# Small Diameter Boring Bar



## benster (Jul 30, 2015)

I'm trying to bore a hole 3/8" Diameter to a depth of ~1". The problem I'm running into is all the boring bars I've been able to find online for that diameter have a maximum bore depth of 3/4". I've tried grinding my own boring bars out of 1/4" HSS bar but grinding the bar is taking an obscenely long time, partly due the hardness of HSS as well as the fact that the blank heats up fairly quickly when removing such large amounts of material. I was thinking of turning the boring bar profile out of CRS and brazing a carbide tip but this seems excessive. Any ideas?


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## purpleknif (Jul 30, 2015)

Reamer ?  End mill ?


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## cwelkie (Jul 30, 2015)

I have had success with turning a chipped tooth slot mill (2 tooth end mill) into a very serviceable boring bar.   Most 1/4" or 5/16" slot mills will give you the inch needed.  Just means grinding away clearance from the unused (chipped) flute.  That's a lot easier than starting from scratch with a lump of tool steel.


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## benster (Jul 30, 2015)

purpleknif said:


> Reamer ?  End mill ?



My Taig lathe doesn't have the length needed for a 3/8" reamer.

Would a regular 3/8" end mill make a clean enough cut? This is for a cylinder bore. I might try grinding down a slot mill.


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## goldstar31 (Jul 30, 2015)

Dead simple!  Get a piece of 3/8th round and grind almost half off. Then grind a lead of 5 degrees and you have a D Bit

I used to do much smaller diameter but 13" long in silver steel rod. 

Classical bagpipe making tool.  Works a treat- hope that this helps you


Norman


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## chucketn (Jul 30, 2015)

What material are you trying to bore? I have made small boring bars out of Allen wrenches. Cut the short leg off at required length to enter starter hole, grind cutting edge and go for it.

Chuck


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## benster (Jul 30, 2015)

Material is brass. I really like the allen wrench idea and I have tons on hand. I'll give that a go today. Thanks for the suggestions all, I'll post the results this evening.


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## benster (Jul 30, 2015)

goldstar31 said:


> Dead simple!  Get a piece of 3/8th round and grind almost half off. Then grind a lead of 5 degrees and you have a D Bit
> 
> I used to do much smaller diameter but 13" long in silver steel rod.
> 
> ...



What material round, HSS?


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## goldstar31 (Jul 30, 2015)

The easiest is obviously Silver steel( drill rod) but you will have to temper it. I used silver steel for Pipe making but perhaps hss will be easier for you. Grind 1" back and leave a couple of thous befiore you half it. 

The 5degree will be OK for most steels etc and if you are careful, the side will not need to be sharpened.

It's sort of a cross between a reamer and a drill.  It's a tool long forgotten but works or worked for all the old boys.

Hope that it works for you.

NB

For those who say that their lathe is not long enough, take the poppet part out of the tailstock and put a drilled bar in instead and work from there- A little at a time and remove the swarf before it jams. 

Any old book on pipe making has this in. Not my invention or anything like that.


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## kvom (Jul 30, 2015)

I would skip the lathe and boring bar and use reamer on a mill.

Brass is pretty soft so I imagine you could make the d-bit from drill rod and it would work un-tempered if you don't have a torch.  But the same applies to the allen wrench, which is an idea that I hadn't heard before.


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## barnesrickw (Jul 30, 2015)

I have a Taig also.  I bought a set of HSS blanks at Harbor Freight (I know, shame on me) and ground the 1/4 inch round blank into a boring bar shape.  To hold the 1/4" tool, I set the tool holder post square on the lathe table and drilled through it and drilled and tapped a hole above it for a 10-32 screw.  Perfectly centered, works very well.


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## petertha (Jul 30, 2015)

Just an opinion & maybe others have more experience - but you don't really need the long stock shank of a typical reamer if that's the issue. Consider lopping it off. You would be sacrificing that particular cutting tool to make a 'shorty' & might lose a bit of centering float, but a reamer is excellent for consistent finish & dimensional control. 

I've only used straight reamers thus far (blades run along the axis). If your bore has any cutaways (like porting windows or through holes) the spiral flutes are supposed to be better I believe.

I haven't had great success using end mills as finished holes plunge-mode even with close diameter pilot holes. Maybe its my tools or technique. For one thing, I think they have a +/- tolerance unless you get specific ones if that's an issue. Also (guessing here) unlike drills which are ever so slightly tapered, if end mills are parallel it would be hard to obtain truly cylindrical hole top to bot, no? Also there is some max ratio of depth to diameter. Not sure how all this relates to your requirements though.


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## mu38&Bg# (Jul 30, 2015)

chucketn said:


> What material are you trying to bore? I have made small boring bars out of Allen wrenches. Cut the short leg off at required length to enter starter hole, grind cutting edge and go for it.
> 
> Chuck



This is an interesting comment. I recently saw/heard that hex keys are made of S7 which is tough stuff. I'd guess you have to have a decent brand of tool to start with.

I've bored 1" deep in aluminum and 12L14 with a 3/16" inserted steel boring bar. This is well beyond suggested use. Light cuts, and steady feed will get it done. Might be tricky without power feed.

greg


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## chucketn (Jul 30, 2015)

I use a large biscuit tin to hold my extensive collection of Allen wrenches. I looked carefully through my collection to choose the Allen key that could be sacrificed for a boring tool, as I did not want to destroy one that had a specific use.
I had to cut the short arm with a Dremel and a reinforced cutoff wheel, as a hack saw wouldn't cut it. As the hack saw, with a new blade, skated on the hex key, I assumed it was hard, maybe not... I ground the boring cutting edge on a bench grinder. Worked for me...
As they say, YMMV, Your Mileage May Vary...

Chuck


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## gus (Jul 30, 2015)

Found it easier to drill and ream 3/8 hole. Bored and ruined 2 pcs before I gave up.
Will try boring again later.


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## goldstar31 (Jul 31, 2015)

Gus, I think that the boring problems which you are experiencing is all too common on on 'light lathes' and really farting about with most reamers is on a hiding to nothing. OK, I have reamers and the facility to sharpen them and whatever but most are tapered and, I'm sure that no  one wants a tapered bore?

Again, you can get a scrap Allen key or even a broken drill or even a Bicycle spoke and broken centre drills but the odds are that - well,, you know!

The only way to achieve 100% 'perfection is to bore between centres. It doesn't matter a hoot if your tailstock is 'out' by a thous or a week, but the bore will be round and parallel. Indeed, if you ever get around to making a Quorn you need to bore TWO  holes in two castings- dead in line and three a dead inch and the fourth an inch plus 3 thous. 

I did mine on a somewhat rickety old Myford and none of this milling machine nonsense. I hadn't a mill and I simply could not afford to buy one. I finally made a Ned Westbury from home made castings full of holes! 

So back to boring bars, well I made TWO because the Quorn needs another bigger hole and I used the George Thomas design in his Model Engineers Workshop Manual. GHT also debunks reamers and describes making ordinary conventional boring tools and those for screwcutting. 

Frankly, you follow him and succeed.

I followed GHT and Martin Cleeve and added Tom Walshaw as Tubal Cain and Dennis Chaddock. All were tool makers of exhibition standard both full size and in models. I simply mumble my appreciation.

Let me know how you get on

Norman


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## Blogwitch (Jul 31, 2015)

If your are going to try boring smaller sized holes, the smaller you go the more rigid you need to make the bar, and of course you will lose length as well.

I use solid carbide tools that will only allow me to go as deep as 1" for 1/8" diameter holes, but for even smaller, I have used small twist drills ground up to use one edge with a flat end on the drill to bore out to 3/32".

Arc Euro do a nice set of HSS boring bars, second from the bottom. They don't need to be bent as much as that, so a bit of drill rod (silver steel) with a small bend on the end could easily be made into a boring bar. Bend when soft, harden, then grind up, I reckon you could get away with 2mm bar, so allowing you to bore to say 1/8". But at least the picture shows what you should be aiming for.

http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Boring-Tools

John


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## SmithDoor (Jul 31, 2015)

Try use a bar for mill machine boring bars
http://www.shars.com/products/cutting/boring-bars
If I need very small one I use drill bit 

Dave


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## goldstar31 (Aug 1, 2015)

I'm sorry but more important family commitments have precluded a reply until now.
Initially, I have to admit that I have been involved in the drilling of long( and I mean long holes) since about 1941 when I met a Wilfred Alfred Cocks of Ryton, then in County Durham. My father had made things for his Blackgates Museum in Newcastle upon Tyne. It's as old as that. Mr Cocks was many things, a philanthropist, a watchmaker and bagpiper maker and a collector of things like Bronze Age skeletons, graves and trepanned human heads. In addition , he ran a youth club in his own home for us penniless lads in a depressed mining village - in wartime. With scant coins and shortages we made model aircraft and with his encouragement, I made my first 'jet engine' at 14 as a pupil on his friend's battered Myford which was too rough to be commandeered for war work.
I go back a lo------------------ng way. 
So boring holes is not exactly new to me.
Northumbrian small pipes  are much much older. There is a stone copy of a set on the walls of Hexham Abbey which was probably made out of- the Roman Wall. I've got a bit of Wall as my boundary wall.
So long thin holes have been made and very successfully with obviously limited tooling. 
Mr Cocks( And a J.F. Bryan) later wrote up a book on making the instrument and there are descriptions of how D Bits were made and the rest of the metal work for what was then a resurrected musical instrument. Mr Cocks died and his collection of stuff is either in the Blackgates Museum or his Bagpipe Museum- which contains drilled holes from many other countries. Drilling holes is NOT a thing which is exclusive to a few Northern English or Scots with boring done on Napoleonic  bayonets( I've done it)

For those who want to access a more modern approach and with more sophisticated machinery, a Mr Mike Nelson of Cambridge has written on how he has made D Bits and so on.
Oddly, I somehow suspect that he is or was a member here.

So you have the story from - the beginning of time.


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## tornitore45 (Aug 1, 2015)

You have received many alternate solutions already.  I just want to address your grinding problems.

If the grinding generates too much heat, most likely you have the wrong type of wheel.
The gray wheels that come with a bench grinder are not the right type for HSS, you need a softer wheel, usually white in color, with a hardness around H or J.

Still heat is generated, to that respect you must know that HSS does not loose its hardness even at the blue color.  The limitation is in your hands.  Since I grind lots of tools bit I have made holders. A bar with the right hole size and 3 set screw.  The holder give me more control and stay cool much longer so U do not need to dip so often.


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## Tin Falcon (Aug 2, 2015)

First of all you have been given lots of otion and I will attempt to not repeat to much. 



> I'm trying to bore a hole 3/8" Diameter to a depth of ~1". The problem I'm running into is all the boring bars I've been able to find online for that diameter have a maximum bore depth of 3/4".


There is a very good reason for this . The rule of  THREE that is a steel boring bar should not stick out more than three times its diameter. This goes for work sticking out of a chuck and lathe tools as well.  And less is better. And do not feel bad if you do not know this it seems to be some dark hidden secret barely talked about much less published. 
As bogs pointed out the answer to the above limit is solid carbide. carbide is stiffer so the length limit is 7 times the diameter. 
So search MSC, enco, travers etc for solid carbide mini boring bars. 








> I've tried grinding my own boring bars out of 1/4" HSS bar but grinding the bar is taking an obscenely long time, partly due the hardness of HSS as well as the fact that the blank heats up fairly quickly when removing such large amounts of material.


first of all a quality cobalt bit may be in order here. second use a good wheel . The gray import wheels are ok for General purpose grinding and a quick touch up but white wheels are a lot better for HSS . If you really want something that will run cool get a norton blue wheel. A bit pricey at $30 for one wheel. but they were developed to grind tools fast and cool. Also use a grit coarse enough to remove some material. Then a finer grit to finish and i do the last bit by hand on  fine oil stone. 

Tin


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## goldstar31 (Aug 3, 2015)

As most will have guessed, I make most of my tools whenever possible. I tend to forget what other people are buying- and whether things are correct for the purpose intended.
Consequently, I am wondering whether our poster is getting the right information in buying stock Boring bars and whether they are correct tools for brass.

Brass is ideally turned with 'negative rake' as I am reminded that when I finish this little tool holder for my Kennet tool and cutter grinder. 

I leave it there.

Norman


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## tornitore45 (Aug 3, 2015)

Brass is slippery. I never tried Negative rake but most likely will result in not "biting" right.
Positive rake is not recommended because of self feeding, I always got good results with zero rake and can reuse the same tool for small cut on steel.


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## goldstar31 (Aug 3, 2015)

It came to me following old experience with a hand held graver. Having said that, I tend to diamond hone tools rather than use something straight from the grinder. Maybe it is a 'My' thing but it seems to be common on a lot of carbide inserts. I have to pass on them- sorry!

Norman


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## MachineTom (Aug 4, 2015)

I use solid carbide for a job like that. Micro100 is brand, get a size of .31 with a 1.2 length. Ebay is a good source. The can be sharpened with diamond wheel. Cuts stainless Ti AL and other stuff fine.


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## benster (Sep 5, 2015)

I ended up using a boring bar that claims the minimum starting hole is 3/8" but I drilled a hole to 11/32" and was able to get the boring bar in and bore to 3/8".


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