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Stephen A. Douglass
08-23-2011, 03:53 PM
I have a problem making cylinders which are very cylindrical. I am using a Bridgeport mill with boring head. I have also made some attempts on the lathe. At present I get better results with the lathe.
If I use an inside mike on the ends, I find non circularity on both machines of up to .0015. The ends are similar with the lathe, but with the mill, the bottom can be up to .003 larger diameter. The first question is, what is an allowable run out, both for steam and for internal combustion? I have seen no figures on this. I am using cast iron piston rings.
Second, what techniques do people use to get good cylindrical bores, and what kind of measurements to they get?
A related question would be: What kind of cylindrical measurements are achieved in automotive cylinders?
Finally, do people use honing to achieve a more cylindrical cylinder?
Thanks,
Steve

gbritnell
08-23-2011, 04:24 PM
Steve,
Some of your question can be answered but to really tell you why you're having trouble we would need to know much more about the accuracy of your equipment.
First off if you're building a model steam engine you can get away with a little irregularity in your cylinder but .003 is way too much. For internal combustion engines you need dimensional tolerance plus very close concentricity. With any internal combustion engine the best way to accomplish this is by honing but the standard hones used the the home shop will generally follow the initial bore.
The purpose of a hone is just to clean up the bore, make it concentric and take off a very small amount of material in the process.
As to why you're getting so much runout with your machines it could be that they aren't accurate (tight) enough to hold extremely tight sizes. It could be partly your setup. It could also be the sharpness of your tooling.
Like I stated at the beginning we would have to know a little more about your machining operation and tooling to give a good assessment of what's going on.
gbritnell

tdmidget
08-23-2011, 05:27 PM
I have a problem making cylinders which are very cylindrical. I am using a Bridgeport mill with boring head. I have also made some attempts on the lathe. At present I get better results with the lathe.
If I use an inside mike on the ends, I find non circularity on both machines of up to .0015. The ends are similar with the lathe, but with the mill, the bottom can be up to .003 larger diameter. The first question is, what is an allowable run out, both for steam and for internal combustion? I have seen no figures on this. I am using cast iron piston rings.
Second, what techniques do people use to get good cylindrical bores, and what kind of measurements to they get?
A related question would be: What kind of cylindrical measurements are achieved in automotive cylinders?
Finally, do people use honing to achieve a more cylindrical cylinder?
Thanks,
Steve
It is hard to tell what you are talking about. There is no such thing as "non-circularity". If you are talking about how round the hole is, that is circularity. It cannot be measured with an inside mike. To measure, sweep the hole or other feature with an indicator. The total movement of your indicator is "total indicator reading" (TIR). This is usually the measure of circularity. The combination of circularity and taper is "cylindricity" and that is what you should be concerned with. If you don't have a coordinate measuring machine you will have to measure the characteristics separately.
We need a LOT more information. What is the material, clamping method, tooling. Are non moving axes locked?
You should get a near perfectly round hole by boring, so something is wrong. Clamping is likely a part of it since it changed from lathe to mill.
Tell us more, with proper terminology and measurement.

vpt
08-23-2011, 06:24 PM
After getting my outboard 3 cylinder block back from being bored I had to bring all three holes up .008 to be within specs. I used My sunnen hone set starting out with I believe the j45 stones and finishing with some sort of 80-85 stones. I could not get a varying measurement anywhere in any of the bores top to bottom and all around with a bore gauge and mitsutoyo caliper to the .000".

I was very impressed with the results and the motor has been running GREAT two years now!

http://img29.imageshack.us/img29/8347/riverhigh007.jpg

vpt
08-23-2011, 06:26 PM
Well ok not two full years but I did run it last fall and all this summer.

loply
08-23-2011, 06:43 PM
If you're finding that your holes are oval both on the lathe and on the mill is it possible you are clamping the part too tightly, thereby egging it up whilst you do your operation?

Dawai
08-23-2011, 06:57 PM
Torque plates put the same stress on the cylinders that the head do. Sometimes they are critical, other times not.

It's hard to find the hole center.
A combustion engine normally "eggs" out the cylinders, boring, you do it "first size" sometimes that is enough to "find the Round HOLE in the non-round bore".. other times Not..
Look for a "shadow" as you bore, meaning you are not cutting "OUT" the previous bore size. You must go beyond the previous non-round hole.

If you have any flex at all in your equipment, it will wander all over the place.

Being a poor boy from Gawgia, I've bored harley jugs on the lathe. I would not know where the jig is today, but zeroing it "once " was enough, it has went back each time.
I spun the jug.

Does any of that make sense.. YOU can "Lose" the true centerline of a engine boring it.. especially quickway bars.. where you run it backwards to FIND HOLE Center after extending the fingers to find it. IE: why a build job changes the way a engine puts out power.. There was a local shop that said they could give me 10+ more horsepower in a bore job. Angle bore.. (offset crank center)

Stephen A. Douglass
08-23-2011, 09:59 PM
Ok, this is a bit of a struggle, because I have never done anything on a bulletin board before. But the two responses so far are stimulating my thinking. First of all, I am not a professional machinist. My degrees are in biology and biochemistry. But I love cutting metal.
First, I suspect that gbritnell is George, who makes incredibly small V8s and lever action rifle, etc. I'm the guy who used to set up air lines for the modelers at the La Grange engine club show, until I moved to Seattle area to be near my daughter.
I thought that if one used an inside mike on a cylinder, that the reading should be the same all the way around. The second person to reply is suggesting that instead I should set up a dial indicator after boring and look at runout. Okay, I can try that.
The materials are cast iron and bronze, but I have been playing with pieces of steel pipe to work on techniques. Tools are sharp. I have clamped in v blocks in the mill vise, or placed in three jaw chuck in the lathe. I'm trying to use minimal clamping forces as I realize that that I can distort the cylinders if I clamp with too much force, and then when I take them out they will relax to a different shape than the desired cylinder.
Thanks for the mention of what is acceptable in terms of runout. It looks like I have a way to go.
Steve

Don Young
08-23-2011, 10:57 PM
I have no direct experience in boring cylinders in the lathe or mill but unless it is very thick walled I am sure that holding one in a 3 jaw chuck or V-blocks with enough pressure to retain it will cause more than just measurable distortion. Many, many years ago my Dad showed me how he could release an inside mike hanging in a car engine bore by squeezing the sides of the block with his hands. I thought it was a trick but learned that the bore was actually made oval enough to do that.

huntinguy
08-24-2011, 12:27 AM
for a good tutorial on measuring round parts do a google search on centerless grinding. A part can be lobed and still measure round across two points. I have seen .32 diameter part measure round with a micrometer and be .01 out of round when measured using a V block. To tell if a part is round you need to measure across three points of contact.

If you are holding the part in a V block, using the V block clamp you do not have a round, nor straight hole. You need to have the maximum amount of contact on the part to reduce clamping distortion.

If you are boring a tube using the lathe bore the jaws to the same size as the tube and then bore the tube, it should be noted that any distortion in the roundness of the tubes OD will be passed to the ID of the tube.

If you are boring a block, such as an engine block, clamp from the top and put the clamping forces parallel with the bore, by clamping the part from the sides you are putting the clamping forces perpendicular to the part and automatically distorting the part.

Also, are you measuring the part as cut in the machine or removed and in the free state? That will also make a difference. Considering you really only care about the part in the free state.

Jaakko Fagerlund
08-24-2011, 12:49 AM
What sort orf mill operation you use for boring? Do you lift the table to the cutter or feed with the quill? If the latter, I'm not suprised it shows up as bigger diameter in the bottom as the rigidity of the cutter diminishes.

uncle pete
08-24-2011, 03:01 AM
Steve,
For the HSM types where our equipment is pretty limited and if your cylinder is small enough, Fixturing it to the lathes cross slide at the correct elevation and then using a between centers boring bar would be the best way to go. One of my prioritys when I was shopping for a new lathe was a cross slide with tee slots in it. How your lathe is built and your own ingenuity would dictate if you can do it this way. But you would get round and true cylinder bores.

Pete

tdmidget
08-24-2011, 03:47 AM
Steve,
For the HSM types where our equipment is pretty limited and if your cylinder is small enough, Fixturing it to the lathes cross slide at the correct elevation and then using a between centers boring bar would be the best way to go. One of my prioritys when I was shopping for a new lathe was a cross slide with tee slots in it. How your lathe is built and your own ingenuity would dictate if you can do it this way. But you would get round and true cylinder bores.

Pete

You still have all the clamping issues as before and more. A picture of the part might net him some real suggestions on how to hold it. This sounds like a simple matter but fixturing is paramount when trying for cylindricity. He needs a way to clamp it axially, preferably exactly like it will be mounted in use.

uncle pete
08-24-2011, 04:55 AM
Td,
Yeah your right about the fixturing, But since that had been already mentioned I didn't think there was much more I could add. Your also right about the need for a picture.

Pete

tdmidget
08-24-2011, 05:08 AM
There's no reason that he can't get a kickass job with the equipment he's got. But not all things can be done in a vise or a chuck, especially if it's a 3 jaw. Probably no access to a real hone and even then you have to learn to use one. If he saves the bores for last, fixtures it to take into account the stresses in service, and cuts them in 2 passes, he should have a hole that a brake cylinder hone or such can finish up nicely.

uncle pete
08-24-2011, 05:23 AM
Td,
Well everybodys experiences and preferances are different, My Bridgeport clone mill has power downfeed on the spindle but I still prefer using a between centers boring bar. It does take longer but with the bar supported at each end there's never any taper. You've obviously got far more experience than I do but I was just pointing out one more method that hadn't been mentioned yet.

Pete

J Tiers
08-24-2011, 09:38 AM
You sure CAN measure out-of-round with an inside mic.

not every kind, of course....

but if you get a measurement of 0.998 "north-south" and 1.001 "east-west", that bore is out of round.... it's "egged".

Mr Douglass is reporting measurements that seem like they were like that.... if so, yes he CAN and DID measure out-of-round.

I wouldn't go to measure an unknown bore with that setup, but if you DO get those measurements, it's OOR for sure. Very possibly a clamping issue.

As for the taper. maybe the mill is a little sloppy in the quill, and it has more "rattle" at one end of the travel. Could make the bore smaller from tool being pushed inwards, OR it could be moving in response to an imbalance of the boring head on finish passes and cutting deeper....as well as out-of-round either way.

Carld
08-24-2011, 10:43 AM
I have to totally agree with J Tiers. I have been using an inside bore mic to measure cylinder bores for years and it's easy to find when a bore is egg shaped. A dial indicator bore mic measures at two opposing points in a bore just as a mechanical bore mic does, it just has two extra feet to keep it aligned in the bore.

The dial indicator bore mic makes it much easier to find out of round bores than using the inside mic.

The problem with measuring small bores is most inside mics won't go below 1.5" but the dial indicator bore gauges will go down to .7" I think. It takes a lot of time but many times I use telescopic gauges to measure bores because the feel of the inside mic is eliminated and I get the same reading time after time in the same spot.

Now that I have a dial indicator bore gauge I use it mostly to find egg shape bores.

Mcgyver
08-24-2011, 11:24 AM
all the things that a non combatant would take for granted, getting something flat, getting a bore straight and round to a high degree of accuracy are in fact quite challenging.

as has been pointed out, clamping something can change its shape certainly there has to be some clearance in the quill, the affect of which is greater the further out it is. A crucial step if these are raw castings, is filing/scraping one datum surface so the casting will sit on the table without rocking. Doing this with some blue will ensure distribution of contact to the point where you can clamp without fear of distortion

What I always do after single pointing is lap the bores of engines. This is offered in the context of models btw, full size engines with their high power may very different requirements...but since you're doing so on a bport I'm assuming its a small engine.

I use adjustable copper laps I make, as below. While laps are normally charged, in this instance I just put some compound on - it is an accepted lapping approach to use both a charged and/or a rolling action of the abrasive. I believe that the lap and bore wear to a perfect circle through this, and in moving the lap along the bores axis wears the lap into a cylinder rather than cone. This won't happen lapping a flat, but does with a circle. The laps are shorter than the bore but long enough to 'register'

When the casting help in the lathe such that distortion is minimized/eliminated and run at low speed, the lap is held by hand. In use it becomes very clear where the tight spots area. progressively finer pastes are used until the bore is perfect. you can feel if there's a cone shape, and you know when its gone, or you can feel where there's a tight spot possibly caused by a hard spot or clamping pressure while single pointing.

I sort of came up with this approach on my own so am not sure how sound its considered by conventional engineering practice, but i get perfectly finished bores that are as round and true as a dial bore gauge can measure

http://i20.photobucket.com/albums/b201/michael0100/lapping/afteruse.jpg

http://i20.photobucket.com/albums/b201/michael0100/lapping/blankreadyforbrazing.jpg

http://i20.photobucket.com/albums/b201/michael0100/lapping/collectionoflaps-1.jpg

http://i20.photobucket.com/albums/b201/michael0100/lapping/results.jpg

531blackbanshee
08-24-2011, 12:52 PM
lots of good info in this thread.


bottom line,


in layman terms.


you have to clamp "inline" (parallel) with the bore.

you can't clamp "across" (horizontal)the bore without distorting it some.

hth,
leon

Ray Sidell
08-24-2011, 02:15 PM
[QUOTE.
The second person to reply is suggesting that instead I should set up a dial indicator after boring and look at runout. Okay, I can try that.


Stephen,
If you use an indicator while the job is in the machine you may well see no runout but still have the problem. If the indicator stylus is in the same postion your tool was it will not show the error because it will be following the path of the tool that created the error.
Ray

Stephen A. Douglass
08-24-2011, 02:32 PM
I shall continue to follow this. I want now to thank all of those who have replied. I feel much less in the dark. Some of the replies, such as on the method of honing, would certainly seem worthy of a full length article in HSM.
So if the Bridgeport can have wobble, then what use is the downfeed? Other than the holes look pretty. I have picked up a used and repairable drive, with I am thinking of putting on the table z drive on the bridgeport. Maybe that in slow motion, with the quill locked, would give better bores. It is just that setup on the vertical mill is a lot faster and easier than in the lathe, and I have about 30 cylinders to bore.
I have been considering getting an aftermarket t bolt cross slide for the Atlas 10. I think the lathe is good, because I have turned to less than .0003 TIR over a foot, between centers, after some careful adjustment of the tail stock set over. I made a spread sheet to see what would happen if I had varying sizes of stock, and had a depression in the lathe bed. With .1 inch stock, and a .01 drop in the lathe bed, trig says that error would be less than .001 inch. I believe in the lathe.
I have seen that idea of cylinder being clamped to cylinder, and using boring bar on cylinders, most often in English publications, where authors did not have a vertical mill.
Clamping remains the problem. I have seen u bolts or a bar with t nuts used to clamp to a cross slide. I have been considering using the mill to face both ends of the casting (which it does a very flat job of), and laying out the bolt pattern, drilling and taping the holes. Then I could make a pair of plates with the bolt pattern drilled, and hold the casting by it's end, minimizing distortion.
Most of the castings are from Stuart Turner, nice fine grained cast iron.
I will definitely make up the copper hone. There are enough engines with the same bore, that it should pay off well.
Hope George Britnell sees this, I would love to reconnect with him. George, 206-780-0982 Pacific Daylight Savings time.
Again, thanks to all, and I shall continue to follow the conversation with much interest. I think putting this all together would make a terrific article for HSM as well.
Steve

tdmidget
08-24-2011, 03:20 PM
Carl and jtiers: when you measure with and inside mic or bore gage you are comparing 2 points to each other. This does not tell you their relationship to the center or to other parts of the hole.
Read hungtinguy post re: roundness. A sweep with an indicator
will show the entire relationship.

Ray: "
Stephen,
If you use an indicator while the job is in the machine you may well see no runout but still have the problem. If the indicator stylus is in the same postion your tool was it will not show the error because it will be following the path of the tool that created the error."
Only on reciprocating machines such as a surface grinder or planer. No problem with an indicator on the cross slide or mill spindle.

Ray Sidell
08-24-2011, 06:12 PM
QUOTE=Stephen A. Douglass]II get better results with the lathe.
I find non circularity on both machines of up to .0015.

QUOTE=tdmidget]
Only on reciprocating machines such as a surface grinder or planer. No problem with an indicator on the cross slide or mill spindle.

td,
I couldn't disagree more, if the mill spindle is causing the non circularity how can you use it to check the hole?

J Tiers
08-24-2011, 10:29 PM
Carl and jtiers: when you measure with and inside mic or bore gage you are comparing 2 points to each other. This does not tell you their relationship to the center or to other parts of the hole.



Eh?

You would not use that method to find "general" OOR conditions, BUT ......


FOR SURE if you find a "cylinder" which is different dimensions in N-S and E-W directions, that sucker is OOR, and no way you can get around that no matter how much textbook you quote.....

And the indicator has to be on-center, AND rotating w/o wobble or no-go.

luthor
08-24-2011, 11:22 PM
Has the head of the milling machine in question been "Trammed", if not this can produce ovality in bores.

tdmidget
08-25-2011, 02:03 AM
Eh?

You would not use that method to find "general" OOR conditions, BUT ......


FOR SURE if you find a "cylinder" which is different dimensions in N-S and E-W directions, that sucker is OOR, and no way you can get around that no matter how much textbook you quote.....

And the indicator has to be on-center, AND rotating w/o wobble or no-go.

The discussion was of circularity and cylindricity, of which OOR is only a part. You can not measure circularity with any 2 point measuring system. Circularity requires the entire feature to be compared with the intended or actual centerpoint.


Ray Sidell: if your spindle is that bad then it will not repeat. It might not show the same exact variations but would show variations that are the same quantitatively. It might also be checked in another machine. Lacking a CMM he does not have the ability to make quantitative measurements of circularity or cylindricity.

vpt
08-25-2011, 10:34 AM
The sunnen set I used is a very very nice hone set! It is NOT a spring loaded deal. You set the hone at a light pressure and then work it in the cylinder until you feel it free up then repeat. I use my drill press to hone the cylinders. Because my drill press is a lower power craftsman type I could tell while honing the cylinders where the tight spots were in the cylinders, top/bottom/middle. I would work the tight spots until the drill press kept constant rpm and feel from top to bottom of the cylinder. Back hone out, measure, repeat. WD-40 for lube and like I mentioned I could not get a varying measurement anywhere in the cylinders, even on the little lands between the 2 stroke ports. Going by feel of the drill press while honing is crude I admit, but knowing your machines and what they do is half the battle of getting the outcome your looking for.

I am very very impressed with the hones! I have never got such a nice finish or such a perfectly round top to bottom cylinders ever before like I did with this hone. I have a few different sizes down to 2" and up to something like 4.5". I used the 3" for the outboard I believe.

http://images.hemmings.com/wp-content/uploads/2007/10/Greenleesboring_2034_resized.jpg