Compass Cutters are cool.

[Jeff Lassahn]

I've been making cardstock transitions and stuff by printing out templates and cutting them out freehand with a hobby knife. This kinda works but I tend to end up with half a millimeter or so of wobbliness around the circular edges that I later have to patch with wood filler or something.

I recently got a compass cutter: https://www.olfaproducts.com/olfa-cmp-1-compass-cutter-6-quot.html

It helps a lot, I'm getting cleaner more circular cuts that line up better when installed.

A couple of problems I've had:
Setup is kind of picky, locking the radius by tightening the set screw tends to slightly change the radius, so I frequently have to mess with it a bet to get a really accurate position.

This version goes up to a bout a 3 inch radius, and for conical transitions three inches isn't as big as I expect it to be, even if the final rocket diameter is only like 1.3 inches when you want a long shallow taper you can easily end up wanting a cut radius of 6 or 8 inches. There are bigger versions of this tool, maybe I'll end up with two or three different sizes.

I also like making centering rings out of papered balsa. So far it hasn't worked well for that. The spike that acts as the center pivot tends to wander while I'm cutting, tearing up the center of the balsa and ruining the accuracy of the cut. I'm hoping I can find some way to improve this...

Another lesson learned, if you use one of these make sure you add a really clear mark at the circle center on your template. Having a good way to place the pivot is essential to making these things work.

 

[mjennings]

I have a similar one, it's ok on paper. Haven't tried it on balsa. Maybe drilling a hole in the balsa and then the pin could poke into a cutting mat underneath? mine came with a small plastic disk for when you didn't want a pin hole in the middle. Something like that could help too.

 

[neil_w]

I also like making centering rings out of papered balsa. So far it hasn't worked well for that. The spike that acts as the center pivot tends to wander while I'm cutting, tearing up the center of the balsa and ruining the accuracy of the cut. I'm hoping I can find some way to improve this...

When I do this, I always cut oversized and rough, and then sand down to size (as marked on the ring in pencil or printed or whatever). It's so easy to sand balsa, much easier than doing a precision circular cut.

 

[Jeff Lassahn]

When I do this, I always cut oversized and rough, and then sand down to size (as marked on the ring in pencil or printed or whatever). It's so easy to sand balsa, much easier than doing a precision circular cut.

That's kind of what I've been doing. It just feels so inelegant...

Many years ago I worked for a company that made sensors for robots. We had a really talented manufacturing engineer, and I still remember the note of horror and contempt that crept into his voice when he talked about parts that were "file to fit". I think of him whenever I'm test fitting something, then sanding it down a bit, and feel shame.

I still do it, of course, but I feel shame.

 

[Funkworks]

There’s quite a difference between sanding a few parts for one model, and setting up a production chain to make 100 parts daily. It’s like comparing a painting with a video.

Anyway, I found an Olfa compass cutter but haven’t used it yet. Its a weakness I have to buy interesting tools when they’re on sale.

 

[Sandy H.]

There’s quite a difference between sanding a few parts for one model, and setting up a production chain to make 100 parts daily. It’s like comparing a painting with a video.

Very true. Back in the day there were talented painters. Today anybody can make a YouTube video.

Sandy.

 

[Funkworks]

Well, to be fair, editing a video can also be an art (and setting up a production chain can be very cool). Just very different. It depends who you ask,

 

[Sandy H.]

Well, to be fair, editing a video can also be an art (and setting up a production chain can be very cool). Just very different. It depends who you ask,

My wife has been a video editor for years, so I obviously agree. A fun YouTube watch is to search for "the shining romantic comedy trailer" which is very old, but highlights the role of the edit vs the movie. There are tons of others, but I just happened to remember that one.

Myself, as a custom machine designer, gets stuck with the 'hate shimming/re-machining' vs cost of tolerancing all parts to such tight tolerances to meet assembly requirements. Due to the size of the equipment we make (or used to make. . . <sad>) sometimes it was much more cost efficient to pre-assemble, measure and then make final fitups with either shims or by machining down spacers that were intentionally oversized initially. A good example was a load bearing set of shims on a 15,000 Ton hydraulic press we built. It was way cheaper to pre-assemble, measure and make the right set of wear plates (shims. . . ) than tolerancing 8 frames that weighed over 25 tons each out of 10" plate and stood 2 stories tall. . .

I did poke fun at your initial statement with my comment, as it was different than my personal experience, but I did so with no ill intent and hope it came across that way or at least not offensively. In 95% of the cases, I agree with what you were getting at and it is those cases that matter most often.

I have never worked in a final production environment where you're talking about hundreds (or even 10's of thousands) of parts a day that go into assemblies of other parts. In those cases, for sure, any form of hand rework is out of the question!

Sandy.

 

[NateB]

Several years ago, I scored an AllPax gasket cutter on Ebay for $30. A cutting board with a hole for the pin keeps cuts accurate. I don't think I'd find worth from the tool at retail price, but if you can find one cheap, get it.

 

[Woody's Workshop]

I used one in my wood working on occasion.
I prefer the 2 blade, I think mine was a General Brand.
They cut by scraping, and bits get HOT.
I believe mine had D2 Tool Steel Bits, and replacements were available.
I know a file would even scratch the bits.
I preferred the 2 bit because I used it in my drill press.
Single bits are off balance and not good on the drill press.
I would use a single bit in a hand held drill though.

 

[icyclops]

This is the type of cutter you want for cutting balsa, card stock or paper laminate balsa center rings.

You can get a double sided or single sided blade for it.....

 

[icyclops]

Made by NT and sold on amazon.

 

[icyclops]

How do you use it? You adjust the blade on the bottom to the diameter you want....place it on the balsa or thick card stock, then twist/spin it. Cuts perfect circles and inside circles too. Don’t try and cut thick balsa all at once, spin it a few times to completely cut through.