Author Topic: Muncaster Grasshopper - Work in Progress  (Read 37903 times)

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #60 on: June 15, 2018, 01:18:11 AM »
I decided to order some 5/8" drill rod for the crankshaft, so while waiting for MSC to deliver I turned my attention to the eccentric.  Julius drew the strap to have a thin bronze inner bearing, but machining that ring means losing the interior as chips.  So I plan to make the eccentric itself from 660 bronze (I have a 2" diameter piece at hand) and the strap from aluminum.

Extracting the side profile from the SW file allowed seeing that the two halves together fit within a 3" circle with enough space between for a 3/8" endmill to pass.  I've had a piece of 3" diameter rod for ages, and slicing off a piece to order means not needed to worry about how thick I'd need to have on hand if I were going to use a bar or sheet.  In this case I had a piece of machined round that was an aborted part for another long ago project, so it was on to the mill to machine the profiles.  I cut them 10mm deep although the strap itself will end up 7mm thick.



Then I cut them loose by parting on the lathe (actually needed to hacksaw the last 1/4"), then face milled both sides at the Bridgeport.



I started late in the day, so this was as far as I got today.   The rest is pretty similar to the process for the bearing block.  Drill and tap to screw the two halves together, then drill/tap for the eccentric rod and cut out the center hold.  The the strap can be used when machining the matching groove in the eccentric itself.

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #61 on: June 18, 2018, 10:39:38 PM »
Last two shop sessions continued with the eccentric.  Here's the two halves of the strap drilled/tapped.  5-40 screws for closure, 8-32 for the rod.



The next op was to interpolate mill a 40mm hole in the center of the strap.



Now the strap can be used to mill the groove in the eccentric itself.  I started with some 2" bronze bar and turned down to 44mm.



The groove was cut with parting tools carefully creeping up on 40mm using the strap to check for fit.



Next op was to mill the boss for the eccentric hub.  I cut a strip of shim stock to fit in the groove and then tightened the strap on it so that it couldn't turn.  The bore for the crankshaft was milled undersize and will be bored to size on the lathe.  As with the main bearing, my small micro carbide boring bar is too short to go all the way through.  I have ordered one with a .5" shank and 2" reach that I'll use for both.



Also TBD are tapped holes for grub screws to attach the eccentric to the crankshaft.

Offline zeeprogrammer

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Re: Muncaster Grasshopper - Work in Progress
« Reply #62 on: June 19, 2018, 12:59:54 AM »
Looking good.  :ThumbsUp:
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Offline Tennessee Whiskey

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Re: Muncaster Grasshopper - Work in Progress
« Reply #63 on: June 19, 2018, 01:04:17 AM »
I like grooving the eccentric rather than the strap, lot more bearing surface.

Cletus

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #64 on: June 19, 2018, 02:27:46 AM »
And a lot easier too.

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #65 on: June 19, 2018, 10:34:15 PM »
After considering different ways to make the various links for this engine, I decided to try to make each from a single piece of stock rather than fabricating.  The main advantage, as I see it, is that the links are to be made in pairs and being able to predrill their mounting holes means that each member of the pair has the same effective length.

The width of the heads is 12mm on the majority of the them, so using 1/2" square bar makes sense.  And I happen to have a 6' stick of 1/2" brass bar, so my intention will be to make them from brass.  Normally steel would look more authentic, but I'll be powder coating these so the yellow color won't be an issue. 

The first to be attempted will be one of the swinging links that attach to the end of the beam.  The holes are 102mm apart, and the length of stock needed is 118mm.  After cutting off a piece and trimming to length, I used a center drill in each end.  That square collet I picked up at CF some years back came in useful.



Then off to the CNC mill to drill the holes and profile the link.  By leaving 1/8" of stock at the bottom, I expect to be able to hold one end still in the 5C collet.



That hope proved true (otherwise I'd need to turn a dead center and use a lathe dog.  Once mounted, I used a parting too tool make space for a turning tool.



After some time at the lathe I arrived at this.  It was necessary to reverse the piece in order to turn both ends.  The hold in the collet isn't exact so there was some runout once I'd reversed it.  For the future parts I'd going to increase the head diameter to 1/2" so that the collet can use all 4 sides to center the work.  In any case, I was able to use the parting blade as a turning tool to make the diameter consistent.



Next it was on to the Bridgeport to take 1/8" off both sides bringing the thickness to 1/4".



At this point I can hold the shaft with the jaws on my regular chuck, which will allow me to remove the center drill portion and possible taper the intersection of the heads and shaft.

 

Offline Gas_mantle

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Re: Muncaster Grasshopper - Work in Progress
« Reply #66 on: June 19, 2018, 10:48:29 PM »
Looking good  :ThumbsUp: :popcorn:

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #67 on: June 21, 2018, 08:17:08 PM »
The new longer boring bar arrived by post today, so I was able to bore both the main bearing and eccentric to fit the 5/8" crankshaft.


Offline Craig DeShong

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Re: Muncaster Grasshopper - Work in Progress
« Reply #68 on: June 21, 2018, 10:55:56 PM »
Nice job Kirk, looks great.  It's interesting to see how others address things you've done yourself.  No single right way, just many ways to achieve the same result.  Who knows, sometime in the future something may prevent me from using a method I've used in the past and one of these ways you've shown here will be the solution I need. Thanks!
Craig
The destination motivates us toward excellence, the journey entertains us, and along the way we meet so many interesting people.

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #69 on: June 22, 2018, 09:58:32 PM »
Today I spent most of the afternoon making these little "stay mounts".  These screw onto the top of the horizontal beam and connect to the middle stays.  The holes in the beams will be located once the stays are all in place.



Quite a few ops needed on these between the CNC and Bridgeport.

Offline RMO

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Re: Muncaster Grasshopper - Work in Progress
« Reply #70 on: June 22, 2018, 10:57:03 PM »
Just read through the build log, lots of fun work there.  Thanks for sharing.

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #71 on: June 26, 2018, 09:47:23 PM »
I completed the mill operations for all the rest of the stays, so next it's needed to turn the shafts.    I wanted to turn these between centers since it's difficult to hold the ends centered in the lathe chuck.  Turning between centers requires a center to be turned and left mounted in the lathe, and as well you need a lathe dog to force the work to turn when mounted.  After some deliberation, I came up with the following.

First, a scrap piece of 1.5" aluminum rod was turned down to provide the center, and a 1/4" hole drilled to become part of the dog.



With the piece mounted and the compound turned to 30 degrees, the center could be turned.



The rest of the dog consists of a short piece of 3/8" brass rod with a 1/4" hole along the axis and another 1/4" cross hole.  Testing for fit:



Once the lengths of the two 1/4" rods were determined, they were loctited in the center and the dog respectively.  The stays could then be mounted and turned.






Offline 10KPete

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Re: Muncaster Grasshopper - Work in Progress
« Reply #72 on: June 26, 2018, 11:21:27 PM »
Very clever!! I love that set-up, just need to remember it...

Pete
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Offline b.lindsey

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Re: Muncaster Grasshopper - Work in Progress
« Reply #73 on: June 26, 2018, 11:23:42 PM »
Some very nice progress Kirk!! I look forward to your updates.

Bill

Offline zeeprogrammer

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Re: Muncaster Grasshopper - Work in Progress
« Reply #74 on: June 27, 2018, 12:52:37 AM »
Following along Kirk.  :popcorn:
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
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