I now have a HF 7x12 mini-lathe and a QCTP with a 1/2in boring bar holder. I would like to get a boring bar primarily to use for boring operations. I understand that some bars can be setup for internal facing operations; that sounds nice but I don’t think I 100% need that right this moment. I would like a 1/2in by 7in bar so that I can attempt boring a 2D sized Maglite.
It seems that indexible boring bars are the thing, but I don’t have a handle on the different types of insert or angles mentioned in listings for boring bars.
Thanks for any advice or pointers to existing write-ups.
I use the largest bar that I have for the hole I'm boring for minimum flex. I only have three bars.I use the same tips on whatever material I'm machining. On larger holes I have used in the past a piece of 1'' diameter 120 round bar with a hole drilled in the end big enough for a piece of square tool steel held in with a bolt and centered. I'll take a picture of something similar and post it up. If I can save money by doing things on the cheap I'll do it.
I hope this is some sort of help wight not that I don't think Helios is wrong.
Small boring bar in a home made holder used for aluminium and steel.
The next one is a piece of hex bar for no other reason that I had it kicking around. The tool steel has been ground to machine an internal circlip groove. There is no reason that this with a bit more grinding could also be used as a boring bar.
And finally what I use for internal threads. Again its a piece of square bar with a long length of 3'8'' square tool steel ground up to suit machining internal threads. Good luck with the machining.
Thanks MRsDNF. What type of insert is that in the first bar you posted? The whole assembly looks similar to this Shars item # 404-1962 I’ve been eyeballing.
A 2D Maglite (5in long?) will be tricky to do on a 7x14 lathe, simply because you’ll need a very thick boring bar to avoid flexing at the end of your cut. There’s a rule of thumb around somewhere along the lines of max length of cut = no more than 3 (or 6?) times the diameter of the boring bar. That’s probably for steel though, so you might be able to get away with a bit more in aluminium. I think that your best bet would be a DIY bar + ground HSS bit through the end, like the one MrsDNF showed, that way you can get the thickest steel bar you can find and somehow attach to your lathe
Whatever you do though, try and support the end of the work with your steady rest, make light cuts (HSS is way better for this than carbide) and do lots of spring passes so that you don’t get a tapered bore. Oh, and avoid those brazed carbide boring bars like the plague, they’re complete junk. The HSS ones aren’t much better, but at least you can grind and stone the correct profiles on them yourself.
Thanks, we’ll have to see. Getting a giant bar attached to the lathe could be fun. Of course at some point having a giant steel bar hanging off of it would overwhelm my little cross slide and compound, so I might have to stop at 3/4in or so…
And crap, I’d forgotten I needed to buy a steady rest.
