Ok, simple (i hope) question that I can't figure out.

I want to drill a hole in a 25mm solid bar accurately (say tolerance of .5mm from the exact centre). I've got new drills, automatic and hammer based centre punch, ruler, micrometer, vernier calliper and a pillar drill (and other assorted tools).

How do i do it with repeatable accuracy?

The only way i can think of is to get a template that fits snugly over the 1" bar with a small hole for the centre punch - except i don't have a template, but could persuade my dad to drill the template on his lathe i suppose, except it would be a while before i get up to see him to do the persuasion.


Template idea,

XXXXXXXX|...|XXXXXXXX
XXXXXXXX|...|XXXXXXXX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX

'.' = space, done so it displays properly on locostbuilders
'X' = steel
'|' = carefully drilled hole in the centre of the top bit of steel.


This is so that i can make a small number (8 to begin with then in batches of 4) a bit of steel like this,

XXXX|...........|XXXX
XXXX|...........|XXXX
XXXX|...........|XXXX
XXXX|...........|XXXX
XXX/..............\XXX
XX|..................|XX
XX|..................|XX
XX|..................|XX
XX|..................|XX

Where the hole at the top is 11mm ID and the whole at the bottom is 19.5mm ID. Total length of the piece is about 25mm and as before 25mm OD. My plan was to get an accurate centre, drill up to 11mm all the way through. Then using a couple of more drills step up to 19.5mm but limit drilling to half way, this way i'll also automatically get a nice chamfer (i appreciate it won't be as gentle a chamfer as my diagram, I don't think that is an issue.

You need to basically turn the pillar drill into a lathe.

You need to hold the work piece in the chuck. Then hold the drill in the drill vice.

So the problem is you need a drill chuck that will hold inch bar.

Adrian

quote:

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Originally posted by AdrianH

So the problem is you need a drill chuck that will hold inch bar.

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Whenever I have problems like this (IE needing a lathe) I usually take a step back and look at how the same problem can be solved using different techniques so you dont need such a critical hole in a centre....

Perhaps not helpful, but worth thinking outside the box...

The first problem with just dotting the centre of the bar will be getting the hole to stay central............if you want any kind of accuracy , that is definitely a lathe job .
I'm not far away - and at home all week

You need a centre finder:

quote:

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Originally posted by StevieB

quote:

---

Originally posted by AdrianH

So the problem is you need a drill chuck that will hold inch bar.

---

and safety glasses, chest shield, gloves, hard hat, sense of adventure and a touch of disregard for your own safety...
[Edited on 15/11/10 by StevieB]

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I doubt you can get a 25mm rod in your pillar drill.

I doubt you can get a 25mm rod in your pillar drill.

I think your template idea is a good one, small one off bit of extra effort instead of buying a lathe. But you need a lathe to make the template, sounds like Claire is your friend on this one.

But make it longer, so you stay parallel.

XXXXXXXX|...|XXXXXXXX
XXXXXXXX|...|XXXXXXXX
XXXXXXXX|...|XXXXXXXX
XXXXXXXX|...|XXXXXXXX
XXXXXXXX|...|XXXXXXXX
XXXXXXXX|...|XXXXXXXX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX


Note sure how you prevent the guide getting worn out.

Matt

if you can get your dad to use a lathe to do a template, he might as well do it! Or ask someone local like Claire Otherwise without a centre finder, i doubt you can get it within that accuracy.

Easiest way is to find some one else with a lathe

I can help if your coming this way....

Get a lathe, I have some spares at work
Easiest route here is to get your Dad/ Claire or whoever to run an 11mm drill through some lengths of 25mm bar so you have a central starting point, you can then twiddle away happily from there, a decent x vice might help but lathe would make it much easier though.
atb
Mike

probably a daft suggestion but can you buy 25mm od tube with suitable wall thickness and / or a cobination of two tubes to get you close to what you require then drill to suit?

I can either make you a jig, or the bits you need.

quote:

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Originally posted by a4gom
probably a daft suggestion but can you buy 25mm od tube with suitable wall thickness and / or a cobination of two tubes to get you close to what you require then drill to suit?

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How long is the bar you need to drill, can your old man no do it in his lathe rather than making all the "jigs"

As a one off Dad could do it no problem and would probably like the project. Thing is, i'm going to want them once in a while and its a bit much to rely on him & drives the cost up if i've got to ask other people to do it (retired dads time is free obviously) - hence wanting to do it myself.

How about a jig like this:

.............|XXX|.............
.............|XXX|.............
.............|XXX|.............
.............|XXX|.............
.............|XXX|.............
.............|XXX|.............
XXXXXXXXXXXXXXXXXXX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX
XX..........................XX

Just put your blank in the bottom, chuck the spindle in the top. Lower the blank into the vice and tighten, unchuck and remove the jig. The piece should now be centered quite accurately, and the jig won't wear out (not too quickly at any rate!)

[Edited on 15/11/10 by Badger_McLetcher]

[Edited on 15/11/10 by Badger_McLetcher]

If you could find a cheap 3 jaw chuck then you could put this on the bed of the drill and clamp a bit of say 12mm bar in it.then clamp the bar in the drill chuck and clamp the 3 jaw chuck to the bed of the drill.It would then be centered to the drilling machine spindle but maybe at the wrong height but if you then need to adjust the height you only need to realign in one axis which can be done either by eye or using a Dti in the drill chuck.
I have done similar a few times at home and work to get around problems even though i have a lathe.If you will be doing the job on a reg basis the cost of a chuck may be justifiable and is a useful addition anyway.
Paul

Also be wary if you're using 25mm bar and the OD is critical (I've always turned things down to the required OD from an oversize in case it's not completely straight etc.) - can't do that without a lathe.

Personally given your design, I would try and jump on someone's lathe for a day, and make 30-40 of these things in one go...


First, get the OD down accurate (if it matters, if not, just get some 25mm bar and use that)

Centre drill to get your pilot hole, then just drill 11mm through, part off with a cutting tool at exactly 25mm. Repeat.

Then once you've got a whole bunch of slugs that are accurate 25mm OD and 25mm depth with a 11mm hole, just stick them into the lathe jaws one by one and drill the other side out to 20mm or whatever you need - your 20mm drill bit will centre on the 11mm through hole.


We had to make several part batches (8 in each batch) of similar things (but with one more operation) for a project back in Cambridge, and once you got going it was fairly straightforward to keep knocking them out all in one stint.

Assuming you have no centre finder or sliding square I find the best way to mark the centre is to clamp two strips together
so that one end is longer by almost half the bar diameter, in your case 11.5mm.

clamp
vvvvvvvvv
____________________
______________<11.5>
^^^^^^^^
clamp


Using this tool as a back mark scribe 4 lines at 12, 3, 6, and 9o'clock on the end of the bar.

This will give 4 lines that form a little 2mm square in the middle.

It always seems easier to get a centre dot in the middle of the square than to try and set the back mark exactly right I find.

Small dot to start with, and if not quite right then angle the dot punch over and "move the dot".


Hope this helps.
Paul G

quote:

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Originally posted by PSpirine
Centre drill to get your pilot hole, then just drill 11mm through, part off with a cutting tool at exactly 25mm. Repeat.

Then once you've got a whole bunch of slugs that are accurate 25mm OD and 25mm depth with a 11mm hole, just stick them into the lathe jaws one by one and drill the other side out to 20mm or whatever you need - your 20mm drill bit will centre on the 11mm through hole.

---

To do this without a lathe will be 'tricky'

The ends of the bar will have to be perfectly flat, or the exit hole will not be concentric, even if the start of the hole is. This assumes your table is also exactly at 90 degrees to the drill bit and the table does not flex. Do not underestimate the amount of movement you will get when you try to use a 19.5mm drill in a pillar drill - not just the headstock bearings, but from the table too. Make sure all adjusters are well tightened. If you grip the bar tight enough to stop the hole being triangular, you will almost certainly mark the outside. Also your vice will have to be perfectly set and very well bolted down. I have tried to do almost exactly what you are proposing with a heavy duty warco drill, and ended up using a boring bar in my small lathe, which took much longer.

Best of luck
Hugh

Simple.....

Buy a long length of fat walled pipe and cut it into many pieces

Answer..........buy my lathe.
Myford ML7 with tons of accessories. Then I can buy Weldermans single seater
Regards Denis

Made a spreadsheet last night and I can almost get there with different thickness tubes but the last tube ends up with walls of .5mm. That doesn't seem realistic to me, any wander with the drill and i'll be through.

Think i'm quite happy with the idea of drilling 1" steel. Just need to get some drills and steel now and give it a go with the jig suggestion from 907 (thank you). If that doesn't work i'll hassle my dad to make a jig to place the centre punch.

easy solution to finding a centre:

One pillar drill with drill installed
One large blob of blu-tac, or other plasticine stuff
One pin
One (preferably) metal ruler

Simply blob the plasticine on the outside of the drill bit & insert pin on one side, put object to be drilled in vice

Switch on drill, and use ruler to guide pin to outside of object to be drilled. Once aligned, the drill is now central, drill

simples.....