making a 5" hole in a non-removable aluminum panel (question)

[Opcom]

I'm about ready to add a modulation scope to the Tucker transmitter. Its a BC-sized rig and I can not easily remove the front panel from the unit. By that I mean there are some 100+ screws that have not been out on 56 years. The screws are some special countersink type, I don't think the OM intended for this to ever be taken apart.

The panel is about 33" x 28" x1/8 or so thick. Its too big to clamp to a drill press because it will flex and that will foul up the fly cutter, been there and done that.

The 5" Tektronix CRT wants to go where the center chart is, in the bottom section of the RF deck under the tube socket - above the panel with the row of meters.

The hardest part for me is always the panels. I only have one chance to do this right.

One friend suggested I could draw a circle and then center-punch and drill a bunch of 1/8" holes, then use some large old dikes to clip out the thin webs between the holes, then file it. I could do that in place..
Does anyone know an easier and more precise way to do this without removing the panel?

Is there any kind of punch that size, like a giant chassis punch I'd turn with a wrench?

[ke7trp]

I am thinking that you can Drill a pilot hole, Then use a caliper to run the hole out.  Then use a Dremel to cut out the hole.  Tape off the panel of course.  An hour or so, you should have the hole. Its slow going but will work. 

[KB5MD]

Do you know anyone in the electrical contracting business?  They sometimes use large hydraulic
punches to cut holes such as what you need.

[KE6DF]

Greenlee makes punches up to 6".

As I mentioned in the other thread, the largest I have is a 4" with a ball bearing draw stud.

The draw stud takes a 2" wrench to turn. I have an 18" Crescent wrench for that purpose.

When you look up the price of a 5" punch, be sure you are sitting down.

[w3jn]

+1 on the hydraulic knockout solution, if you can beg/borrow/rent a hydraulic Greenlee set.   It's a 5 minute job with one of those, including drilling the pilot hole.  5" punches aren't easy to come by, however.  I wouldn't try this with a wrench-turned punch because with all the torque you run the risk of bending the hell out of the front panel.  A hydraulic punch puts no lateral torque on the work.

Clark's idea is a really good one too, but if you don't have an escutcheon or bezel to put over it the hole will be a bit ragged, because the Dremel cutoff wheels obviously only cut in straight lines.  I've done this exact thing in chassis where I've needed an odd-sized or square hole.  With a 5" diameter hole you should be able to get it looking pretty good.

Be careful though, the disks have a habit of catching in the work and shattering.  Get the fiberglas reinforced cutoff disks, they're by far the best for this sort of thing.

[KA2DZT]

I would do it with the circle of holes.  Cut the sections between holes (aluminum) with big dikes.  Then file the hole out to the correct diameter.  You need to put drop paper (taped in place) in the rig and on the front panel to keep chips and filings from getting into the works.  The holes are drilled just inside the diameter needed.  For 5" diameter you could drill 1/4" holes, 1/8" holes would take forever.  Cover the hole area with masking tape and draw the circle on the tape.

With a steel panel, the 1/4" holes are better.  You can use a thin triangle file to cut through the spaces between holes.

You need good files and the right ones to get the job done, but it does take a little time to do it right.

If the panel is aluminum this process is easy.  If the panel is steel, then it will be somewhat harder to do.  Be glad you only need one hole.

Greenlee punches for 5" holes are very expensive, then they will be conduit punches that are not standard diameters.  Maybe a 4" conduit punch may come close to 5".  I'll check my Greenlee catalog for exact dimensions of the punches.

Another thing to consider is the shock to the nearby components doing all this drilling and blasting

Fred

[Dave K6XYZ]

I'm about ready to add a modulation scope to the Tucker transmitter. Its a BC-sized rig and I can not easily remove the front panel from the unit. By that I mean there are some 100+ screws that have not been out on 56 years. The screws are some special countersink type, I don't think the OM intended for this to ever be taken apart.

The panel is about 33" x 28" x1/8 or so thick. Its too big to clamp to a drill press because it will flex and that will foul up the fly cutter, been there and done that.

The 5" Tektronix CRT wants to go where the center chart is, in the bottom section of the RF deck under the tube socket - above the panel with the row of meters.

The hardest part for me is always the panels. I only have one chance to do this right.

One friend suggested I could draw a circle and then center-punch and drill a bunch of 1/8" holes, then use some large old dikes to clip out the thin webs between the holes, then file it. I could do that in place..
Does anyone know an easier and more precise way to do this without removing the panel?

Is there any kind of punch that size, like a giant chassis punch I'd turn with a wrench?

As others have said....I would drill a series of holes in a circle, cut out the center, then using a drill motor, get a large drum sander with mandrel from Lowes and clean it up. I've used the large Greenlee hydraulic punches and they work well on smaller holes but they leave a deformation around the circumference of the hole....it sort of looks like a bullet going through metal, the edges of the hole are bent towards the direction that the piston moves.....and the hydraulic oil always leaks and make a real mess.

[WBear2GCR]

Bah.

They sell hole saws in 5" size.... you want a very heavy industrial hand held drill, the type with the handle coming off the side, one that runs SLOW and has high torque.  Needs to have a big Jacobs chuck. You want the arbor with the HEX end in ~3/8" size. Add lube, cut slow. About 5 min later you will have a clean 5" hole.

Of course if you add a bezel you can cut it with anything...

                   _-_-bear

[M1ECY]

I would go with Bear!

Just change the pilot drill from the hole saw to a bit of silver steel the same diameter as the drill - this will stop the pilot from chewing the hole larger, and allowing the holesaw to wander.

A suitably place vacuum cleaner hose behind the panel should help catch the worst of the swarf.

I think if it were me, I would remove the panel - a 5" hole saw in a big drill is going to vibrate like mad - they arent exactly a precision tool.....

Good Luck though, a nice addition to the rig, and a nice turned aluminium bezel would finish the job a treat.

Sean

[w3jn]

I've used the large Greenlee hydraulic punches and they work well on smaller holes but they leave a deformation around the circumference of the hole....it sort of looks like a bullet going through metal, the edges of the hole are bent towards the direction that the piston moves.....and the hydraulic oil always leaks and make a real mess.

That's a good point on the deformation, Dave.  Hopefully 1/8" aluminum won't deform too much - but there IS a hell of a lot of force acting on that punch.  In any event this isn't really a viable alternative unless he can borrow or rent one - the punch and hydraulic actuator would probably run north of $500 together.

The worry that I'd have with the hole saw or circle of holes methods would be the same - deforming the panel - especially using dikes to cut 1/8" aluminum.  With a 5" hole and a hole saw on 1/8" aluminum you'll have to put a fair amount of force on it to get it to bite.  And a whole mess of holes would just beg for one to walk off and skitter across the panel... I *know* that would happen to me if I did it 

You could do a combination of Clark's idea with the Dremel, and the circle of holes method - instead of using dikes to cut the webs between the holes, use the Dremel.

[WQ9E]

I wouldn't do work like this with the panel on because any method is going to create some conductive debris that is going to go where you don't want it.  Even the hydraulic punch method is going to require drilling a center hole and the other methods are going to create a large amount of bits of conductive aluminum all going where you don't want them.  Just think of what ends up on your shop floor in a typical drilling operation and visualize that all going into your transmitter.

No matter what method you choose I would remove the panel. I have a 34" radial drill press in my wood work shop that will drill to the center of a 34" work piece.  Any chance you have a friend with one?  This would allow either a fly cutter or hole saw to do the job with the panel properly clamped with a sacrificial wood back piece providing support to prevent deformation.

If you do plan to work with the panel in place and you can't come up with a punch then I would use a good quality hole saw and a Milwaukee Hole Hawg (or similar quality equivalent).  The Hole Hawg is a heavy duty drill commonly used by electricians and plumbers for getting between studs where large holes are needed.  It uses a heavy duty single speed motor with a 2 speed transmission providing a lot of torque at its low 300 RPM speed.  The handles can be set up in multiple ways to provide good leverage.  You will find many uses for this <$300 tool around your home.  I recently used mine with a paddle for mixing grout.

Check that both the drill and hole saw have minimal runout before use because significant runout will result in a larger than stated hole diameter.  A quick test in a sacrificial panel (could be plywood) will tell the tale.  Do not apply excessive pressure while cutting or deformation and hole size increase will occur.  Kerosene is one of the old standby drilling lubricants for aluminum and I guess WD-40 would do since it is mostly kerosene. 

If you do have to work this in place consider attaching something behind the panel to catch the debris.  I would want something sticky (mouse catch pad?) that will capture all the debris.

[WBear2GCR]

I think no matter what you do some tests on scrap before attacking the real panel.

I see the screws.  Whew.
Spray 'em all before attempting removal!

If you try the hole saw, I like the drill the pilot hole, then put in 1/4" rod to replace the pilot bit. That and the 300 rpm or SLOWER drill (Hole Hawg), the
FPM rate on the outside of the 5" dia saw will be faster than you might think.

No matter what I think you are going to want a BEZEL when done.

You could make one pretty easy, or get a sacrificial one off an old scope, like a hamfest beater Heathkit, etc...

I think that unless you like the patina of that old paint, IF you pull the panel, maybe a repaint is in order? Fresh screws in black oxide? Dunno.

What's the toobe line up?

                                  _-_-bear

PS. think OUTSIDE the box - put a solid  "shaft bearing" into the center point where the pilot hole will go on the panel! You can make one by just carefully drilling
some steel of say 3/8" or 1/2" thickness (maybe thicker!) for a very close, tight fit to the 1/4" rod that replaces the pilot drill - now you have a solid center. Of course you have to make say 2- 3 holes to mount this affair, but it can just be a rectangular block (for example) of steel and put the screws out a way and in a spot where you can get to the back side for nuts (use lockwashers!!!) This will help get a very clean hole.

Think 1/4-20 tightened HARD.
When cut through the whole thing comes out together.
The whole saw has about a 1" or better cutting depth, so you can make the "bearing" as thick as you can to that depth minus the cut depth - that will make a really stable setup, I think.

[KA2DZT]

With all the comments,  if that panel is 1/8 aluminum I could have made the hole in probably an hour.  I've made meter holes many times using the circle-of-holes method and I have a complete machine shop but still do them the old fashion way.  I also have many Greenlee punches but they can distort the panel.

Drilling the holes does make a lot of chips, you have to mask off the area to catch the stuff.  Also put some masking tape with the sticky side out around the hole (like a cup).  That will catch most of the chips.

Use two drills, one with a small drill to start the holes, then another with 1/4" drill.  Heavy sharp dikes will cut the remaining sections out.  Then you must use a half round files to bring the hole out to the correct diameter.  If you don't have files, it will cheaper to buy them rather than the Greenlee punch.  They make files with rasp like teeth (like ones used for wood) that will file the hole easily. Remember, you can never have too many files.

I have a box full of scope bezels if you need one, they're either HPs or Tectronics or both.

Fred

[N6YW]

Let me offer these ideas.
The circle of holes method is a hobbyist approach and looks like it unless done with absolute care.
The amount of handwork is laborious.
Does the Tektronix scope have a finished bezel? Why not use that same finished look by either incorporating the bezel already manufactured for the scope, or make your own. This would not only make it an attractive professional looking installation, but would mask any imperfections made by boring the hole.
A 5" hole saw using a small amount of cutting agent and a slow speed drill would be far more effective than the circle of holes method. You would have to set up a means to insure the drill is evenly applied parallel to the cutting surface so it wouldn't dance. Once the circle is started and the cutter is digging in properly you would be able to keep and maintain the feel of the cutting. I would make a blot using an old thirsty cotton towel to absorb the cutting agent (marvel mystery oil) and keep things tidy.
Once the hole is cut, you can use de-burring tool to chamfer the edge of the cut on both sides of the panel.
Make a bezel plate from the same type of 1/8 panel stock or sheet metal. You could even fashion a hood from another scope. Better yet, if you plan on using a Bezel, you wouldn't necessarily have to cut a round hole, it could be square. The Bezel would make the hole appear round cosmetically. It could also be made of plastic or Lexan, which could be painted to taste.
Just another perspective.
Good luck.

[Opcom]

I can remove the heavy RF deck so it will be easier to clean out of metal chips no matter what I do. Its easy to work on from the underside.

I already have a few bezels from deceased scopes as well as mounting hardware for the CRT and shield. The bezels have a slightly smaller opening that the CRT size. If the hole can be sized so its edges don't show, it won't matter if they are not 100% perfect.

The CRT is a NOS one for a 545A. I chose it for the brightness. It has a 10KV Ultor as opposed to most modulation scope CRTs using 1000-3000V.-The thing takes a few extra voltages but the manual seems helpful. It should be easy as CRT power is very low current and a tapped bleeder with pots on it is the basic way. It has a 6.3V heater.

The real challenge is the hole, lots of good advice here on that. I need to measure the CRT outer diameter precisely, sure it is not exactly 5". Ideally the CRT should just fit through the hole so its face can be against a graticule. If not, then the graticule must be put behind the panel with the CRT and the bezel out front as usual. At this point there is no decision on whether to illuminate a graticule or even use one. That's not as important as getting the hole done.

[MikeKE0ZUinkcmo]

Perhaps an unorthodox method, but since you're going to have chips where you don't want them anyway, I'd use a Trim Router with a spiral up cut, flush trimming bit, and a template.  This method will give you a nice edge, and most all the effort will be in making the template, which is expendable if you screw it up.  Make the template as large as practicable, then attach the template with double side tape.  Make sure the panel is clean when you mount the template so you have maximum adhesion of the tape. 

This is exactly what I did on this GR attneuator, and this is the trimmed raw edge as the router left it.   I bought The attenuator as a rack mount version and used the faceplate of my other one, as the template.



I'd advise having a drop cloth or old sheet on the floor in front of the cabinet.

[N6YW]

I can remove the heavy RF deck so it will be easier to clean out of metal chips no matter what I do. Its easy to work on from the underside.

I already have a few bezels from deceased scopes as well as mounting hardware for the CRT and shield. The bezels have a slightly smaller opening that the CRT size. If the hole can be sized so its edges don't show, it won't matter if they are not 100% perfect.

The CRT is a NOS one for a 545A. I chose it for the brightness. It has a 10KV Ultor as opposed to most modulation scope CRTs using 1000-3000V.-The thing takes a few extra voltages but the manual seems helpful. It should be easy as CRT power is very low current and a tapped bleeder with pots on it is the basic way. It has a 6.3V heater.

The real challenge is the hole, lots of good advice here on that. I need to measure the CRT outer diameter precisely, sure it is not exactly 5". Ideally the CRT should just fit through the hole so its face can be against a graticule. If not, then the graticule must be put behind the panel with the CRT and the bezel out front as usual. At this point there is no decision on whether to illuminate a graticule or even use one. That's not as important as getting the hole done.

That's why I suggested using the hole saw. 99% of the wasted material would be on the outside of the panel, therefore not making it such a hazard on the inside.
If you cut a square hole, all you would have to do is bore a pilot hole in each corner, and use a Sawzall with a narrow bi-metal blade. I have done this with excellent results but you absolutely have to plan ahead and figure a way to capture the cuttings on the inside.
The hole saw approach has the advantage of not making such a mess on the inside of the cabinet. If you plan on using a Bezel, then consider using one that would allow you to move the CRT closer the the front edge allowing better visibility of the graticule. A 5" inch hole saw may have a slightly larger outside diameter than the OD of the CRT.

[N4LTA]

Get a good Bi-Metal hole saw and 1/2"arbor. It will cost about $35 at the most. Use a variable speed 1/2" drill minimum. Use masking tap and cover the cutout area. Go SLOW and don't let the pilot hole "wallow out'. If this happens it will cause problems - GO SLOW! Make sure the panel is secure.

It won't take that long and won't be near as bad as you think - I  "thought out" ( read dreaded) cutting a 4 1/2" hole for 2 weeks and was amazed at how easy it turned out and how quickly it was done.

[WBear2GCR]

A router will definitely work. but it needs a very solid center hold down if you use the circle cutter approach. Use the smallest carbide bit you can use for the job. It will make copious sliver type chips... Using the router with a follower bit is a good option, make multiple low depth cuts with either approach.

Think I have tried all the known methods.

The best method I know of is to let someone else do it! :p

                   _-_-bear

[KA2QFX]

I would use a hole saw given that you can't remove the panel.  However, I would make a hardwood guide first. Use some oil and turn SLOW!

The hardwood* guide is simply a board through which you've already sawed the desired hole.  Clamp this board firmly on (across) the panel to guide the hole saw through the metal panel. This eliminates the wander that a large hole saw will exhibit. The 1/4" pilot hole will end up 3/8"+ before you're done otherwise, with the accompanying ragged hole.

*Soft pine is usable if you must but if you're clamping across a 19" panel I wouldn't use less than a 1"x 10" plank. Plywood will work as well.   

[N6YW]

I would use a hole saw given that you can't remove the panel.  However, I would make a hardwood guide first. Use some oil and turn SLOW!

The hardwood* guide is simply a board through which you've already sawed the desired hole.  Clamp this board firmly on (across) the panel to guide the hole saw through the metal panel. This eliminates the wander that a large hole saw will exhibit. The 1/4" pilot hole will end up 3/8"+ before you're done otherwise, with the accompanying ragged hole.

*Soft pine is usable if you must but if you're clamping across a 19" panel I wouldn't use less than a 1"x 10" plank. Plywood will work as well.   

Ditto!
Hard Maple would be a good choice for hole guide. Less likely to have hole "run out" from the bit.
By the way, a good quality arbor/hole saw combo will greatly contribute to the outcome of the operation.
The arbor's that I have use a short shank drill for the pilot. This means the actual twist cut of the drill is shallow and is designed so that during the drilling event, unnecessary material removal doesn't occur after the initial hole is established. This helps to minimize making the hole more oval while cutting the 5" area.
A slow and deliberate cutting action will produce the best result, given a steady grip.
Remember this, if you use a hole saw, you HAVE TO use a cutting agent! Not only does this aid in helping the saw cut a smoother hole, but helps to keep the temperature down. Maintaining these requirements gives the best results.

[The Slab Bacon]

We have used routers with carbide cutters here at work for years to do architectural anodized alminum. It works OK, but..........

You got to have a steady hand and a strong grip to hang on to it. It wants to jump all over the place if you don't hang on tight. A milling machine would be a much better choice.

You MUST use a cutting agent. We have used this stinky-assed stuff called "Alumicut" for many years. It smells nasty, but sez it's "non toxic" all over the label. It is fantastic stuff. It works by preventing the cutter from loading up with aluminum. It even makes filing it a joy 'cause the file doesn't load up with shavings. Also works fantastic on a simple old hacksaw. It also makes a hell of a difference tapping aluminum 'cause the tap doesn't load up. "Tap Magic" for aluminum also works pretty well, But I prefer Alumicut.

For drilling and cutting stainless steel we used to use a mixture of denatured alcohol and mothballs. It's purpose was to keep the tool from heating up.

[WA1GFZ]

after you drill the pilot hole put steel rod in place of the pilot drill in the hole saw so it won't deform the hole. Go slow

[KA2QFX]

Also, I forgot to mention, using the external wood guide permits re-cutting an existing opening where no material for the pilot exists. It's great for putting new locks in old doors.

[KL7OF]

Cut a square hole in the panel...larger than the scope. Easy ....use a saw.  Then make a square pc that has a round hole that fits your scope to fit over and trim out the square hole that you cut with the saw....all the work of making the round hole (however you decide to make it) can be done on the bench or the table of the drill press