Question on 3.5" Rob Roy drawings

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WJH
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Location: Florida

Question on 3.5" Rob Roy drawings

Post by WJH » Thu Jul 07, 2016 10:10 pm

I have the book on building the Rob Roy, and I can't figure out the length of the axles.
Image
I can tell you that it is NOT 3 9/32's
Typo in book as far as I am concerned..

Mike Green
Posts: 21
Joined: Wed Oct 15, 2008 10:22 pm
Location: Lindsay, Ontario, Canada

Re: Question on 3.5" Rob Roy drawings

Post by Mike Green » Thu Jul 07, 2016 10:38 pm

Just found that I have the same Rob Roy book as you with the same typo. Checked in my L.B.S.C. book for two of Virginia's axles and they are both 3-9/32" main length with the 1/2" ends. Both designed for 3-1/2" gauge, 3/4" scale. Regards, Mike.

Harold_V
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Re: Question on 3.5" Rob Roy drawings

Post by Harold_V » Fri Jul 08, 2016 1:46 am

Simple, at least as drawn. The center portion is expected to be 3 9/32", with ½" added to each side. Overall length, 4-9/32".
That may not be your question, though.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

WJH
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Location: Florida

Re: Question on 3.5" Rob Roy drawings

Post by WJH » Fri Jul 08, 2016 7:11 am

Heres why I thought the dimension was incorrect
Image
DOH!!! The horn blocks need to be on the inside of the frames, not the outside! :oops:

sncf141r
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Location: Canada

Re: Question on 3.5" Rob Roy drawings

Post by sncf141r » Fri Jul 08, 2016 9:09 am

WJH wrote:Heres why I thought the dimension was incorrect... DOH!!! The horn blocks need to be on the inside of the frames, not the outside!
At least you found it now, and, some UK plate framed locomotives (thinking Brittania here) had the hornblocks half in and half out, to try and minimize frame flexing.

By the way, I now build my locomotives so that the bearing blocks have only one flange; outside, between the hornblock/frame and wheel.

I have no idea why they were drawn with two flanges, (other than it's prototype practice, with the added prototype complications) because, the bearing is not going anywhere, even with the missing inside flange.

RickBarb
Posts: 51
Joined: Sun Jan 05, 2003 2:12 pm
Location: Cape Cod, MA

Re: Question on 3.5" Rob Roy drawings

Post by RickBarb » Fri Jul 08, 2016 12:01 pm

WJH, I would strongly suggest you google "Errors on Rob Roy Drawings". There quite a few listed as I found out during my construction of the 3-1/2" Rob Roy. Good Luck, Rick

JJG Koopmans
Posts: 334
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Location: Netherlands

Re: Question on 3.5" Rob Roy drawings

Post by JJG Koopmans » Fri Jul 08, 2016 2:07 pm

I bought a secondhand Rob Roy in parts which appeared made by the book. On assembly it appeared that it could never have worked properly. My caveats:
a) I could not get the vertical slides steamtight until I made a tiny spring in the slide valve nuts, p 32/33
b) the crosshead pump should be carefully checked for its dimensions and location, mine is too far backward and basically too short for its stroke.
c) as noted in the earlier mentioned error lists, the exhaust system is dimensioned incorrectly, I changed
for my own system,4-orifice and tapered chimney with a smaller(!) diameter
d) the stroke of the oil feed pump as drawn is far too large for the single click needed
Once working, it is a nice engine pulling properly.
Success,
Jos Koopmans

WJH
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Joined: Sat Jan 16, 2010 9:29 pm
Location: Florida

Re: Question on 3.5" Rob Roy drawings

Post by WJH » Fri Jul 08, 2016 2:30 pm

Thanks guys for the information. My standard operating procedure is to build the locomotive entirely in 3D cad, in this case, Fusion360, and discover any issues with bad dimensions and locations, fix them in the 3d model, then generate new drawings to work from based on my 3d model.
It looks like a nice locomotive.
Image

JJG Koopmans
Posts: 334
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Location: Netherlands

Re: Question on 3.5" Rob Roy drawings

Post by JJG Koopmans » Fri Jul 08, 2016 3:27 pm

Nice drawing! There is a strong suggestion to have an additional cross-bar just behind the cylinderblock. I found it indeed necessary.
Kind regards
Jos Koopmans

WJH
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Location: Florida

Re: Question on 3.5" Rob Roy drawings

Post by WJH » Fri Jul 08, 2016 4:19 pm

JJG Koopmans wrote:Nice drawing! There is a strong suggestion to have an additional cross-bar just behind the cylinderblock. I found it indeed necessary.
Kind regards
Jos Koopmans
I'll make sure to do that!

WJH
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Location: Florida

Re: Question on 3.5" Rob Roy drawings

Post by WJH » Fri Jul 08, 2016 7:51 pm

Ok, something like this?
Image

JJG Koopmans
Posts: 334
Joined: Thu Oct 01, 2009 10:01 am
Location: Netherlands

Re: Question on 3.5" Rob Roy drawings

Post by JJG Koopmans » Sat Jul 09, 2016 9:09 am

I think it should be on the upper side, not at the bottom, the main reason is the way both fresh steam
and exhaust steam lines are plumbed. They act as frame stretchers as discussed here:

http://easyweb.easynet.co.uk/~chrish/ca ... robroy.htm
There are more suggestions for modifications/improvements on the web, some time looking for them is very well spent as it saves a lot of frustration.
I myself collected this:
Rob Roy. 0-6-0T in 3½" gauge by Martin Evans.

If built to the drawings (and I don't think they have been corrected yet), the valve gear and the valve spindles don't line up. The difference is 1/8" (?), and the solution is either to make a stepped valve crosshead, or to make the valve face 1/16" further out from the cylinder, and the valve spindle 1/16" higher in the steam chest. (Thanks, to Steve Papworth.)

Change the pitch of the thread on one end of the valve spindle, to allow the setting of the valves to be more easily modified.

Fit thin locknuts to both valve and piston glands.

The bottom section of the crosshead pump is too close to the cylinders.

The blast pipe is in the wrong position.
Increasing the height of the blast pipe by about 3/8" seems to improve draughting.

The dome bushing on the boiler should be 3/4" diameter bore!

Rob Roy by Martin Evans.
Ivan Jacoby says:
The blastpipe is too low and the petticoat pipe has a very small bellmouth. I have fitted a multi jet blastpipe with the jets angled at 1 in 12 and a venturi petticoat pipe. I have raised the blastpipe to within 1/2 inch of the petticoat pipe. I have also reduced the chimney choke by about 1/4 inch. The result is that the draughting is much improved on a bench test and the boiler will maintain pressure whatever the throttle position.

Re: Rob Roy
by Rick on Tue 06 May 2008 02:28 AM BST | Profile | Permanent Link
I am in the process of constructing the tanks for my Rob Roy and have run into a problem which I did not know about, nor have I read about it. I started building the rear tank that is in the back of the cab on the footplate. I built it according to the dimensions shown on the plans, but when I tried to position it, I found that it was interferring with the quadrant, The drawings show the center of the quadrant to be 2-1/2" ahead of the back of the frame. The drawing shows the back of the tank to be 1/4" ahead of the buffer beam. the tank is shown to be 1-3/4" wide. This only allows 1/2" from the vertical centerline of the quadrant to the front of the tank(Coal plate). It just will not fit. I guess I will just reduce the width of the tank by approximately 1/4". Has anyone else run into this "glitch"?

Rick
Cape Cod, MA USA
and:
http://modeleng.proboards.com/thread/6137

http://modeleng.proboards.com/thread/94 ... roy?page=2

Alan Stepney used to have a website which had lists of corrections for a number of models. The
website appears to have hijacked, but the former one might be available from archives.
Found it:
https://web.archive.org/web/20130811220 ... index.html
Kind regards
Jos

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