Protecting Fancy Chassis Finish While Drilling Holes

[David Root]

I just got two of these good-looking hammertone finish chassis from RJ, and I'm wondering if protecting the finish with blue tape is sufficient when using a step drill, or are there better way(s) to do this?

[ampgeek]

Yes! Blue tape is exactly what I use with excellent results!

Most of my builds utilize black Hammond chassis and I, too, desire to protect all surfaces while making swiss cheese with straight drills, step bits, hole saws and jig saws.

Cheers,
Dave O.

[David Root]

Thanx! Glad to hear that.

Have you ever used Forstner bits? On aluminum of course, not steel? They seem to work OK but I have not tried them on fancy finishes like hammertone.

In fact I have never drilled a fancy finish chassis before, just plain aluminum, sometimes wirebrushed, which looks nice too.

[Gaz]

Blue tape works well, just gunks up the bits, which can be cleaned, of course. If I were you I would stick to step-bits and punches for that chassis. Forster bits kinda freak me out on metal.

[M Fowler]

I used blue painters tape on the black Hammond chassis with twist bits, step bits and knockouts. The only problem I had was making good looking grounding spots inside the chassis. I think I ended up inserting a small round grinding stone inside the chassis and the drill on the outside of chassis to create a round grounding point. They should only paint the outside of an electronic chassis box.

[David Root]

Yeah, the inside of these chassis is white primer so all the chassis ground points will have to be ground out a little on the underside. I'll have to get a couple more small cylindrical grinding stones. I have one 1/4" but it's just about worn out.

Thanx for all your tips & comments!

[M Fowler]

The dremel stones would fit the #6 or #8 machine screw holes.

[ampgeek]

Never used a Forstner bit on aluminum. But..hey...if it works...why not!

I have a metallic, ball shaped cutter bit for the Dremel that works great for grinding the paint off of grounding points.

However, I will admit that it doesn't make the prettiest looking work if it wanders off course!

Cheers,
Dave O.

[Firestorm]

Forstner bits can dull pretty quick, so even aluminum seems like a bad idea. If you can control your depth precisely, you can try conical bits.

[funkgang49]

Blue painter's tape & step drill bits is the way to go on aluminum chassis. On my last SE build I sanded the chassis outside with 220 grit and an orbital sander. Wiped it down with a rag & paint thinner to remove any aluminum dust and oxidation, then gave it a flat black primer coat. I finish coated with a Black Hammertone and speckle sprayed some Gold metallic. Final coat was an epoxy resin to seal it all up. After curing in a toaster oven on and off at 15 min. intervals several times then sitting at room temp. for 24hrs. I taped the entire box then measured and marked all holes to be drilled. With a wood block supporting the aluminum from the inside I used a spring-loaded punch and drilled starter holes then used the step bits where required. Paint job unscathed and lookin' fine!

[img:640:480]http://img571.imageshack.us/img571/5534/gpk7.jpg[/img]

[img:640:480]http://img32.imageshack.us/img32/2295/d6na.JPG[/img]

[img:640:480]http://img15.imageshack.us/img15/1632/2l3t.jpg[/img]

This is the prototype test build. Controls are: Vol.1, Vol.2, shared Tone, Presence, then the obvious Standby & Power. Back Panel is: 4/8/16 ohm Selector, Speaker out, Ext. Spkr. out, open hole is where I removed a bad VVR.
I am about ready to paint the slightly larger chassis in a Bright Red with speckled Gold Metallic then the epoxy resin clearcoat - Yummy!

[David Root]

Nice job, funk! I have a big roll of 2" blue tape rarin' to go!

Is that a JJ and a Winged C EL34 there? In parallel SE? Just curious.

BTW I checked the underside of my chassis, they are not white primered, just airbrushed that looked white from a certain angle, so no serious grounding prep needed.

[funkgang49]

Thanks David. No it's not para. SE. The JJ is rectifier tube - GZ34/5AR4. I am using a 6SL7 as the first preamp tube then 12AX7. I was plugging in and out different 6L6's and the Svet was the last one I tried. The best sounding tube in this circuit, by far, was the JJ KT-77. A JJ KT-88 a close second.

[David Root]

Interesting stuff. I like the 6SL7 too, I did a Dumbleized 5F6A with 8417s and 6SL7s some years ago.

My recent SE amp is a 5879 set up for hi-gain, into a 12DW7, gain/CF, to TS, to another 5879 set up as a hi-voltage out driver to a KT66, with "Ghetto UL" Hammond 125E PP OT at 3K pri. Maybe 10-12W. Geezer's HoSo56 with a different driver/power section.

[sepulchre]

Nicely done, funkgang. Very compact. Beautiful paint job!

[gingertube]

I just use low tack masking tape. You can mark the hole positions on it and it does give some protection against dings and scratches.

Early in the life of a London Power Standard.

Cheers,
Ian