How to put a round hole in a convex surface???

[no704]

Working on a project that involves beer. Need to make a clean 6-8 inch hole in the side of a keg to mate up to a tube that will be tig welded together. Looking for good ideas on how to cut the holes in the keg and cut the tube to fit. Have Bridgeport and 15" lathe. This one has me stumped.

Let's hear it!

 

[Vernon1969]

Do you have a plasma torch?

 

[MEngineer]

Use this web page and make adjustments to the diameter, angle of intersection and offset.

Print pattern, and tape to keg and tape other to intersecting tube, and then cut.

http://cq.cx/tubejoin.pl

 

[Ole Slewfoot]

wrap some plywood (use layers) around the keg, band it on good and tight, then run a 6-8" hole saw through the whole mess.

Edit: you have a lathe, i guess you can skip the plywood guide, and just put the hole saw in that.

 

[georgiacox]

If you use Hole Wizard to put the holes one the outer surface then they will automatically go normal to the surface, so I would go that route. Without selecting a surface, start the Hole Wizard and set up the hole settings. Then switch to the Positions tab and either click the 3D Sketch button there or in the graphics area click on the convex surface and it will start a 3D sketch. Now you can place a point on the outside surface near where the line is. Make sure the surface is highlighting when you place the point so it will make an On Surface relation.

 

[gol4]

BTW, Make sure you have drank all of the beer from the keg first before drilling the hole

Additionally, It may be a good idea to let the effects of all of that beer to wear off before operating the power tools required to make this hole.

 

[APEowner]

A hole saw will work just fine without modification or any tricks. Chuck it in a hand drill, center punch the hole location and go to town.

 

[michaelf]

If it is only a al. beer keg and going to be welded a hole saw would be the easy way, if your hole saw is to small just open the hole with a end grinder, no need to over think this.

 

[Roddyo]

Notch your pipe whatever the radis is where you want to join it to the keg. Mark around the pipe and cut inside the line. Grind to fit. We keep a set of these rings in different sizes for irrigation work.

 

[bullnerd]

Whats a 6-8 inch hole?

Is it 6" or 8"?

Between 6 and 8?

6.8?

 

[no704]

Multiple holes between 2 and 8 inches dia. Wish it was as easy as it is in cad world. Beer kegs are stainless steel. Yes I have a plasma cutter, kind of need a cleaner cut than that.

Keep the ideas coming!

 

[MBfreak]

My vote on the poster who recommended applying multiple layers of veneer.
I would build up at least 1/2" of that by gluing consecutive layers on.
After that drill with a real good holesaw, if you can find the required size.
The keg is probably rather thin and the risk of distortion if drilling directly in the metal seems a real risk.

Good luck.

Ola

 

[no704]

Agree with the vaneer plan, not real cozy with a hand held hole saw over maybe 4 inch dia.

 

[bullnerd]

8" hole saw through thin,curved stainless does not sound fun!

Can jigsaw blades handle stainless? Can you slow them down enough?

Plasma with a template to get close then grind to size to get a nice tight edge for tig.

Rotary table for your mill?

 

[no704]

Have got a roterey table, I don't think the bed will go low enough to fit the keg. Really would like to get almost a press fit and tig on the inside.

 

[Zeke]

Well, if plywood is good, a Sonotube is better if you can find one for a close fit.

 

[Gotcha640]

I was promised beer keg on a lathe action! Pics! Video! Hospital wristband pics!

I've done an 8 inch hole saw in a battery drill, surface of a keg would be easier than flat since you're cutting much less at a time. Go for it.

 

[no704]

We will see how this goes. Looking to be able to hold a 8 mba vacuum.

 

[Vernon1969]

Multiple holes between 2 and 8 inches dia. Wish it was as easy as it is in cad world. Beer kegs are stainless steel. Yes I have a plasma cutter, kind of need a cleaner cut than that.

Keep the ideas coming!

I built this handy tool for my plasma torch it would cut a hole even on a curved surface.

 

[Tucko]

What you need is called parallel line layout. It's basically a layout method for the intersection of two round pipes of any given diameter or angle. I could show you in person, but it's impossible to explain via keyboard. Lots of examples of it online...

 

[steel 35]

Is this for Yeast storage?

Plasma's leave a very hard to clean mess inside a SS tube,

I Found a Picture of a no weld seal-able plug for the top I have done a few of.

 

[bullnerd]

"don't think the bed will go low enough to fit the keg."

DOH! forgot about that.

I'd lay it out using the pipefitters templates and use my bosch jigsaw, nice and slow and accurate.

Good point about the hole saw cutting less material on a curve, but it seems like it would really grab on the last little tabs that will be holding the plug?

Grab a spare keg and hit it with the hole saw! Only one way to find out!

 

[CamKong1982]

I would be inclined to use something like a trepanning tool in the Bridgeport. You could use an adjustable circle cutter(they're basically a non-precision boring head) that will accept a 1/4" lathe bit. It's a pretty simple operation, unless I'm misunderstanding what you want to do. Oops, just saw the the above post about the keg not fitting. Can you turn the BP head horizontal and drill it that way?

 

[Marctrees]

Drill starter hole w Unibit, Handheld "jigsaw", appropriate tpi blade, safety glasses, faceshield, earplugs, and keep the other hand away from the cut. Marc

 

[Guster]

The tool depends greatly on whether the pipe joint is on center or more tangential to the circumference.

- Anything close to center on the circumference can be done with a hole-saw. Though closer to 8" pushes the limit of any good quality holesaw making and decent effective cut. Trepanning tool/flycutter might be a better option but needs rigid support and workholding. Otherwise slow, lots of pressure and cutting fluid. Any drill press or hand drill will likely run much to fast for this purpose. Especially in stainless that will want to work harden as soon as the cutter starts rubbing instead of cutting.

- Plasma is quick and effective regardless of hole layout. Can be a bit messy in stainless if not set up right. Suggest not cutting to final diameter to leave a little room for cleanup using a die-grinder or file. Make and use a template if you can.

- Jigsaw will do the job just as well, little cleanup required and will cut close to dimension.

- Small cutoff saw/zipdisk. Dremel, air-cuttoff etc. are a little harder to control but will leave a clean enough cut that may just need to be cleaned up with a file or die grinder.

If you don't have CAD skills, it is easy to make a paper template for the cut on both parts. There are some good internet tutorials on how this is done. Just Google pipe joint template.

TIG welding requires a very tidy and tight fit-up between parts. Take your time and make sure there are no large gaps before welding. Give the thin material you will definitely have to back purge to prevent 'sugaring' on the back of the weld. Also think about how the tube is supported prior to welding. May be worth matching the hole in the keg to the ID of the tube so it has something to sit on rather than falling through.

 

[no704]

Good input, do have cad skills, solid works. Thinking jigsaw is best idea yet. Might look into the big water jet down at chandler tech shop.

 

[dr_clyde]

You guys are over thinking this. I work at a brewery fab shop full time, and I have "drilled" my fair share of large holes in kegs.

On a hole that size, I would cut it undersized with the plasma cutter, and then use a mandrel grinder to manually bring the hole to size to meet my tube or ferrule. It doesn't take all that long. The downside to using a plasma torch is the large amount of **** it puts into the keg. You will have to clean it out before you weld your tube on. I would remove all pressure from the keg, and add some water so its harder for the dross to stick.

As far as layout, I grind my mating tube or ferrule to fit the surface before the hole is cut, then trace around it. If you don't want to do that, there are other ways, but you have to notch the tube anyway, so I figure that's the most efficient way to do it.

The tricky part is getting a good enough fit so the weld joint can be sanitary.


I have never tried to use a jigsaw, but I suspect that would work fine, it would just take a while and probably eat a few blades. Hole saws work ok up to about 2 inch, then they get a little unruly.

Beer kegs are stainless steel, for those not in the know.