Cutting a Shape from Plastic with Manual Router, as opposed to CNC

**Educated Guess** · Aug 27, 2019, 05:41 PM

Hello. I make guitar picks high-end. Most of our materials cut easily with laser, but one does not.

I buy it in a 12-inch rod, then I want to stand the rod up perfectly perpendicular and rout it downward with the shape of the pick, then slice off each one. For CNC I'm getting quotes in the $500 range. Is there a way I can do this manually with a regular router, by building some kind of template or guide?

Our materials are very expensive. For instance, one is DuPont Vespel, which is one of the most expensive plastics on earth. It cuts beautifully with CNN.

Or is there such an inexpensive benchtop CNC machine I could buy or build?

Thank You,
EG

**bruce.desertrat** · Aug 28, 2019, 05:32 PM

Actually I think it would be simpler to use a standard router table, and pass the rod horizontally past the bit. You would need some sort of jig to hold the rod properly for each pass, and the appropriate bits to form the shape. This video shows the basic technique

You might have to invest in a couple custom router or shaper bits to do your exact profile, but I suspect it would be well worth it for the efficiency improvement. You would need one for the sides (since they're symmetric all you need to do is flip the stock end-for end) and one for the top.

**CharlesWaugh** · Aug 28, 2019, 06:12 PM

WOW! From McMaster (NOT the cheapest source, but an easy place to find and price things quickly) here's a price:
1" diameter Vespel rods = $110 P E R I N C H ! !
YIPES!!

I would agree that using custom router bits and running lengths is the way to go.

You'll need to build a fixture that will hold the rods by the ends and is flippable, so you can run side A, then flip it and run side B.

Then, to shape the top (the 'third' side) you'd need another custom router bit and another fixture.

This fixture should be a groove that has been filled with silicone casting compound and the rod (with the first two cuts done, is set into the groove and vacuumed into place so you can accurately index that last router pass.

I have no idea how vespel machines or how harsh it is on tooling, but you may be able to have a local tool grinding shop do the custom tools for you, sicen the epth of cut will be less than 1/2" you can probably use a standard bit that has been modified.

Uh..... more thoughts...

If you cut accurate slots in each end of the rod, you could build a fixture that would pinch it end-to end (maybe 4" lengths at a time, for stiffness) and the router bit could do a complete side at a pass (including the top). Then flip the stock end-for-end, aligning it using those slots, and do the other side.

I would suggest a shaper cutter, since the depth of the cut would end up being half the width of the finished pick and a router bit would be problematic at that diameter.

**CharlesWaugh** · Aug 28, 2019, 06:21 PM

More thoughts:

Use a pin router.
It has a router up above, and a pin under the fixture that holds the work.
The fixture has a groove on it's underside so the pin will track in the slot and guide the fixture.
On light cuts, the depth of cut can be adjusted by using a tapered pin and moving up or down a touch (and to adjust for bit wear)

And, yes, you can buy table top CNC's but they are not too tight and stiff. Having set up, run, repaired, and built any CNC's in production environments, I'm a purist. sorry.
:-)

You might look for a used CNC knee mill and use it instead.

Oh! another way to go is the Thomson Mill-Drill table. I had one for years and never used it, but it would be perfect for this application. There's a couple for outrageous amounts on ebay right now

How funny! I just searched Youtube for videos of the Mill-Drill and found

when selling mine! (I had forgotten entirely that I had made that video)

**Educated Guess** · Aug 28, 2019, 09:34 PM

Charles, Vespel is probably the most expensive plastic per inch on the planet. I mean, it's DuPont, right?

You won't believe this. A Vespel sheet that is 10" x 10" x 1/4 is, wait for it, $1100!!! I kid you not. Now you know why we buy the rods.

Anyway, thanks so much for taking the time to respond. These are all great ideas. We just got a killer deal on an Epilog laser with only about 30 hours on it, so we're tight on cash till the end of the year, so no Mill/Drill Table in our immediate future. But I do believe this may be solvable for much less $$$$. What I can do is do test cuts with Acetal or something, which costs only about $20 a foot.

Thanks again,
EG

**Educated Guess** · Aug 28, 2019, 09:36 PM

Bruce, terrific information, and so helpful. I know I can solve this.

Recently I repurposed a $10 juicer I got at a garage sale into a polishing machine that Rio Grande sells for $600.

Thanks again,

EG

**CharlesWaugh** · Aug 29, 2019, 02:34 AM

EG,
Glad to help brainstorm stuff anytime (my brain runs like a thirsty tourist after a trip to a foreign land).

BTW: those Mill-Drills on Ebay are waaaaaay overpriced - I think one guy listed his too high and the other guy thought that was then the going rate when he posted his.
You might try low-balling them repeatedly over a few months time - they might wear down.

You could also try using a top-bearing flush-trim bit in a router (the bearing is on the shank end of the cutting edges rather than on the dangling end. I don't know how well Vespel glues, but a piece of phenolic glued on the end of the rod with superglue could be your master bearing surface.

I've seen top-bearing bits with only 1/2" long cutting edges and 1/2" diameter shanks so they are quite stiff. Also, if you taper grind to OD of the bearing slightly, you can take two passes, lowering the bit in the router a touch to take a finish pass (or wrap a turn of tape on the master form on the first pass and take it off for the second pass).

You could also try feeding the cat lots of castor oil an hour before the skinning starts...
:-)

**Educated Guess** · Aug 29, 2019, 12:43 PM

Charles, thanks. I may pick your brain until it scabs. More anon.

EG

**CharlesWaugh** · Aug 29, 2019, 01:59 PM

Uh... you're a nice guy all, I'm sure... but... my brain didn't like the last time it got scabs... so...
:-)

**Educated Guess** · Aug 29, 2019, 04:31 PM

Originally Posted by CharlesWaugh

Uh... you're a nice guy all, I'm sure... but... my brain didn't like the last time it got scabs... so...
:-)

Understood.

Are you familiar with the really dry comedy of Steven Wright. Your comment reminded me of one of his best jokes.

"My girlfriend and I went camping, and somehow she got poison ivy on the brain. The only way she could get some relief was if she thought about sandpaper."

EG