Chassis Finishing Question

[Platefire]

I'm working with my Son(Gregg) on our Scott T-Deluxe amp. I'm doing the building and he's doing the finishing. I use normal drills for most holes and use a metal circle/hole drill for the 1 1/8" large sockets. After all drilling I'm using a dremel to grind of the slag/burrs from the drilling to make everything smooth.

Gregg is saying he is having to put multi coats of primer with a lot of sanding in between coats to smooth out my dremel grinding and is asking me if there is a way to cut down on the slag grinding. I use a hammond pre-gray primed steel chassis,  perforated steel cage, steel bottom plate and end up grinding off the primer down to the metal around the drill locations--I think that's where he's having the problem--plus Gregg is a perfectionist, I'm not.

So having said all that---my question is what can I do to cut down on the slag and required grinding?? I know a lot of you guys have already been down this road before. Thanks, Platefire

As a added note: I did the finishing on the first amp and it has had a problem of paint flaking off even though I used paint labled professional industrial grade and he is attempting to improve the finish to get rid of the flaking. Any suggestions on getting a bullet proof solid finish would be appreciated!!!

[tubeswell]

If you use chassis punches, you don't get burrs on socket holes.  For the other (smaller) drilled holes, de-burring them with a slightly larger drill (or counter-sinker) from the other side works for me. JM2CW

[Willabe]

Someone here posted using a de-burring tool from the plumbing section at the big box stores.

I bought one and it works pretty good. I find that if I knock down the burr with a flat file first, it works best. Then I hit it with the de-burring tool. When I didn't hit it with the file first,  I ended up enlarging the hole slightly before/while I was getting rid of the bur.  I think it cost about $6/$7.

But using the flat file will take the primer off so, maybe not the way to go.  

It kinda looks like a string winder. Plastic handle with a little metal hook on the end that swivels. Came with a replacement cutter blade that's stored in the handle.

OTOH, a uni-bit run to the next size but not all the way thru works great, or like tubeswell said, a good counter-sink works great too. 

I've been experimenting with all of them to get a feel for what works best, at least for me.


             Brad        

[kagliostro]

Something like this is very useful

Kagliostro

[TubeGeek]

I was just reading through a book i have last night on this very topic!  The book discusses all the mechanical details of building an amplifier.  If you want a copy, let me know and i can email a pdf of it to you later when im home from work.

The de-burring tools work good.  I find the key to getting a nice clean cut hole is lubrication.  A little goes a long way on the bits.  

As for the paint chipping or flaking off... When i paint a bare chassis i do this and it works nicely for me:

First i will lightly sand the chassis to prep it for adhesion.  I then wipe it down thouroghly with a tack cloth.  Once it's free from any debris and crud i will spray the chassis with an etching primer spray paint i found in an auto zone type store.  Its army green in colour.  It supposedly etches the metal and form a stronger adhesion and preps the metal in a way that paint will stick better.  After that is dry i will begin applying the final paint to the chassis in light coats until i am happy.  Once that dries i will typically apply vinyl lettering to the faceplate etc and finish it off with either a glossy clear coat or matte clear coat until i like what i see.

Doing this method works for me and i have not had anyone complain that the paint is chipping off anymore, it used to drive me nuts until i used this method.  I try to be a perfectionist.

Hope this helps.

[punkykatt]

I use an old wood chisel. Takes them burrs clean off.

[Frankenamp]

The little 'hooky' deburring tool is a decent option. Shaviv makes a decent one; most hardware stores carry a similar one made by General. The Uni-Bit's work OK, you just have to be careful not to let it dig in (hold it straight or use a drill press). +1 for lubrication, 3in1 oil will do in a pinch (or wd40) if your'e out of Tap Magic* I tend to use the Uni-Bit (or the harbor freight version) for laziness sake (less tools to use).

As far as paint adhering- I'm a big fan of Green-Weenie scrubbers and alcohol. followed by a thorough rubdown with a blue shop-towel. I found that there are some types of rattle-can paint that don't work well together. When in doubt either stick to the same brand ie. Rustoleum, or Krylon, see if they have the same base chemicals (sometimes listed in veery small print) I usually ask the paint guy if I'm in doubt- not the kid working his/her summer job, but the geezer that's been there a while. Note: I'm in Kali-FORN-ee-ah, and CARB is demanding changes in lots of different formulas, so things will get more interesting before they settle out...

<Perk> book on amp building .pdf? sign me up please!

[jojokeo]

I use the common deburring tool for straight edges but it doesn't do well on holes. Files and the like are too time consuming and a hassle. I have several dremel tools w/ various attachments but the flex shaft extension works great. I use a step drill & normal bits for holes, a bit cutter for IEC sockets, etc. and an aluminum oxide bit w/ the dremel that grinds away the burrs on the holes. After this I lightly use a long tapered metal reemer to get the holes back to round and sized again to where they were as lightly grinding the edges w/ the dremel tends to slightly close the holes again.
I actually sand my chassis when finished to create a roughed up surface for the primer to better stick. Then I'll use only one coat of primer. I won't wait until fully dry and paint while primer is slightly tacky so that the paint sticks better to the primer and actually slightly bonds w/ it in this way. When paint fully dries, you need a light sanding for it to stick well just like when you varnish multiple coats on wood.
Lastly, I like hammertone paint as it goes on thick, dries hard, is durable, easy to use and looks nice.
Maybe this helps? Keo

[Platefire]

Thanks! A lot of good info here. I think part of my problem here is that the Hammond Steel Chassis with Cage I'm using comes pre-finished with a gray baked painted/primed finish and my dremel grinding around the holes is wearing off the prime coat down to the metal and that is making the uneven appearance when coming back with the extra prime coats. I think I would be better off if I was using a chassis that was bare metal without pre-finish and that way my first coat would be the only primer. If I wasn't using the 16"x8"x2" chassis, I could use bare aluminum but they don't have aluminum in that paticular size--12"x8"x2" would be too narrow.

I think on the smaller holes up to 7/8" in Diameter the step drill bit in my drill press would be the solution. Using the the drill press I could just barley toutch the edge of the hole without enlarging it hopefully. I do use 3 in 1 oil when drilling. On the larger holes I believe the punch might be the solution for the preamp tubes and 1 1/8" Octal sockets. In dealing with the baked on primer, I will have to focus on not disturbing that finish as much as possible.

I wish I had taken pictures before I applied the paint on the first or second one but I didn't--but here is the first one after painting. If you look closely, you can see the scaring through the paint around some holes. Apparently it was even worst on #2. Now that I got a perfectionist (quality control)doing the finishing, I'll  have to tighten up a bit pun intended! I'll be copying all this info here and putting it in the folder for reference on #3. Thanks for all your help, Platefire

[tubenit]

I always use automotive lacquer on my chassis. I just buy the spray cans. Never been a concern and they've held up for yrs.  I don't use a primer and I simply clear coat over the lacquer. I am pleased with how it holds up. I use an orbital sander with 220grit sandpaper, wipe it clean and spray.  Think about it, your car finish is a reasonable durable finish and is resistant to heat.

For what it is worth, I have used Rustoleum and found the auto lacquer to be less likely to chip off.

with respect, Tubenit

[sluckey]

If I wasn't using the 16"x8"x2" chassis, I could use bare aluminum but they don't have aluminum in that paticular size

Hammond Aluminum 16" x 8" x 2" Chassis 1444-26, $25.00 from Angela. It's only .04" thick, which is too light for guitar amps IMO. I'm pretty sure that all sizes of Hammond chassis are available in steel or aluminum.

[Boots Deville]

If I wasn't using the 16"x8"x2" chassis, I could use bare aluminum but they don't have aluminum in that paticular size

Hammond Aluminum 16" x 8" x 2" Chassis 1444-26, $25.00 from Angela. It's only .04" thick, which is too light for guitar amps IMO. I'm pretty sure that all sizes of Hammond chassis are available in steel or aluminum.

that one is .051" thick aluminum:
http://www.hammondmfg.com/dwg21.htm

My first amp build was in one of those.  Single-ended P1 Extreme, so not large transformers, but it's been fine,

[Platefire]

I should have ask this question before he started painting because I think he's using the professional grade Rustodiam. I'm kind of letting him find his own way on this because he has done a lot of research and inquiring on his own to determine what to do---more effort than I ever did regarding finishing on #1. He is using the "inkscape" program to create the text for the faceplate except it won't be an additional faceplate installed but the print out from inkscape will be applied to the finished chassis and he intends to apply clearcoats over the applied face stinsel and finished chassis for added protection. I'm sure he's going to run into some un-expected kinks along the way.

So thanks for all your input. You guys are a blessing with your willing helpful attitude! I'll do what I can in the future to make my chassis prep better with applying finishing coats in mind. He has  borrowed a small portable painting booth from his Father in law and in the process of applying finishing at this time---thus his questions about my shotty grinding into the existing baked pre-finish. So on this present finish job, should all fail and we have to back up and punt--I will be armed with a lot of good information I can provide him and plus there's always #3 to apply our current knowlege to. So I'm glad I ask the question because if your going to sell an amp, it needs to be best it can possibly be. Platefire  

[terminalgs]

high build primer.   If applying to bare metal,  use metal-etching primer first, then high build primer  (or metal etching high build!  -- the only one of know of like that in a rattle can is a WURTH  $18/rattle can).   high build primer fills the nicks.   depending on how deep the nicks are, you might need multiple coats anyhow.

sand between coats and after final prime coat with something like 220 or 400.  then apply paint coats...