Drilling accurate depth holes

[Bob SillitoeParticipant @bobsillitoe83708]

Hi,

I need to drill a 3mm dia hole on my lathe but to a fairly accurate depth. The graduations on my tailstock barrel are 1/16″ but I need more accuracy than that. Just wondering if anyone has any suggestions about how I can measure how deep I am drilling?

Thanks

Bob

[Peter Cook 6Participant @petercook6]

What type of lathe?

Two quick options I can think of. One is to position a dial gauge so that it measures the travel of the tailstock. Touch the drill off on the face of the work and zero the dial gauge, then it will measure the hole depth.

A second is to make/buy a small stop collar that fastens round the drill (grub screw?). Set the collar so that the required depth of the hole is the distance from the tip to the collar. Then you will stop drilling when the collar touches the face of the work.

[JasonBModerator @jasonb]

Touch drill bit against the end of the workpiece.

Put a bit of square bar or back end of a tool bit in the toolpost and bring it upto the front of the chuck, zero handwheel dial.

Now move the bar towards the work by the depth of your hole using hopefully more accurately marked graduations.

Drill hole until the bar stops the chuck going any further,

[DalboyParticipant @dalboy]

If possible make a gauge up like this. Always handy for future projects I got the gauge from Machine DRO and some small pieces of Ali plate from my stockpile.

[BazyleParticipant @bazyle]

Bit of masking tape round the drill at the designated distance. If that isn’t accurate enough you need to decide if it is the tip of the drill or the edge that is your required distance then clean up the hole with a D-bit.

[Bazyle]

On Bazyle Said:

Bit of masking tape round the drill at the designated distance. If that isn’t accurate enough you need to decide if it is the tip of the drill or the edge that is your required distance then clean up the hole with a D-bit.

A vote for this method.  I did something very similar on my WM250 with a scale from Warco.  If you don’t fancy making one yourself, have a look at LINN Tools.  Also, Blondihack’s has a video showing how she made hers.

[Clive FosterParticipant @clivefoster55965]

Sometimes a semi-sacrificial tool is the way to go. Drill a through hole is a suitable bit of material to make a sleeve and fit a setscrew to clamp it to the drill. Adjust so the drill projects the same as the depth needed and make the hole.

Once done put it the possibly useful bits box for next time. Which will either never happen or, if it does, the tool will have migrated to that dimension that stores stuff until the week after you need it!

Generally best to go touch undersize when drilling so the sleeve has t be worked onto the drill. I’d do the setscrew hole before drilling.

Good way to get some use out of the short ends that aren’t long enough to hold in the chuck.

Clive

[duncan webster 1Participant @duncanwebster1]

I made a DRO using a rotary encoder for my tailstock, described in MEW some time ago, but it would be OTT for just a couple of holes

[old martParticipant @oldmart]

I would get a bit of 3mm allthreaded stock with a couple of nuts locked on it. You could face off the end first, and use calipers to set the length. Make sure the hole is swarf free. If you are lucky, your calipers have a depth rod that would go down a 3mm hole, my Tesa will pass down a 2mm hole, but it is a special type.

[FulmenParticipant @fulmen]

There are a million different ways to do this depending on precision, scale and whatever you find in the chip tray. A stop collar is simple and adjustable, just fiddle with it on a scrap part before committing and it should be almost impossible to get wrong.

[Nigel Graham 2Participant @nigelgraham2]

Although not ever-so-accurate, I count tailstock handwheel turns. With a 1/8″ lead barrel screw, a 1/4 turn gives 1/32″ advance.

Adjusting the method according to depth being to drill point or full diameter, I start the hole, stop the lathe, bring the handle to bottom or top dead-centre (judged by eye) then move the whole tailstock to bring the drill end to the required datum point. Then count turns each time I wind the drill back in after withdrawing it to brush the chips off and the cutting-oil on.

The obvious corollary is to make a simple handwheel dial if (like mine) your lathe does not already have one.

 

Jason –

Neat tip. On my Myford the face of the rear tool-post might give that stop. Alternatively to using the top-slide or (if fitted) leadscrew dial, use a suitable spacer such as a bit of stock material, a rule or a caliper to measure the advance.

 

Old Mart –

Ah, but measuring the depth of the drilled hole is rather after the fact!

Bob is asking how to achieve the correct depth while drilling.

 

Duncan –

It may be OTT for just a couple of holes but drilling and counter-boring to set depth is a common operation so your encoder, or a linear scale such as Dalboy’s, is worthwhile anyway.

 

Bazyle –

I’ve often used adhesive tape as an improvised gauge. Not ever so accurate but adequate for many tasks provided you don’t expect it to last for many holes. The emerging swarf erodes the tape.

[Dalboy]

On Dalboy Said:

If possible make a gauge up like this. Always handy for future projects I got the gauge from Machine DRO and some small pieces of Ali plate from my stockpile.

Good morning Bob, me try this post again.

I did something similar to Dalboy’s post on my WM250 with a DRO scale from Warco, and it works a treat (I wish I’d done it years ago).  If you don’t fancy making your own, have a look at LINN Tools (not the HiFi Linn).  Also, Blondihack’s made one for her lathe a while ago.

[Clive FosterParticipant @clivefoster55965]

Further to the stop collar idea it has just occurred to me that there is no need to fix the collar to the drill. Just set the drill projection distance when the collar is pushed back against the chuck jaws.

Simples. (Absolutely not gonna admit how many years it took for the totally obvious to sink in!)

Naturally the collar has to be long enough to cover the inactive portion of the drill whilst still leaving plenty of shank for the chuck to grip but plenty of room to accommodate variation.

A possible advantage of loose collar is that it can spin if it hangs up on the job. Theoretically a fixed one could hang up and break the (small) drill. Bore size probably doesn’t have to particularly accurate either. Rattling good fit or doesn’t wobble too much ought to do.

Clive

[Bob SillitoeParticipant @bobsillitoe83708]

Thanks for all your suggestions. In the end I went for using a bit of steel in the toolpost to act as a stop. I used the end of the tailstock barrel to butt the stop up against – worked well.

In answer to the question what lathe do I have it is a Southbend 9C, manufactured in 1942 and shipped directly to the UK to support the war effort. It has been linked to my family ever since. It was pretty worn but during lockdown I stripped it down to nearly the last nut and bolt and gave it a through going over, including replacing the cross slide feed screw and nut. It is now pretty accurate for an 84 year old machine. Knowing what I know now I would have put a 3ph motor and VFD on it but at the time I didn’t know such things existed.

Next job for today is to drill a 1/16″ cross hole in a 1/8″ dia mild steel bar. – I wonder how many attempts that will require!

[Martin ConnellyParticipant @martinconnelly55370]

For future reference maybe you should check out the tail stock screw pitch so you can do what Nigel suggested regarding counting turns and parts of a turn on the hand wheel. When used with the tailstock scale you can get reasonable accuracy on total depth.

Martin C

[Bob Sillitoe]

On Bob Sillitoe Said:

……………..

Next job for today is to drill a 1/16″ cross hole in a 1/8″ dia mild steel bar. – I wonder how many attempts that will require!

I guess it depends on whether you have a pillar/bench drill as well as a lathe.
How about the following, just as a suggestion?
Take a length of square bar, say ¼ – ½”
Cross drill the centre of it 1/16″
Stand end on
Drill 1/8″ hole along its length intersecting with the small hole.
Insert workpiece and cross drill with your ready made guide.

You could do the same thing with a 4 jaw chuck in the lathe.

Bill

[Bob Sillitoe]

On Bob Sillitoe Said:

…………………

Next job for today is to drill a 1/16″ cross hole in a 1/8″ dia mild steel bar. – I wonder how many attempts that will require!

OK, the text of my previous reply has vanished.

How about the following for a suggestion?
It would depend on you having a bench drill as well as a lathe.

Take a length of square bar, say ¼ – ½”
Cross drill the centre of one side 1/16″ all the way through
Stand on end, and drill 1/8″ hole along its centre

Insert workpiece and drill the 1/16″ hole with your new drill guide.

You could do the same in the lathe with a 4 jaw chuck

Bill

[peak4Participant @peak4]

right, third try from a different browser

 

On 1 October 2026 at 10:47 Bob Sillitoe Said:
…………………

Next job for today is to drill a 1/16″ cross hole in a 1/8″ dia mild steel bar. – I wonder how many attempts that will require!

OK, the text of my previous reply has vanished.

How about the following for a suggestion?
It would depend on you having a bench drill as well as a lathe.

Take a length of square bar, say ¼ – ½”
Cross drill the centre of one side 1/16″
Stand on end, and drill 1/8″ hole along its centre

Insert workpiece and drill the 1/16″ hole with your new drill guide.

You could do the same in the lathe with a 4 jaw chuck

 

Bill

[bernard towersParticipant @bernardtowers37738]

Regardless of what lathe you have a cross drilling jig is a must have. Zero setting up and perfect job every time. can be used for a lot of jobs like screw slotting, square and hex facing you are only limited by your imagination. dont understand why everyone doesn’t have one. I think original came from early MEW

[old martParticipant @oldmart]

I made an adjustable scale for the tailstock of the museum;s Smart & Brown model A lathe about eight years ago, it is in thousandths of an inch as the lathe is imperial. not hard to do if you really try.

 

[Bob SillitoeParticipant @bobsillitoe83708]

The cross drilling jig sounds like a good and useful tool, probably something to put on my Christmas present list.

As I am lucky enough to have an Alexander Toolmaster miller, my first attempt at doing the cross drilling is to try setting it up in the machine. If that fails then I will make a jig similar to the one described by Bill.

Might be a few days until I can try it though as the weather is too nice to be inside in the workshop!

 

Bob

[not done it yetParticipant @notdoneityet]

Depends on curacy/precision required.  ‘Rough and ready’ might be to advance a cutter until it just touches the surface and then spot-mark (dot-punch?) the exact centre of the mark.  The more accurate way is to edge-find each side of the item and halve the distance between the to sides.  Always better to spot drill on a tiny flat on the part, of course.  A DRO makes things so much easier/accurate.

[bernard towersParticipant @bernardtowers37738]

The cross drilling jig I mentioned earlier can be fitted in less than 30 seconds! And it’s set and ready to go no faffing around with edge finders etc. I fitted it today and drilled the hole  in 8 mm bar in less than 3 mins and on measuring the material left on either side it was less than a thou out (with my measuring gear). It’s been in use since 1993.

[JasonBModerator @jasonb]

Don’t think the OP’s Southbend has a slotted cross slide so not so simple to fit in seconds.

[bernard towersParticipant @bernardtowers37738]

Maybe its time to get a bit creative?

[Author]

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