Anyone ever turn down a boring bar?

theKbStockpiler

Registered
Registered
Joined
Dec 12, 2019
Messages
9
I want to go old school as much as possible and approach a task using HSS cutters if possible. Has anyone ever reduced the diameter of a boring bar that holds a HSS square cutter? This is all hypothetical and am still shopping for my first lathe.What if I turned down a 9/16 bar to 1/4 and used it just enough to get a 9/16 to fit?
Thanks for your expertise!
 
Going to need to see some pictures on that one if possible. 1/4" might be a bit weak for boring.
What kind of tool post?
 
As I want to be old schooled based I would be using a lantern tool post. I don't want to be a home machinist that can't use a bench grinder,Lol. I'm hoping to also be less dependent on reamers. This is hypothetical so all of the pictures are in my head. I was wondering if the diameter around the square hole gets smaller it would not hold the cutter anymore. The advantage here would be to use a smaller drill bit to get the bore to be established , then use a mini boring bar to get the bore to size and or maybe use a bigger bar after the smaller one roughed it out big enough. Maybe the reamer use could be skipped because the bar's cutter leaves a better finish than a drill bit.
 
Yes, you can reduce the dia. of a boring bar, but there are limits first you have to look at what size cutter it has and realise that as you reduce the diameter you will also reduce the square hole, and lose clamping efficiency.

You can make a decent bar out of an old car drive axle, talk to a local car mechanic they throw them out all the time. you will probably need a carbide tool to cut it as they are quite hard, HSS will cut it if you go very slow and use cutting fluid. you can try using old broken centre drills as cutters, that way its easier to make the bar as you only need to drill a hole.

You can also weld small bits of HSS to the ends of a bar, done that many times to make a quick cheap bar using up old bits of HSS that are too small for any other use.

Also remember that as you reduce the bar dia. you must also reduce the length of stick out. to prevent bar flex and chatter. So in reality you need quite a range of bars.

You don'y say what size your lathe will be,

I generally advise with buying a lathe ,in fact any machine, get the largest you can comfortably fit in your shop space, without going overboard, also consider what work you intend to do, and always buy the best quality you can afford.

Good luck.
 
If you're going to stick with lantern then also get a 4-way. They're cheap enough and possibly fit a 9/16" DIA. bar without any problems.
Depending on lathe size...

P1060171-r.jpg...1577235058452.png
 
Lanterns have their place....usually in a drawer until that rare case arises where it just is the only way to get a certain cut. That said....QCTP ( or 4-ways as above) is much more ridgid. Less chatter and much quicker and repeatable.
There’s a reason everyone got away from using lantern tool holders.
 
Last edited:
Thanks for the replies. Well it does seem more evident to me that you end up with a lot of tool holders/posts and or methods to hold a cutter now. A carbide cutter would be better to start smaller bores because they would put less force on the holder. I still want to have the capacity to use HSS for learning and back up though. I don't want to be abstracted from the basics and be useless if I get into a pinch.

How about some advice on whether to get a 6 or a 8' grinder. I was going to get a 8' but I saw one in person today and they are mighty big. I'm wondering if I would ever have a benefit to having the 8 over the 6. I was told that their are more wheels available for the 8 but unless I go to welding shop or industrial supplier I would most likely have to order it online anyways. A 8' creates less of a arc naturally as well. Is it worth having a 8' grinder?
 
As far as grinders are concerned a six inch usually good enough for most hobby applications certainly up to a 12 inch lathe, and for HSS tools up to half inch. An 8 inch is fine for larger machine shops and welding shops. You can get plenty of wheels for 6 inch. I would suggest you start with a AL oxide (White) 60 grit. and if you want to use brazed carbide you'll need a silicon carbide wheel. otherwise put an 80 grit on the other side for finishing. Having said that I've always found 60 was fine enough. I know I'll get plenty of arguments on this
 
i would personally go for an 8" grinder, but i do a lot of work with grinders- your results may vary
i can leave the guards on and still grind fairly large objects
with a 6" pedestal grinder this is not possible
i personally use Gray ALO3 wheels 60 grit for roughing HSS and hone with 120 grit CBN
 
Back to the original question. My lathe came with a set of boring bars from 3/16 OD to 7/16 OD. They use a 1/8 round HSS tool bit. The set included two small v blocks that fit the lantern tool post that came with the lathe. I have only used the 7/16 OD boring bar. It has a lot of spring. And I mean a lot of spring. For example if I try to take a .010 cut with the 7/16 BB the actual cut is .005, maybe .006. The smallest hole I have been able to slip the 7/16 BB into is 5/8 ID. I don't have a 9/16 drill. It might fit into a 9/16 ID hole. It won't fit in a 1/2 ID hole. Based on my very limited experience I think that you could clean up a drilled hole taking very light cuts. Remember that a drill cuts a slightly larger hole than the size of the drill. Back to your 9/16 example you would probably need to drill a 1/2 or maybe 17/32 hole to end up with a 9/16 hole.

X2 on the 4 way tool post holder. Also the norman style qctp was designed in either the late 1800's or early 1900's. That's still pretty old school.
 
Back
Top