RE: Fine Running

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Andy Reichert

RE: Fine Running

Postby Andy Reichert » Thu Apr 20, 2023 12:08 am

Re: Fine Running topic.

My 5 year Engineering Apprenticeship in the 60's was with ICT/ICL Peripherals Division in Letchworth, Herts. At the time they probably had as much state of the art small systems electro-mechanical engineering expertise as anywhere in the UK. Amongst many other things, they designed and manufactured their own high speed computer 80 column card readers and punches. The ones that made the rectangular holes in the Hollerith (and IBM) punched cards at high speed.

One of my unforgettable take-aways from that experience was learning that while machining, superb aligning and operating accuracy and precision was relatively easy to obtain for round axles in round holes, achieving the same for small rectangular punch blocks sliding consistently accurately with low friction in parallel guides was at least an order of magnitude more difficult. Such punch parts and their guides needed such tight tolerances, that they were of necessity lapped, rather than merely ground or milled.

Regarding the Fine Running topic, it was notable that almost all the issues mentioned were in regard to making and aligning hornblocks, which in order to work well and achieve correct wheel,connecting rod spacing, fundamentally have similar tight tolerancing issues to the 80 column card punches in their parallel guiding slots.

Rather than continually looping on trying to improve (tighten tolerances) on hornblock spacing, my suggestion, that I have taken up myself, is to try and design chassis that have "virtual" hornblocks, that are instead bearing supports moving in limited vertical arcs, on pivoting beams or swinging arms, that are far more easily accurately positioned.

Andy

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Will L
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Joined: Sun Jul 20, 2008 3:54 pm

Re: RE: Fine Running

Postby Will L » Fri Apr 21, 2023 10:03 am

Andy Reichert wrote:Re: Fine Running topic.

My 5 year Engineering Apprenticeship in the 60's was with ICT/ICL Peripherals Division in Letchworth, Herts. At the time they probably had as much state of the art small systems electro-mechanical engineering expertise as anywhere in the UK. Amongst many other things, they designed and manufactured their own high speed computer 80 column card readers and punches. The ones that made the rectangular holes in the Hollerith (and IBM) punched cards at high speed.

One of my unforgettable take-aways from that experience was learning that while machining, superb aligning and operating accuracy and precision was relatively easy to obtain for round axles in round holes, achieving the same for small rectangular punch blocks sliding consistently accurately with low friction in parallel guides was at least an order of magnitude more difficult. Such punch parts and their guides needed such tight tolerances, that they were of necessity lapped, rather than merely ground or milled.

Regarding the Fine Running topic, it was notable that almost all the issues mentioned were in regard to making and aligning hornblocks, which in order to work well and achieve correct wheel,connecting rod spacing, fundamentally have similar tight tolerancing issues to the 80 column card punches in their parallel guiding slots.

Rather than continually looping on trying to improve (tighten tolerances) on hornblock spacing, my suggestion, that I have taken up myself, is to try and design chassis that have "virtual" hornblocks, that are instead bearing supports moving in limited vertical arcs, on pivoting beams or swinging arms, that are far more easily accurately positioned.

Andy

Hum, I'll have to think on the implications of that.
Whike we are here, how is the L77/N7 and its chassis getting on Andy.
Also as it hapens I spent much of 1968 in Letchworth.

Daddyman
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Re: RE: Fine Running

Postby Daddyman » Fri Apr 21, 2023 10:24 am

Andy Reichert wrote: my suggestion, that I have taken up myself, is to try and design chassis that have "virtual" hornblocks, that are instead bearing supports moving in limited vertical arcs, on pivoting beams or swinging arms, that are far more easily accurately positioned.


You mean like this? Problem is, if you're scratchbuilding, you still have to get the bearings in the right position relative to the rods. But the major disadvantage is the noise: I recently built a model with this system; as it was for display, I wasn't worried about silent running - luckily, as it sounds awful, like a Matchbox toy.
20230421_111833.jpg
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Julian Roberts
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Re: RE: Fine Running

Postby Julian Roberts » Fri Apr 21, 2023 4:55 pm

That's how I originally made my Millholme LNER Q1. The parts you show David there I made using the coupling rods, which fortunately came with just pilot holes. The chassis had just axle holes - but the dimensions between them didn't match the rods. So I just reamed them oversize - then their main function was to restrict the vertical axle movement.

The problem fairly quickly became apparent - wear. Before long there was so much slop the wheels were shorting against the brakes (you can see there's not much space!) A radical solution (by my elementary standards) was required which I briefly described here

viewtopic.php?t=3511#p29414

in Section 8 hornblocks
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Andy Reichert

Re: RE: Fine Running

Postby Andy Reichert » Sat Apr 22, 2023 2:46 am

Image

Will,

The above image is a scan from the very first rough attempt (2019) to try out the pivoting beam approach for the N7 chassis. The transverse equalization mechanism is not shown, and still subject to considerable change. It has however seemed to prove the method, but was not complete enough in the details to make a practical chassis. Unfortunately, due to the combination of the Pandemic and my then developing osteo-arthritic knee immobility issues, and the shut-down of PEC, I only managed to draw up a partial amount of the next stage corrections and additions, for the next version etch. My knee is now fixed, but I'm having difficulty finding enough spare time to complete that next etch soon.

I'm not sure I can write up the entire explanation for all aspects of the methodology shown by means of the unreliable forum posts. But if you would email me directly using the proto87 address, I should be able answer specific questions quite quickly.

Andy

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Will L
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Re: RE: Fine Running

Postby Will L » Tue May 09, 2023 10:19 am

Andy Reichert wrote:...I'm not sure I can write up the entire explanation for all aspects of the methodology shown by means of the unreliable forum posts. But if you would email me directly using the proto87 address, I should be able answer specific questions quite quickly.

Hi Andy

Sorry not to respond sooner. The way the forum works I didn't spot your post until this morning. Email on its way.

Will

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Horsetan
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Re: RE: Fine Running

Postby Horsetan » Sat Sep 16, 2023 5:41 pm

Daddyman wrote:
Andy Reichert wrote: my suggestion, that I have taken up myself, is to try and design chassis that have "virtual" hornblocks, that are instead bearing supports moving in limited vertical arcs, on pivoting beams or swinging arms, that are far more easily accurately positioned.


You mean like this? Problem is, if you're scratchbuilding, you still have to get the bearings in the right position relative to the rods. But the major disadvantage is the noise: I recently built a model with this system; as it was for display, I wasn't worried about silent running - luckily, as it sounds awful, like a Matchbox toy.
20230421_111833.jpg


Yes, that's more or less the system designed by Kemilway and then adopted / copied by Peter K and Crown line, and which is still part of PDK's chassis designs today. As the twin axles are linked more or less permanently in the swivelling cradles, I did wonder if it might cause problems with any adjacent non-linked or rigid axles, as the wheelbase would then vary...
That would be an ecumenical matter.


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