cutting notches in a ring

[SavannahLion]

I'm a little irritated at this.

I'm working with UHMW but rather than screw up what I have, I'm doing test cuts with scrap wood.

I have a flat ring (think donut-like) about 5.5" I.D. that I would like to cut notches about 7 or 8 mm deep on the inside of the ring. The shape of the outer portion is SQUARE and measures about...  6 or 6.5" a side. I'll have to double check that measurement if it's crucial. To give a more solid idea, something like thus: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJK88

Square corners would be more ideal though. I intend to fit LED lights into the notches. I can work with rounded corners like that above I guess.

I tried an experiment which involved picking an arbitrary spot, drilling. Then measuring what I hoped is 180 location, drilling, then measuring 90 from that, drilling etc etc. That was damn painful, sloppy, and not very repeatable.

The best idea I could come up for a jig is to use a Lazy Susan to clamp the work piece(s) to, find the center of it in relation to the drill press, the proceed to mark off each position on the table, then drill, drill drill.

Am I mad or is there an easier trick?

[TopJimmyCooks]

Layout is layout.  get a compass or trammel setup -that's how i would lay out cardinal points on a ring.  No, its not easy in this application but with a compass you can stick the point in the uhmw and pivot nicely. 

as far as the square corners, once your notches are laid out, cut them with a plastic cut file.  it will go through the UHMW like butter and allow you to sneak up to your layout line.  The corners of the file are square, so your notches will be as well. 

What are you making?

[lilshawn]

a protractor is your friend.

here: print this...

[PL1]

Use Adobe Illustrator, Inkscape, or PowerPoint to design your layout including center points for drilling.
Print and measure to verify no resizing/distortion.
Tape down in exact position.
Mark drill centers for center hole and notches thru paper w. small nail and sharp pencil.
Mark the 4 corners for each square notch same way.
Remove paper.
Trace the notch outlines using sharp pencil and ruler.
Drill notch holes first, then drill center hole.
(optional) Use jigsaw to cut close but leave a bit to file for best fit and finish.
File out to edges and corners of notch.


Scott

[SavannahLion]

OK, OK, I got it. I get it.

Here's my mistake. I was trying to drill/cut the center hole, then drill/cut/shape my notches. When I should have been doing the notches then the center hole.

Now that I think about it, the answer should've have been painfully obvious and by changing the order (as suggested by everyone else) it becomes a more natural progression.

Thank goodness I didn't waste my plastics trying to figure this out.

Now I need to find a source for a cow, a tutu and a culottes.

[PL1]

Now I need to find a source for a cow, a tutu and a culottes.

"Pinky, Are you pondering what I'm pondering?"

“Uh, I think so Brain, but how are we gonna teach a goat to dance with flippers on?”



Scott

[SavannahLion]

What are you making?

I didn't answer this at first because I'm not really quite sure how to describe it. It's a custom score reel... sort of.

Not sure if I'll ever put the finished design into a cab. The sketchup model looks very good and my calculations show it to be functional. The major problems I'm encountering are A) finding motors/servos/steppers that will work that are cheap enough (my model requires one for each place value) I can't quite work out the forces involved and B) feedback which is, what I hope, the notches will solve.

The controller requirements are getting beefy too. Every time I add a new feature, it practically doubles my IO requirement. For the morons who will inevitably poopoo that statement. To give you an idea, the motors require two I/O each so for three digits, that's six I/O. Add feedback and I just doubled my requirements to 12 I/O. I know I can reduce the I/O requirements through refining the circuit, such as using only N+1 I/O for each motor, but it's too early to work those out anyways. I'm using an Atmega32U4 so I have plenty of headroom,  I just don't want to commit the final circuit to a controller better used elsewhere.