Deep hole drilling 101 on lathe?

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PeterE:
Interesting subject this.

Just a question, why not step-drill? I mean that one starts with say 6 mm for 50 mm or so, change to a 10 mm and drill 40 mm, then chjange back to the 6 mm who now get guidance from the 10 mm long 6 mm hole, but is not affected by the 40 mm long larger distance. That way I guess that the load on the thinner drill becomes much less and the problem with heating is lowered.

Also by changing drills there will be a natural time for cooling both the workpiece and the drills.

Then the last question; Why not drill to a bit under final size and then bore the rest? That will of course demand that your lathe is long enough :palm:

BR

/Peter

PekkaNF:
The crux of the mater here is that I don't have available easy maching material to make spindles with holes. This material is bit of trouble. On the other hand is's nice to make axles and such. External turing works fine. The touble is only with internal turning or drilling a (relatively) long hole. I have tried several methods with warying decrees of success.

I have got this temprering steel bars from 12 to 25 mm dia and I can buy larger ones in cut length. I have a nice 40 mm dia and 30 cm long for one project. The good (and very important news for me it is that there is plenty of it and I can get always some more). The trouble is that I find it very hard to find anything easier to machine bar here. There are some mystery metals on junk yard and I have bought several bars these mysteries and after a little while I have found out why they were reject. Best gues machined beautifully, but had some inclusions on it. Broke a insert very few minutes....some were gummy and some bent after turnig them then bet other way when drilled. Some turned ugly no matter you tried...

It's 34CrNiMo6 to me, these are other names for same stuff (or close)
4340
817M40
En24

Some of the bars are rolled some bright, but all are in tempered state.

Very nice for external turning and works fine for short drilling (I have drills that eat this no problemo).

BUT: This material tends to make very long stringy swarf and it is workhardening and pretty tough. Therefore any peck drilling does not work. I get few pecks pretty ok and then one that will squal like pig.

Also smaller the drill, nastier it get's do drill long hole. It is easier to get a 10 mm 160 mm long drill than 6 mm 160 mm long drill that takes the beatting. Although I must say that if I had a 6 mm drill of 200 to 300 long that would make a pilot hole I would be very happy to use one and then feed 15 bar coolant trough it and use cheaper long 8 to 10 mm drill for final hole. Pretty good indication of this how drills are rated often something like 3xD or 5xD that means that lenght is 3 or 5 times the diameter.

It's pretty nicely explained here:
http://www.unisig.com/gundrilling-education/deep-hole-drilling.php
http://www.unisig.com/drilling-videos/deep-hole-drilling-101-video.php

Pekka

unc1esteve:
Pekka,

Do you have an hydraulic cylinder repair shop near by? The cut offs and bent pieces
in the rubbish can make good project material. The bars are usually 1045.
The chrome turns off with carbide tools. You can also purchase new material
but in larger sizes than 13mm. It seems you need stress proof steel.

http://www.homemadetools.net/deep-hole-drill?gce=tab50&utm_expid=57824293-7&utm_referrer=https%3A%2F%2Fwww.google.com%2F

http://www.practicalmachinist.com/vb/search.php?searchid=1484507

http://bbs.homeshopmachinist.net/search.php?searchid=763358

PekkaNF:

--- Quote from: unc1esteve on August 23, 2013, 08:56:03 AM ---Pekka,

Do you have an hydraulic cylinder repair shop near by? The cut offs and bent pieces
in the rubbish can make good project material. The bars are usually 1045......

--- End quote ---

THANKS! I was really thinking hard to find right kind of second hand material...never thought of hydraulic cylinder rods. I can find the material used or even "new". I'll check it first weekday. Hmm....what kind of material is the tube? I'm going to check one junkyard and find one to test.

Pekka

NeoTech:
Was more kinda in the lines of this i was talking about.. the "drillhead" holding the spade bit can be mounted onto a thinner rod for making it longer, guides and strong materials is needed though. Unless you are just making a short hole. =)

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