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Jigsaw circle cutting jig fail - now need advice on spiral router bits

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Forum topic by mathguy1981 posted 10-22-2018 06:19 PM 1321 views 0 times favorited 12 replies Add to Favorites Watch
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mathguy1981

60 posts in 77 days


10-22-2018 06:19 PM

I wasn’t happy with the amount of dust/noise/danger when using my router and 1/2” straight bit to cut plywood.
So, I found a neat youTube video on a circle cutting jig/sled for a jigsaw, and went ahead and built it. Turns out, it won’t cut 3/4 plywood and the blade is deflected so badly by the circular motion. Tried a larger and stiffer blade, same issue. It’s making an angled edge – seems obvious now that it was never going to work on material over 1/2”

So I can get out the ol’ Jasper circle cutting jig again, but what’s a better bit to get? I’ve heard of “spiral cutting” up and down bits, and they appear to be more suited to this. But what direction to buy, up or down? And can anyone recommend a specific brand like Freud or Bosch or other? They get pricey, fast.
Thanks, all.


12 replies so far

View John Smith's profile

John Smith

1432 posts in 335 days


#1 posted 10-22-2018 06:30 PM

what are you trying to make and how many ?
I would rough cut the object just shy of touching the line of the circle
and finish it up with the upward spiral router bit.
but – I have had just as much success and clean cuts with a pattern bit.
you make a plexiglass or 1/4” plywood base for the router.
many examples on google on how to do that.
here is a simple jig that will cut a six foot circle down to a few inches.
taking small bites at a time will yield the best results.
[I have never shelled out $$.$$ for a circle jig when I could make it for free].

.

-- I started out with nothing in life ~ and still have most of it left.

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mathguy1981

60 posts in 77 days


#2 posted 10-22-2018 06:39 PM

I’m cutting circles and rings for my dust collector and Thien Baffle, so not too many…3 more at the most I think.
In 1/2 and 3/4 plywood. Thanks John it should of occurred to me to rough cut it close to the line then use the router to make it perfect and smooth. That will reduce wear and sawdust.

View Andybb's profile

Andybb

1376 posts in 776 days


#3 posted 10-22-2018 06:55 PM

The Jasper jig is really designed to be used with the 1/4” bit it comes with. The angle is the issue. Two jigs come to mind. Some are here using a table saw. I used this to make a tapered circle and it worked just fine. The other would be to use a band saw circle jig with the table tilted but blade deflection is an issue with that setup too. (ask me how I know) The blade in the BS has got to be able to cut that radius without binding so that really onlt leaves you with a 1/4” or 1/8” blade. I’d try it with the table flat and if it works try tilting the table.

-- Andy - Seattle USA

View pintodeluxe's profile

pintodeluxe

5783 posts in 2986 days


#4 posted 10-22-2018 07:09 PM

1+ Jasper jig for the router (or a shop made version) and a 1/4” spiral bit.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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Andybb

1376 posts in 776 days


#5 posted 10-22-2018 07:16 PM


1+ Jasper jig for the router (or a shop made version) and a 1/4” spiral bit.

- pintodeluxe


Actually I think a straight bit would work better than a spiral. The Jasper comes with a straight bit. Spirals don’t seem to like that sideways cut as much if it can’t use the tip in my very limited experience. Also, a 1/4” bit doesn’t have to try and remove as much material. I find straight bits are better for cutting.

-- Andy - Seattle USA

View TheFridge's profile

TheFridge

10499 posts in 1658 days


#6 posted 10-22-2018 07:34 PM

Had to be careful with my 1/4” upcut. Too much pressure and it would slide down in the collet.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View mathguy1981's profile

mathguy1981

60 posts in 77 days


#7 posted 10-22-2018 07:54 PM

Somehow I didn’t get a bit with my Jasper template, just the acrylic and some mounting screws. I did buy it several years ago (don’t cut circles often). I have a 3/8 spiral UP bit on the way now, with a 1/2 shank.

View Redoak49's profile

Redoak49

3595 posts in 2161 days


#8 posted 10-22-2018 08:38 PM

I cut circles for my dust collector gates with a up cut bit – 1/2”.

I made a template out of 1/2” plywood with a scroll saw and spindle sander.

View CaptainKlutz's profile

CaptainKlutz

527 posts in 1667 days


#9 posted 10-22-2018 11:49 PM

+1 Jasper jig.
Have used jasper circle jigs many, many times.

Trick to using them is proper router bit for material being cut. Hardwood, softwood and man made materials all need slightly different bit (speed and feed change too) for best overall performance. Plywood is especially hard on small router bits, as the glue gums up the bit quickly and needs to be cleaned often. :(

Challenge is Jasper suggested 1/4 inch bit requires really slow feed rate on thick wood. For a plunge cut, will usually only cut 1/4 inch deep on each pass. That means 3/4 inch plywood requires 3 passes. If you attempt to cut too much in single pass, the bit overheats and breaks as human hands typically feed wood too fast. :(

For hardwood; I like using a 2 flute bit with either a spiral or straight edge up cut. On man made materials like plywood, or MDF/OSB, I prefer to use single flute shear or spiral up cut, or 2 flute compression spiral bit. When milling man made materials, spiral bits will need cleaning less often than straight edge blade; but still need to be cleaned any time you see residue on edge or you risk overheating. If you do not need a perfectly smooth edge, I have used roughing ‘end mill’ bits for cutting circles, and they last longest of any bit I have used on plywood.

You are 100% correct that solid carbide spiral bits can be expensive.
The only way to be cheap on spiral bit is buying HSS instead of solid carbide. I have used many HSS spiral bits, and as long as you avoid overheating the bit, they work very well for a project or two. HSS stays sharp and has decent longevity when cutting softwood. You will get put to sleep using one for hardwood or plywood due ridiculously slow feed rate required to avoid overheating.
Another source is buying import carbide spiral milling bits from a tooling supply house when they go on sale. MSC send me a sale flyer with various type of carbide milling bits on sale every quarter. The best import sale prices are about same as retail HSS, and are 1/3 cost of spiral router bits from Whiteside or Amana.
Before you ask, It is hard for me to compare bit life between various spiral bit brands on plywood. Common issue is that I forget to check, or delay the time between cleanings, and end up overheating bit and it breaks when it hits a knot or gravel (yes, I really find small stones!) inside the plywood. :(
So I can not stress enough the need for keeping spiral bits clean and cool when machining plywood/MDF.

PS – if you need circles below 8 inch OD, highly suggest using a fly cutter on drill press. Works much faster, and lasts much longer than any router bit. Not safest contraption to chuck into a drill press, but it works. There are many existing threads on the topic if you search.

Best Luck.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

View lumbering_on's profile

lumbering_on

563 posts in 662 days


#10 posted 10-23-2018 12:43 AM



what are you trying to make and how many ?
I would rough cut the object just shy of touching the line of the circle
and finish it up with the upward spiral router bit.
but – I have had just as much success and clean cuts with a pattern bit.
you make a plexiglass or 1/4” plywood base for the router.
many examples on google on how to do that.
here is a simple jig that will cut a six foot circle down to a few inches.
taking small bites at a time will yield the best results.
[I have never shelled out $$.$$ for a circle jig when I could make it for free].

.

- John Smith

+1 to not buying a circle jig. I have an adjustable jig I made a few years back, and it works just fine. The only thing is I have a bit of a screw hole in the center of the circle, which can usually be hidden or just sanded out.

View JAAune's profile

JAAune

1846 posts in 2489 days


#11 posted 10-23-2018 05:07 AM

Upcut bits leave a clean lower edge and tend to cause fuzzing and chipping on the top surface of the cut. Downcut bits are the opposite. Be careful when using a downcut in a handheld router. They want to lift out of the cut. Upcut pulls down.

Southeast tools sells solid carbide spiral bits that are excellent and priced lower than most competitors. They aren’t as good as a premium bit from Onsrud or Vortex but they’re close enough that the difference only shows when production cutting with a commercial CNC router.

A curious thing about carbide tooling is that breaking most often happens when the feedrate is too slow. Overheating shortens the life and dulls the edge prematurely so it breaks under the load. The faster the feedrate, the cooler the cut. Taking shallow cuts allows for faster feedrates and better chip removal.

I’d recommend cutting about 1/16” outside the desired radius with the jigsaw then cleaning up the cut in a single pass with a sharp 3/4” straight bit. You don’t need chip clearance capabilities for this type of cutting.

-- See my work at http://remmertstudios.com and http://altaredesign.com

View mathguy1981's profile

mathguy1981

60 posts in 77 days


#12 posted 10-23-2018 04:31 PM

Wow, thanks so much for all the replies! That was exactly what I needed to get back on track. Special thanks to CaptainKlutz for the in depth explanation

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