# Making jig for large radius plywood cuts.



## JohnnyB60 (Jun 15, 2009)

A while back I had asked for advice on making curved cuts on 1/8” plywood http://www.routerforums.com/jigs-fi...-make-flat-curved-pieces-out-1-8-plywood.html and I could not get the router to stay perpendicular with the surface. I finaly gave up and I ended up using my band saw instead. Well I’m not real happy with how it came out using the band saw and I want to do another one only this time with the router.

I recently watched a YouTube video that gave me an idea, Charles Neil Taper Jig - Part 2 - YouTube

Instead of moving the router around the work piece, I’m going to fasten the router to a 4x8 sheet of plywood and rotate the work piece around the router.


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## Cherryville Chuck (Sep 28, 2010)

If you do that keep in mind that you either have to move the piece into the spinng bit, then lock it down when you reach the pivot point or you have to plunge the router on the centered piece.


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## JohnnyB60 (Jun 15, 2009)

Cherryville Chuck said:


> If you do that keep in mind that you either have to move the piece into the spinng bit, then lock it down when you reach the pivot point or you have to plunge the router on the centered piece.


Oh good point. 

I believe in the video the guy mentioned drilling a pilot hole first then set the piece on to the router bit before turning it on.

There is one thing that I’m confused about and that is he mentions “pay attention to the rotation of the bit”. Does it mater which way to go if you are cutting a slot in which the bit is cutting on both sides at once?


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## WillMatney (Oct 6, 2011)

I've never seen any difference in direction for routing slots, but if you're routing an edge, there is.

There was a excellent version of a radius circle-cutter jig like you're wanting in the Woodsmith Router Workshop book. It was made out of plywood, and all of it 3/4 stock if I remember, but that can be changed. The only plastic they used was the knobs for adjustment.

If you're still intending on using the Rotozip, then you could make a clamp with the plywood to clamp around the round nose of the router, and hold it vertical.

Since that's 1/8" plywood, you might be better using a 1/16" bit. I know Freud makes one. Also, you might have to try a spiral bit, I'm not sure due to the thinness of the plywood.


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## JohnnyB60 (Jun 15, 2009)

WillMatney said:


> I've never seen any difference in direction for routing slots, but if you're routing an edge, there is.
> 
> There was a excellent version of a radius circle-cutter jig like you're wanting in the Woodsmith Router Workshop book. It was made out of plywood, and all of it 3/4 stock if I remember, but that can be changed. The only plastic they used was the knobs for adjustment.
> 
> ...


I'm not going to use the RotoZip. I'm planing on using my Porter-Cable Fixed-Base Router and I'm also planing on cutting 3 at a time stacked on top of each other.

I would like to see that Woodsmith Router radius circle-cutter jig


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## bobj3 (Jan 17, 2006)

Hi John

Here's some of the WoodSmith items I did not dig to deep into them but you may want to check them out ,you may find what you need.

Free Woodworking Plans, Downloads and Videos - Woodsmith Shop

http://www.woodsmithshop.com/download/105/105-circlejig.pdf
Router Circle Cutting Jig for Woodworking
Woodsmith Magazine Index

Shop Jig Plans - Build Table Saw Jigs, Router Jigs, Boxjoint Jig
Workshop Projects

http://www.routerforums.com/general-routing/28190-adjustable-arc-circle-jig-plans-needed.html

http://download.plansnow.com/plansnow-router-circle-jig.pdf

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JohnnyB60 said:


> I'm not going to use the RotoZip. I'm planing on using my Porter-Cable Fixed-Base Router and I'm also planing on cutting 3 at a time stacked on top of each other.
> 
> I would like to see that Woodsmith Router radius circle-cutter jig


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## WillMatney (Oct 6, 2011)

I think you can still do a google search for the book in mention, and find a place to download a copy of it.

Do a search for: Woodsmith Router Workshop.pdf

The file should be about 11 megs in size.


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## Cherryville Chuck (Sep 28, 2010)

JohnnyB60 said:


> Oh good point.
> 
> I believe in the video the guy mentioned drilling a pilot hole first then set the piece on to the router bit before turning it on.
> 
> ...


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## JohnnyB60 (Jun 15, 2009)

Cherryville Chuck said:


> As a router bit turns, you should be pushing your piece into the cutter face of the bit. If you go the other way, the bit will "climb cut" and your piece will try to self feed into the bit which can cause very bad things to happen. If you are profiling an edge onto a board, for an example, and the router is trying to pull you along, you are going the wrong way.
> Where both edges are cutting the forces should theoretically balance out but there might be a little bit of a problem at the very end of the cut as the outer piece is ready to part off. I would still feed towards the cutter face just to be sure.


See this is what I’m confused about because there is only one pilot hole and there is only one way to go. Even if the pilot hole is on the other end of the radius there is still only one way to go.


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## jlord (Nov 16, 2009)

JohnnyB60 said:


> A while back I had asked for advice on making curved cuts on 1/8” plywood http://www.routerforums.com/jigs-fi...-make-flat-curved-pieces-out-1-8-plywood.html and I could not get the router to stay perpendicular with the surface. I finaly gave up and I ended up using my band saw instead. Well I’m not real happy with how it came out using the band saw and I want to do another one only this time with the router.
> 
> I recently watched a YouTube video that gave me an idea, Charles Neil Taper Jig - Part 2 - YouTube
> 
> Instead of moving the router around the work piece, I’m going to fasten the router to a 4x8 sheet of plywood and rotate the work piece around the router.


Making a trammel arm for your router is easy with some scrap material. I used 1/4" for this trammel & mounted a PC690 router. I make all markings for measurements before drilling any holes. I like mark one side of the jig for inside radius & the other side for outside radius. I sue a double head nail or finish nail for a pivot point. I like to use a 1/2" straight bit for easy measurements for different radius's. I used this same trammel for a 60" round table top. For thick material just increase the depth on each pass. For 3/4" ply such as in pictures I did 3 passes. Cost can be as cheap as the type of scrap you have lying around.


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## JohnnyB60 (Jun 15, 2009)

jlord said:


> Making a trammel arm for your router is easy with some scrap material. I used 1/4" for this trammel & mounted a PC690 router. I make all markings for measurements before drilling any holes. I like mark one side of the jig for inside radius & the other side for outside radius. I sue a double head nail or finish nail for a pivot point. I like to use a 1/2" straight bit for easy measurements for different radius's. I used this same trammel for a 60" round table top. For thick material just increase the depth on each pass. For 3/4" ply such as in pictures I did 3 passes. Cost can be as cheap as the type of scrap you have lying around.


Thanks James, I like it and I’m definitely going to make one of those for future projects. 

Well I’ve been thinking long and hard about whether to have to router moving around the work piece or have the work piece rotate around the router and I decided that I’m going to fix the router position on a 4x8 sheet of plywood and move the work piece. The reason being that by rotating the work piece, I don’t have to worry about support or cutting something with the router. 

When I tried to do this before the a huge hunk of corner had to hang out over my table so that I didn’t cut my table in half and the weight of it was difficult to support as I was rotating the router. The radius of my cut is a 20” half circle.. 

Just to give you an idea of what I’m making here is a photo of the one I already made with the band saw and its acceptable, but I just don’t like that it’s not perfect. I had to free hand cut on the band saw and the curves are a little rough. I tried to sand it but the curve is not exact to my specifications.


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## JOAT (Apr 9, 2010)

I do it what I consider the simple way. I make as perfect a original as I can, in 1/2" plywood - doesn't matter if the final product is 1/8", 1/2", 3/4", or what, the original is always 1/2", because I use that a lot. Once I have that, I glue it to another 1/2" piece, making 1" and when the glue is dry use the formed piece to route the send out, so I wind up with a 1" thick master. Drill pilot holes for thin nails, then tack the piece to be routed to be base, then rout with a pattern bit. I prefer one layer at a time, but 2 or three are possible, if you take your time, and watch the nails to be sure they don't vibrate loose and popup. That way all your routed pieces are exactly the same. And yes, feed from right to left. I do some pretty intricate pieces that way, and they all come out just the same.


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## JohnnyB60 (Jun 15, 2009)

JOAT said:


> I do it what I consider the simple way. I make as perfect a original as I can, in 1/2" plywood - doesn't matter if the final product is 1/8", 1/2", 3/4", or what, the original is always 1/2", because I use that a lot. Once I have that, I glue it to another 1/2" piece, making 1" and when the glue is dry use the formed piece to route the send out, so I wind up with a 1" thick master. Drill pilot holes for thin nails, then tack the piece to be routed to be base, then rout with a pattern bit. I prefer one layer at a time, but 2 or three are possible, if you take your time, and watch the nails to be sure they don't vibrate loose and popup. That way all your routed pieces are exactly the same. And yes, feed from right to left. I do some pretty intricate pieces that way, and they all come out just the same.


I did think about that and that would probably be the way to do it, but I’m just so dang frugal that I just can’t stand wasting a good piece of plywood. Although I was thinking today that I should just buy 6 sheets of plywood, stack them up on top of each other, and cut 12 total pieces instead of 24. 

That way I would not have to align them in the middle, which was a problem the first time I did it. Somehow when I did it on the band saw I lost my reference marks and cut the ends of the curve out of square. I was able to fill in and make it right, but it was a pain.

I have to check out how much scrap is left over 1st. I use 1/8 plywood a lot and if I’ve enough large pieces to work with then I’ll do it.


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## Cherryville Chuck (Sep 28, 2010)

If a router is upright, feed from left to right. If it is mounted upside down, feed from right to left. If you are not sure, look at the cutter on the bit. The cutter has a face and the bevel is on the backside. As a rule, always feed towards the face of the cutter.


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## JohnnyB60 (Jun 15, 2009)

Cherryville Chuck said:


> If a router is upright, feed from left to right. If it is mounted upside down, feed from right to left. If you are not sure, look at the cutter on the bit. The cutter has a face and the bevel is on the backside. As a rule, always feed towards the face of the cutter.


Thanks, but just out of curiosity,what about up cut and down cut? Does that mater?


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## Cherryville Chuck (Sep 28, 2010)

It won't change feed direction. Up cut is recommended if you are not cutting all the way through because there is nowhere for the cuttings to go otherwise. Down cut is okay if you are all the way thru, it is less likely to tearout on the top edges of the face you are working on.


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## bobj3 (Jan 17, 2006)

Here's a good one to use.

67-314 Onsrud Double Edge Solid Carbide Compression Spiral Router Bit | eBay

Compression Up/Down Spiral Router Bits

This 2 flute solid carbide bit is needed to get clean, chip-free and splinter-free cuts in composite sheet goods such as Melamine or 2-sided Formica/Laminates and veneered plywood. 
The Up-shear/Down-shear design of the bit cuts toward the center of the sheet from both sides at once, saving time and eliminating waste.


OR

http://www.ebay.com/itm/57-281-Onsr...863999443?pt=Routers_Bits&hash=item4ab4fc15d3

==


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## KenBee (Jan 1, 2011)

If you haven't noticed already something to keep in mind about the Onsrud Compression Bit Bob linked to is the fact it is a 3/8 diameter shank. I managed to overlook that detail when I ordered a couple of bits from Onsrud off Ebay but Fred of Onsrud was kind enough the correct my mistake before they shipped and send the correct bit to me. 

That is a great buy for a compression bit even with a 3/8 diameter shank. If you don't have a 3/8 collet you can buy a 1/2 to 3/8 reducer collet from MLCS for $4.00.


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## JohnnyB60 (Jun 15, 2009)

Ken Bee said:


> If you haven't noticed already something to keep in mind about the Onsrud Compression Bit Bob linked to is the fact it is a 3/8 diameter shank. I managed to overlook that detail when I ordered a couple of bits from Onsrud off Ebay but Fred of Onsrud was kind enough the correct my mistake before they shipped and send the correct bit to me.
> 
> That is a great buy for a compression bit even with a 3/8 diameter shank. If you don't have a 3/8 collet you can buy a 1/2 to 3/8 reducer collet from MLCS for $4.00.


Thanks, I did notice that and was wondering how that worked because I've never seen a 3/8" collet before and I wasn't sure how it worked.

Anyway I ordered a 1/8" Spiral Upcut #5141 from MLCS last night


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## JOAT (Apr 9, 2010)

JohnnyB60 said:


> I did think about that and that would probably be the way to do it, but I’m just so dang frugal that I just can’t stand wasting a good piece of plywood.
> I use 1/8 plywood a lot and if I’ve enough large pieces to work with then I’ll do it.


:no: That's one of the nice things about the way I do it, you don't need to waste a good piece of plywood. Of course, my patterns are a max of maybe 9" for a lot of my work, so I don't need more that a piece or three of scrap to make them. Being small tho I don't hesitate to use new plywood if I have to. However, I do make some items considerably larger. So, sometimes wing it.

If you want to use just scrap, and the pieces are all too small, no prob. Butt glue a batch together. Then you carefully cut out the exact pattern you want, have to be a bit careful because if you've got a weak glue joint you could pop it, but then you'd normally be able to glue and clamp it, but you'd lose time. Once you get that done, you can use scrap on top of that, overlapping all joints, then when the glue dries, rout that, so you still wind up with a 1" master pattern. If you're not sure of the strength of it, you can do it again with yet another layer of scraps. This is all with 1/2" plywood, you could do the same thing with 1/8", it would just mean you'd wind up with more layers, and it would take longer for the glue to dry. I have a couple of masters done just that way, and they work as well as the solid plywood ones. However - there is always a however - I normally use that method when working on a pattern that I am making changes in, once I have all the changes made I usually (not always) make a new master. 

I hope that's all clear to you, it is to me. :yes4: It really works well for me.
If you have questions feel free to ask.


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## JohnnyB60 (Jun 15, 2009)

JOAT said:


> :no: That's one of the nice things about the way I do it, you don't need to waste a good piece of plywood. Of course, my patterns are a max of maybe 9" for a lot of my work, so I don't need more that a piece or three of scrap to make them. Being small tho I don't hesitate to use new plywood if I have to. However, I do make some items considerably larger. .........


Well the more I think about it the more I like your idea. I’ve been trying to figure out how to rotate these pieces around accurately on a table without breaking them to make a single piece as shown below. 










Also I made a mistake earlier when I said I needed to make 12 when I actually need to make 24, I need to make 12 of one size and 12 more with the same radius but ½” wider


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## JohnnyB60 (Jun 15, 2009)

*Looks like the trammel arm is the best way to do this.*

Well I’ve been drawing this as many ways as I can think of and the only way to do this is by using the trammel arm James suggested. I’ll be able to just use 2 sheets instead of 12. Only thing is that have to cut each piece at the end of each curve and splice in straight pieces in between the curves. I’m going to have to figure out a system to acutely cut each piece square.

So I guess I’ll be building at trammel arm this week end, :yes4:


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## JOAT (Apr 9, 2010)

JohnnyB60 said:


> Well the more I think about it the more I like your idea. I’ve been trying to figure out how to rotate these pieces around accurately on a table without breaking them to make a single piece as shown below.


I do a couple of pieces that have narrow parts. With a 1" thick master I have no problems about moving the pieces accurately around the router bit, and no worries about them breaking. 

I see in your other post you are thinking to make your parts in three pieces, and splice a straight piece in between the ends. In a case like that I'd just make three separate masters, none less than 3" thick. But, it's your choice, whatever way you feel comfortable with. 

If you have any questions about my method, feel free to e-mail, or message, me.


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