# Flush Trim Bits



## Oberon_1 (Nov 14, 2015)

I’m looking to make a cutout into 1/2” plywood. It’s octagonal, about 6” wide. I was thinking of using my router (prepared a template). However there seem to be no bit, with a bearing (used like flush trim bits) that can also be plunged into the wood. Can anyone offer a solution? It probably needs to be 1/4” in diameter or less...


----------



## DesertRatTom (Jul 3, 2012)

You probably need to use a mortising bit with a bearing on the bottom (on the shaft end, not the cutter end). These bits come in a variety of sizes and you place the pattern on top of the workpiece. This bit makes a flat bottom cut. It can also be done using a bushing, but you have to allow for the gap between the bushing and bit. Here is an example of a mortising bit. 

There are many bits without bearings that can be used to cut a pattern with a bushing, down to 1/8 inch or so, but it doesn't take much to break them.


----------



## Stick486 (Jan 4, 2013)

Oberon_1 said:


> I’m looking to make a cutout into 1/2” plywood. It’s octagonal, about 6” wide. I was thinking of using my router (prepared a template). However there seem to be no bit, with a bearing (used like flush trim bits) that can also be plunged into the wood. Can anyone offer a solution? It probably needs to be 1/4” in diameter or less...


are you trying for a groove or a cut through???


----------



## Cherryville Chuck (Sep 28, 2010)

A pattern bit could be plunged if it's meant to do so. The main difference between a pattern bit and flush trim is that with the flush trim the pattern goes on the bottom and with the pattern bit it goes on top. You need a pattern bit that's the right length or a really thick template if it's a long bit. Personally I would cut close to the line with a jigsaw or bandsaw or with an octagon maybe a table saw first. It's faster and easier on bits that way. Then the routing can be done in one pass.


----------



## Herb Stoops (Aug 28, 2012)

I agree with chuck, take off as much material as possible before you route. Then clean up the last 1/8"-1/16" with the router. It will save the worry about the plunge cutting. Trying it hog it all out with a router is hard on the router and a bit on the dangerous side. If you must cut it out all at once, Use a template bushing https://duckduckgo.com/?t=ffnt&q=Router+template+bushings&atb=v1-1
on the router base plate and cut your template to allow for the bushing as Tom said, Put the template on the top of your work and make sure the template is the same thickness as the bushing protrudes from the router baseplate. Use a bit like Stick /Tom said that has cutters on the bottom end that will cut its way as it goes, then set the cut for not more than 1/8" in depth with each pass then repeat til you are all the way through.
HErb


----------



## Oberon_1 (Nov 14, 2015)

Thanks everyone. Was hoping for an easy one step solution. But It seems the safe way is doing it in two steps. First removing most material with a saw before using the router to trim.


----------



## Cherryville Chuck (Sep 28, 2010)

Oberon_1 said:


> Thanks everyone. Was hoping for an easy one step solution. But It seems the safe way is doing it in two steps. First removing most material with a saw before using the router to trim.


Oberon the usual recommendation for depth of cut is don't exceed the diameter of the bit per pass so no matter what method you chose it was going to be more than one step. Also, plywood is notoriously hard on bits and when you have the full diameter of a bit in the cut the bits tend to get hot which causes them to wear out faster. As in possibly one octagon. Just trimming with a bit the bit will run much cooler and probably last for many octagons before needing replacement. If you are routing an intricate pattern with inside corners then you have to go to a small diameter bit that will fit in those corners. Otherwise I like to use a fairly large diameter bit. I feel like they do a better job. I would go with at least a 1/2" flush trim bit.


----------



## Mike_C (Jul 11, 2020)

@oberon

you havent specifically stated it....but IMO the method used depends on the production setting. if you just need to make one or two of those cutouts then any old trick will do (jigsaw+ template; jigsaw+flush; plunge with bush; plunge type template etc)

BUT - if you need to make quite a few of these, it has been my experience that the jigsaw method is very time consuming since there is no way to make it template based and brainless.

i recently created 25 cabinet doors in which i had to create a 1.7 meter long oblong handle carving using 3 separate types of bits...and like you, had the issue of cutting out the initial chunk of material 

the best solution i have found (apart from a CNC....  is using a stout (1/2" or so) diameter straight or spiral bit with a strong 1/2" shank router and a bushing on my template to very quickly hog out the main chunk of material in one continuous pass (ply is indeed hard on bits, especially dense birch ply...but 1/2" ply is still no match for a 2+ HP router with a sharp 1/2" bit) and then use your other router (or change bits if you must) setup with a flush or template bit to do the final pass

MC


----------



## Oberon_1 (Nov 14, 2015)

Mike_C said:


> @oberon
> 
> you havent specifically stated it....but IMO the method used depends on the production setting. if you just need to make one or two of those cutouts then any old trick will do (jigsaw+ template; jigsaw+flush; plunge with bush; plunge type template etc)
> 
> ...


That’s an interesting suggestion. I’ll try to see how it works with my project. 

On second thought, isn’t a CNC router performing similar plunge cuts all day long (including in plywood)? How does it survive the heat and wear?


----------



## Cherryville Chuck (Sep 28, 2010)

Much faster feed speeds. Faster than anyone is capable of by hand but also light cuts. At the right feed speed the fresh wood cools the bit. A few years ago a member was looking at getting a poly crystalline diamond coated straight bit to do a slotting job in abrasive material that was burning bits up and he asked if maybe a polychrystaline diamond coated bit was the answer. We happened to have the head of Onsrud as a member at the time and he said it was impossible to feed fast enough by hand to make the bit work properly.

I was working at a mantle factory a few years ago and we used a proprietary router bit to cut a channel in the kick boards (veneer covered particle board) that a proprietary plastic clip fit into. We had a run to do and we didn't have enough bits at the rate we were burning them up to make it to the end so I took them to the table saw and set the fence so the blade was slightly off center in the channel and ran them through and flipped them 180 and ran them through again to cut part of the channel. By giving the bits some cooling air and a way for the chips to escape it increased the life of the bits by 300%.


----------



## Stick486 (Jan 4, 2013)

> Originally Posted by Oberon
> Thanks everyone. Was hoping for an easy one step solution. But It seems the safe way is doing it in two steps. First removing most material with a saw before using the router to trim.



why not use a miter or table saw???


----------



## Oberon_1 (Nov 14, 2015)

Stick486 said:


> > Originally Posted by Oberon
> > Thanks everyone. Was hoping for an easy one step solution. But It seems the safe way is doing it in two steps. First removing most material with a saw before using the router to trim.
> 
> 
> ...



Because it’s a cutout in the middle of a larger plywood sheet. (6” octagonal shaped cutout).


----------



## Stick486 (Jan 4, 2013)

Oberon_1 said:


> Because it’s a cutout in the middle of a larger plywood sheet. (6” octagonal shaped cutout).


okay..
go w/ a straight bit and guide bushings...

.


----------

