Another Rupnow 1 by 1

[xpylonracer]

Thanks for the pictures of all your kit. Far more than I need. I guess you have the test bars and gauges for calibrating them as well.
Cheers,
K2
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Hi Steamchick
I don't have any setting rings so have to rely on a mic to set the bore gauges.
I do have some gauge blocks, bought the imperial set from a firm closing down sale in the UK and the metric set from a Russian dealer when visiting Czechoslovakia in 1984 at we now call a car boot sale , it was at an airfield where I was competing in a model plane pylon racing contest, about 50 cars where goods were displayed. The exchange rate was excellent at that time and from memory I paid £15 for the metric set.

xpylonracer
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[Steamchick]

Hi Xpylon, I guess you use the gauge blocks on your surface plate to set heights and set sine bars. If you have any ball or roller races in your spares bins, then you have some gauges... as these are ground to sub-thou tolerances. Easy to look up in the maker's table for bearing sizes. External mics should come with a gauge bar in the kit. But you can use your gauge sets. Internal mics need a gauge, or calibrated mic. ALL my second-hand mics were out of calibration... but make good consistent comparitors, so gauges are most useful. When I was a teenager in the machine shop I was taught to check the mic against the gauge (zero) every time I took it from the box for use. Also with every mic with interchangeable anvil it must be confirmed to the gauge after every anvil change. As I had small hands then, I had the smaller boring jobs as I could get my hands with internal mic down the bore. But even internal mics were always confirmed against external mics when close to finished size. And when possible, Go/No go gauges were used. Often these were made before boring commenced: 0.001" oversize, Size, 0.001", 0.002", 0.003" undersize in 1/2" sections on the end of a test bar - and with tapers and shoulders if appropriate.
For finish Honing, Brian describes a method that is good. Remember, honing is to improve the surface finish of a bore (by taking the peaks off the machinning marks), and eliminate tiny irregularities from the machined bore. It is not a recommended practice to remove quantities of metal if the bore is badly made. The hone will follow the "average axis" of the peaks, not the true axis from machining. So excessive honing can misalign or distort a bore (even microns will lead to excessive wear in use). Think of this... 0.001" ovality or taper from "bad" honing means you need 0.001" wear of high spots before you "run-in" the piston to get a good bore (circular and cylindrical). That is more than 1/3rd of the lifetime of most engines!
Cheers,
K2

 

[ajoeiam]

Hi aj
Nothing wrong with Mitutoyo mics, silky smooth operating adjustment, as I said you are comparing the feel of a turned part and polished carbide mic anvils, all you can do is check at least once to be sure of the reading.
I also use dial calipers in bores, especially useful to check parallelism of the bore.

xpylonracer

wasn't trying to imply anything negative.
IMO there is even better than Mitutoyo and its that absolute top end Swiss tooling.
(Haven't run into others at that level but bet there would be a few more though.)

 

[xpylonracer]

aj

No offence taken as I am aware that Tesa are excellent measuring devices.

xpylonracer

 

[CFLBob]

I got a break between the other things I have to work on, so I got back to the cylinder using the method in that Abom79 video that ShopShoe posted. It dramatically improved my measurement repeatability. I even used my existing telescoping gauge for this, concentrating on the feel and tightening the barrel until it would hold the gauge until a light touch made it fall out of the mic.

Within the last couple of weeks, I had brought the cylinder to just under the 1.000 it's supposed to be. This time, in two sets of four measurements at both ends of the cylinder, my repeatability is .0001 to .0002".

The top (outer) end of the cylinder is 0.9962 and the measurement deep in the cylinder was 0.9976. Yesterday, I decided to press on and finished machining the outline of the cylinder, and cut it off to length. All that's left is eight holes to drill with four to tap. I'll do that using the mill as a precision drill press.

It's time to make the piston to match. First, with the cylinder off the lathe, I can look at some of the leveling questions and other things that have come up.

Footnote: chances are Florida is opposite from where you are if you work in the shop all winter. Around here, I work in the shop all summer to stay out of the sun. If I have anything that needs to be done to the house, the first question is "can it wait til winter?" As a result, every year I have a backlog of projects that start with "when it cools off, I need to..." I was doing the biggest project from about New Year's Eve until Tuesday, and now have just a couple left. One will be "a couple" of days and the other one day.

 

[Steamchick]

Well done Bob,
Learning the various skills is a big part of the fun of this hobby.
K2

 

[CFLBob]

It's time to declare the piston is ready to be put aside so that I can get the piston and conn rod ready for their role in this.

The inside of the cylinder hasn't been lapped, and I'm pretty sure that's something I should do. That will open the cylinder up a little, so it's probably best to do that first, although it can always be used to open it up some more.

One of the things I wanted to do was to verify the numbers for inside diameter that I talked about in the last post. It took me a long time to get numbers I was comfortable with and I wanted to cross check on the completed cylinder. With the cylinder parted off the blank, I get the big advantage that I can now use the telescopic gauge exactly the same way on both ends because I don't have to work from just the one end. Now I can just turn the cylinder around and test from either end.

The numbers I got testing today matched the previous numbers.

I found earlier this week that while I thought I'd ordered the #5-40 screws that hold the head onto the cylinder, I actually hadn't. I need to order some hardware and the piston ring this engine specifies (a Vyton polymer ring).

 

[Steamchick]

Hi Bob,
Just going back a bit, to clarify some odd points:

• Post #126. I had a small boring bar much like this, but it wasn't good for the smallest bore, as the bottom corner of the tool bit was touching the bore before the proper top cutting edge. So I made my own stuff so I could grind away the underside to a smaller radius than the smallest bore the tool could be used in. (I smashed the carbide tool with a hammer, then brazed a suitable shaped piece onto an old boring bar and ground it afresh with a carborundum stone, before I found out about the new diamond "stones".).
• Post#102 and a few following discussion points: I have recently been boring a cylinder - using my cheap and nasty mill-drill. A perfect bore - as far as I can measure... See pickies attached. Bore is perpendicular to one end face - as I sat it on parallels while setting the vice. The other face and bore were machined in the same setting. (locked bed). I think this is self-explanatory? Oh, it also shows I don't just write "boring" stuff, but practice a little boring, myself. The calliper was set to "just touching" and measured in a micrometer pre-set to the size I expected, then +0.001" and -0.001" settings until I got "exactly" the same touching feel. If you "screw" the micrometer onto the comparator, you cannot simulate that "feel". It is the "comparator" hand that has the feel, not the measuring gauge. Callipers just happen to be my preferred "comparator".
• On Lapping the bore - see my comments back around post #104-ish (or wherever) about honing: You are ONLY going to take off the machining peaks, not the whole machining marks, otherwise you risk losing all the PRECISION MACHINING of the shape of the bore. If the V-shaped valleys are (say ) 10 microns deep, you only want to remove "Max" 5 microns. Lapping/honing is NOT the right way to get size of fit, except within the scope of the surface finish from machining. Take out 0.001" with a hone and you'll have to make a new piston - to avoid the noisy, damaging piston slap.

Enjoy,

Ken

 

[Brian Rupnow]

Bob--the cylinder looks good. Try and make the o.d. of the piston so that it is a light press thru fit into the cylinder. You should be able to press the piston all the way thru the cylinder bore with your fingers, but if you stand the cylinder on end, the cylinder shouldn't free-fall thru the bore.

 

[Brian Rupnow]

Bob--anything going on with this build?--you haven't posted for a while.---Brian

 

[CFLBob]

Aside from some "life interrupts us sometimes" stuff, I've mostly been wrestling with software for my CNC parts, both CAD and CAM. I've been meaning to post on it, but I'm working on the piston conn rod. I still haven't finished one, but I'm getting incrementally closer.

I had a couple of page thread under the software and programming section called, "Can We Talk About CAM Programs?"

 

[CFLBob]

While I'm not done with the conn rod, I completed my first experimental piece - which my system turned into scrap very early in the process - but while it isn't possible to complete this, it actually came out fairly well.

As I mentioned in the previous post, several of us have had a lot of discussion of the issues I had with my CAM program. A lot of the story - as it happened - is there.

So let me bring this thread up to date.

What I had started out wanting to do was to duplicate the approach I saw @Mayhugh1 use to make his tiny, two-sided parts in his Ford 300 build, which is to machine one side of the part about half the thickness off the blank, fill the area just machined away with epoxy, flip the part (while maintaining the machine's zero) and then machine away the rest of the excess material on the second side. My approach was to do a rough and a fine pass - so two passes on each side. The rough pass was going to leave margin around the final geometry, using a technique called waterline cutting which is largely cutting away the excess material around the part. I elected to do a fine pass in a completely wrong approach, and it led to a butt-ugly result (which is a comparison that's offensive to butts everywhere). I fixed it by doing a different type of machining strategy. Details over on the CAM discussion.

Once the second side was finished, I baked it in a toaster oven at 250 for two hours. It fell apart perfectly.

Those yellow chunks in the front left are the epoxy, and the leftover, machined metal is in the back. The first side machined is facing you.

As I say, the dimensions I've checked are all within a reasonable tolerance of the intended size (.005" or less), and while a long way from done, if not for the machine screw-up on the first pass, it would be usable. The machine screw up is visible here.

The machine screw up happened in a way I've never had my system screw up before, but in the bottom of the square area on the right, you can see that it's pretty short on the front (first pass side).

From the second side, it looks like this:

It's about .075 extra cut away along that one edge.

I've done one (and only one) conn rod, before and that was for my Webster. For fun, here's the two rods alongside each other. Webster in white.

I did the Webster's in a completely different way, using a larger end mill and cutting the contour of the part and then relieving around the circles in G-code I wrote manually. I put the cutter near the left circular feature so that the end mill was leaving the final shape, and then cut a circle around the center of that feature. Then I moved the cutter to the larger feature on the right and repeated the approach. As a bonus, it cut the area between them to the right depth. The tool paths looked like this

The trick with this rod is that the raised area that looks circular on the big end isn't circular. It's two pieces separated by the thickness of my slitting saw (.047") and then filled in solid. It's still possible to do this sort of tool path with that distortion, I just need to cut two semicircles separated by that distance. I'd post a picture like this but on this scale, with each of the smaller squares 1/4", the .047" straight line segment isn't visible.

So that's where I am right now. If I sound a bit undecided on how to approach making the real part, that's because I am. I'm not sure if I'm going to do the epoxy trick again, or screw the conn rod blank onto a fixture before I attack it.

 

[Steamchick]

Hi Bob, Is it Aluminium? Is there adequate material that you can rescue this with a file? - or are all the edges "sized" - but misplaced? (I think that is what you are showing in the zoomed picture of the big-end).
I like the technique, but not having CNC would have to make the mistakes manually in my shop (not difficult... I do it often for fun of rectifying later!). I am sure you are having fun whichever process you choose.
But with CNC, I would have simply machined the part from a solid billet... the finished bores being done after the big-end had been split, machined and joined by the big-end bolts. But perhaps that is too easy and less entertaining?
(The 1" long steel rods I made for a Stuart SUN engine were made from solid. Not a perfect pair, but work fine and are not visible so I don't care too much!).
Good post!
K2

 

[CFLBob]

Hi Bob, Is it Aluminium? Is there adequate material that you can rescue this with a file? - or are all the edges "sized" - but misplaced? (I think that is what you are showing in the zoomed picture of the big-end).
I like the technique, but not having CNC would have to make the mistakes manually in my shop (not difficult... I do it often for fun of rectifying later!). I am sure you are having fun whichever process you choose.
But with CNC, I would have simply machined the part from a solid billet... the finished bores being done after the big-end had been split, machined and joined by the big-end bolts. But perhaps that is too easy and less entertaining?
(The 1" long steel rods I made for a Stuart SUN engine were made from solid. Not a perfect pair, but work fine and are not visible so I don't care too much!).
Good post!
K2

Yes, it's aluminum. The top and bottom are a little offset, but mostly have a burr that has been hard to remove with a deburring tool or a mild file. The missing area was from when my system had what seemed to be a power glitch and then resumed cutting improperly. It cut in an area it wasn't supposed to cut.

It looks to me like it might even be usable because the area that had too much cut off doesn't seem to do anything. Let me grab a pic:

The red rectangle is about what's missing (not from my CAD program, just MS Paint). It's very close to the hole that needs to be threaded, but I'm not sure if it breaches the screw hole.

This part: "But with CNC, I would have simply machined the part from a solid billet... the finished bores being done after the big-end had been split, machined and joined by the big-end bolts. But perhaps that is too easy and less entertaining?" is exactly what I'm doing. I drill and tap the two holes for #5-40 SHCS before I cut off the end of the rod. When I put it together after that with the screws, I drill and ream the big hole.

 

[Steamchick]

Good stuff!
Well done on tackling this the difficult way by making your own castings.
K2

 

[awake]

Ehh, no problem. Just TIG weld back the missing bit,* file or recut, and off you go.

*Of course, my own aluminum TIG welding skill is not up to this task, but since I'm speaking for you, I feel comfortable advocating this approach ... !

 

[CFLBob]

Ehh, no problem. Just TIG weld back the missing bit,* file or recut, and off you go.

*Of course, my own aluminum TIG welding skill is not up to this task, but since I'm speaking for you, I feel comfortable advocating this approach ... !

And since I don't even own the simplest kind of welder, let alone TIG, it's ... academic.

I looked at this part for hours yesterday. Yes, it might well actually be usable. Yes, it's going into an engine where it will never be seen so "ugly is OK." I just know I can do better, so I'm going to do that.

 

[Brian Rupnow]

There is no shame in using ugly parts, as long as the ugly doesn't interfere with the way the part functions. However, it is vitally important that the ugly doesn't show. If the ugly shows, then regardless of how well the part functions, at least 137 forum readers will step up and offer helpful advice on how to do it right, suggest that you remake the piece, or denigrate your skills as a machinist and suggest that you should take up basket weaving or dog washing as a hobby.

 

[awake]

And since I don't even own the simplest kind of welder, let alone TIG, it's ... academic.

I looked at this part for hours yesterday. Yes, it might well actually be usable. Yes, it's going into an engine where it will never be seen so "ugly is OK." I just know I can do better, so I'm going to do that.

Oh, I'm with you on this - it sounds like this was as much or more of a learning opportunity than it was anticipated to be a final part. I've done some of those (though only manual - no CNC available), and once in a while the experiment is usable ... but always a learning experience!

 

[CFLBob]

... suggest that you should take up basket weaving or dog washing as a hobby.

I never thought of dog washing. My fall back on "I'm going to start a less demanding hobby" was always stamp collecting. There are only two steps:
Buy stamp.
Paste in book.

Neither can be done to even .001"

Dog washing sounds easier, although probably messier. Probably depends on the dog.