Anyone ever turn down a boring bar?

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theKbStockpiler

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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!
 

middle.road

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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?
 

theKbStockpiler

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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.
 

Downunder Bob

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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.
 

middle.road

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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
 

Tim9

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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.
 
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theKbStockpiler

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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?
 

Downunder Bob

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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
 

Ulma Doctor

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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
 

mickri

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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.
 

Downunder Bob

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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.

A .010 cut should be fine with a 7/16 bar. How much stick out do you have. To get that much spring I would suspect one of a few possible problems. Not enough clearance, a cutter that is not sharp, too big a radius, cutter not on centre line, Too much stick out, poorly supported and clamped bar. Have you checked all these things. Some photos might help.
 

matthewsx

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Hi and welcome to the forum.

I was gifted a bunch of reamers so I didn't have to spend the $$ on them. I don't think I would want to trade them for boring bars though, two different tools. Yes it is possible to get very precise hole sizes with a boring bar, but a reamer does it in one pass. I would think reamers are sufficiently "old school" and would have been used back in the day as it were.

I would highly recommend the OP find the lathe he is planning on working with and try for one that comes with some tooling included. Once we know what machine you're talking about and the particular job involved it's much easier to give solid advice. I've found that adding a variable speed motor and QCTP have made my 100-year-old lathe far more functional and I'm pretty sure that the original owner would have agreed. I use both carbide and HSS tools and find that each has their place, also many things we think of as modern do go back quite a while.

I love watching Roy Underhill in "The Woodwright's Shop" on PBS and marvel at some of the things people were able to do hundreds of years ago. Modern blacksmiths practice many ancient arts with metal as well, and I know we have a few members who operate line shaft shops so there's plenty of "old school" knowledge still out there.

Get yourself some "old iron" and start making chips....


Cheers,

John
 

theKbStockpiler

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Thanks for all of the advice. It's appreciated!

I'm still using a imaginary 9" south bend until I can source one. Lol There's what looks like a Heavy 10 for sale near me but that's it for now. https://rochester.craigslist.org/tls/d/mumford-metal-lathe/7043653695.html

For those that have not looked at a piece of merchandise far away in a craigs list ad, be aware that the sellers usually misrepresent the condition and don't care what so every if you have to travel a long ways. My own policy is I won't travel far to look at some thing because I wasted enough time and gas to build the stereotype that craigs list sellers are liars.Lol.

As far as bench grinders go I was trying to find a 6" that has a narrow motor and good rests on it that is priced for the home shop. The issue here is that all of the 6" I can find that have a narrow motor housing are under 1/2 hp. Here's a dayton that is a 8" and does not look massive. https://www.grainger.com/product/DAYTON-8-Bench-Grinder-467L84 Seeing the 8" Delta in person at lowes was intimidating. Lol. If my 4 1/2" hand held grinder will take a lot of metal off pretty fast ,why do I need a 3/4 bench grinder? Dewalt has a 6" with good specs but the motor housing is big. I'll keep searching the net though. I'll most likely get the dayton because its about as heavy as a 1/2 hp 6".
 
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mmcmdl

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A boring bar should take whatever cut is dialed in . You're L over D is the limiting factor when it comes to spring in the bar . The problem with very small bars lies within the SSPM , as most smaller lathes aren't capable of 10,000 rpm .
 
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