site is to assist people, not to brag, and I'm sure they all don't have bottomless pockets that contain $500;00 dollars or so each time they go out.



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post #9 of 19 (permalink) Old 11-04-2011, 02:34 PM
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Hi

For me ,I'm not bragging by the way what did you do with all the money you made over a life time of hard work you did... just asking..

I hope this not bragging , but I started working at 14 and made it a hard fast rule, I always paid me 1st, it may have only been 20.oo bucks a week at times but it always got put into the jar for me and only me.

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Quote:
Originally Posted by derek willis View Post
Thank-you, Harry for elaborating on my post, I don't know what all the kerfuffle that followed is all about, this site is to assist people, not to brag, and I'm sure they all don't have bottomless pockets that contain $500;00 dollars or so each time they go out.



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Last edited by bobj3; 11-04-2011 at 02:52 PM.
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post #10 of 19 (permalink) Old 11-05-2011, 05:28 AM
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Hi

For me ,I'm not bragging by the way what did you do with all the money you made over a life time of hard work you did... just asking..

I hope this not bragging , but I started working at 14 and made it a hard fast rule, I always paid me 1st, it may have only been 20.oo bucks a week at times but it always got put into the jar for me and only me.

===


===
Frankly, I don't see what buisness it is of yours, but, I worked, raised a family, had a buisness buying land and developing property, a massive slump ruined me with a lot of property having to be sold at less than cost, this has happened again in recent times to many people and buisnesses, but if you haven't taken a chance you have never lived.



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