Author Topic: Ridder's Stirling Bobber  (Read 7932 times)

Offline bent

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Ridder's Stirling Bobber
« on: March 28, 2018, 09:45:51 PM »
My next project will be the Stirling Bobber as shown on Jan Ridder's website:

http://ridders.nu/Webpaginas/pagina_stirling_jaknikker/jaknikker_frameset.htm  (this is the Dutch version, you can click the link at the top for English, but the picture in the frame then disappears...)

I don't know why, except that it looked intriguing.  But, to me, the motion of his model seemed a bit...hesitant?  I don't want to use the term jerky, but there is too much variation in flywheel speed for my taste.  Though maybe it's necessary for that hesitation to allow for the expansion and contraction of the air to occur?  So I thought, why not increase the flywheel speed via a gear train, maybe that would smooth out the motion a bit.  Well, one way to find out.  A bit of modeling, and tearing apart an old electric valve actuator to find some suitable gears, and voila (image below).  Gears modeled as simple discs, and the shafts aren't modeled yet either, but enough to get the idea I think.  Of course, some weeks later from starting this, I have come across another video with somewhat the same idea as mine!  Ah well, great minds and all that.

https://www.youtube.com/watch?v=gOClpeq8yVI&t=75s

The mill is trammed, and the new machine vice is mounted and squared to the mill table, test cuts have been made, acrylic chip shields with magnet bases whipped up and ready to go, bearings and test tubes have arrived, and the weather in the garage has gone from glacial to just chilly and damp.  Wish me luck! :zap:
« Last Edit: March 30, 2018, 05:44:10 PM by bent »

Offline Admiral_dk

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Re: Ridder's Stirling Bobber
« Reply #1 on: March 29, 2018, 08:52:38 PM »
Quote
this is the Danish version

Well I'm a Dane and I can tell you that this isn't Danish .... pretty sure the site is in Dutch just as Jan Ridder speaks it. ;)

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #2 on: March 30, 2018, 05:43:26 PM »
Wups!   :embarassed:
fixed it...


Offline bent

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Re: Ridder's Stirling Bobber
« Reply #3 on: April 12, 2018, 09:33:19 PM »
Have not progressed much on this over the past few weeks, other than to finish truing up the blanks for the uprights.  Before drilling all the holes in those, and for the base plate, I wanted to get my DRO's installed (it's been 20-some years since I've had a machine with DRO's, and forgot how handy they are, until reading other's posts on this site).  I did decide to purchase a cast flywheel for this project, just because.  Bought a 3in. "heavyweight" MartinModel.com casting, it looks pretty good.  Pic #1 is raw, Pic #2 after some fettling with a round file to remove the flash between the spokes.  After reading Jo's posts, I think my next steps are to spray a coat of primer on it, then chuck it in the 4-jaw to center on the inside of the rim, and start truing it up. 

I do like that the vendor anneals their castings, and provides a decent sized spud on one end to help in machining.



Offline b.lindsey

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Re: Ridder's Stirling Bobber
« Reply #4 on: April 12, 2018, 11:40:29 PM »
Looking good so far. Nice looking flywheel too.

Bill

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #5 on: April 16, 2018, 06:48:50 PM »
A little bit of work done Sunday afternoon on the first part (the flywheel support standard), and some learning experiences with the DRO's on the mill (it's been a long time since I've used such devices).  I'd laid out hole centers with some blue sharpie marker and light scribe marks, but they got wiped away from handling, so I ignored all that and used the DRO's directly to spot all the features.  Pic #1 below is the part with side notches milled, and holes bored.  First notch milled really nice, but forgot to set the cutter deep enough and only had half a slot.  Argh!  Back up and recut, and hit the same cut depth with the dro - and hey, no visible step in the finished notch, aren't dro's neat!!  After milling the notches and swapping the collet out for the chuck, and re-zeroing the DRO's I noticed that I'd mislocated the notches...figured it out finally - I'd forgotten to adjust for the thickness of the edge finding in spotting one of the pairs of notches.  So yeah, the notches are about 0.1" too close, so spotted the holes with the same offset so it wouldn't look too obvious.  Yeesh, what a noob!  :-[ Oh well, those are decorative bits anyways, and luckily I'd figured out my goof before spotting and drilling the bearing hole.  So, something to remember for next time.

But I was pretty happy using the z-axis DRO to hit the depth of the bearing pocket within a few thou - dropped a bearing in the pocket and it sets back at just the right depth (you can see it doing so in the photo).  Same for spotting and controlling the depth on the hole c'sinks, these came out pretty darn symmetric all around, happy with that.

Flipped the part on edge and spotted, drilled and tapped the two 6-32 holes.  Went slick as snot - even tried "powering" the tap for the first few threads, using the speed control.  A little scary, so I stopped doing that, and instead used the spindle wrench to turn the tap (held in drill chuck) to start it (holding down pressure on the z-axis with t'other hand), and then finished the hole by hand after getting a few turns in.  Pic #2 shows the second hole tapped, with the tap I used - a spiral fluted, TIN coated tap I swiped borrowed from work, this worked beautifully, it ejects chips out the top, leaving a much cleaner hole with no shavings buried down in the threads.  Will need to get a few more of these in other sizes.

Finally, set the part on a 45-degree angle, eyeballed using a trusty old drawing triangle, to mill the chamfers - this too is where the DRO's are handy, the chamfers came out pretty symmetric just by touching off with the side of the end mill and dialing in the cut depth with the DROs.

Pic #3 is the part, completed, sitting on my working drawing with all the markups (note the 3/8 radius modified to 1/4" for the notches, as I have not got a 3/4" mill...).  All in all, am happy with the new toys, though the operator needs more training, and the engineer should work on his drawings before releasing them to the shop. :atcomputer:

Lessons learned:
1.  Always double check the offsets when zeroing the dro's.  And lay out the holes, just as a triple check.
2.  Don't drill big holes with the mill set in high range, or it will stall.  Repeatedly, if you are that dumb to keep trying.
3.  Like when using the lathe, have a set place to put the chuck key, and make a habit to put it there every time; don't carry it around the shop with you when looking for drills, or calipers, or checking the drawing, because you'll put it down somewhere stupid and forget about it and spend 10 minutes searching for it.  Again.  I should probably paint all my keys different colors (drill press, mill, lathe) to keep them straight.
4.  Almost forgot.  When clamping parts in the screwless vice, make sure the clamping screw has a good bite in the slot chosen, or the part will slip even though you think the jaws are tight.

 :cheers:

-Ben

Offline zeeprogrammer

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Re: Ridder's Stirling Bobber
« Reply #6 on: April 16, 2018, 07:28:39 PM »
Looking good.

I'd never seen a tap like that. I'll need to check it out.

Always nice to see 'lessons learned'.  :ThumbsUp:
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Offline MMan

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Re: Ridder's Stirling Bobber
« Reply #7 on: April 16, 2018, 10:05:55 PM »
Hi Ben,

I know I have been guilty of all your lesson learned. what I try to do now is to: Zero the DRO on the edge finder, wind over by the radius and then zero again. Key for me is for it to be a habit. Of course I get distracted and forget, mostly I catch it because the tool looks to be in the wrong place but not always. Sigh.

Chuck keys always find a place to hide, I guess that is why keyless chucks are so popular - just feels wrong to me on a machine tool.

Spiral flute taps are great - lovely to watch the chips climb out of the hole and no need to think about 2-in-1-out. Although thinking back to when I used to drill holes as a sallow kid in production, the tapping machines did not do 2in1out and didn't eject the chips either, no idea how that worked hindsight.

Al the best,

Martin.


Offline bent

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Re: Ridder's Stirling Bobber
« Reply #8 on: April 20, 2018, 09:20:45 PM »
Quote
"Key for me is for it to be a habit. Of course I get distracted and forget, mostly I catch it because the tool looks to be in the wrong place but not always. Sigh."

Argh.  I get you, Martin - I did it again last night (twice, caught it before cutting chips the second time at least). :-[  :facepalm2:

Oh well, once again nothing but the cosmetic details was affected, so decided to press on.  Got the uprights all finished over the last couple nights.  I hope to start work on the flywheel next.

Pic #1 below is the cylinder standard, finishing milling the fork cut-out.  Did this all in one pass.  Originally drawn as an odd size U-shaped cut (full radius on the bottom) which would have required a boring head that I don't yet have, so made the rectangular cut instead.  Expediency and all that.  Also left the dustpan in the shot, you can see how thing the swarf is, as the nervous new mill owner was loathe to crank the handles too quickly.

Pic #2 is the same part flipped up for drilling and tapping the mounting holes - you can see the chip ejection from the spiral fluted tap, here in #8 size.  Love those things.

Pic #3 is the crank/gear support, after final planing to size with a 1/2" end mill.  Not super happy with the surface finish.  Add a flycutter to the shopping list.

Pic #4 is a family shot of the completed parts so far (all 3 upright/support thingies), though I will probably do some sanding on the faces yet.

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #9 on: April 24, 2018, 06:38:16 PM »
Another few days, a little further along. 

Pic #1 below is a family shot as of Saturday, with the base plate (shown upside down with the counterbored screw holes) and 3 uprights finished (less some sanding/polishing).

After reading Brian's posts on his flywheel casting, I decided to get started with mine.  First a coat of paint (thanks Jo!) to better keep the graphite in check from the cast iron surfaces (Pic #2 below).  Gaudy red, because I had a nearly empty can of it, and no primer; not sure if I'll keep it this color or not.  Then into the 4-jaw chuck, and start getting it aligned.  I was checking with a dial indicator on the vertical face of the inner rim, and along the radial direction of the step between the inner and outer rim.  With a bit of fussing, and a piece of 0.060" weld wire for a shim, I managed to get the total play on the indicator down to about 0.010 to .020" FIM.  Not too bad, and the indicator motion was mostly random, with a couple of "wows" (non-circularity) about 90 degrees apart (casting distortion).

I'd seen Brian's and zeeprogrammers posts, and the suggestion of using a mandrel block to support the casting from the inner rim/spokes face.  And that's where the real problem showed up.  This flywheel casting had over .100" of "float" (one side of the mold tilted relative to the other during casting), so there is a pronounced visible wobble when the parts are rotated.  There was also a noticeable shift in the casting (the two mold halves had slid along the parting line) of about 0.06", so another axis of the part was going to look wobbly.  Set down tools and went inside for dinner, as I was getting tired and wanted to sleep on the matter. 

Woke up Sunday, and after a bit more dithering and re-measuring, realized that there wasn't much else to do but start cutting and see if I could make things work.  I could choose to try and balance out the wobble, shimming the part in the chuck, to get a more or less equal amount of wobble on both faces - but then both faces would look like heck when it spun.  Or, dial in on one face, and let the other one wobble.  I took the latter approach, figuring one face was going to be somewhat hidden behind the crank and the rotating gears.  Pic #3 is the flywheel in the 4-jaw chuck, shimmed to get the outside face as centered and as flat as possible.

Machined the hub "spud" to clean it up, and the od and outer face of the rim.  Then reversed the part, exchanging the 4-jaw for the 3-jaw now that I had a cleaned up spud to turn it on.  Wow was that ugly, the wobble on the face and rim were very pronounced relative to the first side.  Oh well, press on, press on!  Cleaned up the o.d. and rim face using very light .005 and .010 cuts due to the heavy interrupted cuts, and then made a series of passes with a 20 degree taper on the cross slide, to get the corner of the rim, where it steps down to the inner rim, to be circular, and carried that across the face of the inner rim until it too was no longer wobbly.  Finally, a pass with a 30 degree taper, to get the corner of the inner rim (where it steps down to the spokes) to be circular.  Pic #4  is the "finished" view of the "bad" side of the wheel.  Finished in quotation marks, I still have to face and bore the hub, and I may cut a 45 or steeper chamfer where the hub machining runs out to the spokes.  I'm not happy that I've lost so much of the cast finish for this part, but better it looks straight/true spinning than not.

Pic #5 is a shot of the "good" side.  I went ahead and trimmed the inner corner of the rim to get that line circular and true, and match somewhat the machining done on the bad face.  Again, need to face the hub and probably chamfer the corner where it meets the spokes.

FWIW, as an engineer that designs castings, this casting comes close to exceeding the limits for float and shift in a production foundry.  Oh well, still beats the amount of work I'd have had to do machining a spoked wheel out of bar stock on a rotary table, which was my original plan.  And as I don't own a foundry or CNC mill, I'm hesitant to invest that kind of time just for one wheel, I'm not retired (yet) :).  Martin Models is not too far a drive from home, so maybe I should plan to do an on-site inspection of the wheels I want to buy?  Hmm.  They'd probably slam the door in my face, now.  Seriously, this was a nice casting to machine, and in the end, I think this wheel turned out pretty good, though it took some work and more machining than I wanted to get it there, so I'd probably do it all again.  Some variation is normal in castings, and our eyes will see these defects when the wheel is turning, so having a plan like mine to get as many of the corners/edges to be circular as possible may be the only way?

The last Pic #6 is my attempt to get a shot of the rotating wheel, so you can see the amount of "wobble" on the good face.  The blur lines of the spokes, and the rim edge where it meets the spokes, show where some of the remaining visible wobble is; but the rim edge and inner step run pretty true (no blur lines). 

Offline zeeprogrammer

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Re: Ridder's Stirling Bobber
« Reply #10 on: April 24, 2018, 07:32:16 PM »
If the rim is running true then I'm thinking you're good to go. (But keep in mind I have had little experience with flywheels.)

I'm curious about the suggestion to paint before machining.
Wouldn't that only help up until the paint is machined off?
Does the same technique apply to metals other than cast iron?

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Offline Tennessee Whiskey

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Re: Ridder's Stirling Bobber
« Reply #11 on: April 24, 2018, 08:20:36 PM »
Looking good so far Bent :ThumbsUp: :ThumbsUp:  Zee, that’s a Mr. Pete trick on the painting: paint it all first and after machining, there is nothing to “tape off and paint”

Cletus

Offline zeeprogrammer

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Re: Ridder's Stirling Bobber
« Reply #12 on: April 24, 2018, 08:25:02 PM »
Looking good so far Bent :ThumbsUp: :ThumbsUp:  Zee, that’s a Mr. Pete trick on the painting: paint it all first and after machining, there is nothing to “tape off and paint”

Ah. It's about having the spokes and inner rim painted. Thanks.
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Offline bent

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Re: Ridder's Stirling Bobber
« Reply #13 on: April 24, 2018, 10:56:15 PM »
Well, yeah, except for the dings and scratches (sheesh), to fix those I'm going to have to tape it off and hit it again anyway.  Also, the inner rim face on the "bad" side I will repaint just to get it to look like the "good" side.  But in theory, it's a good idea... ::)

It still cuts down on the debris/dust from handling the raw casting, and during cutting I found the contrasting color to help figure out how/where to cut next.

Offline bent

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Re: Ridder's Stirling Bobber
« Reply #14 on: May 07, 2018, 09:47:34 PM »
A bit more progress this last weekend, but some frustrations too.  Put another coat of paint on the flywheel, to cover the areas where I had machined to get some of the visible wobble to go away.  Swapped the lathe from 4-jaw to 3-jaw to turn one end of the flywheel (holding the spud of the casting), and sand/polish the o.d. and flanges.  Then went to reverse the part, only to realize that the jaws on the smaller chuck wouldn't open wide enough to hold the wheel by the rim.  Grr.  Oh well, I could finish that part on the lathe at work.  But maybe need to think about getting a larger chuck for the lathe...or just get really good at setting up the 4-jaw.

Onwards.  Realizing I'd not printed drawings for some parts I wanted to work on, and missing material for others, I settled on making the con rod, and decided to turn it from rectangular brass bar stock.  So, back to the 4-jaw, and started whittling.  All went well (photos 1 and 2 below) until it came time to thread the end of the part.  Using my cheap Amazon #5 threading die, I very quickly buggered up the end of the rod.  Grr.  Managed to get a partial thread on the end using a #6-32 die, but I may need to remake this part from scratch.  Took pictures, but everything came out blurry (hands shaking from rage? dunno).  :-[

Frustrated, but also realized that not having a die holder for the lathe tailstock was limiting.  Years ago I bought a #2 Morse taper with a 1/2-20 male thread on one end, just to make such devices with interchangeable ends to hold different sized dies, but forgot about it until now.  So, went to cut off a couple pieces of 1.5" steel bar to make die holders from, and promptly broke my one remaining reciprocating saw blade.  Grr.  Oh well, take it to work on Monday and use the bandsaw.  Good thing I waited, after looking about later online, it looks like the #5 die I have is a pretty crappy example; most dies have at least 4 threading points, mine has three, and the lead-in chamfer is visibly off making the rod to be threaded want to walk out of the die.  Also, the outside diameters of my thread dies are odd sized (3 different o.d.'s for 4 dies), and they don't have adjusting screws.  Hmm.  Need to do some shopping for a good set of threading dies.

Finished the flywheel today at work (except for a setscrew, will finish that at home).  Pics #3 and 4 - both sides of the wheel.  You can see the difference between the two sides in the painted areas of the outer rim if you look closely.  I think it won't be noticeable, and the flywheel definitely looks better now (visibly "not wobbly" when turning) than it did when I started.




 

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