Octagonal aluminum bar stock?

Anyone know of a source for aluminum bar in an octagonal cross section? 5/16 or 9mm across flats, prefer 6061 to insure anodize color match with a related part. I'm guessing this is not available, haven't found anything via Google, but thought I'd ask anyway.

Jon

It's for an ultra high tech carbon fiber violin bow, octagonal profile matches the bow so hex won't cut it. Options are octagon, knurl, or some sort of shallow fluting. But not worth the time/expense of profiling the OD to get the octagon.

(dang, wish my Omniturn had the indexing spindle!)

Jon

If you go to VarmintAls.com , I hope that URL is correct, click on his Mini-Lathe page and scroll down to a direct link to Online Metals. I was just browsing their site today and I am pretty sure I saw some Hex or octagonal bar stock but I am not sure of the alloy number.

Dennis

======== You may want to contact the custom aluminum extrusion houses. They may have a stock die for what you want, or for this simple a profile it should be cheap to edm one. Be sure to check material and physical properties/temper. A few places you can try

web page showing octagons

google on for c. 700 hits. register on

a bunch more.

For short lengths a 5C spin index should work well.

the alloy number.

Thanks, I tried all the online sources I could think of, nobody has it. Funny though, lots of places list weight per foot for octagon materials, nobody supplies it....

Jon

Only problem with extruders is the minimums. A single 20' length would be a several year supply. And there are two other sizes I need to make. A 1000lb order which is a common min. order would last for several centuries! Customer is not unwilling to invest, but probably not for inventory that will outlast him and his kids....

Think I've figured out an approach though, will just chamfer mill short lengths of material in the mill, then turn. Not the most efficient approach, but it's a low volume high value part that would certainly justify it.

Jon

Anneal and press the round stock through a hex hole in hardened steel.

The entire length of the finished part is octagonal. Yes, I could make it out of round stock in this manner, but then would have to move to the lathe to part off, or hack saw off. While quantities are low by production standards, I could be making up to 100 pcs in each of three different sizes, and that would be a big pain. Also, we're looking at multiple grooves, or finning, just as a way to reduce weight. If the part was already to length it would require handling twice, turning the part around in the collet. If I had an 8" length, I could proceed to make the part complete in one smooth process. I'd just be changing 'bars' a lot more often that I'd originally wanted to.

For perspective, this is for a high tech violin bow made from carbon fiber. Customer is going to the expense of buying 5-40 threaded titanium screws from Germany and having me make as light an aluminum knob for the end as we can, all to shave another gram or so. It's a production process, the focus is on end results, not cost. Yet, we don't have anywhere near the volume to justify custom extrusions.

Appreciate the input though!

Jon

Try this site

I was thinking he meant with a square collet. Actually, with a square collet, you may not even need a spin index, just a square collet block, and mount the collet in the block at 45 degrees... --Glenn Lyford

That would require indexing the collet to get the stock at the 45 degrees. Starting with round stock means more passes but much lighter cuts. It still leaves me with either a part I have to handle twice in the lathe to do the grooving, or waste a significant bit of material leaving extra in the collet. Though low production, it's still a production process and flipping a collet block 400 times gets tedious.

Jon

Hey - if it's fairly soft aluminium and you have a good-sized lathe, press an octagonal die over the stock with the tailstock. Drill, thread, press, cut, all with one instance of work-holding.

How much is he going to sell these bows for? My sister told me how much her hi-end bow was once and it made my eyes open *quite* wide.

You can only rotate the collet if you move the guide pin.

I chuck round stock in a 3 jaw chuck with a 5C mount and move it back and forth between the lathe and mill as needed.

======= If you have some sort of mill with the required travel, the easiest thing might be to do two pieces at a time. Clamp/indicate a straight piece of bar stock on your mill table [even a Bridgeport should do fine no cnc necessary] and clamp two pieces of square aluminium against the guide, and run a 90 degree included angle endmill between the two pieces. Rotate stock 3 times. For sample end mill see

?PMAKA=308-0227&PMPXNO=9404927&PARTPG=INLMK32 Good luck and let the group know how you make out.

You COULD set up a mini-rolling mill to produce the cross section you need, my guess would be that you could use rollers maybe 3-4" in dia. with the desired cross-section cut in them and T0 hardness stock. Oven treat afterwards. Would save a lot of mill time if it'd work.

Stan

I don't know, but they will not be cheap. My customer has dome something really new. The bow is fully instrumented. Pressure transducers on the string can resolve if the bow is canted, and where the bow string is in contact with the violin strings. In addition it carries 3 axis accelerometers that resolve the actual 3D motion of the bow in real time. Don't know what software he's doing this with, but he has a solids model of the bow, hooking up the bow to the computer, you can wave the bow around and watch the solids model perfectly mimic the real bow.

I'm looking forward to seeing this thing in action in mid-January, I'll better understand exactly what it can do. But apparently through software there are a ton of things you can do to the sound based on what the bow is doing.

I've been working with him on the frog adapters (where they get these strange names I don't know), they are aluminum and milled to relieve as much mass as we dare. There's going to be three models, violin, cello, and bass.

He was in Ireland a couple weeks ago, some world class violinist from Finland played with it and pronounced it 'historic'. It's first public performance debut is coming up in San Diego in a few weeks or so, and it's also going to be featured at some supercomputer convention.

I am playing a minute part in this, but it's neat to be part of something that's really ground breaking. I'll ask him if he has a web page on it yet and if I can post a link to it.

Jon

That's the approach I've settled on, except I'll do one bar at a time down one side and back the other, rotating 180 just once. I have dual vises and custom jaws for machining long lengths. I'll post a link if my customer says it's OK.

Jon

Ok, this is what the octagon stock is for:

2nd page shows the electronics and housing. Just above the K-Bow legend is the frog adapter that I make. It's hollowed out as much as we can get away with and fits over the octagon shaped carbon fiber bow.

The octagon part I'm looking to make is at the end of the adjusting screw. I was given the option of knurling this, but even with a CNC grade knurling setup, I find getting good knurls to still be something of a dark art. I can produce knurls acceptable for most needs, but we're looking at a high dollar item here, in market where craftsmanship is still highly valued. Sticking with the octagon shape maintains some tradition. I will be machining multiple grooves mainly for weight reduction, though it will put a high tech edge on the traditional shape.

Back up on the URL to the base site and there is an embedded video link of it in action. I don't have quicktime installed so haven't been able to view this myself yet.

Jon