Another Rupnow 1 by 1

[Steamchick]

I think my problem is more fundamental. I can't measure worth a flip.

I just took 20 measurements of the inside diameter of both ends of the bore. There's some sort of taper there, wider at the bottom of the cylinder (lathe chuck end) than the other end, but my measurements are all over. The outer measurements run from .9491 to .9510. The bottom end runs from .9514 to .9550. I did five sets of a few measurements and the variation is mostly between the sets.

I'm using a micrometer and a telescoping ID gauge.

Anybody have any favorite videos for this? Websites?

Or you can do some statistics, and use the average for each measurement point. Normally I would measure each point at least 3 times - using internal calipers to micrometer, because that is how I was taught 50 years ago. But I now double check using an ID gauge as well. But easy to make a stepped checking gauge - 1/4" bands at 0.001" increasing diameter sarod the dimension you are checkingl, and you can more easily what fits and what doesn't. Do not use a tapered gauge, it will only tell you the size at the outer edge of the bore.
Cheers,
K2

 

[CFLBob]

Or you can do some statistics, and use the average for each measurement point. Normally I would measure each point at least 3 times - using internal calipers to micrometer, because that is how I was taught 50 years ago. But I now double check using an ID gauge as well. But easy to make a stepped checking gauge - 1/4" bands at 0.001" increasing diameter sarod the dimension you are checkingl, and you can more easily what fits and what doesn't. Do not use a tapered gauge, it will only tell you the size at the outer edge of the bore.
Cheers,
K2

Statistics is practically my middle name, but I'm not comfortable using them here. Let me show you why. Two batches of ID measurements at the non-chuck end of the cylinder

Test 1
0.9510
0.9510
0.9508
0.9509

Test 2
0.9497
0.9499
0.9495
0.9499

Those are two different populations. The averages for each group are 0.9509 (#1) and 0.9498, with a standard deviation of .0001 for the first group and twice that for the second. Sure those two averages are only 1.1 thou apart, but in standard deviations, they're more than 3 sigma different. If I combined all of those readings into one average, the std deviation would get bigger.

The chuck end is worse. When I figure the std. dev. for the chuck end vs. this end, it's about 2 to 3 times greater. Because of that, the tapers I measure vary more.

What I think I need to do is get more precise settings of the telescoping gauge. I'm not doing as well when it's down the bore as I am when the telescoping gauge is right there at the end.

Since the bore is obviously close to 0.950 and my target is 1.000, I can take off another .040 and then repeat all this. I just don't like the spread in values test to test. Also, this design calls for a Vyton piston ring instead of cast iron. I tend to believe that makes the real application a bit more forgiving.

 

[Richard Hed]

I think my problem is more fundamental. I can't measure worth a flip.

I just took 20 measurements of the inside diameter of both ends of the bore. There's some sort of taper there, wider at the bottom of the cylinder (lathe chuck end) than the other end, but my measurements are all over. The outer measurements run from .9491 to .9510. The bottom end runs from .9514 to .9550. I did five sets of a few measurements and the variation is mostly between the sets.

I'm using a micrometer and a telescoping ID gauge.

Anybody have any favorite videos for this? Websites?

How did you cut it? Did you use a reamer? I never completely trust those telescoping ID gauges. They require the use of two tools, each tool representing another layer of error. Do you have any direct reading micrometers for inside? Since you still have a way to go, why not cut out .030 and then ream it?

 

[Steamchick]

If you have a side lever DTI, you may be able to arrange it as a clock comparitor to the micrometer, by adding a stem behind the ball-ended contact lever. I'll try and do something today and show you a picture.
K2

 

[Steamchick]

Bob, I just produced this "quick check" that you can do on your lathe to give you a clue as to how accurate it is... (Mine is aligned well enough, but the chuck has some distortion - probably strained from some mis-haps that I have had...).
Maybe this quick check can help you decide what to do with the lathe, I.E. show you where the taper is being generated?
K2

 

[CFLBob]

How did you cut it? Did you use a reamer? I never completely trust those telescoping ID gauges. They require the use of two tools, each tool representing another layer of error. Do you have any direct reading micrometers for inside? Since you still have a way to go, why not cut out .030 and then ream it?

I cut it with a boring bar that has a carbide insert. It cuts at a relatively small point; I mean the contact in the telescoping gauge has to be 10 times the width of the cutting point so it's not like one measurement is in a valley and the next measurement is on a peak. They're all over a fairly wide swath.

I don't have any sort of inside micrometer. I don't have a reamer that's 1" diameter.

In terms of buying a tool like a 1" reamer, or a different micrometer, that's possible, but this is a one-off engine. If my bore ends up .987, but otherwise good, I just make my piston a little smaller. It's not like the 1000th piston I make has to fit the 10,000th engine block that someone else makes.

Bob, I just produced this "quick check" that you can do on your lathe to give you a clue as to how accurate it is... (Mine is aligned well enough, but the chuck has some distortion - probably strained from some mis-haps that I have had...).
Maybe this quick check can help you decide what to do with the lathe, I.E. show you where the taper is being generated?
K2

Thanks for that. I'm in the awkward stage of having a carefully set up part in my four jaw chuck and I think the chances of getting everything back exactly where it was (if I take out my work and switch to a round bar, swapping out the chuck or not) are just about zero. Which means I start over. Now if I screw this up badly enough, I may end up starting over again anyway, but I'd rather not risk it.

I figure I'll limp along on this cylinder and try to finish it, then spend some time checking the lathe.

The thing that bothers me is not getting as consistent readings deep in the cylinder as toward the end in that picture. The fact that there's a little taper doesn't bother me anywhere near as much as not being able to tell you how much taper there is. The fact that the cylinder is smallest at the top, where it's going to get the most thermal expansion is better than being the other way around. Some measurements tell me the taper is .001" and some tell me .003. If I look at the averages of every measurement I took, I can see that one or two sets end up moving the average the most.

 

[werowance]

Bob, for what its worth, i also use a telescoping bore gauge and then my mics to measure. i also use a very similar boring tool. and i always have similar measurements of the cylinders i have made on the engines that i have made that run just fine. (which is not a whole lot of engines but a few)

one thing i do is make a lap and use either diamond paste or the last 2 engines i started using clover with silcon carbide suspended in what smells like regular old grease. i start with 600 grit and move on up to 1500 grit.

i then run the piston in usually with the 1500 grit but some times i have to back down to 1000 an then back up to the 1500 in order to get it thru.

hope that this information can help you in some way or other.

 

[Richard Hed]

I cut it with a boring bar that has a carbide insert. It cuts at a relatively small point; I mean the contact in the telescoping gauge has to be 10 times the width of the cutting point so it's not like one measurement is in a valley and the next measurement is on a peak. They're all over a fairly wide swath.

View attachment 132035

I don't have any sort of inside micrometer. I don't have a reamer that's 1" diameter.

In terms of buying a tool like a 1" reamer, or a different micrometer, that's possible, but this is a one-off engine. If my bore ends up .987, but otherwise good, I just make my piston a little smaller. It's not like the 1000th piston I make has to fit the 10,000th engine block that someone else makes.



Thanks for that. I'm in the awkward stage of having a carefully set up part in my four jaw chuck and I think the chances of getting everything back exactly where it was (if I take out my work and switch to a round bar, swapping out the chuck or not) are just about zero. Which means I start over. Now if I screw this up badly enough, I may end up starting over again anyway, but I'd rather not risk it.

I figure I'll limp along on this cylinder and try to finish it, then spend some time checking the lathe.

The thing that bothers me is not getting as consistent readings deep in the cylinder as toward the end in that picture. The fact that there's a little taper doesn't bother me anywhere near as much as not being able to tell you how much taper there is. The fact that the cylinder is smallest at the top, where it's going to get the most thermal expansion is better than being the other way around. Some measurements tell me the taper is .001" and some tell me .003. If I look at the averages of every measurement I took, I can see that one or two sets end up moving the average the most.

What speed are you cutting at? and what feed? If you speed up your cutting speed and slow down the feed, you might get better readings. Also, reverse your feed once your reach the end cut. This is all before you reach within, say .015" of finish. otherwords, take a light cut, reverse feed without changing the setting, then check the bore. If necessary (being very careful not to disturb the setting) take a spring cut. Make sure your carbide bit is clean and new and sharp before doing any of this final business. What kind of lathe do you have. Me thimpfks you told us once, but I doesn't remember. Is it a light machine,? Medium sized? If you have a light machine, you just might have to live with it. One of the fellows on this forum said something about one end of a cylinder is best being .001 smaller than the other end anyway. It made sense what he was saying, but I forget who and exactly what he was saying.

There is a method of making your own reamer. Do you just happen to havve a piece of 1" drill rod? YOu live in Florida, no? As for myself, I bought a 1" reamer from Shars as I need a 1" just often enough to get a cheapo.

Naturally, I am not there to observe your measurements, and I'm sure yhou are being careful to remove the telescoping guage properly, but how about re-viewing Quinn's video on that?

In the mean time, I thimpfks I would order a cheapo (but still quality enough) inside micrometer from Shars or some other cheapo chinese company. I have two, one from .2 to 1.2, nd the other from something like .6 to 2.6". I consider them invaluable.

 

[Steamchick]

Hi Bob, I just tried a quick demo of the idea for using a side-lever DTI for a comparitor against the micrometer. Easier to show pictures...:
The internal calipers I use, with a large diameter thumb wheel for very fine feel. I find these much better than bore gauges for less than 1" bore.

Another alternative to your bore gauge:
A side-lever DTI with a scriber held on the back with a rubber band. - If properly fixed, and adjustable, this could serve as a bore gauge comparitor for use against the micrometer.

The next picture shows how you would set the micrometer to the size to be measured, then set the DTI Bore gauge to zero aganst the mic.

Then it can be used as a comparitor to measurethew undersize or oversize of the bore. = becomes a direct reading bore gauge!
While I have only shown the scriber affixed with a rubber band, there is no adjustment of the gauge to various dimensions. If you made a small clamp-on fixed point that was adjustable with a screw, and locknut, then you would have a more secure but versatile measuring gauge. - This DTI measures to 0.0001" per division, so you can even use it for honing to size, where you may only be removing a fraction of a thou per pass of the hone.
But I would recommend you try and reset the lathe to be closer to a parallel bore before you finish boring the cylinder, anyway.
Cheers!
K2

 

[trackmaggot]

What level of confidence do you have in your tools? Has the mic been calibrated, are it's anvils true, has it been dropped, is the back sprung? You might also look at doing a Gage R&R (just for fun) to see if you can identify where the variations might be coming from during the measurements.

 

[Steamchick]

I have some telescopic bore gauges, - cheap stuff - with poor ends on the telescoping measuring ends. Possibly that is causing the variation? - Which is why I prefer the internal calipers. I think I am more consistent transferring bore size to mic.
Bob, can you show us a picture of your bore gauge?
K2

 

[CFLBob]

This thread got very busy as the day went by.

@werowance Yes, it does help. I think people who tend to say, "meh ... close enough" all the time don't take on machining as hobby, and I can see I might be over analyzing this condition.

What level of confidence do you have in your tools? Has the mic been calibrated, are it's anvils true, has it been dropped, is the back sprung? You might also look at doing a Gage R&R (just for fun) to see if you can identify where the variations might be coming from during the measurements.

The micrometer is new and seems decent. The anvils are good; never been dropped and everything seems to do what it's supposed to. It's midway in price between Shars and Mitutoyo. I had a Shars that died at its first battery change. About a year old? Certainly less than two years old.
https://smile.amazon.com/gp/product/B075K2DJPB/ref=ppx_yo_dt_b_asin_title_o05_s02?ie=UTF8&psc=1

The telescopic gauge is marked as Starrett and came in a box marked Starrett, bought used from eBay. I have a set that's not as good quality, but when this size broke, (3/4" to 1" - I think) I picked up this Starrett.

The Gage R&R studies I've been involved with were all electronics testing and I wouldn't know what to do here.

This would be a good place to post this picture:

The Telescopic gauge we're talking about. Note how the shaft is a few degrees above perpendicular to the head. That's the only thing I know that isn't as good as I'd like to see it.

My technique is to lay this on the side of the cylinder so that the head is on top of the last circular flange, then grab the knurled part of the handle with a pair of long needle-nosed pliers (it's just left of the non-knurled part on the end). Then I put it in place in the cylinder still holding it in the pliers, with the pliers flush with the end of the cylinder, and unscrew the clamp holding the movable pin in place. Jiggle it a bit and then tighten down the screw to hold the position - all the while trying to preserve that angle so that the measuring head is perpendicular to the walls of the cylinder.

Easier to show pictures...:
The internal calipers I use, with a large diameter thumb wheel for very fine feel. I find these much better than bore gauges for less than 1" bore.

I might have a pair of calipers like that around here. Sounds odd, but I know I've had them before. The other trick, the dial indicator with a pointed scriber is interesting, but I don't think I have anything like that pointed scriber.

What speed are you cutting at? and what feed? If you speed up your cutting speed and slow down the feed, you might get better readings. Also, reverse your feed once your reach the end cut. This is all before you reach within, say .015" of finish. otherwords, take a light cut, reverse feed without changing the setting, then check the bore. If necessary (being very careful not to disturb the setting) take a spring cut. Make sure your carbide bit is clean and new and sharp before doing any of this final business. What kind of lathe do you have. Me thimpfks you told us once, but I doesn't remember. Is it a light machine,? Medium sized? If you have a light machine, you just might have to live with it. One of the fellows on this forum said something about one end of a cylinder is best being .001 smaller than the other end anyway. It made sense what he was saying, but I forget who and exactly what he was saying.

My lathe is a SIEG SC4, from Little Machine Shop, their LMS3540. These are 8.5 by 20" so not quite a 9x20 lathe. The spindle motor is 1.3 HP (1000 Watts). I've been taking .020 radius off per pass (.040 diameter), running 300 RPMs. The lathe has power feed, which is coupled to the turning RPMs. It feeds at about .002" per revolution.

What I've been doing is similar to what you describe, not not exactly. I power feed until the boring bar is just about as far as it will go into the cylinder, remove power feed and advance the tool the last .025 to .050. Then instead of reversing the motor and reversing the power feed, I manually turn the handwheel on the cross slide until the the cutter comes back out of the cylinder. Going forward, it takes about 5-1/2 minutes to cut an entire pass. I've never timed myself doing this, but I think it's more like one to two minutes to take that spring pass taking the boring bar back out.

 

[Richard Hed]

This thread got very busy as the day went by.

@werowance Yes, it does help. I think people who tend to say, "meh ... close enough" all the time don't take on machining as hobby, and I can see I might be over analyzing this condition.



The micrometer is new and seems decent. The anvils are good; never been dropped and everything seems to do what it's supposed to. It's midway in price between Shars and Mitutoyo. I had a Shars that died at its first battery change. About a year old? Certainly less than two years old.
https://smile.amazon.com/gp/product/B075K2DJPB/ref=ppx_yo_dt_b_asin_title_o05_s02?ie=UTF8&psc=1

The telescopic gauge is marked as Starrett and came in a box marked Starrett, bought used from eBay. I have a set that's not as good quality, but when this size broke, (3/4" to 1" - I think) I picked up this Starrett.

The Gage R&R studies I've been involved with were all electronics testing and I wouldn't know what to do here.

This would be a good place to post this picture:

View attachment 132045

The Telescopic gauge we're talking about. Note how the shaft is a few degrees above perpendicular to the head. That's the only thing I know that isn't as good as I'd like to see it.

My technique is to lay this on the side of the cylinder so that the head is on top of the last circular flange, then grab the knurled part of the handle with a pair of long needle-nosed pliers (it's just left of the non-knurled part on the end). Then I put it in place in the cylinder still holding it in the pliers, with the pliers flush with the end of the cylinder, and unscrew the clamp holding the movable pin in place. Jiggle it a bit and then tighten down the screw to hold the position - all the while trying to preserve that angle so that the measuring head is perpendicular to the walls of the cylinder.



I might have a pair of calipers like that around here. Sounds odd, but I know I've had them before. The other trick, the dial indicator with a pointed scriber is interesting, but I don't think I have anything like that pointed scriber.



My lathe is a SIEG SC4, from Little Machine Shop, their LMS3540. These are 8.5 by 20" so not quite a 9x20 lathe. The spindle motor is 1.3 HP (1000 Watts). I've been taking .020 radius off per pass (.040 diameter), running 300 RPMs. The lathe has power feed, which is coupled to the turning RPMs. It feeds at about .002" per revolution.

What I've been doing is similar to what you describe, not not exactly. I power feed until the boring bar is just about as far as it will go into the cylinder, remove power feed and advance the tool the last .025 to .050. Then instead of reversing the motor and reversing the power feed, I manually turn the handwheel on the cross slide until the the cutter comes back out of the cylinder. Going forward, it takes about 5-1/2 minutes to cut an entire pass. I've never timed myself doing this, but I think it's more like one to two minutes to take that spring pass taking the boring bar back out.

I think (Oh dang, I misspelled that!) that your cutting speed is too low, especially for a finish cut. What speed do yuou have that is next highest? Do you have a lower feed rate? What do you mean by "I manually turn the handwheel on the cross slide until the the cutter comes back out of the cylinder". This does not sound right. I thimpfks yuo mean something else. Do you mean the handwheel on the carraige? On the way back out, can you see what size of flakes you are getting? You've recently checkt that all the slides are tight? Maybe you could try tightening the gibs so that the slides are immobile whe yu make a cut.

Also, I am not clear on how you do your tele gauge. You mean, you wiggle it before withdrawing it? Utub peeps do it different. First, they have the gauge perpendicular to gravity. they may wiggle it before tightening it to center it in the cylinder, but then they push the handle down only (or up) without any other wiggling. this gets a single sample with no wiggling. Notice that they tighten the handle, THEN push down, this is an important movement. withdraw carefully, measure.

What about a piece of 1" drill rod? not any, huh?

 

[Steamchick]

Hi Bob, on the side-lever DTI.... I just used a scriber from a small marking block I have. Actually, it is just a piece of sharpened silver steel with a bend. What this set-up really needs for use as a bore gauge, is a bracket holding a bar, with a threaded hole, then a screw with a small ball end through the threaded hole and locknut, forming an anvil opposite to the ball on the lever of the DTI. BUT, all that is irrelevant to your current measurements...
Your bore gauge, while having been made by Starrett, and appearing to be OK, may be the culprit. It looks skew... as you are aware. My opinion - as more experienced machinists may have better opinions - is that the skew end of the bore gauge means you cannot get a repeatedly perpendicular diameter of the bore. Also, the ends of the bore gauge need to be a smaller radius than the bore , so you get a contact on the exact centre of each end of the gauge. When the gauge is true and perpendicular to the handle, the tight spot at true diameter of the bore will mean the handle is it the centre of the open end of the bore. Because it is skew, you cannot repeatedly get the gauge end truly perpendicular to the axis of the bore, so may get some readings that are larger than the true diameter.
But there may be another explanation?
K2

 

[CFLBob]

Easy one first, no 1" drill rod.

On withdrawing the cutter: obligatory picture of the lathe:

When power feed is engaged, the handles on the compound (7) and the cross slide (5) do not get touched. I taped those in position to keep them from loosening themselves back when cutting the points off the square bar and I could see the knobs moving. I move the carriage to the right by using that big black wheel on the bottom left of the carriage. Just left of where number 11 points. Yes, I can see the size of the flakes bouncing out of the bore when I make that cut, there are fewer and smaller flakes than when cutting into the bore the first time.

I can adjust the motor speed in 10 RPM increments from 100 to 2000 RPM. I don't think I've ever had it at the top end.

I'm focusing on the gauge because of the reasons you talk about. When I'm measuring the end farthest from the chuck, the gauge is right where I can see it best and touch it. I consistently get the lowest deviation on that end. I consistently get 3 to 4 x that deviation when measuring the end closest to the chuck.

 

[Richard Hed]

I've been wanting to try that method of making your own reamer for a long time. I just don't need any reamers.

Easy one first, no 1" drill rod.

On withdrawing the cutter: obligatory picture of the lathe:

View attachment 132046
When power feed is engaged, the handles on the compound (7) and the cross slide (5) do not get touched. I taped those in position to keep them from loosening themselves back when cutting the points off the square bar and I could see the knobs moving. I move the carriage to the right by using that big black wheel on the bottom left of the carriage. Just left of where number 11 points. Yes, I can see the size of the flakes bouncing out of the bore when I make that cut, there are fewer and smaller flakes than when cutting into the bore the first time.

I can adjust the motor speed in 10 RPM increments from 100 to 2000 RPM. I don't think I've ever had it at the top end.

I'm focusing on the gauge because of the reasons you talk about. When I'm measuring the end farthest from the chuck, the gauge is right where I can see it best and touch it. I consistently get the lowest deviation on that end. I consistently get 3 to 4 x that deviation when measuring the end closest to the chuck.

What control do hyo have on the feed? I thimpfks I would turn that speed up to 6-800 rpms on this cut. Have you tried that yet? Might be miraculous.

 

[Nerd1000]

I've been wanting to try that method of making your own reamer for a long time. I just don't need any reamers.

What control do hyo have on the feed? I thimpfks I would turn that speed up to 6-800 rpms on this cut. Have you tried that yet? Might be miraculous.

I agree with this, carbide tooling likes to run fast. The speed and feed calculator I use suggests 1200 rpm for this cut, but it does seem to assume you're using a big industrial CNC so a reduction to 800 might be sensible.

 

[Steamchick]

ALIGN THE LATHE. I bet it has a twist. The U-tube explanations are pretty simple. Unless it is set "True", Speed and feed won't fix a taper. The lathe probably needs a shim under one of the feet at the tailstock end? (My guess = the back one?).
On Measurement, use internal callipers to develop your skill, as they have rounded points, not large curves on the ends. And you can "feel" much better.... " with small movements, "left-right", Up-Down".

 

[Ken I]

Bob, This is the way I use a telescopic gauge :-
Insert it deliberately skew and very lightly nip it up - then tilt it into alignment (going to be a bit more difficult with your "bent" gauge) - the telescope will collapse - when you feel it is a good fit - tighten more solidly.
Re-check the fit in the bore - a very light interference - tilt to remove and check it with a micrometer.
Repeat several times at the same spot to "calibrate" yourself.
Regards, Ken

 

[Steamchick]

Bob, You are trying to attain the perfect diameter with the gauge, when perpendicular to the axis of the bore. Your "skew" handle does not enable you to judge the "perpendicular to the axis of the bore". The difficulty I find with a bore gauge like that is finding the tightest when rotating the gauge in the bore (true diameter), but at the same time the "loosest" fit when rocking the handle to engage longitudinally in the bore (now perpendicular to the axis of the bore). The curved points (contacts with the bore) and thumb wheel (for fine adjustment) of the internal calliper teach you the "right spot" - in my experience. Then repeated in the jaws of the micrometer, to repeat the "feel", Practice on a KNOWN bore till you get the right measurements... That's what I was taught, and thousands of apprentices can't have been taught any differently?
K2