Trimmer Circle Cutting – Without the (B)dust

  • Advertise with us
Project by LittleBlackDuck posted 06-27-2018 09:32 AM 3187 views 6 times favorited 14 comments Add to Favorites Watch

Trimmer Circle Cutting – with built in dust extraction!

Boys and Girls, Anyone that has cut circles (without a cookie cutter) is well aware of the sawdust/chips generated when using a router or a trimmer. Even the trust bandsaw requires a brush up after completion of the circle.

While I didn’t have the need to make a “largish” circle (or hole) at the moment, a dust free operation somehow got my attention.

Years ago I designed this circle cutter that attaches to my Festool router.

The router itself has great dust extraction, however, once you undertake routing a circle in multiple circular passes, the cord and dust hose comes close to a fishing line’s “birds nest” impersonation. While the Festool router is not overly heavy I thought a trimmer would be easier to handle, however, they are not renowned for dust extraction.

As always I started with a glass of vino, closely followed by a session with SketchUp and an even closer follow up with another vino. After the vino was exhausted, I had no choice but to finish up the SketchUp design,

The jig was designed to be cut out of 3mm and 6mm MDF (easier capacity of my laser) and with locator pins laminated into the final item.

The intention was to provide for some type of dust extraction.

Cut the parts on the laser and down to the workshop

to start gluing.

Everyting progressed well until the final top layer which was not glued but bolted on…

DOH! Should have tested “swings” in the SU model. The retaining bolts obstructed to movement of the trimmer’s depth adjustment latch.

I tried to reposition the bolts’ holes, however, came adrift with the tracks location underneath.

Back to the drawing board and move the holes to a non-obstructive position.

Cut the parts on the laser and down to the workshop to start gluing. Everyting progressed well with the final top layer not glued but bolted on… (heard that before).

Gave it the mandatory coat of tung oil and let it dry overnight in the warmth of the house…

Back in the workshop, I started scrounging around for some waste timber… No Goldilocks was to be found… all too big or too small… bit the bullet and butchered a piece of 18mm MDF to a more manageable size as this was going to be my first attempt and I had planned to record it on film.

Inserted a ¼” router bit into the trimmer, loaded it into the base (which is screwed to the lowest layer in the jig) and set the radius in accordance to the MDF’s size. I opted for 160mm. Now as this was just my first test cut, acute tolerances was not a priority, however, a mental note was taken off the measurements.

Got a small strip of scrap wood, drilled a 5mm hole at one end and routed an arc. The first thing I noticed was the lack of ANY sawdust. Measured the radius which turned out to be around 158-159mm.

Adjusted the pin’s location by eye and repeated the arc on the flip side of the scrap. 160mm exactly… and not dust. While I normally go about 1mm oversize and after the cut trim to exact size without a heavy load on the trimmer due to the minimal reduction required, I couldn’t be bothered for this exercise.

Cut the first circle at approx. 5mm deep… still no dust… dropped the trimmer (a tad too deep) and it labored to cut the next layer to the extent that I had to resort to the ear muffs. Kept reducing (increasing the depth of cut) till there was only about 1-2mm depth left. I then wanted to film the final pass, but after completing the cut and admiring my work… and lack of dust… the bull came thick and fast as I forgot to turn the camera on.

Rather than waste more (fake) timber, I repeated the process using a smaller inside circle.

With the final pass, I set the jig up, upside down in a vice… Prior to that I did a full plunge through…

On hindsight, I should have my very first plunge all the way through and then raise the bit for the first pass. That way the hole would be already there and not have to perform a new plunge with each pass.

Anyway on the flip side I loaded the timber and cut through the last 2mm.

Big mistake was I let go off the piece before I stopped the trimmer which sent the circle into a spin…

No major issue but that was more luck than design… note to oneself… stop trimmer then have the drink!

Bottom line is that the trimmer worked beyond expectations. The first two cut were not perfectly smooth, though easily fixed with a little sanding, however, the emphasis was not on the neatness as much as the concept,

My next circle needed for an actual project, will be handled more diligently.

As I don’t believe in perfection, I will give the dust collection capability about 99% efficiency.

Now I’m not going to say this will happen for all trimmers, as this jig was explicitly designed to accommodate the Ryobi’s orifices and would not be compatible with other brands or even Ryobi models. Nevertheless the concept should be adaptable to most trimmers/routers.

The only downside is that the trimmer is screwed to the jig so if you wanted to use the trimmer (as designed) it’d have to be detached… however, having two of the same model minimises that need.

The jig has the capacity for 40mm to 640mm radii circles. I may reduce that by truncating the protruding track as my bandsaw circle cutter already caters for large circles,

It goes without saying that if you don’t own a trimmer or need to cut circles, you should not read this article.

If you are still interested this video might be easier to digest than the above read.

PS. Late night extra… the Sketchup model link.

-- If your first cut is too short... Take the second cut from the longer end... LBD

14 comments so far

View crowie's profile


5031 posts in 3196 days

#1 posted 06-27-2018 09:58 AM

Cordless tools along with some clever ingenuity have made another “ducky” masterpiece.

Well done Alex.

-- Lifes good, Enjoy each new day...... Cheers from "On Top DownUnder" Crowie

View tyvekboy's profile


2132 posts in 4258 days

#2 posted 06-27-2018 10:44 AM

Thanks for sharing a great idea.

-- Tyvekboy -- Marietta, GA ………….. one can never be too organized

View swirt's profile


6635 posts in 4217 days

#3 posted 06-27-2018 01:08 PM

Pretty clever!

-- Galootish log blog,

View pottz's profile


20683 posts in 2229 days

#4 posted 06-27-2018 01:37 PM

more ingenuity from the duck.anybody that cuts a lot of circles is gonna want to make one of these.i loved the video too but id really love to see your smiling face,i mean we cant be sure it was you and not a stand in-lol.always love your tutorials duckie.

-- working with my hands is a joy,it gives me a sense of fulfillment,somthing so many seek and so few find.-SAM MALOOF.

View WeekendWoodworking's profile


71 posts in 3844 days

#5 posted 06-27-2018 02:49 PM

Nice!!! Thanks for sharing!

-- Steve

View Joe's profile


581 posts in 2332 days

#6 posted 06-27-2018 03:28 PM

Thank you so much for taking the time to post the pictures and instructions for your jig. That’s a great idea. I think I will try to build one myself. Thanks for inspiring

-- CurleyJoe, "You only learn from your mistakes"

View woodbutcherbynight's profile (online now)


10408 posts in 3654 days

#7 posted 06-27-2018 04:15 PM

Cordless tools along with some clever ingenuity have made another “ducky” masterpiece.

Well done Alex.

- crowie

+1 nice…...

-- Live to tell the stories, they sound better that way.

View Dutchy's profile


4194 posts in 3413 days

#8 posted 06-27-2018 04:45 PM

Nice disign.


View helluvawreck's profile


32122 posts in 4112 days

#9 posted 06-27-2018 06:01 PM

This circle cutting jig is so nice and the dust pickup makes it a great addition to your shop.

-- helluvawreck aka Charles,

View Mainiac Matt 's profile

Mainiac Matt

9986 posts in 3573 days

#10 posted 06-27-2018 07:38 PM

I like it!

-- Matt -- I yam what I yam and that's all what I yam

View rtbrmb's profile


821 posts in 3633 days

#11 posted 06-27-2018 09:55 PM

very clever-thanks for sharing.

Bill in MI

View LittleBlackDuck's profile (online now)


8109 posts in 2066 days

#12 posted 06-28-2018 12:34 AM

Thanks all for your kind comments.

With the growing fan base of CNC and laser in the workshop I had little hesitation in posting this project. Unfortunately each trimmer… and I’ll concentrate on trimmers as they are lousy for dust extraction… have their unique shapes so my design (housing and “dusty” duct) will fit the Ryobi 18V Cordless trimmer only. Though not telegraphed, the main purpose of this article was the dust extraction capabilities which is sadly lacking in most of the circle cutting designs I’ve encountered. The second purpose was the use of cordless to eliminate the blasted cord twist inherent in most multi pass operations. The “vertical” dust extraction hole also eliminated the other hassle of twisted hoses.
Nevertheless, this concept could be adapted to any trimmer.

I’ve tried to keep the shapes “simple” so once you make the basic shape you can create additional pieces using a following template. I recommend a lamination build so you can incorporate the dust extraction cavity more easily.

As some of the comments thanked for giving ideas… then I have achieved my aim.

As all trimmers are different, I didn’t post a link to my SketchUp mode, however, on hiindsight, anyone with a laser, CNC or good scroll saw/bandsaw skill could adapt my design to their respective tool. I have added the link to the SU model in the main body (and here). You don’t have to be an experienced SketchUp user to at least look at the model, however, a basic knowledge of SketchUp navigation may translate the “Mandarin” into English.

-- If your first cut is too short... Take the second cut from the longer end... LBD

View Richard's profile


11310 posts in 4278 days

#13 posted 06-28-2018 03:19 AM

Very Nice & Well Done!

-- Richard (Ontario, CANADA)

View bushmaster's profile


4135 posts in 3527 days

#14 posted 06-29-2018 02:04 PM

Very well done, great engineering, enjoyed the pictures etc. Will study this one some more.

-- Brian - Hazelton, British Columbia

Have your say...

You must be signed in to post the comments.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics