Enlarging a template by exactly the size of the cutter-bushing gap? - Router Forums
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post #1 of 45 (permalink) Old 09-14-2019, 01:28 PM Thread Starter
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Default Enlarging a template by exactly the size of the cutter-bushing gap?

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!

-Ashley
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post #2 of 45 (permalink) Old 09-14-2019, 01:44 PM
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Option B is how I would solve the problem. But, depending on how clean you need the final hole to be, I might use a downcut bit instead of an upcut.
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post #3 of 45 (permalink) Old 09-14-2019, 04:30 PM
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I would go with option A, but you would need a 1 inch OD guide bushing. Freud sells a 20 mm bit with a 1/4" shaft.

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post #4 of 45 (permalink) Old 09-14-2019, 05:15 PM
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this might help..

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This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

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post #5 of 45 (permalink) Old 09-14-2019, 05:22 PM Thread Starter
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After another hour or so looking at bits and bushings, reading other forum threads, and then seeing the replies in this one, the problem is coming into focus. The issue isn't option A vs option B - it's where can I get the metric rabbet bit and metric bushing needed to make these work?

Being specific... let's assume option A... and let's pretend we have good access to metric sized bits and bushings (which I'm not sure is true)...

Given those assumptions, I might do it this way...
  1. Use a rabbit bit, say a 5mm rabbit, to enlarge the top half of each hole in the original from 20mm to 30mm.
  2. Use a top bearing flush trim to enlarge the remainder of each hole, so the original now contains 30mm holes at the required spacing.
  3. Mount a 30mm OD guide bushing on the router so it perfectly fits in the newly widened holes in the original...
  4. Clamp the original on top of the workpiece
  5. Mount a 20mm bit and "drill" out all the required holes

That sounds fairly straightforward, except for these issues...
1. I must find a rabbit bit that cuts exactly a 5mm rabbit.
2. I must find a 30mm OD guide bushing.
3. I must find a way to mount that 30mm OD guide bushing on my Bosch 1617. Ideally it works directly with the Bosch quick change bushings, but perhaps I need a PC adapter, or some other adapter.
4. The 30mm size of the guide bushing must actually match the hole I created by using the 5mm rabbit bit to enlarge my preexisting 20mm hole. (Math is supposed to be that easy, but cross-manufacturer math isn't always that easy.)
5. I must find a 20mm bit that plunges straight down.


Of these issues, only #5 is a clearly solved problem. At a glance, there seem to be many viable bits from Freud, Amana, Bosch, CMT, and Festool. Some of these will work with my existing 1/4" or 1/2" collets, and some will require a metric collet, but I suspect/hope that's not hard to find.

On the other hand, finding metric sized rabbet bits and bushings is a big problem. I haven't found a single option for a rabbet bit that specifies it's cut in mm. Any suggestions here?

-Ashley
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post #6 of 45 (permalink) Old 09-14-2019, 05:51 PM
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Quote:
1. I must find a rabbit bit that cuts exactly a 5mm rabbit.
that's controlled by a bearing...
w/ all your talk of metric, I take it you're not in the United States as you state you are...

https://www.whitesiderouterbits.com/...eee3c547&_ss=r
https://www.whitesiderouterbits.com/...s&type=product
https://www.whitesiderouterbits.com/...e&type=product
https://www.amanatool.com/products/r...ng-guides.html
Router Bit Bearings | Retaining Collars | Carbide Processors
https://www.toolstoday.com/woodworki...ic-Router-Bits

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

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post #7 of 45 (permalink) Old 09-14-2019, 06:18 PM
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There is some information missing that may be key to the final decision, namely how deep a hole and how smooth the hole needs to be. I also disagree with the statement that routing is faster than drilling. A sharp drill bit will usually out perform a router bit especially if that bit is not an up cut spiral. If the hole is any depth at all you'll need to use an up cut so that the chips get cleared out of the hole.

As far as enlarging holes, the easiest way I know is on a drill press. Chuck a 20mm bit and locate your jig so that the bit fits the hole and clamp the work to the table. Then remove the 20mm and chuck the larger bit and drill. That's the easiest way to guarantee that the larger hole stays centered with the original.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #8 of 45 (permalink) Old 09-14-2019, 06:35 PM
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fostners to the rescue....

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #9 of 45 (permalink) Old 09-14-2019, 08:02 PM Thread Starter
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Thanks for the additional input guys. I'm responding to Chuck’s comments first, then returning to Stick’s…

Chuck, I appreciate your suggestion that an up cut spiral may be preferable for chip clearing. Given that the final hole depth will be about 3/4” in this project (and vary from 1/2” to 1” in the next two projects), that's great advice.

My bias away from the drill press is because of my jig plans. It’s not that I think the router bit is faster than the drill bit… It’s that my setup and operation is faster with the router (if I can find the right bushing & bit combinations). I’m sure there’s a way to do this with a drill press too, but my thinking in that area lags far behind my clarity on how to do it with a router… and, my drill press is a recent $20 craigslist deal that needs a bit of reconditioning, then a project to build a decent stand, then...

Chuck’s suggestion on enlarging holes with the drill press does make perfect sense. Using my 20mm forstner bit to align the existing hole, swapping bits, then drilling... that will definitely work. It will take a long time to do that for all the holes in my original/template, but for a template I'll use often, that’s a time investment I may be willing to make if I don’t find a perfect solution with the rabbet approach.

Stick, I understand the bearing to rabbet bit relationship. What I was missing before your reply was sources for bits/bearings that spec the size of rabbet I’ll get from a given bearing/bit pair in mm. Your Amana link, and the Amana products at the ToolsToday link have a ton of metric bearings and bits so I’m pouring over them to piece it together. I’d love a simple link to a metric spec’d set if anyone has one… that tells me it supplies the bit and bearings needed for 2mm, 4mm, 5mm, etc… but lacking that, I hope I can figure it out from those Amana links.

At this point I've narrowed to the following candidate parts to do the job..
  • Bosch RA1128, if I don't already have the included RA1126 to allow attaching Bosch quick change template guides to the Bosch 1617.
  • Bosch 2609200142 30mm template guide.
  • The alternate choice to the Bosch guide (which has some fit concerns on some sites) is this screw-on style 30mm from Trend. That would attach to the Bosh 1617 using the RA1100 adapter in the above Bosch RA1128 set.
  • 20mm router bit choice now pending as the ones I named previously would be best replaced by a spiral upcut as Chuck suggested.
  • rabbet bit, with bearing sized for a 5mm rabbet is pending... but I'm deep in Stick's docs looking for it.

Finally, Stick you wondered if I'm not in the US since I'm looking for metric. I am in the US - Texas and Montana - but wanted to build this around 20mm holes to take advantage of some nice add-ons made for the Festool system. Thus far, my experience with the pain of finding metric stuff in the US is seriously tempting me to go to 3/4" instead. I'm just starting a road that might be expensive and painful if this is typical.

Again, thanks for the help!

-Ashley
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post #10 of 45 (permalink) Old 09-14-2019, 10:30 PM
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Quote:
Originally Posted by AshleyJ View Post
Finally, Stick you wondered if I'm not in the US since I'm looking for metric. I am in the US - Texas and Montana - but wanted to build this around 20mm holes to take advantage of some nice add-ons made for the Festool system. Thus far, my experience with the pain of finding metric stuff in the US is seriously tempting me to go to 3/4" instead. I'm just starting a road that might be expensive and painful if this is typical.

Again, thanks for the help!
Disclaimer: The following rant is mostly meant in humor, but there a few tidbits of truth to found as well. I leave it to you, the reader, to figure out which is which.

We are woodworkers! We don't DO metric! The English invented the Imperial System of measurement and they are still the best woodworkers in the world. Yeah I know, the Limeys caved in to the rest of the world and stupidly adopted the metric system years ago. If that bothers you, go punch a Limey. As for me, I would prefer to get them to teach me to properly sharpen Robert Sorby chisel.

Yes I agree, it is much easier to add and subtract numbers using the metric system. But division is a serious pain in the neck! What is half of 1/16 inch? Double the denominator and come up with the answer 1/32 inch. What is a third of 1/16 of inch? Triple the denominator and come up with 1/48 inch. Easy math to do in your head. I do a LOT of division when building stuff.

What is half of a millimeter? Now you have to switch number systems entirely. What is next smaller system from millimeter? - A penismeter? So half a millimeter is 5 penismeters? Dumb!

Complain all you want about the Imperial Measurement system, based on hexadecimal numbers, but it has served us pretty well. The computer, phone or tablet that you are typing on as you read this is also based on the same system.
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