lathe boring advice wanted

[julianthegypsy]

I wonder if anyone can help? I'm trying to set up a small capstan lathe, and one of the operations I want to do is to bore a hole 7.5mm in a piece of 15mm stainless. Normally that would be three operations. Centre drill, pilot and final, but that would take three of my six capstan stations, which is a nuisance. Is there a short cut that I'm missing?
Many thanks,
Julian

 

[Pete.]

Centre drill, finished size. 7.5mm will go in no problem, sharp drill, slow speed and loadsa pressure. If you really need a pilot grind a counterbore in a 7.5mm drill.

 

[madkayaker]

Centre drill then 7.5mm drill bit?


Or am I missing something

 

[julianthegypsy]

Thanks, I assumed I'd need a pilot. What about split point drills, does anyone use them at all? It occurred to me that a split point drill is supposed to centre itself but I don't know how good they are.

 

[Pete.]

The centre drill will centre it, though a stub drill is the right tool. Buy a good quality one and drill it in one hit if it's only 15mm depth.

 

[julianthegypsy]

The centre drill will centre it, though a stub drill is the right tool. Buy a good quality one and drill it in one hit if it's only 15mm depth.

Sorry, my bad, the bar is 15mm round, the hole is 20mm deep. Would a split point drill do the job of centering, or do I need to use the centre drill then the 7.5 final cut? It still saves me one tool station, but I'm just getting to grips with this thing and realising how precious tool stations are!

 

[brightspark]

Sorry, my bad, the bar is 15mm round, the hole is 20mm deep. Would a split point drill do the job of centering, or do I need to use the centre drill then the 7.5 final cut? It still saves me one tool station, but I'm just getting to grips with this thing and realising how precious tool stations are!

a center drill will still be needed split point would be 2 long and thin and run off

 

[julianthegypsy]

Thanks everyone, it looks like I have my answer, I will crack on as soon as I'm allowed back in my workshop, boxing day? Or should I be civilized and wait till the day after?

 

[Robotstar5]

Thanks everyone, it looks like I have my answer, I will crack on as soon as I'm allowed back in my workshop, boxing day? Or should I be civilized and wait till the day after?

Well, no point in going to the sales, they've started already!

 

[CRB]

Picky but boring is not drilling.

As said previously, centre drill and 7.5mm stub, if that is sufficient. It does all depend on how accurate you need the hole to be. A 7mm drill and a reamer would be the next step.

?What else is the capstan being used for, or is it just to lower the operation count?

Happy Christmas and I hope it turns out nice, whatever it/they is/are.

 

[julianthegypsy]

Well, no point in going to the sales, they've started already!

Ooh, don't tell everyone, if they think the sales are on I could still get to the workshop!

 

[julianthegypsy]

Picky but boring is not drilling.

As said previously, centre drill and 7.5mm stub, if that is sufficient. It does all depend on how accurate you need the hole to be. A 7mm drill and a reamer would be the next step.

?What else is the capstan being used for, or is it just to lower the operation count?

Happy Christmas and I hope it turns out nice, whatever it/they is/are.

Thanks, the other part is to turn down a piece of the same bar a bit smaller than the hole to fit inside it. Chamfer and part can be done on the other end, where I have two tool posts on a lever. Doesn't need to be too accurate but would be nice to get both parts done on one set up rather than setting up and doing one part then changing tools around for the other, so yes, its all about the tool count!

 

[ronan]

Don't forget plenty of coolant and a sharp drill , stainless is a git for work hardening. What grade is it ?

 

[graffian]

carbide drill, no need to centre.

 

[julianthegypsy]

Don't forget plenty of coolant and a sharp drill , stainless is a git for work hardening. What grade is it ?

304 or 316, I seem to remember someone telling me cobalt was best for stainless, or is carbide better? I'm happy to pay the premium for really good drills for this job, it'll repay itself rapidly.

 

[hareng]

Is the 15 dia faced off first?

If so i reckon subject to the drill you will get away with going straight in, all depends on tolerance required and how oversize the drill would drill. Maybe a 7.3 or 7.4mm but may leave a slight taper, i would try this first with coolant?
I do this all the time and rarely use centre drills unless below 5mm.

 

[julianthegypsy]

Is the 15 dia faced off first?

If so i reckon subject to the drill you will get away with going straight in, all depends on tolerance required and how oversize the drill would drill. Maybe a 7.3 or 7.4mm but may leave a slight taper, i would try this first with coolant?
I do this all the time and rarely use centre drills unless below 5mm.

It will be faced off with a carbide parting tool, and I expect to spend a lot of time fiddling with it to get it set just right. I have semi synthetic cooling suds which I hope should be what I need. If I was turning the bar down, I'd put a drill on the turning tool but it comes in already to size!
It doesn't matter if it goes slightly oversized as long as its a constant oversize, I can always compensate by making the other part slightly bigger.

 

[Pete.]

304 or 316, I seem to remember someone telling me cobalt was best for stainless, or is carbide better? I'm happy to pay the premium for really good drills for this job, it'll repay itself rapidly.

Is the grade of stainless specified? If not, go for 303 coz it machines and drills luuuuuuuverrrrly.

 

[julianthegypsy]

Is the grade of stainless specified? If not, go for 303 coz it machines and drills luuuuuuuverrrrly.

As far as I know its not specified, but its for canal boats and will need welding to mild steel afterwards. Must be stainless so it doesn't rust solid after being left in the rain for months on end.

 

[Shox Dr]

303 is the one to use. Can't see it been a problem if it's been welded to mild steel