Basic metalworking questions

analog97 · « **on:** 27 Jan 2006, 04:56 pm »

I am definitely gonna build more Hagtech devices. On my first 3 projects, I stayed away from doing the case metal work since The Boss was kind enough to sell a couple finished cases. But, there is no pre-made case for JH's AC Line Conditioner, and it seems to me I am likely to screw it up without guidance. Is there a basic, on-line source for information anyone knows of that would offer me a crash course, suggested tools, etc? Exact cutting of space for four duplex AC receptacles and an AC input device in a small end-panel of JH's Conditioner requires more thought/info. Any help greatly appreciated.

hagtech · « **Reply #1 on:** 27 Jan 2006, 07:07 pm »

You know what, I think the best change you can make is with the outlets. I should not have used the standard cropped circular ones (very difficult cutout), but rather the type that use a rectangular hole. I see these at Mouser, even at the local Home Depot. That will make this much easier.

I can cheat with metalwork, having a CNC machine. But I don't always use it! Sometimes I just go cheap and dirty. I take a 1/8" bit or so and perforate the cutout. Then use a snipper tool to cut out. This leaves a jagged edged hole. A rasp file then (ok, this only works with aluminum) takes this down to a clean edge in no time. Rectangles are not too hard this way. Really, it's only a few minutes of heavy arm labor. And if you are careful, the file will clean up all edges to a fine finish.

Most importantly, wash the chassis in the kitchen sink using a good detergent that cuts oil. Use a sponge in the direction of grain. This removes all grime, fingerprints, and metal dust, leaving the chassis bright and shiny. It's almost like polishing. But don't scrub if it is already anodized.

Paint doesn't stick well and tends to flake. Start with a good primer coat. Then use a hammertone or some other fancy thick paint to hide any scratches or blemishes. You'll be suprised how well you can do.

jh

JoshK · « **Reply #2 on:** 27 Jan 2006, 07:11 pm »

Do you know what kind of primer to use on aluminum? I have pretty much beat to he|| my PC chassis and it could use a paint job.

analog97 · « **Reply #3 on:** 27 Jan 2006, 11:21 pm »

That explanation is a testament to your ability to make things simple. I just ordered the parts. I can see how to do the "rectangles" easily. Next up is the Chime (unless you come up with 100 watt amps).......

JoshK · « **Reply #4 on:** 29 Jan 2006, 04:03 am »

Quote from: analog97

That explanation is a testament to your ability to make things simple. I just ordered the parts. I can see how to do the "rectangles" easily. Next up is the Chime (unless you come up with 100 watt amps).......

Do you have Apogees? Magnepans? I don't see why anyone really *needs* 100watt (tube) amp otherwise. ~50watts would be a very good goal I think as 100 watts involves too many compromises (with tube amps imho).

analog97 · « **Reply #5 on:** 29 Jan 2006, 11:02 am »

I have Polk 1.2TL's. They are big. They eat watts, have 13 speakers/box. They can do up to 1,000 watts. I am taking JH's suggestion and trying to find a big old Macintosh.

JoshK · « **Reply #6 on:** 29 Jan 2006, 04:48 pm »

If I were you, I'd experiment with a MUCH cheaper solution. Try to find someone who can help you calculate a zobel network (cap + resistor in parrallel) for your speakers. Add zobel and your speakers won't gobble watts anymore, so big power is no longer needed.

analog97 · « **Reply #7 on:** 29 Jan 2006, 05:46 pm »

I am clueless about a so-called Zobel Network. I will search the web for any info available, but this seems pretty far-out to me on first glance, i.e. changing the electrical properties of my huge speakers that can eat 1000 watts, to something at least 6-10 db more efficient so they could be fed by JH's Cymbals. If you have anything for me to check out, please post. Thanks.

analog97 · « **Reply #8 on:** 29 Jan 2006, 06:06 pm »

I just looked at the original paper by Zobel, from 1923 and saw a few other informative articles. It is pretty clear I would need to buy JH's RT airfare from Hawaii, reimburse his hourly rate for 2-3 weeks and still have no guarantees about sound quality. I could not undertake this myself. This Zobel Mousetrap looks like it would pretty damn complex to integrate in the Polk SDA speakers. These have huge, complex cross-overs and even use a separate cable to send some info between the speakers for the SDA "effect"........my gut tells me this would be a nightmare for even a real card-carrying engineer like The Boss, JH.

hagtech · « **Reply #9 on:** 29 Jan 2006, 06:49 pm »

Actually, I believe the zobel ends up chewing even more power. Not sure how it could save any, except for the originally intended goal of preventing instability and ultrasonic oscillation (in which case you are correct).

The zobel is a matching network that is a complex conjugate of the existing one. When connected properly, the result is to make a load appear resistive. Let's take a speaker for an example. A simplistic model can paint it as an inductor and resistor in series. The amplifier load is then resistive at low frequencies, but heads towards infinity at the higher freqs. Such may cause a problem with an amplifier employing feedback. To tame this, you add a series resistor and capacitor in parallel. You match the corner frequency of the two networks, and then, magically, the load appears to be a pure resistance at all frequencies. It's a very nice kind load for the amplifier.

So the zobel is not for the speaker. It is for the amplifier. Note, some crossovers already take care of this. Some cables do it (MIT?). Some amplifier don't care. This is a very system specific tune. No single solution for everybody.

If you want to try a zobel, start simple and add an 8 ohm resistor in series with a 0.1uF capacitor. It's a solid load from 200kHz on up.

jh

analog97 · « **Reply #10 on:** 29 Jan 2006, 11:09 pm »

I am a bio-medical scientist, not an engineer. This stuff is a real stretch for me. Unless I understand something, I keep my feet in cement. The Zobel concepts are way over my head. I am sticking to the engineer's earlier suggestion and looking for a Macintosh amp (not in a rush) for my power needs. Drats. I wish the 8 watt Cymbals were sufficient. I would love to try to build them. This is a great hobby for me. So, it's "no" to Zobel.

analog97 · « **Reply #11 on:** 31 Jan 2006, 10:26 pm »

The rectangular outlets will not fit the standard back panel of the C-series Lansing chassis. The rectangular outlets must be mounted by screws very near the end (almost 3 1/4"). They do not have a center hole between the 2 receptacles for a simple installation. If you measure this, you will see what I mean. I think the only way for me to build the Hag "Conditioner" is to use the standard, cropped outlets. Drats. Parts are ordered, so I will just have to do my best. Other thoughts on how best to make a semi-circular cut for the outlets with a flat rasp file and a drill are MORE than welcome.

jules · « **Reply #12 on:** 1 Feb 2006, 01:11 am »

analogue,

I'm not familiar with the exact shape and size of the hole you are trying to cut but ... a flat file in a round hole really doesn't work so I'd suggest you buy a new round file [I'll bet the flat one's worn out anyway

], or half round file with fine teeth and a radius smaller than but close to, the radius of the round section of the hole you are making.

You'll also need a smallish but sharp drill bit and a centre punch [you might be able to cheat on this and use a nail or hard-point self tapping screw of some sort if you have one lying around].

Draw a line inside and parallel with the perimeter of the hole you want to cut. The distance this line is inside the perimter should be slightly greater than the radius of your drill bit.

Punch a series of starting point along this inner line. They should be slightly further apart than the radius of the drill but it's hard to judge and you get it right with experience.

Drill each punch-marked point, preferably with a drill press but this isn't essential. Some will meet. Some will have a bit of metal between them. The result at this point will look horrible. The main thing to avoid is allowing the drill to drift outside the perimeter of the hole you want to make. It isn't all that difficult to file away metal if the drill holes are too far in, so err in that direction if possible.

Break out the centre piece. Sometimes you can join the holes you've drilled by widening them with the same drill. Sometimes you can get a hacksaw in to help. Sometimes it's possible to use an old chisel to cut through the connecting bits though you have to be careful with this as it can distort the sheet metal if the base you use under your work is too soft. [Too hard and you stuff the chisel though, ie hardwood is good].

File off the rough stuff to your marked outer line and bingo ... perfection!

jules

analog97 · « **Reply #13 on:** 1 Feb 2006, 01:53 am »

Thanks, Jules. The shape I need to cut is not a circle. Rather, it has a flat top and bottom, but the sides are arcs. I need to make 8 of these, each about 1 1/2" top to bottom. These holes are for 120 volt AC duplex receptacles, standard in the US. I've done a lot of international travel, but Australia meetings have not called me yet. So, I am unfamiliar with the standard plug receptacle there. Thanks again for your kind help. Larry

jules · « **Reply #14 on:** 1 Feb 2006, 02:33 am »

Larry,

8!!! That's fairly horrible. The same working approach would apply though and with a 1.5" hole you'd be able to get a file in there. Still, I find sheetmetal frustrating to work with even if it is useful.

You could follow Jim's suggestion and do it using CNC via CAD drawings. CAD is great in that it lets you shapes unlimited while CNC faithfully cuts them out with absurd precision. CAD's not all that hard to use for basic stuff like this and I used it for the metal-work on my amp box [see gallery].

I strongly recommend you visit Australia. Our standard plug receptacles are an outstanding drawcard.

jules

DeadFish · « **Reply #15 on:** 1 Feb 2006, 02:38 am »

About those outlet holes.
I've had very good luck getting relatively neat holes made with a 'nibbler' bought at RadioShack perhaps. Under 10 bux, if memory serves. You would use the same basic method Jules outlined with series of holes to remove most of your material, and nibble the edges a little at a time. If you could get a half-round file, it might make the curves on your outlet hole decent.
Although there is an outer escucheon on the a/c power inlet on my Clarinet and Cornet 2, the holes were pretty decent, using this method.
And even if it is a little ragged, you might be able to find some outlet plates small enough to fit where you want them, (metal perhaps?) and even if they are a little big, you could take your trusty flat file to the edges of them.
Sound possible?

Best wishes,
DeadFish

analog97 · « **Reply #16 on:** 1 Feb 2006, 03:32 am »

Thanks. Jules and JH have basically told me enough to let me know this will be hard, but doable. I just have to suck it up and get to it. I had never heard of a CNC machine until JH and Joules mentioned it. I imagine this to be kinda like a computer-driven router/driller invention. I don't know where I could get this done for a fee. I think the CNC idea is dead. I will proceed to follow your leads, make the outlines, do some careful drilling, look for the snippers small enough to cut the holes out. If I can't find them, I'll keep drilling larger holes to insert a jig saw. Then start filing with both the flat rasps and semicircular ones. I figure I could swim to Australia by the time I finish that back panel. If I didn't make it clear, this is the back panel for the Hagerman "Conditioner". Pictures of it are on this site. It basically requires cut-outs for 4 duplex outlets and an AC input in the back panel of the standard Cornet/Clarinet Lansing chassis. Thanks a ton....

hagtech · « **Reply #17 on:** 1 Feb 2006, 05:08 am »

Quote

rectangular outlets will not fit the standard back panel of the C-series Lansing chassis

Ah crap. I remember that now. Gotta rip off the wings and everything. Super tight fit, even side by side. Even with the CNC it's a job. Maybe this is why I didn't put it in the product lineup...

Quote

visit Australia. Our standard plug receptacles are an outstanding draw

Well that's it then. I'm bringing the whole family. They need to see too.

jh

analog97 · « **Reply #18 on:** 1 Feb 2006, 12:55 pm »

I am taking the chicken's way out. I am going to replace the recommended 3 1/4" chassis with the 5" height Lansing chassis. Now, I WILL have enough room for all rectangular cuts for the duplex outlets. This will cost another few bucks, but well worth it in time/aggravation saved. Thanks again to the "skilled" crowd.

pkonin · « **Reply #19 on:** 1 Feb 2006, 04:15 pm »

I'll make the case out of MDF and cut some fairly large holes in the back. I'll screw on a few of those metal, contractor-style outlet panels--the kind on "stage boxes" and basement outlets. It won't look so great in the back, but it should get the job done. If necessary, I'll line the inside of the box with thin aluminum or copper.

And when I can afford some nice veneer, bingo.

-PK