Discussion in 'Finished Projects' started by dvbydt, Dec 15, 2010.
These photos were meant to be attached to the prious post, but I got it wrong somehow!
Very ingenious Ian ! A nice bit of machining too.
I wonder does it self start or do you have to give it a quick flick ?
Seeing Ian's original I shamelessly copied it, but without the wood base. It doesn't self start, but a quick flick will get it going. Runs at surprisingly low air pressure.
It always gets a lot of interest at the small shows I take it to.
The Emerald Isle
Thankyou for your reply. I did wonder if it would self start with it having two stable positions on the rotor. I found the concept fascinating. So much so that I have started to collect a few bits together to try and make one.
Just a thought experiment having read the linked article would it scale to say six cylinders or even more and would an odd number of cylinders allow self starting.
I would love to see yours.
With me camera out, I took a video of my 'rotor Motor'.
Anyone know how you can get rid of the discolouration on the bronze? Normal polishing doesn't work.
The Emerald Isle
Thankyou for that video. What a lovely sound. I was a little surprised at how smooth and stable the speed was. I'm most impressed. th_wav
Re the polish on bronze. I'm sorry ! I don't know. If the truth be known I don't think I could really tell the difference between brass and bronze. Though I did mention that cutting a keyway recently in a brass bush was hard work compared to the same in steel. Someone suggested that it might be bronze and not brass.
you can pickle brass that has been heated and discolored. the discoloration is really just copper, because the zink burned out or migrated away when heated. so all you need to do is mix some vinegar, salt, and hydrogen peroxide. it will etch the copper but leave the brass behind.
to tell the difference between brass and bronze is simple. brass is yellow and hard and makes flaky chips when machined. everything else is bronze. imo brass is just one of the bronzes (copper alloys).
if your material makes stringy chips or makes continuous chips when drilled, or is darker than bright yellow, its bronze of some kind.
In that case the material I used must have been bronze ! When I turned it I needed to hone the lathe tool because it seemed not to want to cut, the tool seemed worn and blunt. The swarf was little fine hair like strings and the tool left patterning when facing.
When I cut the keyway in the bush that I had made, the swarf was little curls that fell out, till I put a drop of oil on the tool holder because it seemed to rub and grab in the bore when retracting.
Yes, colour wise, its a sort of rose gold colour rather than a yellow, more a light copper shade. In fact thinking about it, I have a brass retainer on the lathe and its a much darker colour than that is.
Well at least I now know that I've got a 75 mm by 30 mm AF bit of bronze hex bar left to play with. I originally picked it up in the local scrap yard for a couple of pounds !.
Thanks for that info.
brass and bronze may get oxidation on them but if you sand it to bare metal brass is really light yellow, no red.
Brass is definitely not bronze , the different name is possibly a clue to this fact ! Very few bronzes come in bar form , they are mainly supplied as ingots for casting .
One bronze that does is Aluminium bronze, which looks identical to brass but you will find it almost impossible to machine without newly sharpened cutters, it can be identified from brass as it shows a very slight but noticeable magnetic attraction.
The other bronzes that can be bought as bar or rod for machining tend to be phosphor bronze or gun-metal ( red brass in the US just to be awkward ) which do have a reddish colouration.
Most of the rod brass you will come across is 60/40 copper/zinc with very slight variation , also as 70/30 alloy known as cartridge brass mainly in sheet form.
The ductility and maleability of copper alloys varies greatly , many bronzes cannot be drawn into rods or forged so they will only be found as castings or cast bar.
I'm totally confused now !
The bit of bar is definitely not magnetic. It does have a slight copper hue to it and it seems to be very tough. I tapped six holes in it for M3 and it wasn't as easy as I would have expected.
This picture is a slice off the end of the bar bored out, and drilled.
The other half has the threaded holes in it. I can post a picture of that if you wish me to.
maybe silicon bronze? would have cost you big money tho if it was! most bronze can be a bit hard to machine, almost like machining tough steel. it looks like brass in the pic, but by your description it doesn't sound like it.
where i work there were several sticks of 1.5" dia. silicon bronze rod about 15' long. apparently quite expensive!
they had to be bent and they kept bending back straight after a few hours! tough stuff.
Maybe Tin knows the difference between brass and bronze. Get it....
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260 brass maybe? Kinda looks like it to me. Doesn't machine as nice as 360, but seems to take a better shine when polished.
there are many varieties of yellow looking brass. I have a sample of something called DV metal that is a pig to machine and it looks like that.
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