Cross drilling in the lathe

[Ian ParkinParticipant @ianparkin39383]

[Ian ParkinParticipant @ianparkin39383]

I’m trying to remember where i may have seen a technique for doing this…

i have a 50mm dia x 150mm piece of ms

i need to machine a 1 1/8 thread about 50mm from one end..

how do i centre the part in my 4 jaw so the hole and subsequent thread is bang centred though the bar

[Pete RimmerParticipant @peterimmer30576]

You need a crotch centre for your tailstock. An old-school method for using large drills in the lathe but very effective. Drill a pilot hole using the crotch centre then put the drill in the tailstock, slide the part onto the drill then clamp it to a faceplate whilst using the drill as a guide to keep it aligned. Once it's all clamped up, drill and bore the hole then cut the thread.

Edited By Pete Rimmer on 16/12/2020 17:34:37

[peak4Participant @peak4]

Ian, if you consider the bar as a rectangular cross section, looking end on from the tailstock, you could add a couple of packing pieces on the two jaws which touch the curves sides and use this method of clocking shown by Joe Pie. in one of his videos.

Bill

[Ian ParkinParticipant @ianparkin39383]

Pete

yes that would work but i thought drilling on the mill with say a 10mm drill then putting a length of silver steel in the hole and indicating off that in the 4 jaw..then removing before drilling

Bill

cant see how that would work on a round bar? Am i being thick? Yes just realised what you meant now

Edited By Ian Parkin on 16/12/2020 17:52:51

[Ian ParkinParticipant @ianparkin39383]

Is this a valid way? Centre punch where i need the hole and set this in the 4 jaw and bring the tailstock up with a. Centre in….. rotating the chuck the centre pop would describe a circle if its not spot on?

[JasonBModerator @jasonb]

You would need to make sure the pop mark was dead at the highest part of the bar, it could still be clocked true even is the bar is rotated slightly about it's own axis.

I think the 10mm hole and pin method would be good.

[peak4Participant @peak4]

Another idea, though I've not fully thought it through.

Arrange a stop which will impinge on the lower edge of one of your chuck jaws when that one and the opposing jaw are horizontal as you can get them(maybe use a spirit level).
Chuck up the bar vertically and get it roughly in the right pace with a ruler and sharp centre in the tailstock.

Set one jaw on the aforementioned stop, and clock the front of the bar.
Spin chuck 180° and sit that jaw on the stop.
Clock the bar again.

Even if the bar isn't 100% vertical, it will be the same fraction of a degree off from the previous measurement, and so long as the clock is at the same height, and only just above a horizontal jaw, the error should be minimal.

Bill

[Howard LewisParticipant @howardlewis46836]

Unless I have misunderstood, the wish is to cut a 1.125" thread, 50 mm long, along the axis, at one end of a 150 mm long piece of 50 mm diameter bar.

If so:how about this?

Grip the bar in the 4 jaw chuck, pushed in as far as possible into the jaws.

Clock, cloe to the jaws, to centre it.

Set the moving steady to the bar, as close to the chuck as possible.

Release the bar from the chuck and move the saddle away, to release the bar.

Without removing the bar from the moving steady, replace the bar in the chuck and recentre it with the clock close to the jaws.

With the moving steady supporting the bar, use the Tailstock drill chuck to drill the bar, before turning down the OD to 1.125, and screwcutting..

Alternatively; set the fixed steady at the chuck end, move it to about 60 mm from the end of the bar, and leave it there whilst the bar is bored, turned down and screwcut.

In this way, the thread and the bore should be concentric to each other, But boring all way through 150 mm of bar is going to be difficult, unless the bore is large enough to permit the entry of a long large diameter, stiff, boring bar

HTH

Howard

[Pete RimmerParticipant @peterimmer30576]

He has a 150mm piece of 50mm bar, and wants to cross-drill it 50mm from the end and put a 1.25" thread in the hole.

[Oily RagParticipant @oilyrag]

I think this is what Pete Rimmer was referring to in his earlier post about a 'Crotch'centre:-

This is a tailstock Vee cross drilling attachment from my Raglan LJ – on the front shear by the tailstock is the interchangeable flat plate which allows parts to be clamped to it for drilling.

Edited for spieling mhistake!

Edited By Oily Rag on 17/12/2020 15:25:24

[Howard LewisParticipant @howardlewis46836]

Ah!

So is the lathe large enough to accept the bar across the jaws of 4 jaw without hitting the bed?

Don't like the thought of having to hold the work in just three jaws!

Clamp it up TIGHT, and go very slow.

This calls for the capacity to swing 200 mm, if the overall length of 150 mm is to be maintained

If so, the thread can be screwcut in the normal way for an internal thread, once the bar has been centred in the 4 jaw.

This will probably entail using careful marking out, centre popping and then the use of the two centres method

If a mill is available, it can be used to put a centre drill mark exactly where required, before moving to the 4 jaw chuck in the lathe, and centering .

Lacking a large enough 4 jaw, the bar could be clamped to the Faceplate, (Preferably on Vee blocks to provide clearance between the bar and the Faceplate, for the boring tool and screwcutting tools to pass through ) and carefully adjusted until on centre.

Whether in a 4 jaw chuck, or on a Faceplate, the work will be well off balance so speeds will need to kept low.

Clamping to a Faceplate seems to be safest method.

Howard

[Ian ParkinParticipant @ianparkin39383]

This is what I’m wanting to make a few of.

this is ok but the hole isn’t in the middle of the 50 mm bar

[OldironParticipant @oldiron]

Posted by Ian Parkin on 16/12/2020 17:52:02:

Pete

yes that would work but i thought drilling on the mill with say a 10mm drill then putting a length of silver steel in the hole and indicating off that in the 4 jaw..then removing before drilling

Bill

cant see how that would work on a round bar? Am i being thick? Yes just realised what you meant now

Edited By Ian Parkin on 16/12/2020 17:52:51

If you have a mill why not use it to do the job ? It would save all the faffing about.

regards

[Ian ParkinParticipant @ianparkin39383]

I cant screw cut in the mill old iron

Edited By Ian Parkin on 17/12/2020 16:36:10

[OldironParticipant @oldiron]

Posted by Ian Parkin on 17/12/2020 16:35:39:

I cant screw cut in the mill old iron

Edited By Ian Parkin on 17/12/2020 16:36:10

Oops sorry Ian I thought it was an 1/8th hole not 1-1/8". Misread your thread. There are several video's on YT about cross drilling in the lathe. Good luck.

regards

[peak4Participant @peak4]

Ian, the other thought is, if you have a surface or T&C grinder, just tickle the chuck jaws so they are exactly the same thickness inside to outside on one of the steps, then clock on the outside of the jaws.
I guess the step closest to where the round bit of the bar touches on the inside would be best. (or just use a bit of feeler gauge to make up any difference in jaw thickness.

Bill

[HopperParticipant @hopper]

Posted by Ian Parkin on 17/12/2020 16:18:02:

This is what I’m wanting to make a few of.

this is ok but the hole isn’t in the middle of the 50 mm bar

 

How close to the middle does it need to be? Good enough for aesthetic purposes, or dead on to the nearest thou for precision location purposes? Makes a big difference to how you might proceed.

If the former, ie within a few thou of centre, you might get it by holding the job vertically in the four-jaw and pinching a very thin steel ruler (Pedant Squad, stand down!) between a sharp tailstock centre and the curved surface of the job. Ruler will lie dead straight across the bed visually in line with the leading edge of the carriage etc. if the job is centred.

Otherwise, if you want accuracy to the nearest thou, you might use a dial indicator off the gripping surfaces of the chuck jaws that are holding the curved surface, much like the video about square stock posted above. A 0-0 reading there will mean its centred.

If you are making "a few" as you say, it might be worth making a faceplate fixture to hold successive parts in the same position once the fixture is located correctly. Or for a smaller few, use the old dodge of releasing only one chuck jaw in each direction, marking which ones, and then tighten up only those two when mounting the next job. The two unmoved chuck jaws act as reference surfaces to locate the new job correctly. You might still double check it though if accuracy is paramount.

ON a curved surface like that, you might also create a small flat by holding the end of a slot drill against it in the tailstock before centre drilling, just to help the centre drill get started without wobbling and provide a full circle of guidance for the drill-bit proper to start on. .

Just out of curiosity, what are these things you are making?

 

 

Edited By Hopper on 17/12/2020 23:07:33

[HopperParticipant @hopper]

PS

Or you could search on eBay for a Round Bar Centre Finder and get something like this (UK Seller) **LINK**

And hold it in the tailstock chuck. You then move the job in the chuck until the lines on the centre finder are lined up and you have it centred.

[HopperParticipant @hopper]

PPS

In case the mods delete the above link, despite it being a UK seller it does involve that website whose name we dare not mention, here is a pic of the type of Round Bar Centre Finder commonly available from most of the usual suspects, (except RDG who out of stock and have their last one listed for 990 Quid! They usually cost about 10.)

Edited By Hopper on 18/12/2020 00:15:02

[Michael GilliganParticipant @michaelgilligan61133]

On the reasonable assumption that the four-jaw chuck is big enough to hold the job safely

[ Ian has already made one item, albeit with the hole not on diameter ]

Surely a DTI, reading deflection along the the lathe axis could be used, to position the peak on-centre.

MichaelG.

 

Edited By Michael Gilligan on 18/12/2020 08:19:31

[OldironParticipant @oldiron]

Posted by Hopper on 18/12/2020 00:11:45:

PPS

In case the mods delete the above link, despite it being a UK seller it does involve that website whose name we dare not mention,

I do not know why you think we cannot mention EBAY or similar sites here. I have not seen any ruling that bans us from mentioning EBAY. It seems to be certain knockoff products that trigger the censorship. There are many excellent products on EBAY that many of us buy time and time again and I for one am grateful if another forum user posts a link to a useful UK based item. Also we have comeback on a seller when they are UK based.

Maybe the Moderators will clarify this issue for us.

My grumpy old man syndrome seems to be kicking in again today. Maybe it is the isolation we are all having to put up with these days.

regards

[Martin ConnellyParticipant @martinconnelly55370]

Surely a DTI, reading deflection along the the lathe axis could be used, to position the peak on-centre.

MichaelG.

I was thinking how to do this with the items I have and came to a similar conclusion with a little bit more involved.

Mount a DTI in the tool post.

use a spirit level on the side of the bar to hold it vertical (or near enough, a small error will not matter).

Find the high point with the DTI and note the position.

Turn the chuck 180° and repeat.

If the position of the DTI is the same both times then the bar is centred, if not adjust and repeat the process.

Martin C

[Ian ParkinParticipant @ianparkin39383]

Well guys i think I’ve done it in an acceptable way for me

i do have a Dro fitted on this lathe so just touched off on the jaws holding on the diameter spun 180 and adjusted until the Dro read the same on both sides

Hopper I’d forgotten i had one of those centre finders but digging it out i remembered why i had never used it…its like it came out of a lucky bag

[Ian ParkinParticipant @ianparkin39383]

Oh and its a tailstock adapter for woodworking lathes for holding MT2 tooling

fits in a toolpost

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