Author Topic: Building the Potty Grasshopper engine.  (Read 23604 times)

Offline Gas_mantle

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Re: Building the Potty Grasshopper engine.
« Reply #30 on: October 24, 2016, 03:11:45 PM »
Thanks Stewart, I'm really enjoying building this - are you planning on adding any more engines to the Potty series ?

Offline Jasonb

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Re: Building the Potty Grasshopper engine.
« Reply #31 on: October 24, 2016, 03:24:26 PM »
Its comming along well Peter.

For scale looking metric fastners you really need smaller hex than the standard sizes the likes of Modelfixings do. The only place I know of who do them in the UK are Bruce Engineering. I get mine from the German company that they source them from.

http://www.modellbauershop.de/schrauben/modellbauschrauben.php

The PDF catalogue gives nore detail of the hex sizes

http://www.modellbauershop.de/schrauben/modellbauschrauben.php

You can see the difference between the large flat standard M3 & M4 nuts in the middle and the GHW ones either side


Offline Gas_mantle

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Re: Building the Potty Grasshopper engine.
« Reply #32 on: October 24, 2016, 03:38:32 PM »
Cheers Jason, I see what you mean about a smaller hex having a more scaled appearance

With hindsight I'd have been better using BA threads but when I started making it I only had metric taps and dies - I bought an assortment of nuts and bolts when I started this hobby but they are of very poor quality to used on finished models.



Offline b.lindsey

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Re: Building the Potty Grasshopper engine.
« Reply #33 on: October 24, 2016, 06:09:58 PM »
Peter, that is looking excellent. Should make a fine looking model. Hopefully you can find some more scale fasteners but even so the machining looks terrific thus far!!

Bill

Offline Gas_mantle

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Re: Building the Potty Grasshopper engine.
« Reply #34 on: October 26, 2016, 03:05:45 PM »
Cheers Bill  :)

I thought I'd have a bash at the conrod next, it's a fairly straightforward part made as a single piece from 3/4" square steel bar but I've never turned between centres before and never cut tapers either so wasn't sure how it would turn out.

Anyway, first job mark out the rough shape and drill a hole at either end for the bearings.



So far so good, it's just about roughed out ready to cut the tapers and profile the decorative bulb in the middle



After turning the tapers and working on cutting radiussed corners I eventually end up with this :-



 :(  I'm gutted, it was turning out nicely but destined for the scrap box now  :'(

Peter






Offline b.lindsey

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Re: Building the Potty Grasshopper engine.
« Reply #35 on: October 26, 2016, 03:41:55 PM »
Bummer Peter, but it happens to all of us, nothing to do but remake it. Is there a way to fabricate it perhaps rather than turning it from the solid?

Bill

Offline Gas_mantle

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Re: Building the Potty Grasshopper engine.
« Reply #36 on: October 26, 2016, 03:47:56 PM »
I did think of fabricating one Bill, that's how I've done it in the past but I'm kinda using this build as a learning exercise and want to be able to turn one piece items like conrods and to add decorative tapers etc.

It's a bit of a pain but I've never done it before so I'm still quite pleased that it was actually starting to look ok before the accident, it's a lesson learnt  :)

Offline Jasonb

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Re: Building the Potty Grasshopper engine.
« Reply #37 on: October 26, 2016, 04:07:46 PM »
For a more rigid setup you could hold one end in the 4-jaw and support the other with the tailstock. Do all the work on the half nearest the chuck then flip it end for end and machine the other half. Work the ctr section before you do the tapers so there is some meat in the shaft to help reduce deflection.

Offline Gas_mantle

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Re: Building the Potty Grasshopper engine.
« Reply #38 on: November 10, 2016, 05:17:57 PM »
Hi all

Well I've managed to get a bit further but most of it has been redoing the conrod after the earlier disaster.

This time I held it in the 4 jaw and turned the middle bulb first as suggested (thanks Jason) :-)



Thankfully that seemed fairly painless so it's onto rounding of the ends, moving the part by hand around a close fitting pin seemed to work reasonably well if done carefully.



I added a couple of brass bearing inserts then decided to make the valve as a simple turning job that would just fill in a bit of time - it's a spool valve engine so the valve is a 'dogbone' shaped affair made from a 9mm and a 4mm dia silver steel rods.



With a brass piston rod guide made from 15mm hex bar I now have this trio to cross off the list. The little groove in the con rod bulb is deliberate - I thought it gave a bit of added detail and there is one on the other side. One end could do with a small cut to cut to make the sides parallel - I hadn't noticed it at the time but overall I'm happy it will look ok with a bit of finishing and polishing.

]

I've bought a 10" dia wheel casting and a piece of plate as a base so it's slowly taking shape  :)



Peter.




Offline Jasonb

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Re: Building the Potty Grasshopper engine.
« Reply #39 on: November 10, 2016, 05:27:44 PM »
Looking good, those RDG flywheels come up OK with a bit of fettling, I have used several as they are very good value.

Offline Gas_mantle

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Re: Building the Potty Grasshopper engine.
« Reply #40 on: November 10, 2016, 05:37:01 PM »
Thanks Jason, I thought the wheel castings seemed good value also, I was going to see how this one turned out and maybe buy another as a spare.

I can't turn a 10" wheel on my lathe but another forum member has said he'll help me true it up on his larger machine - am I likely to have any trouble if I get it roughed out using a 6" rotary table on my mill ? I know it's not ideal but sometimes you have to work with what you've got.

I'm looking a buying a boiler soon, do you think it will be ok on steam for short runs once in a while ? The cylinder is aluminium with a silver steel piston rod and a brass piston.

Thanks.

Offline Roger B

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Re: Building the Potty Grasshopper engine.
« Reply #41 on: November 10, 2016, 06:01:18 PM »
Glad you sorted out your rod problem  :ThumbsUp:  :ThumbsUp: Looking good  :praise2:
Best regards

Roger

Offline Jasonb

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Re: Building the Potty Grasshopper engine.
« Reply #42 on: November 10, 2016, 06:43:38 PM »
You should be OK taking teh skin off on a rotary table. I would be wary of clamping it by the spokes which are quiet thin on that particular style of flywheel. Best to make up a sub table from a piece of 18mm MDF or ply and clamp the flywheel rim to that with several clamps on teh inside and just remove one as it gets in teh way then replace and remove the next one.

Anothre method I have seen is to cut two MDF "washers" that will clear the hub and fit inside the rim bosses then sandwich it between them and fix right through to the rotary table.

A god bit of oil through it after steaming should be OK and keep the rust at bay.

Offline b.lindsey

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Re: Building the Potty Grasshopper engine.
« Reply #43 on: November 10, 2016, 08:26:45 PM »
That is really looking great Peter. Thanks for the family shot too!!

Bill

Offline Gas_mantle

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Re: Building the Potty Grasshopper engine.
« Reply #44 on: November 10, 2016, 08:34:52 PM »
Many thanks guys, I'm quite pleased with how it's starting to look - it's hardly advanced engineering but is far more complicated than anything I've made so far.

I've now bought a boring head so I'm hoping to give that a practice run on some scrap tomorrow then hopefully tackle the pivoted supporting beam over the weekend. The idea is to try and cut decorative circular rings to match the 'A' frame - watch this space  ;)


 

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