chassis conundrum

[stevlech]

Long story short: I've got a blank chassis that was powdercoated before any work had been to it and I'm wondering what I can do with it. I'd like to use it for a project but have no idea how to approach drilling it. Any advice would be appreciated.

[skyboltone]

Try to find some brad point drills for the little ones. I use carbide forstner bits for aluminum, but if your chassis is steel you are stuck with holesaws or step drills for the tube sockets and larger openings. Use a Dremel with a carborundum grinding wheel on it to make ground points.

Shouldn't be too hard to make a good job of it. Use masking tape on the top side of each hole to avoid scratching the powder coat with drill swarf.

[M Fowler]

I proceed exactly as skyboltone stated using masking tape over the top, faceplate and back plate and then measure and mark all my holes. I use high quality drill bits 5/16 starter holes and then mostly used step drill bits and punch set for the tube socket holes and cap can hole for chassis that are already painted for powder coated.

Here is one I did a few months back that way.

Mark

[FunkyE9th]

Try to find some brad point drills for the little ones. I use carbide forstner bits for aluminum, but if your chassis is steel you are stuck with holesaws or step drills for the tube sockets and larger openings. Use a Dremel with a carborundum grinding wheel on it to make ground points.

I'm curious... What would be the advantage of using forstner bit over a hole saw? Cleaner holes? I've been using hole saws for tube socket holes and then a deburring tool. Thinking of trying a forstner... Thanks!

[Phil_S]

It's not that big a deal. Here's one I received already coated: http://home.comcast.net/~psymonds/TMB18W.htm I just ignored the coating and ground it off the inside with sandpaper where I needed a clean ground. All the regular tools worked fine. I started the holes with a small sharp bit. The big holes were done with a step bit. Just take care not to scratch off coating on the outside.

[Structo]

Yes if you cover it with masking tape then you can draw your layout on the tape.
It should protect the chassis from most slips.

The one piece of advice I can offer is, measure, measure, measure before starting the drill.

Be sure to take into account the diameter of the knobs when drilling pot holes as well as tube socket holes, think about spacing.

Another good way is to draw a template on paper then tape the paper on the chassis.

[skyboltone]

Try to find some brad point drills for the little ones. I use carbide forstner bits for aluminum, but if your chassis is steel you are stuck with holesaws or step drills for the tube sockets and larger openings. Use a Dremel with a carborundum grinding wheel on it to make ground points.

I'm curious... What would be the advantage of using forstner bit over a hole saw? Cleaner holes? I've been using hole saws for tube socket holes and then a deburring tool. Thinking of trying a forstner... Thanks!

MUCH cleaner holes. As clean as punched, without the shape distortion you get with a punch. Try it you'll like it.

[stevlech]

Thanks a bunch, guys. I was worried the coating might have an effect on the bits and I don't want to ruin a step bit! I'll keep you guys posted on my endevour when I get to it, probably around Christmas break...

Thanks again.

[M Fowler]

I have done so many amps with the same step bits I got two years ago from Harbor Freight and plan to get another set tomorrow for spare but the olds one keep right on working fine in aluminum and steel.

I am going to to try the Forstner bit trick on an aluminum chassis.

[Andy Le Blanc]

Step drills work, cheaper than a punch, but they wear. Going to weldable
mild steel the tooling needs to be maintained, not the same gumming up
issue as aluminum. There's still warp and you need to mind the bit speed...

How long will a fostner bit last in aluminum?

Another issue around tooling.... If you have a break... to reduce time and
improve accuracy of a layout you should plan ahead to work the chassis in
the flat. Drill, punch, whatever..... but plan ahead for the bend radius's
when you take it to the break or press. Aluminum tricky on a break, I think press is better there.

Beside powder coat, are there any lacquers that could be applied then baked on after the fabrication process,
to avoid complicating the issue.

Ive got an old wards/airline PA head, painted inside and out and it looks like
they took a wire brush or grinding point to the spots they needed metal contact.

[skyboltone]

How long will a fostner bit last in aluminum?

Literally hundreds of cuts. I've got a set of Bosch from 1/4 thru 1" by eights that I've been using on aluminum and wood for 15 years. I doo use Rapid Tap on every hole.

I do recommend the carbide tipped ones though as long as you're buying. Should last indefinitely. I think DrHulsey bought a set of carbide Forstners.

Oddly enough, some woods, including Teak and most fruit woods contain bits of sand and stuff and will tear up a forstner much more quickly. I do not use my Bosch set on Teak. They would be good for about one hole. I know router bits, even carbide die quick deaths in Teak. There is sand in it or something.
This all assumes a decent drill press and proper speed. Medium to Medium Slow in aluminum. Steady pressure, don't let the blade slip on dry material....wood or aluminum. Lubrication on any metal cutting job is a must for a clean hole.