This a request for your collective expertise as I try template routing for the first time. I'm certain the problem I face has been solved many times before...
The goal: I'm creating something that requires a grid of 20mm holes, spaced precisely on 96mm centers. A Festool MFT or Ron Paulk bench is a reasonable comparison, though neither is exactly what I'm building. The number of holes required is large, and this is an operation I'll likely repeat many times in the future, so speed and repeatability are very desirable. Precision is essential.
I do have a pattern to work from, a piece of 18mm baltic birch with the required grid of 20mm holes. Let's call this the "original", since it matches what I need to make and has no additional margin to allow for template-cutter gap.
I have four options to cut those holes, listed from least to most desirable...
D. I could drill them with a 20mm forstner bit that I already have.
C. I could buy a top bearing bit, suitable for plunging, perhaps 3/8" diameter; clamp the original on top of the workpiece as a template; carefully align and plunge into each hole, and use the top bearing along the original to complete the cut.
B. I could create a template from the original (more later), buy a bushing set, and route the holes using a 1/4" solid carbide spiral upcut bit that I already have (Freud 75-102).
A. I could create a template, buy a bushing set, buy a 20mm bit, and complete each hole with a single plunge.
I have strong preferences on this, and I'll share my thinking so your experience can question my logic as appropriate...
- Option D is my last choice because I strongly prefer routing over drilling, as it's faster more precise, and fits details of the context better.
- Option C saves me the hassle of making a template (as required by A & B), but it's far slower and more error prone. A single error in alignment before plunging could ruin my project. I have hundreds of these holes to drill over my next 3 projects, so I strongly prefer making a template and using approach A or B.
- I prefer option A over B for speed. I'm willing to buy a 20mm bit for that benefit.
Assuming I proceed with option A, I'll need...
- a 20mm router bit (and probably a new collet, since my Bosch 1617 came with 1/4" and 1/2", and metric bits probably come with metric shafts)
- an appropriate guide bushing, in this case large enough to use with the 20mm bit
- a way to enlarge the original to work with the bushing.
The challenge here is that last point - how to enlarge the original to work with the bushing... ensuring that the enlargement exactly matches what's required by the bushing.
I think the general process is:
Route a rabbet around each hole in the original.
Run a top bearing bit along that rabbet, enlarging the entire hole to match the rabbet.
Select a guide bushing & cutter combination that precisely matches the amount which the rabbet enlarged the hole.
My problem is that I'm somewhat lost in a maze of router bits and specs, trying to find combinations of rabbet + bushing + final cutter (probably 20mm) which works. This is nicely complicated by my target metric measurements and my imperial tools and thinking.
Can anyone point me in the right direction out of this maze?
Here's a few details of my setup in case they're relevant...
- My router is a Bosch 1617 with both fixed and plunge bases. I have only the 1/4" and 1/2" collets but I'm willing to buy a metric collet if needed.
- I don't yet own a bushing set. As I'm using a Bosch router, I expect to buy the Bosch quick change bushings... but I'm willing to purchase a different set, buy adapters, and/or make a replacement sub-base to hold PC or other bushings if needed.
- I don't own a rabbet bit, so I can buy whichever one is appropriate to match the dimensions needed.
Thanks in advance for any help!