Improved Router Circle Cutter (pics)

[vinceb]

Or at least compared to my last attempt it's improved. I was about to order a working one and read some comments and some of the issues were things I had trouble with already, so why pay $$ and still have issues? Maybe this will be helpful to someone, so far I think it will take care of my circle cutting needs for the foreseeable future.

Problems I saw with existing commercial designs/my old design...
1. Can't see pin under router base, hard to ring right hole (Jasper)
2. Can't cut small enough, large enough, etc., designs where pin can't get under base not very useful for speakers. Or buy a bunch of hole saws just for this = expensive.
3. Pin is removeable or is a drill bit (my old design, drill then unchuck and use the drill bit as pin) or other annoyance.
4. Limited hole diameter increments (Jasper - 1/16").
5. Accuracy/calibration issues/questions (Router Buddy).
6. Expensive.

Nice features of my new design...
1. Fixed pin that drops into work so it's easy and no doubt where to stick it.
2. 2" to 20" holes.
3. Infinitely adjustable, calibrateable (is that a word?), and hopefully accurate. And hopefully reasonably repeatable.
4. Built in ruler.
5. Cheap and pretty easy to build. Even if you bought everything from scratch it would be about $20, and I had almost everything on hand.
6. Keeps calibration when removed (by design anyway).

Possible issues/annoyances:
1. A bit of flex side to side between pin and base of router, probably not enough to matter but might have some slight effect on roundness of hole. Might be alleviated by fixing where the aluminum bar slides through the calibration bracket side to side. Probably not going to worry with it.
2. A bit fiddly to adjust but not too bad, screwing the nuts in and out. They kind of need a nip from a wrench to stay put.
3. Math to set up cuts when not using a 1/4" bit, but isn't this fairly an issue for the other setups too?

On to the pics, man I love pics!



Top View, on the left is the fixed angle bracket where calibration is made and dimensions are read. The ruler is a $0.99 tape measure epoxied to the aluminum bar. That's 1.5" by 1/8" aluminum bar, 5/8" all thread, 1/16" aluminum angle bracket, and an 1x3" oak hardwood block drilled 11/32" for the all thread. Note the right end of the bar is doubled and drilled/tapped for the pin. Dimension adjustment is by moving the lock nuts around the oak block. I calibrated for a 1/4" bit and made notes for quick reference for other bit sizes. I put +/- allowance on the pic, but really it's always minus some amount for larger bit sizes.




Close of the angle bracket where you calibrate, read size. Filed down the edge to minimize the shadow making it hard to read the ruler.




The oak block, to which the flat aluminum is screwed from the bottom. There is a 1/4" thick block between the oak and the aluminum that can't be seen here.




The end of the all threads going in to the router base. I don't know if most routers have this but I understand the Porter Cable is pretty much industry standard so maybe this or a modified version will work for others. Note the pins that stop the all thread in the right place. This is so that the cutter can be removed and replaced without blowing calibration, hopefully. The pins are 6 penny nails through 3/32 holes drilled through the all thread. File a flat before drilling to make it easier. Cut the nail with a dremel, then squeezed the middle flat with vise-grips so it had to be tapped in tight with a hammer. Check to make sure they are tight, should stay forever.




Finally the business end, the pin is a 1/4" bolt cut off with about 1/4" of thread remaining, the aluminum is doubled up on top with a small piece to make 1/4" thick bar, glued with epoxy, then drilled and tapped for the pin. Make sure and put Lock-tite on this as well or like me you'll have it unscrew in the work sooner or later. Note the screws holding the oak to the bar and you can just see the 1/4" shim between the two. Glued the screws in with some wood glue. Also note the router base that is cut to allow the aluminum to slide up close for small radius holes. This could be made from 1/4" ply but I had a spare base so there it is.




Bottom view.




Here I set up for a 7-3/16" cut using a 3/4" bit.
So that's 7-3/16" divided by 2 = 3-19/32"

Now minus 1/4" for the bit (since it's larger than 1/4" which is what we're calibrated for) = 3-11/32"

I set it up and made a cut, then measured and re-adjusted the angle bar. Note the lock-tite on the calibration nuts so they don't come out of whack. Can still be adjusted, just requires tools.

[---k---]

Nice work. So how long did it take you to build?

[ripcard]

Very interesting design. You mention a little side play. Do you think this is a function of the wood or the allthread rods flexing slightly because of their length? I can see this being great for larger circles but do you think it might be a little unwieldly for smaller ones? Maybe a smaller version for 2" to 10" and that one for 10" to 20". That would allow the bar to be shorter thus making it easier to swing around. Just some thoughts. Nice work though. :T I really like the concept.

[vinceb]

Thanks guys!

It's hard to say how long since probably half the time was head-scratching, even though I knew what I wanted before 'construction' began, the alignment of the pieces particularly in the 'flat' dimension wasn't worked out. I would say 3-4 hours including on-the-fly re-engineering.

I thought it might be unwieldy, or at least large-radiused when spinning it around (make sense? hits you when coming around...) BUT in use it's not bad at all. The unwieldy part would have to be that it would help to have a flat surface to stick it on when not in use instead of my usual precarious sawhorses. In use while cutting, it's fine, it would almost be handy to have a handle on the calibration angle iron to pull it around, it's kind of nice to have the leverage to swing the router.

The flexing is seen between the bar and the router base particularly when plunging and wiggling the router back and forth. In practice I think the out of round that might happen is beyond the tolerances we're dealing with, that's just my sense of the angle it might achieve during the 'slop' etc. The wood is drilled just large enough to let the all-thread slide with as little slop as possible. This is also why I used oak and a block long enough to keep it all square. A drill press would have helped, if you have one you are likely to get better results.



Slop in the side-to-side, not much, really flex of the overall assembly. This is a non-issue to me so far.



A smaller version would be tighter and have less slop although one-jig-to-rule-them-all was a requirement for me. If you build one, I would build a big one and be done.

I cut some holes just now, and it worked great. The adjustment works pretty easily, need a wrench to put a nip on the locknuts around the wood, not too bad. The ability to set to a dimension and be very close is nice. There is a bit of 'slop' in that the overall jig is pretty long - this comes in to play where you set a measurement and then the hole comes out 1/32 small, you bump the nuts a quarter turn and then it's perfect. This has to do with flex top to bottom between the aluminum bar and the measuring point - this affects repeatability for sure. Setting the dimension while the jig is resting on the table causes it to flex and makes this more of an issue. Also some of this is that 1/32 of diameter accuracy requires 1/64 radius accuracy so ultimately there is a practical limit without some sort of micrometer built in. This is working for me, I was able to cut all the holes for the mini-statements with little to no fuss, and that was mostly depth adjustment issues and then I dropped the router and bent the all-thread, geesh. Also the ruler popped off due to the bar flexing and is now re-expoxied and curing.



Slop in the dimension, this is an issue for repeatability. Test cut baby, test cut.

[ripcard]

Lot's of good info here Vince, thanks. As soon a I decide on a replacement for my old Makita plunge ,I think I just may "borrow" your design and try this. The Jasper jigs work ok but they are difficult to use for the smaller holes like you mentioned because of the pin being under the router base. Durability is an issue as well for me with my Makita as only two of the mounting holes are used to fix the jig to the base(unlike most other models/brands that have three holes line up). On my first project using it, I already broke the flimsy plastic jig lifting the unit off the pin(probably not squarely)when it flexed right around the mounting holes. Left the screws and two little circles of plastic on the router and the jig still sitting on the pin. :E Crazy glue to the rescue and I was able to finish the baffles, but I was not impressed.

A new router using three or even four mounting points would probably solve this but like you, I said to myself, there has to be a better way. You may have just come up with it. ;x(

[vinceb]

Thanks! I'm glad it might be useful to someone else. I found it very much easier to cut my holes today. My old jig was free-sliding and was very trial-and-error prone to get the right diameter, very frustrating. I would have it close but not right, loosen the lock screws, and adjust and then end up just as far out on the other side.

This makes that a thing of the past. When you're very close to the right radius, you just turn the nuts locking the wooden block the same amount and you have a very controlled increase/decrease in size.

I added a note as well to lock-tite the pin, it came out in the work and luckily the router stayed put, could have been a drag but was fine. At one point I was aware it needed to be locked in somehow and forgot later.

The size is actually a good thing. I forgot how tedious it is to spin the router 50 times or so in slow motion to cut holes. The larger radius allows you to hook a finger on and just easily drag it around making it less tiring over the long haul. It's pretty effortless at that amount of leverage.

You could definitely improve some of the flex issues with heavier bar stock and possibly bigger all-thread, but you'd have to file the all thread a lot to get it into the router base. Might be worth it, step on up to 1/2" and some steel 1/4" for the bar stock. Would get heavier but maybe that's a heavy-duty precision model :B