Boring conversation

I have a mini lathe which I use for turning up spacers and undercarriage bits, I also have an HSS drill set from 1mm to 6mm in 0.1 mm steps for making small holes. But I have found that I also need to drill slightly larger holes of non-standard sizes (e.g 6.4mm diameter for a wheel bearing on a 1/4" axle). Does anyone have any experience or recommendations for very small boring bars for carrying out this sort of work? Kevin?

John - Being a pre- metric man, you may wish to look around for Letter & Number Sized drills plus drills in 1/64 in increments
which may come in useful.
Letter "F" is .257in dia - just search on Letter & Number drill sizes and suppliers come up.
No doubt Kevin will come up with a less boring solution.
Colin.

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JRI wrote: I have a mini lathe which I use for turning up spacers and undercarriage bits, I also have an HSS drill set from 1mm to 6mm in 0.1 mm steps for making small holes. But I have found that I also need to drill slightly larger holes of non-standard sizes (e.g 6.4mm diameter for a wheel bearing on a 1/4" axle). Does anyone have any experience or recommendations for very small boring bars for carrying out this sort of work? Kevin?

please clarify - do you want boring bars because you drill wont accept larger sizes - in which case its possible to turn down the softer shanks of larger drills - provided the drill has sufficient head room
I use and find stepped drills invaluable and have found them in metric & Imperial

The ones with a hex drive are best. the depth is limited but you could bore a prop or wheel from both sides - The next cutter automatically

Hi Kevin, I have chucks and collets up to 14mm so no problem there. My wish is to be able to turn holes in things mounted in my lathe chuck (like ally wheels) to a few thou' accuracy where I don't have a drill that suits. I could buy a 6 to 10mm drill set in 0.1 increments but it would cost around £85 and 90% of the drills will never be used, and the chances are my next job will need 10.3mm !
Also some existing bores on items that I am working on are slightly off-centre or gone eccentric so a drill bit tends to wobble rather than follow the true centre!

JRI wrote: Hi Kevin, I have chucks and collets up to 14mm so no problem there. My wish is to be able to turn holes in things mounted in my lathe chuck (like ally wheels) to a few thou' accuracy where I don't have a drill that suits. I could buy a 6 to 10mm drill set in 0.1 increments but it would cost around £85 and 90% of the drills will never be used, and the chances are my next job will need 10.3mm !
Also some existing bores on items that I am working on are slightly off-centre or gone eccentric so a drill bit tends to wobble rather than follow the true centre!

If you try to true up for example an off centre wheel bore, the boring bar would need to be so fine, it would tend to bend with the hole eccentricity so In that case i would use an end mill or slot drill in the tailstock chuck to create an centred bore then adjust the bore accuracy. You could search for small adjustable reamers
www.tracytools.com/1-4-9-32-adjustable-reamer?keyword=reamer
or make your own D bit from silver steel -

These are posh D bits - for a one off I would simply hacksaw and file the segment away. You could also make one with a pilot spigot to ensure accuracy

The following you tube offers more options for mini boring tools

John Axminster power tools sell drills in increments of .1
www.axminster.co.uk/axminster-m2-ground-hss-drill-bits-ax22813
The D bit works fine just grind it to exactly 1/2 diameter drill out to 6mm and slow feed if you just want a couple of holes you might get away without hardening it.