Author Topic: Test Bed  (Read 21749 times)

Offline Roger B

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Re: Test Bed
« Reply #30 on: November 06, 2014, 08:03:40 PM »
That's a very neat solution  :praise2:  :praise2: I had to read it a couple of times to fully understand  ::)

According to Terry Pratchett (an English SF/Fantasy author) the  :ThumbsUp: can also mean 'I hope that your donkey explodes'
Best regards

Roger

Offline Captain Jerry

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Re: Test Bed
« Reply #31 on: November 06, 2014, 11:54:08 PM »
My donkey did not explode, Roger.  I checked!

Thanks, Jo, Stuart and Bob.  This was really a simple solution. It just took a few years of on and off head banging to clear my head of all of the complicated solutions that got in the way of success.

Today, I bent some springs.  I went from .004" to .005" thickness and I think it is better.  I need to work out a better method of shaping it though. 

The cam was a bit of a rush job so the finish is awful but I wanted to check clearances before spending more time on it.  The control arm is also rough.  It was a reject or a left-over from my previous Corliss project, acceptable for a trial but will be replaced along with all of the other parts on the final version.  Here is a full assembly of the parts that float on the valve stem.









The last remaining part to make is the valve arm that is attached to the valve shaft.  It holds the latch pin that is picked up by the hook and is also attached to the dashpot arm that closes the valve when the hook releases it.

Jerry                                                                                                                                                            1245
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There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline Captain Jerry

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Re: Test Bed
« Reply #32 on: November 11, 2014, 01:30:03 AM »
In my previous post, I said that the CAM CONTROL ARM was from the box of rejects from a previous build but was going to stand until I made the VALVE CONTROL ARM for this version of the Reynolds release.  The more I looked at it, the more it bothered me.  It is not right for this one. It is not the right size.  The curvature does not match the other parts. It looks wrong.  So I decided to remake the CAM CONTROL ARM in a style that matches the other parts.

The feature that is common to the other parts is a cylindrical form that is .25" diameter and in line with the axis of the valve shaft.  This shows as The boss on the release lever and the visible part of the cam.  It will also be seen on the shaft end of the VALVE CONTROL ARM and the outboard end of the valve bonnets.  The CAM CONTROL ARM is a split clamp with a clamp screw on the lower side and a boss on the top surface to hold the arm.  In the old version, the arm and the clamp were turned in one piece and that is why the curvature is wrong or this design.  The axis of the cylindrical body of the clamp and the axis of the arm must be at right angles so the part will have to be a two piece fabrication with the arm boss will be set into the surface of the clamp cylinder, but the clamp cylinder can't be turned in the lathe because of the protruding clamp lugs.  It will have to be carved in the mill.

I worked on this all day yesterday, ending in complete failure.  Wrong concept, wrong order of ops, with nothing to show for it.

Today was better.  I made three copies.  All are workable.  All have faults.  Each fault was a lesson learned and I am confident that I have the right design and methods and can be improved on by more careful attention to detail.  I'll do better tomorrow.  Here are some poor photos of today's results.







I hope you can put up with the poor descriptions and photos.  I keep thinking I will get better at it.  Maybe you do too.
                                                                                                                                                                                                          1342

Jerry
« Last Edit: November 11, 2014, 01:50:56 AM by Captain Jerry »
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Online steamer

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Re: Test Bed
« Reply #33 on: November 11, 2014, 02:11:58 AM »
Nice looking parts Jerry!
Glad you're back in the shop!

Dave
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Damned ijjit!

Offline Ramon Wilson

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Re: Test Bed
« Reply #34 on: November 11, 2014, 04:20:57 PM »
Hi Jerry, I'm watching your progress with more than a modicum of interest  ;)

As one with a slight penchant for 'carving' in other directions I'm truly impressed with the scale at which you are working  :ThumbsUp:

It's good to see you back on this - sounds like you are enjoying yourself - please keep up this informative posting.

Regards - Ramon
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline Captain Jerry

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Re: Test Bed
« Reply #35 on: November 12, 2014, 01:06:33 AM »
Hi Dave and Ramon.  Your interest and encouragement are very much appreciated.

Scale? Yes these are tiny parts and the photos show every blemish in the finish, but after all, this is just a test bed to try some new methods and new ideas and to regain my feel for the machines.  Scale? Oh yeah, I'm supposed to include something in the photo for reference.  Since I swore off of M&Ms long ago, I'll just use a scale.  How's this?



Short time in the shop today so I worked on the Cam Arm.  I tried several different materials, stainless, hot rolled steel, and cast iron.  All worked out but I dropped the stainless one (gone!) and the cast iron looked best.  Here is the group:



Here is something I have discovered while working on this.  Even my smallest and sharpest spotting drill seemed to wander a bit.  A four flute end mill (1/16") at high speed does not skate off the mark and was followed up with 5/64" drill to finish size.



I have used the 1/16" end mill a lot on these parts.  I upgraded my mill to belt drive (Little Machine Shop Kit) and it has worked wonders with these little end mills.  The increased speed helps but the smoothness over the old gear drive makes it a joy to use them. 

I hope to get to the Valve Control Arm tomorrow.

Jerry
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline pgp001

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Re: Test Bed
« Reply #36 on: November 12, 2014, 01:15:40 PM »
I am watching this with great interest, the valve gear on my Pollit & Wigzell "Agnes" will work on a very similar principle (Hopefully)  :ThumbsUp:



Some of the parts are into watchmaking sort of sizes.

Phil

Offline Captain Jerry

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Re: Test Bed
« Reply #37 on: November 13, 2014, 01:50:12 AM »
That's a great picture, Phil, and a beautiful engine.  I try to keep an eye out for your project.  Anything new to show us?

The certainly some similarity in that valve gear and the design that I am building, and a lot of differences as well.  Most obviously, that is a real live machine that has worked reliably for a hundred years and mine is an unproven compromise with scale and skills.  I'm not sure why engines from your side of the water all seem to use spring actuated valve closers and over here they mostly went for gravity activated dash pots.  Maybe it has something to do with tectonic drift or distance from Greenwich.

My progress today was both rewarding and disappointing.  I am getting close to having a working model here and as I get closer, I tend to get in a rush and the finish of the parts suffer.  Today's part is a very simple one, the Valve Control Arm (with latch pin).  It is a simple bar with two holes in it.  One hole is a tight fit on the end of the valve shaft.  In full size, the arm would probable be keyed to the shaft but in this case, the shaft is only .094" dia. so the key is out.  I settled on a slightly tapered shoulder with a threaded extension so that the nut on the end of the shaft drives the arm onto the taper.

The other hole is for the latch pin/dash pot pin.  On the hook side of the arm, the latch pin it file to a trapezoidal shape that the hook engages with.  On the other side of the arm, the dash pot pin has a .094" dia. shoulder to carry the dash pot, and a #2-56 threaded end for the retaining nut.  The pin is an interference fit.  At this size it doesn't take much of a press to seat the pin.  Of curse, the critical dimension is the distance from the valve shaft center to the engagement face of the pin that is picked up by the hook.  Here is a photo of the hook above the pin, ready to engage.



The next photo is after the hook has engaged with the latch pin with a satisfying click.



My design dimensions were right on.  It is still a "file to fit" adjustment but it was well within the anticipated range.  And here is a final photo with the dash pot arm and retaining nut.  The threaded end is way to short.  The threaded end of the hook pivot screw above the arm will be filed back even with the face of the hook.



Now for the disappointment.  It does not release!  The cause is obvious...not enough cam lift.  There are four possible fixes.   

  1. File more off of the latch pin face.
  2. Remake the cam with greater lift.
  3. Remake the Arm with less distance  from shaft to latch pin.
  4. Remake the Hook with greater angle on the cam follower leg.

I will probably try them in the above order, I'll let you know.                                                                                                  1551

Jerry
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline Captain Jerry

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Re: Test Bed
« Reply #38 on: November 14, 2014, 01:40:57 AM »
 :whoohoo:

It releases!  As it turns out, there was another solution to above.  Since the threaded part of the pin was not long enough, it had to be remade anyway so instead of filing a trapezoidal shape on the latch pin, I rigged up a toolpost grinder and ground a triangular shape on the latch pin.  The faces of the pin are actually concave, matching the radius of the grinding wheel.  It has a much better formed latch/release face.  Just a touch of dressing with a file and the latch and release is smooth and regular.   

I do not have enough of the valve linkage, wrist plate, etc. to make a video and the parts are so small that I was not able to get any photos in the shop that were clear enough to post.  If I can get a PDF or Capture of the Alibre' screen, I will post it.

I will probably spend a few days re-making most of these parts to achieve a better finish before moving on to the linkage and dash pots.  This will be dull and repetitive so I won't post more until I move on, unless someone want clarification.

Jerry
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« Last Edit: November 14, 2014, 01:54:42 AM by Captain Jerry »
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Online Jo

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Re: Test Bed
« Reply #39 on: November 14, 2014, 08:14:03 AM »
 :ThumbsUp: Well done Jerry.

You are tempting me to have another play with my Corliss Cross Compound  :naughty:

Jo
Enjoyment is more important than achievement.

Offline Ramon Wilson

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Re: Test Bed
« Reply #40 on: November 14, 2014, 08:22:39 AM »
That's brilliant news Jerry - Congratulations, nothing like success after some dogged persistence  :ThumbsUp:

Good luck with the remaining work too - awaiting the outcome with eager anticipation  ;)

Regards - Ramon
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline Captain Jerry

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Re: Test Bed
« Reply #41 on: November 21, 2014, 03:32:37 AM »
Here is a method that I discovered by accident for fixing a lever or a hub to a small shaft.  In this case, the shaft is 1/8" dia. and the hub or base of the lever is 1/4" OD.  I had been cutting a #2-56 thread on the end of the shaft and then cutting a taper from the OD of the screw thread up to the 1/8" shaft.  Wit a hole slightly smaller than the 1/8" shaft, a nut on the threaded part could be used to drive the lever up the taper until it jammed tight.  It seemed tight but I was worried that the constant back and forth rotation of the lever would eventually cause it to slip.  Even though the force involved is small, any slip would cause a change in the valve timing.  That plus the appearance is not right scale wise.

In fact, the location of the arm on the shaft is most critical in adjusting the valve opening, and I am sure that before I get it worked out, the nut will have to be loosend and tightened many times.  Each time that is done, wear is induced until slipping must finally occur.  There are other problems with the design so it has to be rethought.

I thought about using a split clamp like I have used on the cam control lever arm.  It holds well and is easily adjustable.  I is used to adjust the valve closing regulated by the governor.  It is OK on the cam arm because it is mostly hidden but it looks too clumsy on the valve arm.

A shaft key is too small to consider and is not adjustable.  A cup point set screw (grub screw) will mar the shaft and will re-seat itself in the indentation, so small angular adjustments cannot be made reliable.  A flat or oval tipped set screw might overcome the marring but would have to be torqued hard and I don't think there is enough thread between the OD of the hub and the OD of the shaft  (.031") to take the load.

In the original MEM Corliss design, a set screw was shown but it was rotated around the shaft bore so that there was more meat for the screw thread.  I don't know if it was ever built that way but the idea was instrumental in my new plan.

A taper pin is a well recognized solution for this application but it requires very precise machining to be effective so that won't work well for me.  Taper pins usually pierce the shaft on center but they can also can be used tangent to the shaft.  I just had to replace the PTO drive shaft for the 18' 9 bladed mower and one of the CV joint hubs was attached to the shaft with a taper pin.  The taper pin was a little bit unusual in that it had threaded extensions on both ends.  A nut on the small end was used to pull the pin into the bore, and could be used on the big end to pull it out. 

That was the answer and here is my version on a #0-80 screw. 



The end of the screw does not contact the shaft.  It is tangential to the shaft and wedges in the annular groove.



It does not take much torque to jam, but I have rotated it to the bottom of the lever arm to increase the number of threads.  The groove also sets the longitudinal position n the shaft.  In the photo below, I am showing an overly long screw to emphasize the angle.



That is a socket cap screw and I am waiting delivery of some headless set screws which will disappear into the hole.  The hex on a #0-80 set screw is only .028" across the flats. 

This might work in many other applications.  I hope you can find some use for it.

Jerry                 
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« Last Edit: November 21, 2014, 03:40:35 AM by Captain Jerry »
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline Ramon Wilson

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Re: Test Bed
« Reply #42 on: November 21, 2014, 07:56:48 AM »
Another fine solution Jerry  :ThumbsUp: 

A concerned thought though - is there likely to be any eventual wear/distortion on the groove/taper due to the parts being soft? That might make future dis-assembly a bit testing.

Still watching with a keen interest 

Ramon
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline Captain Jerry

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Re: Test Bed
« Reply #43 on: November 21, 2014, 11:39:11 PM »
Ramon,

Thanks for your interest and comments.  I share your concern about distortion, more than wear, on soft parts.  The arm is cast iron because it is so easy to run a tap through and an #0-80 tape is pretty small.  I haven't decided on the shaft material but will likely settle on steel (1018) mostly because TGP shaft material is not available smaller than 1/4".  If you think there is a better choice, let me know.  I really don't know much about steel properties.  The shaft will be 1/8" for its full 2.25" length.  There will be two flats, 1/2" long and 1/32" deep at the midpoint.

The screw is stainless because that is all that I can find in the length that is needed to allow room to file or grind the taper ( #0-80  x 3/8").  I can find alloy steel set screws only 1/8" long.  If anyone can point me to a source for longer ones, I would use them.  Once it is adjusted, there should be no more movement so I don't worry about but I do worry some about the tapered part bending.  The long taper on the screw above may not be necessary.  The contact with the shaft groove should be on the big end of the taper but should not involve the screw thread.  I may try a steeper taper angle but until I get my hands on the headless set screws, I don't know.

The groove in the shaft can either be a "V" groove (60° threading tool) or opened up to 1/2 round with a needle file.  I don't think it makes much difference.

Thanks for watching.                                                                                                                                          1878

Jerry
« Last Edit: November 21, 2014, 11:43:15 PM by Captain Jerry »
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline Stuart

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Re: Test Bed
« Reply #44 on: November 22, 2014, 07:58:15 AM »
Fine work ther Jerry and wel documented

But I am intrigued what are the numbers at the end between thanks and your name


Stuart
My aim is for a accurate part with a good finish

 

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