Drilling 38 x 1.5mm 316 polished stainless tube.

Looking for some advice please.

I have to drill a number of 6 mm holes in polished 316 stainless tube which is 38mm diameter and 1.5mm wall thickness. The added complication is that it is nowhere near my workshop (and power) and will need to be carried out using a battery-powered drill (although powerful).

Would I need to use a pilot drill first? How to start without skidding all over the surface – center punch start or a clamp-on guide? What spec drill bits – I am worried that by using high cobalt drills it may be difficult to prevent them shattering using a handheld drill. Obviously need to drill at slow speed and use a cutting fluid but has anyone got any specific tips.

Thanks in advance

Steve

Take a piece of the hardest wood you can find. Bore a 1 1/2" hole through it. Bore a hole through one side of it. Split that side of it with a saw and insert clamping bolt and nut. Bore another hole through the centreline of it to suit a 6mm ID steel tube that you secure with epoxy.Good quality HSS drill will do (Dormer A002 or equivalent).

Hi Steve

A centre pop may work but I assume the holes go right right through the tube so alignment is important?

I would note a square block to git over the tune and then drill the cross hole.

Do this on a cross slide, drill and bore the hole to size then rotate the block 90 degrees and drill the cross hole.

I would make one side of the cross hole the size of the drill you want the hole to Ben.

The other hole about 3 mm larger and make a hardened bush from silver Steel.

the bush should have a simple location pin to stop the bush from toning.

Drill the first hole, remove the bush and deburr the hole so the block slides around the tube.

Put a round bar through the unbushed hole and drill the other hole through the hardened bush.

You should add a grub screw to the block to stop it moving on the tube.

Done carefully this should work.

if you have a mill, you can make the block on that.

Use a sharp drill. Stainless can work harden if the drill rubs and does not cut.

Dot punching stainless is not always a good idea and IF you use 4facet or split point drills you should not need to ! A jig would be a good idea and definitely use cutting fluid Rocol RTD - it is expensive but the spout allows for very little wasteage, you only need a drop ! Doing this by hand is not going to be easy or accurate I would consider a bench drill and generator if IN THE FIELD.

NEVER DRILL STAINLESS WITH A BLUNT DRILL, or you will need carbide to finish ! Good luck Noel.

and definitely keep the drill speed low

I'd be tempted to do a workshop trial using a 6mm centre drill to both start and complete the hole.
They work well on stainless, with a suitable lubricant, and are less likely to snatch and run up the spiral than a conventional drill geometry. (HSS, rather than carbide)

Bill

I would make a drilling jig with a 38mm hole in it, perhaps cut in half to fit on the tube with a 6mm hole in it to guide the drill. I agree about slow speed, a sharp drill bit and plenty of pressure, you don't want the bit to rub.

Sorry for the delay in getting back.

DC31K and David-Clark 1 like the idea of a wood block, I was originally thinking of 3D printing something but think that would not be robust enough.

Noel I am also thinking a centre punch may not be a good idea, as Paul points out work hardening on a minor scale may result.

Peak4 and old mart - this is what I am planning to do.

I have some hardwood blocks kicking around in the shed so will experiment with them using a sharp drill (I cant use a centre drill as it would need to be long enough to go through the wooden block) using slow speed and maybe flooding with cooling water as it will be done outside where water will not be a problem.

I will try on some scrap SS and see what happens, I cannot do the actual job until May but wanted to get ahead of any likely problems.

Many thanks

Steve

Take a dremel tool with you. If the stainless work hardens you can grind your way through and finish off with a drill as a last resort.

Hopper I had thought of that and even using a diamond tile cutter as the main cutting device but felt it would be too slow.

I would highly recommend using a decent cutting oil instead. It doesn't need much, so shouldn't make additional mess. There are many, many available, but I tend to use CT-90 as it is cheaper than most.

I would also lightly centre punch the hole location. If you're drilling polished stainless tube, the drill point will want to skate off it until it gets going which could result in the drill bit chewing away at the side of your jig.

Otherwise, as above: Decent HSS drill bit; slow speed & apply as much pressure as you need to keep it cutting - it doesn't need huge pressure, but you need enough pressure to get it cutting right from the start. Be bold and keep going! (Bear in mind that you will need to ease off the pressure as the drill breaks through). FWIW, I would go straight for 6mm.

USE A SPLIT POINT OR 4 FACET DRILL - IT SHOULD SELF CENTRE ! Noel.

Thanks everyone for your help.

I bought an off-cut length of 38mm polished stainless tube and manufactured a crude jig out of a lump of oak I had lying around.

Using a Dormer split point A108 drill in a Bosch battery drill on slow speed with a lot of pressure, along with CT-90 cutting oil I had no problem in cutting a number of 6mm holes in the tube.

So all I have to do now is to take all the kit with me and try it in situ (in about a month).

Photos as below:

Steve,

Will you have a vice or a clamp in the field to firmly your jig in position?

Ches.

Hi Ches, I only used the vice once - for the other holes I held the jig in one hand whilst holding the drill in the other so it will not be a problem having to find some way to clamp the jig.

Steve