Drilling deep holes – 10x drill diameter – Runout?

[Neil LickfoldParticipant @neillickfold44316]

My Approach is different. Use a slightly longer blank than the finished length and bigger than the finished diameter. The very start of the hole for the first 1.5 diameters is the most important. Spot or centre drill the start. Then drill with a slower initial start rpm with the shortest drill you have. In the OP case using a 5.3 or 5.4mm drill. Then when at 1 diameter in, you can then change to the normal drilling speed. Drill right through then ream the hole. I leave the end of the hole sharp, and turn taper to suit the lathe centre for about 1mm long. I then set up a centre in the head stock, and turn the OD true to the hole that has been made between centres. The turned taper sits on the headstock end centre. I rely on the friction drive for the 1mm long to hold the part while I take very fine cuts on the OD. The drilled out end, the sharp end, is the end at the live centre. The stock will be the best average of the generated hole.

[Sam Longley 1Participant @samlongley1]

Posted by The Merry Miller on 31/10/2011 13:44:08:

 

That's very true Chris, especially when using large hand operated ratchet drills (shades of the 1950's)

 

Len P.

I watched one of my fathers operatives drilling 3/4 holes in an RSJ really quite quickly & probably with less fuss than one might with an electric drill today. I know that I have had occasion to drill such holes on site & thought how much easier it would be with a ratchet drill if one had room for the clamp

I have often wondered how accurate the finished hole diameter would be. ie would there be less tollerance than one usually gets with drilling at speed. I might also ask what the smallest diameter of sharp drill one could successfully use with such equipment. Would the hole wander & would it be oversize? Are high speeds really the answer.

[Clive FosterParticipant @clivefoster55965]

Another job where having access to a first class drill sharpener like my Clarkson helps.

Minor wear or even tiny damage to the drill on a scale essentially invisible to anything short of a really forensic examination can make all the difference between a true true running, on size, hole and one close but no cigar.

Now I have my Clarkson set up I routinely re-sharpen a drill before any critical holes. However good it looks. I used to manage pretty well before but did get the odd few that weren't up to scratch. With a resharpened drill I know it will do the job right unless I cock-up.

Best results if you can follow book speeds and feeds but that needs a properly sharp drill too.

MT taper drill will behave better than an ordinary straight shank one in a chuck. I've invested in one or two odd sizes that had to be right.

Clive

[SillyOldDufferModerator @sillyoldduffer]

Posted by Sam Longley 1 on 06/02/2022 08:53:57:

Posted by The Merry Miller on 31/10/2011 13:44:08:

 

That's very true Chris, especially when using large hand operated ratchet drills (shades of the 1950's)

 

Len P.

I watched one of my fathers operatives drilling 3/4 holes in an RSJ really quite quickly & probably with less fuss than one might with an electric drill today. I know that I have had occasion to drill such holes on site & thought how much easier it would be with a ratchet drill if one had room for the clamp

I have often wondered how accurate the finished hole diameter would be. ie would there be less tollerance than one usually gets with drilling at speed. I might also ask what the smallest diameter of sharp drill one could successfully use with such equipment. Would the hole wander & would it be oversize? Are high speeds really the answer.

Is this the original 'gut-buster' drill? There's a reason – think hernias!

They have pros and cons.

• High torque, but power limited by the human. A strong, fit operator can produce over a kilowatt in short bursts, he will only average a tenth of that over an an hour. 100W isn't impressive compared with an electric drill that doesn't get tired.
• Low rpm (about 100rpm?) , which is good for drilling large diameter holes, but carp for drilling small ones. Approx rpm = 10000 / diameter in millimetres, so a 20mm diameter drill suggests 500rpm and a 1mm drill would prefer 10000rpm.

I have one for drilling big holes in wood, and it does a good job, though I find it tiring. I've also sued one to cut a 50mm-ish hole in a galvanised water tank with a sort of fly-cutter thing. Sweaty hard-work in a cramped loft that went straight on my "Don't Do That Again" list.

Mostly power tools do a better job faster than hand-tools, but there are plenty of exceptions!

Dave

[BufferParticipant @buffer]

Thanks to you all for all the ideas and advice.

[Author]

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