Author Topic: Muncaster Grasshopper - Work in Progress  (Read 8525 times)

Offline kvom

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Muncaster Grasshopper - Work in Progress
« on: April 24, 2018, 06:01:31 PM »
I decided to start a new thread for a build as opposed to keeping on with the discussion of the plans.  As I mentioned in the other thread, I will be using Julius' original SW parts plus any modifications needed to use the two piece beam in V2.

As I wrote in the NAMES thread, I'm going to adopt Cliff Roemmich's idea of using honed hydraulic tubing for the cylinder.  I have ordered a piece of 2" OD x 1.5" ID tube from Bailey Hydraulics of Knoxville TN.  Since the OD is close to the OD of the cylinder itself, this tube will be the cylinder body and not a sleeve.  I had to order the minimum 24", enough for 4 engines.  If anyone else wants to share, I paid $90 for the tube, so a 6" piece would be 22.50 plus shipping.  I'll do an evaluation as soon the piece arrives.  FWIW, this is the 2nd smallest tube they have, and the smaller is 1.875" OD.

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #1 on: April 26, 2018, 09:36:22 PM »
My piece of tube from Bailey arrives this afternoon, so I was able to take the first baby steps in this project.  Here's the raw tube as shipped:



I cut off ~ 5.25" with the bandsaw, then  mounted on the lathe.  Faced both ends and applied a chamfer to remove the internal burr, then a second face/chamfer to length.  Finally a pass with some Scotch Brite to remove the external mill finish.



The OD of the tube measures 2.002" and the ID 1.502".

I also ordered a piece of 6061 4" round bar on eBay from which to make the beam mounting bracket.  I noticed that this bracket attaches to the top flange of the cylinder via 6 M4 screws, which means that the matching holes in the flange must be clearance and the holes in the bracket tapped.  But the other two hole in the flange (those over the port block) must be tapped in order to secure the matching holes in the cylinder cover.

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #2 on: April 27, 2018, 09:02:41 PM »
More work on the cylinder.  First, I turned down each end to 1.75" diameter for a length of 8mm.  DRO makes this mix of metric/imperial relatively math free.  The tube sticks out a bit more than I like, but I don't have a live centerlarge enough.  I used the nose of a large drill chuck to align it.



Now for the bottom flange, I used a length of 3" 6061 bar to turn down the outer diameter to 65mm and the inner to 51x4mm.  Then opened up the center with a 1-3/8" endmill that I've never otherwise used.  Then boring bar to creep up on a sliding fit to the cylinder tube.





Then parted off and faced flange to 4mm thickness.  The mounting holes will be drilled and tapped later on.  Then I repeated the operations for the top flange, that differs in being 70mm diameter.

With both flanges done, the assembly was clamped on the Bridgeport's vise, and a flat machined for mounting the port block.  Julius drew the port block with a concave inner surface to match the outer surface of the cylinder, but I feared being able to get an air tight fit that way.  The two steam ports were then drilled with a 5/32 endmill.






Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #3 on: April 29, 2018, 10:51:34 PM »
This weekend's shop time was occupied with the port block.  Again I used imperial measurements but needed to retain the metric spacing of the mounting holes for the steam chest.  I started with a piece of 6061 5x2x1 inches and whittled it down to this:





Posing with the cylinder:



I still need to drill the exhaust outlet and tap the mounting holes 8-32.

Offline Gas_mantle

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Re: Muncaster Grasshopper - Work in Progress
« Reply #4 on: April 29, 2018, 11:27:24 PM »
Looks good, a lot bigger than I expected  :)

Offline b.lindsey

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Re: Muncaster Grasshopper - Work in Progress
« Reply #5 on: April 30, 2018, 12:37:30 AM »
The cylinder is coming together very nicely Kirk. Its bigger that I had expected too, should make for a very nice model though.

Bill

Offline Craig DeShong

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Re: Muncaster Grasshopper - Work in Progress
« Reply #6 on: May 01, 2018, 02:05:26 AM »
Looks great.  That is an interesting method of creating the ports.  At that size it's going to have quite a bark. :popcorn:
Craig

Offline Jasonb

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Re: Muncaster Grasshopper - Work in Progress
« Reply #7 on: May 01, 2018, 07:11:49 AM »
Hope it will bark loudly as I can't see much point in milling out the nice wide passage and then squeezing all that air/steam through one small hole at the end of the cylinder? I think I would at least have made the cylinder holes the same area as the ones from the ports, easily done my making them a slot about the width of the visible steel.

It's also usual to have a larger exhaust area so you are not using up energy forcing the exhaust out but with just 3 holes from the port you have the same area as the inlets.
« Last Edit: May 01, 2018, 07:18:45 AM by Jasonb »

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #8 on: May 01, 2018, 02:45:03 PM »
The exhaust holes are larger than the inlet holes (.155" vs .125").  I didn't want to attempt a deep pocket with a 5/32" endmill on the ports.

I suspect that the bottom inlet port into the cylinder should be enlarged, but I'm also thinking that the the down stroke won't need much pressure at all.

Offline Jasonb

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Re: Muncaster Grasshopper - Work in Progress
« Reply #9 on: May 01, 2018, 04:57:35 PM »
That still sounds very small for a large cylinder. Looking at the Muncaster origianls Jo posted I would say he had the ports and passages the same cross section all the way to the cylinder about 3/16 x 1 and you only have ONE 5/32" hole at the ends of the cylinder, that's less area than a little 3/4" bore Stuart 10V. and only about 10% of Muncasters.

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #10 on: May 01, 2018, 10:43:31 PM »
On the valid assumption that Jason knows more about this than I, I decided to enlarge the ports, although probably not as much as he recommends.  Going by Julius' SW assembly the piston as drawn has a stroke the entire length of the bore, meaning enlarging along the vertical would be problematic.  If the model turns out to have need of more air, the length of the piston can be reduced allowing further enlargement of the opening. Time will tell.  I suspect Julius didn't do any calculations of air supply issues.

So first I needed to orient the cylinder with the flat horizontal.  This was my method:



With larger ports machined:



I decided that to attach the steam chest to the port block, I'd use screws from the back of the flange.  This allows the chest to remain firmly attached to the port block when the cover is removed.  The cover and chest are attached with longer screws using the other 4 holes plus shorter screws for the flange holes that are through tapped.





The steam chest is the first metric CNC part I've made.  I exported the DXF from the SW part given metric measurements for all dimensions.  When loaded into my CAM program, the fact that the drawing is metric meant that all generated moved were in mm.  Of course, not having any metric endmills or drills, I had to calculate their diameters, and likewise needed to get used to specifying feeds in mm/min.  The fact of G21 occuring in the g-code file caused my mill control to switch as well.

For edge finding I typically jog down to .001" accuracy, which matches the accuracy of the mill.  However, in metric the .001 jog button changed to .01mm, which is about .004".  SAo now I have to also use the .0025 mm button to get to the same accuracy.  And since my edge finder is imperial (.200), I'm better off finding edges in imperial before switch to metric.

I still need to drill the holes for the valve rod and steam inlet in the chest, along with holes for the mounts.

Offline john mills

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Re: Muncaster Grasshopper - Work in Progress
« Reply #11 on: May 01, 2018, 11:19:20 PM »
.01mm  = .0004" that shifting of decimal points causes all sorts of problems and can be very dangerous.
i learnt to stick to metric years ago i did one program in imperial but that was because was a bigger complex part

and i didn't want to change it all to metric stored offsets changed i didn't have drawing or cad programs i did lots of profile shapes in 2 and 3d  just a calculator and pencil .with older machines it was safer and less problems
to stick to metric.






Offline Tennessee Whiskey

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Re: Muncaster Grasshopper - Work in Progress
« Reply #12 on: May 01, 2018, 11:59:31 PM »
Kirk, sorry for shooting my mouth of on the NAMES thread; guess it was a bad day  :facepalm:. I guess I can see at that size of cylinder a nice pre bored cylinder would make sense. Great build and Iíll be following, even if I donít understand a thing about G this or that.  :popcorn:and  :DrinkPint: in hand

Cletus

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #13 on: May 02, 2018, 01:03:51 AM »
I just regard this material like drill rod, already polished and ready to use.   :)

Last jog button under metric is .025 mm or .00098", close to a thou. 
« Last Edit: May 02, 2018, 01:07:49 AM by kvom »

Offline kvom

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Re: Muncaster Grasshopper - Work in Progress
« Reply #14 on: May 03, 2018, 01:00:57 AM »
This morning I spent working on the steam chest cover, using some 1/4" brass.  Pretty simple part other than getting the corners of the inside spigot to fit tightly to the chest.





In the afternoon made a start on the cylinder cover.  First op was turning the top surface and its spigot.



After parting off, then the bottom surface and the spigot to fit the cylinder bore.



Next time in the shop I'll finish the mounting holes.  I was waiting for the post to deliver some 4" aluminum round for making the beam collar, but for some reason moving the package from North Atlanta the final 15 miles takes more than 2 days.   :shrug: