View Full Version : Boring

10-16-2001, 08:29 PM
Ok i got one. I have been racking my brain on this one and now i need some help. What it i want to bore a piece of metal that is loger than my bits. Suppose 6"-8" long. How can i bore through all the way? Right now i am using my bits to drill a hole 1/2" in dia. then i use my boring bar to enlarge the hole. What if i want to make the hole longer than my bits can go?

2nd Is there a quick way to make sure the boring bar is square with the work. I machine a part out last night and it seemed to be tapered. I am assuming my bar wasn't square with my work. Thanks in advance


10-16-2001, 09:59 PM
Since you don't have any hits yet, I'll give it a crack at an answer. Then you can hope something better comes along.
Question 1, I'd drill about half way through from both ends, then use a boring bar that uses the small bits. You can make your own as long as you need. The hole won't be perfectly aligned after drilling, so leave enough meat for cleanup.
Question 2, I would suspect your chuck, be it a three or four jaw. If it comes on and off the machine, chances are it is in less than perfect alignment. I spent the better part of the day once grinding the four jaws in 'perfect' alignment while on the spindle, and did real square work for awhile. Until I spun the chuck off to do something else. I THINK the D series hold their alignment better when they come on and off than threaded chuck backs, but I don't know that.
I've got a plan! Mind you, my lathe is pretty big, and the four jaw only handles down to 1/2" stock. I will spin on the chuck back, true it, mount the four jaw, true the body, then true the jaws as before, then NEVER take it off again. I'll buy a small three jaw and chuck it in the four jaw when I want to do small stuff. Whadaya think?

10-16-2001, 10:02 PM
OK, I'll take the gravy and leave the thinking to the other guys. :-) Can you turn the part around and drill from the other end? You may even be able to bore it this way if you're careful and if the hole isn't critical.

Nothing says the boring bar has to be square with the work. If you have taper, it's most likely caused by flex in the bar or the bar is dragging somewhere. Check for shiny spots or scratches on the bar. I'm assuming this is in a lathe? What kind of bar are you using?

OK, I just reread your post and it appears you're trying to bore a 1/2 inch hole 6-8 inches deep. Jeepers! I better leave this one for the experts.

10-16-2001, 11:30 PM
I am making the holes in a lathe. This all came up because i want to make inserts for my dad's tractor pins. Some of them are 6 to 8" long.

I have a 3 jaw chuck. The best i seem to beable to get it is within .002" true. It is a bolt on. 3 bolts hold it on. You mentioned trueing the body? How does one do that?

I love the idea about the 4 jaw and 3 jaw.


I have a little boring bar. a 3/8" shaft. I guess the deflection is from the bar. I had it extended as far as it would go, just to bore a 2" piece. Unfortunately that is all my toolpost will handle. For now. Everyday i learn something new...and realise i have to buy another tool to make things easier. Hahaha

Thanks guys. http://bbs.homeshopmachinist.net//smile.gif Spkrman

10-16-2001, 11:55 PM
I'm definitely not an expert here, but here's a try.
What about drilling the hole from both ends and ream it to size from one end. If you use a center drill on each end and then cut it with your 1/2" drill you should be able to get them to meet in the center fairly well .
I guess it depends on what size your after, but most reamers 1/2" and up are 8 in. overal length and longer. That won't help you on the 8 in. pieces, but it should get you up to 7".

Hope this helps
Mike Edwards

[This message has been edited by medwards (edited 10-17-2001).]

10-17-2001, 03:12 AM

You could buy a long Aircraft drill 12" or 18". You would need to support the drill in the middle to prevent flexing. A Morse Taper Shank Twist Drill might be long enough to do the job

Alternate method is drilling from both ends. This requires extra care in centering the piece. Otherwise the hole will not come out where you expect.

Make your own Gun Drill or D-bit just long enough to drill it.

I have used #60 6" Cobalt Aircraft bits to drill brass handles down the center 5" to hold the same bit I drilled with. Hole was within .001" of center when finished.

Your boring bar should be as large as possible while still allowing adequate chip clearance. It is very important to insure the tool is on center or you will have trouble. If your bar is not square, use a steel square to align it with the face of the chuck. It can also be clocked in with an indicator. IF YOU ARE THREADING WITH A BORING BAR YOU MUST DO THIS!!!

If the holes are not critical, just drill it.

Sounds like you have a wee lathe. My 7"x18" maximat7 has a 1 1/2"x8 TPI spindle with Class 7 Precision tapered bearings - the runout is only .0002". To keep the runout low I bought Precision steel chucks and machined the cast iron backplates myself as carefully as possible. The cast iron back plates are just snug enough that finger pressure seats it in the chuck register. It was worth the fidgeting - I think.

Hope that helps a little.

10-17-2001, 04:58 AM
Yeah, I hate boring with a bar and consider it as innacurate a way as is available to us. The bars flex, there's heavy loads on the cut so there's high heat with slow progress. I'd drill it, probably from both sides because long bits move around and work gets hotter than with shorter ones. Do an undersize and then ream it to your size.

C. Tate
10-17-2001, 07:36 AM
Take your part and drill with aircraft extension drill just looked one up in MSC it was about 10.00 for .5 dia. Then ream this hole. Boring with a .375 bar 8" deep is very difficult. If you can ream, it would be easier and much faster. I use solid carbide or heavy metal bars in my shop for this kind of boring work and they are expensive and fragile. The taper is a combination of the drilled hole being tapered and the bar flexing as it follows the hole. If you are taking more than a few thou. with the bar on each pass it will follow a tapered hole. It is not supposed to do this in theory but when you use this small of a bar as deep as you are many things can happen.

Good Luck,

10-17-2001, 08:05 AM
A boring bar doesn't need to be square to the work to give a straight hole. If you're really boring a tapered hole, your lathe bed is worn or twisted. See http://people.ne.mediaone.net/wasser/NEMES/RDMLatheAlignment.html for what I think is THE way to make sure your lathe is in alignment.

Boring is the only way to guarantee a hole is truly concentric with the o.d. of a part youi're turning. Drills can (and do) wander off-center, but a bored hole will be concentric. It will be parallel if your lathe is set up properly.

10-17-2001, 10:16 PM
I don't mean to be a smart ass but this is the way I do this job. First of all never try to bore such a small deep hole with a boring bar. I is not stiff enough. Drill the hole with an extended drill. If it must be as close to .500 as possible, drill 1/64 under size and buy a 1/2" reamer,chucking type or Morse taper. Another way to do it is to drill 1/64 under size and feed the 1/2" drill through after with of course cutting oil. You will be surprized how accurate that is. Be sure to start with your center drill to insure that there is no runout of the drill. It is a deep hole so you must keep clearing the chips and again, use any kind of cutting oil. Please let us know how you make out. If you want to know how to make neet little boring bars, e-mail me.

10-17-2001, 10:51 PM
Ah, some more hits, good. You bolt your three jaw on? So you've got a flange on the output spindle? I don't know much about the little lathes, most of the stuff I'm familiar with has a backplate that either screws on to a threaded spindle, or has locking pins that suck it up, called D series, I think. Either way, the backing plate generally stays with the chuck, not with the lathe. I've only been able to screw up the screw on type.
To do the truing, you spin on the backplate and make an index mark. Then machine it until it takes an even cut across the entire face. Generally there's an alignment flange or recess to deal with as well, but you get the idea, right?. Then you bolt the chuck on the back plate, machine face and OD true, then take a light pass on the ID, again, just cleaning and squaring it up. Then a witness mark, chuck to plate, to match later should you have to unship the chuck to clean the scroll or something. Mind you, I'm not real sure about any of this, just telling you what I did. For the jaws, I turned a piece of stock to the diameter I wanted to be most concentric when I got done. In my case, 1.250" which is nominal barrel blank diameter. Chuck and indicate it in close to the jaw, then wedge one jaw at a time in position with toothpicks and shims and whatever so it stays put. Then back off the other three, and gently grind the jaw face with a poor man's tool post grinder. (Mine's a Dremel with the cutoff wheel, that's about all the torque a Dremel can handle) Very slow going, and nasty, so protect your bed if you do this. You want them all to be the same radius when you're done, but the abrasive wears away, so it's a bit tricky. I took the last few passes with a new cut-off wheel, and worked to the same outfeed number on the cross slide. When its all done, the chuck is spinning in reasonable harmony with the center line of the lathe.
Want to check it, before you go through all this silliness? Chuck and center a stiff bar about 10" long that you know to be true, using the full length of the chuck jaw for clamping. Mount a dial indicator near the jaws, and one out about six inches. They either run out the same or your chuck is whopper-jawed. (gonna assume your headstock bearings are ok, cuz I can't help ya there)
Clear as mud, right? My work here is done!

10-23-2001, 07:09 PM
If you have a milling vice for your lathe mount the work in the vice on the cross slide and use a boring bit mounted in a mandrel running thru the work after rough drilling. Less deflection of bit. I bored a 10 inch 3/4 hole using this technique. Turned out OK. Still .001 large at center but I could live with it. Smooth sailing, Bruce

10-24-2001, 07:05 AM
Hey Gents,

I have been reading everyones posts. One thing i wanted to ask is when you all say reem out the hole. Does that mean i will have to buy a reamer that is the exact size for every hole i want to do. I was boring a 3/4 inch hole so i would dirll it 1/64 under, then use a 3/4" reamer to take the hole to the proper 3/4 inch diameter. Or can i just put a smaller reamer in the toolpost and gently push it to the wall of the part?

Here is one i thought of. For big holes, if you had a boring bar with two bits at oposite axes from each other, and everytime you wanted to make the hole biger you just expanded the bits the same amount. This would always keep pressure on both sides of the bar decreasing deflection. What do you all think?

Hey Gizmo. I am still re-reading your post. I kind of got lost for a newbie but once i get it i will drop you an email

Later Spkrman

10-24-2001, 02:01 PM
You need a specific reamer for every size of hole.

I think your two-bit boring bar arrangement might tend to chatter pretty badly. It would also be next to impossible to extend the cutters "the same amount." But maybe I'm imagining your idea incrorrectly.

10-24-2001, 07:28 PM
Hmm, that sounds like a drill to me spkrman.
SGW is correct, a standard reamer cuts one size hole.

10-24-2001, 09:53 PM
Yeah it would be hard to extend the boring bits the same amount and as snorman said it...that is a bit. I was just woundering a cheap, and safe way to make a bit that would cut holes to exact sizes. I haven't come across any sets of reaming bars. Do you have to buy them individually?


10-24-2001, 10:52 PM
Well, you can buy reamers in sets but they ain't cheap. Forget about resharpening unless you have a tool grinder. Boring bar bits are cheap and do a pretty good job. Plus you can make your own bars.


10-25-2001, 10:15 PM
Reamers do produce a lovely smooth hole - provided you don't do something stupid like turning it backwards (it is not a tap) in a hole. Reaming holes should be reserved for dowel pins or any hole that actually needs a smooth bore (such as a shaft housing or bronze bearing, blah, blah,...)


10-26-2001, 09:30 PM
Just curious as to what you are doing with the tractor pins? I've got a couple of tractors and I go through pins on a regular basis. In my experience they are made to tolerances you can measure with a yardstick.

James Kilroy

10-27-2001, 07:39 PM
I know that pins in tractors don't have tight tolerance, but i figured i would learn the right way befor doing tons on mistakes. Also the problem of boring a long piece on work was puzling me for a while. The input i have gotten from everyone has helped emensly. Thanks everyone.


11-01-2001, 08:46 PM
If you want long smooth small holes bushings a reamer is the way to go, start the project with oversize stock on the outside diameter, drill and ream whatever size hole required & then turn the OD to the specified size between centers on the lathe. Works everytime.


11-01-2001, 10:50 PM
u can make ur own d bit style 1/2 reamers from drill rod for pennies ....they will be as accurate as u make them.....slow & single edge cuts clean!!!!
best wishes

11-02-2001, 04:12 PM
so docn8as. Can you email me telling me how to make those d-bits out of drill rod? The only drill rod i know of is the type used to make hole in bedrock for blasting. Let me know. This sounds interesting


11-02-2001, 10:41 PM

Guy Lautard's "Machinist's Bedside Reader" describes, with enough detail how to make a D-bit and heat treat it. They are "not fast" but provide a quality hole for minimal cost.


Steven L Jones
11-04-2001, 10:57 PM
one way to drill a hole longer than the drill is to turn the shank of the drill down to a smaller size say 3/4 " long then find a length of steel slightly smaller than the the drill size drill a hole in it to match the turned down portion of the drill and either drill and tap for a small set screw or braze it on,now you have a longer drill.the reason that you are getting a tapered hole could be that the boring bar is being flexed over due to the tool pressure of the cut,due to the slender size of the bar compared to the length of the hole being bored.which is a common problem,so take several passes thru the hole without advancing the depth of cut.i call it" making some dry runs " trying to bore a 1/2" hole to a bigger size 6 to 8 inches long with a boring bar just big enough to enter the 1/2" hole is a real exercise in futility.
good luck. Steven Jones

11-04-2001, 11:15 PM
Way too many Steves on this thing imo. ;-)


11-06-2001, 12:54 AM
I have a few other friends with the same first name - it is a riot when we get together and BS.

"This is for all the Dave's I know" - The Kids in the Hall

Dave, Grand Imperial Pooh-Bah of the International "Dave" club