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Author Topic: Drilling holes in sheet metal  (Read 25531 times)
KB1WSY
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« Reply #30 on: February 26, 2012, 01:32:59 PM »

Shopping for a drill press, I almost bought the Harbor freight Item # 38119 recommended by Allison (on sale at $69) then noticed a parameter called "vertical capacity" which is the distance between the chuck and the table at its lowest point. The HF drill is listed as only 7.5" which I think is a problem if (for instance) you are drilling a hole in the front edge of a chassis that is 8" deep -- the upended chassis will not fit under the chuck. Thus, have decided that it is worth spending a bit more to get a model that has a greater "vertical capacity." A point worth making, for those who are working on larger form factors -- as is often the case with tube electronics.

The other, related parameter is the "throat" which seems to be the horizontal distance between the center of the chuck spindle and the edge of the support pillar (and also the "swing" which seems to be simply the throat multiplied by two). That could be a limiting factor if you are drilling a hole in the central areas of a larger chassis or panel.

At least I think I'm right about all this. Those of you with more machine shop experience should please correct me if there is something I have overlooked.

73

Martin
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G3RZP
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« Reply #31 on: February 27, 2012, 02:43:11 AM »

Martin,

You are correct. I have a vertical drill made mainly for woodworker, but it can take  a vertical piece about 3 feet long. The throw is about 10 inches. Much more than that and stability and rigidity can be a problem, and the big machines use a 'radial arm'  drill, with a rigid 4 inch or so diameter along which the drill can be moved. Massive castings and you need a floor rated in tons!

In fact for my workshop, we had a structural engineer calculate the floor loadings for the effectively point loads of mill, shear and lathe, and the pre-stressed concrete beams were upgraded to make sure the floor was good enough with a fairly big safety factor.

A relatively small vertical capacity drill capable of high speed can be useful for drilling PCBs A small vacuum nozzle to remove the dust is a good idea, as well as wearing a mask.
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K1CJS
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« Reply #32 on: February 29, 2012, 02:31:30 PM »

Unibit. Second best thing to a hole punch.  Especially if it is new--and sharp.  The trick is to go slowly and to have backing (a piece of scrap wood) clamped to the work.  When you press lightly, you're not flexing the metal, you're putting pressure on the wood, pressing the metal against the wood.  

If you do this, even if you don't use a drill press, you'll get good results.  The problem with most people is they force the bit into the work, and that will never give good results--it will always twist and warp the sheet metal.
« Last Edit: February 29, 2012, 02:33:50 PM by K1CJS » Logged
KB1WSY
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« Reply #33 on: March 03, 2012, 05:47:05 AM »

I am building a Novice transmitter from the 1960s and the advice, after drilling the holes in the aluminum chassis, is:

(1) with fine sandpaper, to sandpaper the entire surface of the outside until the surface has a bright sheen, which is easy enough;

(2) "as soon as the sanding is finished, wipe all surfaces clean with a cloth, then spray lightly with clear acrylic from a pressure can; don't attempt the same process on the inside of the chassis since this will make it difficult to secure electrical contacts to the chassis."

Any recommendations about what brand/type of "clear acrylic"? These instructions date from the mid-1960s....

I'm not sure whether this is in addition to the lye-cleansing process described in the ARRL manual (and also quoted earlier in this thread). I suspect the lye procedure might be useful with a deeply soiled chassis (for instance, a renovation of an old set) but is perhaps superfluous on a brand new, recently sanded chassis.

73

Martin
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G3RZP
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« Reply #34 on: March 03, 2012, 06:55:06 AM »

I lightly wirebrush out the scriber marks, but find the lye pickle gives a somewhat better key for paint. Swab it with a rag soaked in vinegar to get rid of any black deposit. Slightly better is 20% concentration of nitric acid - we used to know it as a 'caunit dip' finish. The nitric acid helps produce a thin layer of protective oxide. Then both sides of the chassis with acrylic - the only differenceIi've found is that some rub on lettering and some acrylics don't go together well. Where you need a connection, there are a number of approaches. One is a small end mill. I made a similar tool from silver steel but with a locating pin, and hardened it. An alternative is to take a piece of wooden dowel and drive a small nail into such that the nail is coaxial. Cut off the nail head, cut a piece of emery cloth or sandpaper and glue it to the dowel with the nail sticking through, rough side out. Then use this tool in a drill press or even a handdrill, going as slowly as the press can. It only needs a touch to the chassis to give a good clean contact area.
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KB4XV
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« Reply #35 on: March 07, 2012, 07:40:40 PM »

I have been in the glass business for over 35 years building aluminum storefronts. I have drilled thousands and thousands of holes in aluminum. First and foremost to drill a good clean hole your bit must be running true. The drill cannot have slack in the bearings running the chuck. After that a good quality bit with oil will drill a clean hole. Step bits are good. A good quality countersink will clean the hole up nicely. Pilot holes help.And clamp the peice down. You can drill with a sharp spade bit but they won't last long.
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KE6WNH
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« Reply #36 on: March 11, 2012, 07:00:05 PM »

Use a center punch to make a small pit in the metal first. Those split-point cobalt bits seem to drill through metal faster than the regular-point HSS bits. Cobalt bits are expensive, but IME they keep their edge 3x as long as HSS.

If you need to use a hole saw on sheet metal, make sure it's clamped pretty firmly to the drill press bed, use the lowest speed, keep the teeth lubricated, and don't use the hole saw on tough metals such as stainless which will dull the teeth.
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KC9KEP
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« Reply #37 on: May 18, 2012, 09:34:00 AM »

re: Drill Press - I bought one a Sears a ways back for about $100.  Now, the cheapest Sears I see online is about $150.
You may want to compare the Sears to the Harbor Freight to see what you get for your money.
I haven't used the Harbor Freight but I've built countless radios using the Sears drill press.
Harbor Freight also has a nifty small metal brake if you need to bend light weight brass, etc.
And Harbor Freight has the step-bits too.

73!

--KC9KEP
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K8AXW
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« Reply #38 on: May 20, 2012, 06:54:21 AM »

I bought a Sears floor stand drill press many years ago.  A friend recently bought a Grizzly brand floor model drill press.  The Grizzly is much higher quality than the Sears and approximately the same price.

Which ever the way you go when buying a drill press, get the best you can afford.  They will be used more than you might initially think.

The second recommendation is to be sure to buy one with an vertically adjustable stage using a crank.  Lifting the stage by hand is extremely difficult.

My first project with my drill press was drilling 6,000 holes!  Try that with a hand drill!!
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K4DPK
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« Reply #39 on: July 13, 2012, 09:02:35 PM »

Wow, there have been a lot of really good tips and tricks mentioned here.  I hope by adding a few I’m not stretching the intent of the original post too terribly far.

Lessee….

Bar hand-soap and liquid dishwashing soap are both excellent lubricants for cutting, drilling and threading aluminum.

When cutting sheet aluminum with a hand-operated jig-saw, it is best  not to use a fine-toothed metal cutting blade.  Use a slightly coarser pitch blade, and the space between the teeth will allow the chips to clear without galling.  The secret is to run the blade fast, but feed it very, very slowly to the metal.  I often tape a sheet of cardboard to the underside of the saw skid plate, to prevent scoring or marking the aluminum.  You can lay out a large hole, drill a starting hole in each of two diagonally opposite corners (hole has to clear the saw blade), and you’re off.

Someone mentioned drilling a great many holes to create a venting grill.  Years ago, I found a sheet of steel that was pre-drilled with .125” holes and was a grill in a large cabinet.  Since then, I’ve found several more of different sizes and patterns.  Here’s how to use them for drill guides:

Locate and mark where you want the grill to be on the new metal, and, using the steel grill as a template and drill guide, drill through the four corners.  Then bolt the mask to the work, using appropriately sized screws and nuts.  I use masking tape to outline the grill area I intend to drill, so I don’t absent-mindedly put a hole outside the intended area.  Once all this is in place, you can use a hand drill or a drill press to simply drill through all the template holes, and you don’t need to lay out anything except the first four holes.  No punching, either.  These holes can be de-burred using a woodworking chisel and a palm sander.  I have three drill presses, but this can just as easily (and more comfortably) be done with a vari-speed hand drill.

If you don’t have a sheet metal shear, you can still make nice cuts in sheet aluminum, simply by clamping the work to a table, and clamping a wood strip for the side of the hand-held saw to run against as a guide.  You can measure the distance from the blade to the edge of the saw skid plate to aid in positioning the guide.

If you have sawn an edge, and want to clean it up, it can be made to look like a shear cut if you clamp a steel straight edge over it and use a file or a disc sander to bring the aluminum’s edge down even with the steel.  Old pieces of bed railing are a good source for angle steel like this.

Before I got a metal break, I used such angles to clamp and bend my own homebrew chassis and boxes.  C-clamps and vise-grips come in handy for this.

Small holes that won’t accommodate a swivel de-burring tool can be cleaned up using a larger drill bit (just twist it by hand) or with a woodworking chisel.  Be careful with the chisel so it doesn’t dig into the sheet stock.  This takes a little practice but works really well over large areas with numerous holes.

Phil C. Sr.
k4dpk
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K8AXW
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« Reply #40 on: July 14, 2012, 08:43:09 AM »

0G: 
Quote
I just wouldn't even consider using one for drilling a 1/2'' hole in aluminum

I concure.  While holesaws are useful, they make a mess out of aluminum.  The hole they cut is seldom an exact diameter that is needed because of "slop" in the drillpress or the hole saw itself.  I use them for meter holes in metal but that's all. 

Bottom line, if you intend to start building to any extent, invest in a decent drill press.  I bought a Sears floor model many years ago which I'm still using.  However, Grizzly (tools) sells drill presses that blows away the Sears brands for less money. 

Another almost necessary item is a big vise..... at least 5".
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N4NYY
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« Reply #41 on: July 14, 2012, 08:48:03 AM »

I use a UNIBIT (stepped bit) i got mine at LOWES.

Amen
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G3RZP
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« Reply #42 on: July 14, 2012, 11:34:11 AM »

Even better than a drill press (although not all have as much height capability below the drill) is a vertical mill. That allows very accurate spacing of holes.

More expensive, though, but worth it.
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KB1WSY
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« Reply #43 on: July 14, 2012, 01:27:41 PM »

If anyone knows of sources for the following I would be grateful. I have searched high and low ...

--Chassis punch for keyed octal/magnal (8-pin or 11-pin) chassis mount male connectors (so that I would not need metal flange adaptors).
--Chassis punch for IEC a/c male connectors. The Internet traffic on this is huge but I'm still not getting anywher). The consensus is that making the hole yourself, with drills and nibblers, is arduous to say the least, and prone to coining new 4-letter words. However, finding the punch is complicated by the non-existence of an international standard for the cutout. (The IEC itself is an international standard, but the hole into which you mount it is not.)

In both cases the price may be beyond my budget. Those who bought these items say they are in the hundreds of dollars -- but where did they buy them? (My inquiries so far have yielded nought.)

Tnx.

73 de Martin, KB1WSY
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KB4QAA
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« Reply #44 on: July 18, 2012, 12:55:28 PM »

http://www.radiodaze.com/product/1206.aspx

Radio Daze has this set, or individual punches for $19.   I have seen no-name sets on Ebay, but didn't find one in a quick search.
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