Drilling in tubing...

[rocket01]

Apologies if this is in the wrong place but...

Does anyone know of an accurate way of drilling holes in tubing? I need to drill 24 holes around the circumference of a 75mm length of tubing. The drawing I have done shows the holes to be 30 degrees apart on two axis. They need to be accurate but my mind has completely gone blank on how to mark it out. Any help will be much appreciated!

 

[123hotchef]

u need pi

 

[Woody.v8]

u need pi

Yes and while you eat that, you will think of something

 

[WorkshopChris]

When you say accurately how accurate?
Are we talking rotary table / dividing head or would a sheet of paper marked out on the flat then wrapped around be accurate enough?
All depends on tolerance and diameter of tube in relation to hole diameters.

 

[rikrobson]

The Circumference is 75mm x pi = 75 X 3.1416 = 235.62mm

you want 24 holes so the centre of each hole is 253.62/24mm apart = 9.82mm

Mark up a piece of paper and wrap it round then centre punch the marks.

 

[Robotstar5]

The Circumference is 75mm x pi = 75 X 3.1416 = 235.62mm

you want 24 holes so the centre of each hole is 253.62/24mm apart = 9.82mm

Mark up a piece of paper and wrap it round then centre punch the marks.

and if you mark 25 holes the first should overlay the last and you know you've got it right

 

[Lemo]

75mm od? multiply that by 3.1416 which gives a circumference of 235.62. divide that by 360 which is 0.6545mm per degree. Multiply that by 30 which means your holes should be 19.63mm to the centres.

 

[Pete.]

When you say accurately how accurate?
Are we talking rotary table / dividing head or would a sheet of paper marked out on the flat then wrapped around be accurate enough?
All depends on tolerance and diameter of tube in relation to hole diameters.

This is the big question. 24 holes on a 40:1 dividing head is a piece of cake to get accurate to less than a thou, just advance 5 holes on a 3 hole plate and drill. If you're wrapping paper take the OD of the tube and remember to add 0.1mm for the paper thickness then multiply by pi or your last hole will be 0.3mm/12thou out.

 

[rikrobson]

I just re read the OP. It Doesn't say the diameter, just it's 75mm long.

24 holes are mentioned, but 30 degrees is also mentioned, which is 12 holes. So is this 2 rows of 12? If they are staggered the you'll want to mark them out as 24 to ensure they are equally spaced.

 

[graffian]

That's a job for the spin indexer. I can't afford expensive things like dividing heads;-)

It sounds like they are two sets of 12 holes and as they are not on the same axis the
spin indexer will have to be tilted.

 

[rocket01]

I didn't mention the dia because it wasn't something I considered important. I have no problem in determining the circumference of the tubing using Pi. I was more concerned with the actual method. The tubing is 75mm long and there will be 12 holes equally spaced around the tubing that (which equates to 30 degree's from an imaginary centre point on the non existent face (as it is tubing) in two rows 15mm and 45mm from the datum edge respectively. I have attached the drawing I produced for the holes. I don't particularly have access to anything overly technical, a drill press and measuring tools of course but nothing to rotate it accurately by a set amount of degree's while clamped.

 

[AndyStobbs]

Talk about drip feeding the information. Use paper, or linear distance as the guys say.

 

[skotl]

I didn't mention the dia because it wasn't something I considered important. I have no problem in determining the circumference of the tubing using Pi. I was more concerned with the actual method. The tubing is 75mm long and there will be 12 holes equally spaced around the tubing that (which equates to 30 degree's from an imaginary centre point on the non existent face (as it is tubing) in two rows 15mm and 45mm from the datum edge respectively. I have attached the drawing I produced for the holes. I don't particularly have access to anything overly technical, a drill press and measuring tools of course but nothing to rotate it accurately by a set amount of degree's while clamped.

The methods the guys mentioned above should work for you, tho, shouldn't they? Lay out two tracks of holes/marks across the length of the circumference.

 

[I'm getting on a bit]

Is this a one off ?

 

[rocket01]

Yes this is a one off

 

[WorkshopChris]

If i had to get accurate with basic kit should get close marking datum points on face then align with 30 /60 and 90 set squares. Just need to find something to use as a vee block. That gets you rotation then back to the paper for the centres.

 

[rocket01]

I have a vee block in my locker at work, I think I'm going to have to use paper and give it a go that way. I have plenty of tubing with which to get it accurate anyway. Thanks all for the replies

 

[I'm getting on a bit]

Yes this is a one off

Well the paper method using a clamped vee block on a drill press will get you to 0.5mm per hole accuracy, as others have suggested