[mwebbo]

Hello, I am new here and just getting into routing, more specifically template routing.
Here is my question. I have a 30mm circle template. I need to make a 20mm hole using that template. Could someone give me the bushing and bit combo that will allow me to do this?
I have tried a 30mm bushing with a 20mm bit and just plunged, but I am getting some inconsistent results due to slop in my router. What other combos can I try? Thanks in advance.

If I understand this at all, I am looking for a 10mm offset combination, right?

 

[Marco]

I believe there is a formula to your answer. I have it (somewhere) but try searching (Guide bushing offset maybe)on this sight or Mr. Google as where I have it written down and my memory is here somewhere. Good Luck!

Here is a link that will get you started

 

[old55]

Welcome to the forum @mwebbo

 

[jw2170]

Welcome to the forum,

If you have a 30mm and 20 mm cutter I would use that combination.

The big issue is, why are you getting slop in your router ?

 

[mwebbo]

I believe there is a formula to your answer. I have it (somewhere) but try searching (Guide bushing offset maybe)on this sight or Mr. Google as where I have it written down and my memory is here somewhere. Good Luck!

Here is a link that will get you started

Welcome to the forum,

If you have a 30mm and 20 mm cutter I would use that combination.

The big issue is, why are you getting slop in your router ?

Thank you. The router is an old Ryobi. I can wobble it, ever so slightly, at the handles (as if I am turning a steering wheel). It is just enough to cause the hole to be too big. If I lock it after the plunge, it does not do that. But at that point it is too late.

 

[MEBCWD]

20mm bit + 10mm (5mm offset X 2) = 30mm bushing .... This is what you already have.
6mm bit + 10mm (5mm offset X 2) = 16mm bushing
8mm bit + 10mm (5mm offset X 2) = 18mm bushing
12mm bit + 10mm (5mm offset X 2) = 22 mm bushing

 

[TWheels]

If your router has that amount of slop, I would suggest that the proper solution is to get a new router. The “official“ router of RouterForums seems to be Bosch but there are several brands.

 

[DesertRatTom]

You have to make sure your router base is centered. You use a centering cone for that purpose. Insert it into your collet and lay the base down on it. Raise the router (bit up), until the loose base is seated on both the cone and the router metal base. Lock the base down with the screws you removed to release the base. Now it's centered, and you will now have a centered bit. Put in a bushing on it and the bit is now centered in the bushing. This is a critical first step. Now you can use the formulas to compute the offset between the outside edge of the nipple of the bushing and the cutting edge of bit.

The circle template will need to be the same measure larger than 30 mm. so if the measure is 4mm, then your pattern needs to be 34 mm. That is if you are cutting a hole. If you are cutting plugs, you use the distance from the edge of the nipple to the cutter on the far side. If that is, say 16 mm, then your template would need to be 46 mm . If you haven't centered the bit, the results will be poor.

Or, if you are cutting an opening, use a drill press and a 30 mm forstner bit that has and edge cutter at the tips. Theoretically you could just use a drill for this, but it is really hard to get a really clean opening without a drill press. And back up the piece you're drilling with another board to avoid any tearout. Here's a 30 mm Forstner bit for $13. https://www.amazon.com/Roman-Carbid...words=30mm+forstner+bit&qid=1657589604&sr=8-5
Here's a picture of a forstner bit that has the tips to make a really clean edged opening:
:

If I were cutting 30mm pucks, I'd probably use a band saw or jig saw with a thin blade, to cut out the first plug, then perfect the edge with sandpaper, After that you could use a small bottom bearing trim bit, tape the plug down, then use the router to cut the rest of the plugs.

If I were making a lot of these plugs, I'd find someone to turn a 30 mm rod and cut the pucks off using a stop block for length, and some sort of V shaped carrier to hold the round steady for the cutoff. Sandpaper the ends a bit and that would allow for as many plugs as I wanted. You might also be able to special order the 30 mm dowel from a mill that makes such things.

If there is a wobble in your router it may be that the bearings are worn, or worn unevenly, or there's something stuck in it. Get it serviced or replace it. A wobble makes a router the enemy of good work.

Lots of ways to skin this particular cat. FYI, here's a picture of a centering cone. You'll find them at Amazon or any woodworking store.

 

[DesertRatTom]

I just re-read the original post and darn my old eyes, missed the 20 mm reduced size. Again, I'd prefer to use a forstner bit for a hole, preferably with a drill press. For a puck, 20mm is pretty small, so you'd need to have 5mm between the edge of the cutter to the outside lip of the bushing. BUT you MUST center the base, and if the router has a wobble, even a small one, it's not going to be round.

And for pucks that size (about the size of a piece in a piece for checkers), I'd definitely look for a 20 mm rod. You can probably find that exact size in a decent wood.

Sorry for the slight misdirection.

A BIT more information...
If you don't have a drill press, I suggest you get one. WEN makes a very nice pair or presses, on smaller, the other has a much taller post.. It is identical, down to casting marks, to a Jet. And it has a Rockwell clutch drive so you changing speeds is done with a dial, and it has a digital RPM display. It even has a laser crosshair for perfect positioning. Here's a picture.

WEN 4214T 5 amp 12 inch variable speed, Cast Iron, Benchtop Drill Press with laser and worklight $256 on on Amazon, or you can order it from Home Depot for direct delivery. https://www.amazon.com/WEN-4214T-Va...755646&sprefix=WEN+drill+press,aps,644&sr=8-3

I used to have one of the small, cheapo models, and the difference in precision and the depth of plunge is soooo much better with the WEN. When I started woodworking I thought a drill press was an unnecessary luxury, but now I realize it is a must have, very basic tool. BTW, the exact same DP by Jet is $520.

 

[pennview]

The offset you want (the difference between the diameter of the bushing and the diameter of the router bit) is 5mm (that is, 1/2 of the difference between the diameter of the template and the diameter of the hole you want, or 30-20/2). I use imperial measurements and tools, so I don't know what diameter metric bushings and bits come it, but if you have a 10mm bushing and a 5mm router bit that would get you a 20mm hole while using a 30mm template. Other combinations would be a 15mm bushing and a 10mm bit, or a 20mm bushing and a 15mm bit.

Since you router has some slop in it until you lock the depth, you should plunge with the bit in the center of the hole you want to make and then lock the depth, you don't want the bushing touching the template when plunging initially as this might ruin the accuracy of the hole.

 

[4DThinker]

I own the Wen 4214T drill press mentioned above, and highly recommend it. I'll also recommend you get a new router as play in the plunge base will continue to aggravate you.
4D

 

[bfblack]

The attached pdf file is supporting information for the response by MEBCW.

 

[mwebbo]

Thank you everyone for the responses. I ended up purchasing a new router. I figured this issue would cause future problems so I bit the bullet. Thank you for all of the options and solutions offered.