Drilling accurate depths

[Chris ParsonsParticipant @chrisparsons64193]

I have never really used the micrometer dial on the tailstock to measure depths of holes (I use the markings on the quill) but now want to drill to a more accurate depth and use a D bit to flatten the bottom of the hole?

If I spot drill the start for the main drill, how do I (re)set the drill point at 0, other than the mark one eyeball? If I zero the drill on the end of the work, and then swap it for the spotting drill it's difficult to get the drill back to the same position in the chuck?

I was also wondering If there is a formula to calculate the depth of the tip compared to the drill diameter? Guess I could dig out some geometry books and see if I can work it out myself – it was the relationship between the diameter of hole and the cone at the bottom on the hole, to know how far to advance the D bit to remove the cone?

Any thoughts would be welcome

Chris

 

 

Edited By Chris Parsons on 31/05/2013 09:12:32

[Chris ParsonsParticipant @chrisparsons64193]

[Chris ParsonsParticipant @chrisparsons64193]

Ahhh…use a shim material (I will need to get some!)

I did think about a metal rule and measuring the thickness etc but didn't think it would be that accurate – but of course shim material is a known thickness, obvious really, thank you

Chris

[CabengParticipant @cabeng]

I've put 2 photographs in a new album (drilling to depth in lathe) to show how I do this – you might not be able to adopt the method directly (depends on what kit you have – I have a DRO on the lathe, plus a Dickson toolpost that has 3 mounting faces, which combine to make it very easy) but it might give you some ideas.

It's simple, quick and effective. Put a bar in the toolpost, with sufficient protrusion to contact the nose of the drill chuck. Put the drill point up against the work, lock the tailstock and barrel , then move the saddle to the right until the bar contacts the front of the drill chuck, as per first photograph.

Now move the saddle to the left, a distance equal to the required depth of drilling – second photograph. (DRO, saddle handwheel, DTI, ruler?)

Lock the saddle, drill until the nose of the drill chuck touches the bar again, and you've drilled to depth. But be careful when touching the bar, a screw feed tailstock can push a locked saddle along if applied with enough enthusiasm, and that would mess up your pre-set depth.

[JasonBModerator @jasonb]

It does not have to be shim stock anything of a known thickness will do but having something 0.010" 0.100" or 1.0mm just makes for simple maths.

Feeler gauges may be more useful than buying shim stock or just machine a bit of bar down to 0.100" and keep it for that purpose.

Myself I would opt for something thicker than 0.010" as if you are drilling a largish hole it may deflect

 

J

Edited By JasonB on 31/05/2013 10:33:46

[DismalduncParticipant @dismaldunc]

Thank you chaps, I've been playing "guess the depth"for ages and now feel as thick as mince. So simple!

[Chris ParsonsParticipant @chrisparsons64193]

You are such a helpful lot!

I thought about feeler gauges, sure I have some somewhere from the days when I used to do car maintenance (before all the electronics and turbochargers…)

Might treat myself to a new metric set, and agree with Jason that a bit thicker would be a bit easier

Glad someone else found this useful, sometimes one feels a bit stupid asking but there are lots of clever 'tricks' to learn…

Regards

Chris

[Sub MandrelParticipant @submandrel]

How accurate do you need?

One way is to use a depth gauge to measure along from the end of the drill or d-bit and put on a mark at the required depth. Accurate to within a few thou if done with care. That's what I do for jobs like holes that must not break out at the other end.

Neil

[Author]

Posts