Circle cutting

[JR]

I'm making progress on my Patio Cart project. I'm pretty much down the wheels now, which has been looming for weels. The project plan calls for a pretty intricate assembly of four parts mitered together and four dowel-spokes driven into a hub. The mitered parts are assembled with screws, cut into a circle, then unscrewed for final assembly with hub and spokes. Here's the plan.



I think this is the suggested process:

• Cut the four mitered rim pieces
• Drive the holes for the spokes into the rim pieces while they're still square. Also drive holes into the hub blank at this point.
• Assemble the four rim pieces with screws at the outside corners, then use a circle-cutting jig cut the inside rim of the wheel.
• Make the hub into a circle.
• Then you dis-assemble the four pieces, reassemble with spokes and hub with glue.
• Cut the outside of the wheel.

So the question is how to cut the circles. I've never done a jig for this before and don't have any suggestions at hand.

As I'm typing this it occured to me that I could double-stick tape a piece of 1/4" plywood to the assembled four pieces, driving a hole in the center of that to act as a pivot. Would I mount that to another piece of plywood for clamping to the bandsaw table?

Any suggestions would be appreciated.

JR

[LCHIEN]

Perfect circles with a router.

if you can put a center pivot in, I find it real easy to use a scrap piece of 1x4 or plywood about 10-12 inches for the 11" dia circle you want to cut.

For the pivot, use a finsih nail and a 1/16th hole in the 2x4. Or, a 1/4" hole and a temporary 1/4 dowel peg at the center of your workpiece.
fasten the workpiece to the workbench with double stick tape or otherwise secure it so it won't move.

Put a matching hole "A" close to one end of the 1x4, maybe 1" from the end, centered.

Put a 1/2" template guide bushing on your router.
Put a 1/4" spiral upcut bit (or a 1/4" straight bit if you don't have the spiral upcut) into the router.
Drill a 1/2" hole "B" in the 1x4 so that the center to center distance to the hole A is the RADIUS (half the diameter) plus 1/8th inch.
Put the hole A over the pivot.
Put the router into Hole B, lower the bit until it will cut ~1/8" into the workpiece (e.g. 1/8th plus the 1x4 thickness from the baseplate). Turn on the router and holding the two handles constantly oriented the same way to you, rotate the router around the pivot. As the router makes one circle around the workpiece, the router will NOT rotate with respect to you (hold your hands steady, don't cross them over or anything) but will rotate once around the workpiece.

Then lower the bit 1/8th inch and repeat as many times as it takes to go through. Oh yeah, you need to do this on a sacrificial surface, on the last pass it will score your workbench otherwise.

Perfect circles.

You can buy these jigs with a number of holes predrilled but they cost a small fortune and this works every bit as well.

[JR]

Uh-huh. I think I get it. A sort of tramel set up for the right radius.

You've got my thinking cap on now, Loring. Thanks.

JR

[Pappy]

If you have a router table, double stick tape patterns to the pieces, rough cut them on the band saw and finish them off on the router table with a patter following bit.

[LCHIEN]

you can make one the way I suggest and the remaining three like pappy suggests, its a little less labor that way (1 router pass per wheeel vs. maybe 6 passes per wheel) but my method will give you the perfect pattern to use, if you don't have one.

And yeah, I guess you could call it a tramel - it basically a board with two holes in it. Wide enuf to support the router.

[LarryG]

Another method, similar to Loring's, is to make an oversize, custom subbase for your router (1/2" MDF is an ideal material). The shape of the custom subbase doesn't matter; it only need be large enough to cover the radii you need. Make one large(ish) hole for the bit opening and then drill 1/4" holes at the appropriate radii from the center hole, to receive the pivot pin. When this particular project is finished, remove the subbase and store it with your other jigs. Next time you need curves or circles with relatively small radii, just drill a new pivot hole at the appropriate location.

I prefer this method because there's only one pivot point; i.e., the subbase moves with the router rather than being a separate piece that's floating freely between the router and the workpiece.

Just in case I'm not being clear, this custom baseplate from Pat Warner illustrates the principle.

[JR]

Ok, it's starting to click now.

I've been using a pattern bit on this project for the first time. (There's plenty of "firsts" on this project!). I only have the one router, and it's fixed base, so i'm going to have to noodle through how to do the first circle. Once having done that, though, I should be golden.

Larry, thanks for the pics. Between those and Loring's description I think I can rig something up.

Thanks, guys.

JR

[LCHIEN]

Another method, similar to Loring's, is to make an oversize, custom subbase for your router (1/2" MDF is an ideal material). The shape of the custom subbase doesn't matter; it only need be large enough to cover the radii you need. Make one large(ish) hole for the bit opening and then drill 1/4" holes at the appropriate radii from the center hole, to receive the pivot pin. When this particular project is finished, remove the subbase and store it with your other jigs. Next time you need curves or circles with relatively small radii, just drill a new pivot hole at the appropriate location.

I prefer this method because there's only one pivot point; i.e., the subbase moves with the router rather than being a separate piece that's floating freely between the router and the workpiece.

Just in case I'm not being clear, this custom baseplate from Pat Warner illustrates the principle.

Compared to my method, this method is
1) more complex (you have to mount the router vs. a 1/2" hole)
2) makes the router spin around relative to you, I think its harder to hold and it twists up the cord
3) on the plus side, this mothod will center perfectly around the pivot, in my method, if the bit is slightly offcenter in the guide bushing then you'll get a slight concentricity error.
4) either way, you can add new pivot holes as you wish, they don't need to be perfectly on the center line of the jig, slightly offset allows close spacing of pivots. mine is saved on a hook on the wall. I rounded off the corners and the edges to lessen any scratching.

[LarryG]

I only have the one router

Oh, the humanity ...

and it's fixed base

Well, now you have the perfect, iron-clad, honey-don't-argue-with-me, I-really-need-this-tool excu^H^H^H^H reason to buy a plunge router. She wants a patio cart, you gotta have a plunge router. End of discussion.

Seriously ... having only a fixed-base router would definitely be the one fly in this particular jar of ointment. For the outer circle you can position the workpiece such that the cut begins right at a tangent point, but obviously that's not possible for the inner circle. Best approach would probably be to drill a thru-hole, the same size as the router bit, at exactly the required radius and start each incremental pass with the bit inserted into this hole.

EDIT: The above applies whether you use Loring's method or mine. And Loring, yes, your method is marginally faster since the subbase doesn't have to be attached to the router. Your method will work fine, but as stated I personally prefer the one I use because there's only one moving part, and less chance of a slip messing up an expensive piece of wood. I've not found cord-twisting or the change in handle orientation to be a problem. One of those YMMV things, I guess.

EDIT2: JR, Pat Warner mentions cutting the circle most of the way through and removing the last bit of flash as a separate operation. Since the "hole" in your "donut" will be scrap, you can cut all the way through, BUT be sure this center scrap piece is securely attached to the sacrificial carrier ... otherwise, when the cut completes, the router could slip and the bit chew into your finished piece.

EDIT3: JR, I have this episode of NYW on tape at home, and if memory serves Nahm cut out the hub using a bandsaw or jigsaw and then faired it round using a disc sander. I could be wrong but I don't recall him using the router to make this part.

[LCHIEN]

A plunge router works well for this, BUT, it works equally well using a fixed base router, since the depth is only 1/8 per pass, it's easy to start the router tilted slightly out and drop it in. With the jig you have perfect registration so there won't be any wallowing out at the entry point.

If you are saving the outside then its important to fasten the inside and the outside both to the table with double-stick tape otherwise when the inside is cut free the router will no longer be fixed with respect to the outside and you stand to gouge it if the inside or the outside moves.
It's hard to gouge the inside circle piece because the router is constrained by the jig at a constant distance.

You can cut, like Larry suggests, to a very thin piece before breaking through, then separate with a knife and sand off the edges to avoid damaging the table and having the pieces come loose. Still you should have a protective something underneath (cardboard?), just in case.

[Stytooner]

At the end of the day, would it be cheaper and just as appropriate to buy some HF wheels and tires?
They are dirt cheap and will outlast wooden wheels.
I do feel this thread does highlight the way to cut wooden wheels. Its just in this day and age, is it practical?

[JR]

Oh, the humanity ...

Well, now you have the perfect, iron-clad, honey-don't-argue-with-me, I-really-need-this-tool excu^H^H^H^H reason to buy a plunge router. She wants a patio cart, you gotta have a plunge router. End of discussion.

If only it were that clear. Actually, the project is a wedding gift for my niece. Apparently everything I've spent so far on mahogany and a few blades and bits has been an inappropriately expensive alternative to the $99 patio cart available at the local hardware store. There's no new 2-1/2 hp three base kit in my immediate future.

I'm going to have to tough it out with Loring's 1/8" drop kick technique. The wheel edges get roundovers in the end anyway, so any slop resulting from the drop in should get erased.

Details of a "trammel" to follow, but a lot of good ideas have been presented.

JR

[JR]

At the end of the day, would it be cheaper and just as appropriate to buy some HF wheels and tires?

A perfectly valid question, Lee. I'll admit to being a bit obsessed by the wooden wheel concept. I mean it's as much a problem to be solved as it is a poject to be built at this point. I suspect I'm not the first woodworker to get hung up like that.

So, I've actually been to HF and examined the wheels there. They're just not going to cut it, unless I hit a brick wall on the alternatives. This thing is made of mahogany, with some nice atributes that make the old white plastic wheels unacceptable. I think the first alternative to the wheels in the plan will be to make "ox-cart" wheels in which I'd just glue up a block, cut it into circle and drive an axle hole through it.

BTW - Of course the cart on MY patio is made of redwood 2-by stock has HF wheels...

JR

[LarryG]

If it were my project (which, of course, it's not), I could go either way on the wheels, I guess. When I watched Nahm build this on NYW, it occured to me even then that he was going to a h3ll of a lot of trouble just to prove that the whole thing could be made out of wood ... and especially the parts that will take the most abuse, be most exposed to water if left outside, etc. For my own cart, I might do it. For a gift for someone else, probably not unless I knew for certain that someone else would be fully appreciative of the effort that went into the wheels' creation. (IOW, a breezy, "Oh, look, the wheels are made of wood, too!" wouldn't cut it.)

As regards alternatives, you might consider gluing up the wheels using four pieces as the plans show, and then using your router to relieve the hub area with some sort of faux spoke design. That is, like ox cart wheels, but fancy ox cart wheels.