Marking out and drilling tube ?

[Rich2502Participant @rich2502]

<p style=”text-align: left;”>I had to drill 10mm holes in 50mm steel tube to put a bar through, I used the paper wrap method of folding a crease to get the 180⁰ mark on the opposite side of the tube , is there a more accurate way to mark out the centre line of a tube ?</p>

[Alan CharlestonParticipant @alancharleston78882]

Hi,

I use the following method.

Measure the OD of the pipe accurately.

Lay the pipe on a couple of Vee blocks on a flat surface.

Measure the height of the top of the pipe using a height gauge.

Decrease the height of the scriber on the height gauge by half of the OD of the pipe.

Hold the pipe in position and scribe lines on both sides of the pipe.

The scribe lines will be diametrically opposite.

Regards,

Alan C.

[JasonBModerator @jasonb]

I would approach it differently.

Mark out the position of one hole lengthways, set up and locate the middle of the tube either with edge finder or rule trapped under a point and then spot drill followed by drilling right through so opposite side does not need marking out.

Depending what you have available I would actually not even mark out the first hole but edge find the end and then move to where I want the hole.

[Brian WoodParticipant @brianwood45127]

I have marked the centreline of tubes in a rather different way.

Grip the tube in a known to be good 3 jaw chuck on the lathe and scribe down one side of the tube with a tool you know to be on centre.

Without moving the tube in any way, move the tool across to the rear of the tube, angled appropriately on the compound swivel, and mark the tube again.

These two marks will be diametrically opposite each other

Regards   Brian

[Nigel Graham 2Participant @nigelgraham2]

The Vee-block method is even more secure if you can clamp the tube to the block (not all Vee-blocks have this facility).

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