Good advices for a newbie (threading tools lathe)

[rendoman]

Thanks for advices!
here in my area the best advice given in metal shop is : use a pen
I want to use this prussian blue for layout, i thinked to use as witness line, but it's hard. i create a simple steel template with 6\10, but the finishing after tool isn't good, and maybe it's not necessary to copy so close to perfection the line. I used angled turret, and then files by hand, searching to copy the profile. Not a good job, not simple and very long... if you have some better ideas i have to do another one of this ...
I tired the boring bar... not to excellent, the perpendicular insert cut better, but there is something wrong in angles. with long arm (12cm) it vibrates like a dildo of sasha grey , very poor finishing, but good for cutting lot of alu. with short arm (6cm) no great vibrations, better cut, poor finishing. i tried to cut 2mm each time at dia, maybe too much.
Strange thing, i used a Seco boring with triangular insert (Tomorrow i'll take a pic), got some problem with finishing with angled turret, maybe something to setup (gib?).

I got another little problem, protractor engraved under turret is semi-erased as you can see, some good and easy way for engraving a new one? yes, this lathe is pretty old and used.

You're right, when i studied for the tweeter horn i read that the final edge should be sharp. i left the first pair of horns with cm more than designed for trying the "round" final edge. if something didn't go well i might change the final edge easily. At listening even with round edge are not bad. now i got microphone , for sure i can make
measures and then try the correct profile.
with this new horns i followed different path, i got alu in right diameter for the profile, no more cm to use, i can only cut some thents for finishing, as you can see the exit angle is sharp.

formulas... i think the Excel sheet is good, there is a coefficient from 1 to 8 in calculations that is used for lowering dimension of horn in order to create "bass" horn positionable in the corner of a room. For stand alone, pure horn this coefficient is 1, with this the horn is the bigger possible. curious thing is that if you calculate an horn with 1200 hz or higher is really tiny!

[PJs]

So does this mean there's going to have to be a major redo in the outer edge of the horn?

Dunno C-Bag its a bit ambiguous. My hit is it's saying that on these "exponential" cones, if the length of the exponential curve (frequency tuning) is reached before the radius to the 90º curve starts the formulas don't work and you are on your own. So I think it's saying that the 90º must be included in the overall calculated length to work for mids and tweeters¿

From a physics standpoint my understanding is that sound waves are actually spherical in nature so in this case at these mid frequencies the when the spherical wave front passes through the cross section of the root of the 90º it starts to expand too rapidly and causes distortions in the wave front, generating noise of some kind...maybe a tinny sound or maybe an off scale harmonic¿¿ @¿@ -Dunno...a bit out of my league here.

Stefano: Great job on the profile, amazing you pulled it off so cleanly considering the issue with your vibrator! LOL As I indicated earlier I thought the index bit didn't have enough front rake on it so that may have contributed greatly to your finish. The other thing I prefer is to use hi-speed steel on aluminum and a fairly generous radius will give a much better finish. Aluminum can be a bit gummy and the radius makes the contact minimal so chips are easily discarded. A sharp tip angle will give problems if you have run out or slop in gibs or rigidity of the holders, compound or cross slide.

Would love to see a picture of your template if you have time and inclination. I was thinking that it would be much easier to machine a reverse cone as a template, then use that and Prussian Blue or Dykem to dial in your final cone to match.

formulas... i think the Excel sheet is good, there is a coefficient from 1 to 8 in calculations that is used for lowering dimension of horn in order to create "bass" horn positionable in the corner of a room. For stand alone, pure horn this coefficient is 1, with this the horn is the bigger possible. curious thing is that if you calculate an horn with 1200 hz or higher is really tiny!

Interesting about the coefficient, but like I said a mid or in particular a tweeter needs to be tiny at 1 wavelength so they must be exact multiples of a specific frequency at the starting point. For instance based on 340m/s speed of sound in air, 800hz would have a wavelength of 425mm but at 10khz it would be only 34mm and would have a LCD (least common denominator) of 1. This also doesn't compensate for the sound actually traveling through the Aluminum which result in respective wavelength of 7900mm & 632mm and creating some synthesis based on the coupling to the transducer... So I am still confused how it works for a range (800 - 10k)??? My hit is the exponential or hyperbolic curve is what allows that range, but there has to be some Guess and By-golly in it to tune it well?? Probably making this Way to complicated!!

Love what you made...can't wait for more!! Thanks, ~PJ

[rendoman]

The other thing I prefer is to use hi-speed steel on aluminum and a fairly generous radius will give a much better finish. Aluminum can be a bit gummy and the radius makes the contact minimal so chips are easily discarded. A sharp tip angle will give problems if you have run out or slop in gibs or rigidity of the holders, compound or cross slide.

I think you've hit the issue! Tomorrow i'll take some pics of the inserts, maybe the angle is too narrow, combined with vibration and other things the finishing is not good. I tried a (brazed?) tool 20x20, but the result is similar... maybe something wrong in setup of lathe

Would love to see a picture of your template if you have time and inclination. I was thinking that it would be much easier to machine a reverse cone as a template, then use that and Prussian Blue or Dykem to dial in your final cone to match.

you're so professional! you're right, maybe it's best way to achive perfection! the problem is that i'm a novice, with no much skills and tools for doing similar perfect object. As first step, I left some more alu inside in the processing (mostly in the inner part), not because necessary as for my possible mistake... that makes the job too long.
I'd like to show you the template, unfortunately my father threw away chips and other metal debris, for sure he Exchange the steel template for something to throw But not a great problem, i drew some lines with angles on a used piece of paper, i can replicate the second horn. for now i havn't a template to show you
I think at starting of polishing i'll try an internal mold with plaster or other material, in order to obtain a positive. Few words on contour, it's not completely a tractrix, i've modified the original drawing, half conical first part and half tractrix. I made this experiment some years ago and the results were excellent.
I have no answer to your questions about "numbers" of horns, i'm not so studious unfortunately still prefer trying and listening

[rendoman]

et voila!
Past few days i had some problems, above all the breaking of cesso (wc)

I take some pic of the inserts, i don't know what's the best use for them.
I tried to polish the horn with sand paper from 40 to 1200, but i found some problems. Sometimes maybe some dust from paper left ugly signs during passage, and the second, more important : i need to learn polishing
i tried with horn on lathe to put some white paste (i think the first of available in grit), difficult to apply because the shape, it sticks like glue to the inside of the horn, forcing me to remove with a wooden piece. the last pic is White + polish for car , not enough for me, it doesn't shine! it's something between satin and glossy ...
someone has some good advice?
thanks!
saluti
stefano

[PJs]

Hi Stefano, Thanks for the update...sorry to hear about your plumbing problems...

As for the inserts: These inserts have 0º rake (clearance angle) and in my opinion the .4mm (1/64") radius tip is way too small for a good finish. Here are some links to the Widia Pages for your inserts. Here is a chart for the Number description (Pages F8 & F9) to figure out what you have. D=Romboid, N= 0º clearance angle, M=Tolerance Class, G=Features (chip relief) etc. Yours are listed on page F13 at the top.

If these are all you have the only thing I might recommend is if you have a diamond stone you might Try to adjust the rake to 10-15º and give it about a ~1-1.5mm radius. This is approximate to what I use (final couple of passes) to get a pretty good finish to start polishing...but again I prefer Hi-Speed steel to carbide on aluminum.

Polishing: My experience is that you work a grit until you have a very even finish all over, then move to the next grit up...to say 1200G which should be fine. If you are having a dust issues use a tiny amount of water on the Wet or Dry 1200 paper. I have some 3000-10k grit foam pads I use once in a while but typically don't need to. For aluminum and brass I always use Simichrome on a soft lint free cloth, as a final polish...best I have ever found...and tried a lot of fancy hi$$ stuff. Should be able to find it in good hardware stores or automotive store, even in Italy. Think it used to be made in Germany (Happich)?...its everywhere I think.

Hope this helps? Good Luck!

[rendoman]

Thank you very much for the info PJs! I will focus on angles and good steel!
I think Tomorrow i'll try to find some simichrome or other italian available compound, i tried some minutes ago from start, adding ooo steel wool, some better result, but nothing of special

1200 grit, old photo


000 steel wool


"polish" with cotton cloth, 3 hands

[PJs]

Looking Good Stefano. Hopefully you can find some Simichrome and can rework you inserts or some HSS ones for the other horn. Looking forward to your test results! Thanks, ~PJ

[rendoman]

I went to the dark side 6cm drill buffer, and a home made not good small buffer for the inner part... i hope monday i will find some better commercial new one. polishing with drill maybe it's the better way to do this job, now the horn is shining more than in photo. I hope i'll finish the first flange and do some test! See you on the next episode

[rendoman]

Hi! it's long time since last update ,I got a long flu and had to do other works unfortunately
I still have difficulties finding a tiny buffer for the small inside of the horn, dremel cloth insert are too short and I see that for polishing i need to press a lot. I will have the same problem for the next small horn of only 1cm throat ... i need to find something!

apart polishing, i mounted driver-flange-horn for some test, sound is really good to my ears very detailed and focused! i build a simple rod for microphone, i'm waiting the key of a beta test program (medianet audio pro solution), hope that program is easier than "speaker workshop" who needs specifics cables with test resistors and an Lcr bridge.

OT: i'm planning a plasma tweeter
OT2: i found a box with Emergency button in scrap, i added last night a contactor, need a bulb light for voltage presence. I mounted on my lathe, it didn't have the Emergency stop

some pics as usual, the third photo is a generic layout of the new plasma speaker (horn will be 1\3), fifth pic it's a rat9 big mouse for size comparison

[C-Bag]

Funny, i was just wondering about what happened to you yesterday Stefano! I guess that cold shop got to you I'm glad you are over your flu and back at it.

Good pix as usual. As to a polisher, have you seen those special polishing balls for polishing aluminum wheels on cars. I think they have tapered ones.

I have one of those Berhinger mic's and I believe because it's omni directional, it needs to be mounted vertically. I could be wrong. The whole sampling/testing/pinking the room is a very tricky thing I learned from my buddy who does pro sound for a living. From what he told me you have to be kinda close to get more of the speaker and less of the room. Im sure PJ's knows more about this than I do and will be along soon and enlighten us both.

Great score on the control box/ emergency stop! What a find.

What I'm wondering is how to make some kind of pantagraph/ duplicator for your lathe to duplicate the next horn. I would think it pretty critical to make them the same. Anyway good to see you back, carry on!