Trimmer Circle Cutting – Without the (B)dust

Boys and Girls,
There have been countless articles about bandsaw circle cutters (no article by me... yet, but the picture’s free)
large circles,

small circles,
and nearly countless articles involving routers (another freebie picture),
however, I would like to tread where most ducks would not drake dare… circle cutting, using a bench mounted Carvex (jigsaw for the Philistines).
But before you start salivating, and while I draft my proposed project, let me whet your appetite by this article I previously posted on Lumberjocks back in 26th June, 2018 which bragged, “Trimmer Circle Cutting - with built in dust extraction!”
It was about circle cutting without the sawdust using a router (trimmer). You’d have to be a tad gullible if you actually believed without the sawdust, as routers, even with small router bits, create a helluva lot more than bandsaws, however, this jig has a dust collection built in, which is a mean achievement for using a RYOBI trimmer renown for NOT being sawdust friendly… 
FAIW, I used my laser’s cutting ability to facilitate the makin of the jigg, however, using the SketchUp output, there is no reason why it could not be fabricated using conventional tools. The only problem I could possibly envisage is that you would have to go out and buy the old model Ryobi trimer which are no longer produced.  Nevertheless, the concept could be adapted for other trimmers... I have a swag of other trimmers, however, there is no desire to venture down that path as I own two of those obsolete trimmers.


 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. 

Everything 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


Dandy design, looks great. Duck.

-- Soli Deo gloria! ( To God alone be the Glory)

Trim routers work great for circles, and that is a fancy jig to handle the job, well done.

Main Street to the Mountains

Cool solution, Alex!!

Cheers, Jim ........................ Variety is the spice of life...............Learn something new every day

no dust on MDF  is very impressive GR8 JOB 😍😎👍

where is Marvel nighty ? ? ? 


wow thats quite the setup duckie. im afraid i dont cut enough circles to invest in something like that.

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

Can't complain about double sided taping the trim router base to a scrap of masonite and having a go, but I gotta admit your device has a bit more elegance and utility! 🤠 👏

Impressed with your solution to gaining thickness beyond what your laser can cut, Something I'll always have stashed in the brain pan, along with making locating pin holes for the final assembly of the stack 👍
I have still got mine and it works great!
Masonite ... now there is legal stupidity completely out of hand in a big way.
Just exactly what is our society/world coming to?

Regards Rob

Came out great. You must be going to make a lot of circles. What’s a Ryobi trimmer?
That’s an excellent design, LBD! Very clever.
Thanks all for looking and the encouraging compliments.

No idea what spurred me on to make this jig as I already had circle cutters... OK, at least one idea,

My bandsaw jig can't make an inner circle and while my Fe$tool jig had good dust collection (approx. 75%), the cord and dusty hose was a PITA for multiple passes due to incremental depth plunge...  router bits make a bucketload of sawdust.

The inspiration was mainly the cordless feature.  While the dust hose was designed to be inserted vertically, so as the jig was rotated, it spun on its rotating end nozzle as it was suspended from the ceiling, it was by pure chance as to it's efficiency... the flat, wide base of the jig sealed the bottom and the collar sealed the top... only one path for the sawdust. 
I don't believe in perfect (everything can always be improved), so I'm only bragging 99.9% dust collection... and maybe a few "dandruff flakes" on the shoulders...

The beauty of the concept is that it can be adapted for most trimmers as long as the top layer (of 3mm MDF) fits snug around the body of the trimmer (that's why it's in 2 halves... or maybe 3, for those suffering dyscalculia). 

 commented about 12 hours ago
Can't complain about double sided taping the trim router base to a scrap of masonite and having a go, but I gotta admit your device has a bit more elegance and utility! 🤠 👏

I wear the nightie for elegance... Tools/jigs are a different story.
Sort of agreeing with RC about masonite... however, my simple opinion on it's use is the potential for 0% dust collection.

When it comes to 0% efficiency (dust collection), my next project to be posted, will show that in trumps....and not the Donald type.

 commented about 6 hours ago
Came out great. You must be going to make a lot of circles. What’s a Ryobi trimmer?

I may have mentioned in another blog that to me, micro adjustment in a trimmer/router is a must.  After Ryobi upgraded their trimmers with a micro adjustment feature, I was compelled to buy it, making my rack & pinion Ryobis redundant.
What better was to use one then in this jig where micro controlled plunge was not an issue 
... and now sports the pivot pin mechanism unobtrusively on board...
The other one is set at a constant height for my 1.5875mm (1/16" to Philistines) round-over bit, with a 3D printed dust port shroud, semi-permanently clamped to one end of my tabletop,

As for "make a lot of circles"... This is an old post moved across from Lumberjocks.  At the time I used to make a lot of circles/clocks... had a lot of dirty minded (I prefer to call appreciative) HWOs (He WHo Obeys) with understanding wives...  I still churn out a few a year... a dirty mind is born every day... though 365 clocks (366 in a LY) is a tad too many to make.
The above linked project has a fairly good write up on the use of the jig.

To make the jig more accurate, I laser print a gauge for desired radii, that makes bit displacement setting a no brainer,

0.001mm accurate...

It's not a matter of a "lot of circles", but just "1 large circular hole".

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

 commented about 21 hours ago
no dust on MDF  is very impressive GR8 JOB 😍😎👍

where is Marvel nighty ? ? ? 

Yeah... the amount of "lack of sawdust" absolutely floored me... would have been a nice bonus but wasn't my primary intention... it was the raveling of the cord and hose that I wanted to overcome... all the rest was glitter.

Apologies for the civies... must have just got home from either my parole officer or psychiatrist... long time ago... could have been a double booking on the day.

The Marvelous will feature in my next project.  Had to steal some happy snaps from the videos(s) as I forgot the film, so it will be immortalised in the upcoming stills as well.

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

I just had to have another read of your post,  as you have motivated me to make one up for my Makita Trimmer too
I am always running around in circles so I thought I could do it on my head.

If it works out OK I might just change the blades on my Makita planer while I am a roll

 Sorry the coffee hasn't kicked in yet!

Regards Rob

Great brainstorming RC...only issue I can potentially see is "dust collection"... grass clippings come in greater granules than sawdust... the collector bag may need a trolley on wheels rather than just a backpack... or maybe just sit back and imbibe in a 6 pack.

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

what just only one six pack!

BTW I have a robot dog like yours, I  saw it in the kitchen this morning!

How lucky is that!

Regards Rob

I see. There’s that pink boot again. I never saw a blue cordless Ryobi before. Are the batteries interchangeable with the green ones?

Can you make circle’s with this one?

Seeing your skills I think you could figure it out. 😃 
They were originally blue.  I guess in line with their corded range,

then they changed colour...

however, the new model incorporated micro adjustment (circled, +++²)

The colour change was probably because Ryobi didn't want to be mistaken for that other crappy blue line products some dare to call... Bos¢h!

Still have a few blueys,

uses the same battery...

Still, router/trimmer circle cutters are ho-hum... it's the unplanned extent of the dust extraction, that blew me away.

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

Great looking jig.
I would copy it but I try not to go around in circles....LOL