Best router bit and general tips for counter-bored holes

[xillur]

Hi All, 

Introduction:
This is my first topic, I have been reading on this forum a lot lately.
Its been great and I really dig the way you share knowledge about these great tools!

I am living in Denmark(nothern europe) and earn my living as an electronics engineer. Woodworking has always fascinated me, but I have never spend that much time doing it.
Up until now anyway.. One of my hobbies is Hifi and I am helping a close friend starting his Business www.holmacoustics.com

The real issue:
The task in question is making some holes for a 6?" woofer and a 1" tweeter with a bafflesize of 72mm as I recall it.
For this I have bought a secondhand FESTO OF 900 E router and a circle-jig from practical technologies. The circle-jig is able to assist me in making holes from about 2 to 18inches.

The holes I am going to make, need to be counter-bored to make the speaker drivers flush with the cabinet baffle. The cabinets are made of 26mm MDF.
I prefer Festool products, they generally produce the best end result and lasts for a long time!

Which tool bit should I choose for this task? a straight bit or a down/upwards-spiral cutter? I won't be rounding the edges and want them to end up real nice and clean.
In a previous thread I read a down-cut spiral bit would be the best for plywood. Does that apply to this task as well?

Here is a picture to compensate for my lacking abilities with the english language: 

Cheers

Kristian

 

[woodshopdemos]

Kristian,
  First, a welcome to you. There is a great deal of knowledge that  you can find here. I;ll start. As to the spiral bit, you would want an "up-spiral to clean the chips up and out of the substrate. That said, I think a 1/2" straight bit might work better for you. It is less aggressive and should leave a smoother cut. You can use a collar for the router but a top bearing on the bit might be easier and better.
  Your circle jig should be able to give  you the hole and the rabbet of the hole. If you use a straight bit with a patternnearing, you will have to locate one with a one inch cutting length so that the bearing will be able to be set to touch the circle jig -- actually, the circle jig doesn't require a bearing.
  What ever you do, practice the cuts on a scrap piece of MDF.

 

[xillur]

Kristian,
   First, a welcome to you. There is a great deal of knowledge that  you can find here. I;ll start. As to the spiral bit, you would want an "up-spiral to clean the chips up and out of the substrate. That said, I think a 1/2" straight bit might work better for you. It is less aggressive and should leave a smoother cut. You can use a collar for the router but a top bearing on the bit might be easier and better.
   Your circle jig should be able to give  you the hole and the rabbet of the hole. If you use a straight bit with a patternnearing, you will have to locate one with a one inch cutting length so that the bearing will be able to be set to touch the circle jig -- actually, the circle jig doesn't require a bearing.
   What ever you do, practice the cuts on a scrap piece of MDF.

So a rabbet is what its called 
Well as I stated my craftsmanship with regards to woodworking is at an early stage, so forgive me if I ask to many "no brainers".

The router is supplied with a collet for 8mm shank bits. Is this the bit you are referring to: D12 NL30 GL60 12mm is about half an inch for the metric challenged 
That means several passes for the rabbet for the tweeter. Will stepping up to larger bit, like 20mm give me a worse cut?

I will definitely be practising before diving in to the actual piece, its been to many years since last time I used a router.

I counted on using the circle-jig: first to make the passes for the rabbet and next to make the final cut all the way through the MDF.
Are you suggesting that I cut the hole first and then use a bearing bit for the rabbet? just making sure I end up with the best result.

Cheers

Kristian

 

[Michael Kellough]

Kristian,
   First, a welcome to you. There is a great deal of knowledge that  you can find here. I;ll start. As to the spiral bit, you would want an "up-spiral to clean the chips up and out of the substrate. That said, I think a 1/2" straight bit might work better for you. It is less aggressive and should leave a smoother cut. You can use a collar for the router but a top bearing on the bit might be easier and better.
   Your circle jig should be able to give  you the hole and the rabbet of the hole. If you use a straight bit with a patternnearing, you will have to locate one with a one inch cutting length so that the bearing will be able to be set to touch the circle jig -- actually, the circle jig doesn't require a bearing.
   What ever you do, practice the cuts on a scrap piece of MDF.

So a rabbet is what its called 
Well as I stated my craftsmanship with regards to woodworking is at an early stage, so forgive me if I ask to many "no brainers".

The router is supplied with a collet for 8mm shank bits. Is this the bit you are referring to: D12 NL30 GL60 12mm is about half an inch for the metric challenged 
That means several passes for the rabbet for the tweeter. Will stepping up to larger bit, like 20mm give me a worse cut?

I will definitely be practising before diving in to the actual piece, its been to many years since last time I used a router.

I counted on using the circle-jig: first to make the passes for the rabbet and next to make the final cut all the way through the MDF.
Are you suggesting that I cut the hole first and then use a bearing bit for the rabbet? just making sure I end up with the best result.

Cheers

Kristian

That is the way I'd do it and you only need one straight bit for the whole job.

BUT, you need to double stick tape the center of the cutout to a smooth backer board so it doesn't move when you near the end of the through cut.

 

[xillur]

That is the way I'd do it and you only need one straight bit for the whole job.

BUT, you need to double stick tape the center of the cutout to a smooth backer board so it doesn't move when you near the end of the through cut.

Thank you for the good answers so far, you don't know how much this helps me with my project.

Michael: I once saw Brice using an MFS I think, to make a circle cut. He used double stick tape on a backer board, slightly bigger than the cutout as I recall it.

Actually one of my arguments of making the rabbet first, was to make sure that the outside edge of the rabbet would be perfect.
Even if the backer board and the inside cut away piece would move at the end of the through cut, that wouldn't be so critical to the end result.

 

[Michael Kellough]

Kristian, you understand this stuff way better than you think! 

It's all governed by the rules of basic physics. If you think it through,
as you have done, you shouldn't have a problem.

Experience is needed most after you make a mistake, which is usually the result
of not thinking it through carefully enough.

 

[josephgewing]

Hello Kristian,

I add my welcome.

I think your way of cutting the rabbet first and then cutting the hole is good.  That is the way I would do it.

Be sure to use double stick tape, like John said to keep the center piece as a steady piece for your circle cutting jig.

Joe

 

[xillur]

thanks guys, for the answers. I will post a follow up, to let you know how it went 

 

[ken257]

Cut the rabbit first with the circle jig. It may take some tests in scrap to get the right diameter and depth so that the speaker fits in just right. It would be easiest if you got a straigt bit (plunge bit) that is the same diameter or slightly bigger then the size of the rabbit you need. To cut the hole you can do as stated above and use double sided tape. But if you are like me it is late at night and you don't have the tape when you want to do this. You can set the depth of cut to just a hair shy of the material thickness and then finish with a razor knife.

 

[xillur]

ken: the tip with the knife is certainly a good tip to! maybe I will try it. The inside edge is going to be rounded anyway to avoid acoustic reflections from sharp edges.

 

[xillur]

I received the circle jig and router bit some day ago. Unfortunately the circle jig doesn't fit the bottomplate of the OF900. I will modify it at the workshop at work next Monday, so it will fit. these day I am on vacation and remodeling the kitchen.

stay tuned 

 

[insurroundsound]

xillur:

looking forward to what you discover.  I've just recently picked up my Festool router [1400] and still playing around with it.  I'm like a baby with a new toy.  ;D

InSurroundSound