Thread: Boring bars and small holes

Hey guys

im looking for some advice on boring bars to re-centre a hole in a long piece of stock. This is a Damascus steel bar that I made and drilled the centre out. I was adventurous and hoped I could keep it pretty centres over about 130mm of length but ambition was higher than skill as usual! So I have a 1/4 inch hole that can be expanded to 8.5mm and needs centering. Depth does not have to go full 130mm - 100mm probably enough. Will I be able to do this with one of the small boring bars using 06 carbide inserts? I’ve used boring bars before but not in such small or deep situations. Of course I can go very slow and using fluids etc. I really don’t want to have to start again. Current OD of bar is just over 12.5mm but will be finished to 11mm in the end.

if you have a tool you think will do the job could you post a link for me to follow please? I am really not sure what I should be looking for here.

7EF22DF4-F520-4AB6-9EB7-B8173326157C.jpeg

Boring 8.5 diameter x 100 deep? Not gonna happen.

There's probably ways to make it kinda work with multiple tools from both ends, but it's not going to be a simple process.

Hi Ian,

Boring out a hole that small and deep isn't going to be an easy task, a piece of carbide rod the right diameter and ground as a "D" bit will get you close to finish size, but its going to be a slow gentle job with lots of clearing the swarf. I've done similar jobs of over 150 mm lengths in hard aluminium, steel is much harder to machine and I suspect that your Damascus steel might be even more difficult.

You might get some more information from looking up "Gun Drilling".

Good luck ! Please keep the forum upto date with pictures.

You could just drill the hole with an electric hand drill to get your 8.5mm (step drill it) and then turn the od with the job held between centre's to finish to size and to regain concentricity.

Ummm...just looked at the pic and now can see why you need to move the hole, personally i would throw that in the bin and start again.

So is the hole centered at one end and off center at the other, or somehow off center all the way through?

Joe Pie on YouTube did a really good video a while ago on deep hole drilling. Worth a look even if it doesn’t help much with fixing this part it may help for next time.
His “bumping the carriage” technique has to be one of the most useful tips I’ve picked up for drilling on the lathe.

Steve

Honestly bin it and start again using the lathe centre drill etc

Sent from my SM-A135F using Tapatalk

Hey thanks for the various replies. Well the feeling is to mark it down to experience and start again but I’m not going to die wondering on this. If it really is stuffed then no harm in trying to get it back on track. Making a new bar of twist Damascus isn’t as easy as grabbing another bar of round stock so it’s worth fighting for!

Yea the hole is centered at one end and the project is a bolt action pen. I’ve made a couple now from aluminium but this is obviously a different ball game and I was rushing! The hole down the centre is the barrel of the pen and it only needs to be 1/4 inch for the ink refill. The very end needs to be 8.5mm to fit the end cap. Currently the end where the cone (nib?) end is is on centre but the action of sliding the cartridge in and out is not good because of the off centre hole up the barrel. My thinking is if I try my best at getting the bore opened up and closer to centre it will improve to the point of a functioning pen and given it is for personal use I’ll be very happy if I can achieve that. I’ll be sure to provide some updates as I progress and see if I can save this project.

In that case perhaps use an end mill as a boring bar to centralize the hole. If you have a collet chuck that will go in the tailstock you can push the endmill back into the collet when you first start to increase the rigidity. Then slowly pull it out of the collet as you move deeper. Light cuts.
Sounds like if you’d even get 30mm might give a decent improvement.

Good luck!!

Steve

Given its worth going to some effort.
How far off center are you?
You did this in a lathe right?

One idea that came to mind that might work.
Take an 8mm four flute milling cutter.
Make up a plate say 5mm thick you can mount to your tool post.
Then center drill/pilot hole/mill through the plate with the tools held in the lathe chuck.
Put you workpiece in the chuck with the plate almost touching.
Use the milling cutter in the tailstock though the plate to true things up.

That should get you ends pretty close. Then run an 8mm drill though the middle from the end of your choice

Stupid idea?

Could you soft-solder a piece of ¼" mild steel bar into the hole and start again?

Milling cutter in either the tailstock, or in some sort of lathe tool holder, is a good idea,
but even it will wobble a little from the existing off-centre hole
– especially if this steel is tough.


I would actually machine a tapered centre on the bad end, so the cutter starts off true!

Either hand grind (Dremel) the bad side so it matches the other,
or use your biggest lathe centre drill in the tailstock?

You guys are being a great help - thanks!

Originally Posted by Stustoys

One idea that came to mind that might work.
Take an 8mm four flute milling cutter.
Make up a plate say 5mm thick you can mount to your tool post.
Then center drill/pilot hole/mill through the plate with the tools held in the lathe chuck.
Put you workpiece in the chuck with the plate almost touching.
Use the milling cutter in the tailstock though the plate to true things up.

That should get you ends pretty close. Then run an 8mm drill though the middle from the end of your choice

Stupid idea?

Yes I did it on the lathe - I held the barrel in a ER collet chuck on the headstock and drilled using my tail stock. This is a novel approach and yes it sounds like it could help with rigidity so definitely worth trying. It is almost like using a travelling steady on the cutter. Not stupid I don't think.

Originally Posted by jack620

Could you soft-solder a piece of ¼" mild steel bar into the hole and start again?

I was thinking this as well Jack but worried any new drill would just follow the softer metal?

Originally Posted by nigelpearson

Milling cutter in either the tailstock, or in some sort of lathe tool holder, is a good idea,
but even it will wobble a little from the existing off-centre hole
– especially if this steel is tough.

I would actually machine a tapered centre on the bad end, so the cutter starts off true!

Either hand grind (Dremel) the bad side so it matches the other,
or use your biggest lathe centre drill in the tailstock?

Thanks Nigel - I did anneal the steel but it is tough and two different grade (145N20 and 1084) so who knows how that machines as a non-uniform piece! I did think of the grinder ideas as well but getting depth would be tough. I think the machining a taper in on the end to start true has a fair bit of merit as well.

I do have a QCTP holder for a 30mm shaft that I was thinking to make up a grinding attachment down the track. I also have a Morse taper insert that goes in it but again not sure what good it does me here? I could mount my drill chuck in the tool post using the MT (instead of the tail stock) and then use that yo line up with the bore on centre and use an end mill. Maybe that is worth a try?

Originally Posted by Danger Mouse

I did think of the grinder ideas as well but getting depth would be tough.

I was thinking just to grind the very end - like a countersink - so that the milling cutter (or a boring bar) starts off true, and not wobbling.

I do have a QCTP holder for a 30mm shaft that I was thinking to make up a grinding attachment down the track. I also have a Morse taper insert that goes in it but again not sure what good it does me here?

The tool post is sometimes more rigid than a tailstock and chuck. Depends on the lathe.

So a quick update on my project. I have successfully recentered the hole! I used an end mill in the tail stock - 7mm first then moved to 8mm. Once I had a depth of around 25mm with 8mm end mill I swapped to 8mm twist drill. Taking things very slowly I got the hole in the right place and I’m back on track.

Thanks for all the great suggestions and advice. I’m really hopeful I can get this one finished in the next week or so.

Originally Posted by Danger Mouse

I’m really hopeful I can get this one finished in the next week or so.

Make sure you post a pic of the finished pen.