The AM Forum

I work working on building a tube amplifier that may be used as a modulator.  What is the best way to drill the holes in the chassis for the tube sockets, tranformers, caps, etc......


thanks

Tom - AB3FL

I read an article a while back in Electric Radio that touts the benefits of Step-Bits.  Sounds like a great idea to me.

I've used Step-bits quite a bit on various projects and they work great. I drill a small pilot hole just to ensure the accuracy of the center point. Just have to be careful and not overshoot the step you want. Also, it's worth the money to get the good bits. And no, from experience, Harbor Freight does not sell the good ones.

Greenlee punches

Thanks All.   Looks like I need to get a good set up of punches.  That looks like the safeest way for me to make holes.  The step bits look good too, but I don't have a drill press.

Tom - AB3FL

What do you look for to determine if a bit is good or not?

You have not even told us what metal you are working with.  That tells me you are already in over your head.

I don't know Jack about metal work either but sometimes a noob can help another noob best.  Get yourself a textbook on machine tool practicies.  the kind used in schools that teach metal shop.  You can get them used from abebooks.com
Start reading it.  You'll learn about how different types of metal behave; hand tools, cutting oils for different metals, taps, most important, safety practicies.   Before you go out and blow a ton of money on greenlee punches, you might discover there are other ways.   Good luck.

Either steel or aluminum is what I would be using.  I built a small chassis before, but the holes were terrible as I was using normal drill bits.  I looked for a video on punches on youtube and found one that looked good. 


Tom - AB3FL

Feel free to use conduit punches; they're only slilghtly off-size of normal 7 and 9 pin miniatures, and octal sockets.

You don't need a drill press to use step bits, but you should clamp the chassis in something for when (not IF) the bit binds in the hole.  The other thing is there seems to be plenty of crap left over on the opposite side that needs to be filed/ground away using these bits.  Or maybe I'm just doing it wrong  ::)

Here is a list I've compiled over the years:

Drill bit set.
Flat & rat tail files.
Greenlee punches.
Small triangle square.
Countersink bit.
Nibbler tool.

With these tools and some practice, you can build up some really pro-looking gear.

Punches are not cheap, but they do the best work and will last a lifetime.

73DG

If you are going to do any significant chassis work, a drill press should be on your short list.  Even an inexpensive one is going to outperform a handheld drill and will allow you to do much better and safer work. 

For any hole saw or fly type cutter you should use a sacrificial piece of scrap wood to back up the drilling surface.  This will provide a much cleaner cut and reduce binding and chatter.

Before cutting a hole in an expensive large chassis I would try your cutting tool in a cheap piece of aluminum to find the true resulting hole size.  Many hole saws will produce a hole slightly larger than the specified size and any runout in your drill or the cutting tool shaft will increase this discrepancy.

Consider using a subchassis mounted on the main chassis for high power final or modulator tubes as this will make future changes to a different tube type simple and won't result in a kludged up chassis.  You can also use a lighter gauge material for this subchassis which will decrease the difficulty of cutting large openings.

I didn't list hole saws in my previous post, as most of them are really hard to handle and don't provide fine results without much care & practice.

The ones from Blair are a cut above (pun intended), and work more like a precision milling tool than a rotary blade:

http://shop.blairequipment.com/SearchResults.asp?Cat=4&gclid=COCz4Ku2tK0CFaQbQgodiwFQnw

If you elect to use a holesaw, I highly recommend these...they are the deal for the $$.

73DG

That pretty much sez it all ! ! ! !  With PRACTICE being a key word here!
that is pretty much all I use.

But Dennis, you forgot 2 very important items......................
A fresh Sharpie and a bottle of alcohol.
Depending on the complexity of the item you are building, you WILL lay it out, clean the ink off and lay it out again quite a few times before you drill the first hole if you want a good professional looking layout. ;D  ;D

But Dennis, you forgot 2 very important items......................
A fresh Sharpie and a bottle of alcohol.
Depending on the complexity of the item you are building, you WILL lay it out, clean the ink off and lay it out again quite a few times before you drill the first hole if you want a good professional lookig layout.


I usually consume the alcohol after the drill walks away a makes a new hole location .... then I clean off the drill press like I shoulda in the first place

Add a roll of masking tape to minimize marring when drilling.

all of the above and this too:

(http://upload.wikimedia.org/wikipedia/commons/thumb/b/bc/Taper_reamer_K-442.jpg/704px-Taper_reamer_K-442.jpg)

the title is building chassis.  if you are going to make your own chassis from sheet of metal you need to make bends.  i would like to own one of these:

http://www.grizzly.com/products/24-Box-and-Pan-Brake/G0557

I'd also like to own a milling machine but i would settle for a floor mounted drill press.  I'd also like to have a table top band saw.

are those nibbler tools any good for aluminium and steel or are they just meant for plastics?

OK, I'll bite.

Drill press! I can't emphasize this enough when using step drills. Actually I can. DRILL PRESS!!!  :P

Slow gradual drilling, using lubricant/coollant at the same time will eliminate burrs and erratic hole sizes when using step drills with Steel or Aluminum.

Greenlee punches are the only way to go. I have bought others (cheaper) and the aggravation created by them is worth the extra money you will spend to buy Greenlee.

I own a table top ten-speed Porter-Cable drill press that I bought from Loews. It's just fine, but make sure you firmly mount it to the table. I also added a nice milling vise for smaller projects. All told cost me about $250, including the milling vise.

Never buy cheap bits or mills, and always buy the right bit for the material. This is important for three reasons. Quality of the hole, durability & therefore longevity of the bits, and safety!

Also never put a piece to be drilled down without it being firmly mounted to something. Clamp it to the drill base, use a milling vise or a drill vise mounted to the base of the drill press. Most binding occurs because the piece moves, vibrates or is on angle not perpendicular to the drill. Rigid mounting of the piece and having a press is mission critical for perfect holes that need little hand work after drilling (deburring, etc) Safety is also a big issue here! Many a finger/arm/eye have been lost due to people drilling chassis held only by hand, being drilled with a hand drill with no lubricant. OUCH!

Clamps, various wood blocks, drill specific vises, correct drill types, etc will all make the job go well with high quality results, go quickly and happen safely. Here's the milling vise I bought, from [yikes] HarborFright (the mis-spelling was intentional.) It's not ultra-precision but works fine for most Amateur Radio uses.


John

I second John's call for a drill press.  I generally have a cross slide vise mounted to both my straight and radial Delta presses.  The Harbor Freight vises have worked fine for me and I have had them for about 10 years.  I also have another mounted on my mortising machine and it has also performed flawlessly.

For chassis use, you will often need to build a simple jig that will go into the vise and support the chassis, generally a piece of plywood with attached cleats to clamp to the chassis sides and to clamp into the vise.  This style vise takes most of the frustration out of putting smooth cuts exactly where you want them.

I have to jump in here.
I have built close to 100 amplifiers so far and may offer some wisdom in no particular order.
Plan, plan and re-plan. Your end results are ONLY going to be as good as your planning and layout.
Once you have arrived at this critical place, the best quality tools you can afford is a safe and sure investment.
Your drill bits should be as sharp as possible, and the use of a "Uni-Bit" is encouraged.
You should consider using a high quality snap punch. If you plan on fabricating your own chassis, be sure
to accommodate the radius of your bends with your finished measurements. Once you bend, that's it... you can't go back. Using a block of wood behind your material while drilling will help to eliminate "blowout" or slagging of leftover material from the hole. A plumbers pipe reamer or hand trimmer is ideal for clean holes.
The use of green masking tape is also encouraged when laying out your drill marks and helps to keep the material clean and also helps in case you "dance" a tool or bit across your chassis.
I should also stress the use of high quality files and this includes fine jewelers files. And please, buy a file card to keep your files clean. They can build up aluminum in a hurry and foul out.
NEVER use a hole saw on a drill press!!! This is fool hardy and dangerous as hell. Use the slowest drill speed you can to make your drilling operations not only clean but safe and it helps to maintain the structural integrity of your drill by not overheating them. It is best to use real cutting agents intended for cutting and drilling metal because they can handle the heat. Certain types of lubricants like light machine oil and WD-40 should be avoided.
Back to the layout...
If you can afford the space, make sure you have an adequate area to layout and fabricate. Working in cramped quarters can cause mistakes. Making absolutely sure that your measurements are truly square is made easy by having at least a Tri-Square and a T-Square. The cool thing about most Tri-Squares is they include a handy scribe that nests in the square so you can make scribe marks along a line.
More to follow.

All this stuff has been covered ad nauseum on this forum, some very recently....do a search...All the varied opinions will drive you nuts....There are many ways to do this...Most all work for the most part....My opinion.......I am a metal guy...made my living as a sheet metal worker, machinist, welder.....I've homebrewed 3 big rigs and modified many others...I have all the tools...My advice... if you are only building a chassis or two....KEEP IT SIMPLE....You don't need to spend a boatload of money for tooling......Good luck and keep on homebrewing!!!

Quality of workmanship in the bit and how long it lasts. I ordered my Harbor Freight ones on-line and wasn't impressed when I got 'em. The cutting edges didn't last either. Just bad metallurgy. I bit the bullet and paid the price for Irwin brand at the local ACE hardware. They look like a high quality piece and live a lot longer. Reminded me not to grumble about the price for good quality tools.

I'm a newbie, and the "keep it simple" advice given above has been good to me.

I've been doing a fair bit of metal work with two hole saws, two step-drills, a nibbler, a reamer, a collection of files, a collection of drill bits, a black&decker, a dremmel, a pair of lab goggles, a hand saw, and my own two hands. I also use my thighs and feet to hold stuff in various orientations during drilling. Finally, a bunch of wood pieces and clamps are sometimes used.

Here's something I've been putting together recently (I've cannibalized the aluminum enclosure and other parts of a BC-375 tuning unit in which I put a chassis cover with angle stock):

http://imageshack.us/f/215/img1655gf.jpg/

http://imageshack.us/f/853/img1671m.jpg/

Now where can I get a chassis from that doesn't cost a fortune?

Try this place out. I know it's geard to CB but nice cabinets cheap.
http://icamanufacturing.homestead.com/

John N8QPC

Chassis can be made inexpensively. If you do the proper layout and allow for the radius's and corner bend holes, a local sheet metal shop will usually charge you a nominal fee for bending. Make sure the type of material you use can be bent without splitting. If you do not plan on bending a chassis, then fabricate it using 90 degree corner stock and screws or rivets etc... just like they did in the ARRL handbooks.
We all have ideas on this subject and let me state something obvious, you DON'T have to spend a bunch of money, just spend wisely where needed. Attention to details is key and if you have doubts about doing certain operations then consult with someone who can. Common sense and sharp tools.
A Uni-Bit costs around 20 bucks for the standard 1/8" to 1/2" model. These will stay sharp a long time if you use cutting fluid and go slowly.
I forgot to mention the most important aspect of all...
HAVE FUN!

Old HP test equipment from the 50's, the really big stuff can be had for pennies and stripped down to the chassis. Cut out the entire chassis face with the exception of a 1/2" to 3/4" lip all the way around. You then attach a new chassis face complete with your holes in place.
Done.
You also have the benefit of the cabinet and associated hardware, that includes all of those 4-40 and 6-32 screws in abundance. Your fastener cost is already paid for.
I built a linear amplifier out the same model unit shown in the picture here. Great hardware too. I made a different faceplate to accommodate my layout. Fun.

I am curious as to your reasons for "NEVER use a hole saw on a drill press"??? 

Also,  someone new to machining might misinterpret your slowest speed comment since too slow a speed for the cutting bit also is bad for the cutting tool and leads to a poor cut.  Manufacturers (both cutting bits and the machine tools that use them) generally provide recommended cutting speeds which should be followed.

Has anyone used the chassis cases from tubesandmore.com?  They have some nice Hammond cases for reasonable prices.


Tom

LOOKIN' GOOD!!!

Buy an old used chassis at a hamfest that's full of holes for cheap.  Cut off the top leaving 1/2 around the edge.  Pop-rivet a new top of fresh aluminum on it.

This was built with a hand held electric drill, a saber saw, and a couple files.  I was much younger when I did it. If you have time you can get by with some simple tools.

(http://img529.imageshack.us/img529/6681/1000467t.jpg)

Step bits can be sharpened.......Look at the edge that cuts...If you dress a grinding wheel to a square (90 deg face to edge) and the radius of your grinding wheel is close to the one the factory used, it is simply a matter of holding the bit on the face and side of the wheel...The side of your grinding wheel is what will sharpen your unibit...take a close look at the bit and you will see how the factory did it.....

By my experience.
Most drill presses don't have a slow enough gear ratio to allow for a hole saw. Just sayin.
For the inexperienced it is a safe bet not to. I agree to your comment about too slow to an extent.
Mostly, if you follow the tables set forth by machining practices and procedures.
Anyway, we are both saying the same thing.
A rule of thumb is this: A too fast cutting or drilling speed can screw something up much worse than using too slow a speed. Your reaction time is better with a slower speed too. There is a balance here for sure.

second that. Nice holes for Octals! Irvin "Frank" Miller W5PBN (SK) gave me an old set long ago and I've always loved them.

For chassis building method, a transmitter here used exclusively 90 degree, 1/8" stock and aluminum 1/16"panels except for the front. To the best of my observation, the stock and the aluminum panels were cut to size and these chassis parts were laid next to each other, clamped, and a hole drilled every inch or so through the panel and angle as a unit. The holes in the steel angles were then tapped, and the holes in the panel were slightly enlarged to accommodate any errors in the hand assembly process, and machine screws were used to assemble the RF deck, piece by piece. Just saying, it is extremely rigid despite its size and can be tilted up on a corner without deformation despite the thin materials and 100 LB weight.

N6YW,

Thanks for the explanation.  Both of my drill presses have a slowest speed of around 200 RPM and the charts specify hole saw operation at the low end.  I agree that these hole saws should never be used at high RPM and they certainly aren't balanced for smooth operation at high speed.

I have purchased some hand tools from Harbor Freight but one thing I do not trust from them are high speed cutters like router bits.  Although they are probably OK when I have something spinning at >20K RPM I don't want to chance poorly brazed carbon cutting tips.  

I like the simple list above and I do use step drills in my cordless hand drill.  A 1 Inch Greenlee punch is a natural and chainsaw files and the like are great!

Well, a good place to start (if your cheap like me) is the local landfills reclaim/recycle area.  A lot of folks dump old Microwave ovens and such. Take one or two home, pull the guts salvage every usable part (and there can be a lot, microswitches, relays, the transformer, diode & HV oil cap, etc), the cases make nice enclosures for just about anything from a home brew 100watter up to a pair of 4-400 in a linear.  Sometimes sheet aluminum can be had at the scrap yard in odd sizes. Cut to squares, use thin aluminum angle stock and rivets and you can make a very nice chassis and enclosure.   Store-bought stuff is very nice and purty , but you pay for it. With a bit of sweat equity you can make something more durable, and just as good looking.

And you can say, "I carved this rig out of solid steel with my bare hands." or something similar and REALLY impress the visitors to the shack.

That's really a nice looking job for the tools used. It's more the workman than the tools.

When building a power supply chassis or combining the supply with the deck components, it is best to use thick enough material to handle the weight. Transformers and big chokes can cause the chassis to dish or distort.
To remedy this, I use a stiffener plate that bolts through the chassis deck. It adds more integrity and if done real neat can add a very cool industrial finish that speaks old school. A less elegant approach but very suitable is to use a stiffener made from 90 degree angle stock running lengthwise along the longest width of the chassis.
Use what ya got, and what Ed said is the best. Making use of already discarded materials rocks.

Here is an example of when I cut out the chassis deck of an old video clamper that was riddled with holes. It was the perfect donor for this LA2A compressor project at my old recording studio. I ended up riveting the new plate in place. I left the old logo too, that jet motif looks really cool.
This chassis was being thrown away as useless junk. I scavenged it right away! The comments from clients was rewarding in that not many recording studio's have in house built equipment. They took a different view towards you upon that little discovery. Anyway, you get the idea.

The best way I have found to build a chassis is with street sign aluminum and C-channel.  The aluminum in the signs is hearty stuff;  consider the forces on it on a post with 2 bolt fasteners.  Used with the C-channel, you don't need bend the aluminum sheet.  I get mine from the local street dept when they take signs out of service.  May take some straightening at times, but for what you get it's worth it.  Made this way, you can put a KW power supply on a chassis without having to worry about structural integrity.  And for VFOs and receivers, less flex means better stability.

I will echo the need for a drill press if you do much homebrewing.  For me, it makes things easier.  For layout I have used wide masking tape on the chassis.  Also keeps scratches, etc, down.  One note on chassis punches:  If you use the heavy aluminum like I do even some of the Greenlee punches are not up to it.

You may find using the optional ball-bearing pull studs make for easy work up to 3/16" T-3 plate.

Keep the parts freely lubricated whilst working them.   I use synthetic motor oil, it really makes things slippery and you use a LOT less energy.

If your punch really distorts the metal, it is most likely dull and needs to be hit by a good stone to get that edge back to cutting cleanly.

If you have access to a hydraulic press like those in auto shops, you can punch anything up to 1/4" alum. & 3/16" steel with a Greenlee.  Set up the punch as usual, and let the ram do the work rather than the screw action.

73DG

Quote: "One note on chassis punches:  If you use the heavy aluminum like I do even some of the Greenlee punches are not up to it."

Ditto. There is a limit to those punches. 1/8" is the max I have ever tried and it distorts the plane or flatness of the surrounding area. At that point you need a hydraulic press with the proper bed or caul to maintain flatness.
A hole becomes a good friend at that point.
 *** sorry I posted at the same time ***

The Hammond chassis are good quality and available in aluminum and painted steel. They have a good selection of sizes. I use them all the time. I especially like the black poweder coated ones. The steel is mild and drills and punches easily.

Pat
N4LTA