Making a round hole

[Jorg 50]

I want to make a 80 millimeter hole on a 3 millimeter thick metal. This can be acomplished with a plasma machine but there isn´t one, so my taugh was to make small holes around the diameter then cot them. The quetion is how many holes there is in a diameter of 80 millimeter if you want to drill with a 4 millimeter bit or 6 milllimeter??
Is there a better way to do this????
Thanks in advance!

[tigmusky]

OK I'm a little lost. If you don't have a plasma or flame. How about a jig saw . hole saw I don't know how big 80 kilomilesmutimeters is.

Daye

[ccawgc]

Get a circle cutter or a hole saw. Or rent a plasma with a circle cutter guide.

[tanglediver]

80 mm = 3.14960 " = 3 & 5/32 "
2 mm = 0.078740 " = 5/64 "
3 mm = 0.118110 " = 1/8 "
4 mm = 0.157480 " = 5/32 "
6 mm = 0.236220 " = 15/64 "

I would get a hole saw, and put the piece in a drillpress. Use lots of oil and cut slowly, and steadily.

[Donald Branscom]

Thanks TANGLEDIVER for a little (a lot) of clarification.

Lets talk inches or thousandths of an inch when possible.

1/8 inch plate, and with a 3 inch hole saw and a little wobble and kerf of the teeth you will be right at 3.14

100-200 rpm max.

But if you cannot do that, get a machine shop to mill the hole for you ,then it will be perfect.

[zipzit]

I want to make a 80 millimeter hole on a 3 millimeter thick metal. This can be acomplished with a plasma machine but there isn´t one, so my taugh was to make small holes around the diameter then cot them. The quetion is how many holes there is in a diameter of 80 millimeter if you want to drill with a 4 millimeter bit or 6 milllimeter??
Is there a better way to do this????
Thanks in advance!

You want to chain drill the hole. That makes perfect sense, very economical. What tools do you have available? Grinder? Drill press? hand electric drill? Do you have a CAD system available? Do you have cold chisels and a hammer available?

I would create a CAD template, full size. Draw an 80mm diameter hole first. Lets assume you are going to use the six mm drill bit. Draw another circle at 74mm diameter. Hopefully you have a CAD program. Take that smaller circle and divide it up say into 35equal slices of pie. Why 35? Thats the diameter of the small circle (times) PI divided by 6.5... 6.5mm would give you approx 1mm web between holes. You don't want to overlap the holes, too easy for the drill bits to get stuck and hang up that way.

Cut out the pattern full size from CAD, contact cement it to the workpiece. Center punch the intersection of the pie section line and the inner ~74mm circle. Drill out 35 holes. Remember when I asked if you had access to a grinder? 35 holes in 3mm steel is probably going to wear your drill bits. Thats cool. Remember how good you got sharpening your tungsten electrodes cause you dipped it in the puddle? Now you get to practice freehand sharpening drill bits. (love it?)

After drilling out the 35 holes, use the cold chisel and hammer to break the web between holes. knock the center plate out. Use large half round file to clean up the edge, result = one 80mm hole, lots of practice with CAD system, lots of chances to hand sharpen drill bits so they cut thru steel like butter, and a chance to work in hand filing skills. Yowza.

If you want to do less filing, instead of using the 6mm drill bit, create the CAD file for the 4mm drill bit instead. You will have to sharpen the bit more often, and drill more holes, but you will have lots less filing to do when you are finished.

Here is a CAD sketch. In ACAD the command to divide up a line is Draw --> Point --> Divide. Change the point call outs so they are easily visible. I think its PDMode or something like that.

and yes, it would be easier to use a plasma torch, or even a 80mm hole saw. But that wouldn't be as much fun, now would it?

Good luck. --zip.

[Donald Branscom]

You want to chain drill the hole. That makes perfect sense, very economical. What tools do you have available? Grinder? Drill press? hand electric drill? Do you have a CAD system available? Do you have cold chisels and a hammer available?

I would create a CAD template, full size. Draw an 80mm diameter hole first. Lets assume you are going to use the six mm drill bit. Draw another circle at 74mm diameter. Hopefully you have a CAD program. Take that smaller circle and divide it up say into 35equal slices of pie. Why 35? Thats the diameter of the small circle (times) PI divided by 6.5... 6.5mm would give you approx 1mm web between holes. You don't want to overlap the holes, too easy for the drill bits to get stuck and hang up that way.

Cut out the pattern full size from CAD, contact cement it to the workpiece. Center punch the intersection of the pie section line and the inner ~74mm circle. Drill out 35 holes. Remember when I asked if you had access to a grinder? 35 holes in 3mm steel is probably going to wear your drill bits. Thats cool. Remember how good you got sharpening your tungsten electrodes cause you dipped it in the puddle? Now you get to practice freehand sharpening drill bits. (love it?)

After drilling out the 35 holes, use the cold chisel and hammer to break the web between holes. knock the center plate out. Use large half round file to clean up the edge, result = one 80mm hole, lots of practice with CAD system, lots of chances to hand sharpen drill bits so they cut thru steel like butter, and a chance to work in hand filing skills. Yowza.

If you want to do less filing, instead of using the 6mm drill bit, create the CAD file for the 4mm drill bit instead. You will have to sharpen the bit more often, and drill more holes, but you will have lots less filing to do when you are finished.

Here is a CAD sketch. In ACAD the command to divide up a line is Draw --> Point --> Divide. Change the point call outs so they are easily visible. I think its PDMode or something like that.

and yes, it would be easier to use a plasma torch, or even a 80mm hole saw. But that wouldn't be as much fun, now would it?

Good luck. --zip.

Don't forget that even though you can use all the math you want but you still will have tolerance stack up issues unless you use a milling machine with indexing wheel.

[SEAR]

80 mm = 3.14960 " = 3 & 5/32 "
2 mm = 0.078740 " = 5/64 "
3 mm = 0.118110 " = 1/8 "
4 mm = 0.157480 " = 5/32 "
6 mm = 0.236220 " = 15/64 "

I would get a hole saw, and put the piece in a drillpress. Use lots of oil and cut slowly, and steadily.

gotta say, MM is a much cleaner system

15/64's ? :eek:

[Jorg 50]

Sorry, zip for my delay in answering. Thank you for help, you got my idea. I do have the CAD program but do not use it much. There ia a formula if have the number of holes that you want in a circuference how they are going to be spaced out. Shoudn´t the small circle diameter be 77 millimeters?? the 6 millimeters holes are going to be divided in half below and above the 77 millimeter circunference and this way tere is going to be am 80 mm hole. If the circuference is 74 mm the hole is foing to be 77 mm. I am missing something??? You are right with a plasma would be much faster and with a hole saw it would be faster, but how many holes I am going to open wit that size??? Thanks agin for your HELP.

[Jorg 50]

SEAR, the metric system is better. I was was born with it then when I studied in the United States had to learn the imperial system ( what a confusion) dealing with fractions and in the physics classes got more confusing. In Europe the only thing that is in inches are the rims of the cars. I don´t know why. I can see that you have your metric system well sorted out. no ofense for the ones that still like the imperial system.

[brucer]

I want to make a 80 millimeter hole on a 3 millimeter thick metal. This can be acomplished with a plasma machine but there isn´t one, so my taugh was to make small holes around the diameter then cot them. The quetion is how many holes there is in a diameter of 80 millimeter if you want to drill with a 4 millimeter bit or 6 milllimeter??
Is there a better way to do this????
Thanks in advance!


hell of an excuse to go buy a plasma cutter :)

[zipzit]

Sorry, zip for my delay in answering. Thank you for help, you got my idea. I do have the CAD program but do not use it much. There ia a formula if have the number of holes that you want in a circuference how they are going to be spaced out. Shoudn´t the small circle diameter be 77 millimeters?? the 6 millimeters holes are going to be divided in half below and above the 77 millimeter circunference and this way tere is going to be am 80 mm hole. If the circuference is 74 mm the hole is foing to be 77 mm. I am missing something??? You are right with a plasma would be much faster and with a hole saw it would be faster, but how many holes I am going to open wit that size??? Thanks agin for your HELP.

Jorg,
Relax, have some fun with this. Sorry I'm not into formulas much... beyond just the basics.

Key pieces of info:

The diameter of a circle is two times the radius of a circle.
The circumference of a circle is (PI x Diameter) or (PI x 2 x Radius). PI is a constant = 3.14159 (Thats the extent of the formulas you need to remember..)
When chain drilling you don't want to overlap the holes. That messes up the drill bits terribly.

Now look at your question, and look closely at my CAD sketch. Can you see what I did, and how I came up with 80mm - 3mm (drill radius @ left side of sketch) - 3mm (drill radius @ right side of sketch) = 74mm ?? (oops.. I will say, the first time I sketched this I used 77 mm too, and I realized the error of my ways...)

74mm diameter circle... find the circumference, then divide it by (drill bit diameter + desired web gap between drilled holes)... --> # of holes to drill

Is this making more sense? --zip