# Pattern bit / inverted flush trim bit



## matt1710 (Sep 21, 2010)

Hello

I have a few questions re pattern bits / inverted flush trim bits. Let me first define my understanding of that bit : shank mounted bearing, cutting edges flush with bearing. 

I understand these are one of the methods one can use with a template : template on top of stock, bearing engages on template, cutter trims stock flush with template. The cutter must enter the stock from the side - it can't be plunged. The bit I'm looking at buying (primarily for making the recess for my RT mounting plate) is 19mm diameter (bearing & cutter) and cutter is 19mm high - here's the link : Linbide: Tungsten Tipped Router Bits The one I'm looking at is the 19M4B - I'll have to get a adapter as it's a 1/4" bit and my router is 1/2". 

Anyway, let's say I want to use this bit to cut a very shallow (say 2mm) rabbet for a hinge. If I made the template of 6.5mm MDF, the cutter is going to chew away much more than 2mm as it's 19mm deep. Correct? So either I make the template out of thicker stock - or use a packer - as per my diagram? Or is there another way?

Matthew


----------



## jlord (Nov 16, 2009)

Hi Matthew,
The bit can be plunged if it has cutters on the bottom. You can use it for shallow work as long as your template is thick enough for the bearing to ride on. Like your diagram. Make sure your template does not move.


----------



## jschaben (Jun 21, 2009)

matt1710 said:


> Hello
> 
> I have a few questions re pattern bits / inverted flush trim bits. Let me first define my understanding of that bit : shank mounted bearing, cutting edges flush with bearing.
> 
> ...


Hi Matt - your system looks spot on to me. Just have to make sure your rebate won't exceed the 6.5mm of your template or your guide bearing will slip below it. Idea should work but with caution. 
Incidentally - they make those cutters with cut length as short as ~3 mm. Don't know how available they are for you though. Around here if you search for "flush trim" bits you get mostly 25 mm and longer. Search for "pattern bits" and you get the shorter versions.


----------



## Racer2007 (Nov 3, 2010)

Matthew, Why not just use a regular rabbeting bit with the bearing on the bottom instead of the top ?


----------



## bobj3 (Jan 17, 2006)

Hi

MLCS Dado Clean Out Router Bits

1 pc 1/2" SH 3/8"Blade Dado Planer Pattern Router Bit - eBay (item 140493375852 end time Jan-21-11 16:31:43 PST)

3 pc 1/4" SH Top Bearing Trim Pattern Router Bit Set - eBay (item 140502507246 end time Jan-25-11 12:19:59 PST)

5pc Top Bearing Dovetail Router Bit Set For Keller Jig - eBay (item 130472188064 end time Feb-04-11 13:54:43 PST)


4 pc Collet Reducer Bushing for 8mm, 1/4" Router Bit - eBay (item 140495269963 end time Jan-28-11 11:00:48 PST)

=======


----------



## matt1710 (Sep 21, 2010)

Thanks for all the advice, once again. I'm somewhat limited by which bits I can purchase here in NZ - we don't have the huge range that you do in the US. Bob - the 3 piece set looks just what I need - shame they're in the US. I've only found one suitable bit here (and it's 3/4" x 3/4" with a 1/4" shaft - so not only a little too big when the rabett is only 2mm, but the wrong shaft size too - and while it's a very good bit (Linbide) it's US$40! 

I actually need the bit in question for cutting the recess for my RT mounting plate - and as I can't get what I need, I'm going to have to find a work around. I saw an alternative method (see this video : Popular Woodworking - VIDEO — No–nonsense Router Table— Inset a Router Base Plate) which I tried - however I need to start working with two different offsets : one with a 12.7mm spiral bit and a 40mm collar which itself is run along a straight edge offset from the outline of the plate. This is because the the slot cutter I have produces an offset different to that of the spiral bit/40mm guide collar. It's getting complicated....I've already done two trial cuts - one was a shade too big, the other too tight. I think I'll get it right on the next one - but might use a few layers of masking tape on the straight edges just in case...

Wish me luck!

Matthew

PS - Richard - I'm only a newbie to this routing game, so correct me if I'm wrong, however my understanding is that to use a top-mounted template with a bearing guided bit, the bearing must be on the shaft - not on the bottom.


----------



## bobj3 (Jan 17, 2006)

Hi Matt

Sorry, but like they say it's a very small,small world now days  your front door is a pickup up point for just about anything you want now days...it maybe a long way from you but it maybe cheaper in the long run..with the cost of gas, by the way what do you pay for it in NZ ?

=======



matt1710 said:


> Thanks for all the advice, once again. I'm somewhat limited by which bits I can purchase here in NZ - we don't have the huge range that you do in the US. Bob - the 3 piece set looks just what I need - shame they're in the US. I've only found one suitable bit here (and it's 3/4" x 3/4" with a 1/4" shaft - so not only a little too big when the rabett is only 2mm, but the wrong shaft size too - and while it's a very good bit (Linbide) it's US$40!
> 
> I actually need the bit in question for cutting the recess for my RT mounting plate - and as I can't get what I need, I'm going to have to find a work around. I saw an alternative method (see this video : Popular Woodworking - VIDEO — No–nonsense Router Table— Inset a Router Base Plate) which I tried - however I need to start working with two different offsets : one with a 12.7mm spiral bit and a 40mm collar which itself is run along a straight edge offset from the outline of the plate. This is because the the slot cutter I have produces an offset different to that of the spiral bit/40mm guide collar. It's getting complicated....I've already done two trial cuts - one was a shade too big, the other too tight. I think I'll get it right on the next one - but might use a few layers of masking tape on the straight edges just in case...
> 
> ...


----------



## matt1710 (Sep 21, 2010)

bobj3 said:


> Hi Matt
> 
> Sorry, but like they say it's a very small,small world now days  your front door is a pickup up point for just about anything you want now days...it maybe a long way from you but it maybe cheaper in the long run..with the cost of gas, by the way what do you pay for it in NZ ?
> 
> =======


Hi Bob

Yes - it's the delay in getting them here that's most frustrating! We pay US$1.50/liter for 98 Octane gas - the crappier stuff is cheaper, but less powerful and dirtier. 

The eBay seller you've linked to above - do you have good experience with his bits? I might select a few that I can't get here (such as a 1/2" pattern bit) and have them sent down. Care to recommend any other online sources of good bits?

Matthew


----------

