Author Topic: Muncaster Grasshopper - Work in Progress  (Read 37867 times)

Offline Jasonb

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Re: Muncaster Grasshopper - Work in Progress
« Reply #90 on: July 19, 2018, 07:22:44 AM »
With threaded ends to the rods you are only ever going to be able to set the rod length to within half a thread pitch if you are going to keep the ends lined up. May be better to put a spigot on the end of the shaft, drill the end and then loctite/pin together. Trim the spigots shoulder to set exact length.

Also any slight bend in your drill bit or runout in the chuck that you are using in your photos above to set lengthwill throw the measurement off, try a short pin in a collet.

Offline Brian Rupnow

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Re: Muncaster Grasshopper - Work in Progress
« Reply #91 on: July 19, 2018, 03:27:40 PM »
I like that jointed mechanism on the end of the beam to keep the piston rod travelling straight up and down. Sooner or later I am going to build a mechanism like that just to see it work. You are doing a great job.---Brian

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #92 on: July 20, 2018, 12:48:24 AM »
Turns out that the collar around the cylinder had slipped, causing the mismatch between the stays and beam.  One issue I've been seeing is that the stays can move around on their shafts causing binding.  The solution is to make spacers that keep the ends of the stays in place.  Rather than drill out 3/8" rod, I ordered some 3/8" steel tube from McMaster that I l'll ream .251.

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #93 on: July 24, 2018, 11:20:45 PM »
I finally got all the spacers made and put it all back together.  If I operate by pulling and pushing the piston rod it's stiff but not binding.  However at TDC and BDC of the crank, I have to push the crank past in order to continue.  It's very difficult to drive via the crankshaft, but when one considers the lever arms of the two options it's easy to see why.

I still need a couple of spacers to center the conrod on the crank pin, and need to fasten the crank to the crankshaft more securely than just a single grub screw if I want to try to run it in using the crankshaft as input.


Offline crueby

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Re: Muncaster Grasshopper - Work in Progress
« Reply #94 on: July 24, 2018, 11:30:07 PM »
Its not bottoming out the piston at tdc and bdc? I have had ones where I needed to take a smidge of thickness off the piston.


Looking great!

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #95 on: July 25, 2018, 12:22:53 AM »
Travel of the piston is good. The edges end up right at the steam port margins.  I adjusted bottom position via the piston rod and top position via the conrod.  By TDC/BDC I was referring to when the conrod and crank web are parallel.
 

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #96 on: July 27, 2018, 09:19:58 PM »
Today I attacked to eccentric rod.  Starting with some .5" diameter drill rod, I drilled and tapped a 10-32 hole about .3" deep.  This will form the "head" of the eccentric.  Next with some 3/16" drill rod cut to length, I thread milled 10-32 threads on one end and 8-32 threads on the other.  That was because I'd tapped the eccentric strap 8-32 thinking I use 1/4" rod here and join it to the strap with threaded rod. 



An advantage of thread milling here vs. a die is that I didn't need to turn down the 8-32 end.  I basically used the 10-32 g-code and added a couple of more passes to reach the minor diameter.

Next I drilled and reamed the head .1885" with the rod in place.



With the pieces assembled:


Offline crueby

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Re: Muncaster Grasshopper - Work in Progress
« Reply #97 on: July 27, 2018, 10:10:54 PM »
Nicely done!   :popcorn:

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #98 on: July 31, 2018, 09:36:51 PM »
This edition was spread over several days because of life getting in the way.

The motion of the eccentric is transmitted by a pair of rockers that pivot on a shaft at the end of the engine.  The rockers in turn push onto assemblies that move the valve up and down.  The first step in making the rockers was to profile them in some 1/4" Mic6 plate.



Then, using a technique (supposedly) learned from Terry McHugh, I filled them up with Darvon gel epoxy and let it cure overnight.



A preliminary measurement shows that the lifting ends of the rocker have a vertical travel of ~11.5mm, while the valve travel is 9mm.  Since the rocker arms are fixed length, the only way to adjust the travel is changing the length of the eccentric rod.

I looked a bit further into how the valve mechanism works.  The way Julius drew the valve and valve rod together there's no way it can be inserted into the steam chest.  I have redrawn the valve and separated the valve rod from it, although in doing so I had to reduce the depth of the valve's cavity by half.

The next morning I took off the bottom stock with a face mill.



At this point I went astray.  Supposedly heating to 300F will allow the parts to be removed from the epoxy while still hot.  I heated them to 400F for too long, which baked the plastic firmly to the parts.  The only option now was to burn off as much as possible with a torch and try to sand or file off the reside.  While this yielded usable parts, I intend to remake these.  Terry says he just fills the troughs with epoxy using a disposable syringe, so I've got an eBay order in for some of these.



To connect the eccentric rod to the first rocker one needs a short length of drill rod threaded on both ends 8-32.



The setup wit preliminary assembly.




Offline Tennessee Whiskey

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Re: Muncaster Grasshopper - Work in Progress
« Reply #99 on: July 31, 2018, 10:26:01 PM »
I am following along with you  :popcorn:. I hope that was some Devcon gel and not Darvon gel: that Darvon is a great pain reliever.

Whiskey

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #100 on: July 31, 2018, 10:40:35 PM »
I probably need both.  Devcon it is.

Offline b.lindsey

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Re: Muncaster Grasshopper - Work in Progress
« Reply #101 on: July 31, 2018, 10:43:21 PM »
Whatever you used Kirk, the results look good  ;)

Bill

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #102 on: August 05, 2018, 11:10:54 PM »
I have been struggling trying to figure the best way to attach the port block to the cylinder.  Relying on a layer of powder coat as both adhesive and air enclosure seems risky, so I think a thin layer of JB Weld is the way to go.  I did an experiment on some test pieces, and got an airtight seal.

To mate the two parts while the epoxy cures I'll use two .062" locating pins.  By drawing up the cross section of the cylinder, I was able to see that at the position of the pins the hole could be up to .226" deep before it would intersect the inner wall.  I drilled the two holes a conservative .150" deep.



And the corresponding holes in the port block.



Did a few other things for which I didn't take pics, so I'll save those for later.

The first actual part to be powder coated is the steam chest cover.  I'm debating using the red as an accent color, so this is a test part.



The red was brighter when I tested on aluminum, but here it's over sprayed onto the cast iron with the material being brass.

Offline zeeprogrammer

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Re: Muncaster Grasshopper - Work in Progress
« Reply #103 on: August 06, 2018, 12:10:27 AM »
 :popcorn:

Your powder coating learning and experimentation is very interesting.
Probably not something I can (I mean, would) do given my shop constraints. (Similar to the fact that I will never do welding.)

But none-the-less interesting to learn about.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #104 on: August 06, 2018, 12:32:06 AM »
Powder coating is both easier and cheaper than welding.  Easier than painting in some respects.

 

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