Suggestions needed - flutes in nylon rod.

[BCRider]

I am satisfied with using my mill. The ball end mill has to go only about 1/4" deep. I'll make a 12 position index tool of some sort using one of the suggestions here.
FWIW these two cylinders don't come in contact with each other. There will be at least one hundred thousandths separating the two.
Thanks for all the suggestions.

Based on them not touching with that sort of gap I'd say just marking out twelve index marks on the end of the cylinder and "index" to some handy point by eye would be fine. The precision you can get with a cheap school protractor and eyeball can pretty easily be plus or minus a half a degree based on the fine point felt marker as a marking tool. And that would be way more than good enough when you've got 100 thou of play room.

[George Bulliss]

Mount it to a clock and make one cut every hour

[Illinoyance]

Buy a Kalamazoo indexer with tailstock. They are often available used. I think there are Chicom copies as well.

[BCRider]

Mount it to a clock and make one cut every hour

You don't post often but when you do it's almost always a good one!

[Paul Alciatore]

If you don't have any indexing device, how are you going to space them in the lathe? No matter where you do the job, you still need to do some indexing.

I would probably do this in the mill, not the lathe. But then, I have the ability to index in both. A crude indexing arrangement can be made with a 12 tooth (or 24, 36, 48, 60, etc.) gear or sprocket or whatever. The relatively inexpensive spin indexing devices others have mentioned are one way and with one degree increments, they certainly are capable of 12 divisions. (360 degrees / 12 = 30 degrees). With a spin index and a matching (improvised?) tailstock it would be easy to do this in the mill.

[Paul Alciatore]

But do it quickly or you will have a helical flute. Of course, you would not have that problem if you use a digital clock as it would only change on the hour.

Mount it to a clock and make one cut every hour

[mattthemuppet]

If you're doing it on the mill, clamp the rod in a table slot and cut your first flute. Rotate it to the next one based on your scribe marks and mount some kind of pointer or clamp that locates the first flute you cut. Cut the 2nd, reclamp with the pointer in the 2nd flute, cut the 3rd and so on. Not as fast as an indexer, but faster than shaping it on the lathe.

[Paul Alciatore]

OK, you may regret this as my evil mind has started working.

Construction:
Start with an old fashioned, analog clock.
Remove the escapement or synchronous motor.
Drive it with a stepper motor. One step equals one clock second.
Couple the hour hand (it's shaft actually) to a spindle.
Add some drag to take up backlash.
Have a locking mechanism on the spindle.
Mount work to be indexed on that spindle.
Arduino, Basic Stamp, Propeller, etc? Up to you.

Math:
12 hours x 60 minutes x 60 seconds = 43200 steps
43200 is evenly divisible by 2, 3, 4, 5, 6, 8, 9, 10, 12, and many more factors.
For instance: 12 divisions = 43200 / 12 = 3600 steps
With micro-processor and partial steps almost any number of divisions are possible, within the accuracy of the clock gears of course.

Operation:
Release brake.
Index with stepper motor using math above.
Tighten brake.
Machine feature.
Repeat as needed.

Accuracy?
I really don't know.
Resolution:
One step = 6 arc seconds (1/10 arc minute or 1/120 degree)


A Clock Based Indexing Head

Article to follow. But probably not soon.

For the mathematically inclined, the prime factors of 43200 are: 2^6, 3^3, 5^2. That leaves out multiples of 7, 11, 13, etc. But it does include all the possible divisions that a spin index is capable of (2^3, 3^2, 5) and a lot more.

I told you that I have an evil mind.

Mount it to a clock and make one cut every hour

[garyhlucas]

I've made improvised indexers using gears from my lathe! Problem with any process on nylon or a low melting pt plastic is keeping it cool so you don't end up with a gummy mess. I hadn't worked with acrylic in ages and cut a cat door opening out of a piece of 1/4" with a jigsaw, what a PITA mess!

Plexiglass cuts very nicely if you use a jigsaw with the blade oscillation feature. The blade cuts on the upstroke and backs up so it does drag on the downstroke. This stops the heat that melts the plastic. At my last job I cut 1” thick HDPE with a Bosch oscillating jig saw and got nice smooth cuts.

[gellfex]

Plexiglass cuts very nicely if you use a jigsaw with the blade oscillation feature. The blade cuts on the upstroke and backs up so it does drag on the downstroke. This stops the heat that melts the plastic. At my last job I cut 1” thick HDPE with a Bosch oscillating jig saw and got nice smooth cuts.

That's what I was using and I tried all sorts of settings and could not get it to not gum up. HDPE it's a totally different animal, cuts great on most saws, I've cut 4" dia rod on my 12" miter saw, though on a bandsaw the swarf really gathers into a nasty ball below the plate. And forget about a lathe, those rubber bands it makes are deadly!

[darryl]

Short of purchasing something to index with, I'd be inclined to come up with an assortment of indexing discs, or whatever format suits what you might be holding with. A 36 tooth gear would be a good start, giving you 12 positions easily as every third tooth. How often are you going to need to index? This is one of those 'make a tool to make a tool' things. At its simplest, you could wrap a piece of paper around the workpiece, the nylon rod in this case, then divide the circumference by 12 using carefully placed pencil markings. You lay out at an angle so you can get 12 equal divisions between the circumference markings, then extrapolate those markings to a perpendicular line corresponding to points on a circumference line. You can divide a circumference of say 10.5 inches into 12 divisions this way, and you don't have to know the exact distance between the final markings- they automatically fall where they need to be. This of course means transferring pencil marks, which has it's own error potential- but maybe it's close enough for what you're doing.

For my part, I mounted a disc behind the chuck on the lathe, and this disc is laid out with equidistant holes which can be divided into several groups- I went 15 degrees between markings, which gives 24 divisions, 12 divisions, 2,3,4,6, and 8 divisions. If I need to make a division wheel to suit some holder I might make for the mill, I can do so.

I've also used chain to make a division wheel. The number of links on the chain loop decides the capability, and the chain loop can be pressed onto a suitably machined disc to give the suitably spaced 'interlocks'. If you need a large number of divisions, this can result in a fairly large diameter 'division disc' so you might instead use a toothed belt. For instance, with a roughly 12 inch diameter disc and a tooth spacing of .1 inch, you can lay out 1 degree per notch, which is 360 divisions. With that, every 30 notches is 1 of 12 divisions.

A change gear of 36 teeth gives you 1 of 12 every 3 teeth- that's a common gear and a reasonable size too.

[sarge41]

Challenger: The quickest and dirty indexer for your lathe is your lathe chuck. Wrap a tape measure around the chuck and measure the circumference and divide that number by the number of flutes you need. Wrap a piece of masking tape around the chuck in place of the tape measure. Mark the tape with the correct number of spaces and at the correct spacing for each flute. Use a piece of sheet metal, clamped to the lathe bed and to the chuck, then use your carriage as a shaper with a tool shaped to cut the groove. Index it twelve times, job done.
Sarge41

Took longer to describe it than to do it.

[Paul Alciatore]

The thing with plexiglass and other plastics with low melting points is to keep the speed of the tool low enough while actually cutting them.

For straight lines in plexiglass I use a scraping blade in a utility knife. I have a blade that looks like the common hooded ones but it is not sharpened inside the hook. It has a straight sharpened on the outside of the hook and the edge of the hook forms a triangle cutter that scribes a line and removes a little plastic in the process. Several passes create a deeper scribed line and I then do the same on the back side. Once both sides are scribed, I just break it apart like one would with a sheet of glass that has a line scribed on it with a glass cutter. Neat and sweet with no loss of dimensions: a 10 inch piece becomes two 5 inch pieces with chamfered edges.

Hand operated, hack saws and scroll saws are also good ways to cut plastics if you don't try to go too fast.

Plexiglass cuts very nicely if you use a jigsaw with the blade oscillation feature. The blade cuts on the upstroke and backs up so it does drag on the downstroke. This stops the heat that melts the plastic. At my last job I cut 1” thick HDPE with a Bosch oscillating jig saw and got nice smooth cuts.

[psomero]

get a $10 5c hex collet block on ebay/amazon, cut half of the flutes with the flat in the horizontal, then re-clamp on the vertical face, re-indicate and cut remaining 6?

[challenger]

I found a cutter with twelve teeth and a 7/8" bore. I also scrounged up a machine bushing with the same OD and the 5/8" ID. I put blue locktite on it and set it in the gear and will look at it today to make sure it is really locked tight. Then I need to figure out how to mount the rod on the mill table because the cutter is slightly larger than the nylon rod. Shouldn't be a problem.