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Another newbie question!

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Mark Gould 119/02/2019 09:27:23
82 forum posts
47 photos

Gents,

What is the best way to centre drill a rod that doesn't pass through the head stock? Our S7 (not a big bore S7) can't pass a 1 inch bar and we have to centre drill it for support. Should I be breaking out the fixed steady and doing it that way or are there simpler (read: faster) methods of doing this?

And secondly, is 640 rpm a good speed for centre drilling or should that be bumped up a notch? The reason i ask is that we struggled to centre drill at this speed and I was concerned that perhaps the drill itself wasn't any good.

Apologies for the simple questions and thanks,

Mark

John Haine19/02/2019 09:42:30
2461 forum posts
132 photos

I don't see why you need to support it, assuming you have a (ideally) a reasonable 4-jaw chuck. Just centre the bar as close as possible in the chuck, it'll stick out a lot, try to make sure it's parallel to the lathe axis, and centre drill from the tailstock. (I assume since you mentioned using a fixed steady that the bar isn't too long for the lathe.) Drilling only exerts axial loads so steady shouldn't be needed.

What size centre are you trying to make? I'd have thought 640 rpm should be plenty fast enough, maybe your CD is blunt.

vintage engineer19/02/2019 09:46:22
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116 forum posts

You could use the steady to support the end of the bar.

old Al19/02/2019 09:47:39
137 forum posts

ctr drill should be run as fast as possible. Sometimes your set up dictates you have to slow down a bit and take it more carefully.

Brian Wood19/02/2019 09:56:37
1884 forum posts
36 photos

Hello Mark,

A lot depends on how long your bar is. I got over that problem with bars of 750 mm in length with the tailstock off the bed and the steady fitted at that end, the other end of the bar was supported in a small vice carried on the vertical slide, centred up on the lathe axis. The bar was 'cradled' in the vice jaws.

Held like that you can readily centre and drill the end of the bar from the headstock, using the carriage movement to feed the work onto the tooling. The speed you mention of 640 rpm should be adequate.

Regards

Brian

Mark Gould 119/02/2019 10:41:00
82 forum posts
47 photos

Thanks for the replies. The stock was 300mm, so sticking out a fair bit from the 100mm 3 jaw chuck. I will use a DTI to ensure the stock is as centered as I can get it and go from there. An increase in speed is a good idea Al, I will try that too.

Thanks again,

Mark

David George 119/02/2019 10:48:43
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756 forum posts
261 photos

Lubricate with cutting oil or coolant etc, I use tapping oil RTD.

David

XD 35119/02/2019 12:43:47
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1228 forum posts
83 photos

If your stock is 300 long x 25mm dia and you have it in a 4 “ chuck there would be around 200 - 250 mm stick out which would be ok for a centre drill . The difficulty with centre drilling could be a dodgy drill or the the piece you are trying to drill - what material is it ? Some types of steel can be problematic or the pice could be hardened so you need to check that as well . Running a drill too slow never hurt anything , it will just take longer to get there !

P.S Make sure you have the lathe running in the right direction also ! You won’t be the first or last person to have it running in reverse !

Edited By XD 351 on 19/02/2019 12:45:30

Peter G. Shaw19/02/2019 18:57:26
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953 forum posts
39 photos

Well, I'd be absolutely scared stiff of trying to centre drill a 1 inch bar with something like 10 in sticking out and unsupported.

What is wrong with using your fixed steady? Here's how I would do it.

Preferably I'd use the 4 jaw independant chuck, centralize the bar adjacent to the jaws by moving the jaws, then set the fixed steady to fit the bar adjacent to the jaws. Now I would open the "gate" on the steady, move it to the free end of the bar, close the "gate" and drill away. The point is, by setting the steady adjacent to the jaws, and moving it without upsetting the arms, you stand a very good chance of keeping the bar centralized as accurately as it was adjacent to the chuck. Ok, it might take a few minutes extra, but what is a few minutes against the possibility of the free end flailing about dangerously.

Regards,

Peter G. Shaw

p.s. Somewhere I have seen a recommendation to limit the free unsupported end of a bar to perhaps 3 or 4 times the diameter.

Edited By Peter G. Shaw on 19/02/2019 18:59:50

Neil Wyatt19/02/2019 19:27:28
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Moderator
15839 forum posts
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73 articles

Thinks about a foot of 1" bar coming adrift...

I'd do it properly and use the fixed steady.

Neil

Neil Wyatt19/02/2019 19:30:59
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Moderator
15839 forum posts
672 photos
73 articles

Alternatively, if it's not too hard a steel, in the old days you might use a bell centre or another method to mark the centre of the bar, hand drill a small hole and then use a square centre* in the tailstock to open it up into a proper centre hole, before switching to a dead or rotating centre.

Neil

*I've only ever seen one of these in the flesh, and it's in my workshop

Neil

not done it yet19/02/2019 19:33:49
2816 forum posts
11 photos
Posted by Neil Wyatt on 19/02/2019 19:27:28:

Thinks about a foot of 1" bar coming adrift...

I'd do it properly and use the fixed steady.

Neil

And there is a fixed steady just waiting to be used! It is a no-brainer in my book. Being safe is far, far better than being sorry that you tried to take a shortcut.

Howard Lewis19/02/2019 20:02:39
1884 forum posts
2 photos

Careless, stupid, or whatever else, that I am; DEFINITELY a fixed Steady job.

10" of 1 inch bar will whip a little at speed. Your object is to centre drill, not end up wearing it!

And why deliberately abuse the Headstock bearings?

Set up the steady close to the chuck, and then set it at the outer end of the bar, and then apply the centre drill.

Remember "There are old pilots and there are bold pilots but not many........ )

Howard

Mark Gould 119/02/2019 21:04:46
82 forum posts
47 photos

Thanks for the very helpful replies gents. Using the steady seems a good idea. I think I was perhaps trying to cut the corner a little bit and gain some time. Thanks again for taking the time to help,

Mark

not done it yet19/02/2019 22:46:39
2816 forum posts
11 photos

12 hours since your original posting. Could not have taken that amount of time to fit the steady and do the job - even setting up the steady at the free end (which I usually do). smiley

My lathe will pass 1” (just), but the fixed steady gets a reasonable amount of use - far more than the traveling steady has!

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