# cylinder boring problems



## hammers-n-nails (Jul 12, 2009)

i bored the cylinder for the beam engine today and had the same problem as i did when i bored my first engine. the problem is that the boring bar seems to be pulling itself into the metal causing "rings" in the cylinder wall so its very uneven and has an overall poor finish. i think i will be able to hone it out and get it good enough but this isnt going to be the last cylinder i bore. i took .0025-.010 cuts with a speed of 100-150rpm and a quill feed of .002-.006/revolution i also played with the rake angle of the bar but none of these things seemed to have much effect, is there something im missing or is my chinese boreing bar to blame?


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## Davyboy (Jul 12, 2009)

Hello hammer. We'll need a little more detail to help. What *material* for the cylinder? Some metals are notorious for bad finishes. Also, the *size of bore*, and tool type *carbide or HSS*? The rpm will depend on "Surface feet per minute", depending on bore size, and tool type. The phrase 'quill feed' in your post sounds like a milling machine, so we can build from there. I'm sure there will be qualified help along shortly.....Any chance of reaming the hole? (My reamers only go up to 1/2".) 

DB


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## justlesh (Jul 12, 2009)

The actual problem may be the cutting edge has burnished a little and when you think its pulling itself in is when its actually cutting where when it's not is when it is actually rubbing. Davyboy is right, more info does add to better conclusions.

Les


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## tel (Jul 13, 2009)

Yep, more info needed, but it sounds like your boring bar is _too light_ - you need to use the heaviest one you can get in the 'ole.


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## Philjoe5 (Jul 13, 2009)

Hammers,
Are you getting taper in the your bore?

I have a few steel (CRS 1018) cylinder blocks Ive bored that have the appearance youre describing. Ive had reasonable success using these in compressed air engines as long as there isnt a taper in the bore that exceeds 0.001 over a length of 2.5. 

Over time, Ive found I can eliminate the rings by using the slowest feed rate on my lathe which happens to be 0.0015/rpm at a spindle speed of 150 rpm. 

I have an inexpensive boring bar with indexable inserts and near the end of the boring operation I use a new edge on the insert. I can tell if Im going to get a good result when I make a free pass (no change in crosslide setting) and get a very fine hair chip curling out of the bore. A second free pass produces no cutting that I can see. 

The tool cutting edge has to be on dead center in my setup or I get poor results, another point to check.

Also Ive found a good sulfur containing cutting oil helps for finish.

In my usual stream of consciousness I hope I havent confused you (LOL)

Cheers,
Phil


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## Mainer (Jul 13, 2009)

Make sure there is enough side clearance on the boring bar so it doesn't rub on the curved cylinder wall.
Sharpening a boring bar can be tricky. I've got some Everede boring bars that accept small triangular bar HSS inserts and work very well, but it took me a while to figure out how best to grind them.


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## IanN (Jul 13, 2009)

Hi,

There are three distinct types of boring bar profile and the three tools are designed to do different jobs. You will not get the best results if you use the wrong tool in the wrong application.

To identify the type of boring tool it is best to look at the tool tip from above and look at the cutting edge formed across the end of the tool. The cutting edge may go from the tool tip and slope away from the headstock (positive lead), it may slope from the tip towards the headstock (negative lead), or it may be at almost 90 degs to the lathe axis (zero lead) - see the picture here:

http://www.criterionmachineworks.com/Graphics/leads.gif

Positive lead tools are designed for facing - i.e. to cut from the centre of the bottom of a hole towards the outside of the bore. They are used to produce flat bottomed blind holes or shoulders (in bearing housings etc.)

You should never use a positive lead tool to cut down the length of a bore. Boring tools are (by nature of the work they do) relatively thin for their length, so thet tend to be flexible. If you cut the side of a bore with a positive lead tool the tip tends to dig in and the tool bend away from the axis of the bore which produces a bore that is narrower at the entrance and wider inside. If the tool does this then springs back out and then repeats the cycle it could give the effect you are seeing.

To cut the side of a bore the best tool shape has negative lead. This can only be used if the tool can pass right through the bore as the front end of the tool is in front of the cutting tip. The slope of the cutting edge flexes the tool towards the axis of the bore producing a hole that is narrower inside than at the entrance - repeating the final cut several times at the same setting will correct for this "spring".

The zero lead tool is a compromise - it is not the best profile but it lets you bore the side of a blind hole, or bore to a shoulder. These tools are normally 91 degrees to the axis rather than the theoretical 90 degrees suggested by the name "zero lead".

For photos of 91 degree zero lead tools see:

http://www.greenwood-tools.co.uk/ishop/728/shopscr22.html

For positive lead see:

http://www.nmri.go.jp/eng/khirata/metalwork/lathe/drill/bit01_big.jpg

I couldn't find a pic of a negative lead bar so here is a pic of one of my boring bars with negative lead:

http://i219.photobucket.com/albums/cc210/ian-new/boring%20bar/plan.jpg

Ian.


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## Florian (Jul 13, 2009)

Alright so far...

What has also a very big influence on the surface quality is the shape of the cutting edge. If it is a sharp edge, the surface will be grooved more than if the edge is rounded. 
It also has a very big influence how sharp the tool actually is; what rpm you work with, what material you are machining. 
For brass, its good to have a very small chip angle (0 to 10° depending on the type of brass)

Anyway; you won't get perfect bores with boring. 
There is a very good trick you can apply: Take a piece of round hard wood and turn it to the cylinder diameter but with very few oversize. You need to be able pushing it into the bore with very few force. (but it should not slide by itself!)
This is your wooden lapping arbor!
Then put a few polishing compound and some oil onto the wooden arbor, chuck the arbor on the lathe or mill and lap your cylinder with roughly 200-300 rpm. You should hold it with your hands (if it sticks on the arbor, just let it go and nothing will happen) Move it back and forth during the lapping process.
I achieved mirror-like surfaces in brass!

Florian


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## hammers-n-nails (Jul 13, 2009)

ok i will try to bring my previous post up to standard i am boring on a mill i dont know what type of boring bar you would call it but im going to try to put a picture of it on here, it does have a carbide cutting edge that appeared to be fine but last time i used it i ground it to a point. i have ground a small radius on it since my last post but didnt have a chance to try it. the cylider is steel as you can see but i couldnt say what alloy, in finishing the outside and drilling it i saw no indication that it was abnormally hard it produced long curls a36??? the bore size is 1.000" i suspect that this problem is as simple as having the wrong cutter profile but heres some pictures see what you think i apprecciate all your help you guys are all ive got i dont know anyone locally that is a machinist so ive been figuring this out as i go.

http://s827.photobucket.com/albums/zz200/knilhcaz88/?action=view&current=012.jpg
http://s827.photobucket.com/albums/zz200/knilhcaz88/?action=view&current=014.jpg
http://s827.photobucket.com/albums/zz200/knilhcaz88/?action=view&current=015.jpg
http://s827.photobucket.com/albums/zz200/knilhcaz88/?action=view&current=018.jpg

there are a few mor pics f the same thing you can see them all at

http://s827.photobucket.com/albums/zz200/knilhcaz88/

again thank you guys for your input, i need it


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## hammers-n-nails (Jul 13, 2009)

let me try that again


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## Loose nut (Jul 13, 2009)

A better way to do it is to machine the bore until it is a few thou. undersized, .005 would be good, then ream it to size and finish by lapping it. If it is a "non-standard" size bore, when there isn't a reamer that will finish it, adjust the diam. to the nearest reamer size, it won't be very much and the piston can be altered to suit.


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## rake60 (Jul 13, 2009)

Boring with a mill is tough.
The eccentric motion of a boring head can be very 
difficult to manage on a small scale. 
Using a lathe would be a much better option.

Rick


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## Davyboy (Jul 13, 2009)

Hi Hammer. Oh yeah, I think we've ALL seen finishes like that. :'( I'll bet you can feel the ridges with your finger. Looks like honing or lapping are in order. Your original post said 100-150 RPM. Much too slow! 153 RPM @ 1" dia= 40 SFM. For HSS cutters, I would run at 80-100 SFM, about 350 RPM. You could easily double that with carbide. Limitations will be rigidity of machine, balance of the boring head setup, and vibrations in the tool. 
 Many charts are available for direct reading Surface Feet per Minute to RPM for a given diameter. Formula for calculator is:  SFM= ( (PI x dia)/12 ) x RPM
A couple more general tips:
* A36 steel is hard to get a good finish. Even cold rolled 1018 would be better. "Generally", harder, tougher alloy steels tend to give better finishes.
*"Generally", HSS tools give better ( light ) finish cuts than carbide. Carbide needs a couple thou minimum to work. Your .0025-.010 depth of cut probably OK.
*Good cutting oil will help, brush some down the bore to stop the metal from welding to the tool tip. Do this BEFORE you start the cut!!!!
*Sometimes a sharp corner on the tool, or a minimum nose radius leaves a more consistent finish, although you'll still need to lap it or hone it. 
*Generally I hone a nose radius on my tools, by hand, much easier to control than a bench grinder.
*Don't be discouraged, you've got it on the run, just need a little tuning up and practice.

Good luck,  DB


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## hammers-n-nails (Jul 14, 2009)

yes i agree loosenut that would be alot easier but i connot justify a minimum of $30 that it would take to get a 1.000" reamer to my house since it would be fairly unlikely that i would need one that large again in the forseeable future, that is if a fair result is possible using the tools i already have.
davyboy
yes you can feel the ridges with your finger they are DEEP. the reason for going ony 150rpm is because of what i belive rake is talking about that being because the boreing head isnt balanced turning it up faster causes alot of vibration.
*#1 good tip i had noticed that to a certain degree but nothing like this, do you know of some sort of manual or something giving the properties of various alloys?
*#2 yes i have a soluble oil pump on the machine but i couldnt say just what kind of oil, it came from grizzly
*#3 im going to go try the radius tool when i get dont typing i thought that might be something to try since almost all of the carbide inserts have a radius

in conclusion i think if i can get a fair result without too much oversizing ill just let it be, otherwise ill just have to sleeve it or start over


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## Foozer (Jul 14, 2009)

hammers-n-nails  said:
			
		

> let me try that again



I had to bore a hole like that and used a similar carbide tipped cutter. Could not get a decent finish. Looked like yours. So used the carbide tool to bring hole near size, its stiffer, less flex etc, and ground a boring bit from an old HSS drill bit. Could only cut a few thou at a time but the finish was much nicer. That carbide was happy as a pig in a wallow making cuts that caused the machine to groan, but light cuts, just wasn't gonna happen. It just road the surface building up heat till "Bing" dig in, then back to ridding the surface.

Robert


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## Florian (Jul 14, 2009)

What often gets forgotten is that carbide tools cant be grinded as sharp as HSS tools. 
It has to do with the structure of carbide: 
These are little particles (very hard) which have been sintered together using a filler material. 
If you now have a sharp edge, the single particles easily break off at the edge. 

On HSS, this can't happen as it is a "single" alloy. 
Thats also a reason why you should use (plated!!) HSS tools for working on titanium. 

These standard-Carbide boring bars are not worth the money; they are just rubbish...





Here another picture how a boring bar can be made (that one's for brass):





And here the boring bars i would use:
http://www.ifanger.ch/fileadmin/Webmaster/Produkte_EN/B_01/020102_Facing%20and%20bottoming.pdf

Florian


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## Jasonb (Jul 14, 2009)

The way you have the boring bar mounted in the boring head is giving zero or possibly even negative top rake to the tool. Try rotating the tool to give about 5deg of top rake, you will possibly have to grind in some more back clearance. 

I have a set of bars like in the last post and provided they are set with positiev top rake and the back edge is not rubbing they will cut steel & iron without problem.

Jason


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## shred (Jul 14, 2009)

hammers-n-nails  said:
			
		

> yes i agree loosenut that would be alot easier but i connot justify a minimum of $30 that it would take to get a 1.000" reamer to my house since it would be fairly unlikely that i would need one that large again in the forseeable future, that is if a fair result is possible using the tools i already have.
> davyboy


You could make a D-bit or toolmaker's reamer if you had some reasonably good 1" steel round handy. For one-time use it might not need hardening.


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## Hilmar (Jul 14, 2009)

Could you have bored the cylinder on the late?
You would have gotten a much better finish.
Hilmar


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## hammers-n-nails (Jul 14, 2009)

i got some time to try the re-ground boring bar today, with initial success, a near-mirror finish beieve it or not, but there was still one ring i didnt quite get out, so another try yeiled the origonal result. after regrinding a couple more times,giving more clearence all around each time, i got a good even bore but now had problems with the tool vibrating. at the end of the day im .020 oversize but with a fair bore so i think im going to call it good enough, for better or worse. the piston ring has a gap that is bigger than i would like, but it will run ok, im trying to get done to start on the next project. florian, im interested to know why you are opposed to the use of this type of boreing bar and prefer the other, please elaborate.
here are the pictures


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## Florian (Jul 15, 2009)

I don't like them because it is much easier to sharpen a HSS boring bar. 
You can also use these carbide bars but you will first have to sharpen them. The hss version can be used directly after buying them. Carbide boring bars are very sensitive to things like interrupted cut and inpacts from other tools. Also they don't forgive an immediate loss of rpm (for example if you switch the motor of though it still cuts)
Last but not least is the carbide used on these cheap tools not of a good quality... 
(I used some carbide tools on my watchmakers lathe for the very hard stuff; they were cheap but the carbide splits at the slightest "misuse" of it... Now i don't use them any more because after almost every cut they need do be sharpened...)

Oh and most of the problems just happen with cheap boring bars; if you buy quality tools, most of it is different!


Florian


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