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kendall
07-04-2007, 11:42 PM
Have been thinking about throwing some velocity stacks on my bike, and while I can get them cheaply, I thought I'd try spinning them, which is generaly a bad thing to do because it opften leads to large spending sprees to make a $2 part.

Looked into what I could find on the net, and it seems that for some reason they always start out with flat stock for spinning.

What I'm thinking is that I have some tubular aluminum that is pretty much exactly the base inner diameter I want, so instead of making a male form and spinning flat material into the cone shape I want, why couldn't I make a female form (3 parts I'm thinking for release) and 'expand' the tube into it with spinning?

Is there some reason they use flat, alloy maybe?
any ideas why I can't seem to find a reerence to starting from tubular material?

Any ideas on whether that would work?

similar, not identical to those shown on top here:

http://www.nextag.com/velocity-stack/search-html

tried to link directly, but the url was humongous.

Thanks
ken

lane
07-05-2007, 12:05 AM
I don't know .Give it a try . You don't have any thing to loose but Time .I spun down some tips Tuesday for the mig welders at work to get in some tight places to weld. Might work Play around with idea and let us know what happens.The differenc being you have to spin from the inside out .Not the out side in.

Evan
07-05-2007, 12:58 AM
Is there some reason they use flat, alloy maybe?
any ideas why I can't seem to find a reerence to starting from tubular material?

I see no reason why that wouldn't work. It should be seamless and it needs to be one of the softer non heat treatable alloys such as 1100 or 3000 series. Heat treatable alloys such as 6061 can be used also but will need to be annealed first to avoid cracking. Once annealed you have about six to twelve hours to do the work as it will age harden on it's own.

It so happens that a self clean oven is just about right for annealing 6061 alloy for non critical uses. The annealing temp of 6061 is around 800F for a couple of hours followed by a slow cool down. A self clean oven hits about the same temp in the cleaning cycle and has a protracted cool down also. By packing the part in glass wool in a coffee can a pretty good job of annealing is possible. Simply put the can in the oven for the cycle and let it do it's thing. Once done then make your parts. If for some reason you can't use the annealed stock the same day then put it in the freezer. That will maintain it in the annealed condition for a couple of days. Note that annealed aluminum has very poor machining properties. Spinning is a different matter.

http://vts.bc.ca/pics/spinning.jpg

DR
07-05-2007, 03:32 AM
I see no reason why that wouldn't work. It should be seamless and it needs to be one of the softer non heat treatable alloys such as 1100 or 3000 series. Heat treatable alloys such as 6061 can be used also but will need to be annealed first to avoid cracking. Once annealed you have about six to twelve hours to do the work as it will age harden on it's own.

It so happens that a self clean oven is just about right for annealing 6061 alloy for non critical uses. The annealing temp of 6061 is around 800F for a couple of hours followed by a slow cool down. A self clean oven hits about the same temp in the cleaning cycle and has a protracted cool down also. By packing the part in glass wool in a coffee can a pretty good job of annealing is possible. Simply put the can in the oven for the cycle and let it do it's thing. Once done then make your parts. If for some reason you can't use the annealed stock the same day then put it in the freezer. That will maintain it in the annealed condition for a couple of days. Note that annealed aluminum has very poor machining properties. Spinning is a different matter.

http://vts.bc.ca/pics/spinning.jpg


6061 can be annealed easily by marking all over the piece with a felt tip marker. Then use a torch to burn the ink off. It'll air cool quickly in still air.

We've done the above procedure a number of times on 1/8" thick machined pieces needing a small tab bent 90 degrees.

For a test I've annealed and bent, then tried to bend back. The tab breaks off. Anneal again and the tab can be bent straight again and the operation repeated as long as there's an anneal prior to each bending.

Evan
07-05-2007, 04:24 AM
It would be pretty hard to evenly anneal a sizable part that way. It's a valid way to anneal small pieces and is used in aircraft fabrication. Aircraft rivets are commonly dyed some color. The color isn't significant. To place a rivet in a very difficult location it is helpful to have the rivet in a full soft condition. A rivet may be heated with a torch while sitting on another piece of aluminum to stabilize the temperature. When the color vanishes it is at the anneal temperature.

A felt tip marker probably isn't a very good temperature indicator as there are many different types and dyes used. In particular, for spinning the properties should be very close to the same throughout the material.

Alan Smith
07-05-2007, 04:58 AM
Ken, I've been down this road. I needed some velocity stacks (we call them air trumpets in the UK) for motorcycle carbs that I use on my sports car. Off the shelf only short trumpets suitable for a high revving m/c engine were available. I needed longer trumpets. I played around with spinning and came to a few conclusions 1. I need a heavier lathe 2. short trumpets are relatively easy but the lengths I needed was a job for a pro 3. be prepared to anneal repeatedly, best way is oxy/acetylene soot the component all over with a pure acetylene flame, then bring in the oxygen and carefully and systematically burn the soot off this gives you dead soft condition.

Re your idea of starting with tube, I think it could work. You would need a female mold and then need to lever the bell mouth from the inside out and then over a lip.

My solution in the end was to purchase trumpets of correct length but oversize diameter and swage/shrink the ends down to fit into a flange to which the trumpets were then welded. A bit of fettling with the die grinder and all was well.

Your Old Dog
07-05-2007, 08:24 AM
A felt tip marker probably isn't a very good temperature indicator as there are many different types and dyes used. In particular, for spinning the properties should be very close to the same throughout the material.

When heat soaking the books usually specify time over cross section of area usually an inch. So for 1/8th thick material the heat soak need not be nearly as long as for an inch of cross section.

I like the felt tip marker approach on sheet stock. Will have a chance to try it out today on project I'm working on.

One last thing, the folks here at Metal Supermarkets tell me one form of aluminum is better at bending then another, can't remember if sheet or flat stock (same as tubing) would fail first under bending. I expect it has to do with the grain structure setup during the manufacturing process such as rolling mill versus extrusions.

john hobdeclipe
07-05-2007, 09:45 AM
Keep in mind that if you start with a cylinder and expand it to a larger diameters, you are stretching and thinning the metal.

Could become a problem.

Evan
07-05-2007, 09:49 AM
I expect it has to do with the grain structure setup during the manufacturing process such as rolling mill versus extrusions.

Yep. When bending aircraft alloy sheet in the hard condition such as 2024 T-4 there is a clear difference between bending across the grain (across the sheet) as compared to with the grain. With the grain will bend easier. Bending across the grain with a proper radius makes a stronger bend though.

Extruded doesn't have as clear an anisotropic grain structure. I expect this is because of the much greater degree of flow produced at once during extrusion compared to rolling.

DR
07-05-2007, 12:36 PM
Velocity stacks can be made another way instead of spinning, this is in an hydraulic press.

http://www.metalmeet.com/photopost/data/500/tube2.jpg

Makes some metal plugs with a loose fit in the tube. Between the plugs put a piece of soft urethane or rubber. Stand upright in the press and apply pressure. The tube bulges. Cut on the bulge center to get two parts.

Width and contour of the bulge depends a good deal on the thickness/hardness of the urethane/rubber and pressure.

kendall
07-05-2007, 11:02 PM
appreciate the info guys. Will get started on them this weekend.

I'm not sure what the alloy is, but it's seamless so hopefully it will work out!

Plan to dig the old logan out from under the bench and using that one, know logan used to sell a spinner attachment (toolpost like deal, slide carriage all the way right then mount the spinning toolrest on the ways) so figure it's worth a try. Spindles messed up and haven't had any luck at all finding one so it's pretty much bench filler as it is.

Wasn't sure if there was some special 'spinning alloy' that was only available in sheets or not, but not being able to find anything similar

my problem with commercialy available stacks is that they are either far too long, or so short they look like a simple flange on the carbs, and they don't fit the look I'm after.

I might have to get a press and experiment with that rubber, have a few projects that something like that will come in handy.

Thanks again!
Ken.

john hobdeclipe
07-05-2007, 11:15 PM
appreciate the info guys. Will get started on them this weekend.
Go for it. Take pix along the way and let us know how it works out.

Evan, that's an interesting metal spinning picture. But it sure is a huge velocity stack! What ship does it fit?

J Tiers
07-05-2007, 11:32 PM
Looks more like a big fan inlet, as used in mines. I've seen them 20 feet across.

oldtiffie
07-06-2007, 09:16 AM
Deleted/edited-out

lazlo
07-06-2007, 11:54 AM
6061 can be annealed easily by marking all over the piece with a felt tip marker. Then use a torch to burn the ink off. It'll air cool quickly in still air.

It would be pretty hard to evenly anneal a sizable part that way.

Discovery Channel showed Jesse James making his fuel tanks the way DR describes: he takes a large sheet of 6061, cuts it to the approximate shape, then anneals the whole sheet with a blow torch.

At that point, he goes to the lead bag with the nylon hammer. Amazing craftsmanship!

lazlo
07-06-2007, 12:01 PM
By the way, for the spinning aficionados, look for the "How Its Made" episode called "Aluminum Pots."

I was really surprised to see the company making aluminum pots with a CNC'd metal spinning lathe. The machine used what looked like roller blade wheels at the end of the spinning "paddle" (don't know the proper spinning terminology) instead of the normal spoon end. I would imagine the urethane was a lot harder than a rollerblade wheel though, since they were spinning relatively thick aluminum sheet for commerical cookware.

The second part of the same segment showed production manual spinning. It's amazing to watch. It made me nervous watching the operator rushing to finish piecework with a long spinning paddle under his armpit.

How many retired one-armed spinners are there? :D