The AM Forum

I know JJ said he fabricates all his stuff from off the shelf angle aluminum and flat stock sheet aluminum. I would really appreciate seeing some pictures of your handy work even if it was posted before in some other context.

I need some hints for construction of my dooms day machine hopefully that I'll build this winter for 75 meters. So if you have an amp or a power supply or something built for other than a radio, I still would like to see it.


tnx om's de w2pfy.

I'll post some pictures of one I built I think it is all 1/8 inch plate. 28 inches deep so could hold a large jug.

Terry

I used 1/4" key stock.  The basis for the whole structure's stability was the front and rear panel.  Might not work for you but it worked for me at the time.  Right angle stock might work if you were to put some square stock in where it attaches to the panels.

Then, Mark QFX can braise aluminum -- just a thought.

Al

Terry,

I'm planning to pull my HB linear out to replace a tube, so will take some pics then for you.  The chassis is HB as well as the C1/C2 mounting bracket.

The way I build it is like this:  Every place where one edge of sheet needs to join another (right angle) I use a strip of alum angle. I first drill a line of holes in the two sheets and then lay them, one at a time, onto the angle and mark the hole alignments. Then drill the angles and pop in the 6-32 screws and nuts.  

This eliminates having to bend corners in case you don't have a metal brake. ( I don't)  In the case of air sub-chassis, I sometimes will add a bead of RTV to seal an edge that is not tight. Do it from the inside and it's hidden.

I usually brillo pad the box when finished and it looks like a commercial piece. Depending on the requirements, I use 1/16" to 1/8" aluminum sheet and 1/16" angle. You can buy the sheet cheap at a recycling scrap yard - the angle may be harder to find there and may need to be bought at any hardware store or metal distributer.

The sample pics will show what you need to see so you can duplicate my work.



BTW, What is the doomsday machine, a big MOFO linear?... :o

T

This exciter chassis was made from

2,  12 x 12 x 1/8 sheets
1, 1/2 x 1/2 x 12 angle supporting chassis to front panel
1, 3/8 x 3 x 12 bar stock holding up back of chasis

.........

This 810 RF deck was made pretty much the same way.

Jack

I like 1X1 1/8 angle. Nice overlap to provide a good ground termination and much stronger. I Drill the angle or plate then C clamp it to the mating piece and use it as a template. Key stock is nice when there isn't much spare room. You can tap it for a real pro looking job. I suppose you could tap 1/8 angle but pem nuts would be stronger for blind mate top and bottom plates.

Similar work done here, except I use alum channel stock and pop rivets. The channel stock is 1/2 X 1/2  type with about 1/16 or 3/32 walls. (It was what I had at the time). 

I don't know if the rivets will hold up (could loosen over time?) but the are nice and tight and very quick/inexpensive to put in enough for a good joint heck they use em on aeroplanes.

Yep -- that's what I did.  Worked for me.  I still have some of that stuff after 30 years.

Al

How do you cut the sheet aluminum? I have a table saw and an expensive metal cutting blade but after getting my finger trimmed off a few years ago, I am a bit hesitant.

Pat
N4LTA

Yep, those table saws can be hard to control. I cut all my Plexiglass on one and some sheet. But for smaller sheet cuts (12" or less) I use my band saw. The edges aren't perfect, but I use the sander to clean them up.

Another thang I will do for a BIG job is mark up all the aluminum sheet and bring it to a local shop. They will usually use their cutting brake for no charge if you do biz with them.  Or, I have one shop that lets me personally use any machine there for a nominal charge that usually amounts to less than $20 per visit.

Pat, please tell us the gory details about the table saw accident so that we may avoid the mistake... :o

T

For a lot of metal cutting advice, check out this thread from a little while ago.  I think we ran the gamut from the Scribe and bend method to The Plasma cutter. 

http://amfone.net/Amforum/index.php?topic=21633.0

Just the usual STUPID table saw story.

I was cutting some phenolic sheet that was warped so bad that I had to raise the blade up to about 1 1/2 " to cut it in the center of the warp.

I should not have done it - but I needed a piece and was in a hurry. The whole large piece of phenolic kicked back and hit me really really hard in the gut and I fell forward and my right had hit the blade. It just cut the end of my index finger and took about a half inch off my fourth finger. I was very very lucky as it could have easily cut off my hand. Stupid Stupid Stupid!

I thought I was safe by having my hands away from the saw but the kickback force was way more than I ever expected (way more). I am a pretty big guy and it was a hard lick t the gut and happened like an explosion.

I have plenty of respect now. I had just purchased a $125 metal blade and I have not used it since the accident.

I built an explosive locker from 1/4" sheet steel and angle a few years ago using similar construction. I had a meatl fabricator shear the steel for me.  It worked out well and the ATF approved it. I was using it for storing rocket motors, black powder, and igniters.


Pat
N4LTA

Wow, quite the story.

Yes, the kick-up of the sheet is what causes problems here too.  I've had a piece of Plexiglass fly 50' across the yard once. Brutal. You would think the blade would keep the work down on the table since the blade turns in the "down" direction.

What is the significance of keeping the blade rolled down as low as possible? You mentioned you had to roll it up higher than normal cuz of the warping.

I've heard others having problems with table saws like this. What keeps the work down on the table safely in the more expensive machines, some kind of framework that rides along with the cut?  All I have on my $200 table saw is a guide slider thingy.

T

Pat,

The place where I used to buy a lot of my hardwood had a major dent in the steel wall 30 feet from their table saw.  The dent was from a kickback and fortunately for the operator he wasn't the one who was hit.  

Cutting wood is tricky enough but for other materials it really is critical to make sure the fence is properly aligned to the blade and the proper hold downs are used.  Although the anti-kickback pawls can be a nuisance on my unisaw they stay in place whenever I am ripping stock.  For warped stock the bandsaw is a good idea and after I properly aligned the fence on my 24" Italian made beauty I am very happy with how nicely you can rip a straight line.

The one piece of shop gear that still makes me nervous is my shaper and using it for curved raised panels is something I will always watch closely.  I will never forget when I bought it the "old timer" salesman said "keep in mind-when someone came in to see the shaper operator in a furniture factory they just asked to speak with stubby".   A big carbide winged shaper cutter makes a pretty evil sound while spinning.

JJ,

Feather boards can be used both on the fence (to hold down the stock) and in the miter slot (to hold the stock to the fence).  Of course a push stick is also a good idea and as much as possible you want to stay out of the path of the likely kickback.

The plastic feather boards (readily available from any tool supply house) work pretty well and can make it a lot easier to control the work piece and also to get a much cleaner cut.  You don't want to put so much tension on the work piece that it is hard to move since the jerkiness that results from this can induce a kickback.  For cutting wood and other materials that tend to close up after the cut having a splitter in place will greatly reduce the odds of a kickback.  The front of the blade is pushing the material down but if it pinches on the back of the blade after the cut then it will tend to pick up the piece and throw it at you. 

But these tools are no more dangerous than our usual work with electronics EXCEPT they are even less forgiving of tired and careless behavior.  It is also critical to keep the work area clean so something else sitting on the table saw doesn't jump into your work space.  An example I use when I do risk management seminars:  It you have two guys using chain saws to clean up identical fallen trees the guy who doesn't work properly and clear the area of the cutoff material is more likely to be injured not just because he may trip or lose his balance but because when something does happen and he needs to move quickly he has to spend a split second thinking about what might be in his way.  The other guy with the clear area doesn't have this time "penalty" and is far more likely to escape serious injury.

Rodger WQ9E

Here is an example from the Gallery of how I do it.

The front panel and sides are 1/8" aluminum sheet cut with a jig saw with a metal cutting blade. Half by half angle is used to secure the chassis "top" to the panel and sides. The angle is drilled and tapped with the 1/8" sheets counter sunk to take flat head screws. Makes for a neat and strong assembly.

http://amfone.net/Amforum/index.php?action=gallery;sa=view;id=86

Bill  KA8WTK

How 'bout a jig saw?  They have metal cutting blades these days and you can clamp the crap out of the metal before attempting the cut.  I've had to cut 3/8" plastic recently at work and was successful.  They have some really fine toothed blades now - you just have to look hard.  I'd be REALLY AFRAID of using a relatively higher speed table saw for cutting anything but wood.

Al

Terry,
I posted this on another topic to JJ........not sure if u saw it:

I like the jig saw idea - I have a very good one made by Boshe with an edge guide.

If the phenolic had been flat - I would have not had the problem. I looked at the warp and thought  "this is not going to be real safe" - Then I proceeded to be stupid and raised the blade high enough to cut the raised warped area.

I now never get in a hurry when saws are involved.

For everyone out there who hasn't learned the hard way - Take your time and plan ahead - and then look out for the unforseen.

Pat
N4LTA

My 1st homebrew project back in 1977 was building a P/S for my Elmac AF-67 TX.  I made the chassis from 1/8" 6061 aluminum that I tig welded then cut all the holes on a vertical mill.  That chassis was STRONG!  I built the P/S from a circuit in "104 Projects for Novice & Technician".  All toob rectifiers & regulators & TV set xfmr.  Still have the book.

about those table saws and kickback... depending on the make and design of ur saw... if you have a "real saw" like the one I have (a Powermatic) it is a belt driven arbor that holds the blade. The force of a kickback is dependent upon the power available at the end of the saw blade. In my saw, which was designed to not slow down on a rip of a fat hardwood board, I have installed a "weaker motor" and have some slop in the belt, or else I am using only one of three belts (don't recall which). This means that I can cause the blade to slow and stop if I make a fast heavy cut, and can either stall the motor or cause the belt to slip. Yep, I know that if I need to make the heavy cut my RPM will drop unless I make a rather slow cut. But since 98% of everything that gets cut on my saw is thin stock or aluminum it's not a problem. The energy available for a kickback is very very reduced compared to the same saw with all belts on, tight and the standard full power motor (or worse, a 3 phase one of equal or greater HP) is far far less. Puny in fact by comparison. If there is a dangerous downside to doing this, I don't know what it is. Been running this way for more than a decade or so and have cut a ton of stuff on the saw... worked out very nicely so far. Just an idea...

On the angle iron and aluminum construction technique, I've done the tapping and the "clinch nut" (PEM). I found the PEM to be better and faster, once you have the squish method figured out. But the alignment of the holes is a tricky biz. I went with making the clear hole in the panel a bit large, so that the drilling alignment has some slop - then the panel gets aligned and held by the screws being tight, not the precise location of the hole on top of the threads (hard to do). Doing this with flathead screws is not possible.

That aluminum "braze/solder" stuff I think is a best bet... wish I had an inexpensive source for that rod. I saw a guy demo'ing it at a recent hamfest - not too many takers, but I watched him solder together soda cans. The stuff seems to work nicely. I think I'd use it given a choice between hours of drilling and tapping or drilling and squishing pem nuts. Of course panels that need to come off can't get slobbered together! But you could braze on one side of the angle iron and have screws on the other face...

                         _-_-bear

Bear,

Interesting thoughts on reducing saw power.  I have a Delta Unisaw and I am using all three belts with the three horse motor but if I am still doing woodworking when I get old and feeble I hope I still remember your solution! 

Another thought for increasing operator safety would be to use one of the many available power feeders.  I don't know how well they would work for thin sheet goods like aluminum stock.  If I ever need to run a lot of trim work on the shaper I will add one since there is no way I can feed stock as smoothly as the motorized unit but for now I don't run much trim on the shaper.

The small skilsaw (6")with a thin kerf carbide blade cuts aluminum very well....clamp your metal to the bench when cutting...A 7 1/2" skilsaw works as well but of course is heavier and a little harder to manuver...makes nice straight cuts...

Variations of that stuff have been around for years . Actually a Zinc based material .

  As an alternative to screws and angles ; most metropolitan areas have a shop or two with a good press-brake. Takes a little blank development time but the results are quite professional and structurally sound.  Kind of spoils a person after having access for almost 40 years !

Lots of great ideas and workmanship coming my way and please keep it coming ;D

Bill, You gave me some of those rods, never tried them. Now if I can just find them ??? ???

KG8LB-Looks like you have something to post but left it out. Try again OM 8) 8)

Just picked up 2- 8 foot lengths of 1/8 inch angle aluminum at home Depot
They were 3/4 by 3/4 and 1 1/2 by 1 1/2 inch $55

Mostly use a hand-held saber saw with metal blades here.  Usually does OK if you take your time.  Sometimes has a rough edge, but that is easily fixable.  I have found that old street signs make really good chassis and  mobile antenna mounts for locations where a commercial mount would cost too much for cheap people like me.  They have tough aluminum; don't know the alloy, will have to find that out some day.  If you know somebody at the local municipal sign shop, sometimes you can get ones taken out of service for nothing or close to that.  Use the aluminum angles to joint the pieces at the edges using either pop rivets or screws according to what it is and the stresses it will have to put up with.

Repurposed stop signs make both EXCELLENT tops for V/UHF discones as well as ground planes for 220 and above verticals for repeater work.

And to the original poster, almost ALL my chassis are made from angle iron and home cheapo parts.  I haven't wasted my dollars on a BUD or similar in years.

Make a friend at the HVAC shops around town, they usually have shears, brakes, etc. for metal work.  I've found it costs about a 6 pack to 12 pack if I bring all the metal in, and about 20 minutes.

--Shane

Also works well.  Another trick when using the jigsaw or the "sawzall" type devices is this.  When you clamp it down, sammich your piece of work between two pieces of wood.  I'm not an engineer, and I can't tell you why, but it really helps the cuts come out cleaner.  No chance of kicking out or at you, either.

--Shane

Good idea for safety. The sandwich will keep the work piece from flexing or lateral movement, thus preventing binding and causing a kick-back.  

It appears most accidents occur cuz the work doesn't flow straight and true - and without flexing. The clamped down sandwich appears to handle both problems.   Otherwise, the blade gets a grip on the binding work and all hell breaks loose, as well as creating shoddy cut lines.

Because of this thread, I'm gonna be REAL careful and take new precautions with my table saw. I kinda thought my few bad experiences were random, but evidently it's a real hazard to avoid.

T

Siding guys mount a carbide blade backwards in a saw. I wonder if it works with thicker stuff.